Time‐Dependent Analysis of Cracked Partially Prestressed Concrete Members

Abstract

The analysis to compute prestress loss and the stress redistribution in concrete and nonprestressed reinforcement due to the time‐dependent effects of creep, shrinkage, and relaxation of prestressed steel, in partially prestressed concrete members cracked under the influence of dead load and initial prestress is presented using the method of creep‐transformed sections. The method involves an easy‐to‐use procedure repeated a number of times depending on the desired accuracy of the results. No cubic equation need be solved to obtain the time‐dependent neutral axis. The method is convenient to use for members with multiple layers of prestressed and nonprestressed reinforcement and can be programmed on any desktop computer. In a cracked partially prestressed section, the neutral axes of stress and strain change with time and generally there is an increase in the neutral axis depth. In certain cases, there may be an increase in tension in the prestressed tendons due to creep and shrinkage, and the actual relaxation loss will be greater than the intrinsic relaxation in such cases. In the proposed method, the relaxation loss need not be assumed a priori, but can be accurately calculated based on the diagram provided in the paper. Two numerical examples are presented to illustrate the proposed method.