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

钢筋混凝土柱在两个正交水平方向同时受到地震地震动时，比仅在一个水平方向上受到地震地震动时受到的损伤要大得多。在过去的二十年中，专门针对角柱在任意定义的循环位移模式（如三叶草模式、方形模式等）下在两个方向上承受较大载荷的建筑结构进行了一些试验和分析研究工作。在这项研究中，拟动力（PSD）加载系统能够承受柱试件的双边地震激励已经开发和实施。通过一系列模拟单自由度桥墩的钢筋混凝土柱试件试验，清楚地显示了双向荷载对钢筋混凝土桥墩的影响。此外，各构件的抗剪抗弯强度和延性对刚架桥墩抗震性能的影响。从试验结果可以看出，双向荷载的相互作用对每个迟滞变形水平下的可用强度能力影响很大，而这反过来又对较大变形过程中随后的强度退化影响很大。这种相互作用是非常复杂的，并且非常依赖于施加在桥墩上的加载路径历史。双侧PSD试验方法是研究双侧荷载对桥墩在实际类地震作用下性能和响应影响的有效方法。阐明了两层刚架桥墩在强地震动作用下，柱构件必须比梁构件具有更强的延性。

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.