A Prestressed Composite Girder for Short Span Bridges

During the last two decades, a great deal of research has been done on various types of girders for bridges—namely, prestressed steel girders, composite steel girders, prestressed concrete composite girders, and prestressed steel composite girders. The prestressing of a steel girder (plate or lattice girder) can be achieved by using prestressed high strength steel cables anchored at the bottom flange of the girder. Composite construction has successfully been substituted for noncomposite construction in bridges and buildings since the 1950s. Prestressed composite design is similar to conventional composite design except that the composite girders are prestressed by means of high strength cables after the concrete has reached its required strength. The analysis of composite steel girders prestressed by using high strength cables before the concrete slab is cast has been discussed by Hoadley9 and by Reagan and Krahl. These studies show that the use of high strength cables for prestressing is not as effective as the addition of a cover plate in conventional composite design for working stress. However, prestressed composite beams of this type have been used both for bridge and for building construction.