Reo Detailing Handbook 4o6m4q

Concrete Institute of Australia RECOMMENDED PRACTICE

Z6

Reinforcement Detailing Handbook

RECOMMENDED PRACTICE

Reinforcement Detailing Handbook For Reinforced and Prestressed Concrete

Z6

RECOMMENDED PRACTICE

Reinforcement Detailing Handbook For Reinforced and Prestressed Concrete

Based upon the Australian Concrete Structures Standard – AS 3600:2007

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Produced by TechMedia Publishing Pty Ltd for Concrete Institute of Australia ACN 000 715 453 Z6 First published 1975 Updated and republished 1988 Rewritten and republished 2007 ISBN 0 909375 69 0

ii Reinforcement Detailing Handbook

Preface The basic requirements of good reinforced concrete detailing are clarity and conciseness. Unfortunately, there has been a steady deterioration in the quality and quantity of drawings supplied for reinforced concrete over the last twenty years. The net result of poor quality drawings is increased costs in the material supply and construction sectors and unacceptable levels of dispute. Detailing of reinforcement is the interface between the actual design of the concrete structure and what is to be constructed. There is no point in having the most sophisticated analysis and design if it cannot be constructed in the field. Designers must be aware of practical limitations of construction. Detailing is also important for durability, as poor placement of reinforcement leads to insufficient cover and long term problems. Detailing of reinforcement is not taught to designers and yet it is fundamental to the proper design of reinforced concrete. Unlike some countries (and in particular the United Kingdom) reinforcement is scheduled by the reinforcing suppliers based on the concrete drawings provided. If the drawings are poor, the actual reinforcing provided on site may not match the designer’s expectations.

This is the third edition of the “Reinforced Concrete Detailing Manual”; first published in 1975; and rewritten in 1988 to match the publication of AS 3600. Substantial sections of this document remain unchanged from the 1988 edition prepared by Mr. Brian Ferguson and his committee. However, the review team has addressed the following issues: ■ Progressive revisions of AS 3600. There is a major revision of the Concrete Structures Standard in course of preparation and where appropriate the anticipated changes and previous amendments have been incorporated in this document. ■ Introduction of 500 MPa reinforcing steel. The standardisation of steel strength for both mesh and bar and the increased focus on ductility has affected how and where reinforcing steel is used. The increase in strength has also necessitated the revision of bond and anchorage lengths. ■ Detailing for seismic response. The 1998 edition was published prior to the Newcastle Earthquake. This edition has taken the opportunity to discuss detailing issues, which affect the safety and ductility of concrete structure under extreme seismic events. ■ Update diagrams and drawings to comply with new edition of AS 1100.501. The Concrete Institute of Australia is pleased to acknowledge the valuable contribution of the following people and organisations: ■

The aim of this manual is to guide designers, draftsmen and other professionals toward a uniform method of communicating the design intention to the

■

construction team so that confusion cannot arise from the misinterpretation of the drawings. ■

■

■

Brian Ferguson. As noted above a large proportion of this edition is unaltered from the excellent work of the 1988 edition. Smorgon Steel. Humes ARC held the copyright of the previous edition. In order to facilitate this revision, Smorgon Steel has generously assigned copyright to the Concrete Institute of Australia. Queensland Branch of the Concrete Institute of Australia. The Branch has provided funds to expedite the typing and publication of this document. Steel Reinforcement Institute of Australia. The recommendations on seismic detailing have been drawn from the SRIA’s Reinforced Concrete Digest, RCD 17. David Beal. The project management and finalisation of this substantial rewrite of the original edition would not have been possible without his untiring efforts on behalf of the Concrete Institute of Australia.

iii Reinforcement Detailing Handbook

6.11 Compression Lap-splices for Bundled Deformed Bars (As 3600 Clause 13.2.5) 6.12 Summary of Development Lengths and Lap-lengths for Compression 6.13 Tension Splice or Compression Splice. Which Should be Used? 6.14 Lap Splices and Overlapped Bars 6.15 Stress Development and Coupling of Prestressing Tendons 6.16 Crack Control Reinforcement 6.17 Welded and Mechanical Anchorages

Contents Introduction 1

Scope and General Principles 1.1 1.2 1.3

2

Reinforcement Detailing 2.1 2.2

3

Source Tolerances for Reinforcement Prestressing Ducts, Anchorages and Tendons ts and Embedded Items Structural Robustness

Drawing Standards 7.1 7.2 7.3 7.4 7.5 7.6 7.7

8

General – Australian Standards Deformed Bar, Grade 500N Selection of Member Size Plain Round Bars, Grade 250N Low Ductility Deformed Bars, Grade 500L Reinforcing Mesh, Grade 500L

8.3 8.4 8.5 8.6

5.1 5.2 5.3

8.7 8.8

5.5 5.6 5.7 5.8 5.9

Introduction General Comments Step-by-step Selection of Exposure Classification and Concrete Strength for Durability Resistance Other Factors Affecting Selection of Cover for Corrosion Protection Selecting Cover to Reinforcement and Tendons for Corrosion Protection Selection of Cover for Fire Resistance Final Selection of the Appropriate Design Cover “c” Selection of Member Size Bar s and Spacers for the Maintenance of Cover

Stress Development and Splicing of Reinforcement 6.1 6.2 6.3

General Principles of Stress Development Compression Development Length of Deformed Bars, Lsy.c 6.4 Bundled Bars’ Development Length (AS 3600 Clauses 8.1.10.8, 10.7.2, 13.1.7, 13.2.5) 6.5 Development Length of Mesh and Wire in Tension 6.6 Strength Development by a Welded or Mechanical Connection 6.7 General Comments on Splicing Reinforcement 6.8 Tensile Lap-splices for Deformed Bars (AS 3600 Clause 13.2.2) 6.9 Mesh Lap-splices (AS 3600 Clause 13.2.3) 6.10 Compression Lap-splices for Deformed Bars (AS 3600 Clause 13.2.4) iv Reinforcement Detailing Handbook

9

Australian Standards Drawing Standards for Reinforced Concrete Plan Views Elevations and Sections Holes, Recesses, Plinths and Set-downs Dimensioning Scales

Identification and Dimensioning of Concrete Elements 8.1 8.2

Cover

5.4

6

7

Properties of Reinforcement for Detailing Purposes 4.1 4.2 4.3 4.4 4.5 4.6

5

Technical Definitions Basic Considerations for Detailing Reinforcement

Material and Construction Requirements 3.1 3.2 3.3 3.4 3.5

4

Scope General Principles Certification of Reinforcing Steel

Preliminaries Structure Element Consecutive Number System (AS 1100.501) Grid-line System (AS 1100.501 and AS 1100.301) Suggested Abbreviations for Locations, Materials and Reinforcement Placing Structural Element Numbering Dimensioning Outlines 0f Structural Elements Dimensioning Concrete Outline Shapes Dimensioning Formwork

Identification and Dimensioning of Reinforcement Components 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8

Preliminaries Reinforcement Shapes Reinforcement Location Specification of Steel Strength Reinforcement Quantity for Strength Capacity –“Basic Design Notation” Placing Information Bar Marks Special Details

10 General Comments on Presentation of Details 10.1 Important Message 10.2 Details Accompanying the Text 10.3 Selection of Examples 10.4 Technical Terminology 10.5 Detailing of Elements for Seismic Resistance

11 Footings 11.1 11.2 11.3 11.4 11.5 11.6 11.7 11.8

General AS 3600 Requirements Footing Plan-views Footing Elevations Footing Cross-sections General Comments on Footing Details Strip Footings Pad Footings, Isolated Footings and Spread Footings 11.9 Combined Footings and Cantilever Footings

11.10 Raft Footings 11.11 Residential and Commercial Buildings – Slab-on-ground 11.12 Pier and Beam Footings 11.13 Piles and Pile Caps 11.14 Example of Footing Details 11.15 Detailing 0f Footing Systems for Seismic 11.16 Detailing Examples – Drawing Sheets Numbered 11.1 To 11.7 12 Columns 12.1 General and Purpose 12.2 AS 3600 Requirements (Section 10.7) 12.3 Column Plan-views 12.4 Column Elevations 12.5 Column Cross-sections 12.6 Detailing Columns for Construction 12.7 Ideas for Prefabrication 12.8 Examples of Standard Details for a Reinforced Concrete Column 12.9 Example of a Column Schedule 12.10 Detailing for Seismic (Intermediate Moment-Resisting Frames) 13 Beams 13.1 General 13.2 AS 3600 Requirements 13.3 Beams in Plan-view 13.4 Beam Elevations 13.5 Beam Cross-sections 13.6 Intersecting Reinforcement at Ends of Beams 13.7 Intersection of Reinforcement in Beams and Columns 13.8 Intersection of a Rectangular Beam and a Column 13.9 Intersection of Four Beams over a Column 13.10 Intersection of Four T-beams over a Column 13.11 Intersection of T-beams without a Column 13.12 Opportunities for Prefabrication 13.13 Example of Standard Detail for Narrow Beams 13.14 Detailing for Siesmic (Intermediate Moment-Resisting Frames) 14 Suspended Slabs and Slab Systems 14.1 General 14.2 AS 3600 Requirements (Clauses 9.1, 9.2 and 9.4) 14.3 Slab Plan-views 14.4 Slab Elevations 14.5 Slab Cross-sections 14.6 Interference of Slab Top Reinforcement with Columns and Beams 14.7 T-beams with Heavy Top Reinforcement 14.8 Simplification of Slab Reinforcement 14.9 Holes and Openings 14.10 Standard Detail Drawings for Slabs 14.11 ts and Set-downs in Suspended Slabs 14.12 Detailing for Siesmic (Intermediate Moment-Resisting Frames) 14.13 Standard Details – Numbered 14.1 to 14.8

15 Reinforced Concrete Walls 15.1 General 15.2 AS 3600 Requirements (Clauses 11.2, 11.6.4, 11.7) 15.3 Wall Plan-views 15.4 Wall Elevations 15.5 Wall Cross-sections 15.6 Sequence of Construction 15.7 Straight Bars Preferred 15.8 Reinforcement at Wall Corners 15.9 Holes and Openings 15.10 Standard Detail Drawings for Walls 15.11 Detailing for Siesmic 16 Cantilever 16.1 General 16.2 AS 3600 Requirements 16.3 Cantilever Reinforcement Location 16.4 Cantilever Plan-views 16.5 Cantilever Elevations 16.6 Cantilever Cross-sections 16.7 Corbels and Nibs 16.8 Cantilevers as Architectural Features 16.9 Care in Detailing 17 Reinforced Concrete Stairs 17.1 General 17.2 AS 3600 Requirements 17.3 Stair Plan-views 17.4 Stair Elevations 17.5 Stair Cross-sections 17.6 Methods of ing Stairs and Methods of Construction 17.7 Reinforcement at Bends of Flights 17.8 Standard Details 18 Concrete Pavements, Floors and Residential Footings 18.1 General 18.2 AS 3600 Requirements (Sections 4, 9 and 15) 18.3 Detailing Slabs on the Ground 18.4 Special Details for Slabs on the Ground 18.5 Mesh in Slabs on the Ground 19 Bridges – Civil Structures 19.1 General 19.2 Reasons for Differences Appendix A Summary of Bridge Design Standard

(Section 5) and the Concrete Structures Standard Appendix B General Notes on Drawings Appendix C Checking of Concrete Drawings Appendix D Bibliography

v Reinforcement Detailing Handbook

Introduction

The Handbook is based on the Concrete Structures Standard, AS 3600:2007. There are also references to the differences in the Bridge Design

Until the mid-1960’s, the strength of the

Standard AS 5100. The Handbook follows these guidelines:

structure and its elements were always considered to be the prime design parameter. With the introduction

■

as replacing the judgement of a person

of higher-strength concretes and reinforcing steels,

professionally-qualified in the area of design

shallower were adopted. Combined with the

and/or construction of concrete structures;

effects of internal air-conditioning, this led to situations inside buildings where deflection and cracking became

■

■

obtain ideas to simplify detailing and to reduce

concrete structures and cladding.

design and construction costs;

All concrete elements which are reinforced are ■

cover the full range of detailing situations;

thicker and heavier than lines on a drawing. There must ■

stringent requirements than that standard. This

The Handbook discusses detailing insitu

is because the lack of attention to detailing

reinforced concrete using reinforcing mesh and bars.

reinforcement is a major cause of “failure” of

Other manuals describe the particular requirements

used in zones where the durability or

of prestressed concrete and precast concrete.

serviceability of the structure has been at the

This Handbook deals with only the untensioned

greatest risk;

conventional reinforcement in prestressed concrete the Precast Concrete Handbook (Z48) although the detailing in this publication most likely is very similar. The correct position of reinforcement and the maintenance of cover are the major factors controlling the principles of this Handbook.

vi Reinforcement Detailing Handbook

As an extension of the scope of AS 3600, the Handbook in many instances sets out more

concrete.

. Precast concrete detailing can be found in

It is not intended to exclude alternatives where particular detailing situations occur, nor will it

appreciate this concept. Reinforcement on-site is much be sufficient room between the reinforcing to place the

The information is provided as a basis upon which individual designers and detailers can

and industrial pollutants which affected the external

three dimensional, and designers and detailers must

It is not intended for use as a legal document forming part of a building contract;

of concern to owners and designers alike. Over this same period, there was a large increase in atmospheric

The contents are in no way to be considered

■

Examples of “Standard Details” for various types of are presented for adoption as they stand or for adoption within individual offices.

Special Note

Clause Number Changes in AS 3600

This book is based on the unpublished updated version of the AS 3600 Concrete Structures standard. It is assumed that it will be published in 2007. The draft Concrete Structures standard used to prepare this book was dated July 2006 with some further updates provided from the committee meeting held in October 2006. The major Chapter changes between the 2001 and the 2007 versions of the standard are as follows. Sections from 2001 Standard Remarks Section 3

Transferred to Loading Standard AS/NZS 1170.0

Section 6

Now Section 3 of 2007 Standard

Section 7

Now Section 6 of 2007 Standard and resequenced

N/A

New Section 7, Strut-and-Tie Modelling

Section 17

Deleted from 2007 Standard. Use AS 3735

Section 18

Deleted from 2007 Standard, Use AS 4997

Section 19

Now Section 17 of 2007 Standard

To allow you to be able to reference the Clauses in the current 2001 Standard for Concrete Structures, the following Table has been prepared to show the Clause Numbers changes between the two versions of the Standard. If the Clause Number has not been changed, there is no reference to it in this Table.

AS 3600:2007 AS 3600:2001 Clause Clause Where Clause are referenced in this Handbook Number Number 4.5 4.6 4.7 4.8 4.10.3.5

4.6 4.7 4.8 4.10.3.3

5.3 5.3, 18.2.1 5.3 5.3 5.5

5.3 5.4 5.5 5.6 5.7

5.4 5.5 5.6 5.7 5.10

5.6.2 5.6.2, 4.3.2 5.6.2 5.6.2, 4.3.2 5.6.2

6.1.4 6.9 6.9.5.3 6.10.2 6.10.3

7.1.2 7.5 7.5.5 7.2 7.3

14.2.8 Table 14.2 14.2.8.3 14.2.5, Table 14.2 14.2.5, Table 14.2, 14.2.7

6.10.4 6.10.4.3 6.10.4.5 7.2 8.1.10.1

7.4 7.4.3 7.4.5 8.1.8.1

14.2.5, 14.2.7, 14.2.9.2, Table 14.2 Table 14.2 Table 14.2 13.2.3 13.2.2

8.1.10.2 8.1.10.3 8.1.10.4 8.1.10.5 8.1.10.6

8.1.8.2 8.1.8.3 8.1.8.4 8.1.8.5 8.1.8.6

13.2.1 13.2.2 13.2.3 13.2.4 13.2.5, Table 14.2

8.1.10.7 8.1.10.8 8.4.4 9.1.5 10.7.4.3

8.1.8.7 8.1.8.8 8.4.5 9.1.4 10.7.3.3

13.2.6 13.2.7, 12.2.2 13.2.10 14.2.8.3, 14.2.10 Table 12.4

10.7.4.5 10.7.5 11.6.4 11.7 11.7.1

10.7.3.5 10.7.4 11.5.4 11.6 11.6.1

12.2.8 12.4.4 15.2, 15.2.1 15.1.3, 15.2 15.2.2

11.7.2 11.7.3 Section 17 17.1.3 17.2.1.2

11.6.2 11.6.3 Section 19 19.1.3 19.2.1.2

15.2.3 15.2.4 3.1 5.4.1 3.1.1

17.2.2 17.2.3.2 17.2.5 17.3 17.4.1

19.2.2 19.2.3.2 19.2.5 19.3 19.4.1

3.2.1 6.2.4, 9.8.4, 13.2.8 3.1.3, 5.9 3.1.2 3.4

17.5.3 17.6

19.5.3 19.6

3.2.1, 3.2.3, 3.2.4, 3.2.5, 5.1, 5.4.3 5.4.1

vii Reinforcement Detailing Handbook

viii Reinforcement Detailing Handbook

1 Scope and General Principles

1.2

GENERAL PRINCIPLES The design of a structure or member to

which AS 3600 applies is the responsibility of an engineer, although AS 3600 is not permitted to state this. The Building Code of Australia sets out these

1.1

SCOPE

responsibilities. Therefore, the responsibility for the preparation

This Handbook illustrates detailing of reinforcement in insitu reinforced concrete and partially-

of the drawings, which form part of the documents

prestressed concrete structures and . Precast

setting out the work to be executed, lies with an

and prestressed concrete detailing is not specifically

engineer also. These responsibilities should include

covered (refer Introduction) Information for design

the checking and co-ordination of the drawings before

purposes is also provided.

construction. The definitions given in AS 3600 also apply

For the proper application of this Handbook, s must have a copy of the Australian Standard

here, in particular: Drawings - the drawings forming part of the

AS 3600:2007 and the accompanying Commentary.

documents setting out the work to be executed.

Also essential is a copy of AS 1100.501:2002, Technical drawing – Structural engineering drawing.

Specification - the specification forming part

This sets out methods to be used in structural

of the documents setting out the work to be

drawing. Each drawing office should also have the

executed.

other appropriate parts of AS 1100. This Handbook is

Conditions of Contract - they also are

prepared under the recommendation of Clause 1.2 of

generally part of the contract documents for a

AS 1100.501.

project. Not mentioned in the standard are:

For bridges, the AS 5100.5:2004 Bridge design –

Detailer - the person, to whom this Handbook

Concrete, should be followed.

is primarily directed, who prepares all details of the design or construction as appropriate to the job. In this broad context “the detailer” could be a draftsman, a design draftsman, a design or construction engineer, a reinforcement scheduler or a steel fixer. The details so prepared may or may not form part of the contract documents but preparation of a drawing or sketch is implied. Scheduler - the person who extracts from the structural drawings all necessary information about the reinforcement to enable it to be manufactured, labelled, delivered and located in its correct position in the formwork. 1.2.1

General Drawings provide the means for the engineer

to communicate the design requirements through the detailer to the contractor’s site operators in a clear and concise manner. Adequate drawings will eliminate the need for contractors to ask the designer for additional information.

1:1 Reinforcement Detailing Handbook

1.2.2 Quality of Drawings and Prints Building site conditions are very different from those in an air-conditioned drawing office, and

(h) Any required properties of the concrete. (See Specification and Supply of Concrete AS1379 Clauses 1.6.3 and 1.6.4).

drawing preparation must allow for this. Details which

AS 5100 Clause 1.6.2h. The minimum strength

appear to be easily read in an office can be obscured

the concrete has to obtain before the application

on site by dirt, oil or clay. Drawings can get wet or

of prestressing forces.

be folded and unfolded many times so that they

(This requirement should be given in all

become illegible. Therefore for site use, drawings must

prestressed concrete jobs).

be to a reasonable scale with the line thicknesses

(i) The curing procedure.

recommended in this Handbook. Prints of drawings

(j) Grade, Ductility Class and type of reinforcement

should be on good quality paper. Also, the trend of using A3 copies of larger drawings on site, means the details must be clear and concise. 1.2.3 Information on Drawings AS 1100.501 gives general guidelines. AS 3600 clause 1.4 is quite specific on the design details to be given on drawings and, because they are so important, they are quoted here with additional comments. There are minor differences in the AS 5100 clauses 1.6.1 and 1.6.2. (Author’s comments are given in parentheses). AS3600 CLAUSE 1.4 DOCUMENTATION The drawings or specification for concrete structures and shall include, as appropriate, the following: (a) Reference number and date of issue of applicable design Standards. (Material properties may need to be checked sometime in the distant future, say for renovations or demolition). (b) Imposed actions (live loads) used in design. (c) The appropriate earthquake design category determined from AS1170.4. (d) Any constraint on construction assumed in the design. (There is not much point in preparing an innovative design if its special features are not clear to the tenderers. In other situations, the construction techniques to be used by the contractor will not be known to the design engineer at the planning stage. The earlier the construction team can be brought together, the better it will be for all parties). (e) Exposure classification for durability. (f) Fire-resistance level (FRL), if applicable. (g) Class and, where appropriate, grade designation of concrete.

and grade and type of tendons. (k) The size, quantity and location of all reinforcement, tendons and structural fixings and the cover to each. (This Handbook is written to explain how to specify all these items including tolerances, techniques for proper chairing for strength and durability; supervision of construction, and many other items). (l) The location, and details of any splices, mechanical connections and welding of any reinforcement or tendon. (m) The maximum jacking force to be applied in each tendon, and the order in which tendons are to be stressed. (n) The shape and size of each member. (Because these drawings will be the basis of the formwork drawings, the concrete outline must be clearly defined and dimensioned. The author of this Handbook questions the omission of valuable information from structural drawings of buildings by leaving this work to the architect. It is the designer’s responsibility to control strength and serviceability of the structure and omission of critical dimensions of structural elements can no longer be justified as a minimum structural depth and width must be shown even if the plan dimensions for the gridlines are shown by the architect). (o) The finish and method of control for unformed surfaces. (Reference should be made to AS 3610. There are also many excellent publications on these topics issued by Cement Concrete & Aggregates Australia). (p) Class of formwork in accordance with AS 3610 for the surface finish specified. (Detailing of formwork is beyond the scope of this Handbook).

1:2 Reinforcement Detailing Handbook

(q) The minimum period of time before stripping of forms and removal of shores. (r) The location and details of planned construction

1.3

CERTIFICATION OF REINFORCING STEEL In the last few years, reinforcing steel in Australia

has been sourced from around the world, not just from

and movement ts, and the method to be

local mills and processors. Designers should satisfy

used for their protection.

themselves that the reinforcing steel used in their

(This has considerable relevance for designers. It requires them to specify every t in both concrete and steel, and to state how laps are to be made, their length, and so on. Unfortunately, many designs do not show the construction ts often resulting in argument and cost on these matters). 1.2.4 Information in the Specification In most large contracts, the materials to be used will be fully described in a separate Specification and subsequent reference in the drawings to concrete or other materials will be in abbreviated form. From a contractual point of view, information

projects complies with AS/NZS 4671 and is processed to the requirements of AS 3600 or AS 5100 as appropriate. This includes the requirements of ensuring long-term quality statistics. Third party product certification is a cost effective means of demonstrating compliance. The Australian Certification Authority for Reinforcing Steels, ACRS, has been established in Australia to provide this service. The certification program offered by ACRS covers steel mills, reinforcement processors and mesh manufacturers. ACRS-certified steel can be identified by the ACRS mark attached to all ing documentation for the steel.

given in both drawings and Specification must be consistent and not in conflict. However, the Specification is not always made available to men in the working areas or to every subcontractor. Information which is critical for day-today construction should not be confined solely to the Specification. 1.2.5 General Notes Requirements common to many parts of the

Figure 1.1 The ACRS Mark

structure can be stated in a set of General Notes, often printed as the first sheet of a set of drawings. Examples

Specifiers should ensure that both the

of General Notes are given in Appendix B of this

manufacturer and processor of reinforcing steel are

Handbook.

ACRS certified. Research conducted by ACRS has

Notes are instructions to the contractor and should therefore always be written in the imperative. 1.2.6 “Standard Details” The term “standard” means a standard method of detailing produced by a particular design office, not an Australian Standard detail. In some cases, there may be advantages in presenting “standard details” in a set of drawings. Where they bear little relevance to the actual situation, they should not be used because confusion and loss of time will result. Possible uses for standard details are the layout of main column bars and their associated ties in columns having a common shape, the predominant grid of bars in flat slab floors, staircase details and footings.

shown that the mechanical properties of steel can be significantly altered through uncontrolled processing. More details of ACRS certification and a current list of Certificate holders and products can be obtained from

www.acrs.net.au. Appropriate specifications are provided below: SUGGESTED ACRS SPECIFICATION Steel reinforcement for concrete shall comply with AS/NZS 4671. It shall be cut and bent in accordance with AS 3600. Acceptable manufacturers and processors of steel reinforcement must hold a valid certificate of approval, issued by the Australian Certification Authority for Reinforcing Steel (ACRS) or to an equivalent certification system as may be approved in writing by the specifier. Evidence of compliance with this clause must be obtained when contract bids are received. 1:3 Reinforcement Detailing Handbook

SUGGESTED WORDING FOR STEEL NOT COVERED BY LONG-TERM QUALITY LEVEL Should the Contractor wish to use reinforcing steel that is not covered by long-term quality levels of AS/NZS 4671, approval must be obtained in writing prior to such use. In seeking such approval, the Contractor shall nominate the in which each individual batch of reinforcing steel is to be used and shall also state the country, mill of origin and the specification to which the reinforcing steel for that member is produced, and clearly demonstrate how it is equivalent to that specified by AS/NZS 4671. Certificates from a NATA laboratory of chemical composition and physical properties of all reinforcing steel will be required. All testing will be in compliance with Clause B7 of AS/NZS 4671-2001, including frequency of sampling and testing. Reinforcing steel not covered by the long-term quality level of AS/NZS 4671 shall not be ordered or placed before written approval has been obtained.

1:4 Reinforcement Detailing Handbook

2

(2.4 m is a common maximum) whilst the length of the

Reinforcement Detailing

generally supplied in 6-m lengths. The resulting product

longitudinal bars determines the sheet length, which is of a mesh machine resembles continuous computer paper. Like paper, it can be cut to any desired length, limited only by handling capability and the configuration

2.1

TECHNICAL DEFINITIONS

of the machine itself. Mesh can be cut off the machine

These definitions are from AS 3600 Clause 1.6.3

to a range of lengths between, say 2 to 10 m, or to

with extra comment to show the intentional differences

produce a roll up to 60 m. A width range from 100 mm

between various .

(2 longitudinal bars as for trench mesh) up to 2400 mm

Reinforcement, reinforcing steel. Steel bar, or mesh but not prestressing tendons. In AS/NZS 4671, reinforcing steel is described by its strength and ductility class rather than by type of manufacture. Reinforcing steel bars are often referred to

or more (with various numbers of longitudinal bar/ spacing combinations) is possible depending on the machinery. Mesh must comply with AS/NZS 4671. Fitment. A unit of reinforcement commonly known as a tie, stirrup, ligature or helix. Fitments may be made from individual Grade N

as “rebar” or “reo”, or in the case of deformed bars,

or L bars, cut to length and then bent to shape, or

“debar”. Although bars are sometimes called “rods”,

from mesh by bending a flat sheet into the desired

this name can be most misleading and should not be

shape. Fitments are often assumed to have a shape

used. Bars are usually hot-rolled at the steel merchant-

resembling the surrounding concrete surface; however,

mill and then cut into straight “stock lengths” with a

unless care is taken in detailing, the shape can be so

traditional maximum of 12 metres. Bars up to 16 mm

complex that the bars inside the fitment cannot be

diameter are also obtained from a coil by straightening

placed.

and cutting it to length. The coil can be several

Tendon (prestressing steel). A wire, strand

hundred metres long and is formed whilst red-hot in a

or bar or any discrete group of such wires, strands or

rod mill – hence the term “rod”. But as the straightened

bars, which is intended to be pretensioned or post-

and cut length of rod is almost indistinguishable from

tensioned.

a hot-rolled bar, it is recommended that the term “bar”,

The method of manufacture and the resulting

and not “rod”, be used in structural detailing. Rebars

properties of tendons are best obtained from

and coiled-rebar must comply with AS/NZS 4671.

manufacturers’ literature.

Wire (AS/NZS 4671 also describes this as

Prestressing steel must comply with

reinforcing bar) is a material manufactured also from

AS/NZS 4672, and prestressing anchorages with

rod in coils of mass between 700 to 1300 kg; but in

AS/NZS 1314. If prestressing steel is imported,

this case the rod is additionally cold-worked by drawing

engineers should satisfy themselves such steel

or rolling to increase its strength. Typically, this steel

complies with the Australian Standard.

is low ductility and is classified as grade 500L steel.

Plain concrete member. A member either

Grade 500L bars must comply with AS/NZS 4671.

unreinforced or containing reinforcement but assumed

AS 3600 has placed some limitations on the use of

to be unreinforced.

Grade 500L bars. Welded Mesh is often called just “fabric” or

While many plain concrete are designed for strength and durability without

“mesh”. It is manufactured from Grade 500L bars by

reinforcement, steel is often included for crack control

a process of resistance welding every intersection of

purposes, or for added continuity or for aesthetic

a series of longitudinal and cross bars. Some Grade

reasons. The principles of this Handbook still apply in

500N mesh can be manufactured to special order. The

these cases.

difference between “longitudinal” and “cross” bars is important; they refer to the direction in which the bars proceed through the mesh machine. The length of the cross-bars determines the width of a mesh sheet

2:1 Reinforcement Detailing Handbook

Construction t. A t, including a t

Then the lowest suspended floor would be

between precast segments, that is located in a part of

taken as one horizontal zone – although in practice

a structure for convenience of construction and made

the floor area is often subdivided into several zones

so that the load-carrying capacity and serviceability of

by construction ts. After the floor is cast, the walls

the structure will be unimpaired by the inclusion of the

and columns ing the next floor are constructed.

t. A typical location of a construction t is at the

Their outlines have been defined by their size and

top of slabs at walls and columns. The ts between

shape and their upper and lower limits (horizontal

precast segments may be treated differently to ts

construction ts this time) are the top of the lower

between insitu cast segments of the structure.

floor and the soffit of the floor above.

Movement t. A t which is made in or between portions of a structure for the specific

This concept continues to the roof. Thus reinforced concrete construction consists

purpose of permitting relative movement between the

of being able to subdivide the whole structure into

parts of the structure on either side of the t.

manageable blocks which are built almost individually. It really does not matter whether the structure is of

2.2

BASIC CONSIDERATIONS FOR

insitu concrete entirely, or of prestressed concrete, or

DETAILING REINFORCEMENT

of steel frame with concrete floors, or of fully precast

Since reinforcement is generally to be encased by concrete, the first step in structural design is to define the proportions of the structure as a whole and the concrete outline for each member from the architectural and structural requirements. To a large extent, this will have been done during the planning and analysis stages. After this, the appropriate forces and stresses can be calculated. The next step is to define the quantity of reinforcing steel in each face of the member and to determine how that steel can be fixed there (using fitments, tie wire, chairs and spacers) until the concrete is placed and has hardened. Then it is necessary to ensure that the whole structure can be built using the assembly of the reinforcing steel and concrete as designed. This is done by dividing the structure into small placing zones comprising one or more of the individual . Let us use a small building with a single level basement as an example. Firstly the foundation is prepared and the footings constructed within a horizontal zone taken over the whole site. Of course, these may not be at exactly the same level but it is the principle we are concerned about. The next division would be a vertical zone consisting of the basement walls and columns, stairs and lift shaft walls if they are of concrete – these are built as a number of individual vertical elements.

2:2 Reinforcement Detailing Handbook

concrete. This Handbook explains detailing the reinforcement of individual concrete elements so that they can be economically connected with their ading elements by using insitu concrete.

3 Material and Construction Requirements 3.1

SOURCE Section 17 of AS 3600 sets out the

3.1.2 Prestressing Ducts, Anchorages and Tendons The main points in AS 3600 Clause 17.3 which concern the detailer of prestressed concrete are the specification of the tendon or duct profile and the methods to be used to maintain the profile. Of critical importance to the prestressing contractor are the jacking forces to be applied during the stressing

requirements for reinforcing steel, ducts, anchorages

operation. Determination of these is a matter of design

and tendons, ts and embedded items, and

and beyond the scope of this book, but the appropriate

tolerances for structures and . For bridges,

forces and the times for stressing must be given in the

the equivalent section is AS 5100 Part 5 Section 16

drawings.

for materials and construction requirements. In this chapter, similar clauses exist to those referred to in AS 3600 Section 17. s of this Handbook should familiarise themselves with these clauses. Some will be referred to directly because they are very important to detailing procedures, whilst other clauses may not even be

3.1.3 Fixing The “catch-all” clause in AS 3600 Clause 17.2.5, when read in conjunction with AS 3600 Clause 1.4, clearly indicates that all reinforcement and tendons required for whatever purpose must be shown in the drawings. Provision for tie-bars and so on may be

discussed.

made in the form of General Notes in the drawings. It

3.1.1 Reinforcement

but by whom is not clear. Plastic-tipped wire chairs

Materials. Reinforcement shall be deformed

is also implied that the chairs should also be specified should not be used in B2 or more severe environments

Class N bars or Class L or Class N welded wire mesh

due to the potential for corrosion and subsequent

(plain or deformed), with a yield strength of up to

staining of concrete surfaces. Plastic bar chairs should

500 MPa, except that fitments may be manufactured

be used in these severe environments. Chapter 5

from Class L wire or bar (plain or deformed), or plain

describes how to select the appropriate concrete

Class N bar. Fitments can also be manufactured from

cover. Further guidance on spacers and chairs for fixing

plain Class 250N bar which is commonly designated as

of reinforcement in its correct position can be obtained

R bar. All reinforcement shall comply with

from British Standard BS 7973

AS/NZS 4671. All rules related to development and

Parts 1 and 2.

anchorage are based on this requirement. Protective coatings such as galvanising or epoxy are allowed but bars so coated are not allowed to have reduced cover. (Refer AS 3600 Clause 17.2.1.2). Bending. The term “bending” includes hooks and cogs at the ends of bars. Throughout AS 3600, the term “standard hook”

3.2

TOLERANCES FOR REINFORCEMENT

3.2.1 Introduction to Tolerances for Reinforcement AS 3600 tolerances for fabrication (Clause 17.2.2) and fixing (Clause 17.5.3) provide

defines the dimensions required to provide additional

structurally reasonable and commercially realistic

anchorage for a bar when sufficient embedment length

values bearing in mind traditional industrial practices.

in concrete is not available. Hook and cog lengths

Reinforcement cannot be bent to tighter tolerances

depend solely on the bar diameter and the bending pin

without an increase in costs; fixing tolerances are

diameter; by Australian Standards, the physical length

considered reasonable to ensure adequate strength.

of steel required is independent of the angle of bend,

Designers must be aware that bending and fixing of

ie 180°, 135° or 90°. Details are given in Clause 6.2.4

reinforcement is not precision engineering.

of this Handbook.

3:1 Reinforcement Detailing Handbook

Tolerances in engineering work are an allowance for variations in manufacturing operations. Cutting and bending rebars is not a precision operation. Nevertheless, in some jobs it may be necessary to

3.2.2 Application of Fabrication Tolerances Shape Codes for reinforcement are described in Chapter 9 Clause 2.1. Figure 3.1(a) shows a bar in the bottom of a

specify tolerances tighter than given in the AS 3600

slab. The slab length is “a” and the cover is specified as

despite a significantly higher cost. As an alternative,

“c” without other explanation. Thus the bottom cover,

specifying a higher cover with normal tolerances may

end cover and face cover are all assumed to be “c”.

be an easier solution. No special allowance is made in the AS 3600 for precast concrete. Although a smaller cover is

The bar dimension A is calculated as follows: A = a – 2c Based on this calculated length, applying the

permitted (see Clause 4.10.3.3) it does not require

cutting tolerances in AS 3600 Clause 17.2.2(a), the

reinforcement to be fabricated to smaller tolerances

fabricated length varies from:

than given in Clause 17.5.3 for insitu concrete.

a – 2c + 0 to a – 2c – 40 mm,

Cutting and bending. The reinforcement fabrication tolerances (AS 3600 Clause 17.2.2) are put

for A more than 600 mm, or a – 2c + 0 to a – 2c – 25 mm,

in a “+ 0, - t mm” format so as to avoid a reduction in cover. These tolerances must be considered in conjunction with the cover specification for durability and fire resistance (refer Chapter 5). Bar bending dimensions are nearly always controlled by the nearest concrete surfaces. The scheduled length of reinforcement required to fit inside a concrete shape is obtained by subtracting the specified cover or covers from the concrete dimension. The negative tolerance on length should then ensure proper cover at each end of the bar. Placing. It is important to understand that when a specification says “Cover must not be not less than ‘c’ mm”, this should be interpreted as meaning cover to the ends of the bar as well as cover to the nearest parallel surface. This cover ‘c’ is the design or actual cover derived in Chapter 5. Placing tolerances (AS 3600 Clause 17.5.3) are of the “+t, - t” type, that is the bar may be so placed that a small reduction or small increase in cover is permissible. Because of this, the cover required for corrosion resistance (AS 3600 Clause 4.10.3) includes an allowance of +5 mm (which is not specifically stated in the standard but implied from Clause 17.5.3) should placing inadvertently reduce the cover. However, combinations of tolerances will require the designer to use a reduced effective depth for top steel than is theoretically required. This would normally only be a problem in thin slabs and the like or top steel in beams. In critical situations, heights should be calculated and specified on the original drawings. In some cases, a height greater than theoretically assumed may be desirable to allow for deviations in formwork and for the mass of the ed steel. 3:2 Reinforcement Detailing Handbook

for A less than 600 mm. Figure 3.1(b) can be considered as a slab with the left edge turned up. In this member the cover “c” applies to all slab faces and also to the ends of the bar in the upstand and the right edge. Two dimensions ‘A’ and ‘B’ are required for cutting and bending the bar. They are calculated and shown on the schedule as follows: Dimension ‘A’ = a – c – c = a – 2c, Dimension ‘B’ = b – c –c = b – 2c, so that The scheduled length ‘L’ = A + B If we assume that dimension ‘A’ is less than 600 mm, and dimension ‘B’ is more than 600 mm, then the permissible range of fabricated dimensions are: ‘A’ ranging from a – 2c + 0 to a – 2c – 25 mm, ‘B’ ranging from b – 2c + 0 to b – 2c – 40 mm, and ‘L’ ranging from L + 0 to L – 40 mm. Obviously, if the length ‘L’ is cut within tolerance, the individual dimensions ‘A’ and ‘B’ should also be within tolerance. Figure 3.1(c) can be regarded as a crosssection through either a column or a beam. In practice, the cover is usually specified only once and is assumed to apply to all surfaces of the member. It is unwise to specify more than one cover value for a concrete element such as a wall, beam or slab. The scheduled dimensions for bending the fitment are: Dimension ‘A’ = a –2c, Dimension ‘B’ = b – 2c, Scheduled Length ‘L’ = 2(A + B) + two 135° hooks The scheduled length does not depend on the size of the bar used to make the fitment, but we

will assume it is a N12 deformed bar. Allowing for fabricating tolerances, for each leg of the fitment the

3.2.3 Fixing Tolerances for Reinforcement As said earlier, the designer and detailer rarely need to take of fabricating tolerances. Fixing

fabricated dimensions are: ‘A’ ranging from a – 2c + 0 to a – 2c – 15mm,

tolerances are another matter – not because the

and

tolerances are given in the drawings but because

‘B’ ranging from b – 2c + 0 to b – 2c – 15mm.

awareness is critical if design accuracy is to be understood. An excessive expectation of placing accuracy is unwise. When deg thin elements with small effective depths for design in bending, the

������������������ ����� ���

theoretical effective depth may not be the actual one ����� ���

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achieved on site. AS 3600 Clause 17.5.3 refers to deviation from the “specified position”, and this is very important because the detailer’s job is to define this “specified

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Handbook). However, to understand the relationship between specified position and the possible location of the bar in the actual member, a placing envelope can

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be calculated. This is illustrated in the following Figures.

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Note again, that the cover at the ends of the bar are

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position” (see Clause 1.4(k), Clause 1.2.3 this

usually not specified directly, but they are assumed to be the same as the face cover.

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Figure 3.2(a). The placing envelope of a straight bar is defined by the placing tolerances and the cover to each end and to any surface of the slab.

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By comparing the scheduled length in Figure 3.1(a) with the placing-envelope in this example, it can be

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seen that maintaining bottom cover requires adequate chairing; to maintain the end cover depends on the cutting tolerance. In practice, it is possible that an excessive

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cover will occur at the ends; this has no effect on the strength and in fact could lead to improved durability. Figure 3.2(b) illustrates the placing-envelope within which a fabricated L-shaped bar should fit.

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Figure 3.1 Fabrication Tolerances

When the bar is fixed, its position in the formwork can be checked by measuring the cover at each end. The placing tolerance occurs twice – once at each end. Therefore, it can be seen from Figure 3.2(b) that, where the bar’s position is controlled by cover at each end, then the fabrication tolerances will always assist in providing the design cover. In fact, if the bar is fabricated to the exact length then the bar will always fit into the placing-tolerance envelope of “cover – 5” mm to “cover + 10” mm. However, if the fabricated dimensions have maximum undersize tolerances of –25 mm and –40 mm respectively, then the end covers would be greater than “cover + 10” mm. 3:3 Reinforcement Detailing Handbook

Since it can be expected that the length ‘L’ after cutting will range from L + 0 to L – 40 mm, then

3.2.4 Fixing Tolerances for Footing Reinforcement These are given in AS 3600 Clause 17.5.3(a).

the fabricated bent bar should fit inside the placing

Fabrication tolerances are unchanged but the fixing

envelope.

tolerances are increased to allow for considerable

The major concern here is that chairs must be

unevenness of the foundation profile, consequently

specified to provide the appropriate cover on the soffit

chair heights may need to be greater than specified

of the slab and along the upturned edge on the left.

cover. This is a case where specifying a greater cover

Care must be taken during construction to prevent the

than AS 3600 may assist construction on site.

bar ends from touching the formwork. Figure 3.2(c) describes the placing-envelope of a fitment within a beam cross-section.

3.2.5 Fixing Reinforcement not Controlled by Cover At ends of reinforcement. Figure 3.3 gives cases controlled by AS 3600 Clause 17.5.3(b)(ii). In

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general, splice locations do not need to be constructed

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to an accuracy any greater than 50 mm.

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Fixing bars to comply with spacing. The tolerance on “position” given in AS 3600 Clause 17.5.3(b)(iii) again refers to “specified position”.

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Figure 3.4 illustrates how an unexpected hole in a slab

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could require that a bar be moved sideways during fixing. This displacement (of 60 mm say) may exceed

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the permitted tolerance range of “+/- 10% of the �

specified spacing or 15 mm, whichever is greater”, but

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it is certainly preferable to cutting the bar.

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perpendicular to span of slab will be required.

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must be used. Provided the correct total area of steel

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Figure 3.2 FixingTolerances

3:4 Reinforcement Detailing Handbook

spacing varies from bar to bar. The AS 3600 tolerance on spacing is there to control excessively bad steel fixing, not to force unrealistic demands on a simple

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There will also be cases where an extra bar is embedded, it does not matter greatly if the individual

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If the hole is large, trimmer bars each side

process.

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3.3

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��������

PRESTRESSING DUCTS, ANCHORAGES AND TENDONS

3.3.1 Continuity At some stage of its life, a prestressing tendon will be expected to impose a very large force on its anchorage. The detailer must therefore show exactly where the anchorages are to be located and how they

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will be reinforced if extra steel is required. If the tendon profile is curved as with most post-

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tensioned work, or deflected in a series of straight lines as for some pre-tensioned designs, it must be defined before any additional reinforcing steel is detailed around it. Rebars can be cut or bent to fit around tendons which must be continuous from anchor to anchor and

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have as smooth a line as possible.

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As a result, good detailing should allow for some of the reinforcing steel to be fixed before the

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ducts and tendons as a means of securing the latter,

Figure 3.3 SplicingTolerances

and the remainder should be in smaller pieces fitted later around the profile. As an example, “open top” fitments of bent mesh can be used in the soffit of band beams; a short bar resting on and tied to the horizontal cross-wires will provide vertical for the tendon profile and for any slab top-steel placed after the tendons are secured. ����������

3.3.2 Fabrication and Fixing These are specialist tasks and will not be discussed further, other than to say that for post-

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tensioned tendons the tolerance for fixing is based on the final location of the tendons, not on the surface of the duct. Obviously, the stressed tendon will follow the shortest path through the member, and extensions should be based on this length. When multiple strands form the cable, they will be forced to bunch together on the inside of every curve of the duct. The specified tolerances of “+/- 5” mm can only be maintained by adequate, correctly-placed s or tie bars whose location in elevation and cross-

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section are accurately defined in simple, clear details by the designer.

Figure 3.4 SpacingTolerances

3:5 Reinforcement Detailing Handbook

3.4

TS AND EMBEDDED ITEMS AS 3600 draws a distinction between ts

which are “detailed”, that is they are defined by the designer, and those which occur unexpectedly

3.5

STRUCTURAL ROBUSTNESS The commentary to AS 1170.0 gives the

following advice: “A structure should be designed and

during construction. To comply with Clause 17.4.1(b),

constructed in such a way that it will not be damaged

the prudent detailer will show in the drawings how

by events like fire, explosion, impact or consequences

construction ts are to be made – whether or not

of human errors, to an extent disproportionate to the

these are likely to occur.

original cause. The potential damage may be avoided

It should be noted that the detail is very dependent on the location and that approval must be sought from the designer as to where and when the detail must be used. Obviously not every situation can be included so it is possible that alternative t details will be required

or limited by use of the following: (a) Avoiding, eliminating or reducing the hazards which the structure may sustain. (b) Selecting a structural form that has a low sensitivity to the hazards considered. (c) Selecting a structural form and design that

if amendments are made at short notice during the

can survive adequately the accidental removal

job’s progress.

of an individual element or a limited part of

In reinforced concrete, a t generally implies that splicing will be needed. By far the most common t occurs in columns and walls at the junctions below

the structure or the occurrence of acceptable localised damage. (d) Avoiding as far as possible structural systems

and above beams or slabs. Splices have considerable

that may collapse without warning.

effect on construction techniques. See Chapter 6.

The design should provide alternate load

Some fixtures and other items can be

paths so that the damage is absorbed and sufficient

embedded during construction and need not be

local strength to resist failure of critical so

referred back to the designer. The drawings or

that major collapse is averted. The materials design

Specification should contain clear instructions on the

Standards usually contain implicit consideration

procedures to be taken in these cases. All embedded

of resistance to local collapse by including such

items which are manufactured from metals which are

provisions as minimum levels of strength, continuity,

dissimilar to reinforcing steel must be isolated from the

and ductility. Connections for example should be

reinforcement to stop galvanic cells forming.

designed to be ductile and have a capacity for large

The design of fixings is covered by AS 3600 Section 14.3; particular care is required in detailing fixings used for lifting purposes. Under no

deformation and energy absorption under the effect of abnormal conditions”. Reinforcement detailing for robustness should

circumstances should reinforcing bar or strand loops

address the issues raised above. The guidance

be used as the lifting hook. These materials are not

given later in this Handbook on detailing for seismic

meant for this purpose and can fail unexpectedly. For

resistance gives some examples of how robustness

lifting concrete, there are proprietary cast in lifters

can be achieved.

with clutches for lifting. If the fixing is for later , then a purpose designed fixing must be cast into the concrete section which is correctly load tested.

3:6 Reinforcement Detailing Handbook

4

Table 4.2 Regulations and Design Standards

Properties of Reinforcement for Detailing Purposes 4.1

GENERAL – AUSTRALIAN STANDARDS There are a number of Australian standards

which specify the mechanical and design properties of reinforcement. These are listed in Table 4.1 and should

Reference number

Short title

Comments

–

Building Code of Australia (BCA)

Basis of state building regulations

Minimum design loads on structures AS 1170.4:1993 Earthquake loads

be referred to for further information. Table 4.1 Australian Standards which Relate to Reinforcement and Tendons Reference number

Short title

AS/NZS 4671:2001

Steel reinforcing All types of untensioned materials reinforcement

AS/NZS 4672:2006

Prestressing steel

AS/NZS 1314:2007

Prestressing anchorages

Comments

All types of tendons for prestress

AS 2783:1992

Concrete for small swimming pools

AS 2870:1996

Residential slabs and footings

AS 3600:2007

Concrete structures

AS 5100:2004

Bridge design

AS/NZS 1100.501:2002

Structural engineering drawing

AS 1379:1997

Specification and supply of concrete

For tendons only

AS/NZS Welding of Permissible 1554.3:2002 reinforcing steel arrangements

Part 5 Concrete

Note: A design or detail prepared under one standard cannot be expected to comply retrospectively with a standard published after the design is prepared. Dating the drawings should ensure that designs can

For bar, wire and mesh, the design strength is the “characteristic yield strength” and this is called the

be checked for future renovations, safety after fire, demolition, etc.

“Grade” of the steel. It is measured in megapascals (MPa)

4.2 The strength of prestressing tendons is given

in several ways and AS/NZS 4672 should be used to avoid mistakes. This standard also highlights the commonly-available prestressing steels. Other standards and regulations which crossreference the reinforcing steel and tendons Standards

DEFORMED BARS, GRADE 500N Physical properties are given in Table 4.3 while

design properties are given in Tables 4.4 and 4.5. Suggested specification. Reinforcing bars shall be hot-rolled deformed bars of grade 500N complying with AS/NZS 4671 + year.[Note 1]

are given in Table 4.2.

Note: 1 “Year” must be that of the current version.

4:1 Reinforcement Detailing Handbook

Table 4.3 Physical Properties of Deformed Bars D500N Bar size, Design area [Note 1] db (mm) (mm2)

Theoretical area [Note 2] (mm2)

Calculated mass [Note 3] (kg/m)

Nominal mass [Note 4] (kg/m)

10 12 16

80 110 200

78.5 113.1 201.1

0.6162 0.8878 1.5783

0.6316 0.9100 1.6178

20 24 28

310 450 620

314.2 452.4 615.8

2.4662 3.5513 4.8337

2.5278 3.6400 4.9545

32 36 40

800 1020 1260

804.2 1017.9 1256.6

6.3133 7.9903 9.8646

6.4712 8.1901 10.1112

50

1960

1963.5

15.4131

15.7984

NOTES: 1 The design area of a deformed bar is the theoretical area, rounded to two significant places. 2 The theoretical area of a deformed bar is calculated from the bar size as if it was a circle. 3 The calculated mass is the theoretical area multiplied by 0.00785 kg/mm2/m. 4 The nominal mass includes the rolling margin of 2.5% based on the calculated mass.

Table 4.4 Design Area by Number of Deformed Bars (mm2) Number of bars 1 2 3

D500N bar size (mm) 12

16

20

24

28

32

110 220 330

200 400 600

310 620 930

450 900 1350

620 1240 1860

800 1600 2400

Table 4.5 Design Area for Distributed Deformed Bars (mm2/m) Spacing of bars (mm) 60 80 100 120

D500N bar size (mm) 12 1833 1375 1100 917

16

20

24

3333 * * 2500 3875 * 2000 3100 4500 1667 2583 3750

28

32

36

* * *

* * * *

* * * * *

5167

140 160 180 200

786 1429 2214 3214 4429 5714 688 1250 1938 2813 3875 5000 611 1111 1722 2500 3444 4444 550 1000 1550 2250 3100 4000

220 240 260 280

500 458 423 393

909 833 769 714

300 320 340 360

367 344 324 306

667 1033 625 969 588 912 556 861

380 400 450 500

289 275 244 220

526 500 444 400

*

1409 2045 2818 3636 1292 1875 2583 3333 1192 1731 2385 3077 1107 1607 2214 2857 1500 1406 1324 1250

6375 5667 5100 4636 4250 3923 3643

2067 1938 1824 1722

2667 2500 2353 2222

3400 3188 3000 2833

816 1184 1632 775 1125 1550 689 1000 1378 900 1240 620

2105 2000 1778 1600

2684 2550 2267 2040

A centre-to-centre spacing of less than 4db is not provided because concrete is difficult to place and splitting can occur along this plane.

36 1020 2040 3060

4.3

SELECTION OF MEMBER SIZE Check that beam and column sizes are

4 5 6

440 550 660

800 1000 1200

1240 1550 1860

1800 2250 2700

2480 3100 3720

3200 4000 4800

4080 5100 6120

adequate for fire resistance and concrete compaction

7 8 9

770 880 990

1400 1600 1800

2170 2480 2790

3150 3600 4050

4340 4960 5580

5600 6400 7200

7140 8160 9180

4.3.1 Minimum Beam and Column Sizes for

10

1100

2000

3100

4500

6200

8000

10 200

NOTE: Before selecting the number of bars in one layer of a beam or column, check Clause 4.3.1 for minimum beam and column widths.

purposes before selecting the number of bars in a layer.

