Abstract

A simple procedure for the nonlinear analysis of externally and/or internally prestressed reinforced concrete beams including the time-dependent effects caused by creep and shrinkage of concrete and relaxation of prestressing steel is presented. The procedure is capable of tracing the structural response of these structures through their service load history as well as throughout the elastic, inelastic, and ultimate load ranges. Sections can change throughout the length of the member and the variation of the material properties within the element is accommodated. The section is divided into concrete parts of different materials and the reinforcement steel is divided into layers of different properties. Each concrete part and steel layer is considered in a uniaxial state of stress. Time dependent variation of concrete properties is considered. The instantaneous loss in the prestressing force due to friction and anchor setting in posttensioned structures is also recognized. The time domain for which the analysis is required is divided into a number of time intervals. At any instant, the instantaneous changes in stresses and deformations are calculated and added to the existing values. For any time interval, the gradual change in stresses and deformations are determined and added to update the existing values. Also for each time interval, nonlinear equilibrium equations which are valid for the current material properties are set up and solved using the displacement method. An initial stiffness method combined with the unbalanced load iterations for each load increment or time interval is used for the nonlinear equilibrium. A series of numerical examples are tested and comparisons are made with other analytical and experimental data. Numerical data from the nonlinear and time-dependent analyses of prestressed posttensioned reinforced concrete simple beams are presented