Slab Bridge 454s57

Aalto University School of Engineering Department of Structural Engineering and Building Technology Rak-11.3001 Design of Bridges

10.10.2012

Slab Bridges Teemu Ahonen Martina Jurigova

Contents 1 Introduction

2

1.1 Present day definition

2

1.2 General definition

2

2 Classification

3

2.1 Main parts of the slab bridges

3

2.2 Types of slab bridges (material)

3

2.3 Types of slab bridges (structure)

3

2.4 Another method of classification

4

3 Cross sections

5

3.1 Different cross section

5

3.2 Different types of cross section

5

4 Structural behaviour

5

4.1 Design phases

6

4.2 Analysis

.6

4.3 Reinforcement concrete T-beam bridges

7

4.4 Construction

8

1 Introduction Slab bridge is probably the most common bridge type. It is mainly used in crossings and over waterways and also as an under for walkways. Slab bridge has two fundamental features compared to other bridge types. First its superstructure is substantially wide compared to the height of the slab. Secondly by reason of the former, slab bridges can divide loading to a very broad area. Slab bridges have usually a span length of 10…20 meters and it would be good to make the slab continuous over more than one . Structurally it would be economic if all middle span length proportions would be equal and edge spans would be 80% of this length. 1.1 Present day definition A bridge with a superstructure that is composed of a reinforced concrete slab that is either singular, constructed in place, or a series of narrow, precast slabs. This slab is parallel with the roadway alignment and spans the space between the ing abutments or other substructure parts. 1.2 General definition A bridge with a superstructure that is composed of a slab that is either singular, constructed in place, or a series of narrow, precast slabs.(The material often used in early times are stones and timber) A short- bridge consisting span of a reinforced-concrete slab resting on abutments.

Fig 1. . Štefánikův Bridge in Prague

2 Classification 2.1 Main parts of teh slab bridge

Fig 2. . Main parts 2.2 Types of slab bridges (material) • • • •

Timber slab bridges Stone slab bridges Steel slab bridges Reinforcement concrete slab bridges

2.3 Types of slab bridges (structure) •

Slab bridges: Structure comprises a slab, ed at it ends. Usually made of concrete(with reinforced),also possible in laminated timber.

•

Beam-slab bridges(Slab girder bridges): Structure comprises one or more beams. Commonly used for simple bridges with a span of up to 200 metres. The beam height is roughly 1/20th of the span, made of steel concrete or timber.

Fig 3. . General types 2.4 Another method of classification Slab bridge is the most common form in small span structures, and also can be divided into two types: overall structure and assembly structure (hollowcore slab and solid slab).

Fig 4.

3 Cross sections 3.1 Different cross section The height of the cross-section is determined by the longest span length. The height can be calculated with the equation h = 0,22 + 0,04·lmax , where lmax is the length of the longest span. The equation is very simple and of course the height depends also of the width of the slab, the number of s and the obliquity of the bridge. 3.2 Different types of cross section

Fig 5. Types of cross section

4 Structural behaviour The structural analysis of a slab bridge is based on different computer software and the software use mainly difference method or element method. A loaded slab bends in longitudinal and in transverse direction. The calculation of stresses caused by bending is a very complex mathematic problem and it is possible only in simple cases.

Fig 6. Bending in a slab due to loading

4.1 Design phases Design is a two-phase process: •

The first phase involves determining the design loads and their effects in of moment and shear forces

•

The second phase involves selecting that have sufficient strength to resist the effects of the intended loads on the bridge. Before considering the design process complete, the failure modes (lateral buckling, excessive deflection, end bearing, and so forth) as well as moment and shear must be checked

• 4.2 Analysis The analytical method only applies to slab bridges with the main reinforcement running parallel to the direction of traffic. The slab acts as a one-way slab in the direction of traffic . Area above the neutral axis acts in compression the reinforcing steel in the bottom of the slab carries all of the tension and the concrete carries no tension Only the moment capacity is determined for the slab since shear generally will not control in thin, reinforced-concrete Only a one-foot-wide strip of slab at the midspan should be considered. The longer the slab is in proportion to its width the more the slab is similar to a beam. In long span slab bridges the slab can be calculated as a beam and only in details the influence of the slab can be taken into .

Fig 7.

4.3 Reinforcement concrete T-beam bridges T-beams are used to obtain longer span lengths than those allowed by slab bridges

Fig 8. Reinforcement

4.4 Construction A slab bridge can be built as in-situ or prefabricated and the material in slab bridges is in actual fact always reinforced concrete. In-situ process is usually used in cantilevered slab bridges. Cantilevered slab bridges are typical bridges in underes when span length is 8…10 meters and over waterways with a span length of 10…18 meters. The economy of a cantilevered slab bridge is based on that the bridge type has no massive abutments. A prefabricated reinforced slab bridge is used in crossings, underes and over waterways with a span length of 4…10 meters. A prefabricated slab bridge is built up by using foundation, abutment and superstructure elements.

Fig 8. Aleksanterinkatu Street bridge in Porvoo

Literature [1]

Paavola, H. Loikkanen, P. Jutila, A. Sillanrakennustekniikan perusteet. First Edition. Otakustantamo. 1979. ISBN 951-671-201-0

[2]

Hambly, E.C. Bridge Deck Behaviour. Second Edition. Taylor & Francis. 1998.

[3]

Suomen Rakennusinsinöörien Liitto RIL ry. RIL 179 Sillat. Hangon Kirjapaino Oy. 1989. ISBN 951-758-196-3

[4]

http://alk.tiehallinto.fi/sillat/suunnit2.htm#tuottajat