TIME-DEPENDENT ANALYSIS OF CRACKED PARTIALLY PRESTRESSED CONCRETE MEMBERS

The analysis to compute prestress loss and the stress redistribution i n concrete and nonprestressed reinforcement due to the time-dependent effects of creep, shrinkage, and relaxation of prestressed steel, in p artially prestressed concrete members cracked under the influence of d ead load and initial prestress is presented using the method of creep- transformed sections. The method involves an easy-to-use procedure rep eated a number of times depending on the desired accuracy of the resul ts. No cubic equation need be solved to obtain the time-dependent neut ral axis. The method is convenient to use for members with multiple la yers of prestressed and nonprestressed reinforcement and can be progra mmed on any desktop computer. In a cracked partially prestressed secti on, the neutral axes of stress and strain change with time and general ly there is an increase in the neutral axis depth. In certain cases, t here may be an increase in tension in the prestressed tendons due to c reep and shrinkage, and the actual relaxation loss will be greater tha n the intrinsic relaxation in such cases. In the proposed method, the relaxation loss need not be assumed a priori, but can be accurately ca lculated based on the diagram provided in the paper. Two numerical exa mples are presented to illustrate the proposed method.