different types of structural systems are used in bridges depending
upon the span, carriageway width and types of traffic. Classification,
according to make up of main load carrying system, is as follows:
Girder bridges -
Flexure or bending between vertical supports is the main structural
action in this type. Girder bridges may be either solid web girders or
truss girders or box girders. Plate girder bridges are adopted for
simply supported spans less than 50 m and box girders for continuous
spans upto 250 m. Cross sections of a typical plate girder and box
girder bridges are shown in Fig. 2(a) and Fig. 2(b) respectively.
Truss bridges [See Fig. 2(c)] are suitable for the span range of 30 m
to 375 m. Cantilever bridges have been built with success with main
spans of 300 m to 550 m. In the next chapter girder bridges are
discussed in detail. They may be further, sub-divided into simple
spans, continuous spans and suspended-and-cantilevered spans, as
illustrated in Fig. 3.