Prestressed composite girders under positive moment

According to the 1986 U.S. Federal Highway Administration statistics, there are 575,607 bridges on the highway system. About half of these bridges are structurally deficient and/or functionally obsolete. To strengthen the structurally deficient bridges without replacing the girders, external prestressing techniques can be used. In this paper, the behavior of prestressed, composite steel-concrete beams under positive bending moment is examined, and the benefits of different types of prestressing are compared. These specimens were tested to study various aspects of prestressed composite girders, including tendon type and profile. Two methods of analysis are discussed, i.e., the transformed area method and the strain compatibility method. The test results show that prestressing a composite girder increases the range of elastic behavior, reduces deflections, increases ultimate strength, and adds to the redundancy by providing multiple stress paths. Based on the experimental results, a comparison was made between three tendon types and profiles. It was concluded that strands are more effective than bars for the tendon type, and a straight tendon profile is more effective than a draped profile with regard to stiffness.