Fire Resistance Table 4.6 is derived from AS 3600 Section 5 using the minimum thicknesses for various fire resistance periods. Exposure classifications other than A1 and B1 for buildings are unlikely to be exposed to fire and are not included. Rectangular beams which may be exposed to fire on all sides must also have a depth not less than the width required for fire resistance. T-beams and L-beams need only comply for the web width because the top surface is protected by the slab, see Figure 4.1.

4:2 Reinforcement Detailing Handbook

Table 4.6 Minimum Beam Web Width for Fire Resistance, bw.fire (mm) Assuming Fitments to be 10 mm or Larger

Example 4.1 A continuous beam has an exposure classification of A1, which leads to a cover to the fitment of 20 mm for corrosion protection (Clause 5.5). Enter Table 4.6 at the A1 classification. Assume the fitment is R10, so that the side-cover and soffit-cover to the main steel is 30 mm. This is the value of cfire. For an FRP of 120 minutes, the minimum continuous-beam width bw.fire is read as 500 mm. If the beam is exposed to fire on all sides then this is also the minimum overall depth, D. However if the required FRP is 240 minutes, then a side cover of 30 mm will never be adequate regardless of the beam width. To obtain an FRP of 240 minutes, the continuous-beam width must be at least 700 mm with 50 mm main-bar cover. Thus for an FRP of 240 minutes, continuous band-beams with banded slabs require 50 mm cover to the soffit and sides provided they are over 700 mm wide.

Main-bar Fire Resistance Period (FRP) in minutes cover,* Exposure Cover Class cexp (mm) cfire (mm) 30 60 90 120 180 240 SIMPLY-ED BEAMS A1

20 25 30

30 35 40

80 80 80

200 160 120

N/A 400 300

N/A N/A N/A

N/A N/A N/A

N/A N/A N/A

B1

40 45

50 55

80 80

120 120

175 150

500 300

N/A N/A

N/A N/A

CONTINUOUS BEAMS A1

20 25 30

30 35 40

80 80 80

120 120 120

200 150 150

≥ 500 300 250

N/A N/A ≥ 600

N/A N/A N/A

B1

40

50

80

120

150

200

400

≥ 700

* Assuming 10-mm fitments, cfire = cexp + 10

For columns (Figure 4.2) the minimum dimension for fire should be obtained from AS 3600 Table 5.5.3 or Table 5.5.4, depending on whether the column is braced or unbraced. The value also changes depending on the ratio of actual load to the load capacity of the column and the reinforcement percentage. � ����

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Figure 4.1 Minimum Beam Widths for Fire

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Figure 4.2 Minimum Column Widths for Fire

4:3 Reinforcement Detailing Handbook

4.3.2 Band-Beam and Slab Systems, and Blade Columns There is no distinction for flexural-strength calculations between beams and slabs. For fire resistance, the cover to the longitudinal bars of a

Table 4.7 Beam Web Widths and Column Sizes (mm) for 2db Clear Distance Between Bars Cover to Main-bar size (mm) main bars No. of (mm) bars 12 16 20 24 30 (20-mm cover +10-mm fitment)

28

32

36

2

110

3

150 180 200 230 260 290 N/A

4

180 220 260 300 340 380 N/A

5

220 270 320 380 430 480 N/A

requirement for shorter FRP’s. For further details on fire

6

260 320 380 450 510

resistance of slabs including flat slabs, flat plates and

7

290 370 440 520 600 670 N/A

ribbed slabs, refer to AS 3600 Clause 5.4.

8

330 420 500 590 680 770 N/A

wide beam is the same as that for a slab when the web width is at least 700 mm for a simply-ed member, or continuous member. In each case, there is a reduced cover

For fire resistance of walls, AS 3600 Clause 5.6

130 140 160 180 190 N/A

580 N/A

9

360 460 560 660 760 860 N/A

10

400 510

620 740

850 960 N/A

Extra

36

60

84

2

130 150 160 180 200 210

230

3

170

340

4

200 240 280 320 360 400 440

5

240 290 340 400 450 500 550

size of the main bar (2db.main), that is the centre to

6

280 340 400 470 530 600 660

centre spacing is 3db.

7

310

These limitations are related to AS 3600

8

350 440 520 610 700 790 880

Clause 13.1.2.1 for tensile stress development. One of

9

380 480 580 680 780 880 980

should be used for obtaining full details. 4.3.3 Minimum Beam Web Width and Column Sizes for Concrete Compaction Purposes Table 4.7 gives the minimum web width of beams and minimum width of a column. They are based on a clear distance between bars of twice the

40 (30-mm cover +10-mm fitment)

48

72

96

200 220 250 280 310

N/A

390 460 540 620 690 770

the factors is that the cover to the main bar

10

420 530 640 760 870 980 1090

(cmain = cfitment+db.fitment) must not be less than

Extra

36

2

150 170

3

190 220 240 270 300 330 360

4

220 260 300 340 380 420 460

5

260 310

6

300 360 420 490 550 620 680

7

330 410

480 560 640 710

790

8

370 460 540 630 720 810

900

one-half the clear distance between parallel bars (clear distance = 2db.main in this Table). It is assumed that the member has properly designed fitments to control longitudinal splitting. There are minimum values – generally columns

50 (40-mm cover +10-mm fitment)

less than 200 mm x 200 mm are difficult to build. Wherever possible, wider should be selected. NOTE: While the beam widths in Table 4.7 may meet the requirements of AS 3600, generally a gap of 60–75 mm is required between top bars to allow the use of a thin poker vibrator. This means a beam may have to be wider, especially for narrow beams. Hence sections less than 200 mm thick may be difficult to construct, and place and compact the concrete.

60 (50-mm cover +10-mm fitment)

48

60

Reinforcement Detailing Handbook

84

96

108

180 200 220 230 250

360 420 470 520 570

9

400 500 600 700 800 900 1000

10

440 550 660 780 890 1000 1110

Extra

36

48

2

170

190 200 220 240 250 270

3

210

240 260 290 320 350 380

4

240 280 320 360 400 440 480

5

280 330 380 440 490 540 590

6

320 380 440 510

7

350 430 500 580 660 730 810

8

390 480 560 650 740

60

72

84

96

108

570 640 700 830 920

9

420 520 620 720 820 920 1020

10

460 570 680 800 910 1020 1130

Extra

36

48

60

See Note in text (Clause 4.3.3).

4:4

72

72

84

96

108

4.4

PLAIN ROUND BARS, GRADE 250N

4.5

LOW DUCTILITY DEFORMED BARS, GRADE 500L

Physical properties of plain round bars for fitments are given in Table 4.8.

There is a greater range of D500L bar sizes

Suggested specification. Plain round

available as shown in Table 4.9. If the designer’s

reinforcing bars for fitments shall be hot-rolled bars of

calculations use 250 MPa as the design strength for

grade 250N

fitments, then either R250N or D500L can be specified; if 500 MPa is used as the design strength, only the appropriate D500L bar size should be detailed. D500L

Table 4.8 Physical properties of plain round bars for

bar can only be used for fitments or for making of

fitments, Grade 250N

mesh in accordance with AS 3600.

Bar size, Design Theoretical Calculated Nominal area mass area mass db (mm) (mm2) (mm2) (kg/m) (kg/m)

Table 4.9 Physical Properties of Low Ductility Deformed Bars for Mesh or Fitments, Grade 500L

6.5 10.0

Bar size, db (mm)

Design area (mm2)

Nominal mass (kg/m)

6.00 6.75 7.60 8.60 9.50 10.70 11.90

28.3 35.8 45.4 58.1 70.9 89.9 111.2

0.222 0.281 0.356 0.456 0.556 0.706 0.873

30 80

33.2 78.5

0.2605 0.6165

0.2670 0.6320

NOTE: 1. Availability of these sizes can depend on local practice throughout Australia. They may in fact be available only as coiled rod (see Clause 2.1) of grade 250N. 2. Plain round bars for dowel bars are available in larger sizes.

NOTE: 1. For bar, the design area and nominal mass are calculated from the actual bar size.

4:5 Reinforcement Detailing Handbook

4.6

REINFORCING MESH, GRADE 500L

Table 4.10 Mesh Specification for Preferred-Size Mesh to AS/NZS 4671 Using D500L Bars

Mesh ref. No.

Longitudinal bars

Cross bars

Mass (6 x 2.4 m sheets)

Cross-sectional area

No. x dia. (mm).

Pitch (mm)

No. x dia. (mm)

Pitch (mm)

Unit area (kg/m2)

Sheet (kg)

Longitudinal Cross (mm2/m) UNO (mm2/m)

Rectangular RL1218

25 x 11.9

100

30 x 7.6

200

10.5

157

1112

227

RL1018

25 x 9.5

100

30 x 7.6

200

7.3

109

709

227

RL818

25 x 7.6

100

30 x 7.6

200

5.3

79

454

227

Square, with edge side-lapping bars SL102

10 x 9.5 + 4 x 6.75

200 100

30 x 9.5

200

5.6

80

354

354

SL92

10 x 8.6 + 4 x 6.0

200 100

30 x 8.6

200

4.6

66

290

290

SL82

10 x 7.6 + 4 x 6.0

200 100

30 x 7.6

200

3.6

52

227

227

SL72

10 x 6.75 + 4 x 5.0

200 100

30 x6.75

200

2.8

41

179

179

SL62

10 x 6.0 + 4 x 5.0

200 100

30 x 6.0

200

2.2

33

141

141

454

Square, without edge side-lapping bars SL81

25 x 7.6

100

60 x 7.6

100

7.1

105

454

Trench Meshes L12TM

N x 11.9

100

20 x 5.0

300

N/A

N/A

N x 111.2 (mm2) 65

L11TM

N x 10.7

100

20 x 5.0

300

N/A

N/A

N x 89.9 (mm2)

65

L8TM

N x 7.6

100

20 x 5.0

300

N/A

N/A

(mm2)

65

N x 45.4

NOTES: 1. The edge bars on SL meshes may be replaced by smaller edge bars of equal or greater cross-sectional area, in total, that the main longitudinal bars being replaced provided the smaller bars meet the minimum ductility requirements of the bar or bars to be replaced. 2. Mass of mesh is based on a piece cut from a full sheet and being one metre square with equal overhangs on opposite sides. 3. Trench mesh is normally specified by the number (N) of bars used in either the top and/or bottom of the footing so that the cross-sectional areas are not often utilised. Common strip widths are 200 mm (3 bars), 300 mm (4 bars), and 400 mm (5 bars). See AS 2870 for applications. 4. Mesh configurations are not limited to those shown in the Table 4.10. Mesh main bar spacings are the most critical factor for special meshes, and detailers should check with mesh manufacturers before finalising a design. 5. The design characteristic yield strength of mesh is 500 MPa but at low ductility.

4:6 Reinforcement Detailing Handbook

5

5.2

Cover

5.2.1 Cover Selection for Durability

GENERAL COMMENTS

In AS 3600, durability of the structure is very much related to individual surfaces of a member and

5.1

INTRODUCTION According to AS 3600:2007, “cover is the

distance between the outside of the reinforcing steel or tendons and the nearest permanent surface of the member, excluding any surface finish. Unless otherwise noted, the tolerances on cover given in Clause 17.5.3 apply”. It should be noted that AS 3600 only sets minimum standards, including cover. Designers may choose a larger cover if they consider it warranted. The two primary purposes of cover are for durability and for fire resistance. As a general rule, cover is selected from an appropriate Table but there are several cases where additional cross-checks are required. A secondary reason for adequate cover is to ensure that the stresses in steel and concrete can be transferred, one to another, by bond. These actions are called stress development and anchorage. The “cover” required for these purposes is measured not to the “nearest bar” but to the bar whose stress is being developed. An example is the “cover” to a longitudinal

to the compressive strength of the concrete and its exposure to elements that may affect its durability. For one member having the same durability resistance as another member, AS 3600 requires the same cover, but the method of selecting the exposure classification and the appropriate concrete strength requires a number of factors to be considered. The following information should be derived from Clause 5.3, before cover for corrosion protection is calculated by Clause 5.5. (a) The most severe Exposure Classification for durability (A1 to U); (b) the characteristic compressive strength of the concrete (f’c) for the most severe situation for use in strength, serviceability and durability design, allowing for abrasion and freeze/thaw conditions; (c) the degree of compaction; and (d) the type of formwork. 5.2.2 Cover Selection for Fire-Resistance Design for fire resistance by AS 3600 is based

bar in a beam which is enclosed by a fitment

on overseas and Australian information. Details are

– the latter piece of steel is therefore the “nearest”

given in Clause 5.6.

surface. Anchorage is dealt with in Chapter 6 of this Handbook. Fortunately, in practice, designers and detailers recognise the different meanings of the word “cover”, but in a Handbook such as this, clear distinctions may be necessary at various times. Selection of cover is a design decision for the engineer as it influences the mathematics of design. However, the detailer should also have a clear understanding of the method of selection of cover. (See Clause 1.2.3 in this Handbook). For bridges, whilst the general principles are the same, the details are different from this chapter. See Chapter 19.

5:1 Reinforcement Detailing Handbook

5.3

STEP-BY-STEP SELECTION OF EXPOSURE CLASSIFICATION AND CONCRETE STRENGTH FOR

2

Determine Exposure Classification from Table 4.3. Refer AS 3600 for notes on Exposure Classification

DURABILITY RESISTANCE s of this Handbook are advised that the following flowchart is illustrative only, and must be verified from the applicable published edition of AS 3600 before being applied to an actual design.

1

Select the member to be designed and refer to AS 3600 Table 4.3 (Step 2)

Record member:

Surface of the member and its exposure environment 1. In with the ground (a) protected by damp-proof membrane (b) Residential footing in non-aggressive soil (c) Other in non-aggressive soils (d) in aggressive soils (refer to AS 3600 Clause 4.8 and Clause 4.5) 2. In interior environments (a) Member fully enclosed within a building except for brief period of weather exposure during construction (i) Residential (ii) Non-residential (b) Member in (industrial) building and being subjected to repeated wetting and drying 3. In above-ground exterior environment, in areas which are: (a) Inland (> 50km from coastline) – (i) Non-industrial and arid climatic zone (ii) Non-industrial and temperate climatic zone (iii) Non-industrial and tropical climatic zone (iv) Industrial and any climatic zone (b) Near-coastal (1km to 50km from coastline) – Any climatic zone (c) Coastal (up to 1km from coastline but excluding tidal and splash zones) – Any climatic zone 4. In water (a) In fresh water (b) In sea-water – (i) permanently submerged (ii) in spray zone (iii) in tidal or splash zones (c) In soft or running water 5. In other environments Any exposure not otherwise described above Record Exposure Classification:

5:2 Reinforcement Detailing Handbook

Classification reinforced & prestressed A1 A1 A2 U

A1 A2 B1

A1 A2 B1 B1 B1 B2

B1 B2 C1 C2 U U

3

Select concrete strength for Exposure Classification

Exposure Classification (AS 3600 Table 4.3)

For details see AS 3600 Clause…

Select concrete strength (MPa)

A1 A2 B1 B2 C1 C2 U

4.4 4.4 4.4 4.4 4.4 4.5

20 25 32 40 50 Designer specifies

Record strength as fc.xc:

4

Is surface subject to abrasion action? No: Go to AS 3600 Clause 4.7 (Step 5) Yes: Go to AS 3600 Clause 4.6 (below) Minimum strength (MPa)

Type of abrasion 1. Footpath or residential driveway 2. Commercial and non-trafficked industrial floor 3 (a) Pneumatic-tyred traffic (b) Non-pneumatic tyred traffic (c) Steel-wheeled traffic. Designer to assess, but not to be less than

20 25 32 40 40

6

Summary

For exposure conditions, take the highest value of fc.cx, fc.abrasion and fc.freeze/thaw, then… Record this as fc.exposure : For various structural reasons, such as strength or serviceability, the designer may require a compressive strength different from the value of fc.exposure… Record this as fc.structural : For design purposes, select the higher value of fc.exposure or fc.structural and call this the 28-day characteristic compressive strength of the concrete… Record this as f’c : Check AS 3600 Clause 4.3.2 (see Clause 5.5 this Handbook) for any concession on fc.exposure for a member with only one exterior surface exposed to a worst situation… For this member, record previous fc.structural as f’c :

In the drawings, for every member, you must specify in some way: ■

Exposure Classification for durability; ie A1 to U.

■

Class of concrete (normal or special) and its strength grade or characteristic strength, ie the final value of f’c.

■

Any other required properties of the concrete.

Record worst case as fc.abrasion:

5

Is part of member subject to freeze/thaw? No: Go to summary (Step 6) Yes: Go to AS 3600 Clause 4.7 (below)

Number of cycles per year

For details see AS 3600 Clause…

Minimum strength (MPa)

< 25 ≥ 25

4.7a(i) 4.7a(ii)

32 40

Record as fc.freeze/thaw:

5:3 Reinforcement Detailing Handbook

OTHER FACTORS AFFECTING

5.4

5.4.3 Interpretation of the Relevant Value of

SELECTION OF COVER FOR

“ccorrosion”

CORROSION PROTECTION

Tables 5.1 to 5.4 give the cover to the nearest steel as required for corrosion protection. We shall call

5.4.1 Formwork and Compaction Effects AS 3600 Clause 4.10.3 allows the concrete to be placed in various types of formwork: ■

For slabs, walls, footings, etc “ccorrosion” applies to the steel nearest the appropriate surface. Cover from

Forms which comply with AS 3610 (See

both surfaces of thin must be checked, even

AS 3600 Section 17.6).

if there is only one layer of steel.

■

Against the ground.

■

In the ground with a suitable separating membrane.

■

this “ccorrosion”.

For beams and columns which have fitments, “ccorrosion” from the tables applies initially to the fitments. The actual depth to the main bars will be

For precast concrete, using rigid forms.

greater than the tabulated values by the bar diameter

For each formwork situation, AS 3600

of the fitments and this increased value is effectively

Clause 4.10.3 has an associated compaction method: Standard compaction which implies that at least a hand held vibrator is used correctly and that there is sufficient room for it to penetrate the

“ccorrosion” for the main bars. The negative tolerances on position (equals reduced cover) given in AS 3600 Clause 17.5.3(a) are included already in the values for “ccorrosion” shown

reinforcement cages (see AS 3600 Clauses 4.10.3.2

in Tables 5.1 to 5.4. This means that to select the

and 17.1.3), and

appropriate cover to the nearest steel, read the values

Intense compaction of precast concrete only with rigid formwork, which implies that intense external

direct and do not select a higher cover. The resulting cover for corrosion protection to

vibration, perhaps from vibrators attached to the forms,

the appropriate fitment, main bar or tendon is recorded

will be applied.

as “ccorrosion”.

Because of its importance for corrosion protection, formwork and methods of compaction are required to be given in the drawings as an instruction. 5.4.2 A Reminder In any one member it is impossible to provide concrete with more than one specified strength. One exception is floor slabs in high rise buildings where the section of the slab at the column may need a higher strength than the floor and a higher strength is used. (Refer Section 10.8 of AS 3600). However it is quite possible for one member to have different exposure conditions on various faces. For example, an external wall or a roof would be subjected to the weather on its outside face and to a protected environment inside; that is, there can be a combination of A1/B1 or A1/B2 with these . It is permissible to specify different cover on these faces, but beware of the high risk of error. In the case of beams and columns, however, different covers on different faces must not be specified.

5:4 Reinforcement Detailing Handbook

Example 5.1 For exposure class A2, 25 mm cover with 25 MPa concrete was considered adequate by the AS 3600’s committee. To allow for the tolerance of – 5 mm, the cover specification in Table 4.10.3.2 was set at 30 mm.

5.4.4 Additional Check on Minimum Cover for

■

5.5

Concrete Placement and Compaction

REINFORCEMENT AND TENDONS

(AS 3600 Clause 4.10.2)

FOR CORROSION PROTECTION

The actual cover to any fitment, bar or tendon,

Tables 5.1 to 5.4 apply to the steel nearest the

must not be less than the maximum nominal

surface.

aggregate size “caggregate”. See Chapter 19 for ■

s of this Handbook should that the

bridges.

values in these Tables apply to the current edition of

The actual cover must not be less than the

AS 3600. They are based on AS 3600:2007.

diameter “db.fitment” of any fitment being covered. ■

■

■

SELECTING COVER TO

In Table 5.1 and Table 5.4 only, the covers

The actual cover must not be less than the

shown in parentheses are those appropriate to the

diameter “db.main” of any main steel being

concession given in AS 3600 Clause 4.3.2. This

covered. Because the diameter of any fitment

permits the concrete strength grade for exposure

provides an effective cover to the main bars of

condition (fc.exposure) to be reduced by one grade (eg

“ccorrosion.fit + db.fitment”, this value should be

N32 to N25) when one face of a member has a higher

used when checking cover.

exposure classification than the other faces and the

Additional Clauses are given for bridges which

concrete strength for other reasons (fc.structural) is also

will affect tendon and reinforcement layouts.

one grade less than fc.exposure.

If a blinding layer has been previously placed, it can act as a formed surface for cover requirements. In any member, each layer of steel will have its

own cover for durability and the designer must take this into . The cover for durability design “cdurability” for each steel item is the largest of the covers for corrosion protection, the cover for placement of concrete based on aggregate size, and its own diameter.

Example 5.2 Assume the fitment is R10 with a corrosion cover of 20 mm. This would be satisfactory for the fitment. However, if the main bar diameter was greater than 30 mm, an increased cover to that bar must be specified in the drawings, usually by increasing the cover to the fitment to 25 or 30 mm. Generally these can be checked mentally without need for calculation.

Example 5.3 The exposure classification is B1 for the outer face of an external column. The internal faces are protected and have classification A1. The two combinations for the column as a whole are (from Table 5.1): (i) Concrete grade 32 MPa with 40 mm cover to fitments, or (ii) Concrete grade 25 MPa with 60 mm cover to fitments. The fact that, for classification A1, grade 20 could apply to the other surfaces has no influence on the decision.

Table 5.1 Required Cover (mm) for Corrosion Protection, ccorrosion, where Standard Formwork and Compaction Used. [Based on AS 3600 Table 4.10.3.2] Exposure Classification

Compressive strength, f’c (MPa) not less than 20

25

32

40

≥ 50

A1

20

20

20

20

20

A2

(50)

30

25

20

20

(60)

40

30

25

(65)

45

35

(70)

50

B1 B2 C1 C2

65

NOTE: Pairs of values with grey background correspond to concession given in AS 3600 Clause 4.3.2

5:5 Reinforcement Detailing Handbook

Table 5.2 Required Cover (mm) for Corrosion Protection, ccorrosion, where Concrete is Cast on or Against Ground Protected by a “Damp-Proof” Membrane and Standard Compaction Used [Based on AS 3600 Table 4.10.3.5(a)] Exposure Classification A1

Compressive strength, f’c (MPa) not less than

5.6

SELECTION OF COVER FOR FIRE RESISTANCE

5.6.1 Guidelines for Fire-Resistance Protection During the course of a fire, temperatures

20

25

32

40

≥ 50

30

30

30

30

30

both steel and concrete. Fortunately, the insulation

40

35

30

30

properties of concrete are greater than those of steel

50

40

35

55

45

A2 B1 B2

in excess of about 200°C reduce the strength of

and the concrete cover is the best and cheapest method of increasing the fire-resistance of structures. The cover for fire-resistance (c fire) depends

C1

60

on the type of member, how that member carries the

C2

75

loads imposed on it, whether or not it is continuous (flexurally or structurally) with other , and the

NOTE: No AS 3600 Clause 4.3.2 concession permitted

type of fire protection it provides. Concrete strength is not taken into

Table 5.3 Required Cover (mm) for Corrosion Protection, ccorrosion, where Concrete is Cast Directly Against Ground Without a “Damp-Proof” Membrane and Standard Compaction Used [Based on AS 3600 Table 4.10.3.5(b)] Exposure Classification A1

Compressive strength, f’c (MPa) not less than 20

25

32

40

≥ 50

40

40

40

40

40

50

45

40

40

A2 B1

60

B2

50

45

65

55

C1

70

C2

85

when selecting cover for fire-resistance. Similarly, the effects of fire need only be considered for inside the shell of a building which is required, by Building Regulations or through other Authorities, to attain a specified fire-resistance level. In certain structures which have a high exposure-classification, due to proximity with hazardous materials for example, resistance to fire must be considered very seriously. To use Section 5 of AS 3600, a member must be classified as a beam, a slab, a column or a wall. For example, a staircase would be of slab form, whilst its may be a wide beam or a slab. In all cases, a thicker member of concrete with greater cover will have a longer fire-resistance period. AS 3600 is quite explicit that a wide beam

NOTE: No AS 3600 Clause 4.3.2 concession permitted

can be treated as a slab and that an exposed column cannot be treated as a wall. Table 5.4 Required Cover (mm) for Corrosion Protection, ccorrosion, where Concrete is Precast in Rigid Formwork and Intense Compaction Used. [Based on AS 3600 Table 4.10.3.3] Exposure Classification

Compressive strength, f’c (MPa) not less than

5.6.2 Step-by-step Selection of Cover for Fire Protection Because there are many interlocking provisions in AS 3600 Section 5, the designer and detailer should

20

25

32

40

≥ 50

A1

20

20

20

20

20

In particular, the required fire-resistance level of each

A2

(45)

30

20

20

20

member should be obtained from the Building Code of

(45)

30

25

20

(50)

35

25

(60)

45

B1 B2 C1 C2

60

NOTE: Pairs of values with grey background correspond to concession given in AS 3600 Clause 4.3.2

5:6 Reinforcement Detailing Handbook

refer directly to both the standard and its Commentary.

Australia (BCA). Architectural design should also have allowed for the required member thicknesses – if it has not then there could be some drastic changes to dimensions.

The following procedure may assist: ■

Obtain required fire-resistance level from BCA;

■

Having already determined the cover for

� ����

durability for the member concerned, go to the

�����������

� ����

relevant sub-clause of Section 5 of AS 3600:

� ����

• For beams, to 5.3 • For slabs and ribbed slabs, to 5.4 • For wide beams, compare 5.3 with 5.4

� ����

�������

• For columns, to 5.5

� ����

�������

• For walls, to 5.6 and possibly 5.5; and

� ����

• For where the insulating properties need to be increased because of inadequate cover, to 5.7. ■

From the relevant Sub-clause of Section 5: • If the member is a slab or wall, check that the thickness is adequate for “insulation” and “integrity”. The wise designer will have done this before starting the analysis. These two

� ����

�������

Figure 5.1 Minimum Beam Widths for Fire

properties are needed to stop the spread of

� ����

fire and smoke beyond the compartment (room) where the fire occurs. • For all types of member, check that the cross

� ����

�����

sectional dimensions are structurally adequate for fire-resistance. Structural adequacy for fire � ����

resistance permits lower load factors than those for normal strength calculations.

������������������������������������

• For fire resistance, the cover to the longitudinal bars of a wide beam (called here band-beam and slab systems or just band-beams) is the

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same as that for a slab when the web width is at least 700 mm for a simply ed member, or continuous member.

� ����

�������

� ����

• If a wall does not have a fire-separating

� ����

function, it cannot be designed as a wall for fire-resistance. It must be treated as a column.

� ����

�����

Figure 5.2 Minimum Column Widths for Fire

• For prestressed , check cover to tendons exceeds the increased amount. • From the appropriate Sub-clause, Figure or Table, read-off the cover for fire-resistance (cfire). 5.6.3 Actual Cover for Fire Protection For slabs and walls, cfire refers to any load-

5.7

FINAL SECTION OF THE APPROPRIATE DESIGN COVER “c” The design cover for each component of

steel in the member, “c” is the largest value of the covers required for corrosion protection of the steel (Clause 5.5), the cover for placement of concrete

carrying reinforcement, but obviously the critical steel is

based on aggregate size, bar size, duct size, etc

that closest to the surface to be protected.

and concrete compaction (Clause 5.4.4) and for

For beams and columns, cfire refers to the

fire protection (Clause 5.6.2). The Bridge Standard

load-carrying longitudinal bars or tendons, not to the

AS 5100 has some differences in cover (refer AS 5100

fitments, see Figures 5.1 and 5.2.

Part 5 Section 4).

5:7 Reinforcement Detailing Handbook

SELECTION OF MEMBER SIZE

5.8

Now that the design cover is determined, design

Not only does the weight of steel have to be ed on bottom formwork, but sideways shifting

for strength and serviceability may be carried out for

of cages or mats must also be prevented. Beam and

each member.

column cages have different requirements, as do slab

It is essential to check that beam and column widths are adequate for fire resistance and concrete-

and wall mats. It is therefore logical, after taking so much care

compaction purposes. Tables given in Chapter 4 of

to calculate the cover, that the methods of chairing

this Handbook should be consulted.

and spacing the steel should also be specified in considerable detail.

BAR S AND SPACERS FOR

5.9

THE MAINTENANCE OF COVER ■

Selection of the relevant cover includes consideration of: • The environment to which each concrete surface is exposed. • Whether surface abrasion and/or freeze/thaw is possible. • The characteristic compressive strength of the concrete used in the design. • The type and quality of the formwork. • The quality of compaction of the concrete. • The maximum nominal aggregate size. • The size of the bar, tendon or duct being covered (ie near the surface). • The degree of risk to life and property should a fire occur. • How the member is intended to act structurally (ie simply ed or continuous) under normal and fire conditions.

■

Factors which affect the final position in the concrete include: • The effects of variations during fabrication of bars, and • Variations from the designed (specified) position during construction. Both of these have a set of tolerances for each

situation. The designer therefore uses calculated values of design cover, the detailer shows the relevant values in the drawings and the steel is fixed within the placing envelope. Onsite inspection must therefore not penalise placement within the allowable range. As noted before, if a designer has concerns with tolerance, it is better to increase the cover.

5:8 Reinforcement Detailing Handbook

Clauses 3.1.3 and 3.2 of this Handbook, together with AS 3600 Clause 17.2.5 should be consulted. Some limitations may also be placed on the use of types of bar chairs, eg The Steel Reinforcement Institute of Australia recommends that plastic-tipped wire chairs not be used in exposure Classification B2 or worse.

6 Stress Development and Splicing of Reinforcement Special Note

SECTION 1 (AS 3600:2001 Version)

This Chapter has been broken into two standalone sections. This is due to the major changes proposed in the 2007 version of Chapter 13 of AS 3600 Concrete Structures Standard. The Clause numbers will appear twice in the Chapter and each will refer to similar information. Section 1 of the Chapter is material in the current 2001 version of the AS 3600 and begins on page 6:1. Section 2 of the Chapter is material in the draft 2007 version of the AS 3600 which begins on page 6:14. It has been prepared this way so the book is useful now and can be adjusted easily when the new version of the standard is finally published. In some parts of the Chapter where there has been no change in content between the two versions of AS 3600, the wording is the same. Readers should use the 2001 version of the standard and Section 1 of this Chapter until the new 2007 version of the standard is published.

6.1

GENERAL Earlier sections of this Handbook referred to

the fact that whilst structures are generally designed in quite large pieces (such as a complete frame or a continuous beam), they must be constructed in quite small segments, called elements. The art of detailing is to ensure that the materials which connect the individual elements together will provide adequate strength and ductility for the total structure. AS 3600 Section 13.1 is concerned with developing stress in reinforcement by bond with insitu concrete. AS 3600 Section 13.2 describes methods of splicing reinforcement within an element or for ting elements together. The methods used are laps, welds and mechanical splices. The purpose of the Tables in this Handbook is to provide consistent values for detailers, schedulers and inspectors. Most values are rounded-up as appropriate. 6.2

PRINCIPLES OF STRESS DEVELOPMENT This Handbook assumes that the reader has

a basic knowledge of topics such as bond strength, development length and so on. There are a number of publications available from the Cement Concrete & Aggregates Australia, the Concrete Institute of Australia and by other well-known authors. AS 3600 Section 13.1 and its associated commentary give the technical background to stress development as required by the standard. The background to the formula for the development length of a deformed bar is also given.

6:1 Reinforcement Detailing Handbook

6.2.1 Development length of deformed bars in tension, Lsy.t (AS 3600 Clause 13.1.2) The development length formula is: Depth factor x spacing factor x bar yield strength x bar area

Lsy.t =

[(smaller of twice actual cover or clear spacing) + bar size] x √concrete strength The formula, as expressed above, shows that as the cover and spacing increases, the development length decreases. This approach differs from previous

�����

�����

standards and is based on research results. ����������� �������������

�� ��

��� �������

���������� ��������� ������� ���������������������������������������������������

Figure 6.1 The Development Length “Cylinder”

6.2.2 Expanded-Range Tables for Tensile Development Length of Deformed Bars This Handbook provides a range of values of Lsy.t for: ■

Slabs, walls, pad footings and similar wide , in Table 6.1;

■

Columns and the bottom bars of beams with fitments, in Table 6.2;

■

The top bars of beams with fitments, in Table 6.3; and

■

Bars in any member which is not covered by the above, in Table 6.4. The value of “a” used to calculate the Tables,

is purely a number representing the smaller of the cover to the bar whose stress is being developed and half the clear spacing between adjacent parallel bars (horizontally and vertically). As a general rule, “a” may be taken as the design cover. “2a” can also be the clear spacing between parallel bars in two layers. See Figure 6.2 as well as the Diagrams with each Table.

6:2 Reinforcement Detailing Handbook

�����

�����

������ �� ������������������������������������������������������������������������� � �������������������������������������������������� �� �������������������������������������������������������������������

Figure 6.2 The Length over which Adjacent Bars Develop their Tensile Strength

Please read the restrictions and note that some are more severe than AS 3600. Values are rounded-up to the nearest 10 mm and provide for tolerances. The cover in these Tables is the actual cover to the deformed bar being detailed. No allowance is made for a possible reduction in cover due to placing or other tolerances because the strength reduction Ø factor of 0.8 is included in the formula for this purpose. If the designer believes the situation is critical, a longer development length for that smaller cover can be obtained from the Table. Development lengths can be checked visually or with the computations. They are generally not put in the drawings.

Table 6.1 Development Lengths(1), Lsy.t (mm) for Grade D500N Bars in Wide For bars in walls and slabs, footings and stairs (top or bottom) where Sc is equal to or greater than 150 mm

k1 = 1.0

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�������� ������������

f’c a (3) (MPa) (mm)

Bar size N10

N12

N16

N20

N24

N28

N32

N36

f’c a (3) (MPa) (mm)

k 2 = 1.7

Sc = clear distance between adjacent bars (or bundles of bars) developing stress c = minimum cover to bar under consideration

Bar size N10

N12

N16

N20

N24

N28 N32 N36

20

20 25 30 35 40 45 50 55 60 65 70 75

300 250 250 250 250 250 250 250 250 250 250 250

410 350 300 300 300 300 300 300 300 300 300 300

680 1000 580 850 1160 500 750 1020 1330 440 660 910 1190 1500 400 600 830 1080 1360 1670 400 540 750 990 1250 1540 400 500 690 910 1160 1420 400 500 640 850 1080 1330 400 500 600 790 1010 1240 400 500 600 740 940 1170 400 500 600 700 890 1100 400 500 600 700 840 1040

40

20 25 30 35 40 45 50 55 60 65 70 75

250 250 250 250 250 250 250 250 250 250 250 250

300 300 300 300 300 300 300 300 300 300 300 300

480 410 400 400 400 400 400 400 400 400 400 400

700 600 530 500 500 500 500 500 500 500 500 500

820 720 650 600 600 600 600 600 600 600 600

940 840 1060 770 970 1180 700 890 1090 700 820 1010 700 800 940 700 800 900 700 800 900 700 800 900 700 800 900

25

20 25 30 35 40 45 50 55 60 65 70 75

270 250 250 250 250 250 250 250 250 250 250 250

370 310 300 300 300 300 300 300 300 300 300 300

610 520 450 400 400 400 400 400 400 400 400 400

890 760 1040 670 920 1190 590 818 1070 1340 530 740 970 1220 1490 500 670 890 1120 1370 500 620 820 1040 1270 500 600 760 960 1190 500 600 710 900 1110 500 600 700 840 1040 500 600 700 800 980 500 600 700 800 930

50

20 25 30 35 40 45 50 55 60 65 70 75

250 250 250 250 250 250 250 250 250 250 250 250

300 300 300 300 300 300 300 300 300 300 300 300

430 400 400 400 400 400 400 400 400 400 400 400

630 540 500 500 500 500 500 500 500 500 500 500

730 650 600 600 600 600 600 600 600 600 600

840 760 700 700 700 700 700 700 700 700

950 860 1050 800 970 800 900 800 900 800 900 800 900 800 900 800 900

32

20 25 30 35 40 45 50 55 60 65 70 75

250 250 250 250 250 250 250 250 250 250 250 250

330 300 300 300 300 300 300 300 300 300 300 300

540 460 400 400 400 400 400 400 400 400 400 400

790 670 590 520 500 500 500 500 500 500 500 500

920 810 1050 720 940 1180 650 860 1080 1320 600 780 990 1210 600 720 920 1120 600 700 850 1050 600 700 800 980 600 700 800 920 600 700 800 900 600 700 800 900

65

20 25 30 35 40 45 50 55 60 65 70 75

250 250 250 250 250 250 250 250 250 250 250 250

300 300 300 300 300 300 300 300 300 300 300 300

400 400 400 400 400 400 400 400 400 400 400 400

550 500 500 500 500 500 500 500 500 500 500 500

640 600 600 600 600 600 600 600 600 600 600

740 700 700 700 700 700 700 700 700 700

830 800 800 800 800 800 800 800 800

930 900 900 900 900 900 900 900

Minimum:

250

300

400

500

600

700

800

900

NOTES: (1) Development lengths have been calculated using the nominal areas as per AS/NZS 4761 and have been rounded, generally to the nearest 10 mm within the accuracy of normal design limits. (2) If the depth of concrete below the bar is > 300 mm, a k1 factor of 1.25 applies and the values of Lsy.t can be obtained by multiplying the above values by 1.25. (3) Smaller of 0.5Sc and c.

6:3 Reinforcement Detailing Handbook

Table 6.2 Development Lengths(1), Lsy.t (mm) for Grade D500N Bars in Beams and Columns with Fitments For bars in columns with properlydesigned fitments and bottom bars in beams with properly-designed fitments

f’c a (2) (MPa) (mm)

k1 = 1.00 ��

Bar size N10

N12

N16

N20

N24

N28

N32

N36

k 2 = 2.2

Sc = clear distance between adjacent bars (or bundles of bars) developing stress c = minimum cover to bar under consideration

f’c a (2) (MPa) (mm)

Bar size N10

N12

N16

N20

N24

N28 N32

N36

20

20 25 30 35 40 45 50 55 60 65 70 75

390 320 280 250 250 250 250 250 250 250 250 250

530 450 390 340 300 300 300 300 300 300 300 300

880 1290 750 1100 1500 650 970 1320 1720 580 860 1180 1550 1940 520 770 1070 1400 1770 2160 470 700 980 1280 1620 1990 430 640 900 1180 1500 1840 400 590 830 1100 1390 1710 400 550 770 1020 1300 1600 400 520 720 960 1220 1510 400 500 680 900 1150 1420 400 500 640 850 1090 1350

40

20 25 30 35 40 45 50 55 60 65 70 75

270 250 250 250 250 250 250 250 250 250 250 250

380 320 300 300 300 300 300 300 300 300 300 300

620 530 460 410 400 400 400 400 400 400 400 400

910 780 1060 680 940 1220 610 840 1090 1370 550 760 990 1250 1530 500 690 910 1150 1410 500 630 840 1060 1300 500 600 780 990 1210 500 600 720 920 1130 500 600 700 860 1070 500 600 700 810 1010 500 600 700 800 950

25

20 25 30 35 40 45 50 55 60 65 70 75

350 290 250 250 250 250 250 250 250 250 250 250

480 400 350 300 300 300 300 300 300 300 300 300

790 1150 670 990 1340 580 860 1180 1540 510 770 1060 1380 1730 460 690 960 1250 1580 1930 420 630 870 1150 1450 1780 400 580 800 1060 1340 1650 400 530 740 980 1250 1530 400 500 690 920 1160 1440 400 500 650 860 1090 1350 400 500 610 810 1030 1270 400 500 600 760 970 1200

50

20 25 30 35 40 45 50 55 60 65 70 75

250 250 250 250 250 250 250 250 250 250 250 250

340 300 300 300 300 300 300 300 300 300 300 300

560 470 410 400 400 400 400 400 400 400 400 400

810 700 610 540 500 500 500 500 500 500 500 500

950 840 1090 750 980 1230 680 890 1120 1370 620 810 1030 1260 600 750 950 1160 600 700 880 1080 600 700 820 1020 600 700 800 950 600 700 800 900 600 700 800 900

32

20 25 30 35 40 45 50 55 60 65 70 75

310 250 250 250 250 250 250 250 250 250 250 250

420 350 310 300 300 300 300 300 300 300 300 300

700 1020 590 870 1190 510 760 1050 1360 450 680 940 1220 1530 410 610 850 1110 1400 1710 400 560 770 1010 1280 1570 400 510 710 940 1180 1460 400 500 660 870 1100 1360 400 500 610 810 1030 1270 400 500 600 760 970 1190 400 500 600 710 910 1120 400 500 600 700 860 1060

65

20 25 30 35 40 45 50 55 60 65 70 75

250 250 250 250 250 250 250 250 250 250 250 250

300 300 300 300 300 300 300 300 300 300 300 300

490 420 400 400 400 400 400 400 400 400 400 400

710 610 540 500 500 500 500 500 500 500 500 500

830 730 660 600 600 600 600 600 600 600 600

950 860 1080 780 980 1200 710 900 1100 700 830 1020 700 800 950 700 800 900 700 800 900 700 800 900 700 800 900

250

300

400

500

600

700

NOTES: (1) Development lengths have been calculated using the nominal areas as per AS/NZS 4761 and have been rounded, generally to the nearest 10 mm within the accuracy of normal design limits. (2) Smaller of 0.5Sc and c.

6:4 Reinforcement Detailing Handbook

Minimum

800

900

Table 6.3 Development Lengths(1), Lsy.t (mm) for Grade D500N Bars in Top of Beams with Fitments For top bars in beams with properlydesigned fitments

k1 = 1.25 ��

f’c a (2) (MPa) (mm)

Bar size N10

N12

N16

N20

N24

N28

N32

N36

��������

f’c a (2) (MPa) (mm)

k 2 = 2.2

Sc = clear distance between adjacent bars (or bundles of bars) developing stress c = minimum cover to bar under consideration

Bar size N10

N12

N16

N20

N24

N28 N32 N36

20

20 25 30 35 40 45 50 55 60 65 70 75

480 400 340 310 310 310 310 310 310 310 310 310

670 1100 1610 560 940 1380 1880 480 810 1210 1660 2150 420 720 1070 1480 1930 2420 380 640 970 1340 1750 2210 2700 380 580 880 1220 1600 2030 2480 380 530 800 1120 1480 1870 2300 380 500 740 1040 1370 1740 2140 380 500 690 970 1280 1630 2010 380 500 640 900 1200 1530 1890 380 500 630 850 1130 1440 1780 380 500 630 800 1060 1360 1680

40

20 25 30 35 40 45 50 55 60 65 70 75

340 310 310 310 310 310 310 310 310 310 310 310

470 400 380 380 380 380 380 380 380 380 380 380

780 1140 660 980 1330 580 850 1170 1520 510 760 1050 1370 1710 500 680 950 1240 1560 1910 500 630 860 1130 1430 1760 500 630 790 1050 1320 1630 500 630 750 970 1230 1520 500 630 750 900 1150 1420 500 630 750 880 1080 1330 500 630 750 880 1020 1260 500 630 750 880 1000 1190

25

20 25 30 35 40 45 50 55 60 65 70 75

430 360 310 310 310 310 310 310 310 310 310 310

600 500 430 380 380 380 380 380 380 380 380 380

990 1440 840 1230 1680 730 1080 1480 1920 640 960 1330 1730 2170 580 860 1200 1570 1970 2410 520 790 1090 1440 1810 2220 500 720 1000 1320 1680 2060 500 660 930 1230 1560 1920 500 630 860 1140 1460 1790 500 630 810 1070 1370 1690 500 630 760 1010 1290 1590 500 630 750 950 1220 1500

50

20 25 30 35 40 45 50 55 60 65 70 75

310 310 310 310 310 310 310 310 310 310 310 310

420 380 380 380 380 380 380 380 380 380 380 380

700 1020 590 870 1190 510 760 1050 1360 500 680 940 1220 1530 500 630 850 1110 1400 1710 500 630 770 1010 1280 1570 500 630 750 940 1180 1460 500 630 750 880 1100 1360 500 630 750 880 1030 1270 500 630 750 880 1000 1190 500 630 750 880 1000 1130 500 630 750 880 1000 1130

380 320 310 310 310 310 310 310 310 310 310 310

530 440 380 380 380 380 380 380 380 380 380 380

870 1270 740 1090 1490 640 950 1310 1700 570 850 1170 1530 1920 510 760 1060 1390 1750 2130 500 690 960 1270 1600 1960 500 640 890 1170 1480 1820 500 630 820 1080 1380 1690 500 630 760 1010 1290 1590 500 630 750 950 1210 1490 500 630 750 890 1140 1410 500 630 750 880 1070 1330

65

20 25 30 35 40 45 50 55 60 65 70 75

310 310 310 310 310 310 310 310 310 310 310 310

380 380 380 380 380 380 380 380 380 380 380 380

610 520 500 500 500 500 500 500 500 500 500 500

890 770 1040 670 920 1190 630 820 1070 1340 630 750 970 1220 1500 630 750 890 1120 1380 630 750 880 1040 1280 630 750 880 1000 1190 630 750 880 1000 1130 630 750 880 1000 1130 630 750 880 1000 1130 630 750 880 1000 1130

Minimum

310

380

500

630

32

20 25 30 35 40 45 50 55 60 65 70 75

NOTES: (1) Development lengths have been calculated using the nominal areas as per AS/NZS 4761 and have been rounded, generally to the nearest 10 mm within the accuracy of normal design limits. (2) Smaller of 0.5Sc and c.

750

880 1000 1130

6:5 Reinforcement Detailing Handbook

Table 6.4 Development Lengths(1), Lsy.t (mm) for Grade D500N Bars in Any not Covered by Tables 6.1 to 6.3 For bars in walls or slabs (top or bottom) where Sc is less than 150 mm and beams and columns without adequate fitments

f’c a (2) (MPa) (mm)

N12

N16

N20

N24

k 2 = 2.4

Sc = clear distance between adjacent bars (or bundles of bars) developing stress c = minimum cover to bar under consideration

Bar size N10

k1 = 1.0

�����������

N28

N32

N36

f’c a (2) (MPa) (mm)

Bar size N10

N12

N16

N20

N24

N28 N32 N36

20

20 25 30 35 40 45 50 55 60 65 70 75

420 350 300 260 250 250 250 250 250 250 250 250

580 490 420 370 330 300 300 300 300 300 300 300

960 1400 820 1200 1640 710 1050 1450 1880 630 940 1290 1690 2120 560 840 1170 1530 1930 2350 510 770 1060 1400 1770 2170 470 700 980 1290 1630 2010 430 650 910 1200 1520 1870 400 600 840 1120 1420 1750 400 560 790 1050 1330 1650 400 530 740 980 1250 1550 400 500 700 930 1190 1470

40

20 25 30 35 40 45 50 55 60 65 70 75

300 250 250 250 250 250 250 250 250 250 250 250

410 350 300 300 300 300 300 300 300 300 300 300

680 580 500 440 400 400 400 400 400 400 400 400

990 850 1160 750 1020 1330 660 910 1190 1500 600 830 1080 1360 1660 540 750 990 1250 1530 500 690 910 1160 1420 500 640 850 1070 1320 500 600 790 1000 1240 500 600 740 940 1160 500 600 700 890 1100 500 600 700 840 1040

25

20 25 30 35 40 45 50 55 60 65 70 75

380 310 270 250 250 250 250 250 250 250 250 250

520 440 380 330 300 300 300 300 300 300 300 300

860 1260 730 1080 1470 630 940 1290 1680 560 840 1160 1510 1900 500 750 1040 1370 1720 2110 460 690 950 1250 1580 1940 420 630 880 1150 1460 1800 400 580 810 1070 1360 1670 400 540 750 1000 1270 1570 400 500 710 940 1190 1470 400 500 660 880 1120 1390 400 500 620 830 1060 1310

50

20 25 30 35 40 45 50 55 60 65 70 75

270 250 250 250 250 250 250 250 250 250 250 250

370 310 300 300 300 300 300 300 300 300 300 300

610 520 450 400 400 400 400 400 400 400 400 400

890 760 1040 670 910 1190 590 820 1070 1340 530 740 970 1220 1490 500 670 890 1120 1370 500 620 820 1030 1270 500 600 760 960 1180 500 600 710 900 1110 500 600 700 840 1040 500 600 700 800 980 500 600 700 800 930

32

20 25 30 35 40 45 50 55 60 65 70 75

330 280 250 250 250 250 250 250 250 250 250 250

460 390 330 300 300 300 300 300 300 300 300 300

760 1110 650 950 1300 560 830 1140 1480 500 740 1020 1330 1670 440 670 920 1210 1520 1860 400 610 840 1110 1400 1710 400 560 770 1020 1290 1590 400 510 720 950 1200 1480 400 500 670 880 1120 1380 400 500 620 830 1050 1300 400 500 600 780 990 1230 400 500 600 730 940 1160

65

20 25 30 35 40 45 50 55 60 65 70 75

250 250 250 250 250 250 250 250 250 250 250 250

320 300 300 300 300 300 300 300 300 300 300 300

530 450 400 400 400 400 400 400 400 400 400 400

780 670 580 520 500 500 500 500 500 500 500 500

910 800 1040 720 940 1170 650 850 1070 1310 600 780 980 1200 600 720 910 1110 600 700 840 1040 600 700 800 970 600 700 800 910 600 700 800 900 600 700 800 900

Minimum

250

300

400

500

600

NOTES: (1) Development lengths have been calculated using the nominal areas as per AS/NZS 4761 and have been rounded, generally to the nearest 10 mm within the accuracy of normal design limits. (2) Smaller of 0.5Sc and c.

6:6 Reinforcement Detailing Handbook

700

800

900

6.2.3 What to do if Less than Full Strength is

6.2.5 Cautionary Note on the Use of Hooks

to be Developed

Whether or not a bar should be hooked is a

AS 3600 Clause 13.1.2.2 permits a reduced embedment of a bar if the stress to be developed is

matter for the designer to specify, not for the detailer to decide.

less than the yield strength fsy. Use of this Clause by detailers requires

Although hooked deformed bars can reduce the development length, hooks cause congestion

considerable caution. If used, the value of the actual

of steel in critical areas and are a primary source of

design stress must be stated so that checking

rusting if allowed to enter the concrete cover. Straight

engineers and inspectors will realise that a short

bars are much easier to fix and protect. If there is so

length is acceptable. It is strongly recommended that

little room available that hooks are required, it may be

development lengths less than L sy.t should not be used.

a better solution to use more smaller-sized bars with a

6.2.4 What to do if Inadequate Length is available for Stress Development Use standard hooks. There are several reasons why a hook would be used. ■

To anchor the ends of fitments so that the yield strength of the steel is developed at middepth of the member. If the hook wraps around another bar, it is deemed to develop a stress of 0.67 fsy.fit; if there is no bar inside the hook, the stress developed is 0.5 fsy.fit.

■

To provide end anchorage of a bar where there is insufficient embedment for a straight length to develop its design stress.

smaller development length. Table 4.4 helps select bar combinations for area requirements. Hooks should never be used in sections thinner than about 12 bar diameters or as top bars in slabs. Table 6.6 show minimum overall dimensions of a hook or cog. The physical size of the hook is defined by its stress-development capacity. Hooks must never be specified as being cut back in size because they are then useless for anchorage. Because of the weight of a hook, it will tend to point downwards to the soffit unless properly tied. A straight bar will not rotate in this way. Table 6.6 Overall Dimensions (mm) of 180° Hooks and 90° Cogs

Hooks are defined in AS 3600 Clauses 13.1.2.5 and 19.2.3.2. The length of steel needed to physically make each hook (which must be scheduled) is given in

��

Table 6.5 and shown in the Diagrams with the Table.

