Chapter 12 Maximum Deflection in Bridges

The elastic deflections of girders due to L.L. (without dynamic effect) shouldn’t exceed:- Category Max allowable deflection Railway bridgesL/800 Roadway bridgesL/600 Structural buildingsL/300 Crane track girdersL/800

To cancel the deflection due to dead load a cumber is done during the construction of the beams or trusses, where the structure will be have the required shape after erection. In case of suspension bridges the cumber is done by adding both the deflection due to D.L. and L.L. into consideration. The minimum sections to be used in structural steel works shall be as follows:-

Section Railway bridges Roadway bridges Structural buildings Equal angles unequal angles S.I.B. No20No16 No12 Channels No16No12 No8 Plates mm88mm 5mm Gusset plates for main truss 12mm10mm 8mm 75  75  865  65  745  45  5 75  50  865  50  745  30  5