There are four types of girder bridges, classified depending on the construction material and type of girders used. A rolled steel girder bridge is built using I-beams made from prefabricated steel, while a plate girder bridge is constructed by welding flat pieces of steel together on-site to make the I-beams. Concrete girder bridges are constructed using concrete I-beam girders that can be made from various kinds of reinforced concrete, including pre-stressed concrete and post-tensioned concrete. A box girder bridge can be made from either steel or concrete, and uses box girders to support the bridge deck.
Whether I-beam girders or box girders are used to construct a girder bridge depends on various factors. It is easier and cheaper to build and maintain a girder bridge using I-beam girders. However, these girders do not always offer sufficient structural strength and stability if the bridge is very long or the bridge span is curved, because they are sensitive to the twisting forces, or torque, such a span is subject to. Box girders are preferred for such bridges. There have been concerns raised of corrosion of box girders, especially if rain water seeps into the open space inside the girders.
Girder bridges belong to a category of bridges called beam bridges. This category of bridges includes girder bridges, truss bridges and trestle bridges. Beam bridges can be constructed by using a wide variety of materials including stone, timber, steel, iron, and concrete. An example of a basic type of beam bridge is a log or slab of stone laid across a creek.
Credit: Written By: M. Haskins