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

钢筋混凝土（RC）柱在两个正交水平方向上同时受到地震作用时，其破坏程度要比在一个水平方向上受到地震作用时大得多。在过去的二十年里，人们专门针对角柱在任意确定的循环位移模式下（如苜蓿叶模式、正方形模式等）承担主要侧向荷载的建筑结构进行了一些试验和分析研究工作。摘要研制了一种能使柱试件承受双向地震激励的拟动力加载系统。一系列的钢筋混凝土柱试件模拟一个单自由度的桥墩和双向荷载的钢筋混凝土桥墩的效果清楚地显示。从试验结果可以看出，双向荷载的相互作用对各滞回变形水平下的承载力影响很大，而这反过来又对随后较大变形过程中的强度退化影响很大。这种相互作用非常复杂，并且非常依赖于施加在桥墩上的荷载路径历史。双向PSD试验方法是研究双向荷载对桥墩在真实地震激励下的行为和反应影响的有效方法。阐明了在强地震动作用下，两层刚架墩柱构件的延性必须大于梁构件。

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.