Reinforced concrete columns under seismic lateral force and varying axial load

The project is carried out with the intention to study the strength and ductility of reinforced concrete columns subjected to simulated seismic horizontal loading and varying axial load. First, an extensive review of previous research on the behaviour of reinforced concrete members and hysteretic modelling is provided. Then, the experimentally investigation which involves testing a total of nine reinforced concrete specimens under simultaneously cyclic lateral loading and varying axial load is carried out. The first series of six reinforced concrete column units were tested to obtain the variations in flexural hysteretic behaviour with fluctuation in axial load level. In the second phase of experimental investigation, three specimens were tested to study the shear strength of reinforced concrete columns subjected to cyclic lateral loading and varying axial load with emphasis placed on the study of degrading concrete shear resisting mechanisms and comparisons with the present design code equations for shear strength. Following the experimental program, the mechanisms of shear resistance and the factors affecting the shear strength are considered. In particular, the effects of alternating tension and compression axial load on the shear resisting mechanisms are studied. On the basis of experimental results, proposals are made for predicting shear strength of reinforced concrete column of ductility and limited ductility. Next, the theoretical work was undertaken to investigate the elastic and post-yield flexural rigidities of reinforced concrete sections. The equations for determining the elastic and post-yield flexural regidities are presented. Also, a moment-curvature hysteretic model including varying axial loading effect is proposed. The theoretical predictions for the moment-curvature hysteresis relationship were found to compare well with the experimental results. Finally, an example is given of inelastic dynamic response analysis of reinforced concrete frame using the proposed moment-curvature model which includes the effects of varying axial load on the yield moment, and loading and unloading stiffness of the structural members