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��

������� ���������

������� ���������

��� ��

The length of steel in a bar with one hook is the overall length of the straight portion plus the hook length requirement. Figure 6.3 illustrates the reduced development length using a standard hook. Lsy.t is the length required for a straight length. 0.5Lsy.t is required with a hook. �����

�����������������

Pin dia. di

Bar diameter, db (mm) 6

10

12

16

20

24

28

32

36

*

*

*

*

*

*

180° Hooks 3db

30

50

60

4db

40

60

70

100 120 140 170 190 220

5db

40

70

80

110 140 170 200 220 250

6db

50

80

100 130 160 190 220 260 290

8db

60

100 120 160 200 240 280 320 360

90° Cogs ���������

�����������������������������

Figure 6.3 Reduction of Straight Development Length through use of a Hook or Cog

3db

120 140 160

4db

130 150 170 200 240 280 330 370 420

5db

130 160 180 210 260 310 360 400 450

6db

140 180 200 240 290 340 400 450 510

8db

160 200 230 280 340 400 470 530 600

*

*

*

*

*

*

* Not to be used (See Table 6.5 for other limitations) The bar sizes are nominal, including deformed bars. No allowance for spring-back is included

6:7 Reinforcement Detailing Handbook

Table 6.5 Hook and Cog Length Requirements ������������ ������������

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�� �� �� �� ����� �� � ���

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���������

������������ ������������

������������ ������������

������������ ������������

���

���������

���������

Minimum length of bar, L a (mm) to form a standard hook or cog

Type of bar

Min. pin dia., di

Bar diameter, db (mm) 6

10

12

16

3 db 4 db

100 110

110 130

120 140

170

200

230

270

300

340

Reinforcement other than those below

5db

120

140

160

180

220

260

300

340

380

Bends designed to be straightened or subsequently rebent

4db 5 db 6 db

110

130

140

170

* *

* *

* *

* *

*

* *

* *

* *

Bends in reinforcement epoxy-coated or galvanised either before or after bending

5 db 8 db

120

140

160

180

*

*

*

*

Fitments: D500L & R250N bars D500N bars

*

Not to be used

6:8 Reinforcement Detailing Handbook

*

20

*

*

24

*

220

260

*

*

*

290

*

340

28

*

330

*

390

32

*

380

*

440

36

*

430

*

500

6.3

COMPRESSION DEVELOPMENT LENGTH

The shear strength developed by each weld is

OF DEFORMED BARS, Lsy.c

at least 250 MPa, provided that the relative diameters

The value of Lsy.c is not affected by various

of the bars do not differ by more than 3 mm. Adhesive

concrete strengths, or by the width or depth of the

bond to the bar is usually neglected for cross-bar

member, and is equal to 20 db.

spacings up to 200 mm. Thus embedment of two

Although it is not stated in AS 3600 Clause 13.1.3, the minimum cover and spacing rules still apply. (See Clause 5.4.4). Compression causes splitting of

cross-bars 25 mm or more from where full strength is required can be assumed to develop 500 MPa. See Figure 6.4. ���������������������������

the cover in a different way to tensile forces. Compression bars should not be hooked. For values, see Table 6.9. 6.4

BUNDLED BARS’ DEVELOPMENT LENGTH (AS 3600 Clauses 8.1.8.8,

��������

��������������� �� ������� ����

Figure 6.4 Development of Yield Strength for Mesh

10.7.2, 13.1.4, 13.2.5) Two bars may be tied together to form a bundle, but no increase in development length is specified. Three or four bars can be tied tightly together to form a bundle. Each bar of the “unit” therefore presents a smaller surface area in with the surrounding concrete. This requires an increased development length for both compression and tension.

In certain circumstances such as at a , the bond of the overhanging bars can be utilised for stress development. Table 6.8 shows how an overhang of 25db.wire can enhance the development strength of one crossbar. This is illustrated in Figure 6.5.

In beams, the bar cut-off point of each bar in a

���������������������������

bundle must be staggered by 40 db. See Table 6.9 for values. 6.5

DEVELOPMENT LENGTH OF MESH AND WIRE IN TENSION

��������

(AS 3600 Clause 13.1.2.1)

��������� ���������������

AS 3600 Clause 13.1.2.1(c) allows a development length of 50 db.wire for plain wire. Values are given in Table 6.7.

Value of L sy.t (mm) for grade 500L wire of sizes (mm) Length 4.0

4.75 6.0

6.75 7.6

8.6

9.50 10.7 11.9

50db

240

340

430

475

300

380

Figure 6.5 Embedment Length of One Welded Transverse Wire plus Overhang Table 6.8 Guide to Embedment Length of One Welded Transverse Wire plus Overhang

Table 6.7 Development Length Lsy.t for Plain Wire (Also known as Bar)

200

�������

535

595

Welded mesh develops stress in one bar

Value of embedment (mm) for 25db.wire overhang + one welded wire + 25 mm for wire size (mm) Length 4.0

4.75 6.0

6.75 7.6

8.6

9.5

10.7 11.9

Lsy.t /2 + 25 mm 125

145

195

240

265

295

175

215

Note: Values are approximate and for guidance only

through its normal adhesive bond with concrete, plus bearing of the cross bars welded to it against the concrete.

6:9 Reinforcement Detailing Handbook

325

STRENGTH DEVELOPMENT BY A

6.6

Lap-lengths need only be based on the

WELDED OR MECHANICAL CONNECTION

diameter of the SMALLER bar to be spliced because

The design and location of these anchorages

the force in that bar is the maximum which can be

requires calculations beyond the scope of this

transferred. If the size of only one bar is known, then the lap

Handbook. Section 14 of AS 3600, and AS 1554, Part 3, should be consulted together with the

length should be specified for that bar. This situation

manufacturer’s technical information if applicable.

commonly occurs when adjacent concrete elements are detailed on different drawings, or when protruding

GENERAL COMMENTS ON SPLICING

6.7

REINFORCEMENT 6.7.1 General Whether or not the project being detailed is a small building or a large civil engineering structure, the

bars are to form part of a future construction t for which details are not yet available. The reason is that if the second bar is found to be smaller, then the lap length provided will be longer than necessary; if the second bar is larger, then the original lap length for the known bar will be acceptable.

location and design of splices to hold the concrete elements together is a critical factor for the designer

6.8

and builder, and the necessary detailing will occupy much of this Handbook. All splices must be designed to carry the full design strength of the steel fsy in tension or

The development length and the lap-splice length of a bar in tension is the same value, L sy.t. See Tables 6.1 to 6.4 for tensile lap-splice lengths.

compression. No reduction in the splice length is permitted even when the calculated design stress is less than fsy.

TENSILE LAP-SPLICES FOR DEFORMED BARS (AS 3600 Clause 13.2.2)

Lap-splices must always be based on full yield stress transfer. ■

Included within the topic of splices will be the

Application of the values are not as complicated as they seem at first sight. For example, on each

connection between:

floor of a building, the same concrete strength

■

A footing and the column or wall that it s,

is usually specified. The cover also will be the

■

A column below a floor and its continuation

same in most cases (if not, then this fact must

above,

be made very clear to the construction workers!).

■

A column and the beams it s,

Detailers should therefore select a small set of

■

The elements connected by a construction or

combinations which will apply most of the time,

movement t,

and these can be tabulated in the drawings.

■

Walls at corners,

■

Walls and slabs, particularly if the former are

choice even further, in which case the largest

being slip-formed.

splice-length should be given. As a general rule,

AS 3600 Section 13.2 and its commentary

provide a table for only one combination of f’c

■

provide the rules and the background. 6.7.2 Lap-Splices of Bars and Mesh

and cover, and give exceptions on each detail. ■

be spliced in any element at points of maximum

input and reference to manufacturers’ catalogues, and

design stress, but the above values must still be

cannot be tabulated.

used.

The dimension of a lap-splice is so important millimetres, must be given in the drawings to ensure consistency and avoid errors during detailing, checking of the design, reinforcement scheduling, construction and supervision.

6:10 Reinforcement Detailing Handbook

Splice away from maximum stress zone. Although it is a design matter, bars should not

Welded and mechanical splices need design

for the strength of the structure that its length, in

On small jobs, it may be advisable to reduce the

■

Dimension it. Only the designer has access to the calculations and understands them. Only he will know whether the bar is stressed in tension or compression. Wherever there is a doubt, the required lap dimensions should be shown.

Example 6.1 Specification of Lap Splices in a Drawing Specification: Reinforcement shall not be spliced except where shown in the drawings. The splice length of bars shall be as given in the following Table, except where other dimensions are stated on the actual detail.

Type of member

f'c Cover (MPa) (mm)

Slab or wall

25

Other main bars

25

■

Tensile lap length (mm) for grade 500N deformed bars of size (mm) 12

16

20

24

28

32

36

20 25

370 310

610 520

890 760

1040

-

-

-

40-45 50-60

300 300

460 400

690 580

960 800

1250 1060

1580 1340

1930 1650

Tolerances. The lap-lengths taken from Tables 6.1 to 6.4 allow for the bar tolerances given in

�������

������� ������

AS 3600, section 19. See also Chapter 3 of this Handbook. ■

Overlapped bars not a splice. See Clause 6.14

�������

�������

for comments on overlapped bars which do not

������

require full strength lap-splices. ■

Plain bars. There are no values given for lapsplicing plain bars.

�������

������� ������

6.9

MESH LAP-SPLICES (AS 3600 Clause 13.2.3)

�������

�������

Mesh laps are generally much easier to specify ������

than bar laps, as they are not dependent on concrete strength or cover, or on the bar strength. The laps are specified only in relation to the spacing of the cross-

Figure 6.6 Correct and Incorrect Mesh Lap-Splices

bars. In this part of the Handbook, the term ‘cross-

CASE ‘B’ Cross-bars have same spacing.

bar’ is used to describe the bar which is welded to the

Spliced bars have useable overhang. The two

bar being spliced. The ‘cross-bar’ therefore provides

outermost bars of ‘Sheet 1’ overlap the two outermost

the anchorage necessary for strength development.

bars of ‘Sheet 2’, but the overhangs do not contribute.

Although it is common to describe laps in

CASE ‘C’ Cross-bars have differing spacing.

relation to the sheet edges, that is as ‘end-laps’ or

Spliced-bar overhang not significant. The two

‘side-laps’, this distinction is not really necessary. The

outermost bars of ‘Sheet 1’ overlap the two outermost

following four cases for all combinations of

bars of ‘Sheet 2’, but the overhangs do not contribute.

cross-bar spacings and spliced-bar overhangs. Figure 6.6 shows the same orientation of

CASE ‘D’ Cross-bars have differing spacing. Spliced-bar overhang not significant. The two

bars; that is the sheets are shown as not nested. This

outermost bars of ‘Sheet 1’ have not overlapped the

orientation is illustrative only. The critical factor is the

two outermost bars of ‘Sheet 2’, the overhangs do not

amount of overlap of the outermost bars. The lapped

contribute, and the splice is NOT CORRECT.

bars may be in the same plane or be separated by one or two transverse bars.

Suggested specification: Mesh sheets shall be lap-spliced so that the two outermost transverse bars

CASE ‘A’ Cross-bars have same spacing

of one sheet overlap at least the two outermost bars of

Spliced-bar overhang small. The two outermost bars of

the other sheet. (Sketches similar to Figure 6.6 may be

‘Sheet 1’ overlap the two outermost bars of ‘Sheet 2’.

added if desired).

6:11 Reinforcement Detailing Handbook

6.10

COMPRESSION LAP-SPLICES FOR

6.11

COMPRESSION LAP-SPLICES FOR

DEFORMED BARS

BUNDLED DEFORMED BARS

(AS 3600 Clause 13.2.4)

(AS 3600 Clause 13.2.5)

For bars in a compression zone of the concrete,

Lap splicing of bundled bars is messy,

the lap length is 41 db. This is approximately two times

complicated, uses excessive steel, and causes

the compressive stress development length. Under

overcrowding of the column area. Such splices should

AS 3600 Clause 13.2.4, there are two other conditions

be avoided.

that reduce the lap-splice to 0.8 of the value given above.

See AS 3600 Clause 13.2.5 for the design requirements for splicing main bundled bars.

See Table 6.9 for values which may also

Wherever possible, bundled bars should be

be used for lap-splice lengths for column bars (see

spliced by end bearing (no laps) or by a mechanical

Clause 6.3).

splice because these give a simpler solution.

Compression bars should not be hooked.

Two bars may be tied together as a bundle but

Values are not restricted to use in columns and

no increase in development length is specified.

walls. Where the concrete at the bottom of a beam

The values in Table 6.9 apply also to an extra

over a column carries an excessively large compression

splice bar added to a bundle which did not have a

load, extra bars lapped for compressive stress transfer

sawn-end preparation for an end-bearing splice. The

will be required there. (See Chapter 13 on beam

splice bar would be at least twice the lap length given

cages).

in Table 6.9, and located centrally about the section where the splice was to be. 6.12

SUMMARY OF DEVELOPMENT LENGTHS AND LAP-LENGTHS FOR COMPRESSION These values rationalise the values given in

AS 3600. Lap splices of a bar are always based on full strength fsy. To permit other values would create uncertainty in the mind of fixers and inspectors, and would certainly require more work from detailers. Table 6.9 Compression Development and Lap-Splice Lengths Rationalised Value (mm) for grade 500N single and bundled bars of size (mm) Length

12

16

20

24

28

32

36

640

720

L sy.c Development Length – these are too small for lap lengths (AS 3600 value) 20 db

240

320

400

480

560

L sy.t Tensile Stress Development Length – minimum value (AS 3600 value) 25 db

300

400

500

600

700

800

900

810

975

1135

1300

1460

Compression Lap-Splice (AS 3600 value) 40.5 db

490

650

3- and 4-Bar Bundle Tensile Development Length (rounded-off value) based on minimum values 3-bar 20% increase

360

480

600

720

840

960

1080

4-bar 33% increase

400

540

670

800

940

1070

1200

3- and 4-Bar Bundle, Extra Bar for Compression Lap-Splice (rounded-off value) 3-bar 20% increase

590

780

975

1170

1365

1560

1755

4-bar 33% increase

660

865

1080

1300

1510

1730

1945

6:12 Reinforcement Detailing Handbook

6.13

TENSION SPLICE OR COMPRESSION

6.16

SPLICE, WHICH SHOULD BE USED? The simple answer is that if a bar can be in

CRACK CONTROL REINFORCEMENT This topic is dealt with in the relevant chapters

for each type of member. The quantity of reinforcement

tension under one loading condition, and change to

is a design matter, and detailing is similar to that for

compression under another (or vice versa), then the

other reinforcement requirements.

splice must carry the “worst-case” load. As examples, the above situation can occur when the wind blows alternately from opposite directions, or when trucks move across a bridge. Values given previously are summarised in Table 6.9. 6.14

6.17

WELDED AND MECHANICAL ANCHORAGES These must be detailed in accordance with

the manufacturers’ instructions and with AS 1554 if applicable.

LAP SPLICES AND OVERLAPPED BARS There are obviously many situations where there

is no need to transfer stress from one bar to the next, except that the ends of bars should be overlapped and tied together for fixing purposes. In the latter case, the overlap may only need to be 100–150 mm for a small bar and up to 300 mm for a large bar. In each case, the overlap should be specified in the drawings, otherwise a full splice may be provided, or even worse, a short overlap provided where a full lap is essential. These overlaps can be tabulated in many cases to avoid repetitive notes. At the end of some bars a 90° bend can be mistaken for a 90° hook. Without knowing the purpose of the bend, a clear distinction often cannot be made. As a general rule, most 90° bends are taken to be cogs (90° hooks) having the steel allowance given in Table 6.5. that these lengths are the smallest lengths which can be bent around the given pin sizes. Where the bar dimension appears to fit into the concrete, allowing for covers, a 90° bend would be assumed. Where it will not fit, then the detail should be revised to avoid the bar-end from sticking out of the concrete. 6.15

STRESS DEVELOPMENT AND COUPLING OF PRESTRESSING TENDONS This is best left to the designer and prestressing

supplier because of the very high forces involved. Proprietary anchorages, couplers, anti-burst reinforcement and other details are beyond the scope of this Handbook, other than in general statements from time to time in later chapters. 6:13 Reinforcement Detailing Handbook

SECTION 2 (AS 3600:2007 Version)

6.2.1 Basic Development Length of Deformed Bars in Tension Lsy.tb

6.1

(AS 3600 Clause 13.1.2.2)

GENERAL Earlier sections of this Handbook referred to

the fact that whilst structures are generally designed

The development length formula can be expressed as follows: Lsy.tb =

in quite large pieces (such as a complete frame or a continuous beam), they must be constructed in quite small segments, called elements. The art of detailing is to ensure that the materials which connect the individual elements together will provide adequate strength and ductility for the total structure. AS 3600 Section 13.1 is concerned with developing stress in reinforcement by bond with insitu concrete. AS 3600 Section 13.2 describes methods of

A tabulation of the basic development length Note: The basic development length of a plain bar should be taken as 1.5 times the development length calculated by Clause 13.1.2.2. 6.2.2 Refinement of the Basic Development Length.

elements together. The methods used are laps, welds The purpose of the Tables in this Handbook is

Factor related to bar diameter x √concrete strength

Lsy.tb is given Table 6.1.

splicing reinforcement within an element or for ting and mechanical splices.

Depth factor x bar yield strength x bar diameter

AS 3600 Clause 13.1.2.3 provides for the refinement of the basic development length by multiplying it by up to three factors as applicable.

to provide consistent values for detailers, schedulers

Most designers will take advantage of the k3 factor

and inspectors. Most values are rounded-up as

that relates to cover and/or the clear distance to the

appropriate.

next parallel bar. This is tabulated in Table 6.2. An

The clauses related to stress development and splicing of reinforcement are new in this edition

explanation of ‘cd’ is provided in Figure 6.1, based on Figure 13.1.2A of AS 3600.

of AS 3600. Designers and detailers familiar with previous editions of AS 3600 will note that, in most

The effect of transverse reinforcement is ed for in the k4 factor, Table 6.3. An

practical applications, development lengths and

explanation of ‘K’ is provided in Figure 6.2, based on

splice lengths have increased significantly, especially

Figure 13.1.2B of AS 3600.

for bars in slabs. Whether these increased lengths are justifiable is a moot point.

Care should be exercised when using this factor as it may result in two different development lengths depending on the position of the bar; especially in

6.2

PRINCIPLES OF STRESS DEVELOPMENT

slabs. For example a bar in a slab laid in the first layer

This Handbook assumes that the reader has

could have a longer development length than a bar in

a basic knowledge of topics such as bond strength, development length and so on. There are a number of publications available from the Cement Concrete &

the second layer. This is one instance where it would be desirable to specify the development length on the drawings.

Aggregates Australia, the Concrete Institute of Australia

The k5 factor provides for a reduction where

and by other well-known authors. AS 3600 Section 13.1

there is transverse compressive pressure along the

and its associated commentary give the technical

development length perpendicular to the plane of

background to stress development as required by

splitting. See Table 6.4. the product k3.k4.k5 must not be

the standard. The background to the formula for the development length of a deformed bar is also given.

taken as less than 0.7. In practice this means that the maximum reduction of the basic development length is 30%.

6:14 Reinforcement Detailing Handbook

Table 6.1 Basic Development Lengths, Lsy.tb (mm) for Grade D500N Bars calculated by AS 3600 Clause 13.1.2.2

��������

k1 = 1.0 Concrete f’c (MPa)

Basic development length, L sy.tb (mm) for Grade D500N bars of size (mm) 10

12

16

20

24

28

32

36

40

50

460

560

780

1000

1250

1510

1790

2100

2440

3410

25

410

500

690

900

1120

1350

1600

1880

2180

3050

32

370

450

610

790

990

1190

1420

1660

1930

2700

40

330

400

550

710

880

1070

1270

1490

1720

2420

50

300

360

490

640

790

960

1140

1330

1540

2160

65

300

320

430

560

690

840

1000

1170

1350

1900

20

80

300

300

400

500

630

760

900

1050

1220

1710

100

300

300

400

500

600

700

800

940

1090

1530

���������������

��������

k1 = 1.3 Concrete f’c (MPa)

Basic development length, L sy.tb (mm) for Grade D500N bars of size (mm) 10

12

16

20

24

28

32

36

40

50

20

600

730

1010

1300

1620

1960

2330

2730

3160

4440

25

540

650

900

1170

1450

1750

2080

2440

2830

3970

32

480

580

800

1030

1280

1550

1840

2160

2500

3510

40

430

520

710

920

1150

1390

1650

1930

2240

3140

50

380

460

640

830

1030

1240

1480

1730

2000

2810

65

340

410

560

720

900

1090

1290

1520

1760

2460

80

300

390

520

650

810

980

1170

1370

1580

2220

100

300

390

520

650

780

910

1040

1220

1420

1990

Notes: Values are rounded-up to the nearest 10 mm and provide for tolerances. The basic development length of a plain bar should be taken as 1.5 times the development length calculated above.

The cover in these tables is the actual cover

Development lengths can be checked visually

to the deformed bar being detailed. No allowance is

or with the computations. They are generally not put in

made for a possible reduction in cover due to placing

the drawings.

or other tolerances because the strength reduction φ factor of 0.8 is included in the formula for this purpose. If the designer believes the situation is critical, a longer development length for that smaller cover can be obtained from the Table.

6:15 Reinforcement Detailing Handbook

Table 6.2 Value of k3 Factor after AS 3600 Clause 13.1.2.3 Effect of cover and bar spacing

See Figure 6.1 for value of cd

k3 = 1.0 - 0.15(cd - db)/db (but 0.7 ≤ k3 ≤ 1.0

cd (mm)

Value of k3 Factor for Grade D500N bars of size (mm) 10

12

16

20

24

28

32

36

40

50

20 25 30 35 40 45 50 55 60 65 70 75

0.85 0.78 0.70 0.70 0.70 0.70 0.70 0.70 0.70 0.70 0.70 0.70

0.90 0.84 0.78 0.71 0.70 0.70 0.70 0.70 0.70 0.70 0.70 0.70

0.96 0.92 0.87 0.82 0.78 0.73 0.70 0.70 0.70 0.70 0.70 0.70

1.00 0.96 0.93 0.89 0.85 0.81 0.78 0.74 0.70 0.70 0.70 0.70

– 0.99 0.96 0.93 0.90 0.87 0.84 0.81 0.78 0.74 0.71 0.70

– – 0.99 0.96 0.94 0.91 0.88 0.86 0.83 0.80 0.78 0.75

– – – 0.99 0.96 0.94 0.92 0.89 0.87 0.85 0.82 0.80

– – – – 0.98 0.96 0.94 0.92 0.90 0.88 0.86 0.84

– – – – 1.00 0.98 0.96 0.94 0.93 0.91 0.89 0.87

– – – – – – 1.00 0.99 0.97 0.96 0.94 0.93

NOTE: When using multiple Factors, k3 x k4 x k5 ≥ 0.7

Table 6.3 Value of k4 Factor after AS 3600 Clause 13.1.2.3 Effect of transverse reinforcement

See Figure 6.2 for value of K

Note: 0.7 ≤ k4 ≤ 1.0

Value of k4 Factor for λ

k4 = 1.0 - Kλ

K

6.0

5.5

5.0

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.10

0.70

0.70

0.70

0.70

0.70

0.70

0.70

0.75

0.80

0.85

0.90

0.95

0.05

0.70

0.73

0.75

0.78

0.80

0.83

0.85

0.88

0.90

0.93

0.95

0.98

NOTE: When using multiple Factors, k3 x k4 x k5 ≥ 0.7 λ = (ΣA tr - ΣA tr.min)/A s where: ΣA tr is cross-sectional area of transverse reinforcement on development length Lsyt ΣA tr.min is cross-sectional area of minimum transverse reinforcement (may be taken as 0.25 A s for beams and 0 for slabs A s is cross-sectional area of a single anchored bar of diameter d b

Table 6.4 Value of k5 Factor after AS 3600 Clause 13.1.2.3 ��������

ing for transverse compressive pressure

��

��

Value of k5 Factor for pressure, pp (MPa)

�

� �

�

��������������������� �����������������

������������������ ������������������

������ ����������

���� ��

�����������������

�����������

Figure 6.1 Values of cd for Beams and Slabs

Reinforcement Detailing Handbook

3

4

5

6

7

0.96

0.92

0.88

0.84

0.80

0.76

0.72

NOTE: When using multiple Factors, k3 x k4 x k5 ≥ 0.7 k5 =1.0 -0.04 pp where: pp is transverse compressive pressure (MPa) at ultimate limit state along development length perpendicular to plane of splitting

�� � ��

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6:16

2

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� ��

1

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�� � ��

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Figure 6.2 Values of K for Beams and Slabs

� �� ��

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6.2.3 What to do if Less than Full Strength

6.2.5 Cautionary Note on the Use of Hooks

is to be Developed

Whether or not a bar should be hooked is a

AS 3600 Clause 13.1.2.4 permits a reduced

matter for the designer to specify, not for the detailer

embedment of a bar if the stress to be developed is

to decide. Although hooked deformed bars can reduce

less than the yield strength fsy.

the development length, hooks cause congestion

Use of this Clause by detailers requires

of steel in critical areas and are a primary source of

considerable caution. If used, the value of the actual

rusting if allowed to enter the concrete cover. Straight

design stress must be stated so that checking

bars are much easier to fix and protect. If there is so

engineers and inspectors will realise that a short

little room available that hooks are required, it may be

length is acceptable. It is strongly recommended that

a better solution to use more smaller-sized bars with a

development lengths less than L sy.t should not be used.

smaller development length. Table 4.4 helps select bar

6.2.4 What to do if Inadequate Length is Available for Stress Development Use standard hooks. AS 3600 Clause 13.1.2.6 allows the development length of a deformrd bar with a standard hook to be reduced to 0.2Lsy.t. For plain bars, the development length may be reduced to 0.5Lsy.t. There are several reasons why a hook would be used: ■

To anchor the ends of fitments so that the yield

combinations for area requirements. Hooks should never be used in sections thinner than about 12 bar diameters or as top bars in slabs. Table 6.6 shows minimum overall dimensions of a hook or cog. The physical size of the hook is defined by its stress-development capacity. Hooks must never be specified as being cut back in size because they are then useless for anchorage. Because of the weight of a hook, it will tend to point downwards to the soffit unless properly tied. A straight bar will not rotate in this way.

strength of the steel is developed over a shorter distance. ■

To provide end anchorage of a bar where there is insufficient embedment for a straight length to

Table 6.6 Overall Dimensions (mm) of 180° Hooks and 90° Cogs

develop its design stress. Hooks are defined in AS 3600 Clauses 13.1.2.7 and 17.2.3.2. The length of steel needed to physically

��

make each hook (which must be scheduled) is given in

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Table 6.5 and shown in the Diagrams with the Table. The length of steel in a bar with one hook is the overall length of the straight portion plus the hook length requirement. Figure 6.3 illustrates the reduced development length using a standard hook. �����

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Figure 6.3 Reduction of Straight Development Length through use of a Hook or Cog

Pin dia. di

Bar diameter, db (mm) 6

10

12

16

20

24

28

32

36

*

*

*

*

*

*

180° Hooks 3db

30

50

60

4db

40

60

70

100 120 140 170 190 220

5db

40

70

80

110 140 170 200 220 250

6db

50

80

100 130 160 190 220 260 290

8db

60

100 120 160 200 240 280 320 360

90° Cogs 3db

120 140 160

4db

130 150 170 200 240 280 330 370 420

5db

130 160 180 210 260 310 360 400 450

6db

140 180 200 240 290 340 400 450 510

8db

160 200 230 280 340 400 470 530 600

*

*

*

*

*

*

* Not to be used (See Table 6.5 for other limitations) The bar sizes are nominal, including deformed bars. No allowance for spring-back is included

6:17 Reinforcement Detailing Handbook

Table 6.5 Hook and Cog Length Requirements ������������ ������������

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Minimum length of bar, L a (mm) to form a standard hook or cog

Type of bar

Min. pin dia., di

Bar diameter, db (mm) 6

10

12

16

3 db 4 db

100 110

110 130

120 140

170

200

230

270

300

340

Reinforcement other than those below

5db

120

140

160

180

220

260

300

340

380

Bends designed to be straightened or subsequently rebent

4db 5 db 6 db

110

130

140

170

* *

* *

* *

* *

*

* *

* *

* *

Bends in reinforcement epoxy-coated or galvanised either before or after bending

5 db 8 db

120

140

160

180

*

*

*

*

Fitments: D500L & R250N bars D500N bars

*

Not to be used

6:18 Reinforcement Detailing Handbook

*

20

*

*

24

*

220

260

*

*

*

290

*

340

28

*

330

*

390

32

*

380

*

440

36

*

430

*

500

COMPRESSION DEVELOPMENT LENGTH

6.3

6.4

BUNDLED BARS’ DEVELOPMENT

OF DEFORMED BARS, Lsy.c

LENGTH (AS 3600 Clauses 8.1.10.8,

AS 3600:2007 has a new clause covering

10.7.2, 13.1.7, 13.2.5) Two bars may be tied together to form a bundle,

development length for bars in compression. Previously all development lengths were 20 db but this new

but no increase in development length is specified.

provision is slightly affected by concrete strength.

Three or four bars can be tied tightly together to form

Values for Lsy.c are given in Table 6.7. The k6 value

a bundle. Each bar of the “unit” therefore presents a

of 0.75 may only be used where the transverse

smaller surface area in with the surrounding

reinforcement complies with AS 3600 Clause 13.1.5.3.

concrete. This requires an increased development length for both compression and tension.

Although it is not stated in AS 3600 Clause 13.1.3, the minimum cover and spacing rules still apply. (See Clause 5.4.4). Compression causes

In beams, the bar cut-off point of each bar in a bundle must be staggered by 40db.

splitting of the cover in a different way to tensile forces. Compression bars should not be hooked.

Table 6.7 Compression Development Lengths, Lsy.c (mm) for Grade D500N Bars calculated by AS 3600 Clause 13.1.3 Where non-complying transverse reinforcement present k6 = 1.00 Concrete f’c (MPa)

Compression development length, L sy.c (mm) for Grade D500N bars of size (mm) 10

12

16

20

24

28

32

36

40

50

20

250

300

400

500

600

690

790

890

990

1230

25

220

270

360

440

530

620

710

800

880

1100

32

220

270

350

440

530

610

700

790

870

1090

40

220

270

350

440

530

610

700

790

870

1090

50

220

270

350

440

530

610

700

790

870

1090

65

220

270

350

440

530

610

700

790

870

1090

80

220

270

350

440

530

610

700

790

870

1090

100

220

270

350

440

530

610

700

790

870

1090

Where complying transverse reinforcement is in place k6 = 0.75 Concrete f’c (MPa) 20

Compression development length, L sy.c (mm) for Grade D500N bars of size (mm) 10

12

16

20

24

28

32

36

40

50

220

270

350

440

530

610

700

790

870

1090

25

220

270

350

440

530

610

700

790

870

1090

32

220

270

350

440

530

610

700

790

870

1090

40

220

270

350

440

530

610

700

790

870

1090

50

220

270

350

440

530

610

700

790

870

1090

65

220

270

350

440

530

610

700

790

870

1090

80

220

270

350

440

530

610

700

790

870

1090

100

220

270

350

440

530

610

700

790

870

1090

Note: Values are rounded-up to the nearest 10 mm and provide for tolerances.

6:19 Reinforcement Detailing Handbook

6.5

DEVELOPMENT LENGTH OF MESH IN TENSION (AS 3600 Clause 13.1.8)

Table 6.8 Development Length in Tension, Lsy.tb (mm) for Grade D500L Mesh calculated by AS 3600 Clause 13.1.8 sb = 200

Welded mesh develops stress in one bar

��

through its normal adhesive bond with concrete, plus bearing of the cross bars welded to it against the concrete. The shear strength developed by each weld is at least 250 MPa, provided that the relative diameters of the bars do not differ by more than

Concrete f’c (MPa) 20

Development length in tension, L sy.tb (mm) for Grade D500L mesh of bar size (mm) 6.0

6.75

7.6

8.6

9.5

10.7

11.9

100

100

100

110

130

170

210

3 mm. AS 3600:2007 has a more complex formula for

25

100

100

100

100

120

150

190

calculation of a basic development length for mesh,

32

100

100

100

100

110

130

160

where reliance is made in full or in part on the weld

120

150

40

100

100

100

100

100

shear strength. This formula depends on the spacing of

50

100

100

100

100

100

110

130

the bars, sb and concrete strength. For deformed wire

65

100

100

100

100

100

100

120

80

100

100

100

100

100

100

110

100

100

100

100

100

100

100

100

meshes values may be chosen from Table 6.8. For meshes with no cross bars within the development length the provision of Clause 13.1.2

��

sb = 100

or 13.1.3 apply and designers can use the Tables in Clause 6.2. 6.6

STRENGTH DEVELOPMENT BY A WELDED OR MECHANICAL CONNECTION The design and location of these anchorages

requires calculations beyond the scope of this Handbook. Section 14 of AS 3600, and AS 1554, Part 3, should be consulted together with the manufacturer’s technical information if applicable. 6.7

GENERAL COMMENTS ON SPLICING REINFORCEMENT

6.7.1 General Whether or not the project being detailed is a small building or a large civil engineering structure, the

Concrete f’c (MPa) 20

6.0

6.75

7.6

8.6

9.5

10.7

11.9

110

140

170

220

260

330

410

25

100

120

150

190

240

300

370

32

100

110

140

170

210

260

320

40

100

100

120

150

190

240

290

50

100

100

110

140

170

210

260

65

100

100

100

120

150

190

230

80

100

100

100

110

130

170

210

100

100

100

100

100

120

150

190

Note: For plain bar meshes, the minimum length is not to be less than 150 mm.

location and design of splices to hold the concrete elements together is a critical factor for the designer

Development length in tension, L sy.tb (mm) for Grade D500L mesh of bar size (mm)

Included within the topic of splices will be the connection between:

and builder, and the necessary detailing will occupy

■

A footing and the column or wall that it s,

much of this Handbook.

■

A column below a floor and its continuation

All splices must be designed to carry the

above,

full design strength of the steel fsy in tension or

■

compression. No reduction in the splice length is

■

permitted even when the calculated design stress is less than fsy.

A column and the beams it s, The elements connected by a construction or movement t,

■

Walls at corners,

■

Walls and slabs, particularly if the former are being slip-formed. AS 3600 Section 13.2 and its commentary

provide the rules and the background.

6:20 Reinforcement Detailing Handbook

6.7.2 Lap-Splices of Bars and Mesh

■

Application of the values are not as complicated as they seem at first sight. For example, on each

Welded and mechanical splices need design input and reference to manufacturers’ catalogues, and

floor of a building, the same concrete strength

cannot be tabulated.

is usually specified. The cover also will be the same in most cases (if not, then this fact must

The dimension of a lap-splice is so important for the strength of the structure that its length, in

be made very clear to the construction workers!).

millimetres, must be given in the drawings to ensure

Detailers should therefore select a small set of

consistency and avoid errors during detailing, checking

combinations that will apply most of the time,

of the design, reinforcement scheduling, construction

and these can be tabulated in the drawings. Care should be taken if the k4 factor has been

and supervision.

used to refine the development length as it will

Lap-lengths need only be based on the diameter of the SMALLER bar to be spliced because

not apply to the outermost layers of reinforcing

the force in that bar is the maximum which can be

bars

transferred.

■

On small jobs, it may be advisable to reduce the choice even further, in which case the largest

If the size of only one bar is known, then the lap length should be specified for that bar. This situation

splice-length should be given. As a general rule,

commonly occurs when adjacent concrete elements

provide a table for only one combination of f’c and cover, and give exceptions on each detail.

are detailed on different drawings, or when protruding bars are to form part of a future construction t for

■

Splice away from maximum stress zone. Although it is a design matter, bars should not

which details are not yet available.

be spliced in any element at points of maximum

The reason is that if the second bar is found to be smaller, then the lap length provided will be longer

design stress, but the above values must still be

than necessary; if the second bar is larger, then the

used.

original lap length for the known bar will be acceptable.

■

Dimension it. Only the designer has access to the calculations and understands them. Only he

6.8

will know whether the bar is stressed in tension

TENSILE LAP-SPLICES FOR DEFORMED

or compression. Wherever there is a doubt, the

BARS (AS 3600 Clause 13.2.2) When lapped portions of bars are in or spaced less than 3 db apart, the lap splice length of a

required lap dimensions should be shown. ■

Tables 6.1 to 6.4 allow for the bar tolerances

bar in tension is the value of the development length,

given in AS 3600, Section 17. See also

Lsy.t, multiplied by 1.25. Use Tables 6.1 to 6.4 for tensile development lengths.

Chapter 3 of this Handbook. ■

Bars spliced by non- lap splices further

splice). Lap-splices must always be based on full yield

Overlapped bars not a splice. See Clause 6.13 for comments on overlapped bars which do not

apart than 3 db, the lap length is the larger of 1.25 Lsy.t and Lsy.t +1.5 sl (distance between bars of the non-

Tolerances. The development lengths taken from

require full strength lap-splices. ■

Plain bars. There are no values given for lapsplicing plain bars.

stress transfer. These factors significantly increase the lap splices from previous editions of AS 3600

6:21 Reinforcement Detailing Handbook

Example 6.1 Specification of Lap Splices in a Drawing Specification: Reinforcement shall not be spliced except where shown in the drawings. The splice length of bars shall be as given in the following Table, except where other dimensions are stated on the actual detail. Splices shall

be in or spaced less than 3db. The old values of lap length based on AS 3600:2001 have been shown in italics. This shows how these new rules affect the splice lengths. In this Table, the k3 factor have been applied only as the k4 and k5 cannot be applied with certainty.

Type of member

f'c Cover (MPa) (mm)

Slab or wall

25

Other main bars

6.9

25

Tensile lap length (mm) for grade D500N bars of size (mm) 10

12

16

20

24

28

32

36

20

440 270

570 370

830 610

1125 890

-

-

-

-

25

400 260

530 310

800 520

1080 760

1390 1040

-

-

-

40

360 250

440 300

680 460

960 690

1260 960

1590 1250

1920 1580

2310 1930

50

360 250

440 300

610 400

880 580

1180 800

1485 1060

1840 1340

2210 1650

MESH LAP-SPLICES (AS 3600 Clause 13.2.3) Mesh laps are generally much easier to specify

CASE ‘A’ Cross-bars have same spacing

than bar laps, as they are not dependent on concrete

Spliced-bar overhang small. The two outermost bars of

strength or cover, or on the bar strength. The laps are

‘Sheet 1’ overlap the two outermost bars of ‘Sheet 2’.

specified only in relation to the spacing of the crossbars.

CASE ‘B’ Cross-bars have same spacing. Spliced bars have useable overhang. The two

In this part of the Handbook, the term ‘crossbar’ is used to describe the bar which is welded to the bar being spliced. The ‘cross-bar’ therefore provides the anchorage necessary for strength development. Although it is common to describe laps in relation to the sheet edges, that is as ‘end-laps’ or ‘side-laps’, this distinction is not really necessary. The

outermost bars of ‘Sheet 1’ overlap the two outermost bars of ‘Sheet 2’, but the overhangs do not contribute. CASE ‘C’ Cross-bars have differing spacing. Spliced-bar overhang not significant. The two outermost bars of ‘Sheet 1’ overlap the two outermost bars of ‘Sheet 2’, but the overhangs do not contribute. CASE ‘D’ Cross-bars have differing spacing.

following four cases for all combinations of

Spliced-bar overhang not significant. The two

cross-bar spacings and spliced-bar overhangs.

outermost bars of ‘Sheet 1’ have not overlapped the

Figure 6.4 shows the same orientation of bars; that is the sheets are shown as not nested. This orientation is illustrative only. The critical factor is the

two outermost bars of ‘Sheet 2’, the overhangs do not contribute, and the splice is NOT CORRECT. Suggested specification: Mesh sheets shall be

amount of overlap of the outermost bars. The lapped

lap-spliced so that the two outermost transverse bars

bars may be in the same plane or be separated by one

of one sheet overlap at least the two outermost bars of

or two transverse bars.

the other sheet. (Sketches similar to Figure 6.4 may be added if desired).

6:22 Reinforcement Detailing Handbook

6.10

COMPRESSION LAP-SPLICES FOR

6.11

COMPRESSION LAP-SPLICES FOR

DEFORMED BARS

BUNDLED DEFORMED BARS

(AS 3600 Clause 13.2.4)

(AS 3600 Clause 13.2.5)

For D500N bars in a compression zone of the

Lap splicing of bundled bars is messy,

concrete, the lap length is 40 db. This is approximately

complicated, uses excessive steel, and causes

two times the compressive stress development length.

overcrowding of the column area. Such splices should

Under AS 3600 Clause 13.2.4, there are two other

be avoided.

conditions that reduce the lap-splice to 0.8 of the value given above.

See AS 3600 Clause 13.2.5 for the design requirements for splicing main bundled bars.

Compression bars should not be hooked. Values are not restricted to use in columns and walls. Where the concrete at the bottom of a beam

Wherever possible, bundled bars should be spliced by end bearing (no laps) or by a mechanical splice because these give a simpler solution.

over a column carries an excessively large compression load, extra bars lapped for compressive stress transfer

Two bars may be tied together as a bundle but no increase in development length is specified.

will be required there. (See Chapter 13 on beam cages).

6.12

TENSION SPLICE OR COMPRESSION SPLICE, WHICH SHOULD BE USED? The simple answer is that if a bar can be in

tension under one loading condition, and change to compression under another (or vice versa), then the splice must carry the “worst-case” load. As examples, the above situation can occur when the wind blows alternately from opposite directions, or when trucks �������

������� ������

6.13 �������

�������

move across a bridge. LAP SPLICES AND OVERLAPPED BARS There are obviously many situations where there is no need to transfer stress from one bar to the next, except that the ends of bars should be overlapped and

������

tied together for fixing purposes. �������

������� ������

In the latter case, the overlap may only need to be 100-150 mm for a small bar and up to 300 mm for a large bar. In each case, the overlap should be specified in

�������

�������

the drawings, otherwise a full splice may be provided, or even worse, a short overlap provided where a full lap

������

Figure 6.4 Correct and Incorrect Mesh Lap-Splices

is essential. These overlaps can be tabulated in many cases to avoid repetitive notes. At the end of some bars a 90° bend can be mistaken for a 90° hook. Without knowing the purpose of the bend, a clear distinction often cannot be made. As a general rule, most 90° bends are taken to be cogs (90° hooks) having the steel allowance given in Table 6.5. that these lengths are the smallest lengths which can be bent around the given pin sizes.

6:23 Reinforcement Detailing Handbook

Where the bar dimension appears to fit into the concrete, allowing for covers, a 90° bend would be assumed. Where it will not fit, then the detail should be revised to avoid the bar-end from sticking out of the concrete. 6.14

STRESS DEVELOPMENT AND COUPLING OF PRESTRESSING TENDONS This is best left to the designer and prestressing

supplier because of the very high forces involved. Proprietary anchorages, couplers, anti-burst reinforcement and other details are beyond the scope of this Handbook, other than in general statements from time to time in later chapters. 6.15

CRACK CONTROL REINFORCEMENT This topic is dealt with in the relevant sections

for each type of member. The quantity of reinforcement is a design matter, and detailing is similar to that for other reinforcement requirements. 6.16

WELDED AND MECHANICAL ANCHORAGES These must be detailed in accordance with

the manufacturers’ instructions and with AS 1554 if applicable.

6:24 Reinforcement Detailing Handbook

7 Drawing Standards

7.2

DRAWING STANDARDS FOR REINFORCED CONCRETE

7.2.1 Sizes of Drawings (AS 1100.101) Recommended sheet sizes are given in

7.1

AUSTRALIAN STANDARDS

7.1.1 AS 1100.101:1992 Technical Drawing, –

Clause 2.4 and layout of drawing sheets in Clause 2.5. Prints of both architectural and engineering drawings for a particular job should always be on the

General Principles

same size cut sheet.

It contains all the relevant information on

7.2.2 Drawing Types (AS 1100.501)

drawing sheets, lines, letters and numerals, scales and sectioning. It cross-references other AS 1100 standards such as Parts 201 to 501. This “Reinforcement Detailing Handbook” assumes the detailer/reader is familiar with this standard. Much of Part 501 was based upon the CIA’s “Reinforced Concrete Detailing Manual”, 1975 edition. 7.1.2 AS 1100.501:2002 Technical Drawing – Structural Drawing It contains recommendations for the classification of drawings, dimensioning lines, symbols, identification of structural elements, and other matters. Many of the items related to detailing of reinforced and prestressed concrete will be covered in greater detail in this Handbook. Clause 1.2 Application reads in part: “The standard is intended as a basis for common practice and consistency of application upon which technical organisations can base their own detailed rules or manuals for the preparation and presentation of drafting work”. This Handbook is prepared under that authority.

Of those listed in AS 1100.501, Clause 1.5, the following are most applicable to structural concrete, with reinforcement and prestressing steel as applicable: (d) general information drawing often containing the “General Notes”, and including the requirements of Clause 1.4 of AS 3600 covering such matters as covers, lap lengths, etc. (a) design layout drawing. (b) design detail drawing. Also listed are: (c) shop detail drawing, which is applicable more to precast concrete and would include items such as formwork, fixings, etc, and have been prepared by the precast concrete manufacturer. (e) as-built drawings, which are not common in smaller projects. Additional drawings sometimes prepared are: (f) design intent drawings, which show the concrete shapes, and reinforcement areas and arrangements, for further detailing by draftsmen. (g) reinforcement marking plans are usually prepared by the reinforcement scheduler to correlate the reinforcement schedules with their

Where it is considered necessary, some sections of

bar marks to the most applicable of the other

Part 501 will be repeated in this Handbook, although

structural drawings.

the source may not always be quoted.

Not covered, but of considerable importance for building works are the architectural drawings (AS 1100.301). In building work, it is common practice to combine the reinforcement and the concrete outlines on the same drawing, but this should only be done where the reinforcement is simple in plan. In both civil engineering and structural work, it is also common to prepare a dimensioned concrete outline and a separate reinforcement drawing with the concrete outline drawing not dimensioned. In many cases where there are two layers of reinforcement, each layer would be shown on a separate plan-view. Hard and fast rules cannot be made; clarity and good communications are the ideal. 7:1 Reinforcement Detailing Handbook

7.2.3 Title Blocks (AS 1100.101) Typical layouts are given in AS 1100.101,

7.2.5.1

Types of Lines (AS 1100.501)

Line types for use in reinforced concrete

Figure 2.9, with the type of information to be shown.

detailing are given in AS 1100.501, Table 2.1. Each line

The initial date of issue must be shown. It is also

type is defined by a designating letter, an example of

extremely important that the amendment number and

its appearance and the applications for which each are

a brief description of changes are shown when they

recommended.

occur as they have significance in the building contract.

The designating letters are “A” to “K”, plus

It is common when making revisions to provide a thin

“M”, “N” and “P”. The types of line are “continuous”,

wavy line (cloud) around the section of the drawing that

“dashed” and “chain”. “Full”, “broken” and “chain” are

has changed to highlight the changes.

also used.

Adequate use of revision letters (A, B, C etc for first, second, third, etc) must be made on all drawings,

7.2.5.2

Line Thickness (AS 1100.101)

In addition to the above, there is a range of

particularly when A4-size sheets are used to amend

line thicknesses given in AS 1100.101, Figure 3.1, Line

details given on larger size sheets. Revision dates are

Groups. Each line group consists of three thicknesses

extremely important.

which bear a consistent relationship to each other,

The system for specifying drawing numbers is left to each individual office practice. 7.2.4 Key Drawing and North-Point Where a portion of the work has to be divided over several drawings, a small diagrammatic key plan on each drawing should be used to define the portion covered. Always show the North-point on all plan views for rapid orientation. A “Project North-point” is often used so that the “North, South, East and West” can be established more easily. 7.2.5 Lines (AS 1100.101 and AS 1100.501) The object of the line thicknesses recommended in this Handbook is to show how differentiation between line thicknesses can improve clarity of details rather than insisting upon a rigid set of rules. This will permit detailers to maintain a drafting style consistent with the procedures used in their own drawing office. With CADrafting it is a simply matter to draw complex rebar layouts to any desired scale and even to

the “thin-line” being 0.5 times the “thick-line” and the “medium-line” being 0.7 times the thickest of the group. The thickness range is suitable for both pen and pencil; when pencil is used, a heavier line is strongly advised to obtain the necessary density and contrast on subsequent prints. A line thickness of 0.25 mm is common for all dimension, grid and “call-up” lines but AS 1100.101 only permits three thicknesses per group. A four-pen plotter should be adequate for all concrete work. Table 7.1 Range of Thicknesses in Each Line Group (AS 1100.101) Line thickness (mm) for: Line Group

Thick

Medium

Thin

1.0 mm group

1.0

0.7

0.5

0.7 mm group

0.7

0.5

0.35

All lettering should comply with Section 4 of AS 1100.101. Line thicknesses for lettering of general notes, material lists, dimensions, reinforcement notation, etc, should not be less than 0.35 mm.

use double lines to get the diameter into scale; in these

7.2.5.3

cases “thin” lines are appropriate. CADrafting also has

Parallel lines drawn too close together will tend

Line Separation

the ability to change the intensities of lines at any time

to merge into one when printed, photocopied or photo-

from thick to thin, and vice versa.

reduced. This is a real problem when reinforcement,

NOTE: The choice of thick or thin lines for

actually occurring in the same plane, is drawn using

concrete outlines or reinforcing bars as adopted in

two parallel lines or with reinforcement drawn close to a

practice is left to individual office practice. In many

concrete surface.

situations both systems can be used, even on the

A physical gap of 1.5 to 2 mm on the final print,

same drawing sheet, for differing types of details.

should be allowed. When CADrafting is used, such

Because of the problem of line separation and ensuring

a spacing must be allowed for during detailing; this

clarity of detail, this Handbook has a preference for

may create inaccurate scaling with incorrect automatic

“thin” concrete outlines to define the limits of the bar

dimensioning as a result. Bent bars and fitments will be

shape and a “medium” line for the reinforcement itself.

the most likely to suffer.

7:2 Reinforcement Detailing Handbook

7.2.5.4

Selection of the Line Type and Thickness Groups

Line Group 0.7 mm should be the smallest

7.2.6 Drawing Outlines of Structural Elements Outlines of structural elements are shown in plan-views, elevations and cross-sections. These topics

group used for reinforced concrete detailing, regardless

are covered in detail in the chapters which relate to the

of the size of drawing sheet and therefore degree of

particular elements. The following Clauses cover the

photo-reduction. This assumes that sheets A0 and A1

general requirements.

may be reduced to A2; sizes A2, A3 and A4 would not be reduced. Because site conditions are considerably dirtier than a drawing office, thin lines and printing are more likely to be unreadable than thicker lines. Drawings which will be microfilmed for storage purposes should have line thicknesses and line separation as large as practicable. Table 7.2 reproduces Table 2.1 of AS 1100.501 because of its importance to the topic. Line thicknesses from the 0.7 mm Group are shown to assist pen selection. In the same way as CADrafting systems permit the selection as desired of drawing scales and the appropriate sheet size for the final drawing, so line thicknesses also can be selected to match each individual detail without incurring a penalty for photo-

7.2.7 Shading, Stippling and Cross-Hatching “Shading” means colouring-in (painting) the enclosed area which is being discussed. This treatment indicates that the member below (column or wall usually) s the member above (column, wall, slab or beam). “Stippling” means dotting the enclosed area, or at least around the edges (stippling indicates aggregate-exposed by the plane of the cross-section). “Hatching” means drawing, within the outline of the element, a series of lines or symbols to highlight it. “Fill” is a term used with CADrafting whereby an enclosed area can be highlighted from a set of patterns. In this Handbook, computer aided “fill” patterns are used rather than hand methods, see Figure 7.1.

reduction. For example, if a CAD detail requires a “thick” line (0.7 mm) when drawn on an A0-size sheet, then the same 0.7 mm line would be used on a similar CAD detail on an A2 or A4 sheet. If the original A0 drawing was detailed manually, the line should probably

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be 1.0 mm “thick” for similar reductions. In this Handbook, the deg letter has combined the type with the thickness based on the 0.7 mm Group as this will be most suitable for CAD work. This is not part of AS 1100.501. Lines representing parallel reinforcement will be

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Figure 7.1 Shading, Stippling and Hatching Examples as Used in this Handbook

drawn closer more often than concrete surfaces; thus concrete outlines should be selected as “continuous medium” lines (M.5 mm) and reinforcement as “continuous thick” (A.7 mm). In large scale details, where a reinforcing bar is drawn with two lines to define its real size, “continuous thin” lines (B.35 or .25 mm) would be suitable.

7:3 Reinforcement Detailing Handbook

7.3

PLAN-VIEWS

7.4.2 Cross-sections In this Handbook, the “section” and

Plan-views are used to show the location of elements such as footings, columns, beams, slabs and

“cross-section” mean the same thing. A section is a

walls and also to show their grid or number reference

view from a cutting plane located through a structural

as applicable. They should be drawn as a horizontal

element previously drawn as a plan-view or an

view of all structural elements taken immediately above

elevation. Only material intersected by the cutting plane

the level of the structural element under consideration. Figure 7.2 illustrates detailing the outlines of

should be shown; details beyond that section should

beam and columns in plan view. For plan-views, the

be omitted but outlines may be indicated only if they do

cross-section is usually taken just above the slab.

not confuse but clarify the section. A section should be drawn close to the plan or

Reinforcement is generally omitted. Figure 7.3 illustrates walls of various materials and situations. Clarity of wall views is critical to ensure

elevation to which it relates and both should be crossreferenced by a suitable system. See AS 1100.501 for conventions for cross-

is properly provided. Columns and walls are the most critical loading in a structure. In a plan-view, the cross-section of each column and wall which s part of the structure above it

referencing sections to the relevant plan-view or elevation. This method will be used throughout this Handbook. Changes in direction of the cutting-plane should be shown by a chain line as in Table 7.2. Outlines of sections should be continuous lines;

must be shaded to indicate that it is a .

the enclosed area may be stippled. 7.4

ELEVATIONS AND SECTIONS

7.4.1 Elevations

Figure 7.4 illustrates detailing the outlines of beams and other elements taken in side elevation and in cross-section, but with reinforcement omitted. Figure 7.5 illustrates selected examples of

In reinforced concrete construction, an elevation is drawn as a section defined by a vertical cutting

reinforcement located within concrete outlines.

plane located immediately in front of the element under consideration.

