chapter  6
Flexure: Prestressed concrete
Pages 64

In reinforced concrete, concrete resists compressive forces whereas reinforcing steel resists the tensile forces. In prestressed concrete beams, the contribution of concrete is maximized by precompressing it with highstrength steel bars, wires, or cables. The ultimate strength of prestressed cables could be as high as 270,,000psi as compared to 90,000psi for typical steel used for reinforcement. By optimizing the prestress and the shape, beams can be designed so that they do not crack under normal service loads. This allows for the utilization of the entire cross-section resulting in much smaller deflections. The prestress can also be designed to compensate dead load so large spans can be covered.