Type and Shape Of Substructure
Plate type of piers is considered appropriate for bridges on river / stream / canal. Alternatively single circular piers with cantilever pier cap may also be used. Multi-column piers are not desirable in bridges over canals / streams as floating debris, trees, timber logs on the stream may get entangled in the pier frame resulting in obstruction to flow and hydraulic loss in case of canal structures. Piers shall be placed parallel to the flow direction under HFL condition. Suitable cut waters shall be provided at the ends to ease the water current force.
For urban interchange structures and road over bridges, the pier shape is extremely important from aesthetic considerations. The piers should look lighter and less massive. It may be useful to adopt multi-column circular piers in this cases. Elimination of pier caps by providing bearings directly over columns is also useful in achieving lightness and smooth transition between substructure and superstructure. In order to enhance the aesthetics, the columns may be provided with vertical grooves.
The abutments in case of bridges on canal / streams shall be solid cantilever type having a wall face in front. Spill through abutments may be provided in cases where the front of the abutment is well protected by means of a suitably designed stone pitching and launching aprons.
In case of urban interchange structures, the wall face of the abutment needs architectural treatment to break the feeling of massiveness. The wall face can be used to form sculptural treatment (say embossing logo of the concessionaire & client) or with vertical grooves.
Figures below shows the appropriate type of substructure for different boundary conditions.
Choice of Appropriate type of Pier
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