7.5

The outline of shown in elevation

HOLES, RECESSES, PLINTHS, AND SET-DOWNS

should be continuous thick lines (A.7).

Figure 7.6 illustrates detailing the outlines of

The outline of in front of (and

holes, recesses, plinths or set-downs. More than one

connected to) the member being viewed in elevation is

view may be necessary to define the complete shape

also shown by a continuous medium line (M.5).

of the outline. The sizes and depths of these must be

The outline of behind the member being detailed in elevation should only be shown if it

specified on the plan or elevation, and in additional sections.

is essential that special features are being highlighted; they are drawn in dashed medium lines (N.5). The shape of a connecting member cut by the cutting plane may be highlighted by stippling. Beam elevations are normally drawn as viewed from the bottom or right-hand side of the sheet. Wherever possible, elevations should be drawn

7.6

DIMENSIONING

7.6.1 Value Expression All building dimensions, including those used in the specification of section, must be expressed in millimetres (mm) as a whole number. Values should

as the view seen by the form-workers and steel fixers –

be expressed as a multiple of 10 mm if possible, but

that is from the position where the member will be

certainly not less than a multiple of 5 mm. The letters

viewed when standing on the formwork or scaffolding.

“mm” generally may be omitted, for example 3330.

This applies particularly to the outermost of

Site layout and external measurements should

a building such as walls, except for beams as stated

be in metres (m), expressed to three decimal places.

above.

The unit “m” can sometimes be omitted, for example 3.330, provided each set of drawings is consistent.

7:4 Reinforcement Detailing Handbook

7.6.2 On the Drawings

7.6.3.2

Levels on Plan Views

It is important to indicate on site plans the

Arrangement drawings should show all settingout dimensions and sizes of . Reinforcement

difference between existing levels during construction;

drawings should contain only those dimensions which

for example, a level may be shown to structural floor

are necessary for the correct scheduling and location

level (SFL) or to finished floor level (FFL). 7.6.3.3

of the reinforcement including concrete member sizes if

Elevations

applicable.

The same methods should be used as for

It should not be necessary to reduce or scale any dimensions although in many cases the location of ends or of bends in reinforcement will be obvious without the need for exact dimensions. Architectural dimensions normally take precedence and engineering drawings should avoid duplication to reduce possible conflict, but dimensions

levels on plan views. The level may be shown on a line projected beyond the drawing with an arrowhead indicating the appropriate line; minor dimensions may be shown from this projection. SCALES

7.7

Scales should comply with AS 1100.101, and be

critical to the design should be stated in the engineering drawings. The thickness, length, etc of a structural element should be given once only. Figured dimensions should be placed in such a way that they may be read when viewed from the bottom of the drawing or, if essential, from the right-hand side.

in the form of a ratio, eg 1:100. The scale should be as small as will clearly show the desired amount of detail, yet large enough to avoid possible reading errors. The following scales are suggested but larger scales may be used if desired: ■

automatically during CADrafting may be too accurate for practical construction. Default values should be structured to produce values rounded off to 10 mm or ■

5 mm as above. Although there are some valid reasons why architectural dimensions should not be repeated on structural drawings, “fast-track” construction makes it essential that the most recent dimensions are available to reinforcement schedulers, formworkers and others on site.

“Small scales” Site layout and

As previously mentioned, dimensions calculated

simple general arrangement

1:200 or 1:500

General arrangement

1:100 or 1:50

Simple wall and slab details

1:50

“Large scales” Beam and column elevations

1:20

Beam and column sections

1:20 or 1:10

Large size details

1:5 or 1:2 or 1:1

When laying out a drawing by hand on tracing paper, an underlay of graph paper in millimetre squares will save considerable time. Such a grid will not readily match 1:25 or 1:250 scales. When more than one scale is used on a

7.6.3 Levels All levels should be expressed in metres to three decimal places to either Australian Height Datum (AHD) or a site datum. 7.6.3.1

Levels on Sections and

Datum

As a minus sign may be misread, a suitable fixed point should be taken as job datum such that all other levels are positive. This datum should be clearly indicated or described on the drawings and all levels and vertical dimensions should be related to it. Particularly on large jobs, it is necessary to relate the job datum to the local survey datum or AHD.

drawing, the scale should be shown under each detail, and the notation “SCALES AS SHOWN” entered in the title block. Where a dimension on a scale drawing is “not to scale”, the dimensioned figure should be followed by the abbreviation “NTS”. Drawings which may be enlarged or reduced should show a graphic scale as well as a descriptive scale. Where microfilm is used, special methods may be necessary. Final prints should have a prominent note such as “DRAWING REDUCED TO HALF-SIZE”. Distortion of scales should be avoided. Techniques for CADrafting provide the facility to manipulate scales to either enlarge or reduce details for any desired result. The drawing size notation (A0, A1, A2, A3, A4, B1, etc) must be shown on the original sheet in case reduction occurs later. 7:5 Reinforcement Detailing Handbook

Table 7.2 Lines and Their Application Designation (thickness in mm) Type of line A.7

Example

Continuous thick

Application Visible lines and change-in-level lines. Reinforcement where ‘M.5’ or ‘B.35’ concrete outlines used (preferred method). M.5

Continuous medium

Application Concrete outlines where ‘A.7’ reinforcement used (preferred method). Reinforcement where ‘P1’ concrete outlines used. Elevations of intersecting beams and slabs. P1

Continuous extra thick

Designation (thickness in mm) Type of line F.35

N.5

G.35/G.25

B.35

H.7 + H.35

B.25

Continuous extra thin

Application Reinforcement extent lines across slabs (plan view), walls (elevations), beams and columns for fitments. Dimension lines, leaders and associated lines. C.35

Continuous thin (drawn freehand)

Application Break lines around large areas such as slabs and special details to large scale or as a cloud to a revision. D.35

Continuous thin (ruled with zig-zag)

Application Break lines in individual elements such as at sections and elevations.

7:6 Reinforcement Detailing Handbook

Dashed medium

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Application Gridlines. Centre-lines.

Application Visible masonry walls in elevation and plan. Hatching of masonry walls over. Diagonals across holes or recesses (under or over). Welding symbols.

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Application Hidden masonry, particularly walls under, including hatching. Column-strip and middle-strip outlines on plans for flat slabs.

Application Concrete outlines where ‘M.5’ reinforcement used. Continuous thin

Dashed thin

Example

Chain thin/extra thin

Chain, thick at ends and change of direction; thin elsewhere

Application Cutting plane for a section indicating direction of view. If the G.35 chain line conflicts with other lines, it may be omitted leaving only the cross-reference and change-of-direction lines.

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Chain thick

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Application Indication of a surface to meet a special requirement (eg granolithic or terrazzo finish) or to receive special treatment. Match lines between drawings. K.35

Chain thin (double dashed)

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Application Outline of adjacent or existing parts.

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Figure 7.2 Columns and Beams in Plan View (a) Column under and over, with offset face (smaller size) above. Any “visible” face of the column-under is enclosed by dashed medium lines. The whole column section-under must be shaded to define its ing action. The column-over area is enclosed by continuous thick lines and must be both shaded and stippled. (b) Column under and over without change in size. The outline is a continuous thick line. The enclosed area must be both shaded and stippled. This example illustrates an internal column through a slab and is very common. (c) Column under with no column over (internal column). The area is enclosed by dashed medium lines and must be shaded. The example is of an internal column at, say, roof level. (d) Column under with no column over (external column). A corner column at roof level is illustrated. It shows a combination of continuous thick lines for the slab and column edges, and dashed medium lines for the column faces below. The enclosed area should be shaded. (e) T-beam, implying a beam with a slab at the top surface. The outline of the web is given by two dashed medium lines because it is always under the slab. No stippling or shading is required for beams. (f) L-beam at the edge of a slab (often called a spandrel). The exposed outer edge is shown in a continuous thick line and the hidden edge by a dashed medium line. No stippling or shading is required.

(g) Upstand beam. The example shown is a spandrel, so both edges are visible and therefore are in continuous thick lines. (h) T-beams intersecting under a slab without column under. Both outlines are in dashed medium lines. This situation often requires extra details to define which is the ing beam. (i) T-beams intersecting over a ing column under. All outlines are in dashed medium lines. For structural safety, the column area must be shown shaded to distinguish it from case (h) above, where there is no below the beam intersection. (j) T-beams intersecting over a ing column under and over. The beam outlines are in dashed medium lines. The column is shown by continuous thick lines. For structural safety, the column area must be shown shaded to distinguish it from case (h) above where there is no below the beam intersection. (k) Drop for flat slab and column heads for flat plates (with column under and over). The column outline is a continuous thick line and the enclosed area is stippled. The drop outline is in dashed medium lines and is neither stippled nor shaded. The plan view dimensions, including the depth, should be given on the planview in note form, for example 2400 x 2400 x 350 deep.

7:7 Reinforcement Detailing Handbook

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Figure 7.3 Walls in Plan Views (a) Concrete wall under and over, with offset face (thinner wall) above. Any “visible” face of the wall-under is enclosed by dashed medium lines. The whole wall section under must be shaded to define its ing action. The wall-over area is enclosed by continuous thick lines and must be both shaded and stippled. (b) Concrete wall under and over without change in thickness. Each outline is a continuous thick line. The ing area must be stippled and shaded This example illustrates an internal wall viewed through a slab and is very common. (c) Concrete wall under with no wall over (Example #1). The ing area is enclosed by two dashed medium lines and must be shaded. The example is of an internal wall at say, roof level. (d) Concrete wall under with no wall over (Example #2). An external wall at roof level is illustrated and shows a combination of continuous thick and dashed medium lines. The ing area must be shaded. (e) Masonry wall under and over. A single-skin wall is shown ing a slab. Both faces are in continuous thin lines. The wall area is shown cross-hatched in continuous thin lines and must be shaded if it is a loadbearing wall.

7:8 Reinforcement Detailing Handbook

(f) Masonry wall under, with no wall over (Example #1). The example illustrates a double-skin wall ing a slab on the inner skin. For the inner skin, the internal face is shown by a dashed thin line and the outer face by a continuous think line indicating the edge of the slab in this case. This skin must be shaded to indicate that it s the slab. The outer skin is defined by full thin lines. Both enclosed areas are hatched with continuous thin hatching. (g) Masonry wall under, with no wall over (Example #2). A double-skin wall is illustrated, both faces being drawn in dashed thin lines and hatched with continuous thin lines. Both ing areas must be shaded if loadbearing. AS 1100.301 recommends double hatching to be used for brickwork and single hatching for concrete blockwork. If the wall-under is to be non-loadbearing, this must be stated in a note (eg NON-LOADBEARING WALL UNDER) and the method of separating the wall from the slab above must be detailed to show the separating material. Note: Continuous-line hatching is quicker than using dashed-lines.

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Figure 7.4 Beam Elevations and Sections Note: Detailing of outlines shown, reinforcement omitted for clarity. (a) Section through a spandrel or L-beam with slab. Continuous thick lines are used. (b) Beam/column t in elevation (Example #1). Example illustrates an external column ing a rectangular beam without a slab. The outlines are thick, continuous. (c) Beam/column t in elevation (Example #2). Example is of an external column with the view taken just in front of the column. The spandrel and slab (together forming an L-beam) are shown as a cross-section in medium full lines. The exterior T-beam and the column are shown as a sideelevation in continuous thick lines. The slab is common to both beams. (d) Beam/column t in elevation (Example #3). Example is of an external column at a corner with intersecting L-beams. Here the L-beam is behind and hidden by the column, so both spandrel and slab are shown as a cross-section in dashed medium lines. The L-beam extending right and the column are shown in side-elevation in continuous thick lines. The slab is common to both spandrels.

(e) Intersection of two T-beams (Example #1). The view is taken at the near surface of the deeper beam which is defined by full thick lines. The shallower beam and the common slab are shown in cross-section by full medium lines. (f) Intersection of two T-beams (Example #2). The view is taken at the near surface of the shallower beam which is defined by full thick lines. The deeper beam and the common slab are shown in cross-section by full medium lines. NOTE: Without more information, it is impossible to tell which is the ing beam. In cases such as these, both views Example #1 and Example #2 should be detailed to ensure that the correct reinforcement is continuous through the t. (g) Elevation of external L-beam intersecting a T-beam. The spandrel is defined by full thick lines and the T-beam and the common slab by broken medium lines. In this case, again determination of the ing beam requires further details; the T-beam could be a cantilever ing the spandrel.

7:9 Reinforcement Detailing Handbook

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Figure 7.5 Reinforcement Within Outlines

7:10 Reinforcement Detailing Handbook

Only selected examples are given, since this topic is the major purpose of the Handbook. Line separation is illustrated, based on the use of the “M.5” (medium) line type and thickness for concrete outlines and the “A.7” (thick) lines for reinforcement. Bars in cross-section are shown in “P1” dot form. (a) Column or beam in cross-section. The concrete outline defines the dimensions and shape of the fitment drawn inside it. The spacing between the main bars must be adequate for placing and vibrating the concrete to AS 3600 requirements, but is generally diagrammatically represented in this type of detail. A bar is relatively thicker than a dot from a pen. (b) Beam with one layer of bars. Only the line types and separations are illustrated, not the structural requirements. This detail shows top and bottom bars with fitments (stirrups) separating and ing them. Indicate longitudinal bars of different lengths in same layer with a circle. (c) Elevation showing two layers of bar in the same face of a member. The lower and upper layers of bottom reinforcement are shown and the space between both layers is detailed with a minimum distance. (d) Mesh in plan and elevation. Mesh is already a twodimensional material and may require more than one view for complete definition. The bars being viewed are shown as continuous thick lines. Transverse bars shown in plan-view or elevation are in continuous thin lines. The detailer should take special care when showing mesh to distinguish between rectangular and square meshes. The direction of the main (longitudinal) bars is shown in thicker lines and the thinner lines indicate the total width made up by the sheets (cross-bars). See also later Chapters for applications. Note: 1. Bars in cross-section are shown as “P1” dots. 2. In some cases, it is important for design purposes to define which bars are closest to the concrete surface. This can be done by careful location of the “dots” in each view, for example in a cantilever retaining wall. Where it is not important structurally, excessive description is not required. 3. The same comment applies to bar arrangements, except that the order in which bars are fixed will need to be considered. (See later Chapters).

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Figure 7.6 Holes, Recesses and Set-Downs (a) Significant change in concrete level (in plan-view). The example illustrates a plan-view of a step-down in a slab, or possibly over a concrete beam. The visible edge is shown by a continuous thick lines, and the hidden face by a broken medium line. The ing beam neither hatched nor shaded. Note that the levels are given in metres to three decimal places (see Clause 7.6.3). (b) Holes through the element (in plan-view or elevation). The concrete edge is shown in thick full lines. Two diagonal continuous thin lines define the opening. This detail could apply to holes through a slab or to a door opening in a concrete wall. (c) Recess into, or small set-down, on near side of member (in plan-view). The concrete edge is shown in thick full lines. One diagonal continuous thin line defines the extent of the recess.

(d) Plinth or a thickening on near side of member. The concrete outline is shown in thick full lines, but the area is not defined by a diagonal line. Levels may be advisable, with or without a cross-section. Examples are a machine base or a corbel in end elevation. (e) Recess under or on far side of member. The concrete outline is shown by broken medium lines, and the extent is defined by one continuous thin line. This case is unusual and may require extra descriptive notes. (f) Section taken through a hole. The surfaces of the member and the sides of the opening are defined by full thick lines. One diagonal thin continuous line defines the extent of the opening as if it was a recess. Stippling of the remaining concrete may assist the visual impact, but reference to the section cutting plane is essential.

7:11 Reinforcement Detailing Handbook

7:12 Reinforcement Detailing Handbook

8 Identification and Dimensioning of Concrete Elements

STRUCTURAL ELEMENT CONSECUTIVE

8.2

NUMBER SYSTEM (AS 1100.501) With this method, the elements at each level are numbered consecutively using a combination of letters and numbers. The levels are determined from the “prefix” defined below. The full reference should comprise the following:

8.1

PRELIMINARIES

■

by sequential levels or by the traditional storeys.

a reinforced concrete structure using the concept of placing zones. It was suggested that structural

■

Stem – the type of structural element such as beam, slab, etc.

were built by alternating horizontal zones with vertical zones, for example footings followed by

Prefix – the location or floor level of the structural element. Floor levels may be designated either

Clause 2.2 described the construction of

■

Suffix – the individual number of the structural

columns, floor, columns and walls, floor, columns and

element, which is explained further in the

roof.

following sections. This concept is too vague for real design and

construction. At many stages, it is necessary to define both large portions of the structure (such as the “1st floor” or the “roof”) and the individual structural

Table 8.1 shows the numbering system described in AS 1100.501. Further examples will be given throughout this Handbook. See also Clause 8.5.1 on plan-views.

“”, called “elements”, which when combined make up the floor or roof. In a building, the most common method of

Table 8.1 Consecutive Numbering System for Elements

describing vertical position is to use the term “level”

PREFIX

or “floor level” for the horizontal floor zone and the column/wall system immediately above that level, and

Location or floor level

the term “element” to describe the individual member,

Sequential levels

say “beam, slab, wall, column or footing” which makes up that “level”. Having defined the level at which each element is located, its position horizontally is defined in two ways – by either structural element number or by gridline references. Within each of the elements will be found reinforcing steel (mesh or bar), prestressing materials (ducts, tendons and anchorages) and perhaps some extra fixings, etc. For convenience, here we will refer to these as the “components” which combine to make up the “element”, and which in turn combine into the structural “level”. All of these will eventually require identification. If architectural drawings use a particular method of referring to levels and elements, the identical system must be adopted for the engineering drawings. To do

STEM Structural Code element

Code

Selected

1 Lowest level, then in ascending order to top-most level (eg tenth level) 10

Column Slab Beam Joist Lintel Footings: Traditional storeys Footing beam Pad footing Roof R Strip footing Third floor, etc 3, etc Raft footing Second floor 2 Cantilever footing First floor 1 Pier (or pedestal) Mezzanine M Pile cap Ground floor G Portal Frame Basement B Stairs: Footing level F Stair flight Stair landing Truss Retaining wall Construction t

C S B J L FB FP SF RF CF P PC PF F L T W CJ

otherwise, would cause confusion. Example 8.1 Fourth floor, beam 21 Example 8.2 Level 10, slab number 4

4B21 10S4

8:1 Reinforcement Detailing Handbook

8.3

GRID-LINE SYSTEM (AS 1100.501 AND

Wherever possible, the direction from which the

AS 1100.301)

member is viewed should be from a location which is

A grid-line system is used generally to define

at least attainable; that is, if a view of a lift well wall is

the horizontal location of elements at any level. Vertical

required, do not draw the view from inside the well if

location is defined by the “level” or “storey”.

there is no scaffolding there or, if a retaining wall is to

A grid reference system consists of one set of

be cast against the earth, do not detail the view from

grid-lines in one direction with a second set of grid-

the earth side. However, it is common practice to give

lines in, generally, a perpendicular direction. (See

elevations of external beams as viewed from either

Clause 11.16 Drawing Sheet No 11.1). Grid systems

the bottom or the right-hand side of the sheet, not as

are most often used with regularly shaped floor plans,

viewed from inside the structure. If in doubt, spell it out in full.

but grid-lines do not necessarily have to be straight or at right angles to each other. Additional secondary gridlines can always be incorporated on the original grid to cater for amendments during construction. Where architectural or project drawings use grid-lines as reference, the engineering drawings must refer both to the identical grid dimensions and the numbering method. It is recommended that, for structural grids, the grid-lines running down the sheet should be marked alphabetically (A, B, C, etc) and the grid-lines running horizontally should be marked numerically (1, 2, 3, etc). Grid directions should be chosen to allow for any future expansion, nevertheless a project grid may be adopted with a completely arbitrary orientation, bearing no relation to any recognised map grid or to “true north”. Grid system notation is not abbreviated.

Table 8.2 Abbreviations for Locations, Materials and Reinforcement Placing Words

Abbreviation

Locations Structural floor level Finished floor level Existing level Reduced level Horizontal Vertical

SFL FFL EXL RL HORIZ VERT

Materials Reinforced concrete Precast concrete Prestressed concrete Brickwork Concrete Reinforcement

RC PC PSC BWK CONC REINF

Reinforcement placing information 8.4

SUGGESTED ABBREVIATIONS FOR LOCATIONS, MATERIALS AND REINFORCEMENT PLACING. In the same way as element labels are given

in an abbreviated form, so can many other names of construction items be shortened. It is essential that the abbreviation is common throughout the construction industry and is clearly understood. Various examples are given in AS 1100.101, AS 1100.301 and AS 1100.501; traditional abbreviations for reinforced concrete construction are given in Table 8.2. Other abbreviations should not be used unless clearly defined on every sheet on which they appear. Abbreviations mean the same in the plural as in the singular. Only capital letters are to be used. Full-stops and apostrophes should be omitted.

8:2 Reinforcement Detailing Handbook

Each way Each face Near face* Far face* Horizontally Vertically Maximum Minimum Top or Top-face Centrally placed Bottom or Bottom-face Internal face External face At centres (spacing) Continuous Typical Note:

*

EW EF NF FF HORIZ VERT MAX MIN T or TOP CENTRAL B or BOT INTF EXTF CTS CONT TYP

In these cases, the direction of viewing must be carefully defined.

8.5

STRUCTURAL ELEMENT NUMBERING

Further, misfits between elements are

Structural element numbers for footings,

discovered during design or early scheduling, and not

columns, walls and slabs are written consecutively from

at the last minute before a concrete pour. As a general

left to right in each horizontal row starting from the

rule, faster real-time construction can be achieved

top left corner, working downwards and read from the

also. The following sections apply particularly to the

bottom of the sheet.

reinforcement drawings.

Beam numbers should be consecutive from left to right “horizontally” in each row reading from the bottom of the sheet, and consecutive from bottom to top of the page for each “vertical” row reading from the right-hand side of the sheet. Grid references for columns and footings are described in Clause 8.7; lettering should be read from the bottom of the sheet. See Clause 8.3. For the method of dimensioning elements in plan-views, see Clause 8.7. Any necessary dimension lines on plan-views should be kept clear of structural details.

8.6.2 Compatibility of Dimensions Where dimensioning of concrete outlines is required for satisfactory construction, the method adopted must be compatible through the various drawings. For example, if architectural drawings use centreline dimensions for beam and column locations, the engineering drawings should use the same method. Fast-track methods of construction throw an extra burden on all of the design and construction team. Where drawings are amendments to the original set, there will always be the likelihood that dimensional changes are not transmitted to the site. It is strongly recommended that dimensions essential

8.6

DIMENSIONING OUTLINES OF

to strength and stability of the structure should be

STRUCTURAL ELEMENTS

highlighted on these amendment sheets.

8.6.1 General Sufficient dimensions to describe the structure must be given on the contract or construction drawings whether they are architectural, concrete-outline or reinforcement-placing drawings. In Australian practice for detailing buildings, the designer often combines concrete outlines and reinforcement details on the same drawing. Dimensions are obtained from the architectural drawings.

It will be obvious that extreme care must be taken to ensure that a dimension shown twice or more must be identical in each case. With CADrafting, where dimensions can be generated automatically, the addition of critical dimensions are not time consuming and they should be included as a matter of course. 8.7

DIMENSIONING CONCRETE OUTLINE SHAPES

Many civil engineering structures however show

Engineering drawings are used for erection of

concrete outlines with dimensions on one drawing, and reinforcement details on another because architectural

formwork as well as for reinforcement details. Whilst the

drawings are rare for these structures. This method is

architectural drawings will show the basic dimensions

used when it is necessary to provide more dimensions

of the building as a whole, the size and shape of each

and details of holes, pockets, inserts, etc, than is

structural element must be shown on the engineering

required when architectural drawings are supplied.

drawings. This is done by numbering each element

Reinforcement details are then given on separate

(see Clauses 8.2 and 8.3) and by indicating the overall

construction drawings or even on separate sheets.

structural dimensions (mm) as shown below. A combination of the element-number/

On projects where the structural engineer details concrete outline dimensions, member sizes

dimensions is most effective in providing the maximum

and associated locations of reinforcement and tendon,

amount of information with the minimum amount of

the job can be formed and scheduled from common

effort.

information, and consequently built with greater accuracy.

All the following should be regarded as minimum requirements for satisfactory communications.

8:3 Reinforcement Detailing Handbook

8.7.1 Beams Dimensions of beams should be given once

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only, and that must be on the plan-view. AVOID repetition of dimensions on a section because it

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requires considerably more effort to check that future amendments have been transferred to all details. It does not matter if the section is slightly out of scale. See Figure 8.1 for the following examples.

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(a) Rectangular beam (ie one without an integral

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slab) Specify on the plan-view, the overall depth first, following by the width. The floor level and beam number is also given. eg

4B21 – 650 x 300

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Specify on the plan-view the overall depth first,

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including the slab thickness, followed by the web width. Also give the floor level and beam number. eg

MB6 – 500 x 275

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In major projects, beam dimensions may be set out in a separate schedule, but plan-views must still indicate these values to assist construction

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trades. For example, air conditioning and electrical trades use plan-views, not cross-

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sections, for information. (c) Beams with non-rectangular shapes

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Figure 8.1 Beams

8:4 Reinforcement Detailing Handbook

8.7.2 Columns See Figure 8.2 for the following examples. (a) Rectangular columns – minor projects Specify on the plan-view the orientation of the column faces and the dimensions. The column number is given but the floor level is not required. eg

C15 – 450 x 350 (on the plan-view)

(b) Rectangular column – major projects Specify on the plan-view the column reference number or use the grid-line reference. The floor level is not required. eg

C15 (on the plan-view)

If a separate column schedule is provided, specify the orientation of each column face (say by drawing a North Point) and the dimensions. Such a schedule should have full details of the reinforcement as well. (c) Circular column Specify as in (a) and (b) as applicable. eg

C9 – 700 DIA (on the plan-view)

If the orientation of the main bars in the column are critical, additional dimensions should be given.

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8:5 Reinforcement Detailing Handbook

8.7.3 Slabs, Walls and Stairs

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See Figure 8.3 for the following examples. (a) Slabs

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thickness, together with major variations. The slab number should be given; it is often shown in

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a circle for clarity. On cross-sections, dimension all relevant thickness, recesses, step-downs, etc. Where

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a slab outline is indicated on an elevation, its thickness may be dimensioned if this will save an additional detail without loss of understanding. (b) Walls Draw and dimension the outline on the plan-

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view. Do not repeat the thickness dimension on sections. The location and size of penetrations such as doors and windows should be indicated on an

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elevation; the dimensions are obtained from architectural drawings. (c) Stairs Draw the outline as an elevation for flight and

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landings. Dimension the landing and flight throat thicknesses. Tread and riser dimensions are generally fixed by architectural requirements such as floor-to-floor heights and the requirements of the Building Code of Australia (BCA) for tread and riser dimensions.

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Figure 8.3 Slabs, Walls and Stairs

8:6 Reinforcement Detailing Handbook

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8.7.4 Footings

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See Figure 8.4 for the following examples. (a) Pad footings, pile caps, etc. A footing drawing must show its own orientation in relation to the structure and also that of any associated columns. In particular, the details of the column’s starter bars must be given in the footing drawing.

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Pile-cap drawings must show the location of the piles as well. Draw a plan-view and dimension length and

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width.

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Below a separate cross-section of elevation, specify the “length x width x depth”, and dimension the depth. eg

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column which it s where possible. This recommendation applies particularly when a column schedule is provided.

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(b) Strip footings (generally ing a wall) Draw the outline in plan-view and dimension each width. If cross-sections are not given, specify on drawings or in the Specification the

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dimensions as: DEPTH x WIDTH. If cross-sections are drawn, dimension the width and specify underneath as for beams the element number and dimensions as:

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DEPTH x WIDTH. eg

SF6 – 750 x 300

THIS DESCRIPTION MAY CONFLICT WITH PAST PRACTICE IN SOME DESIGN OFFICES, BUT IT IS STRONGLY RECOMMENDED BECAUSE DIMENSIONING OF GROUND BEAMS AND STRIP FOOTINGS MUST BE CONSISTENT WITH AS 2870.

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Figure 8.4 Footings

8:7 Reinforcement Detailing Handbook

8.7.5 Length and Height of Various , Areas of Slabs and Walls, etc. For elements having an irregular shape or variable dimensions, the outline must be drawn separately in plan-view, elevation and section with all dimensions shown. Examples are: ■

Haunched beams.

■

Columns with irregular shape for architectural purposes, particularly precast concrete units.

■

Floor joists with webs tapered in plan-view.

■

Corbels

8.8

DIMENSIONING FORMWORK Chapters 3 and 5 have considerable

information about allowing for tolerances in construction and the effect of insufficient cover on the durability of the structure. Rebates and drip grooves will reduce cover and therefore are a potential source of corrosion of reinforcement if they are not properly detailed. Architectural drawings tend to show finishedsurface drawings; these may not be suitable for formwork dimensions! Properly-dimensioned reinforcement drawings are more suited for formwork manufacture as formwork size and reinforcement scheduling can be better coordinated. Failing this, separate dimensioned concrete outlines are required. Element sizes should be related to formwork surfaces with any additional finishes to the concrete shown by extra dimensioning. Fillets are drawn only in large-scale details when their omission would affect cover, etc. Special details on fillets may be given in the Specification. Consideration should be given at the design stage to the use of standard formwork s or sheet sizes. Table-forms, “left-in-place forms” and similar methods for maintaining the planned cycle times must always be considered. Multiple re-use and ease of erection and stripping of forms are an essential part of economical construction.

8:8 Reinforcement Detailing Handbook

9 Identification and Dimensioning of Reinforcement Components

The most common basic shapes are shown in Figure 9.1. Throughout the rest of the Handbook, these shapes will often be referred to by the codes given there. Some shapes require additional explanation. The first five groups constitute about 95% of all bars fabricated, sizes notwithstanding. Comments on some of the shapes in Figure 9.1

9.1

PRELIMINARIES

are as follows:

Within each “element” of structural concrete,

SHAPE

COMMENT

S

A straight bar referred to in this context, really means a “straight bar”. It could be a stock length bar (see Clause 2.1), or it could be a bar cut from a stock bar without any bending being done.

L, LL

These bars include cases where a 90º hook (cog) is added at one or each end as dimensions ‘A’ and ‘C’. If you are in any doubt as to the use and specification of hooks and cogs, please re-read Chapter 6.

CC

This shape allows for a small offset (dimension D ≥ 2db) so that column bars can be lapped, dimension ‘A’ represents the lap-splice. The crank dimension ‘C’ should be no less than 6db, but for smaller bars 300 mm is used. (See Clause 12.2.10). It can also be used for beam bars.

there will be “components” such as reinforcing mesh and bar, tendons, fixings, and similar items. Each component must be capable of definition to show: ■

What it looks like (shape, product number). See Clause 9.2.

■

Its location within the element (cover, dimensional position). See Clause 9.3

■

Its performance specification (steel strength, reference code). See Clause 9.4.

■

How many of them (number of bars and tendons, wires/sheets of mesh, basic design notation). See Clause 9.5.

■

Where it goes (placing information). See Clause 9.6.

■

How to identify it from schedules, etc (element labels, bar marks). See Clause 9.7.

■

Special features (laps and anchorage, proprietary splices, welding, bending-pin size, galvanising or epoxy-coating). See Clause 9.8. Designers are required by the AS 3600 to

provide certain information on the drawings and this

T, HT, DT These are “closed ties”; used principally with rectangular . SH, SC, RT

These are “open ties”; give easy access for fixing beam cages (See Chapter 13).

J, JJ

These shapes should be used where a small crank is required at bar ends to avoid interference with intersecting steel. The shapes used to be known as “bent-up” bars for shear stress design in beams and slabs. They are now obsolete. (Dimension ‘D’ approximated the depth of the member, and the angle was 45º).

is quoted in Clause 1.2.3 of this Handbook. In many cases, preprinted General Notes can have spaces for details to be inserted. See Appendix B. 9.2

REINFORCEMENT SHAPES Steel reinforcement is incorporated in concrete

to resist tensile, compressive, shear and torsional forces. It is therefore located in the concrete section where it best serves its purpose and this, with the concrete outline, dictates the actual shape. Although more than sixty percent of bars used are straight and more than this percentage of mesh

V, VL, VV If known, the angle of bend can be given. The other dimensions are often obtainable from the concrete shape. A, AL, AV The latter two are logical extensions of shape A, similar to shape V above. U

This should be specified in lieu of shape LL if the overall dimension ‘B’ is less than about 200 mm; LL cannot be bent to that size.

H, HH

Both of these bars are defined as having 180º hooks at one end or each end respectively as dimensions ‘A’ and ‘C’. For bars other than these and some fitments, hooks can be added as shown later.

is in flat sheets, both materials are also required to be shaped (bent) to reflect the shape of the concrete surface and often for structural reasons. 9.2.1 “Standard shapes” for reinforcement The Standard Shapes in AS 1100.501 are used in reinforcing steel schedules for manufacturing purposes.

9:1 Reinforcement Detailing Handbook

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9:2 Reinforcement Detailing Handbook

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9.2.2 Addition of Hooks to Standard Shapes

9.2.3 Tendon Shape and Reinforcement

As a general rule for good design and detailing,

In prestressed concrete, the tendon is the

hooks and cogs should never be used unless structural

primary longitudinal strengthening component. The

requirements for end anchorage cannot be achieved

position of the tendon and duct must be located and

without them.

dimensioned first, then the reinforcement must be

Hook length allowances are given in Table 6.5.

detailed to fit around the tendons. In some cases, the

Anchorage with hooks or cogs is incorporated

reinforcement will need unusual bending shapes which

with fitment shapes T, HT, DT, LH, SH and SC, and

can only be classed as NS.

with RT having dimensions ‘A’ and ‘E’ as out-turned cogs. 135º hooks are included with shapes HT and DT. No provision need be made for 90º cogs under this system. In most cases where they would be needed, shapes L, LL, VL, LJ and RT are adequate and are easily recognised. Clause 6.2.5 advises precautions on use of cogs in thin because they can protrude into concrete cover if care is not taken.

9.3

REINFORCEMENT LOCATION Tolerances are allowances for inaccuracies

of manufacture or for placement from specified dimensions or position. Tolerances are dealt with fully in Clause 3.2 9.3.1 Effect of Cover A longitudinal bar will have its shape defined

Except for the fitment shapes and H and HH, all

by that of the surface to which it is parallel so that this

standard shapes can have a 180º or 135º hook added

surface cover has almost no influence on the bending

to either or both ends. To enable the steel to be bent,

dimensions. A fitment is defined by the cross-sectional

the type of hook and its orientation in relation to the

shape of the concrete and the cover is critical to the

next bend must be defined. An indication that a hook is

bending dimensions.

required is given by the letters “H” (one hook) and “D” (two hooks) with the normal shape code.

Chapter 5 describes how to select durable concrete and the appropriate cover for corrosion

The range of hook combinations is illustrated in

resistance and general durability.

Figure 9.2. Example 9.1 An “L” shape with a hook at one end is defined by “LH”, whilst one with two hooks is called “LD”. In addition to this combination are the letters “I” (means the hook is bent “into” the next bend) and “O” (means it is bent “outward” from the next bend). See Figure 9.2.

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9:3 Reinforcement Detailing Handbook

9.3.2 Effect of Position Main bars enclosed by the fitment require

The location of the steel must be definable on site. For example, as will be seen in Chapter 14, with

additional information such as the span length for their

slabs and slab systems, the “clear span” for the placing

dimensions to be determined.

strips is measured from a line drawn between the faces

The calculation of dimensions takes into

of columns some distance away, so that a dimension

the type of member (beam, slab, column) and

on the “standard detail” such as “0.3 TIMES CLEAR

the particular type of end condition (for top-bars, the

SPAN ” may not always be appropriate. Steel-fixers and

extension into the span; for bottom-bars, the extension

inspectors rarely have a calculator so that a figured

into a , for columns the floor-to-floor height;

dimension is always preferable. “Standard details” can be supplemented by

lapping requirements; and so on). Cover to the ends of bars is often not a

tables which contain numbers of bars in each placing

dominant factor. Span length and floor height are

zone, the label and even the spacing. When extra

critical.

bars are needed, say at a hole, these are shown As an example, if the soffit of a beam is flat,

then the main bottom bar will probably be straight,

on supplementary views or cross-sections on the appropriate drawing sheet. Often it will be essential to state a figured

but the length of the bar cannot be calculated without knowing the design factors which affect the end

dimension, for example at lap splices, or where the

anchorage. This is a design matter and must be

anchorage length is critical, or where bars are not

specified in some way.

symmetrically placed.

9.3.3 Dimensioning of Reinforcement with “Typical” and “Standard” Details Reinforcement bending dimensions are usually obtained by subtracting cover from the concrete sizes. In other cases, a dimension is required on the detail to enable the scheduler to calculate the bar length and for the steel fixer to locate the bar in the formwork. As a general rule, always establish the location of the bar by reference to a setting-out line or to formwork, and not by reference to a grid-line which cannot be readily identified on the site. Although “typical details” for minor sections are not recommended, such details may be of value if they are located close to the plan-view or cross-sections to which they apply (on the same sheet obviously), if one detail truly represents every case to which it meant to apply, and if the shape and dimensions are clearly stated. Another useful drawing is a “standard detail” which applies for the whole project, and would therefore be shown in the introductory drawings. Standard details should define such matters as bar arrangements in columns, or bar and fitment cut-off points in beams or slabs.

9:4 Reinforcement Detailing Handbook

It is designer’s responsibility to locate the reinforcement correctly and to state this in the drawings. (See Clause 1.2.3). 9.4

SPECIFICATION OF STEEL STRENGTH

9.4.1 New Projects There is one primary strength grade for reinforcement – 500 MPa for hot-rolled deformed bars and mesh. There is also a 250 MPa grade for plain round bars, but these are generally allowable only for dowel bars and fitments. A 250-MPa deformed bar is also available only in a 12-mm diameter and is used for freeform swimming pool reinforcement. There are also eight Standard Grades of concrete (20, 25, 32, 40, 50, 65, 80 and 100 MPa), each of which can be ordered as either Normal Class concrete or Special Class concrete. The applicable Australian Standards are quoted in Chapter 4 with other pertinent information such as bar sizes. To ensure that the correct strength of materials is specified, there are a number of recognised conventions that must be followed.

The Australian Standard AS/NZS 4671 has

9.4.2 Renovation of Older Structures

three levels of ductility that are designated by the

Sometimes in the course of renovations, the

letters L, N or E representing Low, Normal or Seismic

strength of materials has to be determined. If a sample

(Earthquake) ductility respectively. The shape is also

of steel can be obtained, it should be tensile tested. If a

designated by the letters R, D or I, representing plain

test cannot be made, the surface appearance is often

(Round), Deformed-ribbed or deformed-Indented,

a good guide. Reinforcement used prior to 1914 was

surfaces respectively. The strength grade is a numeral

most likely imported.

value of the lower characteristic yield stress expressed in megapascals. The bar is designated with the shape

All mesh since 1914 can be assumed to be of grade 450 MPa until year 1998.

factor first, the strength factor second and the ductility

If the bar surface is “plain” then a yield strength

last. A typical reinforcing bar grade is D500N, ie a

of 230 MPa should be the maximum assumed. Since

deformed bar of normal ductility and a yield strength

wire is indistinguishable from plain bars, use 230 MPa

of 500 MPa. The indented shape is not used in the

also.

general construction industry and is mainly used in the

If the surface is “deformed”, only 230S grade

manufacture of reinforced concrete pipes. The seismic

should be assumed for a non-twisted deformed bar

“E” ductility for bar is required for New Zealand only.

if construction occurred up to 1986 and it cannot be

To simplify the notation on drawings, a simple code is

positively identified. Construction after 1986 would

provided in the Table 9.1 which is used by the general

probably use grade 410Y or 400Y deformed bars as

industry.

main reinforcement. From 2003, this allows 3 years for all old stock to be used up, the grade can be assumed to be 500N.

Table 9.1 Notation for Commonly-Available Reinforcement

Construction from 1957 to 1963 often used a twisted, square bar; its yield strength was 410 MPa. The surface should be easily identifiable.

Yield strength, fsy (MPa)

Bar notation

Simplified notation

Welded Mesh (Square)

500

D500L

SL

Welded Mesh (Rectangular)

500

D500L

RL

off first.

Deformed Bar

500

D500N

N

and mesh yield strengths.

Deformed Bar

500

D500L

L

Deformed Bar

250

D250N

S

Plain Round

250

R250N

R

Material type

Between 1963 and 1983, twisted deformed bars may be assumed to be of grade 410C. If it is intended to old and new bars by welding or mechanical splices, any untwisted portion at an end must be cut Table 9.2 provides a chronological list of bar

NOTE: For mesh notation, ‘S’ and ‘R’ are Square or Rectangular meshes respectively. The normal spacing of bars in mesh is 200 mm with some meshes with 100 mm spacing of bars. This spacing if not given in the mesh notation will be standard at 200 mm centres for bars. Other spacings of bars can be manufactured such as 300 mm but this would be classified as nonstandard. These meshes can be manufactured on a project by project basis to the engineer’s design.

9:5 Reinforcement Detailing Handbook

Table 9.2 Historical Values of Yield Strengths (as at November, 2005)

Surface appearance of steel

Year of construction

Mesh

9.5

REINFORCEMENT QUANTITY FOR STRENGTH CAPACITY –

Probable yield strength, fsy MPa

psi

Before 1914 to 1995

450

65 000

Deformed Mesh

1995 to now

500

-

Plain round or any other unidentifiable steel

Before 1914 to 1988

230

33 600

“Basic Design Notation” The strengthening effect of reinforcement depends on the total area of steel of the required yield strength being provided at each appropriate crosssection. This is done by specifying the number of bars of the selected size, each having a known strength. In this Handbook, we use the “Basic Design Notation” to provide this information. The Basic Design Notation should only be

Twisted square [Note 4] 1957 to 1963

410

60 000

Deformed Intermediate Grade [Note 1]

1960 to 1962

275

40 000

Deformed Hard Grade [Note 2]

1960 to 1964

345

50 000

Twisted deformed [Note 4] (CW60)

1962 to 1983

410

-

Deformed hot-rolled

1983 to 2000

410 [Note 3]

-

Deformed hot-rolled

2000 to now

500

-

shown once for each bar in an element and this should be on that portion of an element which is cast first. For example, a starter bar is drawn with the footing, not the column. The reason should be obvious! The actual shape of the bar must be defined in this view of the element, even when it is indicated again on a separate detail. To assist in identification, draw a small sketch of the shape, or enter the “shape code” described earlier, after the notation.

NOTES: 1. Intermediate Grade was rare and probably only in Victoria. Weldability very doubtful. 2. Hard Grade was common in NSW, but unusual elsewhere. Unweldable. 3. After 1988, AS 3600 specified only a design yield strength of 400 MPa for deformed bars. 4. Remove untwisted ends (about 150 – 200 mm) before splicing by end-butt welding or mechanical splicing.

9.5.1 Examples of Basic Design Notation See Table 9.3 and Figure 9.3. From the information given in column 3 “Notation” of Table 9.3, it would be possible to check the strength of the section by calculation at any time in the future – the yield strength is defined by the simplified notation N and RL, and the steel area is obtained from a combination of bar size and number off, or bar size and spacing, or directly from the mesh reference number. Area values would be obtained from Tables in Chapter 4.

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Table 9.3 Examples of Basic Design Notation Typical basic information Member Type Position of Steel

Notation

Actual area provided

Beam

4N36

4080 mm2 total

Column All bars in section 8N24

3600 mm2 total

Slab

Bottom bars

Bottom mesh

Flat Slab Bottom Bars

RL918

636 mm2/m width

(a) 20-N16-160 4000 mm2 total, or (b) N16-160 1250 mm2/m width

9:6 Reinforcement Detailing Handbook

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Figure 9.3 Examples of Basic Design Notation

9.5.2 Reasons for the Recommended Basic

Provided that cover is maintained, the location

Design Notation

of the outermost bar is often not critical. Because

Several variations of notations are suggested

this fact is often not appreciated by site inspectors,

because each correspond with the way different

the designer should state the number of bars. Some

are designed, see Figure 9.3.

designers also require a trimmer bar around the edge.

(a) The number of bars in narrow such as beams or columns is calculated from the total cross-sectional area of steel

(mm2),

hence a

In this case it too should be specified so that it will be included. Mesh. Standard mesh sheets are made

notation like 4-N36 for bars in one face, or

2400 mm wide. When a slab width is less than this,

8-N24 for the total.

mesh can be cut from a standard sheet, or a narrower

(b) For wide such as floors and walls, the

sheet can be manufactured to the specified width

area of steel is calculated as area per unit width

for large projects where the mesh manufacturer is

(mm2/m), hence notations like 20-N16-160 or

prepared to make special sheets.

N16-160 or RL918. (c) For certain structural elements such as flat

When a member width exceeds 2.4 m, two or more sheets are required. However, on a

slab floors, it is strongly recommended that the

drawing it is not necessary to specify the number of

designer specifies the number of bars as well as

sheets required for coverage. Provided that the side

the spacing, or that the width of the column and

overlap is specified (if not the AS 3600 lap will be

middle strips are dimensioned on the structural

assumed – see Clause 6.9) the total width of mesh

details and the number of bars in each strip

can be determined. It is then up to the mesh supplier

are specified with the assumption that uniform

to decide whether to provide several sheets 2400 mm

spacing is implied. By this means, the correct

wide with a “make-up” sheet less than 2400 mm, or to

total cross-sectional area of steel is specified

manufacture all sheets the same width but which will

and the spacing has secondary importance.

total the slab width plus side laps. This latter method

(The steel fixer still wastes time working out the

will also permit the sheet length to be cut to size from

spacing however!). Preferred methods are

the machine without creating scrap.

20-N16-160 and RL918. 9.5.3 “Number-off” Calculations for Wide Sections The methods differ for bars and mesh. Bars. The preferred method of calculating the number of bars is to obtain the overall width (mm) and divide by the bar spacing. If the answer is not a whole number, take the next higher number of bars.

Standard mesh sheets are made 6000 mm long, but this is just traditional. Longer or shorter sheets, with almost any width; can be manufactured to suit the project so that the specified steel area is provided in each direction. Transport lengths and mass for handling are the two major constraints; the latter can often be solved by using a number of narrower strips; for example, twice as long, half as wide.

As an example, if the N16-160 bars were located in a slab 3100 mm wide from edge to edge, 3100/160 = 19.4 bars would be required; because part of a bar cannot be provided. 20-N16 are specified. Note that the calculation is based on the “total width of the slab” not “total width minus side cover” because the bars must reinforce the edge cover. The answer gives the number of bars, not the number of spaces between the outermost bars. This means that the extreme bars on each side of the section are located from that side not more than one-half the specified spacing.

9:7 Reinforcement Detailing Handbook

PLACING INFORMATION

9.6

For design purposes it was necessary to identify

9.6.2 The “EACH WAY” Abbreviation The loose term “both ways” must not be used.

every structural element. (See Clause 8.2 for element-

“Each way” means that the same component of

numbering system). Each component within the

reinforcement is required twice – once in one direction

element must also be identified and located, and this is

and again at right angles.

done with bar marks and other notes. (See Table 8.2 for placing abbreviations).

When the “EW” instruction is given, do not use the complete basic design notation stating both “number off” and “spacing” unless it is absolutely

9.6.1 Abbreviations for Placing Steel The reason for using an abbreviation is to

certain that the identical number of bars is required in each direction. As an example, if say N16 bars are to

separate the different sets of bars into their correct

be placed in two directions in the same element, then

layers and directions. Abbreviations have greater

use EITHER;

value when cross-sections are not drawn and the

(i) 20-N16-160 EW where the spacing is known;

designer uses a plan-view or an elevation to detail the

or

reinforcement.

(ii) 20-N16 EW

■

be placed in its correct location, preferably without the need for an excessive number of

■

■

9.6.3 Comments on Placing Abbreviations Abbreviations EF, NF, and FF refer to the

cross-sections, etc. Too many cross-sections of

layer(s) of reinforcement adjacent to a surface of a wall

obvious details will confuse rather than instruct.

drawn in elevation. Whether or not the face is “near” or

Extra details of complex arrangements may well

“far” depends on the direction from which the elevation

save many man-hours later when interpretations

is viewed, so this direction must be made clear. It is

are requested.

also essential that a workman can position himself so

Where different layers of reinforcement are

that he can in fact see the element from that view.

superimposed on one detail (eg bottom and top in a plan-view, or near-face and far-face in an elevation of a wall) the detailer will improve

Abbreviations INTF and EXTF may be better for exterior walls. Abbreviations B and T refer to the position of

communications by indicating the layer, and

reinforcement near the surfaces of a thin element such

sometimes the direction, in which the steel is to

as a slab or a staircase.

be placed. ■

when spacing is not critical.

Sufficient information is needed for the bar to

Abbreviations HORIZ and VERT apply to the

The simplest method of providing placing

direction of the axis of a bar at the time concrete is

information is by making use of the preferred

cast. VERT cannot be used with slab reinforcement.

abbreviations given in Table 8.2. No other abbreviations should be used unless clearly defined on every drawing on which they appear. All abbreviations mean the same in the plural as in the singular. Only capital letters are to be used and full stops are not required after them. The placing information is located after the Basic Design Notation, or as a special Note to that detail.

Two or more abbreviations may be used together, particularly for bars which form a grid. Examples are: (i) N12-200-EW-EF – there are four layers of bars, but take great care about specifying number of bars in this case. (ii) SL102-EF – there are two sheets of mesh, one in each face. (iii) N16-100-FF-VERT & N12-200-FF-HORIZ – there is one grid of bars in the far face. (iv) RL818-FF-MAIN BARS VERT – there is one sheet of mesh, but because of the difference between main- and cross-bar areas, the orientation must be specified. Detailers will easily distinguish the circumstances where these extra instructions will clarify a difficult detail, or will remove the need for additional crosssections.

9:8 Reinforcement Detailing Handbook

9.7

BAR MARKS

■

The Basic Design Notation together with the

It is often the case that several (especially columns) have bars which are

Placing Information will enable a group of components

identical (shape, diameter, length, etc). All

to be identified as belonging to a particular concrete

of these bars can be bundled together with

element. In some cases, it is necessary also to

one over-riding label. The grouping would be

distinguish between the individual bars within that element. The traditional method is to use a system of bar marks. The term “bar mark” refers to mesh as well. The bar mark is a number or letter-number combination which identifies one bar or a group of bars with (usually) one placing location. The bar mark must always be shown on the reinforcement schedule and also on a metal or plastic tag attached to each bundle of steel. See both Clauses 9.7.1 and 9.7.2. 9.7.1 Bar Marking by Structural Element Number (Placing Zones) Each footing, column, beam, slab or wall

identified on the schedule. ■

If bars are extracted from a bundle containing steel for several elements, the bundle should be retied and the tag replaced.

9.7.2 Bar Marking of Individual Bars This method is common for many civil engineering structures, particularly where individual elements are large and contain a number of different bar shapes and lengths. The individual elements are still numbered but, in addition, the bars themselves are marked by an additional number or letter-number combination. This bar mark is shown in the reinforcement

element is identified by a structural element number or

drawings by the detailer so that there is no need for

useable grid number. This number also becomes the

the contractor or scheduler to prepare an additional

placing zone. See Clauses 8.2 and 8.3.

marking plan.

The system is common to columns, to bottom

Although the detailer would do more work, the

steel in beams and slabs, and to most fitment

detailer may also prepare the reinforcement schedules.

arrangements. Slabs are usually numbered as well-

These may be separate documents or drawn on the

defined placing zones bounded by column centre lines

original tracings.

or slab placing strips; typical placing-zone labels for bottom steel are S1, S2, etc. Top steel in slabs is often not identified by the designer, and the scheduler may need to invent a system. For both methods the placing zones must be identified on a marking plan to assist the steel fixer. Individual bars or sheets are not marked on the drawings. Each item on the schedule is labelled with

9.7.2.1

Identical Bars

Throughout this Handbook, the term “identical bars” will often be used. For bar fabrication purposes, two bars would be regarded as being “identical” only if they were exactly the same for grade of steel, bar-size, bent shape, cutlength and individual bending dimensions. For placing purposes, a group of bars in the

the structural element number into which that item is to

same placing zone may have the same bar mark if

be placed provided that the scheduler can identify it.

they have the same grade, bar-size and bent shape,

This method reduces the amount of work of all concerned, but it does require the detailer to provide

although they may have different individual bending dimensions and different cut-lengths.

adequate element numbers. Some simple rules should be followed by the scheduler: ■

If there are several items or bundles for one structural element, the same element mark can appear more than once on the same schedule; for example, bars and fitments in the same

Example 9.2: A typical situation would be a sloping retaining wall. Adjacent bars will have a different length and significant sorting of bars will be necessary, but the placing zone can be identified with one mark. The situation is similar to that of Clause 9.7.1.

beam. ■

There should always be as many tags with labels as there are bundles, even though they bear the same placing zone reference.

