Long-Term Behavior of Prestressed Composite Beams at Service Loads for One Year

Abstract

The combined effects of creep and shrinkage of concrete and relaxation of prestressing tendons cause gradual changes in the internal forces and deflections of composite beams. However, most of the research work conducted on prestressed steel–concrete composite beams has focused on short-term behavior; research findings on the long-term behavior are scarce in the literature. For the wide-scale use of prestressed composite beams in civil engineering applications, the long-term behavior must be investigated. This paper presents an experimental program designed to examine the long-term behavior of prestressed composite beams under sustained load conditions for one year. The test program consisted of two prestressed composite beams and one nonprestressed composite beam. On the basis of the age-adjusted effective modulus method and energy principle, the creep stiffness matrix and the creep force matrix of prestressed composite beams were developed. A time-dependent analytical model is presented to predict the long-term behavior of prestressed composite beams. Close agreement is observed between the analytical and experimental results. It is proposed that the Multiplier 3.1 of the instantaneous deflection be used to calculate the deflection of prestressed composite beams for one year.