Estimation of Long-Term Prestress Losses in Post-Tensioned Girders

Post-tensioned concrete girders are commonly used in bridge structures. Long-term prestress losses due to the creep and shrinkage of concrete in post-tensioned girders are smaller than those in pretensioned girders because of the higher amount of non-prestressed steel present in the former, and also the fact that post-tensioning can take place a long while after a girder has been cast and when the concrete has reached a mature age. Two methods that can be used to estimate long-term prestressed losses in post-tensioned girders are presented in this article. One is a refined method and the other is a simplified method. The accuracy of the methods has been verified by field data collected from two bridge structures monitored for long-term losses. A numerical parametric study conducted with these methods has shown that the concrete strength, the amount of non-prestressed steel, the relative humidity, and the age of concrete at post-tensioning are equally important for the assessment of prestress losses.