9:9 Reinforcement Detailing Handbook

9.7.2.2

Basic Rules for an Individual Bar Marking System

Rules (f) and (g) illustrate advantages of individual bar marking. (a) Identical bars for fabrication, as defined, may

9.7.3 Other Aids to Reinforcement Identification (a) Check the tags to select the correct bars on site. Coloured tags can often be provided to a prearranged system. (b) On a civil engineering site, the different colours

have the same mark even if they are not in the

can be used to differentiate between various

same placing zone.

areas within the project.

(b) Where a clearly defined placing zone requires

(c) In buildings, the layer into which slab bars

numerous bars which differ marginally in length,

are placed can be defined by coloured tags

the bars may have the same mark.

(Figure 9.4) which would be defined on the

(c) The mark should be placed near the Basic

schedule, as for example:

Design Notation. Sample drawings may show

TOP UPPER LAYER – BLUE

them in different ways.

TOP LOWER LAYER – YELLOW

(d) The only restriction on the form of the marking system is that it should be consistent throughout

BOTTOM UPPER LAYER – RED BOTTOM LOWER LAYER – WHITE

any one project and must be consistent on any one structure – particularly if the same

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contractors are involved.

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(e) Letters and numerals may be used in any combination, but it is recommended that the maximum number be limited to six. Only capital letters should be used. Letters “O” and “l” can be confused with numbers “0” and “1” – do not use them. (f) To ensure that reinforcement which may be embedded in two different concrete placements is not omitted, the Basic Design Notation for any one bar must only be given once, and this should be on the detail of that part of the structure where the bar is first encased in concrete; for example, column starter bars are defined with the footing. (g) Where a bar appears elsewhere on drawings, the bar is identified by its bar mark only. Identification on the site is simplified and the detailer is unlikely to duplicate (or leave out) reinforcement. (h) In any marking system with numbers, it is suggested that numbering should commence with the first bar to be placed, that is, at the footings, bottom layer in a slab, etc. Examples of bar marks are given throughout this Handbook.

9:10 Reinforcement Detailing Handbook

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Figure 9.4 Application of Coloured Tags

9.8

SPECIAL DETAILS

9.8.1 Splices All details must be shown in the drawings. Further information is given in Chapter 6 and many examples will be given throughout the Handbook. In many cases, an intelligent use of Notes will help. Column lap splices are the most common splices. They generally occur just above a floor level so that the length of the lower level bar protruding above the floor forms the lap. This length must be adequate – once the floor is poured, the protruding length cannot be increased. End-bearing splices require height above the floor level and the stagger between splices to be specified. In this case, a typical detail may be used. Bundled bars require extra details to show the order in which bars are to be spliced. Tension lap-splices must be located on the drawing and the length of lap shown by figured dimensions or in a table on the drawing. All dimensions are to be in millimetres not in bar diameters. Mesh lap-splices have been described in Clause 6.9. 9.8.2 Proprietary Splices Many types are on the market and details should be obtained from manufacturers’ technical literature. In particular, the location should be specified in the drawing. Requirements for testing these devices should be given in the Contract Specification and reference to this should be in the drawings. 9.8.3 Welding All welding details require special attention. Welding should comply with AS 1554.3 Structural steel welding - Welding of reinforcing steel. 9.8.4 Bending-Pin Sizes Pin sizes are given in considerable detail in AS 3600 Clause 17.2.3.2. Because of the effect of bending on steel strength, these rules must be followed, (See also Clauses 6.2.4 and 6.2.5 in this Handbook). 9.8.5 Galvanising and Epoxy-Coating Coatings such as these are not specifically within the Concrete Structures Standard. Details must therefore be provided individually for each project.

9:11 Reinforcement Detailing Handbook

9:12 Reinforcement Detailing Handbook

10 General Comments on Presentation of Details

When concrete, reinforcement and other details and dimensions are given to illustrate the applicable text, non-essential reinforcement information and concrete outline dimensions are often omitted because the text describes other matters. In no way should the element be considered fully detailed.

10.1

IMPORTANT MESSAGE The details shown in this Handbook are

Most details are not shown to any particular scale.

illustrative only. UNDER NO CIRCUMSTANCES SHOULD THESE

10.3

SELECTION OF EXAMPLES

EXAMPLES BE COPIED INTO CONTRACT DRAWINGS UNLESS THE NECESSARY CALCULATIONS PROVING

10.3.1 Types of Structural Element The most common elements are footings,

THEIR ADEQUACY HAVE BEEN PREPARED BY A PROFESSIONAL ENGINEER.

columns, beams, slabs-on-ground, suspended slabs, cantilevers, walls and staircases. Each is discussed

10.2

DETAILS ACCOMPANYING THE TEXT

10.2.1 Drawing Types The drawings include: ■

■

reinforcement are shown. Other layers are equally satisfactory, but these are left to the individual detailer’s previous experience. However, this Handbook does have many

Two-dimensional plan-views, elevations and sections which illustrate the text.

recommendations to make about good practice and a

Some illustrations showing in three-dimensional

detailer should be prepared to accept and try them at

form how the reinforcement must be fitted

least once before rejecting them.

together on the site; a detailer would rarely need to prepare such a drawing, although it would be a most useful technique with complex or congested bar arrangements where physical size is a problem; and ■

in various detail and suggested arrangements of

“Standard Details” which are examples of a technique used in many design offices to

10.3.2 New Ideas Advice given in the Handbook related to one situation need not be restricted only to one element. Solutions for one problem may be equally applicable in situations not discussed here at all, for example: ■

standardise internal procedures. No attempt is made for these to be taken as the only solutions.

■

The suggested methods of allowing for tolerances in stair reinforcement can be related

They are called “standard details” in the sense

to many where accuracy of formwork

of being “office standards”, and not “CIA

is not critical.

standards” or “AS standards”. ■

“Opening” and “closing” corners of walls are similar to slab/balustrade connections.

10.2.2 Omission of Design Information The purpose of the following Chapters is

Intersecting reinforcement problems are not limited to beam-column connections.

■

Each Drawing Office should assemble a stock

to show how to draw the reinforcement within

of details which are accepted as giving a good

the concrete outline. In this context, the design

solution in several situations. For uniformity, they

requirements and dimensions are not always essential.

should be used by the whole office and not

For the purpose of referring to parts of the drawings

regarded as personal property. In this way, future

in the text, some reinforcement is marked using an

amendments can be made with the minimum of

appropriate system.

difficulty.

10:1 Reinforcement Detailing Handbook

10.3.3 Construction Tolerances

10.4

The location of planned construction and

TECHNICAL TERMINOLOGY Many technical familiar to draftsmen,

movement ts, connections and splices must be

schedulers, architects and engineers are used

shown in the drawings.

throughout the Handbook without further definition.

Also, it is good practice to define how a

The trainee detailer must apply such as

construction t is to be made JUST IN CASE it will

bending moment, strength and stress, tension and

be needed; that is, to plan for an unplanned t. If

compression, positive and negative reinforcement,

reinforcement is to be spliced at the t, the splice

shear, footing, column, beam, etc. For this purpose, a

length should be dimensioned and the location of the

suitable textbook on structural mechanics and design

splice from a concrete surface or set out line must be

should be studied. Consult the Concrete Institute

defined.

of Australia and the Cement, Concrete Aggregate

Where splices are required at construction

Australia for information.

breaks, any reinforcement protruding from hardened concrete will become reduced in length if that concrete is placed oversize. Detailers can allow for this by specifying the extension to be greater than the laplength values given in AS 3600. (See Chapter 6 of this Handbook). The amount of increase will depend on the circumstances.

10.5

DETAILING OF ELEMENTS FOR SEISMIC RESISTANCE

10.5.1 General Comments Detailing of the structure is an integral and important part of the seismic design process. For reinforced concrete, structural detailing centres around

Example 10.1:

arrangement of the reinforcing bars. There must be

(i) Lap-splice bars in columns require a minimum

sufficient transverse steel to suppress brittle shear or

300 mm lap. This column bar extends from

crushing failures and to prevent buckling of the main

the floor below the working floor and the

compression steel, once the cover concrete has been

splice length will be above the working floor.

lost. The main steel bars must not lose their anchorage

Once the column and floor are cast, the

into the surrounding concrete during the repeated

splice length is fixed. An additional allowance

reversing loading cycles to which they would be

may need to be added to the 300 mm to

subjected during a major earthquake.

for any error in either floor level.

Appendix A of AS 3600 sets out detailing

(Refer to AS 3600 Clause 13.2.4 for the

criteria for general, regular and irregular structures,

calculated splice length).

as defined in AS 1170.4. Regular structures in Design

(ii) Allow for variations in concrete sizes. To

Categories A and B do not need to be specifically

permit a bar to be fixed between two

designed or detailed for resistance to earthquake

previously-poured surfaces, such bar should

loads. For irregular structures in Design Category B

be, say 200 mm shorter than the planned

and structures in Design Categories C to E, the design

gap and the protruding bars on each side of

action effects determined in AS 1170.4 are dependent

the gap dimensioned one-half of this amount

upon both the type of structural system adopted and

longer, that is add 100 mm to each splice

the type of member being considered. The relevant

length.

level of ductility is to be met by following the detailing requirements for the particular structural system concerned. It should perhaps be restated here that design and detailing are inseparable. Proper detailing is required to ensure that the structure will respond under seismic loading in the manner for which it has been designed.

10:2 Reinforcement Detailing Handbook

With a limited additional quantity of properly-

available (see as a Reference: Goldsworthy H.M.

detailed extra ligatures and continuity reinforcement,

Earthquake Resistant Design of Concrete Structures:

plastic hinges can be induced to form at a given load.

Design and Detailing Requirements in AS 3600:1994 –

However, yielding will be ductile (gradual) even if the

Appendix A for Moment Resisting Frames, University

design earthquake load is exceeded (ie the hinge will

of Melbourne, 1994), or that detailing is provided

act as a ‘fuse’ preventing transfer of the larger forces).

such that plastic hinges may form. (See Intermediate Moment-Resisting Frames below).

The choice for the designer/detailer is clear. A

It is important to ensure, however, that the

fully-elastic response by the structure, whilst allowed by the Code, cannot be guaranteed. Therefore, to

non-seismically-designed frames are sufficiently ductile

prevent catastrophic collapse and probable loss of

to cater for forces they will attract if the earthquake is

life under a greater than designed-for event, a ductile

bigger than that assumed in the model. The designer

failure must be ensured. This minimum required level of

must detail with care to ensure that plastic hinges, if

ductility may be readily achieved by judicious detailing

any, form at the locations specified in Figure 10.1. It

in selected areas.

is important to that AS 3600, Appendix A, does not specifically direct the designer to provide a

10.5.2 Moment-Resisting-Frame Systems

strong-column/weak-beam mechanism, so any of the

There are three types of moment-resisting

three indicated modes could occur during a seismic

frames:

event of sufficient magnitude to cause yielding of

(a) Ordinary Moment-Resisting Frames.

reinforcement.

These require no specific detailing for seismic resistance. Standard detailing as set out in the body of AS 3600 is considered to provide structural adequacy to reinforced concrete structures when coupled with the higher earthquake design forces consequent from the use of lower ‘R’ values (ie reduce the ‘ductility

(b) Special Moment-Resisting Frames. These will rarely be required in Australia as this will be economically viable only for Design Category F structures. As such, AS 3600 refers readers to ACI 318 and other references for detailing concrete structures for more onerous seismic conditions.

demand’, or likely t rotation, on the frame and

(c) Intermediate Moment-Resisting Frames.

assume they are essentially elastic).

In the following Chapters, attention will be concentrated

The designer should note that for OMRFs,

on the detailing requirements for these systems as

normal detailing to AS 3600 will result in only limited

they will more commonly be seen, especially in dual

frame ductility, primarily as a result of poor t performance. t failure will result in collapse (Kobe, Northridge, Mexico City). In order to achieve the

systems where for instance shear walls are provided only in one direction. Further, some of the provisions must be considered as good detailing practice in

required Rf value of 4, the designer needs to ensure

OMRF systems as well.

that an excess value of this magnitude (or higher) is

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���� ������������������������ � �� ������������������������������������ � �� ����������������������������������� � � ������������������������

Figure 10.1 Three Possible Mechanisms of Post-Elastic Deformation of Moment-Resisting Frames During Severe Seismic Loading [After Goldsworthy]

10:3 Reinforcement Detailing Handbook

10.5.3 Reinforced Braced Systems Bracing of braced frames are to be designed as struts or ties, as they will be subject to alternating compression and tension, and connections between are to have greater strength than each connected member. In of detailing, it is important to provide adequate lateral restraint along the whole length of the longitudinal reinforcement when it is subject to compression in the form of: Helices. The volume of steel divided by the volume of concrete, per unit length of member must be greater than 0.12(f’c /fsy.f); or Closed ties. Asv ≥ 0.30 s y1(Ag /Ac - 1) (f’c /fsy.f) (unless φNuo > N*) or Asv ≥ 0.09 s y1(f’c /fsy.f) whichever is the greater where: s

= centre to centre spacing of the ties

y1 = the larger core dimension Ag = the gross cross-sectional area of column Ac = the cross-sectional area of the core measured over the outside of the ties f’c = the characteristic compressive cylinder strength of concrete at 28 days fsy.f = the yield strength of the ties φ

= a strength reduction factor

Nuo = the ultimate strength in compression of an axially loaded cross-section without eccentricity N* = the axial compressive or tensile force on a cross-section.

10:4 Reinforcement Detailing Handbook

11

11.3.2 Complete Footing Plan for the Whole Structure

Footings

See Drawing Sheet No 11.1 – Clause 11.16. ■

Define the location of every footing. If architectural drawings use a grid-line system, the

11.1

GENERAL

identical system must be adopted. As distinct from many other elements, location dimensions

11.1.1 Foundation

for footings are as much the responsibility of the

The ground on which a structure rests, or is

engineer as that of the architect because the

ed by, is called the foundation.

footing layout affects the strength of the whole structure. Footing centre lines are often used as

11.1.2 Footing

locating dimensions.

A footing is that part of the structure which is in with the foundation. It is essential that the

■

footing and foundation are in complete and, for

of each footing. Detailed dimensions of each

this reason, concrete is the only satisfactory material;

footing are normally given on its own drawing or,

when placed and compacted properly, concrete will fill

where the footings are rectangular, in a footing

any hollows in the foundation and, after it hardens, will transfer the load from the structure to the foundation.

schedule. ■

it. Normally, the footing reference number will

In certain circumstances, it may be necessary

be the same as the reference number of the

to increase the strength of the surface layers of the

ed column; this is mandatory when

foundation by using special techniques. Some of

a column schedule is used, Drawing Sheet

the common methods include compacted back-fill,

No 11.7.

crushed rock, lean concrete, etc, and full details must The minimum depth at which footings are to be founded must be indicated so that an estimate of the excavation cost can be made, together with provision

Give a reference number for each footing and for the column or wall which is ed by

11.1.3 Preparation of the Foundation

be given in the drawings or Specification.

Indicate the general shape looking down at each footing. This view will also show the orientation

11.3.3 Individual Footing Plan-Views Where the shape and dimensions of a footing are not obvious: ■

for altering as applicable the length of the ed

Draw the exact shape of the footing with all necessary dimensions for excavating the hole in

column.

the foundation. ■

Specify the minimum depth to which the

AS 3600 REQUIREMENTS

excavation must be made and, in at least a

The Concrete Structures Standard does not

General Note in the drawing, an indication of the

have a section specifically allocated to footings. For

type of ground expected or allowed for together

design purposes, a footing is considered to act as if

with its predicted bearing capacity. If the

11.2

engineer requires soil tests, this can be stated

it was a beam or a slab, depending on its shape and

in the drawings although it is often given in the

loading condition. 11.3

FOOTING PLAN-VIEWS

Specification in more detail. ■

dimensions of the column or wall ed by the footing. Within this shape will be shown the

11.3.1 Types

location of all reinforcement cast with the footing

Two types of drawings are usually required to

but extending into the column or wall.

describe the footing arrangements: ■

a complete footing plan for the whole structure, and

■

an individual plan-view, depending on the types of footings used in the structure.

Give the location, orientation, shape and

■

Reinforcement of the footing is usually not shown in a plan-view except in the case of simple pad footings. As a general rule, footing details tend to follow beam rather than slab detailing methods in that the number of bars should be stated, not just the spacing. 11:1 Reinforcement Detailing Handbook

11.4

FOOTING ELEVATIONS

11.6

DETAILS

These are usually given as longitudinal-sections; that is, as a view taken along the length of the footing giving the same information as a beam elevation. They will need to be supplemented by cross-sections. See Drawing Sheet No 11.4. 11.5

FOOTING CROSS-SECTIONS These differ with the type of footing being

GENERAL COMMENTS ON FOOTING

11.6.1 Selection of Cover for Footings Refer to Chapter 5 of this Handbook and AS 3600 Section 4.10. Selection of cover must be done by the designer; once settled, values can be tabulated in the General Notes section of the drawings. Note that the increase in cover for footings is to accommodate the uneven nature of excavation.

detailed. ■

Where the footing shape is rectangular, similar to a strip footing, cross-sections like those of

■

Footing reinforcement is generally required

beams are suitable. These would show the

quickly at the start of a job, and must therefore

fitment shape and the main reinforcement layout.

be scheduled as shown on the original drawings.

See Drawing Sheet No 11.4. ■

11.6.2 Starter Bars

■

Once the excavation is completed, the footing

Where pad-footings or complex footings are

steel and starter bars are fixed, and approval is

detailed, the shape of the main steel can be

given to pour a footing, this is done with utmost

defined by the shape of the section.

speed to prevent rain or ground water from affecting the foundation. ■

All starter bars for columns or walls must be detailed with the footings by which they are ed; generally starter bars are an L-shape with the bottom end resting on and ed by the footing reinforcement. The length of this part should be at least twice the spacing between the footing bars.

■

Because the bottom RL of a footing can change from that shown on the original drawings, provision must be made for adjusting the length of main bars in the columns rather than altering the column starter bars at the last minute. An extension to the vertical part of the L-shape starter bars will ensure an adequate lap at the top of the footing. By “cranking” or “offsetting” the column bars, and locating that portion at the BOTTOM of the column, additional changes can

be minimised at a higher level of the building. The starter bars should not be cranked. ■

Fixing of starter bars must be accurate as they affect the position of the whole structure. Inspection for location is just as important as checking that the steel layout is correct. If starter bars are connecting with precast, tie bars may need to be set out using a template or checked by survey prior to and after concreting to ensure they are in the correct locations.

11:2 Reinforcement Detailing Handbook

11.7

STRIP FOOTINGS

“trenchmesh” such as L8TM, L11TM and

Strip footings are traditionally used to

L12TM is the most common form of strip

walls of concrete or masonry.

footing reinforcement. Descriptions are given

11.7.1 Strip Footings for Masonry Walls

nominal-size ties, generally at about 600 mm

in Clause 4.6. The layers are held apart by Drawing Sheet No 11.2 shows a strip footing

centres.

under a masonry wall. See also Drawing Sheet

In heavier construction, strip footings would be

No 11.1.

designed individually with trenchmesh or bars as

■

■

Strip footings for residential work must comply

main steel. Designed ties are used to maintain

with AS 2870, Residential slabs and footings, for

the footing reinforcement relative to the ground

both strength and detailing purposes.

surface. For masonry, steps should match the

The width of a strip footing is controlled firstly

course height. The concrete overlap must also

by the width of the wall it s; accuracy

be dimensioned.

of excavation is generally not great and it is important that the wall above (particularly if it

11.7.2 Strip Footings for Concrete Walls Drawing Sheet No 11.3 illustrates a strip

is of masonry) is seated in its design location (usually central).

footing under a concrete wall. See also Drawing

The second requirement for the width is to

Sheet No 11.1.

limit the bearing pressure of the footing on the

■

foundation. In some cases, the footing width is

similar manner to masonry walls, the strip footing

greater than the depth to spread the load and

will be shown in the same way. Wall starter bars

therefore reduce the pressure; in other types

must also be detailed and scheduled with the

of soil, the width is kept as narrow as possible,

footing.

depending on the wall width, and the depth is

Longitudinal footing reinforcement is more

increased to add flexural strength to the footing.

important in this case than transverse reinforcement.

Dimensioning of strip footings is described in Clause 8.7.4. There it is recommended that

■

Where the concrete wall acts structurally in a

■

Where the concrete wall is used to

the depth of a strip footing be given first to be

horizontal loads, as with a retaining wall,

consistent with a ground beam, regardless of

concrete and reinforcement detailing is critical

which is the greater – depth or width. However,

because of the heavy loads involved.

a dimensioned drawing is far more descriptive.

Concrete walls are described in Chapter 15,

Traditionally a layer of reinforcement is located

with particular attention being paid to detailing

in each of the top and bottom of a strip footing

of corners.

because the force from the ground below

■

Cantilever retaining walls depend on the footing

and that from the wall above may not always

for against overturning forces and

balance, as can occur at doorways in the wall or

footing reinforcement placed perpendicular to

soft-spots in the foundation.

the wall is more important for strength than that

Ties are used both to separate and position the

parallel to the wall.

layers; the spacing between ties is often nominal, and could range from 300 mm to 800 mm. Such ties in residential work are rarely designed as reinforcement for strength, unless the footing is very wide. ■

At corners, the intersecting main steel should extend across the full width of the intersecting strip. Laps within the strip can be specified by notes or a drawing. In residential work, the actual lap should be given rather than a reference to a Standard; onsite copies of these are rare.

■

In residential and commercial work, 11:3 Reinforcement Detailing Handbook

11.8

PAD FOOTINGS, ISOLATED FOOTINGS

11.9

AND SPREAD FOOTINGS These mean the same thing. See

CANTILEVER FOOTINGS ■

Drawing Sheet Nos 11.1, 11.5 and 11.7. ■

that, in most cases, they more than one column. In the case of a cantilever footing,

column over a large area of the foundation.

the second column tends to counter-balance

Reinforcement must be placed in the bottom

the other at the end of the footing. In Drawing

of the pad because the reaction of the ground

Sheet Nos 11.1 and 11.4, element CF3 is a

acts upwards on all sides of the column. Note

cantilever footing. Column 10 is at the boundary

particularly that the reinforcement is placed in

and is counterbalanced by column 7 inside the

TWO directions because of this reaction. Not

building. Footings CF4 and CF8 are similar. ■

complex and outside the scope of this

use of shear reinforcement by using a deeper

Handbook. The main design factor is that the

pad footing or higher concrete strength or both.

concentrated downward loads from the columns

The pad bars are often shown as LL-shaped,

create the upward forces on the bottom of the

but in many cases, this is not necessary

footing, so that in this case, the TOP surface of

unless there is a length deficiency for stress

the footing must be the more-heavily reinforced. This is the reverse loading for a normal pad

bars in one direction is increased by hooks on

footing, and indeed for a suspended beam.

the bars at right angles; thus the number of bars

The elevations and sections in Drawing Sheet

should be stated, not only the spacing.

together. The cross-wires form part of the transverse steel as well. Concrete columns must be reinforced and the bars must extend into the footing pad. As previously discussed, the starter bars are supplied and fixed with the footing reinforcement and adequate lap lengths must be allowed above the pad. ■

The orientation and location of the starter bars in relation to the column shape is extremely important for strength and architectural purposes; a fully dimensioned cross-section will be required for odd-shaped columns.

■

No 11.4 show that the top has much more

Where the pad is less than 2500 mm wide, one or two sheets of mesh may be used, nested

■

The upward reaction of the foundation is

must be checked for punching shear. Avoid the

development. The cover over the outermost

■

These footings are similar to pad footings except

A pad footing spreads the load from a single

only is the pad footing designed for flexure but it

■

COMBINED FOOTINGS AND

Embedment of the starters in the pad is a design matter, and the anchorage requirements may need to be dimensioned in critical cases. Generally, the starter bars will be scheduled as L-shaped to be stood-up on the pad steel. For fixing purposes, at least three fitments should be detailed and supplied with the starters – two go within the pad depth and the other is tied around the exposed lap length. Provided the starters do not have to be cranked (see Clause 11.6.2 earlier), the size of these fitments would normally be the same as those for the column above.

11:4 Reinforcement Detailing Handbook

longitudinal steel than the bottom. ■

Shear reinforcement in the form of mesh or bar stirrups is a critical design factor because the loads are much more severe than for strip footings.

11.10 RAFT FOOTINGS ■

11.11 RESIDENTIAL AND COMMERCIAL BUILDINGS – SLAB-ON-GROUND

A raft footing is used when the soil foundation is poor or it is often regarded as a flat slab

■

upside down with thickenings under the

for a raft but the magnitude of construction is

column. It enables the mass of the building to

much less. In this case, the wall loads are taken

be ed by the lowest-floor (basement)

directly to the ground by the edge footings or by

slab. Similar to the cantilever footing described

internal beams or thickened strips, all poured at the same time as the slab.

above, the foundation reaction requires that the top reinforcement between the columns may be

■

strip footings, with trenchmesh predominating.

considerable reinforcement in the bottom face

Mesh is the preferred steel for the slabs and is

In domestic construction, raft footings are often

located near the top surface. ■

A vapour barrier must be specified together with

used for reactive clay sites and they consist of

reinforcement spacers on a suitable base which

beams in two directions intersecting at 4 to 6

will prevent puncturing the membrane for all

metre centres both ways with a slab ing the beams. ■

Reinforcement in the footings resembles that in

heavier than the bottom. However there will be under the columns, probably in two directions. ■

This element follows the same principles as

habitable areas. ■

Residential work is controlled by AS 2870;

It is not uncommon for two layers of steel to be

commercial buildings may need an engineering

required in each direction top and bottom – that

design because walls will be higher than

is eight layers altogether. Spacing for pouring

permitted by that standard, but the detailing

and vibrating must be allowed, bundling pairs of

principles will be similar.

bars where possible. ■

Where a raft is used for a large multi-storey building, the distance between the top and bottom layers may be one metre or more.

11.12 PIER AND BEAM FOOTINGS ■

Where there is a poor soil overlaying a good material, bored piers are often used to transfer

A considerable amount of extra material will

the vertical loads to the latter. The piers would

be needed just to the two grids of

be detailed as for columns. Wall loads are

reinforcement. The Bill of Quantities if used

transferred to the piers by beams which are

should indicate the quantities involved, and how

detailed normally. The piers may be of uniform

to price this work if extras are to be avoided.

cross-section or be belled out at the bottom. ■

In certain soils, the beam underside must be separated from the earth below – upward expansion can be catastrophic if the gap is inadequate. The method to be used is a design matter, and the solution must be detailed.

11:5 Reinforcement Detailing Handbook

11.13 PILES AND PILE CAPS ■

A group of piles is used to perform the same

The following notes are based on the Detailing

function as a pier when the load exceeds the

Examples shown in Drawing Sheet Nos 11.1 to 11.7

capacity of a single pile. The pile cap distributes

at the end of this Chapter in Clause 11.16.

the column load to the piles. The load transfer system can be very complex and there can therefore be several layers of bars in both top and bottom faces. The bars are often not on a rectangular grid so careful detailing is required if the required arrangement is to be obtained. Large scale details may be advisable. ■

11.14 EXAMPLES OF FOOTING DETAILS

In large buildings and civil engineering structures,

11.14.1 Example of Strip Footings Drawing Sheet Nos 11.1, 11.2 and 11.3 illustrates a footing plan for a small building and details of strip footings. See also the notes in Clause 11.7 for both strip footings ing a masonry wall and ing a concrete wall. 11.14.2 Example of a Cantilever Footing

a piling contract is often let well in advance of

Drawing Sheet No 11.4 shows the details of

the building contract. If this is done, the actual

cantilever footings CF3, CF4 and CF8. The following

location of the piles as driven must be given in

comments discuss factors which must be considered

the drawings for the building contract. It may be

by designers and detailers to ensure the member can

necessary to alter the pile cap design because

be constructed “as designed”. They apply to

the actual locations differ more than expected

other than footings as well.

from the original design.

■

The designer should allow for reasonable

defines the concrete length and the cross-

variation on the location of piles after driving,

section CF4 clarifies the beam depth and width.

say ± 75mm. The tolerance permitted must be

Architectural drawings should be used to provide the column centreline dimensions.

shown in the drawings, with the required cut-off points detailed.

■

The concrete outlines. The elevation CF4

■

Reinforcement layout for strength. Take the

Reference should be made to AS 2159:1995

cantilever footing CF4 as an example. It has

Piling - Design and installation.

been designed as an “upside-down” beam,

As with many footing designs, the top

that is there is more steel in the top than in the

reinforcement will restrict access to the inside

bottom. (See Clause 11.9).

of the cage so that the method by which the

This situation requires strong tie bars to

cage is assembled should be a design and

the top steel, each bar of which weighs about

detailing matter. Access is required for placing

60 kg. These tie bars are shown on cross-

concrete and vibrating it, as much as for fixing

section CF4 as three sets of N16-HT at each

reinforcement and other embedments.

stirrup. The top main steel is the group labelled 20-N36-LL-T. In both cases, LL is the shape, T means TOP and the combination is quite adequate to define the bars and location. The bottom main bars are 8-N28-LL-B, and are drawn inside the fitments. Because of the heavy downward column loads and the footing width being 2000 mm, the ends of the cantilever footing are reinforced transversely with 6-N24-100-LL-B at one end, and 4-N24-100-LL-B at the other. In practice, these 10-N24’s are identical because the footing width is constant. There is no need to show them on the cross-section because they have been fully defined on the elevation by the complete notation, thus eliminating at least one extra detail.

11:6 Reinforcement Detailing Handbook

■

Reinforcement layout for assembly. Footing

11.14.3 Pad Footings - Standard Detail Drawing Sheet No 11.5 illustrates a Standard

CF4 is heavily reinforced. The total steel mass is about 1800 kg (1.8 tonnes), of which the main

Detail for an isolated pad footing under a reinforced

top bars comprise 1.2 tonnes. These bars must

concrete column.

be ed upon the foundation (see also

■

Clause 11.1.3) by means of the vertical legs of

bars and associated ties are not provided with

the N16 fitments.

the Standard Detail because these vary for

Just to assemble the cage as it is drawn, and tie

each footing; neither are column cross-sections

it together with wire, will not be adequate.

given here. All of these are shown in the column

To maintain the whole cage properly will require additional longitudinal bars to be placed under

schedule. ■

Clause 12.9 and Drawing Sheet No 11.7

the fitments resting on strong concrete or

show footing and column details in schedule

purpose-made steel chairs.

format. This combines the application of a

As an alternative, 2 or 3 of the 8-N28-LL-B bars

Standard Detail for a footing and one for a

can be placed first on the s to form the

column (see also Cause 12.8 and Drawing Sheet No 11.6).

initial platform free of the earth. The remainder of the steel can then be built upon them.

■

To assist in construction, note that two of the

Examination of cross-section CF4 shows that

upper-layer pad bars are used as s for

there are actually three “beam” segments, each

the remainder.

of which can be assembled separately and

■

The number, orientation and layout of the footing

■

Splice lengths for column bars and embedment

craned into position upon the pre-set ing

lengths for starter bars would also need to be

bars.

scheduled, such as shown in Table 11.1.

Problem areas. The N24-100-LL-B bars across the bottom of the footing under the columns will need to be assembled early, so that the column

Table 11.1 Embedment Lengths for Starter Bars and Splice Lengths for Column Bars

starter bars (not shown here) can be tied to

Splice length of 30 DIA. (mm)

Number of fitments at column bar crank

Bar Size

Straight embedment in footing of 20 DIA. (mm)

(see Chapter 4). To allow concrete to be cast

N20

400

600

1-R10 or 1-L7

and compacted, and the column starter bars to

N24

480

720

2-R10 or 1-L9

be placed through them, the top bars should be

N28

580

840

2-R10 or 1-L10

grouped into a series of 2-bar bundles or placed

N32

640

960

1-N12 or 1-L11

in two layers with a spacer bar. This requires

N36

720

1080

2-N12 or 1-L12

them. A width of 2000 mm for 20-N36 bars is inadequate if concrete is to be placed properly

designer’s approval, so it is simpler to detail it that way in the first place. The individual stirrups of bars can perhaps be replaced by mesh bent to the fitment shape. This will reduce the time to tie the bars and will provide a rigid cage which does not require bracing. Drawing Sheet No 11.4 gives two examples of cantilever footings.

11:7 Reinforcement Detailing Handbook

11.15 DETAILING OF FOOTING SYSTEMS FOR SEISMIC

Footing Structures for Frames as discussed in Design Methodology, AS 3600 provides some limited guidance regarding footing design and detailing.

11.15.1 General Adequate footing design is critical for ensuring

Although the code stipulates that for footings located in soils with a maximum bearing capacity of less than

that a building structure will be able to resist both the

250 kPa, restraint must be provided in the horizontal

gravity loads and seismic forces calculated.

direction to limit differential movement during an

Where there is no possibility for inelastic

earthquake. It should be noted that reports from Kobe

deformations to develop under earthquake conditions,

indicate that although liquefaction is a problem in poor

it is considered that standard detailing of reinforcement

soils, the water in the saturated reclaimed area acted

as for gravity loads and wind forces will be adequate.

as a dampener, restricting damage to significantly less

This will be the situation in the majority of buildings

than that experienced in the ading ‘dry soil’ areas.

constructed in Australia. However, where design indicates the

The Code considers that there is no possibility for inelastic deformations to develop under earthquake

occurrence, or possible occurrence, of reinforcement

loading, and that standard detailing of footings for

yielding during seismic action, the foundation structure,

gravity and wind induced loads only will be sufficient.

like the superstructure, must be detailed accordingly.

However, the author considers that certain additional

As already mentioned, as a result of code loading

precautions can be warranted.

requirements or design decision, the seismic response of the structure may be elastic. Paulay and Priestley suggest footing systems

11.15.2 Isolated Footings These can prevent a problem with rocking

that may elastic superstructures. (See as a

or tipping if a plastic hinge forms in the base of the

Reference: Paulay, T. and Priestley, M.J.N. Seismic

column. Unless precautions are taken, permanent

Design of Reinforced Concrete and Masonry Buildings,

deformation of the footing can occur due to plastic

John Wiley and Sons Inc, 1992). Two of these will be

deformation of the soil despite both the column and

relevant to Australian designers:

footing remaining elastic. The detailing of the column/

■

Elastic Footing Systems. In regions of low seismicity (as is generally the case in Australia) or for low buildings with structural walls, it will be possible to design and detail the entire structure to respond within elastic limits.

■

Ductile Footing Systems. In certain cases, the potential strength of the superstructure with respect to the specified seismic forces may be excessive (eg large shear wall structures). The designer might therefore consider that it will be preferable for the footing system rather than the superstructure to be the principal source of energy dissipation during inelastic response. A potential drawback for this system is that damage may occur during moderately strong earthquakes. Large cracks may form if yielding of reinforcement has occurred. Further, repairs to footings may be difficult and costly if required below the water table or under a floor slab.

footing t must be carefully considered. 11.15.3 Combined Footings It may prove more feasible to absorb large moments transmitted by plastic hinges at column bases by using stiff tie beams between footings, whereby a high degree of elastic restraint against column rotations can be provided. In fact, this detail is such that reinforcement yielding is unlikely to occur and it is considered that no special detailing requirements for ductility need be provided. It would, however, be necessary for the tie beams to have sufficient reserve strength over that of the hinging columns. If it is required to reduce the bearing pressure under the footing pads, they may be ed to provide one continuous footing. Stub columns do require special consideration if inelastic deformations and shear failure are to be avoided. Paulay and Priestley (see Reference in Clause 11.15.1) consider that plastic hinges should therefore be restricted to the column section immediately above the beam.

11:8 Reinforcement Detailing Handbook

11.15.4 Piled Footings �������������������������� �������������

Piled systems ing structural walls may be subject to large concentrated forces due to vertical load causing overturning moments and shear forces. Careful design is therefore required. Detailing of reinforced concrete piles should

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follow the recommendations set out for columns in Chapter 12. The end region of a pile under the footing structure should be detailed to ensure full confinement of the longitudinal reinforcement using closed or helical ties. The locations of peak moments in the pile may necessitate the length confinement being considerably extended. Further, even if calculations indicate no tension loads, it is recommended that minimum longitudinal reinforcement be provided. The arrangement of longitudinal reinforcement should be as for columns, and the reinforcement should be fully anchored within the pile cap. In non-critical regions, nominal transverse ties or spiral hoops should be provided. Paulay and Priestley (see Reference in Clause 11.15.1) recommend that vertical spacing not

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Figure 11.1 Piled Footings

exceed 16 times the diameter of longitudinal bars. See Figure 11.1.

11:9 Reinforcement Detailing Handbook

11.16 DETAILING EXAMPLES – DRAWING SHEETS NUMBERED 11.1 TO 11.7 The following Drawing Sheets represent selected detailing examples for a small building covering mainly footings and columns. They have been referenced throughout Chapter 11 and are also referenced in Chapter 12.

11:10 Reinforcement Detailing Handbook

11.16.1 Drawing Sheet Number 11.1

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11:11 Reinforcement Detailing Handbook

11.16.2 Drawing Sheet Number 11.2

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11:12 Reinforcement Detailing Handbook

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11:13 Reinforcement Detailing Handbook

11.16.5 Drawing Sheet Number 11.5

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11:14 Reinforcement Detailing Handbook

11.16.6 Drawing Sheet Number 11.6

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11:15 Reinforcement Detailing Handbook

11.16.7 Drawing Sheet Number 11.7

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11:16 Reinforcement Detailing Handbook

12 Columns 12.1

GENERAL AND PURPOSE Columns are vertical of relatively small

size which progressively pick up the vertical loads on each floor and, together with any lateral forces due to wind or earthquake resulting in shear forces if the columns are part of a moment frame, finally transfer all forces down to the footing. The vertical load in the column is smallest at the roof and greatest at footing level. The load is carried by both the concrete and the embedded reinforcing bars. To carry this increasing load downwards from roof to footing, four alternatives may be considered. (1) The concrete size is increased floor by floor, but

Table 12.1 Maximum Square Column Size for 1% Steel Area Maximum square column size (mm) for bar size Number of bars N12 N16 N20 N24 N28 N32 N36 4 6 8 10 12 14 16 18 20

210 260 300 330 360 390 420 440 470

280 350 400 450 490 530 570 600 630

350 430 500 560 610 660 700 750 790

420 520 600 670 730 790 850 900 950

500 610 700 790 860 930 1000 1060 1110

570 690 800 890 980 1060 1130 1200 1260

640 780 900 1010 1110 1190 1280 1350 1430

this makes formwork costs excessive. (2) The concrete size is kept constant and the number of longitudinal bars is increased, but this leads to steel congestion after its area exceeds about 4% of the cross-section. (3) The concrete size is kept constant and its

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compressive strength (f’c) is increased. (4) A combination of alternatives is used. This last solution is common with high-rise

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buildings. Solution (2) is suitable for low-rise buildings to ensure internal dimensions remain constant floor by floor. 12.2

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AS 3600 REQUIREMENTS (Section 10.7) The Concrete Structures Standard has a

Figure 12.1 Maximum Column Sizes for Minimum Steel Areas

Section complete in itself on the design of columns and detailing of reinforcement. The major headings are listed here. 12.2.1 Limitations on the Longitudinal Steel Area The minimum area of steel is 1% of the crosssectional area unless the column is lightly loaded (Refer Clause 10.7.1 of AS3600). See also Table 12.1 and

Example 12.1 A 600 mm square column must contain at least 4-N36 bars or 6-N28 bars or 8-N24 bars to be above the lower limit of 1% steel. See also Clause 4.3.3 for minimum column widths based on concrete placement and Clause 4.3.1 for fire resistance.

Figure 12.1. The maximum steel area is 4%.

12:1 Reinforcement Detailing Handbook

12.2.2 Bundled Bars

For columns where f’c ≤ 50 MPa, confinement

The minimum and maximum quantities are the

to the core reinforcement with fitments shall be as

same as for single bars. Spacing of bundles is based

detailed in Clauses 12.2.4, 12.2.5, 12.2.6 and 12.2.7

on their equivalent diameter; this is the diameter of

of this Handbook. For columns where f’c ≥ 65 MPa confinement to

a circle having the same area as the total of all the

the core reinforcement with fitments shall be calculated.

individual bars, Figure 12.2. Table 12.2 gives rounded-off equivalent

The fitments shall be designed to provide a

diameters of bars using the factors as shown. See also

minimum effective confining pressure to the core of

AS 3600 Clause 8.1.10.8 for bundled bars in beams.

0.015f’c calculated using AS 3600 Clauses 10.7.3.2, 10.7.3.3 and 10.7.3.4. The spacing of the fitments in this case shall not exceed the lesser of 0.5 of the smallest

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dimension of the column or 300 mm. Under certain conditions of axial force and moment on the column as detailed in AS 3600 Clause 10.7.3.1, the confining

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pressure may be relaxed by increasing the spacing of the fitments to the maximum of the lesser of 0.75 of the

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smallest dimension of the column or 300 mm. For columns where 50 < f’c < 65 MPa concrete compressive strength applies, a linear transition

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between the two conditions given above can be applied.

Figure 12.2 Equivalent Diameter Factors of Bundled Bars

12.2.4 Shape of the Ties The shape of the ties is defined in AS 3600 and can be described by reference to Figure 9.1. Shape

Table 12.2 Equivalent Diameter of Bundled Bars Number Equivalent diameter (mm) for of bars bundles, of bar size in each bundle Factor N12 N16 N20 N24 N28 N32 N36 2

1.50

18

24

30

36

42

48

54

3

1.75

21

28

35

42

49

56

63

4

2.00

24

32

40

48

56

64

72

HT would be used for the surrounding (outermost) tie, shapes HT and DT would provide a fitment with a bend of included angle of 135º or less, and an LH or HH shape could be the single tie across the column for internal-bar restraint or a pair of ties of shape HT can be used as shown in Figure 12.3.

12.2.3 Lateral Restraint of Longitudinal Reinforcement

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All the main bars must be enclosed by ties. Whenever the centre-to-centre spacing of adjacent single bars is 150 mm or more (Figure 12.3) extra ties must be used. (See Clause 11.16.7 Drawing Sheet

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No 11.7). Each bundle must be restrained to the other bundles by ties. ����������

Ties may also act as shear reinforcement for columns which resist lateral loads as part of a moment frame system. �����

Figure 12.3 Requirements for Lateral Restraint of Longitudinal Reinforcement

12:2 Reinforcement Detailing Handbook

12.2.5 Circular Ties and Helices

12.2.7 Welded-Wire Mesh of Equivalent Strength to Bars

These are generally made by a machine which curves the wire into a continuous circular helix (or

Table 12.4 gives one solution based on

spiral). A circular tie can be made from a helix by

maximum allowable tie spacing. A strength-conversion

cutting it to the length needed for one turn plus a

factor of 250/500 is used because grade 250 bars are

lap plus two 135º fitment hooks. To ensure a fixed

indicated by AS 3600.

diameter, a welded circular tie without hooks may be specified.

12.2.8 Lateral Shear Forces at Beam-Column or Slab-Column ts.

12.2.6 Design of Ties and Helices

(AS 3600 Clause 10.7.4.5 and others)

This is done by selecting a suitable bar or wire

A calculation is required to obtain the quantity of

size db.fit and then checking that the maximum tie

reinforcement within the t. A formula is provided to

spacing (based on 15 db.m for single main-bars, and

give the quantity of bar or mesh.

7.5 db.m for bundled main-bars) does not exceed the column smaller-dimension for single main-bars and

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half of the column smaller dimension for bundled mainbars, Figure 12.4. Maximum spacings are given in Table 12.3 .

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Figure 12.5 Column-t Shear Reinforcement �

Example 12.2 A column has dimensions 450 x 300 mm with N28 single main bars. Ties can be R10 or L10 or greater. Based on 15 x N28, the maximum spacing could be 420 mm, but the smaller column dimension of 300 mm reduces the spacing to 300 mm. If bundles of N28 bars were used, the ties must be R12, N12 or L12 and the spacing is based on smaller of the 7.5 x N28 = 210 mm or 300/2 = 150 mm and hence spacing is 150 mm.

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Figure 12.4 Tie Spacings Table 12.3 Maximum Tie Spacing – Based on Relationship between Main-Bar Size and Column Smaller-Dimension (AS 3600 Table 10.7.4.3) Maximum tie spacing (mm) for main bar size

Main bar arrangement

Tie size & spacing

N12

N16

N20

N24

N28

N32

N36

N40

Single

R6 @ 15 db.m

180

240

300

N/A

N/A

N/A

N/A

N/A

Single

R10 @ 15 db.m

180

240

300

360

420

N/A

N/A

N/A

Single

R12 @ 15 db.m

180

240

300

360

420

480

540

-

Single

R16 @ 15 db.m

180

240

300

360

420

480

540

600

Bundled

R12 @ 7.5 db.m

90

120

150

180

210

240

270

-

N/A = Not Allowed

12:3 Reinforcement Detailing Handbook

Table 12.4 Mesh Substitution for Ties (After AS 3600 Clause 10.7.4.3d) Main bar and tie arrangement

Table 12.5 Fitment Bar Size Required to Restrain a Cranked Column Bar of Length 10db.main

Smallest main-bar size db.main in the column N12

N16

N20

N24

N28

N32

N36

Bar size, db.main Calculations based on force in main bar N12 N16 N20 N24

Single R6 @ 15db.m

180

240

300

–

–

–

–

Offset (mm) 1.12db.m + 10

23

28

32

37

41

46

50

Equivalent Mesh:

Slope (mm)

120

160

200

240

280

320

360

SL52

SL52

SL52

–

–

–

–

240

300

360

420

480

540

Single R10 @ 15 db.m 180 Equivalent Mesh:

Bundles R12 @ 7.5 db.m 90 Equivalent Mesh:

SL72

SL62

SL62 SL52 SL52 SL52

120

150

180

210

240

270

RL918 RL818 RL718 SL92 SL92 SL82 SL82

Author’s Note: The values in the Tables 12.3 and 12.4 appear illogical because a smaller effective area of mesh will provide “strength equivalent to bar fitments” as the latter spacing increases. The reverse would appear more logical.

N32

N36

Fitment bar sizes, db.fit based on a 90º bend located at a crank Mesh and wire L5

L7

L8

L9

L10

L11

L12

N12

N12

N12

N12

N12

N12

N12

Grade R250N2 R10

R10

R10

2-R103 2-R103 2-R123 2-R123

Grade SL82

N28

D500N1

Notes: 1 N10 is the smallest size of Grade D500N bar. 2 R10 is the most common. Use wire instead if necessary. 3 Use two fitments of common size rather than one larger-size bar.

12.2.10 Restraint of Column Bars at Crank Points The most popular and economical method of splicing column bars is by lapping bars which are offset-bent (cranked). The slope of the inclined part must be less than 1 in 6 to attempt to prevent the

Example 12.3 Referring to the Example 12.2, the mesh substitute is SL92 for the bundled bars because the fitment spacing is 150 mm. Where the smaller column size controls the tie spacing, mesh SL52 is used as an equivalent for spacing of R10 at 300 mm.

bars from buckling at the crank due to the horizontal component of the downward force on the bars. Additionally, extra ties should be required at the offset. Table 12.5 gives some values for the type and size of reinforcement needed to provide this restraint for a slope of 1 in 10. A length of 300 mm along the crank is commonly used by schedulers.

12.2.9 Splicing Column Steel This Handbook is based on the premise that concrete elements are detailed on an element-byelement basis, and that the art of detailing is in showing how the pieces can be ed together structurally. Splicing of column reinforcement is critical. Suitable methods include lap-splices, welding, mechanical splicing, and end-bearing for columns only if always in compression. The length of compressive and tensile lapsplices is given in Chapter 6 for both single and bundled bars.

The bar size of the ties depends on the horizontal component of the vertical force in the cranked portion. These forces are derived from factored loads. The Table assumes that corner main bars are restrained by a 90º corner of a tie, carrying 1.5 times the horizontal component; hence both legs share the load. The 1.5 factor is not stated in AS 3600, but comes from AS 1480:1982 which was not a limit state standard. For an internal bar, a separate link or pair of links with one leg, of the same size shown in the Table, provide restraint for a force of 1.0 times the horizontal component.

12:4 Reinforcement Detailing Handbook

12.2.11 Transmission of Axial Force through Floor Systems If the concrete strength specified for the

12.4.2 Location of Main-Bar Splices The main bars are spliced by lapping, endbearing, welding or by mechanical splices; the form of

floor system is greater than or equal to 0.75 times

splice can be defined by notes, but the location of the

that specified for the column and the longitudinal

splice must be dimensioned in relation to the floor level

reinforcement is continuous through the t,

below the splice.

transmission of forces through the t is deemed to be provided. If the concrete strength specified for the

A “kicker”, or a small (50 mm) plinth, can be cast above the floor to help define the column area and to provide a strong seating for the next set of

floor system is less than 0.75 times that specified

column formwork. Kickers should be detailed. Current

for the column and the longitudinal reinforcement

construction practice does not normally use kickers.

is continuous through the t, then the effective compressive strength of the concrete in the t can be calculated by formulae given in AS 3600 Clause 10.8. The formulae is different depending on whether there are four beams or two beams on opposing sides at the t. 12.3

12.4.3 Lap Splices Lapping is usually done at floor level so that the lower end of the new (upper) bar is ed on hardened concrete. The lap length must be specified in the drawings. The main bars may extend more than one floor

COLUMN PLAN-VIEWS The location and orientation of all columns is

shown on footing and floor plans-views. The scale is far

if there are no changes in column dimensions. Within Chapter 13 on beam detailing, there is considerable comment made on avoiding steel congestion at column-to-floor intersections.

too small to show reinforcement. The column shape is indicated but full

12.4.4 Location of End-Bearing and

details are given separately on cross-sections or by

Welded Splices

reference to the column schedule. Columns which

These splices can best be done when located

are rectangular or circular are easy to define but other

at a convenient working height above a floor, say 600

shapes will require full dimensioning.

to 1200 mm. The splices should be staggered within the column storey to ensure adequate tensile strength

12.4

COLUMN ELEVATIONS

is obtained throughout, Figure 12.6. See AS 3600 Clause 10.7.5 and Clause 12.4.6 of this Handbook.

12.4.1 Column Main-Bars Unless extra cross-Sections and other details are provided, it is advisable to use only one bar size in each storey of a column. If this approach is used, only one bar shape need be drawn in full on the elevation (see Clause 11.16 Drawing Sheet No 11.6). Where a column schedule is not used, the basic design notation

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consisting of number off and bar type-size is given on a leader to this bar and other bars can be arrowed by an extension of this leader. Where circular and rectangular columns are

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shown on the same sheet, more than one column elevation may be useful because the arrangement of ties will probably differ.

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Where column sizes change throughout the height of the structure, adequate elevations and sections must be used to define offsets to concrete and bars. Figure 12.6 Location of End-Bearing Splices 12:5 Reinforcement Detailing Handbook

12.4.5 Main-Bar Arrangement at Lap-Splice Level ����

Lapped longitudinal bars are achieved by using cranked bars (shape CC).

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If a column face is offset by 75 mm or more, the main bars are not continued through the construction t. Separate short straight bars are to be used to splice the lower and upper main-bars. The splice length

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above and below the t will depend on the stress, Figure 12.7. See also Clause 6.12 and others.

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With CC bars, the slope in the crank must not exceed 1:6 and is commonly specified as 300 mm for all sizes. The normal offset of the centre-line is one bar

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size. This allows the overlapped portions to be tied together. There are three common methods of arranging

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the offset portion of the main bars at a lap splice. (1) The offset is located just above the lap at the “working floor level”. Orientation problems of the crank are eliminated, the bar continues straight

Figure 12.7 Splice Treatment at Offset Column Faces

through the floor above and fitment dimensions can be made identical on each floor and through the t itself if shear steel is needed, Figure 12.8. See also Clause 12.2 above. Column bars can be continuous through two floors or more depending on lifting capacity and a continuous mesh cage can provide full-height

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rigidity. Beam details can be standardised to provide repetition of prefabrication. This method is illustrated on the column

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elevation in Clause 11.16 Drawing Sheet No 11.6, where one floor lift is detailed. Note particularly how variations in the levels of the

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footings can be accommodated without any need to replace bars previously supplied. It is strongly recommended that this method be used wherever possible. (2) The column bars are straight and are not concentric throughout adjacent columns. This method has many of the virtues of the first method above, although the changes in location from lift to lift may be of concern. However in wall construction, and with wide blade columns, it has much to commend it for the internal bars, if not for the corner bars.

