Steel Bridge

a bridge with a steel span. Steel bridges are constructed for highways when large spans, that is, spans of more than 100–200 m, are involved. For railroads, steel bridges are used when the span is more than 40–50 m.

The principal designs of steel bridges are the girder, which is the most common, the arch, and the suspension. The roadway is made up of steel plates or reinforced-concrete slabs; in the latter case, the slabs bear the load integrally with the steel span, and the structure is called a steel-reinforced-concrete bridge. The end supports are usually massive and are most often of plain or reinforced concrete. In high bridges and overpasses, the above-ground part of the end support is sometimes made of steel.

In the construction of steel bridges, standardized structural members produced by the metallurgical industry are used in most cases. These members include plates, angles, H beams, and channels, as well as high-strength wire ropes and cable. Structures that must withstand great loads are usually made from high-strength steel, that is, steel to which alloying elements have been added. The components used in bridge construction are prefabricated at special plants and are assembled at the construction site. The advantages of steel bridges over bridges of other materials—light weight and the mechanization of production and assembly processes—account for the wide use of steel bridges; in many countries, most large modern bridges are made of steel. The structures, however, must be protected from corrosion. This protection is afforded by periodic multilayer painting and by the application of protective coatings.