双向地震作用对框架柱端弯矩增大系数的影响分析

在世界各主要多地震国家的建筑抗震设计规范中,普遍采用的柱端弯矩增强措施一般在与柱正交的两个主轴方向上的各平面框架内施行,仅新西兰NZS3101规范采用简化方法考虑了双向地震作用对柱端弯矩增大系数的影响.在OpenSees平台上,以钢筋混凝土6层三维框架为例,采用基于柔度法的纤维模型从而更加真实地模拟柱在双向弯曲和变化轴力作用下的非线性反应.对比双向、单向地震输入下柱端滞回反应的差异及其对框架塑性铰耗能机构的影响.考察双向地震作用下柱端弯矩时程在两个正交主轴方向的相关性,着重研究同一节点处两正交方向的各梁端弯矩时程相关性的定量方法.研究表明,双向地震下柱的强度退化、屈服后变形均明显比单向受力更大,双向地震下X向、Y向柱端弯矩时程,以及同一节点处两正交方向的各梁端弯矩时程的相关性皆极大地依赖于双向水平地震动的输入方式.

Effect of bi-directional horizontal seismic excitation on the moment amplification factor 0f columns

In the codes for anti-seismic design of buildings in countries with frequent earthquakes, the moment amplification factor of columns is generally prescribed to apply within two orthogonal plane frames that intersect at the column, except that the New Zealand Concrete Structures Standard NZS3101 considers the effect of bi-directional horizontal seismic action on the moment amplification factor. Based on the OpenSees framework, a six-storey 3-D reinforced concrete frame was employed as an example, and the flexibility method based on fiber model was adopted to simulate the nonlinear responses of columns under biaxial bending and varying axial forces. The characteristics of hysteresis responses of columns under the excitations of unidirectional and bi-directional seismic actions were compared, and the effects on the plastic hinge mechanism of the frame under rare earthquake were analyzed. The correlativity of moment histories of columns at two orthogonal axes was examined. The focus was placed on the method to numerically describe the correlativity of moment histories of beam ends at two orthogonal axes of the same joint. The results indicate that strength deterioration and deformation after yielding of the column under bi-directional seismic action are obviously larger than those of column under unidirectional action. The correlativity of moment histories of column ends along X and Y directions and the correlativity of moment histories of beam ends at two orthogonal axis of the same joint all seriously depend on the input method of earthquake waves along the two directions.