Guidelines for flexural design of prestressed composite beams

Prestressed steel has only recently been considered in the design of structures, despite along, successful history of prestressed concrete structures. Prestressing the steel in a composite steel-concrete beam increases the load at which the steel beam yields, and also increases the ultimate strength of the composite section. At the same time, precompressing the tension flange reduces the effective stress-range cycle and improves the fatigue strength. Prestressed composite beams can be used in new structures as well as for the strengthening of existing structures. Several analytical studies of single-span prestressed composite beams are reported in the literature, but no comprehensive design methodologies are given. This paper presents guidelines and equations for the design of prestressed composite beams in positive- and negative-moment regions. In the positive-moment region, a steel beam is prestressed first and then compositely connected to concrete deck. In the negative-moment region, a steel beam is prestressed and then compositely connected to a precast, prestressed concrete deck panel. The guidelines and equations are given for working-stress and load-factor design methods and are presented in a manner suitable for easy use by bridge-design engineers. A design example is also given to demonstrate the benefits of prestressing for strengthening existing bridges.