12:6 Reinforcement Detailing Handbook

Figure 12.8 Cranked Column Bars above Working Floor Level

(3) The offset occurs through the beam or floor level. Unless the beam steel can be moved sideways, the cranked portion creates scheduling and fixing problems in deciding how to get beam steel through the cranked portion. Beam-column intersection problems will always be severe with narrow beams. Band beams

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provide a good solution, Figure 12.9. Orientation of the lap at the top and through the beam is critical and must be ensured by robust tying of the main bar to prevent rotation during the column pour. that the crank is waving around in the air one floor or more up. Only one floor lift can be made at one time unless beam details are to be altered on

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alternate floors to accommodate the crank. 12.4.6 Main Bars with End-Bearing and Mechanical Splices

Figure 12.9 Cranked Column Bars within Band Beams

An elevation is essential for defining the location above floor level of the end-bearing splices. In particular, cross-sections are required for bundled bars. Bundled bars in columns require careful attention to layout to ensure bars in each column lift can be kept concentric with the columns above and below, Figure 12.10. A sleeve of some form, or a mechanical connection, must be fixed around each splice to ensure that the sawn ends are concentric. Bar lengths should be multiples of the floor height for any method. All bars used with end-bearing splices must be straight and have ends sawn or machined square. The

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ends must be aligned concentrically by a clamp. Bars spliced by mechanical means such as crimped sleeves may not require special end

Figure 12.10 Bundled Bars Must be Kept Concentric

preparation unless specified otherwise by the manufacturer. Threaded connections require special treatment with reliable protection for both female and male threads.

12:7 Reinforcement Detailing Handbook

12.4.7 Location of Column Ties within the ■

■

Column ties may be required within the depth

Column Height

of a beam or slab under special circumstances.

Spacing is generally uniform but it is necessary

See earlier for appropriate guidance on quantities.

to indicate the location of the highest and lowest ties, usually 50 mm above the floor or kicker

■

Column ties should be located above and

below and 50 mm below the highest soffit

below end-bearing type splices to resist forces,

above, Figure 12.11. See the AS 3600 because

particularly during construction.

the rule is quite complex. ■

For scheduling purposes, the number of ties is

12.5

taken as the height from floor to soffit-above, divided by the spacing, the result being rounded off to the next higher number. ■

The number of turns of a circular helix is given in Figure 9.1 for shape SP, as is the length of wire

To be of use, these sections must be drawn to a larger scale than used with a plan-view. Essential information includes: ■

floor-concrete strength in the vicinity of the

One or more ties should be shown at the point

column, varies from the remainder of the floor-

where the main bar is cranked to resist any horizontal force there. This is a design matter. See Clause 12.2.10.

The concrete strength f’c for each lift, particularly if the column-concrete strength and the

used to make the helix. ■

COLUMN CROSS-SECTIONS

concrete f’c. ■

The orientation, shape and dimensions of the concrete outline for formwork construction. The use of a North Point or relationship to gridlines is essential.

■

The shape and dimensions of the ties (usually determined from the concrete shape) with the basic design notation clearly stated. This should consist of the number-off, the steel type and

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the nominal spacing, Figure 12.12. If there is ��������������

more than one tie at each spacing, the same information must be restated.

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■

The layout of all main bars within the section, often by a “typical drawing” if the section is rectangular or circular. This must include changes to the column size and the appropriate bar re-arrangement.

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Figure 12.11 Location of Column Ties within Column Height 12:8 Reinforcement Detailing Handbook

■

Any special bar arrangements at lap-splices; that is, whether the upper bar is lapped inside or alongside the lower bar.

■

How the bar arrangement is to be modified progressively throughout the height of the building from the footings. A grid system and templates for setting out the centre lines of the starter bars should be detailed on the contract drawings rather than requiring repeated calculations based on nominal concrete dimensions and concrete cover by several other people such as schedulers, formworkers and steelfixers.

■

■

Details of ties which act as shear reinforcement

12.6

DETAILING COLUMNS FOR

within the beams or slab depth.

CONSTRUCTION

Allowances for adequate tolerances for fixing

The following comments are offered to assist

main bars into corners of ties or at lap splices, etc. Generally values are obtained from the

column construction and to reduce cycle times. ■

Use the fewest number of bars possible at any

AS 3600 and are not stated in the drawings

section. This reduces the quantity of bars to be

– perhaps they should be.

handled on site and could reduce the number of ties making concrete placement simpler. ■

Manual hoisting of column bars into place is heavy and time-consuming work. Contrary to the above comment, a greater number of smaller

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size bars may be an advantage in many cases, provided the extra ties do not increase fixing time. ■

Finding the correct bundle of steel for each column, sorting the steel and then moving it

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near to its correct position is one of the most time-consuming tasks on site. It is advantageous if all column bars have the same size and dimensions, and this should normally be possible. When method (1) of Clause 12.4.5 for deg main bars is used, small variations in floor-tofloor heights can be taken up within the splice length above the floor.

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Method (3) of Clause 12.4.5 requires every column bar to be detailed for a particular column; this leads to longer sorting times, more chance of the wrong bars being used, reordering

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of replacement bars because the leftovers will not fit, additional delays, etc. ■

Figure 12.12 Examples of Tie-Bar Notations

Never use more than one bar size in any one column, even if the loads are eccentric. Murphy’s law of material interchange will strike again.

■

Maintain the same column section from footing to roof, particularly if bundled bars are used. If this is not acceptable, restrict changes to one face only.

■

If the same column size cannot be maintained, the column bar arrangement above and below the change point must be detailed. The beam reinforcement layout may also require re-detailing.

■

Where column faces are offset 75 mm or more, the main bars are not to be cranked but additional splice bars are to be used, Figure 12.7.

■

Keep the tie layout as simple as possible. The number of ties is controlled by the centre-tocentre spacing of the bars in each face. 12:9 Reinforcement Detailing Handbook

12.7

IDEAS FOR PREFABRICATION

12.9

EXAMPLE OF A COLUMN SCHEDULE Clause 11.16 Drawing Sheet No 11.7

Column cages can often be fabricated away from the forms and lifted into place by a crane or other

provides a column schedule for a pad footing and the

mechanical method. For this to happen, a reasonably

column above. The example is from the footing plan

rigid cage is required. It is not essential that all the bars

given in Clause 11.16 Drawing Sheet No 11.1 and

be tied or welded before erection.

Examples of Footing Details Clause 11.14.2. Column cross-sections accompany the column

Often the corner bars can be fixed firmly to the outer cage of bars or mesh, and the remainder secured

schedule. Each section is defined by a “type number”

inside during the lift. Once the cage and corner bars

which is common for all columns having the same

are placed over the starter bars at each floor level, the

general shape (rectangular or square, say), the same

others are released and moved into position. Some

number of bars and same tie layout. A well-designed

flexibility should be permitted in the cage until it is

schedule can save detailing time if the number of

positioned, then additional tying will be needed.

possible combinations is reduced to a practical

To prevent movement during concreting, the number and spacing of spacers should be specified in

minimum. Future amendments can be done merely by changing the type number. Column orientation is important; a north-point

the drawings. By placing the lap-splice crank at the bottom

may be necessary especially for rectangular columns. The cantilever footings are detailed in

of the column, a mesh cage for the fitments can be used full height and even through the floor above. This

Clause 11.14.2 and Clause 11.16 Drawing Sheet

method is compatible with the concept of beam caging

No 11.4. The pad footings are detailed in Clause 11.14.3

described in this Handbook. As well as simplifying column-bar placement, this concept enables the main

and Clause 11.16 Drawing Sheet No 11.5. Table 12.6 is an example of the type of details

beam bars to be pre-assembled outside the form, and for shorter splicing bars to be ed through the

which can be given in the General Notes for the

column cage in such a way that there is no interference

project, or on the same sheet as the column schedule.

between column and beam bars. There are no AS 3600 requirements for the bottom bars required at mid span of a beam to be “continuous” into or through a ; “continuity” by splicing is perfectly legitimate. 12.8

EXAMPLES OF STANDARD DETAILS

FOR A REINFORCED CONCRETE COLUMN Clause 11.16 Drawing Sheet No 11.6 illustrates the lapping arrangement for one column of the same size above a floor as below. Another column where the face above is offset from that below is shown in Figure 12.7.

12:10 Reinforcement Detailing Handbook

Table 12.6 Embedment Lengths for Starter Bars and Splice Lengths for Column Bars Splice length of 32 DIA. (mm)

Number of fitments at column bar crank

Bar Size

Straight embedment in footing of 20 DIA. (mm)

N20

400

640

1-R10 or 1-L7

N24

480

770

2-R10 or 1-L9

N28

560

900

2-R10 or 1-L10

N32

640

1030

1-N12 or 1-L11

N36

720

1160

2-N12 or 1-L12

12.10 DETAILING FOR SEISMIC (INTERMEDIATE MOMENT-RESISTING FRAMES)

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12.10.1 General As discussed in Clause 10.5.2, MomentResisting Frame Systems, it is desirable to ensure that any plastic hinges that may form should do so in the beam elements rather than the columns by ensuring

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that the flexural capacity of the column is higher than that of the beam by a significant margin to allow for any ‘overstrength’ due to design or materials. This is

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known as the ‘weak beam/strong column’ philosophy. Although it may not always be possible to achieve this, especially with such forms of construction as band beams (see below), care should be taken that catastrophic collapse, especially due to brittle shear

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failure in the column will not occur. In many cases, the ultimate compression strain of unconfined concrete is inadequate to allow

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the structure to achieve the design level of ductility without excessive spalling of cover concrete. Adequate transverse reinforcement must therefore be provided to confine the compressed concrete within the core region to maintain its axial-load-carrying capacity and

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to prevent buckling of the longitudinal compression reinforcement and subsequent failure. Plastic hinge regions are particularly susceptible where substantial axial forces are present, eg in columns where inelastic deformations must occur to develop a full-hinge

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mechanism. (Note: This may occur even where the design is based upon weak beam/strong column philosophy,

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such as at the base of all columns, see Figure 10.1). 12.10.2 Confinement Close-spaced transverse reinforcement acting

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in conjunction with longitudinal reinforcement restrains the lateral expansion of the concrete. This enables the concrete to withstand higher levels of compression. Circular or helical ties, due to their shape, are placed in hoop tension by the expanding concrete and provide confinement to the enclosed

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Figure 12.13 Confinement of Column Sections by Transverse and Longitudinal Reinforcement

concrete Figure 12.13(a). Rectangular ties apply full confinement only near their corners as the pressure of the concrete bends the legs outwards. This tendency should be counteracted by the use of cross-ties or interconnected closed ties. This has the additional benefit of increasing the number of legs crossing the section. The profiles of the unconfined zones of

concrete between longitudinal bars are shallower, and consequently a greater area of concrete is confined. The presence of a number of longitudinal bars, enclosed by closely spaced ties will also significantly aid confinement. Figure 12.13(b), (c), (d) and (e). 12:11 Reinforcement Detailing Handbook

12.10.3 Lapped Splices

The confinement of concrete is addressed in

It is inevitable that splices will occur in the

Appendix A of AS 3600 by the provision of closed ties,

column reinforcement of multi-storey buildings. It is

where required, over a distance of either: ■

■

The maximum dimension of the column cross-

important therefore to ensure that these are detailed

section; or

and located such that failure will not occur under

One-sixth of the least clear distance between

earthquake action. Splicing is usually achieved by the

consecutive flexural framing into it.

use of overlapping parallel bars. In this method, force

Further, the spacing of the closed ties is to be

transmission occurs due to the bond between the bars

the least of 0.25 do, 8 db, 24 df or 300 mm with

and the surrounding concrete, as well as due to the

the first tie located at 50 mm from the

response of concrete between adjacent bars. Under severe cyclical loading, column splices

face. (Note: do in this case is taken from the larger column dimension). The overall cross-

tend to progressively ‘unzip’. Further, where large steel

sectional area of the ties must obviously be

forces are to be transmitted by bond, splitting of the

sufficient to satisfy the shear requirements of the

concrete can occur. To prevent these occurrences,

column Figure 12.14.

ties are required to provide a ‘clamping force’ to the

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Figure 12.14 Typical Column Details for Intermediate Moment-Resisting Frame Structures 12:12 Reinforcement Detailing Handbook

longitudinal reinforcement against the core concrete. In circular columns, the clamping force is provided by

12.10.4 Beam/Column ts Under seismic loading, reversing moments

helical or circular ties. This form of reinforcement has

induced above and below the column t and

been shown to be very efficient at resisting the radial

simultaneously occurring reversals of beam moment

cracks that can develop. Further, these ties can restrain

across the t, cause the region to be subject to

an unlimited number of splices.

both horizontal and vertical shears of much greater

Unless the capacity has been checked by

magnitude than those experienced by the ading

design, it is recommended that splices should not

beams and columns themselves. However low the

be placed in potential plastic hinge regions. Whilst

calculated shear force in a t resisting earthquake-

transverse ties may ensure strength development of

induced forces, transverse reinforcement must be

the splice under cyclical loading at up to but still below

provided through the t to prevent the occurrence

yield stress of the reinforcement, they will not ensure

of brittle t shear failure, rather than obtaining the

a satisfactory ductile response. This is especially true

desired flexural beam hinges. (See Reference details

where large-diameter bars are lapped in the plastic

at end of this Clause). This transverse reinforcement

hinge zone. The splice will fail after a few cycles of

is provided by continuing the closed ties required for

loading large enough to induce inelastic behaviour

columns adjacent to the t.

in the longitudinal reinforcement, with a consequent

The area required Asy is to be the greater of:

gradual deterioration of bond transfer between the

0.30sy1 (Ag /Ac - 1)(f’c /fsy.f) [unless φNuo > N*]

bars (see Reference: Paulay, T. and Priestley, M.J.N.

or

Seismic Design of Reinforced Concrete and Masonry Buildings, John Wiley and Sons Inc, 1992). For

0.09sy1 (f’c /fsy.f) where:

example, a plastic hinge would normally be expected to

s

occur at the base of first-storey columns. (Note: This is

y1 = the larger core dimension

true for all frame types). Consideration should therefore

Ag = the gross cross-sectional area of

be given to carrying the column bars above first floor level before splicing. A less preferred alternative would

the column Ac = the cross-sectional area of the core

be to locate the splice at mid-height of the column. New Zealand practice allows that columns that

= centre to centre spacing of the ties

measured over the outside of the ties f’c

have greater than 1.25 to 1.4 times the flexural strength

= the characteristic compressive cylinder strength of concrete at 28 days

of the ading beams are unlikely to yield and form

fsy.f = the yield strength of the ties

plastic hinges – providing the column shear strength

φ

is similarly higher, ie matching the column flexural

Nuo = the ultimate strength in compression of

capacity. If the formation of plastic hinges is precluded, then splicing of longitudinal bars by lapping may be undertaken immediately above the floor level. Splicing by welding or the use of mechanical

= a strength reduction factor an axially loaded cross-section without eccentricity

N* = the axial compressive or tensile force on a cross-section.

couplers (eg Alpha or Lenton) is often done where bar

The area of reinforcement required may,

congestion may prove problematic. It is recommended

however, be reduced by half where equal resistance to

that under no circumstances should these be situated

t rotation provided in at least two directions at right

in a potential plastic hinge region, in order to help

angles, but only over the depth of the shallowest of the

ensure a strong column/weak beam failure.

framing . (See Figure 12.14).

Site welding of bar splices requires special consideration and care during execution. It is recommended that lap welding should be avoided. Butt welding is acceptable, provided it is carried out using a proper procedure but, again, it is recommended that welded splices are never used in a potential plastic hinge region. (Figure 12.14).

12:13 Reinforcement Detailing Handbook

Figure 12.15(a) shows the effects of shear

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transfer of concrete compression forces and some bond forces which, especially at external beam/column connections, require special consideration with regard to reinforcement anchorage. A considerable

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length of the top bars is ignored when calculating the development length because of expected bond deterioration under cyclic load reversal. It should also be noted that the bottom beam bars are bent upwards

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at the end, Figure 12.15(b). If they are not, this will result in poor behaviour of the t in the direction of

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loading, In addition, proper anchorage of the bottom

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beam bar is necessary in order to transfer shear through the t via a strut mechanism. However, tests have shown that U-bars are not as effective as top and bottom bars anchored separately. (Reference

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NZS 3101:1995).

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See the following references for more information:

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(i) Paulay, T. and Priestley, M.J.N. Seismic ����

Design of Reinforced Concrete and Masonry

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Buildings, John Wiley and Sons Inc, 1992 (ii) American Concrete Institute, ACI 318-89 (revised 1992) Building Code Requirements for Reinforced Concrete and ACI 318-89R

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(revised 1992) commentary Chapter 21 Special Provisions for Seismic Design. (iii) Irvine, H. Max and Hutchinson, G.I. (eds) Australian Earthquake Engineering Manual 3rd Edition, Techbooks, 1993.

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Figure 12.15 Shear Transfer at Beam/Column Connections and Suggested Beam Reinforcement Anchorage at External Columns

12:14 Reinforcement Detailing Handbook

13

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Beams 13.1

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GENERAL

13.1.1 Purpose For most practical purposes, a beam is a horizontal member of relatively small size which carries a vertical load and transfers that load to its s.

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These s can be either another beam, a column or a wall. For structural design purposes as interpreted by

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AS 3600, some of the methods used to design beams may also be used for slabs and walls. The physical shape of the member, that is its cross-section, has considerable effect on the method to be used.

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Figure 13.1 Beam Shapes

For simplicity of description, beams are usually called “rectangular”, “T-beams” or “L-beams” because

All of these apparently different types of beams

of the way they look and because this shape also

have their own particular methods of design although

illustrates the manner by which the vertical loads are

many are common.

applied to the top face of the beam – directly on to

The span of a beam is a term often used here

the rectangular beam, or on to the attached slab for

and includes “single span”, “continuous span”, “simply

the T-beam and L-beam. In the case of the latter two

ed span”, etc.

types, the attached slab is called the “flange” and this is a very important part of the total beam cross-section. Beams can also be upstand or downstand. For an upstand beam, the slab should remain propped until the top section of the beam is cast and cured. Figure 13.1 illustrates various beam shapes. The rectangular part of a T- or L-beam below the slab is called the “web”, in the bottom of which is the main “bottom tensile” reinforcement. The deeper the beam, the greater will be its load-carrying capacity. The flange at the top carries the compressive forces in

Example 13.1 1. In Clause 11.14.2, the cantilever footing detail CF4 would have been designed as a beam – it is called a footing because of its location – although the load along it comes from the earth below due to the vertical downwards column loads. 2. In Chapter 12 on columns, the fact that some columns must be designed as beams did not need to be known for detailing purposes, but it is important for the designer. Columns do not always have the main bars arranged uniformly around the edges.

the concrete to balance the tensile forces in the bottom reinforcement. To a lesser degree, the wider the flange the greater the load carrying capacity as well. Wide shallow beams (known as “band beams”) are a compromise between shallow beams and deep slabs, whilst narrow closely-spaced beams (called “ribs”) are another form with particular uses. “Prestressed” and “precast” concrete beams including beam shells are not included in this Handbook. Refer to the Precast Concrete Handbook, tly published by National Precast Concrete Association Australia and Concrete Institute of Australia, for details of these.

13:1 Reinforcement Detailing Handbook

13.1.2 Description of Methods of Load-Carrying by Beams

13.1.2.2 Shear Shear forces try to cause simultaneous

Concrete beams are reinforced to carry applied bending moments, shear forces and torsional

horizontal and vertical sliding within the beam. Shear action in concrete is not quite so simple

forces. To find out more about these the reader

because concrete does not crack in nice straight lines.

should consult other texts on the design of reinforced

The positive and negative longitudinal reinforcement

concrete.

already provided is just not enough on its own to strengthen the beam against shear failure, so vertical

13.1.2.1 Bending The “positive” and “negative” require some explanation.

reinforcement is used in addition to, and in combination with, the longitudinal bars. 13.1.2.3 Torsion

Example 13.2 (See Figure 13.2) To demonstrate a positive bending action, place a scale rule on two s and push down on the middle. The rule becomes curved downwards; this is called “positive bending”, the bottom of the rule is in “tension”. To “reinforce” or strengthen the bottom face of a concrete beam, steel bars are placed there – this is the “positive reinforcement” for the “positive” bending. Now ask a friend to restrain the ends of the ruler while you load it again. There is still positive bending near mid-span but “negative bending” is also created at the ends. The top of the rule is in tension for some distance into the span and requires “negative reinforcement”, whilst the mid-span region still requires positive reinforcement. ���������������������������������

Torsion means twisting. If one of the blocks just picked up was longer than the others, it would try to twist out of your grip. Torsion reinforcement is similar to shear reinforcement, but there are two particular requirements. Reinforcement used to strengthen a beam against torsional forces must consist of both “closed ties” and additional longitudinal (main) bars. 13.1.3 Summary of Beam Reinforcement Terminology The AS 3600 standard refers often to “flexural reinforcement”. This term means “reinforcement to resist forces caused by bending” (flexure means bending). It includes both positive and negative moment reinforcement. Common for flexural reinforcement are “main” or “longitudinal” bars. Additional descriptions are “bottom main bars” and “top main bars” depending

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on their location, and so on. Common for shear and torsional ����������������������

reinforcement are “fitments” which in turn include “stirrups”, “ties”, “ligatures”, etc. Fitments may be “open” or “closed” – see Figure 9.1 shapes SH,

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SC and RT for the former, and HT, T and DT for the ���������� ��������

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latter. Torsional reinforcement also includes main reinforcement, as well as closed ties. Figure 13.3 illustrates some of the used

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Figure 13.2

13:2 Reinforcement Detailing Handbook

with beam detailing.

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Figure 13.3 Beam Reinforcement Terminology

13.2

AS 3600 REQUIREMENTS There are a number of Clauses devoted

to detailing of reinforcement in beams for flexure (bending), shear, torsion, and crack control. In the Standard, reference is often made to a quantity of steel such as “one-quarter of the (positiveor negative-moment) reinforcement” being terminated or continued. This refers to the total area of steel specified, not to the number of bars. However, because

13.2.1 Distribution of Tensile Reinforcement (AS 3600 Clause 8.1.10.2) Bars should be spread throughout the tensile zone concrete, but effective depth must be maintained. In particular, avoid bunching beam top-bars together over columns; the top-flange may be used. 13.2.2 Cut-Off Points for Flexural Reinforcement Using the appropriate theory for determining the theoretical cut-off point (AS 3600 Clause 8.1.10.1).

a fraction of a bar is not possible, an appropriate

AS 3600 permits any valid method of

number of bars will be terminated or continued.

determining where reinforcement may be terminated (cut-off). Because the reinforcement is used to resist

Example 13.3 Assume the “tensile reinforcement at mid span” is five bars. One bar = 20%, 2 bars = 40%, 3 bars = 60%. The following combinations are possible: 1. Not less than one-half shall extend: 3 bars must continue, 2 may cut-off. 2. Not less than one-third shall extend: 2 bars must continue, 3 may cut-off. 3. Not less than one-quarter shall extend: 2 bars must continue, 3 may cut-off. 4. Not more than one-half shall terminate: 2 may cut-off, 3 bars must continue. 5. Not more than one-third shall terminate: 1 may cut-off, 4 bars must continue. 6. Not more than one-quarter shall terminate: 1 may cut-off, 4 bars must continue.

forces in the concrete, it may in theory be cut-off when the calculated stress in the bar is zero. The location of the zero-stress point requires a design calculation. However, AS 3600 Clause 8.1.10.1 says that the main bars must be extended past the calculated stress termination point by at least the overall depth “D” of the member, and then be extended for a further development length, Lsy.t. This is because the real stress condition may not agree with the calculations, or perhaps the bar could be fixed out of position. The term “point-of-contraflexure” in AS 3600 Clause 8.1.10.3 applies to continuous and built-in to the . It is a particular cross-section where there is no tensile or compressive stress anywhere across that section. AS 3600 requires the determination of the point of contraflexure for the negative moment reinforcement.

13:3 Reinforcement Detailing Handbook

13.2.3 Theoretical Requirements for

(c) At s where the beam is continuous

Anchorage of Flexural Reinforcement

or flexurally restrained, AS 3600

(AS 3600 Clause 8.1.10.4)

Clause 8.1.10.4(c).

See also Chapter 6 for stress development

Of the number of bottom bars at mid-span, at least 25% must continue past the near face of

information. Positive moment anchorage requirements in beams under AS 3600 Clause 8.1.10.4 requires a

the . The distance is not specified in AS 3600, but a common value is 20 to 50 mm.

design calculation. To illustrate the complexity of a full

If the beam-caging methods recommended in

calculation, the following analysis is provided.

this Chapter are adopted, greater penetration

(a) At all simple s, there is a primary

can be obtained with extra continuity bars, and

calculation – AS 3600 Clause 8.1.10.4(a), see

without interference with column steel. In any

Figure 13.4.

case, if the beam is part of a framed structure

The anchor point for positive moment

that is an IMRF or SMRF, then continuity must

reinforcement shall be taken either halfway

be provided at the column in the bottom in

along the length of the bearing (), or

accordance with Appendix A of AS 3600.

determined by calculating the width of the compressive strut in accordance with AS 3600 Clause 7.2 using the strut and tie model. In this calculation, both shear and torsion, and allowance for the truss angle Θv must be

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considered. Calculate design shear force V* at a distance d cot Θ from this anchor point. The reinforcement shall be anchored for a

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Length Lst past the theoretical cut off point at distance d cot Θ from the anchor point such

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that the anchored reinforcement shall develop a tensile force which is the summation of the following forces. (i) The tensile force V* cot Θv /ø at the

Figure 13.4 Shear Force at a Simple

theoretical cut off point. (ii) The longitudinal torsion tensile force calculated in accordance with AS 3600 Clause 8.3.6 at the theoretical cut off point. (iii) Any other longitudinal tensile forces in the reinforcement at this point (b) In addition, at all simple s, a secondary calculation is needed using

Table 13.1 Common Minimum-Anchorage Factors Minimum anchorage length (mm ) for bar size

assuming they are the same size, the following

option [Clause Factor 13.2.3(b)] kdb

proportion must extend past the face by the

Option (2) 12db

144

192

240 288 336 384 432

length shown:

Option (3) 8db

96

128

160 192

224

Option (1) 6db

72

96

120

168 192

Table 13.1 from AS 3600 Clause 8.1.10.4(b). Of the number of bottom bars at mid-span,

(1)

up to 100% by 6db, or alternatively,

(2)

at least 50% by 12db, or alternatively,

(3)

at least 33% by (8db + D/2).

13:4 Reinforcement Detailing Handbook

N12 N16 N20 N24 N28 N32 N36

144

256 288

NOTES: 1. Rounded-off values should be used in the drawings.

216

13.2.4 Theoretical Requirements for Shear

If there are “N” bottom bars provided at mid-span,

Strength if Flexural Reinforcement is

the minimum number which must continue

Terminated in a Tensile Zone

towards the is:

(AS 3600 Clause 8.1.10.5)

(i) into a simple by 12db extension, N/2, or

If no main bars are terminated in a tensile zone,

into a simple by 6db extension,

then no action is required. Extend all bottom bars

all bottom bars

into the , and all top bars past the point of

(ii) into a restraining , extension unstated,

contraflexure by the development length.

N/4

Of the three conditions, only one need be met for compliance. Two of the conditions require

(iii) to within 0.1 x clear span from , the balance.

calculations before a decision is reached. If termination of main bars is specified by the

For shear strength reasons, do not terminate more

designer, at any section do not terminate more than

than one-quarter of the bars (ie N/4) in the top

one quarter of the bottom and/or top bars with bar

or bottom within a distance of two times the

ends closer than ‘2D’.

beam’s overall depth (that is, within 2D).

13.2.5 Simplified Method for Detailing Flexural Reinforcement in Continuous Reinforced Beams (AS 3600 Clause 8.1.10.6) This section does not apply to prestressed . (a) For single-span, simply-ed beams, AS 3600 clauses 8.1.10.4 and 8.1.10.5 must be used. There is no simplified method given as such. (b) For continuous beams, a series of visual checks and minor calculations are satisfactory. All the following restrictions must be met: ■

■

The beam is continuous over its s, or is

Bundled bars (AS 3600 Clause 8.1.10.8). Four longitudinal beam bars can be bundled together, leaving more space for concrete placement. Ends terminated within the span must be staggered by at least 40db for each bar. Note: It is strongly recommended that detailers avoid multiple cut-off points. The extra cost of detailing and scheduling, cutting and bundling, searching on site for lengths which vary marginally, and then checking that they are placed correctly, often provides no economic gain. 13.2.6 Restraint of Compression Reinforcement

flexurally restrained at a , and

(AS 3600 Clause 8.1.10.7)

For adjacent spans, the ratio of the longer to the

Clause 12.2.3 of this Handbook provides

shorter length must not exceed 1.2, and ■

The loads are uniformly distributed, and

■

The distributed live load must not exceed twice the distributed dead load.

suitable information for beams and columns. 13.2.7 Bundled Bars (AS 3600 Clause 8.1.10.8) See Clauses 13.2.6 and 12.2.2.

Check list for main bar termination in continuous reinforced beams assuming there are “N” bars of the same size. If there are “N” top bars provided at the , the number which must extend away from the and into the beam is: (i) over whole span, N/4 or more

Do this first

(ii) at least to 0.3 x clear span,

N/2 or more

Then do this

(iii) at least to 0.2 x clear span, the balance

Avoid this.

13:5 Reinforcement Detailing Handbook

13.2.8 Shear Reinforcement

13.2.9 Torsion reinforcement (AS 3600 Section 8.3)

(AS 3600 Clause 8.2.12)

Both longitudinal bars and closed fitments

Detailing shear reinforcement requires

must be used in combination for torsion. The standard

calculations and AS 3600 should be consulted. The

should be consulted because calculations are always

following points should be read with Figure 13.5.

required. In most buildings, shear reinforcement will

■

Both mesh and separate bars may be used

generally provide enough steel for torsional strength.

as fitments for shear strength. Each would be

Because of this, torsional reinforcement cannot be

bent to the desired shape. See Figure 9.1 for

checked visually.

standard shapes. ■

Fitments as separate bars may be angled to the axis of the beam, but this requires more than normal design calculation.

■

beam, in each case the spacings are limited to: • A maximum longitudinal spacing less than either 0.5 D or 300 mm, • Or when the shear force is small, less than either 0.75 D or 500 mm, and

longitudinal shear forces across shear planes through for design procedures, and AS 3600 Clause 8.4.4 for reinforcement. Any shear and torsion reinforcement already provided may be included as part or all of the shear-plane reinforcement. 13.2.11 Reinforcement for Crack Control (AS 3600 Section 8.6)

• A maximum spacing across the width of the

■

Fitments or other steel bars must also transfer the web or flanges of beams. See AS 3600 Section 8.4

The maximum spacing of shear steel is restricted. Taking “D” as the overall depth of the

■

13.2.10 Longitudinal Shear

The various clauses generally give “deemed-

beam of less than D or 600 mm. Refer to the

to-comply” rules which must be checked individually.

detail of CF4 in Drawing Sheet No 11.4.

Crack control of beams is based on limiting the spacing

Shear steel spacing is continued for an additional

of longitudinal bars, and on placing reinforcement in

distance “D” beyond the theoretical cut-off

the side faces and around openings. In the side-faces

point in the same way that longitudinal bars are

of deep , N12-200 or N16-300 may be used

extended a distance “D”. The quantities are a

as longitudinal reinforcement known as side-face

design decision.

reinforcement. See Figure 13.6.

Fitments should be as close to the beam surfaces as possible consistent with cover requirements and the location of other bars.

■

The ends of fitments must be properly anchored, and this is done either by hooks for bars and mesh or embedded cross-wires for mesh.

■

Fitment hooks with bars will generally be 135º �����������

or 180º in rectangular beams; 90º cogs may be used in T-beams where open fitments are desirable for fixing and not within 50 mm of a surface of the beam. See AS 3600 Clauses 8.2.12.4, 8.2.12.5, 13.1.2.5 and 17.2.3.2.

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Figure 13.5 Shear Reinforcement

13:6 Reinforcement Detailing Handbook

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Figure 13.6 Crack Control of Beams

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13.3 ■

BEAMS IN PLAN-VIEW Plan-views of beams are drawn as a concrete

13.4.3 Dimensioning Main Beam Bars Generally ■

outline as shown in Figure 7.2. The beams are

floor-to-floor height generally controls.

shown incorporated with the layout of any floor slabs and with the ing columns, beams

■

■

■

Beams are numbered as given in Clauses 8.3

The bar ends are controlled by end anchorage as discussed in Clause 13.2.

or walls. ■

Defining the location of the ends of main bars is more difficult than for column bars where the

■

The most important factor in selecting a

and 8.5.

method of dimensioning is to use a common

The overall dimensions of a beam are given on

system throughout each structure. In this way,

the plan-view with the depth, including any slab

schedulers and fixers can self-check dimensions

thickness, given first. (See Clause 8.7.1).

much more accurately. Consistency will also

Reinforcement within the width considered as

reduce requests for interpretations by the

part of the beam is not shown on plan-views.

designer.

For an exception, see the later comments on

■

The choice of using either formwork or column set-out lines as the origin of dimensions can

T-beams with heavy top steel.

depend on personal preference. The location 13.4

of the set-out line should be marked clearly

BEAM ELEVATIONS

on the formwork to assist in fixing the steel. If the setting-out line happens to be the column

13.4.1 Concrete Outlines

centreline in every case, so much the better,

The outlines of the beam and of all ing or intersecting beams, columns or walls are required.

but this is not essential and not possible in

The outline of slabs ed by the beams is

some cases. Where column set-out lines do

generally omitted other than as shown in Figure 7.4.

not coincide with column centre lines, then this must be clearly shown in the drawings. Using

13.4.2 Beam Main Bars – Basic Design ■

be in the correct location, and may reduce

The basic design notation (see Clause 9.5) must

accuracy of checking.

be given for every bar. The number of bars, their

■

formwork for setting-out implies that it will always

Specification

■

footings and columns are usually obtained

the structure.

from separate architectural drawings. These

Every differing longitudinal bar is drawn

dimensions should be repeated on the

separately in such a way that its shape and

engineering drawings to highlight changes made

bending dimensions are fully defined by the

in the architectural drawings, but not altered in

concrete surfaces inside which it is fixed. ■

In building work, the set-out dimensions of

size and grade of steel is vital to the strength of

The shape can often be easily defined using the shape codes of Figure 9.1, but a drawn

the engineering drawings. ■

The Standard Details 14.1 (Clause 14.13) of beams illustrate dimensioning of main bars.

shape would take precedence because it will be assumed that the detailer has taken more time to draw it. ■

A bar marking system on the engineering drawings will also assist all construction workers to identify each component of reinforcement.

■

Extra dimensions may be required to define the shape or to specify the fixing location. See Clause 9.3.3.

13:7 Reinforcement Detailing Handbook

13.4.4 Specifying Fitments in Beams ■

■

■

The essential basic design information for bar

loaded beam is greater at the ends than at

fitments includes the grade and size of steel, the

mid-span. The fitments will therefore be spaced

number required, the spacing and location.

closer near the s. However when the

The essential information for mesh fitments

beam s a concentrated load, the shear

includes a description of the mesh

forces are more uniform along the beam and the

characteristics (often by a separate schedule),

fitment spacing will be uniform also. This sort of information requires correctly-detailed drawings.

the applicable wire diameters and spacing in each direction, the shape of the cage and its ■

As a general rule, shear stress in a uniformly-

■

A beam subjected to torsion will possibly have

length along the beam.

the fitments at a uniform spacing throughout

Of the above, all details can be given on the

also, and there must always be a longitudinal bar in each corner of the outer fitment.

elevation except for the shape which is best shown in a cross-section, although a shape

■

Wide beams such as used in band-beam and

code is permissible for regular shapes. The

slab systems, enable specification of one mesh-

number of cross-sections can be reduced if they

fitment cage full length (eg SL82) with a short

are used solely to describe the fitment shape,

segment (eg SL92) providing supplementary

using the elevation to show all other details.

shear strength from the to the point of

■

Basic design notation should only be given once.

contraflexure.

■

In all beams, draw the two outermost fitments on the elevation and dimension their location. The dimension may be from existing formwork surfaces, set-out lines, etc as preferred, but use a consistent method. Often a figure of 50 mm from the face of a column or intersecting beam is used.

■

When the fitments are uniformly spaced, the number-off and spacing may be given on the cross-section, with the first fitment location dimensioned on the elevation.

■

13.4.5 Spacer Bars An example is given in Standard Details 14.1 (Clause 14.13). Spacers are usually made from a very short length of N-grade bar not less than the diameter of the bars being separated. Their purpose is to allow two layers of bars to be fitted into the concrete section. This spacing may control the development length. See Chapter 6. �����

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When the fitments are not uniformly spaced, the spread and location of the spacing change points should be defined on the elevation. The total number of fitments should be stated to avoid continual calculation later. The first fitment location from each is also required. See Figure 13.7.

■

When mesh is used, the length of each cage is given in the elevation and the shape in a section. The mesh configuration is given in a separate schedule. Identification of the cage is by a marking system.

■

Provided the number of fitments is specified by the designer, the spacing at the centre of a beam has some flexibility.

■

Do not omit a spacing except in the mid-span region where a “free” dimension is permitted.

13:8 Reinforcement Detailing Handbook

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Figure 13.7 Spacing of Fitments

13.5

BEAM CROSS-SECTIONS

13.6

INTERSECTION OF REINFORCEMENT AT ENDS OF BEAMS

13.5.1 Concrete Outline and Dimensions Draw the outline of the beam and any slab with which it is associated, together with any additional concrete dimensions required to specify the concrete shape. Where beams and columns intersect and have the same width and cover, then the column bars will clash with the beam bars. This can be a significant problem when dimensions are small. Having columns that are larger than beam width may assist in alleviating the congestion of reinforcement. Depth and width dimensions must be shown on the cross-section, together with any rebates and minor shape changes. These details are used by formworkers. 13.5.2 Fitments and their Shape

The location of any main bars of beams which intrude into or through an elevation is shown as in a cross-section (see Figure 7.5). The reason for this requirement is that intersecting bars can be identified and due allowance made for the size of fitments and any special bending of the main bars to avoid interference. Particular care will be needed to ensure consistency in these connections. Column bars and slab steel are generally not shown on beam elevations because they do not contribute to an understanding of the construction methods. Where there is no column ing a beamto-beam intersection, make sure that plan-views, elevations and sections are totally compatible.

The main purpose of a cross-section is to show the shape and dimensions of the concrete beam and of the associated fitments (shear reinforcement). 13.5.3 Dimensions Provide sufficient dimensions for the fitments to be scheduled. In general, the fitment dimensions are obtained from the beam dimensions by subtracting the cover all round. If there is more than one fitment at a crosssection, each must be defined. In Drawing Sheet No 11.4 (Clause 11.16) cross-section CF4 shows that there are three fitments making up each set. In this case, the bending dimensions are not critical and can be derived from the general layout; in other cases, more precise dimensioning will be required. 13.5.4 Spacing for Placing Ensure that there is sufficient space between

13.7

INTERSECTION OF REINFORCEMENT IN BEAMS AND COLUMNS It is a simple matter to detail the elevations of

two beams, or of two beams and a column, to show how the bars in each member are meant to over each other. It is far more difficult to ensure that this can be done on the site. The following sections describe how beam and column reinforcement, which is detailed separately in drawings, can be brought together in the formwork. The recommendations made here may not be applicable to every project, but the principles described will help overcome everyday problems of steel congestion. We are trying to show how the arrangement of reinforcement in one element will affect the

main bars to permit placing and compacting of the

arrangement in other elements. Some three

concrete. Bars rarely fit snugly into the corners of

dimensional views are given to explain the procedure –

fitments and clearances which may appear adequate

it is not suggested that details be presented in this

on paper may be greatly reduced in the field.

fashion, although in very complex situations, similar

See Clause 4.3 for minimum beam widths.

illustrations will be of great assistance to designer, detailer, scheduler, steel fixer and inspector. Applications for this type of detail with CADrafting should be developed as a normal office procedure.

13:9 Reinforcement Detailing Handbook

13.8

INTERSECTION OF A RECTANGULAR

■

Positive moment anchorage is required in the bottom (see Figure 13.9) and consists of short

BEAM AND A COLUMN

bars dropped through the beam cage and the 13.8.1 Assembly Principles

column bars. Their length will depend on the

The column reinforcement will generally be placed and encased in concrete up to the underside

stress level and type – tension or compression. ■

No top tensile reinforcement is placed with the

of the beam before the beam reinforcement is fixed.

initial cage; it is all located after the bottom

The location of the main column bars is assumed to be

anchorage bars have been placed. The top bars

unchangeable.

are tied to the HT-shape fitments.

The beam bottom reinforcement must be capable of being assembled into cages, and placed in the forms without interfering with, or being interfered by, the column steel. Beam top steel must be capable of being added later. ��������

13.8.2 Method The ideal solution requires several principles to be accepted. See Figures 13.8 and 13.9. ■

The beam cage should include the main bottom bars for the beam, the fitments can be in the form of mesh or bars and, if the latter, nominal size bars will be placed in the top to hold the

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fitments apart while being hoisted into the forms. ■

The cage should have as small a mass as possible to permit manual handling. Additional

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material can be added later. ■

The length of the cage should enable it to be

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located between the column bars (assumed already encased). It could be from 100 mm less than the clear span, to perhaps 400 mm less. ■

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Within the depth of the intersection zone, the column bars will be straight; that is the

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gooseneck for a lap splice does not occur in that zone to ensure maximum room for fixing bars. See Chapter 12. ■

Closed ties should be used where torsion is a design condition. Cogs are not allowed on fitments where the ends of the bar are near the concrete surface. Therefore hooks are required on all fitments. As the beam cage has been formed with the HT-shaped fitment, all reinforcement both negative or positive over the

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points of the beam must be threaded into the beam cages and tied to the stirrups. ■

Under the provisions of AS 3600, the covers to beams and columns are the same unless

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fire ratings require different values. Any cover differences are marginal, and will not prevent beam and column bars from clashing without additional treatment. 13:10 Reinforcement Detailing Handbook

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Figure 13.8 Isometric Details of Beam Cages

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Figure 13.9 Basic Assembly of Beam Cages

13:11 Reinforcement Detailing Handbook

13.9

INTERSECTION OF FOUR BEAMS OVER

13.11 INTERSECTION OF T-BEAMS WITHOUT

A COLUMN

A COLUMN

In this situation, all four column cages are made

Because there is no column here for ,

up and dropped into position. The tops are left open. The bottoms and sides of the beam cages

that complication is not added. However, if one of the beams s the other then the designer must

possibly have the same cover but the designer will

ensure that the ing beam is not split into two

need to specify the top cover as will be explained later.

“cages” or there will be a collapse due to loss of tensile

It is possible to add additional main bottom bars

strength in the bottom.

at this stage; the original cage should be kept as light as possible. The detailer will need to decide in which order the bottom anchorage bars are placed; one set will be

This does not mean that the cage method cannot be used – in fact, the beam intersection will be easier to assemble when the ing beam is placed first.

in the same plane as its own main bottom steel, the other set will sit on top at right angles.

13.12 OPPORTUNITIES FOR PREFABRICATION

Once the bottom bars are fixed, the top (negative moment) bars for both are fixed. They will have been slotted down through the column bars, threaded into the cage, and then lifted and fixed to the HT-shaped fitments at the top of the beam. Again, the designer must decide which beam is to have which layer of top steel. Note that because there is not much interference from the column bars (straight not cranked) through the beam-column intersection zone, the layout of the additional loose bars is greatly simplified. If the beams are of different widths or depths, the solution is even easier to obtain because the bottom anchorage and top negative moment bars can be spread out.

If clear spans are of similar length and the loading is essentially uniformly distributed, repetitive prefabrication of many cages should be adopted. The cage length would suit the shortest span and the anchorage bar lengths adjusted accordingly. Extra fitments may be added between the cage and the column on site. The size and weight of each cage will depend on the materials handling capacity on site. If craneage is available, then the cage can contain all positive reinforcement, perhaps being assembled on the ground rather than on the forms, and the top bars can also be loosely tied inside. If craneage is not available, the cages will contain only those bottom bars necessary to get it into place, with the remainder lifted in and tied just enough to prevent them moving during concreting.

13.10 INTERSECTION OF FOUR T-BEAMS

With a mesh cage, the amount of tying is

OVER A COLUMN

greatly reduced and the cage can be made quite rigid.

The situation is the same as above with the

Together with pre-assembled column cages, the total

addition of arranging the slab steel over the column into

system has considerable scope for improving cycle

two layers. It is good practice to spread the top beam

time.

steel into the slab (the flange) rather than concentrate it over the column.

13.13 EXAMPLES OF STANDARD DETAILS FOR NARROW BEAMS (See Standard Details 14.1 in Clause 14.13) The cage consists of the bottom bars (in one or two layers, although the latter is not common), the fitments and two top bars which separate the fitments if they are bars; fitments of mesh will use the continuous negative moment steel. See Clause 13.2.5, Check list, top bars, item (i). With similar beam and column widths, the beam cage is deliberately made shorter than the clear span. Wherever possible, all cages for a floor should be basically identical to permit interchange.

13:12 Reinforcement Detailing Handbook

13.14 DETAILING FOR SEISMIC

result of inadequate transverse reinforcement or poor

(INTERMEDIATE MOMENT-RESISTING

construction ts, for instance.

FRAMES)

The effect of reversing moments is generally concentrated at the junctions between beam and

13.14.1 General

column. Appendix A of AS 3600 therefore, stipulates

Under the effects of earthquake action, flexural

that in a span:

are subjected to a number of reversals of

■

The positive moment strength at a face

bending moment. To ensure adequate ductility potential

is to be not less than one-third of the negative

in IMRFs, beams are always doubly, and continuously,

moment strength provided at the face of the

reinforced. See Figure 13.10.

; and

If yield occurs, the Young’s Modulus of the

■

Neither the negative nor the positive moment

reinforcement will not remain within the elastic part of

strength at any section along the member length

the stress-strain curve, and that Bauschinger softening

is to be less than one-fifth of the maximum

will occur under cyclic loading. (The “Bauschinger

moment strength provided at the face of the

effect’ is the change in the stress-strain relationship

.

that occurs when a reinforcing bar is yielded in

All longitudinal reinforcement must be anchored

tension or compression and the direction of the

beyond the face, so that at the face the full

stress is reversed. The distinct yield point is lost and

yield strength of the bars can be developed. This

the stress-strain relationship takes on a curvilinear

requires that:

form). The stable hysteretic response of the potential

■

plastic hinge region can be diminished through the ‘pinching’ of the hysteretic loop due to the influences

■

of shear degradation of the region. This could be as a

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Longitudinal reinforcement is continuous through intermediate s; and Longitudinal reinforcement extends to the far face of the confined region and is fully anchored.

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Figure 13.10 Typical Beam Restraint Details for IMRF Structures

13:13 Reinforcement Detailing Handbook

13.14.2 Lapped Splices

13.14.3 Detailing for Shear

Lapped splices in longitudinal reinforcement,

Shear type failures tend to be brittle. Also,

located in a region of tension or reversing stress, are to

as mentioned above, maintaining a stable hysteretic

be confined by a minimum of two closed ties at each

response of plastic hinge regions requires that the

splice to inhibit the possibility of non-ductile failure at

compression bars be prevented from buckling. It

this point. The position of maximum moment under

must therefore be assumed that major spalling of

seismic load will be dependent upon the magnitude of

concrete cover will occur and that compression bars

the earthquake. (Figure 13.11).

must rely solely upon transverse provided

The position of the splice should therefore be

by the ties. Limitations on maximum tie spacing are

located at a position of known moment, perhaps in

required to ensure that the effective buckling length the

the middle third of the span, unless the designer is

compression bars is not excessive and that concrete

confident that the splice is sufficiently confined to safely

within the stirrup ties has reasonable confinement.

locate it elsewhere in the span.

Furthermore, due to the possible occurrence of the Bauschinger effect and the reduced tangent modulus of elasticity of the steel, a smaller effective length must be considered for bars subject to flexural compression,

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rather than compression alone. Appendix A of AS 3600

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specifies a minimum area of shear reinforcement: �

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(ie 50% greater than stipulated in the body of the Code) with closed ties provided over a minimum

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distance of 2D from the face of the . The �

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first placed 50 mm from the face, and the remainder spaced at 0.25do, 8db, 24df or 300 mm, whichever is least. Where: bw = width of web. s

= centre to centre spacing of ties.

fsy.f = yield strength of ties. D

= overall depth of cross-section in the plane of bending.

Figure 13.11 Localities of Plastic Hinges when Stirrups are Required. Note: Plastic Hinges will Form when the Flexural Capacity Envelope and the Actual Moment Coincide

do = the distance from the extreme compression fibre of the concrete to the centroid of the outermost layer of tensile reinforcement, but not less than 0.8D. db = the diameter of the smallest longitudinal bar enclosed by the tie; and df = the diameter of the bar forming the tie. Since tension in vertical tie legs acts simultaneously to restrict longitudinal bar-buckling and to transfer shear force across diagonal cracks, it is considered that the tie areas are sufficient to satisfy both the requirements for bar buckling and those for shear resistance. See Figure 13.10. (Note: These requirements do not preclude efficient fabrication techniques such as loose bar detailing described elsewhere in this manual).

13:14 Reinforcement Detailing Handbook

14 Suspended Slabs and Slab Systems

14.1.2 Description of Method of Load Carrying by Slabs ■

Bending. Slabs carry the applied loads either as one-way or two-way bending. Once the magnitude of the bending moments is calculated

14.1

(the analysis), the design of the cross-section

GENERAL

is similar to that for beams. Therefore, as for beams, slabs must be capable of resisting both

14.1.1 Purpose The term ‘slab’ is generally thought of as a floor, although it is equally applicable to a roof or other

positive and negative bending moments. ■

effects on slabs. Spandrel beams and torsion

member whose structural behaviour is the same as a

strips may be needed.

slab.

For flat slabs and flat plates, punching shear

The width and length of a slab are much greater

around the column requires careful

than the depth. Figure 14.1 shows various slab types. The slabs transfer the floor loads to the ing beams, walls and columns and ultimately by footings to the foundations. The lowest level floor slab may transfer its load directly to the ground. Some of the used with slab design are: ■

Single span or multiple span slabs – determined by the number of s.

■

One-way or two-way slabs (see AS 3600 Clause 1.6.3) – depends whether the slab is ed on two opposite sides or on all four sides.

Shear. Shear forces cause complex shear stress

attention by the designer. ■

Torsion. Torsional forces on slabs are treated with the shear stress analysis. The most critical torsion effects occur at spandrels (edge beams) which can require closed-ties to be used as the fitment. Torsion steel may also be required in the corners of slabs on walls. This is to resist stresses caused by the slab trying to lift itself off its s. Without torsion steel here, slabs can crack diagonally across the corner.

14.1.3 Slab Reinforcement – the Meaning of

■

Combinations of the above.

“Grids”

■

Beam-and-slab systems – where the slab is

Suspended slab reinforcement is placed in one

■

ed by the beams and becomes the

or two grids of steel – one always near the bottom

flange of the T-beam, L-beam or band-beam.

surface and one, if needed, near the top surface.

Solid slab – ed by columns without the need for beams. Variations are flat plates in which the slab is of uniform thickness

■

Each grid consists of two layers, usually at right angles. Thus there are four layers of steel. In AS 3600, for strength purposes the term

throughout, and flat slabs where drop s

positive moment reinforcement refers to the bottom

thicken the slab for some distance around the

steel, and negative moment reinforcement means the

column.

top steel.

Ribbed slabs which consist of narrow beams or

Slabs may also be post-tensioned in one or

ribs at close centres and a very thin slab above.

two directions, but this is outside the scope of this

Ribbed slabs can be one-way or two-way (waffle

Handbook.

slabs) in Figure 14.1. ■

Hollow core slabs are floor units, precast and prestressed.

■

Concrete soffit-slabs – where the positive moment reinforcement is included in the precast permanent-formwork soffit-slab.

■

Precast Tee-beams and extruded pretensioned beams.

14:1 Reinforcement Detailing Handbook

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Figure 14.1 Slabs and Slab Systems used in Buildings

14:2 Reinforcement Detailing Handbook

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14.2

AS 3600 REQUIREMENTS

14.2.2 Special Requirements for Two-Way Flat

(Clauses 9.1, 9.2 and 9.4)

Slabs and Flat Plates (AS 3600 Clause 9.1.2) At least 25% of the design total negative

Most of AS 3600 Clause 9 refers to reinforcement. Slab reinforcement detailing is generally

moment MUST be resisted by reinforcement and/or

controlled by “deemed-to-comply” rules. The amount

tendons within a width of (bcol + 2tslab) for flat plates

of flexural steel is calculated similarly to beams, and

and the drop width plus the width of the column

is then evenly distributed across the width of the slab.

centred over the ing columns. (AS 3600

Slab steel areas are therefore stated as area per unit

Clause 9.1.2).

width

(mm2/m).

