双向地震作用下我国“强柱弱梁”措施的有效性评估

以往研究柱端弯矩增大系数时一般基于平面分析模型,双向水平地震作用对框架"强柱弱梁"屈服机制的影响未引起重视。严格按中国规范设计出5个不同地震烈度分区的规则空间框架,在OpenSees平台上,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,对五个框架进行了罕遇地震下的非线性反应分析。结果表明,7度0.1g区三级抗震空间框架形成了柱铰为主的混合耗能机制,7度0.15g区三级抗震空间框架少量楼层发生了层侧移反应,8度0.2g区、0.3g区二级抗震空间框架均是部分楼层出现明显层侧移反应的典型柱铰机制,9度0.4g区一级抗震空间框架则形成了梁铰、柱铰均较严重的梁柱铰混合机制。五个空间框架在双向地震下的塑性铰分布特征均比相应平面框架更不利。我国不同烈度区、不同抗震等级的空间框架结构在罕遇地震下形成了不同的的塑性铰耗能机制。

An evaluation of the effectiveness of the Chinese strong column weak beam measure under bi-directional horizontal seismic excitations

Plane analysis model is commonly applied in the study of the moment amplification factor of columns, and the effect of bi-directional horizontal seismic actions on strong column-weak beam yielding mechanism has not been considered seriously. Five regular reinforced concrete 3-D spatial frames were designed strictly according to the Chinese code for different seismic fortification intensities. Based on the OpenSees framework, flexibility method based fiber model was adopted to simulate the nonlinear responses of the columns under biaxial bending and varying axial forces. Nonlinear dynamic response analyses of the five frames under rare earthquake excitations were carried out. The results showed that the spatial frame of the 3rd seismic grade at 7-earthquake intensity 0.1g-region formed a column hinge dominated mechanism, the spatial frame of the 3rd seismic grade at 7-earthquake intensity 0.15g-region tended to develop story side-sway mechanism at a few floors, and the spatial frame of the 2nd seismic grade at 8-earthquake intensity 0.2g-region and 0.3g-region all formed typical column hinge mechanism with story side-sway mechanism occurred at some floors, while the spatial frame of the1st seismic grade at 9-earthquake intensity 0.4g-region developed a column-beam mixed hinge mechanism with severe column hinges and beam hinges. The plastic hinge distributions of the five spatial frames under bi-directional horizontal seismic actions were worse than that of the corresponding plane frames. The plastic hinge energy-dissipating mechanism of the spatial frames in different earthquake intensity regions and different seismic grades were different under rare earthquake excitations.