Improved prediction of long-term prestress loss in unbonded prestressed concrete members

Abstract

In this paper, an approach based on the finite element method to model the behavior of concrete beams with unbonded prestressing steel over time, and an improved simplified equation for calculating the prestress losses in statically determinate prestressed concrete members with unbonded internal tendons are proposed. Both methods take into account the effects of the concrete creep, concrete shrinkage, prestressing steel relaxation and the presence of the bonded non-prestressed reinforcement. In addition, a generalization of the Step-by-Step and the Age-Adjusted Effective Modulus methods for the time cross-sectional analysis of prestressed concrete members with unbonded internal tendons is presented. The accuracy of the proposed equation is evaluated based on the results of previous studies and is contrasted with the computational implementation of the Step-by-Step Method. As the main conclusions, we mention that the results show that the proposed equation adequately predicts the prestress loss and has higher accuracy compared to simplified existing models.