Detailers must check that adequate room is left

See Chapter 4 for values of steel

areas. See Clause 9.5.3 for calculation of numbers of

for concrete placement. Tendons can be concentrated

bars in slabs.

within this strip whilst reinforcement remains uniformly

14.2.1 Minimum Steel for Bending Strength (AS 3600 Clause 9.1.1) Table 14.1 gives the minimum steel ratio Ast /bd for mesh and bar to be evenly-distributed in each direction as the bottom grid of reinforcement. AS 3600 Clause 9.4.1 gives the maximum spacing of reinforcement for crack control due to flexure as the lesser of 2.0 D or 300 mm.

distributed. Normal beams, band-beams and their associated slabs are not required to comply with this rule. Also, with draped post tensioned cables which are not directly over a column, these can induce local bending and shear in slabs at columns which the designer must consider. 14.2.3 Detailing of Tensile Reinforcement in Slabs

Table 14.1 Minimum tensile reinforcement for strength fsy = 500 MPa

(AS 3600 Clause 9.1.3) Of all parts of a building, slab detailing is the

Slab condition

Bar or mesh area, Ast (mm2/m)

most time-consuming. This is caused more by the

ed by columns

0.24 (D/d) 2 f’ctf /fsy

detailing requirements of the Standard.

ed by beams or walls

0.19 (D/d) 2 f’ctf /fsy

complexity of the shape and layout of slabs than by the AS 3600 divides detailing of slab systems into two major procedures. (a) Where the bending moment envelope is

Example 14.1 A 150 mm thick two-way slab is ed by walls with a concrete characteristic strength of 32 MPa. Allowing for cover of 20 mm plus 5 mm for bar thickness, the effective ‘d’ would be 125 mm. Thus, the minimum mesh area would be 235 mm2/m (L8 @ 200 or SL82) and for steel 235 mm2/m (N12 @ 400).

calculated. It is compiled from the “worst case” situations of bending, and is not just the bending moment diagram for just one worst-case loading arrangement. In fact, the envelope can contain segments which come from normally quite incompatible loading arrangements. Only calculations can define it. (b) Where the bending moment envelope has not been calculated. Appropriate “deemed-tocomply” methods can be used. These are based on slab type, conditions, span lengths, loading conditions, etc. It is requirement that in some cases where the envelope is calculated, the “deemed-to-comply” rules must also be followed. However, the procedures in (a) never override procedure (b).

14:3 Reinforcement Detailing Handbook

14.2.4 Termination when the Hypothetical Bending Moment Diagram has been Calculated.

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(AS 3600 Clause 9.1.3.1(a)) The hypothetical BMD gives the theoretical cutoff point of all bars, but the additional checks are still required. ■

Negative moment steel. Figure 14.2 illustrates a hypothetical bending moment diagram.

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One-third of the negative steel area can be

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provided simply by using one length of steel and staggering alternate pieces so that the ends are

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beyond the hypothetical point of contraflexure by a distance greater than either D or 12db. This actually provides one-half Ast+, but reduces

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detailing times and sorting on site. ■

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Positive moment reinforcement at s. A proportion of the positive moment steel is carried

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to or past the face of the to provide some shear strength there.

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In Figure 14.3(a), 50% of Ast+ can extend past the face of a simple by the greater of 12db or D, or 100% of Ast+ and can extend a distance of 6db or D/2. In Figure 14.3(b) and (c), bottom steel extension into a restrained is nominal and is left to the designer. Fixing of slab steel at beams takes longer and is harder work if the ends must be poked through fitments. Theoretically, there is no need for

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bottom steel to extend into a restrained unless there are reversals of moment – in those cases, a calculated hypothetical bending moment diagram will

Figure 14.2 Termination of Negative Moment Slab Reinforcement

show this.

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Figure 14.3 Termination of Positive Moment Slab Reinforcement

14:4 Reinforcement Detailing Handbook

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14.2.5 Arrangement when the Bending-Moment Envelope is Not Calculated (AS 3600 Clause 9.1.3.1(b)) Typical examples are when the simplified methods of analysis are used. These include AS 3600 Clauses 6.10.2, 6.10.3 and 6.10.4, together with the use of other moment-coefficient tables published elsewhere. Table 14.2 gives a guide to the relationship between the analysis Clauses of AS 3600 Section 6 and the detailing Clauses of Clause 9.1.3.

Table 14.2 Selection of Deemed-To-Comply Arrangements for Slab Reinforcement Condition to be satisfied

Detailing Rule to be used (based on Analysis Clauses)

Analysis Clause

6.10.2

6.10.3

6.10.4

Flexural Action

One-way continuous spans

Two-way, single or continuous spans

Two-way slab system

Method of

Beams or walls on two opposite sides

Beams or walls on four sides

Multispan systems of beamand-slab, solid slabs, flat slabs, waffles, and slab bands

Number of Spans

Two or more in one direction

One or more in two directions

Two or more and continuous, in two directions

Ratio of adjacent spans L x /L x

≤ 1.2

Not specified

≤ 1.33

Ratio Ly/L x within one

Not applicable

2.0 is hinted at

2.0 maximum stated

Ratio of distributed loads

q ≤ 2g

Not limited

q ≤ 2g

Are additional bending moments permitted at s?

No. Go to Clauses 6.9 and 9.1.3.1

No. Go to Clauses 6.9, 6.10.4, and 9.1.3.1

See Clause 6.10.4.5 for flat slabs

Lateral forces may be carried?

No

No

Taken by walls and/or frame

Moments may be redistributed?

No

No

Yes, 10% maximum See 6.10.4.3

For the ing beams

8.1.10.6

8.1.10.6

8.1.10.6

For the slabs

9.1.3.2

9.1.3.3

9.1.3.3 or 9.1.3.4

Limitations on Structure

Limits on Forces and Moments

Reinforcement Arrangement Clause

14:5 Reinforcement Detailing Handbook

14.2.6 One-Way Slabs – “Deemed-to-Comply”

14.2.7 Two-Way Slabs ed by Beams or

Rules

Walls – “Deemed-to-Comply” Rules

See Figure 14.4 for the following discussion. ■

See AS 3600 Clauses 6.10.3, 6.10.4 and 9.1.3.3.

Bottom steel at restrained – the

For this type of two-way system, the shortest span of a

standard does not specify the extension into

is the important dimension.

the so the designer must specify the ■

Figures 14.5 and 14.6 illustrate the effect which

appropriate solution for each case.

the shorter span of a rectangular slab has upon the

Top steel – only one termination point at 0.3

bottom steel of that slab only, and the top steel over its

times clear span past the ’s face is

four s.

recommended for economical detailing and ■

construction.

H have no effect because they are longer than the

Bottom steel at a simple – must go to

corresponding spans A, C and F (twice).

the centre line, but must NOT protrude ■

■

In this example, the longer spans E, B, G and

■

Top steel. Spans C and D of slab (S2) affect

into the concrete edge cover.

the top steel of each adjacent span. Whichever

Outermost bar location – the outer bar parallel

is smaller is used to calculate 0.3C or 0.3D. If

to an edge should be located at a cover of one-

span A was shown larger than span C, then the

half the specified spacing. See Clause 9.5.3 for

top steel to the slab group (S1 – S2 –S3) would

calculation of bar numbers across a slab.

extend 0.3A, but the other top steel of slab (S2)

Tie bars perpendicular to the span are not

would still depend on spans C or D.

shown for clarity. See Clause 14.3.9.

Where both spans of a are nearly equal,

See also Clause 14.13 Standard Details 14.2.

considerable detailing and fixing time can be saved by using one extension length throughout,

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particularly when the widths are

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similar also (internal walls). In these Figures, all extensions could be 0.3C or 0.3D except for

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0.3F between slabs (S4) and (S5). ■

Bottom steel. Again, the shorter span of each individual controls the maximum

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distance from a . External spans are not

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considered. In this example, staggered bottom bars are shown in some slabs. This arrangement can

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double the number of steel items to be drawn, scheduled, fabricated and found on-site, so one length per layer is recommended. ■

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Outermost bar location. The outer bar parallel to a should be located no closer than

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one-half the specified spacing. Bending stresses Figure 14.4 Deemed-to-Comply Rules

in this zone are negligible. ■

Calculation of number of bars. See Clause 9.5.3 for calculation of numbers of bars in slabs and Clause 14.3.9 on the use of tie bars for the top steel only in this case. See also Clause 14.13 Standard Details 14.2.

14:6 Reinforcement Detailing Handbook

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Figure 14.5 Bar Reinforcement Detailing for Two-Way Slabs ed by Beams or Walls. On Small Projects, the Number of Different Lengths should be Reduced for Faster Detailing and to Speed Steel Fixing 14:7 Reinforcement Detailing Handbook

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Figure 14.6 Mesh Reinforcement Detailing for Two-Way Slabs ed by Beams or Walls. On Small Projects, the Number of Different Lengths should be Reduced for Faster Detailing and to Speed Steel Fixing 14:8 Reinforcement Detailing Handbook

14.2.8 Multi-Span, Two-Way, Solid-Slab Systems

14.2.8.1

“Design Strip” for Strength Calculations

To understand the method of detailing a solidslab system requires a short explanation of the design

This is a concept introduced in AS 3600; it

process for slab-systems generally. The whole floor

also applies to slab systems using beams and to

system is divided into a series of strips which for design

band-beam and slab systems. The width of the design

purposes are called design strips, column strips and

strip is half the sum of the distances to each adjacent

middle strips in AS 3600 Clause 6.1.4, and for steel

parallel .

fixing purposes in this Handbook are called placing strips.

For analysis purposes, and the calculation of bending moments, the floor plan of a flat slab is

A solid-slab floor is a special type of slab

divided into two series of parallel strips. One series is

system. Solid slabs are ed by columns and/or

in one direction, say north-south, and the other at right

walls. There are no beams.

angles or east-west. Each series of strips is centred

Placing drawings for solid slabs must distinguish

approximately over the columns. Therefore, each

between the different grids of steel – solid slabs in

column will two design strips which are at right

particular are hard enough to detail without confusing

angles to each other.

the design requirements. Two methods may be used. ■

■

Each design strip carries the full design load

Grid separation. This explains the two-way

applied to its width; there is therefore some “double

bending action by putting the bottom grids of

counting” because any part of the slab is always

reinforcement on one plan-view, and the top

common to two perpendicular design strips. Bending

grids on another.

moments and shear forces are calculated in turn for

Layer separation. In this method, the

each strip in each direction.

reinforcement in the layers running one way is

Figure 14.7 describes slab system design

drawn on one plan-view, and that in the other on

strips; NS for north-south and EW for east-west. A flat-

a separate plan. This explains how the design

plate is illustrated; there are no drop s in this form

strips are acting.

of construction. ■

Dimensions are given only to provide a sense of scale.

■ ■

Columns are 800 mm square. Note that column C12, offset 600 mm within the design strip, and span C10 to C13 will control detailed dimensions over much of the floor; nevertheless design strip NS2 is shown here with a constant width.

■

For example, strip NS2 has a width of 8000 mm whether measured at C6, C9 or C12.

■

As another example, the width of design strip EW3 is (8400 + 9400)/2, or 8900 mm.

14:9 Reinforcement Detailing Handbook

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Figure 14.8 Subdivision of Design Strip into Column and Middle Strips. The Maximum Column-Strip Width is One-Half its Span 14:10 Reinforcement Detailing Handbook

14.2.8.2

“Column Strips” and “Middle

14.2.8.3

Strips” – for Reinforcement Placing

Reinforcement Distribution to the Placing Strips of a Solid Slab

AS 3600 Clause 6.9.5.3 allows the designer to

The term “placing strip” is used in this

allocate the relative distribution of bending moments

Handbook to refer to the reinforcement placing zones

to the column and middle strips, and from these the

in flat slab floors. “Middle” and “column” strips are used

reinforcement size and spacing is calculated.

for detailing and fixing purposes with all floor systems, not just flat slabs. Figure 14.8 illustrates one east-west design

Because of a greater proportion of the design strip bending moment is allocated to the column strip than to its two ading half middle-strips, it probably

strip taken from Figure 14.7. Having calculated the

has a greater proportion of the total design strip

loads and subsequent bending moments, this design

reinforcement.

strip (for the purposes of calculating the quantities and

The column placing strip can be regarded as

placing the reinforcement) is itself subdivided into a

resembling the beam of a beam-and-slab system

central “column strip” along the column line, and two

although it is much thinner and wider.

adjacent “half middle-strips”, one on each side. Design strips, column strips and middle strips are defined in AS 3600 Figure 6.1.4(A). The maximum width of the column strip must not exceed one-half of the centre-to-centre span of the design strip itself. Any width not ed for is added to the middle strips. For T- and L-beams, AS 3600 Clause 8.8.2 defines the “effective width” of the beam which is used for strength and deflection calculations. Although this width will be used in the design of spandrels with flatslabs, the “effective width” should not be confused

It should be noted that the amount of reinforcement in a middle placing strip consists of the total amount allocated to the two ading half middle strips from which it is created. To assist fixing and inspection on site, it is recommended that different bar sizes be used for the column and middle strips in each layer, eg N16 for the middle strip and N20 or N24 for the column strips. Also, the minimum bar spacing of Clause 9.1.5 of AS 3600 should be met.

with the various “design strips” above. See also Clause 14.2.9. The total design strip bending moment is distributed to these three strips and the reinforcement size and spacing can be calculated using AS 3600 Clause and Table 6.9.5.3. This method applies to other slab systems also. This procedure is repeated for each strip in both directions. Figure 14.8 shows the subdivision of the design strip EW3 into column and middle strips. ■

The width of design strip EW3 is

Example 14.2 Using span C9-C10 of design strip EW3 of Figure 14.8 as an example, assume the total reinforcement area is 12,300,mm2 distributed over 8900. One method is to provide 62-N16 in this area. If 60% of the moment resistance is allocated to the column-strip, then 38 bars must be placed over 4000 mm, giving the design notation 40-N16-100. The balance of 22 bars are distributed as 10-N16 and 12-N16, proportional to their widths, at 220 mm spacing. It is the number of bars which is important, not the spacing.

(8400 + 9400)/2 = 8900. ■

The apparent column strip width is (8400 + 9400)/4 = 4450

■

The column strip width for reinforcement placement reduces to one-half of the span in each case, ie 4000 mm from C8 to C10, and 3200 (rounded) between C10 and the west wall.

■

The middle placing-strips form the balance of the design strips.

■

In the North-South direction, the column placing-strip width will be one-half the NorthSouth design strip because the centre-line spans are longer than the design-strip width.

14:11 Reinforcement Detailing Handbook

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Figure 14.9 Bottom Steel Layout for a Flat Plate. Shown is a Typical E-W Strip and N-S Strip. Note how the Bottom Steel is Distributed across One Middle Strip and Two Half-Column Strips

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Figure 14.10 Top Steel Layout for a Flat Plate. Note the Double Layer of Top Steel within the Intersecting Column Strips and a Single Layer in the Intersecting Middle Strips 14:12 Reinforcement Detailing Handbook

14.2.8.4

Reinforcement Detailing for

■

Solid Slabs

Top steel layout. Ensure Clause 14.2.2 is complied with. Top steel for flexural strength is required within and parallel to the column placing

Extension of reinforcement in column or middle placing strips is measured in relation to the line which

strip (approximately one-half as wide as the

s the face of the columns in the transverse direction.

design strip). The column placing strips intersect

The “clear span” (Ln) is the distance from one column-

over the columns so a two layer grid of steel is

face line to the other in the direction of the span of the

used. This is illustrated in Figure 14.10. One layer of top steel for strength is also

design strip being detailed.

required parallel to and within each middle

Top steel must be fully anchored on each side of this column face line using straight bars, L-bars or

placing strip. It is ed by a layer of tie bars

mesh with cross-wire anchorage. The larger value of

which can be an extension of the top column-

Ln each side of a common determines the

strip strength bars. Tie bars are omitted for

extension on both sides.

clarity from Figure 14.10.

Bottom steel cut-off points from the column face line depend on whether the detail is for an internal

■

Cut-off points. These are shown in Clause 14.13 Standard Details 14.2.

or external , whether it is in a column or middle

14.2.8.5

placing strip, or whether there are drop s or not.

A flat plate refers to a column-and-slab system

■

Order of placement. At the commencement of

where the slab is of uniform thickness all over and

the slab design, a decision must be made by the

therefore the slab soffit (underside) is flat. Sometimes

engineer as to which design strip direction (N-S

the top of the ing column is widened to form a

or E-W) will be laid first for both top and bottom,

“column capital”.

as ties will affect the effective depth used for the design. See Figure 14.9. ■

Flat Plates and Flat Slabs

A flat slab is generally of uniform thickness except where it is thickened by a drop-.

Avoiding confusion. From the Figures 14.9 and

A drop- is a thickened area centred over a

14.10 it is obvious that EW and NS layers would

column below, but forming part of, the slab. It is usually

become totally confused if the direction of laying

square in plan but neither the shape nor the thickness

varied from strip to strip. Solid slabs are analysed

is specified by AS 3600. Traditionally, it has been taken

for bending moments on the design strips which

as about 1/6 span in each direction and rationalised to

have their centrelines along the columns and

the nearest 100 mm. In area, it should not be greater

their edges approximately midway between

than that bounded by two intersecting column placing

columns. First one direction is analysed, then the

strips. Dimensions and thickness can be changed to

other. It would be common for the bottom steel

suit the design requirements.

in the longer-span design strip to be laid first. ■

Bottom steel layout. In theory for strength design, the bottom steel in the direction of the span of a design strip is spread out across (distributed across) its column strip and its two adjacent half-middle strips. See Figure 14.8. In practice, the bottom steel must be laid out as a rectangular with corners at the columns. The steel length equals approximately the span on column centrelines. See Figure 14.9. If the spacing varies between the column and middle placing strips, this must be defined, as would the length of bar in each strip.

14:13 Reinforcement Detailing Handbook

14.2.9 Other Multi-Span Systems 14.2.9.1

Band-Beam and Slab Systems

A band-beam and slab consists of several parallel wide beams ed by columns and a continuous one-way slab perpendicular to and ed by the bands. Because the beams are usually wide and shallow, AS 3600 requires them to be checked as both

Because the band beams and the slabs are both one-way systems, a schedule is a convenient method of showing the actual steel sizes and distribution based on a Standard Detail. Four co-ordinated Standard Details are given in Clause 14.10.3. These combine details for the band beam and the slab. AS 3600 Clause 9.1.2, requiring 25% of the total

beams or slabs for their mode of failure. The principal

design negative moment of a flat slab to be resisted by

distinguishing factors are cover for fire resistance and

reinforcement and tendons over the , does not

shear resistance.

apply to band beam systems.

Cover for fire resistance applies to the longitudinal steel. Fitments and tie-bars can be located within the fire resistance cover, provided exposure cover is maintained. As a first estimate, the cover for fire resistance

14.2.9.2

Other Two-Way Slab Systems

Slab systems other than flat slabs are also designed by AS 3600 Clause 6.10.4. However when a beam is part of the design strip, it should be detailed as in Chapter 13 of

of a beam and a slab become equal when the width of

this Handbook, and the slab will be detailed as

the web is 700 mm for a simply-ed beam, or

in this Chapter appropriate to the slab type. See

continuous beam

Clauses 14.2.6 and 14.2.7.

In AS 3600, both beams and slabs are designed for flexural strength by the same rules (AS 3600 Clause 9.1 refers back to Clause 8.1). For shear strength, a slab must be checked for the method of failure, and designed for both failure across the slab (Clause 8.2) or locally around the (Clause 9.2.2). Thus a band beam can be designed as either a beam or slab, and detailed accordingly. Shear reinforcement design requirements for beams are given in AS 3600 Clause 8.2.5, and detailing in Clause 8.2.12. In particular, even the minimum amount of shear steel need not be provided for shallow wide beams if the shear force is less than a certain level, and the band-beam depth, D, is less than the greater of 250 mm and 0.5 bweb. Therefore, for a beam web width greater than 500 mm, and depth greater than 250 mm, shear steel may not be required for strength purposes. If shear reinforcement is required by AS 3600 Clause 8.2.5, the longitudinal and transverse spacing is controlled by AS 3600 Clause 8.2.12.2. See Clause 13.2.8. The wide beam permits the main bars to be moved sideways as necessary to avoid column bars, so a beam cage system is optional. However a wide LL- or VV-shaped mesh sheet, used as a shear cage, reduces tying to a minimum. Nested cages of mesh will provide additional vertical steel over the length of the span where this is needed.

14:14 Reinforcement Detailing Handbook

14.2.10 Spacing of Reinforcement and Tendons There are no minimum values stated in AS 3600 Clause 9.1.5, however Clause 9.4.1 has maximum spacing for crack control of 2Ds or 300 mm. The only requirement is that concrete can be “properly placed and compacted in accordance with Clause 17.1.3”. This statement puts the onus on the detailer to ensure that bars are not too close. As already mentioned in Chapter 6, tensile strength development length is controlled by spacing between, and cover to, the bar. The spacing factor for slab bars in the formula, k 2, is 1.7 when “the clear distance between adjacent parallel bars developing (their) stress is not less than 150 mm”. The value of k 2 is 2.4 in all other cases, an increase of 50%! This does not mean that slab bars must not be spaced closer than 150 mm, but extra checks on development requirements must be made in those cases. See Clause 6.2.2 for development length tables. Staggered bar-ends will obviously reduce the development requirements.

14.2.11 Shear and Torsion Reinforcement in Slabs

14.3

(AS 3600 Clause 9.2.6) This situation is not common but, if torsion

SLAB PLAN VIEWS Plan views are by far the most common method

of detailing slabs. Dimensions are given as necessary

is critical, then it is generally controlled by fitments

to ensure correct scheduling; tabulated values of

in spandrel beams. “Closed-ties” of shape HT

cut-off points can often be adopted. This Clause

(Figure 9.1) are shown in AS 3600 Figure 9.2.6.

also applies to detailing walls in elevation, with the

Closed-tie spacing must not exceed any of 300 mm or Db (beam depth) or Ds (slab thickness). One longitudinal bar must be placed in each corner of these ties. This is very important for adequate

necessary adjustments. 14.3.1 Slab Outlines The outline is drawn to show how the slab

torsional strength.

edges are related to the floor plan and to the slab

14.2.12 Crack Control for Flexure, Shrinkage and

s are clearly defined. See Clause 7.3.

Temperature Effects (AS 3600 Clause 9.4) The maximum spacing of reinforcement for control of cracking due to flexure does not apply to slabs on the ground. (See AS 3600 Clause 9.4.1 and Clause 14.2.1 earlier). AS 3600 Clause 9.4.3 applies to slabs on the ground as well as to suspended slabs. The designer should decide the degree to which the slab will be restrained, and then calculate the amount of reinforcement required. Where a slab is more than 500 mm thick, the steel in each face is calculated by substituting a value of 250 mm for the symbol “D” in the formulae, and

s. For structural safety, it is essential that the

14.3.2 Slab Thickness and Plan-View Dimensions The most common slab thickness and the variations are shown as in Clause 8.7.3. Similarly, other dimensions should be provided as required. 14.3.3 Holes Holes through the slab, recesses over or under, setdowns, plinths, etc, must be outlined and dimensioned as from Clause 7.5. This action is particularly important where there are no architectural drawings. 14.3.4 Structural Element Numbers The location and reference numbers of all

not the actual overall depth as “D” and providing the required steel area in both the top and bottom layers. A

ing beams, columns and walls should be

heavy raft footing could be included in this category.

as shown in Clauses 8.2 and 8.5. Slab reference

AS 3600 Clauses 9.4.4 and 9.4.5 may require additional reinforcement in the areas which connect the slab to a rigid restraint and where openings, discontinuities and re-entrant corners occur. Previous

numbers should define clearly the area to which each applies. 14.3.5 Slab Reinforcement – Basic Design Specification

experience rather than calculations may be used. ■

Specify the basic design notation (that is, the number off, type and size, spacing and placing information) for all slab reinforcement including some means of defining its shape and bending dimensions. See Clauses 9.2 and 9.5.

■

If reinforcement is bent, the shape may be drawn on the plan view even if this is not the true shape when viewed in plan. If there is any doubt as to the shape, draw it on a separate elevation or cross section.

14:15 Reinforcement Detailing Handbook

14.3.6 Reinforcement Location ■

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14.3.7 Drawing Slab Reinforcement in Plan View

The most common placing zones for slab

■

Bars generally. Draw one bar in the direction in

reinforcement are “bottom” and “top”. There

which it is laid in the placing zone indicating its

would normally be two layers of bars in each

shape if suitable.

zone, or one layer of mesh in each. See

Define the width of the zone by an extent line

Clause 9.7 for marking.

perpendicular to the bar axis, Figure 14.11(a).

The area of slab which represents the

Indicate the intersection of bar and extent line

appropriate placing zone is defined by the

with a dot or circle.

“direction line” and the “extent line” as shown in

Specify the basic design notation (the number of

Figure14.11.

bars, the bar size and grade, spacing if required,

The placing zone is generally assumed to have

placing instructions, etc) on the extent line.

the same shape as the concrete outline into

Spacing is always measured perpendicular to

which the reinforcement fits. This outline must be

the direction of the bar.

defined however.

■

Multiple bars. One extent line can be used with more than one bar. A common situation is when bars of one length are to be placed with ends staggered. See Figure 14.11(b).

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Standard rectangular mesh. The main wires are drawn with a short line on each side to indicate the close spacing of 100 mm. The main wires

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represent the sheet length. See Figure 14.11(c). The extent line defines the concrete width to

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be covered by the mesh; the concrete area

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is defined by the outline of the concrete slab. The extent line represents the cross-wire of rectangular meshes.

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The mesh reference number and placing instructions are given on the extent line. ■

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rectangular meshes except that four extra wires define the square mesh. See Figure 14.11(d).

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Standard square mesh. The method is similar to

The extent line represents the cross-wire

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direction; reference number and placing instructions are given there also.

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Strip meshes. Strip meshes, and others which differ in mesh specification and sheet size from

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above. Although a reference number can be placed against each mesh in a placing zone, it

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the standard meshes, are drawn similarly to the

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Figure 14.11 Drawing Slab Reinforcement in Plan View

schedule with the sheet mark on the extent line. See Figure 14.11(e). To specify these mesh types tabulate, for both the longitudinal wires and cross-wires, the wire size, spacing, and number to ensure the correct mesh is manufactured. The overhangs at ends and sides is sometimes critical to the design. Strip meshes are detailed similar to multiple bars.

14:16 Reinforcement Detailing Handbook

■

The location of tie bars is a design decision so

Mesh used for shrinkage and temperature control only. Where mesh is used to cover large areas of slab, the method of Figure 14.11(f)

they must be specified by: ■

Drawing the tie bar and the extent of the placing

may be suitable if confusion with other

zone, with bar notation, as described already.

reinforcement will not occur.

This method tends to clutter-up a small scale drawing.

Contraction and construction ts can still be located on this view; details of ts should be

■

eg “TIE BARS TO BE N12-250-BOT-UNO”.

drawn separately, possibly as a typical detail. 14.3.8 Placing Notation The slab plan-view must describe the placing

“TIE BARS OVER WALLS TO BE 4N16 PER ZONE” ■

short lines perpendicular to the main bar line,

placed usually “bottom” or “top”, and for bars, which

drawn to spacing scale. This is explicit but time

layer is placed first. One method was described in

consuming. It may be necessary to draw the bar

Clause 14.2.8.4 for solid slabs, and it can be applied

layers in a cross section to define the order of

to other systems as well. See Clause 9.7.3 also.

placing.

Where the number-off per placing zone is precedence over a calculation based on spacing

Where more control is required on tie bars, the number and spacing can be indicated by

zone in area and the layer in which the mesh is

given in the drawing or in a table, this value takes

Using one or more General Notes –

14.4

SLAB ELEVATIONS Slab longitudinal-sections are usually used

requirements.

for this purpose. See the Standard Details in 14.3.9 Purpose of Tie Bars

Clause 14.10.

(Cross-Rods, Distribution Bars, etc) Several Clauses of the AS 3600 require reinforcement to provide for shrinkage and temperature control, and also to spread loads across the slab (distribution steel). However, there is no direct reference

14.5

SLAB CROSS-SECTIONS

14.5.1 Concrete Outlines Draw the outline with dimensions of all surfaces

to the need to provide additional steel to

of the slab, particularly any changes in level or

and space the reinforcement required for strength or

thickness, as for example at drop s in flat slabs.

serviceability. This generally means that slabs are reinforced in two directions whether or not bending moments are calculated each way. Tie bars provide a method of keeping the main slab bars apart and, with bar chairs, ing other steel. With mesh, the “cross-wires” perform this task; with bars, extra “tie-bars” are placed perpendicular to the main bars. The quantity of shrinkage and temperature reinforcement in slabs is calculated by AS 3600 Clause 9.4.3.

14.5.2 Slab System Show the which the slab. Show, in particular, the method of by a brick wall (which leaf for example) or, for T- or L-beam s, draw the true cross-sectional shape of the beam. See Clause 13.5. 14.5.3 Reinforcement Shape Generally, dimensions given on the plan-view need not be repeated on a section and vice-versa. Architectural dimensions need not be repeated unless additional information is being supplied, such a defining reinforcement shape or location. Nevertheless, ensure there is sufficient information to define the length, bending dimensions and location of all reinforcement parallel and adjacent to the plane of the section, and the number of bars cut by the section. If the shape of these latter bars is not defined on the plan, another section at right angles to the first is necessary.

14:17 Reinforcement Detailing Handbook

14.5.4 Reinforcement Identification

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Bars fully detailed on the plan-view must be correlated with those on the cross-section. Repeating the bar mark is the best method. The basic design information should be given only once, and that should be on the plan-view. 14.5.5 Sequence of Construction At least illustrate the order in which reinforcement is to be placed; that is, starting from the formwork, the lower and upper layer comprising the reinforcing mesh in each of the bottom and top face. A cross-section will show this automatically, but ensure that cross-sections are consistent with each other. See

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Figure 14.12 Steel Layers at Beam-Column-Slab Intersections

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14.6

INTERFERENCE OF SLAB TOP REINFORCEMENT WITH COLUMNS AND BEAMS �������������

The problems associated with intersecting beam and column bars have been covered in Chapter 13. The situation is worse with two T- or L-beams. When two layers of top slab reinforcement are

Figure 14.13 Anchorage of Slab Steel at Edge-Beams

also required at the same intersection, it becomes necessary to specify adequate depth (actual cover) to beam top steel so that slab steel will also have adequate cover. This can lead to a decreased strength for the beam if it is not treated as a design requirement

14.7

and allowed for in calculations. (For a designer, to

Beam top-steel is actually negative moment

increase cover means the “effective depth” for that beam is less than for the other). Cover for exposure in AS 3600 can be the same for slab steel as for the fitments. Cover for fire applies generally to the soffits of beams and slabs. Therefore,

T-BEAMS WITH HEAVY TOP REINFORCEMENT

reinforcement for the design strip. Therefore, it should be distributed over the column placing strip at the . This steel will also reinforce the slab in the top, so extra slab material may not be required.

if top cover for the fitments and main bars of a T- or Lbeam is not increased, the latter can have inadequate

14.8

SIMPLIFICATION OF SLAB

cover because the slab steel rests on the beam top

REINFORCEMENT

bars.

Wherever possible, different length bar groups A suitable method for either a T- or L-beam is

shown in Figure 14.12. This solution may be used regardless of which beam is the “primary” beam. Where top slab steel can develop its strength at an edge or over a spandrel without using a hook, do not use a hook. If a hook is essential (with a narrow beam, say) locate it within the beam cage, not in the outer cover. See Figure 14.13.

14:18 Reinforcement Detailing Handbook

should be kept to the smallest number consistent with adequate strength. Every extra bar drawn increases detailing, scheduling and fixing costs.

14.9

HOLES AND OPENINGS Holes of dimension more than 150 mm through

a slab or wall must be fully detailed and trimmer bars

Top steel details are also nearly identical. Make sure 25% of the total negative moment is resisted by steel centred over the column. See Clause 14.2.2. Points of difference occur at drop s as

shown. To avoid openings, bars must be moved

noted above. Standard Details 14.3 and 14.4 are “design

sideways because indiscriminate cutting will cause a reduced strength. If some areas of concrete are

drawings” showing only one layer in one direction.

therefore left unreinforced, additional bars must be

The design drawings (probably accompanied with a

specified.

reinforcement schedule) gives steel quantities such as

Even if openings are not shown on the

the size and number of pieces in each placing strip.

drawings, it can be an advantage if typical details are

The method of staggering the bars, etc, is shown on an

given to show what to do should an unplanned hole be

additional “construction drawing”. Elevations on Standard Details 14.3 and 14.4

required during construction. An example of a Standard Detail for

show the required cut-off points. Most projects will provide the standard details

penetrations is shown in Clause 14.13 Standard Detail 14.6.

for a flat-slab system using drop s, or the standard details for a flat-plate system without drop-

14.10 STANDARD DETAIL DRAWINGS FOR SLABS This Clause provides a drawing office with the opportunity to prepare their own standard details for slabs of various types. They are based on various sources, and should not be regarded as the only method to be used. Any such system should be used as an “office standard”, not as an individual person’s standard. The Standard Details are shown in Clause 14.13 and range from Standard Detail 14.1 to 14.8, although not all apply to slabs. 14.10.1 One-Way and Two-Way Slabs The plan-view requirements given in Clauses 14.2.6 and 14.2.7 are shown in a Standard Detail as cross-sections in Standard Details 14.2. 14.10.2 Flat-Slab and Flat-Plate Slab Systems The design principles described in

s. In either case, the full set of “design drawings” will show the complete floor plan and reinforcement layout in two directions, in addition to these standard details. Note that, to improve readability of drawings, it is common practice not to draw the additional tie bars needed for of top steel at edges and in middle strips (see Clause 14.3.9). 14.10.3 Band-Beam and Slab Systems Standard Details for these systems allow the beam and slab steel to be shown together because there is room on the plan-view to define the beam reinforcement. Both top and bottom band-beam bars can be distributed over the width of the beam. Two-bar bundles may be used to reduce steel congestion. Checks for shear reinforcement must also be

Clause 14.2.8 are given in Standard Details 14.3

made; an extra cage over a short length of the span

and 14.4. For both slab-systems, the details are nearly

near the will supplement the minimum shear

identical.

steel requirements.

For bottom steel, 50% of bottom steel must

The Standard Detail 14.5 relates the design

be lapped 25 db near column centrelines; ie alternate

requirements shown on the plan-view (perhaps with

pieces of mesh strips, or bars. This lap need not

a reinforcement schedule) to the actual reinforcement

be centred over the column centreline, but may be

arrangement on the formwork (staggered ends, etc).

located where steel lengths can be rationalised. The

Standard detail of the band-beam in elevation is

cut-off point of the remainder is an extension of 25db

provided in Standard Details 14.5.

past a drop face for flat slabs or, for flat plates, termination no further than 0.1 times the clear span from the column-face line.

14:19 Reinforcement Detailing Handbook

14.11 TS AND SET-DOWNS IN SUSPENDED SLABS Figures 14.14(a) and 14.14(b) illustrate steel arrangements for various situations. They are illustrative only to indicate the problems associated with reinforcing complex concrete shapes. A design check is recommended before adoption. The on-site complications are considerable. Check that adequate space exists for reinforcement thickness and cover. Accuracy of scheduling and steel bending is essential.

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Figure 14.14 Typical Arrangements for ts and Set-Downs in Suspended Floors

14:20 Reinforcement Detailing Handbook

14.12 DETAILING FOR SEISMIC

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At least 50% of all bottom reinforcement at mid-

(INTERMEDIATE MOMENT-RESISTING

span is to be continuous through the

FRAMES)

such that its full yield strength is developed at the face of the .

14.12.1 General

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It has generally been found that insitu floor slabs

At discontinuous edges of the slab, all top and bottom reinforcement at a is to be

spanning in either one or both directions and acting

capable of developing its yield strength at the

monolithically with the ing beams are more than

face of the . These requirements are

capable of acting as a diaphragm unless the number of

illustrated in Figure 14.15.

large openings is excessive. The detailing requirements for slab reinforcement for moment resisting frame systems in Appendix A of AS 3600 are essentially the same as for beams (eg provisions of reinforcement,

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continuity, anchorage, lapping). 14.12.2 Flat Slabs Flat-slab construction has additional

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requirements due to the need to ensure ductility and continuity conditions are met at column and middle

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strips along the line of . Appendix A of AS 3600 sets out the following criteria: ■

All reinforcement resisting the portion of the slab moment transferred to the is to be placed within the column strip.

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A proportion of this reinforcement is to be evenly distributed in a narrower zone measuring 1.5

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times the thickness of the slab or drop beyond the face of the column or capital. This proportion is the greater of 0.5 or 1/1 + 2/3 √(b1 + do)/(bt + do) where b1 = the size of rectangular (or equivalent)

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column, capital or bracket, measured in the direction of the span for which moments are being determined.

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bt = the size of rectangular (or equivalent) column, capital or bracket, measured transversely to the direction of the span for which moments are being determined. ■

At least 25% of the top reinforcement at the in the column strip is to be run continuously through the span.

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Figure 14.15 Reinforcement Detailing for Flat Slabs in Accordance with AS 3600 Appendix A

At least 33% of the area of top reinforcement at the in the column strip is provided in the bottom of the strip, again running continuously through the span.

14:21 Reinforcement Detailing Handbook

With flat-slab construction, it is important to ensure that the slab/column connection can withstand the

14.12.3 Band Beams Shallow beams with large principal

deformation and moments arising from the drift of the

reinforcement ratios and correspondingly large t

primary lateral force resisting system without shear

shears will often give rise to problems in placing all the

failure and subsequent collapse. Booth reports that

required t ties. Irvine and Hutchinson (see details

failure occurs in the slab close to the column rather than

of Reference in Clause 12.10.4) report that in fully-

in the t zone.

ductile frames, the t ties would usually be placed

(See as a Reference: Booth, E. (ed) Concrete

with one tie set directly on top of the next set with no

Structures in Earthquake Regions: Design and Analysis

clear space between, and recommend that for frames

Longman, 1994).

of limited ductility, the principal beam ratios (As /bd) be

The most important factor influencing the

restricted to 0.02 or less, so as to reduce the problems

inelastic deformation that can be sustained in the

of placing the beam/column t ties. This needs to be

slab is the level of axial load to be transferred to the

considered especially at band beam/external column

column at the t zone. As the magnitude of axial

t connections to ensure sufficient ductility in the

load increases, so the available ductility decreases.

column to prevent a plastic hinge and potential collapse

This failure can be brittle in character, leading to the

mechanism forming in the column. If this proves

possibility of progressive collapse.

impractical, the mechanism shown in Figure 10.1(c)

To prevent this, secondary reinforcement should be placed in the bottom of the slab at the column/ slab intersection to resist the gravity loads in a tensile membrane action. See Figure 14.16.

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Figure 14.16 Tensile Membrane Steel at Column-Slab Intersection

14:22 Reinforcement Detailing Handbook

may be considered, provided rigorous analysis and careful detailing are employed.

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14.13.2 Standard Details 14.2 – One and Two-Way Slab and Beams

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14.13.4 Standard Details 14.4 – Flat Plate ������ �����

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14:26 Reinforcement Detailing Handbook

14.13.5 Standard Details 14.5 – Band Beam and Slab ���

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14:27 Reinforcement Detailing Handbook

14.13.6 Standard Details 14.6 – Penetrations in Slabs

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14.13.7 Standard Details 14.7 – Reinforced Concrete Wall Intersections ��������

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14.13.8 Standard Details 14.8 – Reinforced Concrete Wall/Slab Intersections

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14:30 Reinforcement Detailing Handbook

15

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Walls forming part of a framed structure. Depending on the design forces, the wall may

Reinforced Concrete Walls

act as a slab or as a column and would be detailed accordingly. Again, reinforcement details would accord with this Chapter.

15.1

GENERAL Reinforced concrete walls in this Chapter

include service cores. 15.1.1 Purpose Walls have considerable breadth and height in relation to thickness. They may be subdivided into

15.1.3 Wall Reinforcement Wall reinforcement is best described as being in the form of a grid which consists of a two-way mesh of bars, one layer placed horizontally and the other placed vertically. The grid can also consist of a single mesh sheet. Depending on the design requirements, there

loadbearing walls, which transfer loads down the structure, and non-loadbearing walls, which act as

may be either one or two grids in the wall. In the latter

partitions between rooms or as external facades. Walls

case, one grid would be placed in each face so there

often function as fire-separating .

would be four layers of steel, two horizontally and two

Detailers must be told of the intended purpose

vertically. Walls over 200 mm thick require two grids,

as load carrying capacity is critical to building safety. 15.1.2 Description of Method of Load Carrying by Walls Section 11 of AS 3600 differentiates between the various design methods for planar walls. That section of the standard does not apply to the design of curved walls such as circular tanks or architectural features, but the recommendations for detailing which follow later can still be applied. ■

Walls subjected only to in-plane vertical forces. Wind and other horizontal forces are not considered to be active. A braced wall would be detailed as given in this Chapter, or by Chapter 12 if it was designed as a column. In the latter case, there would be a grid of reinforcement in each face, and ties could be required.

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Walls subjected to in-plane vertical and

may be required. Where the wall is designed as a slab, one grid of reinforcement may be used in each of the “positive” and “negative” bending moment zones. Termination points would also be similar to slabs. Bending can be one-way or two-way. For a shear wall, the reinforcement contributes to the strength and the amounts required horizontally and vertically must be calculated. There are several design methods, but the reinforcement requirements of AS 3600 Clause 11.7 still apply. 15.2

AS 3600 REQUIREMENTS (Clauses 11.2, 11.6.4, 11.7) Where the applied loads cause the wall to act

as a column, Chapter 12 may be used for detailing reinforcement in two layers with ties between them.

horizontal forces. Shear walls, and service cores

(AS 3600 section 11.2).

providing that function, fall into this category.

15.2.1 Shear Strength Requirements

They would be detailed using this Chapter. ■

as does a wall designed as a column. Horizontal ties

Walls subjected principally to horizontal forces perpendicular to the wall. Where the vertical loads are small, the wall can act as a one-way or a two-way slab and would be detailed as in Chapter 14. Cantilever walls would also

(AS 3600 Clause 11.6.4) The total steel area horizontally and vertically is calculated. These areas can then be placed in one or two grids. Most commonly, the steel is uniformlydistributed in each direction.

be designed as slabs, and be detailed as in Chapters 15 and 16. ■

Walls subjected to in-plane vertical forces and horizontal forces perpendicular to the plane of the wall. These are designed as columns and detailed as in Chapter 12. 15:1 Reinforcement Detailing Handbook

15.2.2 Minimum Reinforcement in Walls

15.3

WALL PLAN-VIEWS

(AS 3600 Clause 11.7.1) The minimum amount vertically depends

15.3.1 Location of Walls Because lines defining a wall are drawn close

primarily on the quantity needed for strength, provided it exceeds 0.15% of the cross-sectional area of the wall. The minimum amount horizontally is 0.25% of

together, plan-views of walls are used only to define their position in relation to other structural elements.

the wall cross-sectional area. This value is larger than

When a slab-system is ed by walls, the outlines

that for the vertical direction because shrinkage and

are shown in the plan-view as in Figure 7.3. The wall thickness and other dimensions are

temperature effects are more likely to cause vertical cracking than horizontal cracking. Walls less than 2500 mm wide, and with no

given on sections and elevations, rather than on the plan-view. Concrete walls defined in plan-view should be

restraint against horizontal movement, may be used with less reinforcement in the short direction. This

identified elsewhere in elevations and sections by the

applies particularly to precast units such as tilt-up and

same reference number.

prestressed hollow-core . The AS 3600 Clause does not mean that more steel must be used horizontally than vertically. Provided that the horizontal requirements are met, then the same size and spacing can be used vertically. Thus it is common practice to use, for example, bars “N12-200EW” or a square mesh “SL82”. Mesh tailor-made for

a project can also provide for the different directional requirements. If the wall is very thick, AS 3600 Clause 11.7.1 allows a concession for minimum horizontal reinforcement in that only the outer 250 mm thickness need be used in the calculations for each face, instead of using the total thickness. Effectively this means that for each surface of a wall over 500 mm thick, the

15.3.2 Non-Loadbearing Walls Include any special notes above the wall, particularly when the wall is not meant to carry any load from the slab above. This is a common form of construction for masonry walls in a framed structure; the beams the slab and the walls form solid partitions only. All walls may be omitted if they are all nonloadbearing. If some carry loads and some do not, all walls must be shown with suitable instructions defining each type. Masonry walls are often separated from the floors below and above by a suitable membrane. The material and method of application must be specified in

minimum vertical reinforcement is 375 mm2/m length

the drawings.

and the minimum horizontal reinforcement is

15.3.3 Service-Core Walls

625 mm2/m height (ie each grid would be either mesh “100 x 100 - L7 x L9”, or -“N12-290-VERT x N12-170-HORIZ”). 15.2.3 Horizontal Reinforcement for Crack Control (AS 3600 Clause 11.7.2) The requirements are calculated from the

This category includes lift shafts, stair wells, air-conditioning and vertical ducts. They are often loadcarrying, and location and size are critical for strength. Openings are generally not shown on this view. ■

detailed as a cross-section incorporated with the

formulae and require a design decision to be made. 15.2.4 Spacing of Reinforcement

The horizontal layout of a service core is usually floor plan-view.

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Variations in a wall thickness should be drawn

(AS 3600 Clause 11.7.3)

taking special care that line separation is

The minimum clear distance between parallel

achieved. Dimensions are usually given in a

bars is 3 db and this may be applied to the horizontal spacing between the two grids. Maximum spacing is

separate larger-scale drawing. ■

The inside dimensions of a core must remain

limited to the smaller of 2.5 times the wall thickness or

constant throughout the height of the building

350 mm.

to avoid complications with lifts and other equipment. If it is necessary, wall thicknesses are

15.2.5 Restraint of Vertical Reinforcement

varied from the outside face.

For lightly-loaded walls designed as columns, two grids of steel are still required. Ties may not be necessary for strength, but some should be specified to keep the grids in their correct location. 15:2 Reinforcement Detailing Handbook

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The requirements of slip-form or climbing-form systems must be incorporated when they are known.

15.4

WALL ELEVATIONS

15.4.4 Compatibility Between Drawing and Construction

15.4.1 General Elevations of walls should show details

The view shown in the elevation must also be the same view taken by the workmen who will

similar to those required for plan-views of slabs. See

build it. If a retaining wall is to be poured against the

Clause 14.3.

earth it is to retain, the elevation must show all details

15.4.2 Wall Reinforcement – Basic Design Specification ■

Specify the basic design notation (that is, the number off, type and size, spacing and placing information) for all wall reinforcement including some means of defining its shape and bending dimensions. See Clauses 9.2 and 9.5.

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If reinforcement is bent, the shape may be drawn on the elevation even if this is not the true shape

looking towards the bank. A section should always be considered as well. If the wall surrounds a shaft or service core, each elevation must show from which side the formwork and steel will be placed. It may be necessary to use different views as the building proceeds from foundations to above ground. Identical reinforcement layouts in each face are recommended wherever possible.

when viewed from the side. If there is any doubt as to the shape, draw it on a separate crosssection. ■

The basic design notation should be given on the extent line of reinforcement shown in elevation. See Clause 14.3.5.

15.4.3 Reinforcement Placing Notation ■

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15.5

15.5.1 Cross-Sections Must be Drawn A wall elevation must always be accompanied by one or more cross-sections so that there is no possibility of misreading the reinforcement requirements.

There are always two layers of bars in each grid,

In many cases, it may be possible to describe

or one sheet of mesh in each. See Clause 9.7

the walls of a structure with one standard elevation

for marking.

showing the layout, together with a series of cross-

The area of wall which represents the

sections containing the design notation.

appropriate placing zone is defined by the “direction line” and the “extent line” as shown in Figure 14.11. Abbreviations “HORIZ” and “VERT” are recommended. ■

The recommendations for slab cross-sections (Clause 14.5) can be applied to walls also. 15.5.2 Using both Horizontal and Vertical Cross-Sections

The placing zone is generally assumed to have the same shape as the concrete outline into which the reinforcement fits. This outline must be defined; however, one label may be used even if the zone is an odd shape.

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WALL CROSS-SECTIONS

Where both horizontal and vertical crosssections are used, the details must be consistent so that together they show: ■

For walls, the direction from which the elevation

be drawn. Horizontal construction ts are often

will be viewed must correspond with the

specified by notes to the drawings.

position from which the reinforcement can be economically placed. The placing information

■

shape of reinforcement cut by one section,

CENTRAL are most useful. The “near-face”

sometimes it may be necessary to draw another

and “far-face” are purely relative to the direction

section at right angles, or to use an elevation.

of viewing. For slabs, there is no doubt that “TOP” steel will be above it; for walls, the location requires more thought.

The location, direction and shape of all reinforcement cut by the section. To define the

and abbreviations EF, NF, FF, INTF, EXTF and

“BOTTOM” steel is against the formwork, whilst

Concrete outlines, dimensional thicknesses, location of construction ts, etc, which must

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The location and dimensions of lap splices. This includes showing the length of reinforcement (with suitable tolerances for lapping) which will protrude from one pour so that formwork and reinforcement for a future pour can be fixed.

15:3 Reinforcement Detailing Handbook

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The order in which bars are to be placed, if this

■

If there is only one grid, the verticals must be

is critical to strength. Alternatively, show the

fixed first, and the horizontals fixed on the near

simplest method of fixing each layer in each grid.

side from which access is available.

For a wall, these two recommendations are not

■

necessarily the same. See Clause 15.6.1.

first, and the horizontals are then placed on the

15.5.3 Using One Cross-Section Only

outside from each side. This method permits

Where the elevation is used with only one cross-

good central access for vibrating equipment.

section (horizontal or vertical), the details suggested in Clause 15.5.2 above must be combined. It is more important that the direction of view of

See Figure 15.1. ■

then the far-face verticals must be placed first, followed by the far-face horizontals; the near-

15.5.4 Restraint of Wall Reinforcement

face verticals come next and then the near-face

It is very difficult to cast and compact concrete

horizontals. See Figure 15.1.

in thin walls. Reinforcement tends to obstruct the buckle under the mass of concrete. The grids should be braced from the formwork, and restrained by ties between two grids. Specify the type, size and shape of the ties, and their horizontal and vertical spacing, at least in general , and permit the contractor to use a proven alternative.

If there are two grids of bars and if access for placing forward and steel is from one side only,

the elevation is defined on the section.

concrete. Unless the grids can be kept rigid, they can

If there are two grids of bars with access from both sides, then the verticals can be placed

15.6.2 Fixing Mesh in Walls Since the sheet is self-ing, each grid can be placed as one unit. Any lap-slice between sheets should be made in the vertical direction; that is the sheets are side by side, not one above the other. It can be an advantage to splice wall mesh through floors using either long overhangs or extra splice bars to avoid a clash with slab reinforcement.

15.5.4 Cover Particularly where there is only one grid, allow for the overall thickness of the two layers in the grid

15.7 ■

STRAIGHT BARS PREFERRED Vertical bars in walls should be straight. Each

when specifying cover. Ensure that the cover to the

lift can be lap-spliced without cranking because

surface with the most severe exposure is correctly

there is plenty of room for side-by-side laps.

specified; then either omit the other cover or allow a

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reasonable tolerance.

Horizontal bars between corners should be straight, but not so long that they will intrude into the concrete at a corner. Short bent bars should

15.6

be used around the corners.

SEQUENCE OF CONSTRUCTION The sequences described below may not

■

If the wall is curved, it is recommended that bars

appear to provide the best solution for deg walls

over 12 mm in size should be bent to shape

for strength in bending. However if the wall cannot

before lifting into place because Grade 500N

reasonably be constructed, the design method must

bars require a considerable force to bend them.

be changed. For the majority of walls which carry only

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Mesh should always be placed in flat sheets with additional corner reinforcement fitted later. Mesh

vertical loads, the location of the vertical steel within the

can be curved about one axis, but not about

section may not be the controlling factor.

two. 15.6.1 Fixing Vertical Bars First It should be obvious to everyone that until vertical bars are fixed, there is no for the horizontal bars. ■

Horizontal bars should never be specified to be fixed on the far side of the verticals if they have to be lifted over the verticals or be threaded through them; this is unsafe and uneconomic.

15:4 Reinforcement Detailing Handbook

15.8

REINFORCEMENT AT WALL CORNERS Reinforcement for the corners should be short

pieces of L-, LL- or U-shape. The length of each leg should be sufficient to lap with the other wall bars and allow adequate clearance between poured concrete surfaces or formwork which may still be in place. See Clause 15.10.2.

The use of full-length bars of LL-shape around �

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corners should be avoided because they are hard

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to fix and do not provide an adequate tolerance for construction variations. 15.8.1 “Opening” and “Closing” Forces Detailing a corner requires a knowledge of

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the direction of the force which acts on the wall. For

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descriptive purposes, the forces are called a “closing” ��������

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force or an “opening” force after the effect they have on the corner. See Figure 15.2. Reinforcement must not be carried around the

Figure 15.1 Placing Order of Reinforcement in Walls

internal corner subjected to an opening-force because the corner concrete will be “popped-out” by the forces tending to straighten the bar. 15.8.2 For Small Forces – Opening or Closing Examples would be small pits, or internal bracing walls. In many instances, the force is very small and may require only one layer of reinforcement. Such ������������������

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Figure 15.2 Illustration of Closing and Opening Forces

corners are detailed as in Figure 15.3; that is with one L-bar around the corner. The lap length should be specified in the drawings. The bend can encroach on the corner in certain

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circumstances. Figure 15.3 illustrates a detail often

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used to resist “small” forces; the bend radius has been exaggerated to show that the corner should be chamfered to maintain cover.

