Girder Bridge

In a plate girder bridge, the plate girders are typically I-beams made up from separate structural steel plates (rather than rolled as a single cross-section), which are welded or, in older bridges, bolted or riveted together to form the vertical web and horizontal flanges of the beam.

The use of plate girders rather than rolled beam sections for the two main girders gives the designer freedom to select the most economical girder for the structure. The steel main structure is much easier to erect if compared to the construction of a concrete girder and the light structure imposes smaller loads on piers and foundations, allowing for economic design of the substructure. In some cases, the plate girders may be formed in a Z-shape rather than I-shape.

Plate girder bridges can be of steel and concrete composite construction or executed completely in steel.