ABSTRACT
New materials are neither technologically nor economically ready to replace conventional materials in the construction industry. When the two materials oppose each other, the general structural design is always determined by factors other than the material. The function of the structure will be a determining factor. The bridge is a typical example, its general structure depending on the function to be fulfilled: roadbridge, railway bridge or road-rail bridge. The cross section of a bridge can be either a solid web or three-dimensional truss box girder or beams, both for steel and concrete. Efforts are made to combine steel and prestressed or reinforced concrete; an example will be given later. Except for some simple cases of short-span bridges, these efforts come up against two difficulties. They are expensive traditionalism with respect to design of connections between steel and concrete elements on the one hand and cooperation problems between the concrete and steel industries on the other hand.
