Bridge Superstructure

Bridge Superstructure

The loads coming over bridge superstructure are taken by following actions in individual members

• Bending ( Flexure and Shear in Member)
• Axial elongation or axial shortening ( Tension or Compression in Member)
• Combination of Bending and Axial Deformation (Flexure, Shear and Tension/Compression)

Girder Bridges

In this structural form the loads are taken fully by bending of superstructure. In this type of superstructure the loads are taken by members as flexure and shear. The design of superstructure is governed by flexure, shear and deflection criteria. Girder bridges can be anyone of following type

• Solid Slab ( Span 4m – 12m)
• Voided Slab ( Span 8m-16m)
• T Girder ( Girder and Slab) ( Span 12m-25m)
• Box Girder ( Single or Multi Cell) (25m – 60m)

The girder can be simply supported between two adjacent piers or continuous over more than one pier. The Continuous girder provide following advantage over simply supported girder

· Shallower depth superstructure compared to simply supported girders

· Reduce number of expansion joints

· Reduce number of Bearing required to support superstructure

· The continuous girders have redundancy

The continuous girders are not used under weak soil foundation. The settlement of support (Un-even settlement) will generate additional moments and shear in superstructure in case of continuous girder.

In Girder only extreme fibres are only stressed to maximum limit.

Truss Bridges

In this structural form the loads are taken by axial deformation of individual members. In truss bridges the loads are taken by members as axial tension or axial compression. Under axial tension/compression action all fibre of section are stressed to same limit. Hence truss bridges are best structural form for long spans. The truss bridge can be through type or deck type based on traffic movement.

The truss bridges are of following type

• Pratt Truss
• Warren Truss
• Modified Warren Truss
• K Bracing Truss