Engineering and Construction

Girder bridges (Fig. 4.8) predominate over the previously described types for short and medium spans, and generally provide the most economic solution. For highway bridges composite deck construction is generally used unless the depth is very critical in which case half-through girders or through trusses may be necessary. Railway bridges frequently require to be of half-through or through form because of depth limitations; these are more suitable, being generally narrower. Pedestrian bridges are similarly suited to a half-through form so as to reduce the length of staircases and ramps, which can often exceed the length of the span itself. Highway, railway and pedestrian bridges of girder type for short and medium spans are further described below.

1 Highway bridges – composite deck construction   Composite deck construction (Fig. 4.9) should be used wherever the construction depth will permit. If possible, multiple spans should be made continuous over the...

2 Railway bridges – girder type  Many existing small-span railway bridges weather cast or wrought iron girders to which rails are fixed directly without use of ballast or half-through girders with trough floors.As...

3 Pedestrian bridges   A minimum clear deck width of 1.8m is usual, increased to 3.0m or 4.0m in busy areas or if a cycleway is also present. Steel provides an efficient solution because the entire cross-section...

Fig. 4.8 Girder type bridges. (a) Single span; (b) simply-supported spans; (c) cantilever and suspended span; (d) continuous; (e) continuous – curved soffit