Shear Strength and Ductility of RC Piers After Yielding of Longitudinal Reinforcements Subjected to Two Directional Earthquakes

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It has been recognized and verified experimentally that reinforced concrete (RC) columns suffered significantly more damage when subjected to earthquake ground motions simultaneously in two orthogonal horizontal directions compared to earthquake motion in only one horizontal direction. A few experimental and analytical research works had been conducted in the past two decades specially for building structures where the corner columns take major loads in both lateral directions under arbitrarily defined cyclic displacement patterns, e.g.cloverleaf pattern, square pattern, etc. In this study, a pseudo-dynamic (PSD) loading system capable of subjecting a column specimen to bilateral earthquake excitations has been developed and implemented. A series of RC column specimens modeling a single degree-of-freedom bridge pier were tested and the effect of bilateral loads on RC bridge piers were clearly exhibited. Furthermore, the influence of flexural and shear strength and ductility of each member on seismic behavior of rigid frame piers From the test results, it can be observed that the interaction of the loads in the bilateral directions affected very much the strength capacity available at each hysteretical deformation level, and which in turn affected very much the subsequent strength degradation in the course of larger deformations. This interaction is extremely complex, and is very dependant on the loading path histories imposed on the piers. The bilateral PSD test method is an effective way to study the effects of bilateral loads on the behavior and response of bridge piers subjected to realistic earthquake-like excitations. It is clarified that column members have to be more ductile than beam members in two-story rigid frame piers subjected to strong ground motion.