Steel Bridge Counterattack

In bridges, for years steel has been losing market share to concrete, but now the steel industry is making an impressive comeback. One reason is use of load-factor design, which has cut steel tonnage radically, especially on longer-span bridges. A second reason is the trend to permit contractors to bid an alternative design to that provided in the bid documents. A third is use of wider steel-girder spacings, made possible by a new kind of stay in place, steel bridge deck form. A fourth is autostress design, which takes advantage of steel’s strength beyond the elastic limit. Three innovations pushed not by the steel industry but created by individual designers may also help steel. The first is the concept of a hybrid cable stayed bridge with a concrete deck and steel-stringer superstructure. The second is simple, short-span bridges whose deck and superstructure are 100% prefabricated in big panels, each one span long. The third is the idea of supplementing the structural steel tie in a tied-arch bridge with steel cable tendons.