Interaction between Time-Dependent and Second-Order Effects of Externally Posttensioned Members

Abstract

For external tendon members subjected to sustained loads, the time-dependent effects resulting from concrete creep, shrinkage, and tendon relaxation would interact with the second-order effects resulting from the change in tendon eccentricities with the development of time-dependent deformations. This interaction should be adequately considered in a time-dependent analysis of this type of member. This paper presents a numerical model developed to predict the long-term behavior of externally prestressed concrete members at service conditions, taking into account the interaction between time-dependent and second-order effects. The proposed method of analysis is verified with the available experimental results. The time-dependent behavior of externally prestressed concrete members is evaluated, focusing on the effect of deviators and nonprestressed steel. The results demonstrate that the second-order effects result in significant changes in long-term responses other than the prestress loss. The effect of bottom nonprestressed steel on the long-term behavior is found to be limited, whereas the effect of top nonprestressed steel is very important.