ABSTRACT
Prestressed (or Posttensioned) concrete (PSC) bridges have been in use since the middle of the twentieth century. In the United States alone, the number of PSC bridges is almost 20% of all the bridges built between 1950 and 1990 (Yunovich and Thompson 2003). The popularity of PSC systems is attributed to several factors:
Lower overall construction costs• More efficient detailing due to lower reinforcement congestions• Lighter weights, leading to longer bridge spans (see Figure 4.1)•
These advantages can be traced directly to the efficient use of the material properties of concrete and steel. Prestressing utilizes the high compressive strength of concrete, while reducing or eliminating the use of the weaker tensile concrete strength. Use of high-strength steel in PSC systems also enables a more efficient system performance. The concept of PSC systems is fairly simple: apply an initial compressive strain field, εInitial, on the system before major loading demands affect the system. When these loading demands are applied later during the lifespan of the system, the net strain demands, εNet, would be mostly compressive, since any tensile strain demand that might be generated by the loading demands would be greatly offset by the initial compressive strains. The concept is shown in Equation 4.1, with the strain demand resulting from the loading being εLoad. The initial compressive strains are generated by a set of high-strength steel tendons.
