Bridge components

Bridges components with their sketch

1. Bridge

2. Introduction A  bridge  is a structure built to span a physical obstacle, such as a body of water, valley, or road, without closing the way underneath. Most likely the earliest bridges were fallen trees and stepping stones, whileneoliyhiv people built  boardwalk  bridges across marshland. It is constructed for the purpose of providing passage over the obstacle, usually something that can be detrimental to cross otherwise.

3. Structural Components of bridges

4. Components of bridges 1. Foundation 2. Abutement 3. Pier 4. Pile cap & pile 5. Girder Or beam 6. DecKs 7. Bearing in bridges 8. Wing wall & the returns 9. Parapet & handrail/ guird rails/ curb 10. Bridge anchor

5. Foundation which holds the shallow or deep base of the bridge and transfers it’s load to the bearing strata, this includes foundations below the main span of the bridge and the abutments below starting points of the bridge

6. Foundation are structures constructed to transmit the load from the piers, abutments, wing walls and the returns evenly on the strata. The foundation provided for bridge structures are deep in sufficient manner to avoid scouring due to the water movement or to reduce the chances of undermining.

7. Abutment Abutments are vertical structures used to retain the earth behind the structure. The dead and the live loads from the bridge superstructure is supported by the bridge abutments.

8. Abutment The abutments are also subjected to lateral pressures mainly from the approach embankment. The design loads on the abutment is mainly dependent on the: Type of abutment selected The sequence of construction The special care has to be provided for the foundations of abutments. The abutment foundation must overcome the problems of differential settlement and excessive movements caused due to lateral forces or loads.

9. Pier The piers are vertical structures used to support deck or the bearings provided for load transmission to underground soil through foundation. These structures serve as supports for the bridge spans at intermediate points. The pier structure has mainly two functions: Load transmission to the Foundation Resistance to the horizontal forces

10. Pier Types of Piers in Bridge Construction There are different types of piers based on the structural connectivity, the shape of the section and the framing configuration. Based on the structural connectivity, the pier can be classified as  monolithic or cantilevered. Based on the shape of the section pier can be classified as  solid or hollow, hexagonal, round or octagonal or rectangular. Based on the framing configuration the pier can be classified as single or multiple column bent, hammerhead or pier wall type.

11. Pier Most of the cases, piers are designed to resist the vertical loads alone. In areas which lie in the seismic zone, it is recommended to design the pier for lateral loads also. Most of the piers are constructed using concrete. Steel for the construction of pier is used in very few cases till now. Use of composite columns i.e. steel columns filled with concrete is used as new technology of pier construction. The pier is a vertical member that resist the forces by means of shear mechanism. These forces are mainly lateral forces. The pier that consist of multiple columns are called as  bent

12. Pile Cap & piles Pier cap is the topmost part of a pier which transfers loads from superstructure to the pier. It is also known as headstock. It provides sufficient seating for the girders and distributes the loads from the bearings to the piers.

13. Pile is a slender member driven into the surrounding soil to resist the loads. Pile cap is a thick reinforced concrete slab cast on top of the group piles to distribute loads.

14. Girder or beam Beam or girder is the part of superstructure which bends along the span. The deck is supported by beams.

15. Decks The decking is considered as the road or the rail surface of the bridge. The decks are supported by the girders or the huge beams that is in turn supported by the piers. The whole arrangement is supported with a deep foundation mainly piles and cap arrangement.

16. Bearing in bridges The loads received by the decks are properly and safely transmitted to the substructure with the help of bearings. These are components of bridge that enables even distribution of load on the substructure material. This transmission is very essential in situations where the substructure is not designed to take the load action directly.

17. The bearings in bridges allows the longitudinal movement of the girders. This movement is created due to the forces acting on the longitudinal direction. The forces due to the moving loads and the variation in temperature are the main causes for longitudinal forces. The selection of bearing is dependent on certain parameters, which are: Loads acting, the geometry, the extent of maintenance, the clearance available, the displacement, rotation and deflection policy, availability, preference of the designer, the construction tolerances, and the cost criteria. For the bridge design, all the above-mentioned aspect is considered for the design and the choice of bearings. The designer must consider the bearing arrangement in the bridge construction as a separate system.

18. Wing wall & the returns Structures constructed as an extension of the abutments to retain the earth present in the approach bank are called wing walls. This portion will otherwise have a natural angle of repose. These are retaining walls constructed adjacent to the abutments. This wall can be constructed either integrally or independent with the abutment wall.

19. The rear of the wall must consider three design loads while designing. This includes: The earth pressure from the backfill The surcharge from the live loads or the compacting plant The hydraulic loads from the saturated soil conditions The stability of the wing wall is mainly based on its resistance against the active earth pressures. The structural elements of the bridges are hereby designed and constructed to resist the earth pressures at rest.

20. Parapets and Handrails/ Guard Rails or Curbs These components of bridges are not of structural importance, but provided for the safety concerns. These are provided above the decks. This will help in prevention of the vehicle from falling off the bridge into the water body below or as a means for the separation of traffic streams.

21. Bridge anchor Bridge anchor is only used in suspension and cable-stayed bridges to resist the pull from suspension cable or counter span of the bridge