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15.8.3 For “Closing” Forces ✐■

Where closing forces act on the corner, no serious structural problem exists: • With only one grid of steel, use an L-shaped bar or mesh piece as in Figure 15.3 to

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connect each wall.

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• With two grids, use a more complex arrangement as in Figures 15.4(a) and

Figure 15.3 Corner Detail for Thin Walls for Both Closing and Opening Forces

15.4(b). ■

Mesh in sheets can be used as the two grids of the wall reinforcement.

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Loose bars can be used around the corners because mesh cannot be “ed through” mesh. See Figures 15.4(a) and 15.4(b). Note how the bars at the re-entrant corner overlap into the opposite face.

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The corner bars should have the same dimensions so that they are interchangeable and thus avoid sorting time on site.

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Figure 15.4 Corner Details for Closing Forces 15:5 Reinforcement Detailing Handbook

15.8.4 For “Opening” Forces ■

Opening forces require more care when detailing. An opening corner induces tension on the inside face and can cause spalling of the concrete.

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In a thin wall, it is almost impossible to place

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two grids of steel and compact the concrete adequately. The method of Figure 15.3 may be

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the best solution in a difficult situation. ■

The method outlined in Figures 15.4(a) and 15.4(b) may be used for opening corners, provided that the design tensile stress can be developed at the inside corner. In cases where

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the bending stress is not high, a reduced tensile stress may be used for the calculation of the

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development length. ■

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Where the re-entrant corner has a large fillet,

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the method of Figure 15.5(a) may be used, again assuming that the steel stresses can be

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developed at the numerous critical sections.

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The steel layout must permit construction ts

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to be made at suitable locations away from the complex corner. Note that the wall steel is shown continuing into the corner in this example; it would also require the corner bars to be placed from outside the corner. The external Lshaped bar is important as a fixing aid. ■

Layouts similar to Figure 15.5(a) may be used for corners of any angle, or around knee-ts of such as portal frames.

■

The method of Figure 15.5(b) uses two identical LL-shaped bars placed vertically, from inside or outside the t as desired. The external L-shaped bar is important as a fixing aid. The method permits a “cleaner” corner which also can be of any angle. The spacing between the legs of the LL-bar would be the same as the wall-bar spacing. For closely-spaced bars, a U-shape may be necessary. See Clause 9.2.1 for the explanation. Figure 15.5 gives details for strong opening

forces when moment resistance and crack control are essential. Note that they are reinforced by several simple shapes which can be easily assembled. See as a reference “Reinforced Concrete Corners and ts Subjected to Bending Moment”, I H E Nilsson & A Losberg, J Struct Div ASCE, Vol 102, No ST6, June 1976, pp 1229-1254.

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Figure 15.5 Corner Details for Walls with Strong Opening Forces 15.9

HOLES AND OPENINGS These act as crack initiators. Trimming bars

should be located around openings for doors, ducts and windows in the same way as for slabs. See Clause 14.9. Generally, wall openings will be larger than those in slabs. A standard detail of wall openings may be used, with additional information given for situations which are more critical or which require special attention. Where there are two grids, trimming bars would be placed in each face, but concrete thickness must be sufficient to accommodate all layers of steel. Trimmer bars may be placed diagonally or parallel to the concrete corner, the only controlling factor being that the design tensile stress must be developed by the extensions beyond the corner. Figure 15.6 illustrates a Standard Detail for penetrations through walls; such a detail can be limited to openings of a medium size without requiring reference to the designer. Any larger penetration would require further design. The amount of reinforcement will require separate consideration.

15:6 Reinforcement Detailing Handbook

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15.11 DETAILING FOR SEISMIC 15.11.1 Shear Walls As AS 1170.4 assigns a low structural response factor (Rf) to reinforced or prestressed concrete shear walls or braced frames in a bearing wall system, these

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elements attract higher earthquake design forces. They are therefore required to be comparatively heavily reinforced and often will have a reasonable excess of

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strength above that notionally required. Appendix A ����� ����������������������� ������������������������

of AS 3600 allows elements in these systems to be ������������������������������������ ������������������������������������

Figure 15.6 Standard Detail for Penetrations through Walls

designed and detailed in accordance with the main body of the code without further consideration. It must be noted by the designer, however, that the use of any Rf of greater than 1.0 results in a design earthquake force of less than the anticipated actual

15.10 STANDARD DETAIL DRAWINGS FOR WALLS

loading. Reinforcement will then yield once the design earthquake force is reached and plastic hinges form. Detailing must be provided to reflect this.

15.10.1 General Clause 14.13 Standard Details 14.7 gives various plan-view arrangements of horizontal wall steel. Clause 14.13 Standard Details 14.8 shows vertical cross-sections of slab and wall connections. The size and spacing of bars stated here (N12-300 for instance) are strictly for demonstration purposes.

15.11.2 Walls in Building-Frame Systems As building-frame systems are generally more ductile than bearing-wall systems, they are assigned a correspondingly higher Rf value in AS 1170.4. The earthquake design forces are therefore lower. This may in turn result in less longitudinal and shear reinforcement. To maintain the required level of ductility, however, additional detailing is necessary.

15.10.2 Lap-Splices The lap lengths, where shown in Clause 14.13 Standard Details 14.7 are based on an assumed bar

The ductility provision requirements are as follows: ■

The reinforcement ratio Pw ≥ 0.0025 both

size. However, it is important for schedulers to check

horizontally and vertically (ie an increase from

on the method of construction when calculating actual

0.0015 in the vertical direction over AS 3600

bar lengths. Particularly at vertical corners, formwork needed at the corner and left in place while the next section is formed, may reduce the lap length. It is often

Clause 11.6.1). ■

The reinforcement is to be divided between the two faces, if:

an advantage to terminate the wall bars well short of

tw > 200 mm; or øV > (Ag,f’c)/6

the corner, and use an extended length of the L-shaped

where

corner bar.

tw = thickness of the wall øV = design shear strength Ag = gross cross-sectional area f’c = characteristic 28 day compressive cylinder strength of concrete All reinforcement terminating in footings, columns, slabs and beams must be anchored to develop yield stress at the junction of the wall and terminating member.

15:7 Reinforcement Detailing Handbook

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Boundary elements as shown in Figure 15.7 must be provided at discontinuous edges of shear walls and around openings where: • vertical reinforcement is not restrained; and • the extreme fibre compressive stress in the wall exceeds 0.15 f’c. Note: This stress may not be the actual stress developed, but is the ‘trigger value’ for determining when a boundary element is required. Restraint of the longitudinal reinforcement in

boundary elements is to comply with Clause 10.7.3 or, if the extreme fibre compressive strength exceeds 0.2 f’c with the requirements for Reinforced Braced Frames. It should be noted that the above requirements do not necessarily result in an increase in wall thickness for a boundary element, only that the areas concerned are designed and detailed to resist specified axial forces. ���������������������������������

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Figure 15.7 Typical Boundary Element Details from AS 3600 Appendix A

15:8 Reinforcement Detailing Handbook

16

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Cantilever 16.1

GENERAL

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16.1.1 Concept A cantilever is part of a member which projects beyond its . It can include cantilever retaining walls. 16.1.2 The

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A beam, a slab or a wall can “cantilever” over

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one or more of its s. The can be a column, a beam or a wall, or for a retaining wall, its footing. 16.1.3 Location of Tensile Stress Using a scale rule ed as shown in Figure 16.1, press down at one end. To stabilise the “beam”, a downward force is required at the other end. From the shape of the “beam”, there is tensile stress

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occurring at the top face. If the load is applied between the s, tensile stress occurs on the underside as it does with a true beam. ���������������������������������

16.2

AS 3600 REQUIREMENTS There is no mention of cantilevers as such in

Figure 16.1 Demonstration of Location of Tensile Stresses with a Cantilever

this standard. Cantilevers are to be treated in the same way that a normal member would be designed and

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detailed. Corbels, nibs and stepped ts are included in AS 3600 under the topic of “non-flexural ” in Section 12. The design requirements are such that each case must be considered independently. The general principles of this Handbook will still apply; however, specialist references should be consulted. ������������������

16.3

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CANTILEVER REINFORCEMENT LOCATION

16.3.1 Examples Figure 16.2 illustrates common combinations of cantilevers and other structural . Note the need for reinforcement in the bottom of the internal member between the s.

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Figure 16.2 Examples of Reinforcement Location in Cantilever

16:1 Reinforcement Detailing Handbook

16.3.2 Location and Extension of Reinforcement

16.5

CANTILEVER ELEVATIONS

There are two principal structural requirements that must be watched: ■

Elevations of cantilever beams must be drawn,

There must always be reinforcement in the top of a cantilever beam or slab, or in the tensile face of other ; and

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16.5.1 Bending of Beams

Reinforcement must extend beyond both sides of the for a distance adequate to carry all tensile forces on each side. It is normal practice to extend reinforcement out

to the end of the cantilever and back past the face a similar distance. How far back should it extend? This distance must be calculated by and obtained from the engineer – it cannot be guessed, it has no fixed relationship to the normal span and the cantilever may collapse if a mistake is made. The cut-off distance into the normal span MUST be specified (in millimetres) in the drawings. 16.3.3 Effective Depth Place cantilever reinforcement as close as possible to the top surface. The system should be specified also.

with the reinforcement dimensions shown in millimetres. 16.5.2 Shear in Cantilever Beams Shear requirements differ from normal span requirements. The designer must provide the detailer with location, spacing and steel size information. 16.6

CANTILEVER CROSS-SECTIONS These must always be drawn and dimensioned.

16.6.1 Continuity of Reinforcement Because the effective depth for strength and deflection is more critical with thin such as slabs and walls, continuity of reinforcement through and beyond the is essential. Laps and splices must be avoided near the if possible, and they must always be dimensioned. It is wise to dimension the design cantilever length also to highlight the value assumed. 16.6.2 Cantilever Balconies The cantilever balcony causes many problems

16.4

CANTILEVER PLAN-VIEWS

16.4.1 Reinforcement Detailing These are similar to plan-views of the elements which form the cantilevers. For cantilever beams, the reinforcement is not shown in plan-view except in cases where the beam top steel is spread out into the slab forming the top flange. This method is particularly valuable where depth reduction and congestion should be prevented. See Clause 14.7. For cantilever slabs, the top steel is indicated as in Clause 14.3. 16.4.2 Reinforcement Shape The actual shape may be shown on the planview.

16:2 Reinforcement Detailing Handbook

because of the many methods of which are possible, combined with the shallow slab depths involved and the effect of weather step-downs which may also occur at the . Other design problems are caused by the need to slope balconies outwards to shed rainwater, and the need for a balustrade at the extreme end. Figure 16.3 illustrates wall/beam and slab shapes, with possible reinforcement layouts.

16.6.3 Crack and Corrosion Control of Balconies An additional mesh located in the bottom face

16.7

CORBELS AND NIBS These provide the total for

of the balcony, on suitable non-corrodible s, is

the beams or slabs which rest on them. The major

a common practice to assist control of deflection and

requirement is that adequate bearing area is provided,

cracking.

and that the necessary reinforcement is located as

Long cantilever balconies should always

close as possible to the bearing surface and outer

be subdivided by contraction ts into moderate

edge. The loaded area must not project beyond a

lengths to prevent cracking from the outer edge

critical portion of reinforcement. Figure 16.4 illustrates

back to the . Whilst these cracks may not

the problem.

affect the strength, they will certainly detract from the appearance.

AS 3600 requires considerable attention be paid to checking the anchorage of reinforcement. Welded or

In addition to the ts, one or more extra bars located parallel to the outer edge may help to control

mechanical anchorages may be used. Corbels are also used as fixings with precast

cracks which can form due to fixings for the balustrade

concrete units such as façade . See the

for instance. Such fixings and penetrations act as

appropriate detailing Handbooks for full information.

crack starters. AS 3600 Clause 9.4.3 on minimum reinforcement for strong control of shrinkage and temperature will provide guidelines. A further source of trouble is the method of creating a drip groove in the soffit of the balcony. It is essential that the reinforcement is not permitted to rest ����������� ������������

on the groove form when concrete is being poured as the steel will rust here very quickly due to lack of cover. The ends of bars or mesh must not be hooked

������������������ �����������������������������

downwards at the outer edge – this is a constant source of corrosion problems.

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Figure 16.3 Simple Cantilevers and their Reinforcement

Figure 16.4 Details of Corbels and Nibs

16:3 Reinforcement Detailing Handbook

16.8

CANTILEVERS AS ARCHITECTURAL FEATURES Thin concrete are often used as

sunshades and other features of buildings. They are often thin and can be required to project from their ing member. The thinness causes durability problems and the specification of concrete quality and reinforcement cover must be considered with care. See Chapter 5 and AS 3600 Section 4. Thinness also causes problems for fins if the design does not allow for movement of the structure during its lifetime. Creep and temperature effects require realistic tolerances to be specified at the design stage. Projection of these means they will act as cantilevers attached to their s. In the case of beams and horizontal sunshades, extra reinforcement for torsional strength may be required. See Figure 16.5. 16.9

CARE IN DETAILING The overall problem with cantilevers and

similar is that, because of poor detailing, reinforcement congestion is not only unavoidable, but is often increased. All of spacing, depth and cover for reinforcement must be considered.

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Figure 16.5 Cantilever Acting as a Hood

16:4 Reinforcement Detailing Handbook

17

17.3

Reinforced Concrete Stairs

STAIR PLAN-VIEWS

17.3.1 Location of the Staircase in the Structure A staircase plan-view should be incorporated in the plan-view of each floor to locate it within

17.1

the structure. The small scale prevents adequate

GENERAL

reinforcement detailing. A larger scale plan-view of stairs which have a

17.1.1 Terminology Each flight of stairs consists of a sloping slab as

complex outline should be considered, in which case, reinforcement layouts may be shown.

a base. The steps are triangular blocks attached to the top surface. A staircase can consist of one or a series

17.3.2 Information Given on the Plan-View In general, a plan-view would show:

of flights. The base slab may be ed by walls or

■

as a whole;

beams, or by landings which themselves are slabs. The basic layout of a flight of stairs is shown in

■

The outline of the concrete forming the flights and landings;

Figure 17.1. ■ ■

�������

The relationship of the staircase to the structure

The edge of the treads; The location and type of stair s at each end (wall, beam, slab, column);

�����

■

The location and type of of the landings, if any; and

����� ■

The “up-and-down” direction of each flight to ensure that engineering and architectural drawings agree.

��������� ������ ���������

Figure 17.1 Terminology Used with Stairs

Most of the above must be obtained from the architectural drawings, together with the stair and stairwell dimensions. Stairs must comply with the Building Code of Australia which has strict requirements on width and height of steps, etc.

17.1.2 Shape of Base Slab Since the flight is always sloped, the angles which are created require reinforcing similar to the corners of walls as discussed in Chapter 15. The underside of the flight is the most critical.

17.3.3 Information Required from the Job Site This section applies particularly to formwork making and reinforcement scheduling. Stairwell dimensions must be verified on site before formwork construction is commenced,

The bend at the lower is a closing corner, and

because of unforeseen changes in dimensions of the

that at the upper is an opening corner.

ing structure. For example, walls may not be in

Detailing must provide a suitable arrangement of reinforcement around each bend, not only for strength, but also to allow for the construction sequence and tolerances.

their planned position, or the landings may need to be formed and poured at a different time from the flight. These changes can require splicing of reinforcement in positions not actually shown in the drawings, with lap-lengths left protruding through the

17.2

AS 3600 REQUIREMENTS Because a stair is regarded as a slab, or

possibly as a beam, for design purposes, the standard has no special requirements. Detailing of stairs would correspond with the appropriate design type.

forms. Wherever possible, reinforcement should be scheduled from the actual dimensions of the forms, but in any case detailing flexibility is strongly advisable with adequate lap allowances for tolerances and variations. 17.3.4 Landings in Plan-View Plan-view of landings to a scale of 1:50 or 1:20 can be detailed as for plan-views of slabs. Reinforcement for landing and flights should be shown. 17:1 Reinforcement Detailing Handbook

17.4

STAIR ELEVATIONS

17.6

AND METHODS OF CONSTRUCTION

These are used: ■

In combination with a vertical section to show how each flight relates to those above and below; and

■

As line diagrams to provide a general description of the stair and a suitable labelling method.

17.5

STAIR CROSS-SECTIONS

17.6.1 Design Investigation Two factors need to be considered in the design and detailing of stairs. Firstly, stairs can be ed in a number of ways depending largely on the architectural requirements and structural available to provide .

This is the most common method of showing structural details and would show: ■ ■

decided upon, the probable order of construction can influence the shape of the concrete outline and

The basic design specification, shown on

reinforcement layout in relation to length, splice

the flight. As a general rule, stair flights are

locations, top steel, etc.

as slabs. For bars, the notation should include the number required as well as the size and spacing to prevent an error in subsequent calculations and rounding off. The omission of one bar in ten may be serious. ■

Secondly, once the method of is

Reinforcement, detailed as for slabs.

approximately one metre wide and are designed ■

For mesh, either the number of wires or the sheet width out-to-out of the main wires will be

17.6.2 Methods of Several methods of ing the flights and landings are available to the engineer. Because of this, more than one may be used in a structure due to architectural requirements. Care is required to ensure that the relevant method is quite clear to the site trades. 17.6.3 Landings – Determined by Architect

adequate. ■

The size of tie bars across the flight, and the

room to stand at the ends of the flight when opening a door or access to fire hose reels and the like. The

They can be shown by dots on the section

position is the responsibility of the architect and cannot

and numbers can be obtained by counting or

be amended unilaterally by the engineer. This means

calculation. Tie bars should be located where

that sometimes the landing will be the for the

they will assist fixing, for example at bends and

flight and detailed as a wide beam or thick slab.

For landings, the tie bar and main bar arrangement can vary depending on the degree and orientation of s provided by walls or beams.

■

A landing should ensure that there is sufficient

spacing, can be given once in the drawings.

splices. ■

METHODS OF ING STAIRS

17.6.4 Check List before Detailing In addition to following the architectural drawings, the following may be checked: ■

Splice bars for the flight may better be detailed separately from the tie bars of the landing to

Is headroom adequate to permit walking under landings?

■

Can walls be built to full storey-height above the stair, yet still enable landings to be ed in

permit greater flexibility.

block-outs left in the wall? ■

Do the number of risers between landings comply with building regulations? A detailing error of one extra tread may be regarded as a serious matter.

■

Are treads and risers identical on all corresponding flights in each storey? If not, a separate detail for each may be required. Note: The going and risers must have the same dimensions for one flight of stairs. A maximum of 18 risers can be used before a landing is required.

17:2 Reinforcement Detailing Handbook

■

Can formwork be simplified by using flat soffits,

17.7.1 Closing Bends

with the necessary thickening of landings? ■

■

These occur at the lower end of the flight.

Are the ing walls, beams, slabs and

■

columns clearly identified?

may be continuous around the bend. See

Has an allowance been made for the fact that

Figure 17.2(b).

the stair may act in a manner different from

■

■

Where the lower end of the flight forms the

that assumed in the design and shown in the

landing, the flight reinforcement must extend into

drawing?

the . Suitable laps are permissible.

Have extra trimmer bars been shown, particularly along the edge of a landing where up- and down-flights meet? This is a common location for a transverse crack.

17.7.2 Opening Bends These occur at the upper end of the flight. See Figure 17.2(a). ■

17.7

At a closing corner, bottom reinforcement

The reinforcement resembles an “opened-out” 150-degree version of a 90-degree bend at a

REINFORCEMENT AT BENDS OF

wall corner.

FLIGHTS

■

In all cases, reinforcement if it is required to be bent to a shape, should have not more than one bend. Thus shapes S and V should be adequate for most

required. ■

arrangements.

Bottom reinforcement must be carried past the line of the bend; this means that an overlap is Yield strength lap lengths are advisable, even if the design stress is less than fsy. The bend angle

Flights at a common landing can consist of one opening bend and one closing bend; they will therefore

is insufficient to act as a hook and therefore does not reduce the lap length.

create a severe shearing effect in the centre of the 17.7.3 The Flight

landing.

Reinforcement for the flight should be of such a length that variations due to construction can be accommodated. Thus, it should be of S-shape or V����������������������� ���������������������� ������������ ���������������� �������������

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shape – never should it have two bends.

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������ ���������

���������

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Figure 17.2 General Detailing of Stairs including the Upper and Lower Bends and Flight.

17:3 Reinforcement Detailing Handbook

17.8

STANDARD DETAILS The general arrangement of stair and landing

reinforcement can be shown on a standard detail for a project. Instructions on how to handle variations to dimensions should be provided. Regardless of the type of stair, the best solution to a complex problem is to use simple concrete outlines with the least number of different pieces of steel.

17:4 Reinforcement Detailing Handbook

18 Concrete Pavements, Floors and Residential Footings

In addition, without reinforcement, the slab will tend to crack in a random pattern due to shrinkage of the concrete or from changes in surface temperature caused by the sun, or from repeated loading (fatigue). However, in all these cases because of the ing sub-base and the dowel action of any

18.1

GENERAL

reinforcement, the cracked piece cannot fall out

More concrete is used in slabs poured on the

completely. As a result of cracking, the surface can become

ground than in multi-storied buildings. The need for reinforcement is complex and a simplified explanation is given as background information for detailers.

very uneven and will be considered as unserviceable. 18.1.4 Reinforcement for Slabs on the Ground Slab on ground reinforcement is generally

18.1.1 Purpose Concrete pavements and floors are cast against

placed in one grid, the most common layout being with

the ground with either a natural earth surface or on a

equal amounts of steel each way. The reasons for this

prepared sub-base. They provide a long-lasting surface

are:

for foot and wheeled traffic.

■

stresses, upwards and downwards, from vertical

18.1.2 Method of Load-Carrying by

loads of wheels and soil movements. The effect

Slabs on the Ground

of upward forces tends to “dome” the top

They carry their applied loads directly to the

surface of the slab, thus creating a tensile stress

foundation by bearing rather than by the bending

zone there.

resistance of a suspended slab.

For this type of load, the steel grid should be

These concrete are used as roads and factory floors, as well as in residential housing for

placed in the top of the slab. ■

floor slabs, footpaths and driveways.

resist this effect, the steel grid should be located

bottom and top reinforcement will be necessary.

Although a heavy load such as a wheel will cause both the slab and the foundation to deflect downwards, the slab thickness should be designed so the tensile stresses due to bending are low compared to those in suspended slabs. An even greater force can be exerted on a ground slab by vertical movements of the foundation itself. These movements are generally caused by changes to the moisture content of the soil – such as water penetration after rain or by reduction of the moisture content by the roots of trees. Vertical

Shrinkage of the concrete causes uniform tensile stresses through the full depth of the slab. To

To carry loads over soft-spots in the foundation,

18.1.3 Causes of Lack of Serviceability

Reinforcement is required to resist the bending

approximately mid-depth. ■

When the sun heats a slab, it has the tendency to curl at the corners and lift off the ground there. When traffic rides over the corners, it will create a tensile stress in the top of the slab because of the loss of ground . To resist this loading, the slab should be reinforced in the top. On balance therefore, the steel reinforcing

grid is considered to be most effective when placed between mid-depth and the top of the slab. This has an advantage should the mesh be displaced downwards during concrete placement.

movements can be either up or down depending on climatic conditions.

18:1 Reinforcement Detailing Handbook

18.1.5 Control of Shrinkage Plastic shrinkage of concrete can occur within

18.2

AS 3600 REQUIREMENTS (Sections 4, 9 and 15)

the first few hours after casting; it cannot be controlled

Although the previous Chapters of this

by normal reinforcement because the concrete itself is

Handbook also require consideration of the exposure

too weak to carry the induced forces.

condition of the concrete surface, slabs on the ground

Drying shrinkage of concrete can take place

and pavements have needs additional to buildings.

if the slab is inadequately cured. Curing generally means maintaining the water content of the concrete

18.2.1 Exposure Classification and Abrasion

for several days, either by keeping the surfaces moist

Resistance (AS 3600 Sections 4.3 and 4.6)

or by covering the surface to prevent evaporation. The

The flowchart in Chapter 5 Clause 5.3 will give

effect of drying shrinkage is to cause a parallel-sided crack right through the concrete whether reinforcement

guidance here. If a steel reinforced pavement is being designed,

is present or not. Under vertical load and without the

then the exposure classification is based on a

dowel action of reinforcement, this crack can develop

reinforced member and will be subject to the various

into a step, and the slab becomes unserviceable.

climatic conditions. If the slab is to be considered as

The shrinkage stresses acting on the slab can

“plain” concrete, with or without steel reinforcement

be reduced by using slabs of small size, that is the

as allowed in AS 3600 Section 15, the lower exposure

slabs are poured with closely-spaced contraction ts

classification of AS 3600 Table 4.3 may be applicable.

through which are located steel dowel bars to prevent

In any case, exposure of the top and bottom surfaces

vertical movement. Steel reinforcement may or may not

must be determined.

be used. Reinforcement enables larger slabs to be

Overriding the exposure conditions are the requirements for abrasion given in AS 3600 Clause 4.6.

poured, and the amount of steel in each direction

It may therefore be found that the higher strengths

increases with length. Any reinforcement which does

needed for this purpose will allow the reinforcement to

cross a shrinkage crack automatically acts as a dowel

play a more active part by permitting larger slab sizes,

bar.

reduced ting and better serviceability. If a slab is much longer than it is wide, such

as a road pavement, then the amount of steel in the trafficked direction will be much greater than that across the pavement. In fact, when the longitudinal steel area is approximately 0.6% to 0.7% of the concrete area, shrinkage cracking is totally controlled and the pavement does not need any contraction or expansion ts at all even over several kilometres – this is called a “continuously reinforced concrete pavement” or CR.

18.2.2 Cover (AS 3600 Clause 4.10.3.2 and Section 5.5) Obviously the top surface will have a different exposure classification from the bottom. By detailing the steel to be in the top, this should help to provide for any differences in cover, although the thickness of the steel grid itself must be allowed for. Table 5.1 will be used in combination with Tables 5.2 and 5.3 as appropriate. As a guide to steel fixers and for better depth control, it is preferable to specify the height of the above ground rather than cover from the top surface.

18:2 Reinforcement Detailing Handbook

Example 18.1 A reinforced slab is to be cast in the open air on a non-aggressive soil, without a “damp-proof” membrane, and in a near coastal zone. From Clause 5.3, the top surface would have a B1 exposure and the bottom surface an A2 classification. A Grade 32 concrete is required for the worst situation, B1. If the purpose of the slab is to carry traffic, Grade 32 concrete is stated as being adequate for medium to heavy vehicles. The applicable covers with Grade 32 concrete are 40 mm top from Table 5.1 for exposure B1, and 45 mm bottom from Table 5.3 for exposure A2 when cast directly on the ground. Allowing for a total thickness of the steel mesh of 20 mm, then the slab should be at least 105 mm thick. Normal pavement design may show that a greater thickness would be needed for heavy traffic. This example illustrates the need for some care when specifying cover for slabs on the ground.

18.2.4 Plain Concrete (AS 3600 Section 15) Plain concrete may contain reinforcement for various purposes but its strength is not taken into . It is therefore possible to use the reinforcement for shrinkage control of plain concrete without calculations being needed. 18.2.5 Concrete Pavements, Floors and Residential Footings (AS 3600 Section 16) These are additional design considerations which involve investigation of the foundation. Residential floors and footings designed in accordance with AS 2870 should be detailed using the examples given in that standard. They are too numerous to give in this Handbook, although the general principles given here are still applicable. 18.3

DETAILING SLABS ON THE GROUND The same principles as for suspended slabs

18.2.3 Crack Control for Shrinkage and Temperature Effects (AS 3600 Clauses 9.4.3 to 9.4.5) The maximum spacing of reinforcement for

may be used, with modifications as necessary. Generally, plan-views are adequate with cross-sections used to give details of two layers of steel. ■

reinforcement is usually located between mid-

control of cracking due to flexure does not apply to

depth and the top surface.

slabs on the ground. (See AS 3600 Clause 9.4.1). Nevertheless, a maximum spacing of either 2D

■

and spacing. Sections would show the type

AS 3600 Clause 9.4.3 applies to slabs on

of load transfer device (dowels or continuous

the ground as well as to suspended slabs. The

reinforcement) between each slab. Edge

designer should decide the degree to which the slab

thickening may also be shown in cross-sections.

will be restrained, and then calculate the amount of

All necessary dimensions should be given in

reinforcement required.

cross-sections.

AS 3600 Clauses 9.4.4 and 9.4.5 may require ■

Typical details may be used provided the applicable positions are identified on the plan-

the slab to a rigid restraint and where openings,

view and irrelevant details are omitted.

discontinuities and re-entrant corners occur. Previous experience rather than calculations may be used.

Contraction and isolation ts must be defined on the plan-view to show location, shape

or 300 mm should be considered.

additional reinforcement in the areas which connect

Reinforcement depth. As mentioned, slab

■

Cross-sections should show any “damp-proof” membrane under the slab and footings.

■

Special foundation preparation can be given in a general note. For road pavements, a separate specification may be essential.

18:3 Reinforcement Detailing Handbook

18.4

SPECIAL DETAILS FOR SLABS ON THE GROUND

18.4.1 Re-Entrant Corners and Holes These interruptions act as crack initiators. Extra reinforcement extending a full development length past the opening should be used. 18.4.2 Separation of Ground Slabs from Columns At the point where columns through the ground slab to the footing, the two elements must be separated by an isolation t (called ‘ij’ in

18.5

MESH IN SLABS ON THE GROUND Because the stresses in these slabs are

generally the same in both directions, mesh is the most common reinforcement. However, the mesh need not be limited to a square mesh if the slab dimensions require otherwise. Mesh can be produced to fit the layout of the slabs between contraction ts or can be trimmed to shape on site. The steel area cut out for holes should be replaced by bars or a mesh strip. Mesh in plan view is detailed as in Figure 14.11.

Figure 18.1). Such ts must not create a re-entrant

Side laps, end laps and cover should be specified

corner where they intersect; if possible, they should

in a general note. All laps should be made as shown

intersect at the columns so that contraction due to

in Clause 6.9, that is, a “two-wire” overlap of the

shrinkage will tend to pull the slab away rather than

transverse wires.

impose a horizontal force there. See Figure 18.1 for suitable arrangements. The slab and column concrete should be separated by a suitable membrane. Ground slabs should also be isolated vertically from the footing to limit any additional loading, unless this is part of the footing design. 18.4.3 Location of Contraction ts (cj) A complete floor is generally broken up into

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smaller areas for casting the concrete. The pouring sequence may be specified in the drawings if an

�������������������������������

instruction is needed. Contraction ts should be continuous across the floor or pavement. Do not allow a t to stop

��

at the centre of an adjacent slab or the latter will be cracked if movement or shrinkage occurs. Publications of Cement Concrete & Aggregates

��

Australia have more complete information on selecting the size of slabs and provide methods of arranging the

��

reinforcement and ts. ���������������������������������������������������������

��������������� ��

�� ��

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Figure 18.1 Location of Contraction ts and Isolation ts in Slabs on the Ground 18:4 Reinforcement Detailing Handbook

19 Bridges – Civil Structures 19.1

GENERAL The Australian Standard for Bridge Design was

first published in 2004 as AS 5100 with Part 5 being Concrete. 19.2

REASONS FOR DIFFERENCES The design of bridges differs from that of

buildings in some of the following ways: ■

The loading is heavier than in the majority of buildings.

■

The loads are generally point loads, and are often considered as a series of moving pointloads.

■

Structural continuity is often not available; for example, many beams are simply ed.

■

The bending-moment and shear force diagrams are not for specific static load applications, but are envelopes of “worst case” scenarios for moving imposed loads.

■

Important factors to be considered include impact forces, vibration, creep and shrinkage, etc, and parasitic effects of prestress, thermal loading and differential settlement in continuous bridges.

■

Virtually all environments are external and in many cases aggressive external and consequently a greater emphasis is placed on concrete durability. Because of these effects, there are no

“deemed-to-comply” provisions for detailing of bridges in the Bridge Design Standard, Part 5 Concrete. Appendix A of this Handbook gives information on variations between AS 3600:2007 and the AS 5100:2004. Each State Road Authority has a wellestablished detailing standard which will take precedence over this Handbook.

19:1 Reinforcement Detailing Handbook

19:2 Reinforcement Detailing Handbook

A

■

Exposure classifications (AS 5100 Part 5 Clause 4.3) “A1” and “A2” from AS 3600 are

Summary of Bridge Design Standards (Section 5) and the Concrete Structures Standard

combined into classification “A”, and a new topic for “ in salt-rich desert areas – C” is added. ■

Specification of concrete (AS 5100 Part 5 Clauses 4.4 to 4.8) can be regarded as similar

A.1

but there are minor differences. There is no

GENERAL

Grade 20 concrete in the AS 5100.

Full details must be taken direct from the actual standard for either Bridge Design or Concrete

A.3.2 Cover (AS 5100 Part 5 Clause 4.10)

Structures.

■

Concrete cover for concrete placement (AS 5100 Part 5 Clause 4.10.2). Limits on spacing of

A.2

reinforcement, ducts, tendons, etc, are fully

PRELIMINARY DESIGN REQUIREMENTS

defined, unlike AS 3600 Clause 4.10. More A.2.1 AS 5100 Part 5 Section 1,

emphasis is placed on tendons and ducts. In

Scope and General

particular, the minimum cover to the nearest

Minor differences occur between Clause 1.4 of

steel is 1.5 times the nominal maximum size

AS 3600 and the equivalent Clause 1.6.2 of AS 5100

of aggregate, whereas AS 3600 Clause 10.4.2

Part 5 on the information to be shown on the drawings.

requires 1.0 times that size.

A system of notation for variables is provided in Part 5

■

Clause 1.4.

Part 5 Clause 4.10.3). AS 3600 Clauses 17.5.3(a), tolerances, and 17.1.3 formwork and

A.2.2 AS 5100 Part 5 Clause 2.8, Cracking

compaction, are located in this Section because

Clause 2.8 is in addition to the requirements

AS 3600 Section 17 is not included in AS 5100.

of AS 3600 and is referenced by Clauses 8.6 (beams)

■

and 9.4 (slabs). It requires that one or both faces of

Selection of cover for corrosion protection. The general procedures set out in the Reinforcement

concrete are to be reinforced with a minimum

Detailing Handbook are applicable, but the

area of steel of 500 mm2 per metre of face depending

principles used, and values of cover given in the

on the member’s thickness, spaced at 300 mm

AS 5100 are quire different.

maximum. A.2.3 AS 5100 Part 5 Clause 3.2,

Cover for concrete protection (AS 5100

The AS 5100 Part 5 values of cover in Clause 4.10.3 are from 5 mm to 20 mm greater than

Load Combinations

the corresponding values in AS 3600 Clause 4.10 or in

These are covered in AS 5100 Part 2.

Chapter 5 of this Handbook due to the design life of the Bridge Design Standard being a minimum of 100

A.3

DESIGN FOR DURABILITY

years.

(AS 5100 Part 5 Section 4) A.4 A.3.1 Exposure The overall thrust of both AS 5100 and AS 3600

METHODS OF STRUCTURAL ANALYSIS `(AS 5100 Part 5 Section 7) No simplified methods are included. This means

are very similar, but the detailed requirements differ

that the simplified and “deemed-to-comply” detailing

significantly. AS 3600 Clause 4.3.2 concession for

rules of the AS 3600 are not needed either.

exterior exposure of a single surface does not appear in AS 5100 Part 5.

The use of “design strips” for slab systems is not required in bridge design, and are therefore not included. AS 5100 Part 5 Clause 7.2.10 (equivalent to Clause 6.2.3 in AS 3600) gives more guidance on the critical Section for negative bending moments.

A:1 Reinforcement Detailing Handbook

BEAMS (AS 5100 Part 5 Section 8)

A.5 ■

(AS 5100 Part 5 Section 13)

Spacing of reinforcement, tendons and ducts (AS 5100 Part 5 Clause 8.1.7) have more explicit

■

STRESS DEVELOPMENT

A.8

■

rules than in AS 3600 Clause 8.1.9, where no

Clause 13.1.2, but the coefficients in the

values are specified.

formulae are different. To calculate values,

Detailing of flexural reinforcement (AS 5100 Part

the undersize tolerance on cover (AS 5100

5 Clause 8.1.8) requires that the extension of

Part 5 Clause 4.10.3.1(a)) must be subtracted

bars beyond the “worst-case” actual bending

from the nominal cover (Table AS 5100 Part 5

moment diagram is spelt out as

Clause 4.10.3.2) and the result applied as “a”.

“D + development length”, ie “D + Lsy.t” or

The “deemed-to-comply” values in AS 5100

“D + Lsy.c” as applicable. One-third of the total

Part 5 Table 13.1.2 can be read directly by

negative tensile reinforcement extends

applying the cover and f’c values from the Tables

“D + Lsy.t” past the “worst-case” point of

in Clause 4.10.3 because the tolerance has

contraflexure. There are no “deemed-to-comply” provisions for detailing. ■

Displacement of tendons in ducts (AS 5100 Part 5 Clause 8.1.9) is a new Clause but is more aligned with design than detailing.

■

Detailing of shear and torsion reinforcement (AS 5100 Part 5 Clauses 8.2.12 and 8.3.8) sets the maximum spacing of fitments at the smaller of 0.5 D and 300 mm. The corresponding

already been allowed for. Author’s note: Tables 6.1 to 6.4 in this Handbook may not yield the same result as AS 5100 Part 5 Table 13.1.2. The former are based solely on the value of “a” as shown so that if more cover is available, the values can still be read directly. The “nominal” cover, fitment size, tolerances, etc, are not taken into consideration – that is the designer’s decision. Also, in version 2007 of AS 3600 the formula is not the same as the 2001 version of AS 3600 and gives different values of development length (see Chapter 6).

AS 3600 Clauses 8.2.12 and 8.3.8 have some

■

AS 5100 Part 5 Figure 13.1.2 lists a full range of hook allowances. Values are consistent with

similar statements but there are differences with ■

The same formula is used as in AS 3600:2001

more detail given in the AS 5100.

AS 3600 Clause 17.2.3.2 and Table 6.5 of this

Crack control of beams (AS 5100 Part 5

Handbook.

Clause 8.6) requires attention because of

■

Lapped splices in tension should not be made

differences between design stresses and

at points of maximum stress, and not more than

reinforcement detailing. This item is critical in

50% of bars should lap at one Section (AS 5100

bridge design. The AS 3600 under Clause 8.6

Part 5 Clause 13.2.3). If the above cannot be avoided, the lap length is increased to 1.3Lsy.t.

has different requirements.

In effect, this means that the spacing factor k8 A.6

The differences between the AS 5100 and the AS 3600 require individual comparisons. A.7

increases by 30% from 1.7 to 2.2, from 2.2 to

SLABS (AS 5100 Part 5 Section 9)

2.9, and from 2.4 to 3.1. Author’s note: The AS 3600 values are believed to have already allowed for this situation in the election of the original values of k2.

Lap splices in compression should also be

WALLS (AS 5100 Part 5 Section 11) Minimum reinforcement is defined in AS 5100

staggered (AS 5100 Part 5 Clause 13.2.5).

Clauses 11.6.1, and the maximum spacing is the lesser of 1.5 tw and 300 mm. (Refer Clause 11.6.3).

A.9

SECTIONS NOT INCLUDED AS 3600 Sections 16, 17 (part only) has been

omitted from the AS 5100 although some parts of Section 17 are transferred elsewhere.

A:2 Reinforcement Detailing Handbook

B General Notes on Drawings

Loading L.1

This structure has been designed for the following superimposed loads: (i) Permanent actions due to:

This Appendix contains a check list of suitable General Notes in drawings, and is for guidance

General L.2

instructions as may be issued. G.2 IF IN DOUBT, ASK. G.3 Refer any discrepancy to the Engineer/ Architect before proceeding with the work. G.5 all setting out dimensions with the G.6 Materials and workmanship shall comply L.3

principles set out in the CIA “Reinforcement Detailing Handbook” of (date). G.8 All dimensions are in millimetres unless stated

capacity not less than (no.) kPa.

(no.)

Multiplier, Mi

(no.)

Shielding Multiplier, Ms

(no.)

Ultimate Vu

(no.) m/s

Working Vs

(no.) m/s

The design earthquake criteria to AS1170.4 are (Description) (no.)

Importance Factor, I

(no.)

Building Type

Type (no.)

Design Category

(no.) (Description)

Maintain structure in stable condition during Do not place or store building materials on concrete without engineer’s approval.

L.6

Place and trowel smooth and flat a layer of mortar (no.) mm thick on top of all loadbearing brick walls. Place approved non-compressible

Working capacity of piles shall be (no.) (tonnes Found bored piles on (material) having bearing

Topographic Multiplier, Mt

construction. L.5

non-adhering membrane on hardened mortar

or kilonewtons). F.3

(no.) (no.)

Building Frame System L.4

placing concrete. F.2

Region Terrain Category

Regular, Ductile

otherwise.

the (Engineer/Local Building Authority) before

The design wind criteria to AS1170.2 are as

Site Factor, S

G.7 Drawings are detailed in accordance with the

foundation material and obtain approval from

(no.) kPa

Acceleration Coefficient, a (no.)

really required and their date of issue).

of (no.) kPa founded on (material). such

(no.) kPa

Balconies

General Structure

shall be held on site; (list only those which are

Footings are designed for an allowable intensity

Stairs and landings

as follows:

of tender). Copies of the following documents

F.1

(no.) kPa

Basic Wind Speed

Engineer/Architect.

Foundations and Footings

(no.) kg/m run

Structural Importance

G.4 Dimensions shall not be scaled.

appropriate Australian Standards as at (date

(no.) kg/m run

External walls

follows:

and Specifications and such other written

with the Building Code of Australia and the

Partitions

Slabs generally

preferred for use in the Contract Specification.

Architects’ and other Engineers’ Drawings

(no.) kg/m run

(ii) Imposed actions on:

purposes only. A more descriptive wording may be

G.1 Read this drawing in conjunction with

Dividing walls

before pouring concrete. L.7

Concrete shall be separated from the top of non-loadbearing walls by an amount not less than (no.) mm.

B:1 Reinforcement Detailing Handbook

Concrete

Reinforcement

C.1 Concrete quality shall comply with

R.1

AS (no.):(date)

Symbols in drawings for grade and strength of reinforcement are:

(Complete as required. See Example C.1).

SL or RL denotes welded wire reinforcing mesh

C.2 Project assessment of concrete strength

to AS/NZS 4671:(date). L denotes steel reinforcing wire to

(is not/is) required.

AS/NZS 4671:(date).

C.3 Normal class concrete shall have cement of

N denotes hot-rolled deformed reinforcing bar

type (list). C.4 Mechanically vibrate concrete in the form to give maximum compaction without segregation

to AS/NZS 4671:(date). R.2

Bar notation gives the following information in this order:

of the concrete.

No of bars; grade; bar size (mm); spacing (mm,

C.5 Cure concrete as required by Section 17 of

if required), placing information.

AS 3600 and as set out in the Specification.

Eg, 20-N16-200-BOT.

C.6 In the drawings, the beam depth is written first R.3

and includes slab thickness if any.

Mesh notation gives the following information in this order:

C.7 Strip footing depth is written first followed by width.

SL or RL symbol; AS reference number if

C.8 Concrete sizes as drawn are minimum and do

standard mesh or special code if non-standard

not include applied finishes.

mesh; placing information.

C.9 Do not make unspecified construction ts

Eg, RL918 TOP. R.4

without engineer’s approval.

Main wires of mesh and coverage of sheets shown in plan-view and elevation thus:

C.10 Do not make unspecified holes or chases without engineer’s prior approval. C.11 Do not place conduits, pipes and the like within

�����������������

cover concrete. ������������ �����������������

����������������

�����������

Example C.1: Specification of concrete requirements Required properties of concrete in accordance with AS 1379 Structural Element

Exposure Class and Slump at site Nom. Max. Method of Strength at (No.) Classification Grade ± 15 mm Aggregate Size Placement Days MPa

Name

List

N (no.) S (no.)

mm

mm

Pump, etc

Examples: Roof Slab Super-Flat Floor

B1 U

N32 S40

80 40

20 40

Pump Not required From chute 40 MPa at 28 days

B:2 Reinforcement Detailing Handbook

Value in MPa

R.5

R.9

Extent of bars and mesh shown thus:

Where lapping is specified, mesh shall be lapped such that the two outermost wires of

�����������

one sheet overlap the two outermost wires of

������������������

the other sheet as shown: �������

��������������������� ��������������

R.6

Reinforcement is represented diagrammatically

R.10 Welding of reinforcement including tack-

and not necessarily in true projection.

welding for fixing purposes shall comply with

R.7

Reinforcement dimensions shall not be scaled.

AS 3600:(Date) and AS 1554.3:(Date). Welding

R.8

Lap reinforcement only at locations shown in

is permitted only where shown in the drawings or where otherwise approved by the engineer.

the drawings. Lap length shall comply with

R.11 Fix distribution bars (grade and size + spacing)

AS 3600. (See Example R.8)

where shown unless specified otherwise. R.12 Fix (no, grade and size) trimming bars around openings in (each/top/bottom) face of member and extending (mm) beyond their cross-over point. R.13 In drawings, the following abbreviations mean: Example R.8: Specification of lap splices in a drawing Reinforcement shall not be spliced except where shown

Each way

EW

Top or top-face

T or TOP

Each face

EF

in the drawings. The splice length of bars shall be as given in the

Centrally placed

CENTRAL

following table, except where other dimensions are stated on the

Near face

NF

actual detail.

Bottom or bottom-face

B, BOT

Far face

FF

Internal face

INTF

Horizontally

HORIZ

External face

EXTF

Vertically

VERT

At centres (bars)

CTS

Maximum

MAX

Continuous

CONT

Minimum

MIN

Typical

TYP

Tensile lap length (mm) for Grade 500N deformed bars Bar size (mm) Cover Type of f’c member (MPa) (mm) N12 N16 N20 N24 N28

N32 N36

Slab or Wall

-

25

Other main bars 25

20 25

300 500 750 300 450 650

40-45 300 400 550 50-60 300 400 500

850 -

-

800 1050 1300 1550 650 900 1100 1350

Embedment lengths for starter bars and splice lengths for column bars shall be as given in the following table, except where other dimensions are stated on the actual detail. Bar Size (mm)

Straight embedment in footing of 20 DIA. (mm)

N20

400

640

1-R10 or 1-L7

N24

480

770

2-R10 or 1-L9

N28

560

900

2-R10 or 1-L10

N32

640

1030

1-N12 or 1-L11

N36

720

1160

2-N12 or 1-L12

Splice length of 32 DIA. (mm)

Number of fitments at column bar crank

B:3 Reinforcement Detailing Handbook

R.14 Reinforcement shall not be cut, bent or heated on site without the engineer’s prior approval. R.15 The deviation of reinforcement from its specified

Formwork F.1

Formwork shall comply with AS 3610:(Date)

F.2

The contractor shall submit proposals for

position shall not exceed the following (mm): (a) For positions controlled by cover:

formwork at commencement of job. F.3

(i) in beams, slabs,

Section 17.6 of AS 3600:(Date).

columns and walls

-5, +10

F.4

Remove all props and formwork from beams

(ii) in slabs or ground

-10, +20

and slabs before constructing walls and other

(iii) in footings cast in the ground

-20, +40

ed items upon them.

where a negative value indicates a decrease in specified cover, and a positive value indicates an increase in specified cover. (b) For positions not controlled by cover: (i) the location of tendons on a profile

5 mm

(ii) the position of ends of reinforcement

50 mm

(iii) the spacing of bars in walls and slabs and of fitments in beams and columns

the greater of 10% of spacing or 15 mm.

R.16 Spacers and s shall be located at centres close enough to prevent displacement of reinforcement by workmen or equipment during fixing and subsequent concrete placement within the tolerances given in R.15 above. R.17 The cover to the reinforcement nearest the concrete surface shall not be less than the following except where specified otherwise: Example R.17: Member Location

Stripping of formwork shall comply with

Required Exposure Concrete Cover Classification f’c (MPa) (mm)

Internal beams A1 A2 Internal slabs External beams B1

25 25 32

B:4 Reinforcement Detailing Handbook

20 to fitments 30 40 to fitments

C Checking of Concrete Drawings The drawings detailing the concrete along with the General Conditions of Contract, Special

Checking Procedure The following checking procedure should be adopted for all jobs prior to any issue for tender or construction. If for any reason this does not appear practical, you should give early advice to your superior to enable appropriate action to be taken. ■

is available for building projects – if not, procure

Conditions of Contract and the Specification are the

them before commencing – provided time

usual documents, which form part of a contract. They therefore have legal status. Calculations are a one means of carrying out a design but they have no legal

allows. ■

the original drawings if they are in negative

Drawings are used to convey your designs onto

form (generally plans and elevations) over the

paper so the building or civil engineering project can

Architect’s drawings and checking walls, set

be built. As such, they are a vital element of any project

downs and general arrangements. Also check

and the quality and accuracy of drawings can make

the Architectural Sections and details for

or break a project. There will never be a complete and

conformity being careful to note the words “to

total accurate set of documents. However, incomplete

Engineer’s detail” to ensure you have provided

or inaccurate information is one of the greatest risks to

these items which the Architect has assumed

any project.

you are showing. If your drawings say “to

ALL Engineers should be responsible for

Architect’s detail”, make sure the Architect is

detailed checking of their design and checking the is correctly shown on the drawings. Project Engineers

Check structural drawings to ensure they comply with architectural drawings. Start by laying

status.

resultant drawings progressively to ensure their design

Ensure that a set of final Architectural Drawings

aware of this. ■

Fully check civil and structural drawings for content, detail, drafting and general adequacy.

should be responsible for detailed checking of all

Pay special attention to critical detailing and

design and resultant drawings irrespective of whether

connections. Every line and word should be

they personally did the work or not.

individually checked. ■

Look at the drawings and ask yourself is there enough information on the drawings to build it – dimensions, concrete strengths, section, etc. Can it be built as it is shown, with the details as drawn? When the Project Engineer has checked the

job and verified it (only then) should it be ed to a senior member of the office for an independent check and review. The project should be presented as a complete package – all drawings, computations and specification together with a checking sheet wherever possible. Drawings SHOULD NOT GO OUT as final drawings for tender or any other contractual purpose until this final check has been completed.

C:1 Reinforcement Detailing Handbook

Problem Areas The following project or areas have been identified as high risk areas in structural design. Careful attention must be given to these by all engineers: ■

Errors in reading drawings by contractor (poor documentation).

■

Design errors.

■

Inadequate geotechnical information.

■

Inadequate survey of existing services, levels, features, etc.

■

Multi-storey car parks.

■

Roofs of all kinds.

■

Sag and creep in reinforced concrete.

■

Durability of concrete (ie cover and inadequate inspection on site).

■

Post-tensioned and prestressed concrete including shrinkage.

■

Factory and warehouse floors (slab-on-ground).

■

Cracking of concrete.

■

Fairground and amusement equipment.

■

Cladding on multi-storey buildings.

■

Retaining walls.

■

Construction ts in concrete running through hard finishes such as tiles, vinyl, etc, resulting in unsightly cracking.

■

Inadequate control ts in masonry walls for brick growth, deflection of suspended beams and ground movements. that most professional (liability)

claims come from misunderstandings created by the Contract Drawings.

C:2 Reinforcement Detailing Handbook

D Bibliography A number of other publications which may also be useful to obtain additional information on detailing of reinforcement in concrete structure are listed below, in no specific order. 1 Reinforced Concrete Design Handbook (T38) Cement Concrete & Aggregate Australia, 2002. 2 Precast Concrete Handbook (Z48) National Precast Concrete Association Australia and Concrete Institute of Australia, 2002. 3 Concrete Structures, Warner, R.F., Rangan, B.V., Hall, A.S., and Faulkes, K.A., published Longman, Melbourne, Australia,1998. 4 Manual for the Design of Reinforced Concrete Building Structures, The Institution of Structural Engineers and The Institution of Civil Engineers, Second Edition 2002. 5 Structural Detailing in Concrete, Bangash, M.Y.H. published by Thomas Telford Books, UK, 2003. 6 Detailing Manual (Sp66) American Concrete Institute, 2004. 7 Standard Method of Detailing Structural Concrete : A Manual of Best Practice, Institution of Structural Engineers and The Concrete Society (3rd Edition) 2006. 8 Reinforced Concrete Structures, Park, R., and Paulay, T. published by John Wiley and Sons.

D:1 Reinforcement Detailing Handbook

Concrete Institute of Australia RECOMMENDED PRACTICE

Z6

Reinforcement Detailing Handbook

RECOMMENDED PRACTICE

Reinforcement Detailing Handbook For Reinforced and Prestressed Concrete

Z6