柱端弯矩增大系数取值对RC框架结构抗震性能影响的评估

增大柱端抗弯承载力是抗震“能力设计”的关键措施之一,它可以导致钢筋混凝土框架结构形成梁铰型有利的耗能机构。评估不同柱端弯矩增大系数(0.8￣2.4)下钢筋混凝土框架结构的抗震性能。首先采用可靠度理论分析框架结构单节点“强柱弱梁”设计的失效概率;然后,考虑主要影响梁柱强弱的设计参数和地震加速度峰值的随机性,以3层和6层框架结构为分析对象,采用蒙特卡罗模拟分析结构楼层和整体形成“柱铰机构”的抗震位移需求超越位移能力的概率,分析结果表明柱端弯矩增大系数大于2.0,框架结构才能达到可以接受的形成“柱铰机构”概率;最后,以6层确定性框架结构为例,通过增量动力分析建立能有效评估柱端弯矩增大系数的易损性曲线。

Evaluation of influences of various moment magnifying coefficients at column ends of RC frames on seismic performance

Enlarging the flexural strength at columns ends is one of the key measures in the seismic perfomence-based design,which could induce the"column hinge mechanism"in the RC frames to dissipate energy during earthquake.The present study is to evaluate the seismic performance of RC frames with various moment magnifying factors of columns(from 0.8 to 2.4).At first,the failure probability of"strong column-weak beam"design for a RC frame with single beam-column joint is analyzed.And then the randomnesses of peak ground accelerations and major design parameters influencing flexural strength ratios between columns and beams are considered in 3-and 6-storey RC frames.The Monte Carlo simulation is performed to evaluate the probabilities of aseismic demands exceeding the column side-sway capacity for both storeies and buildings during forming"column hinge mechanism".The results indicate that the acceptable probability of forming"column hinge mechanism"can be achieved if the moment magnifying factors of columns are no less than 2.0.An incremental dynamic analysis is conducted for a 6-storey frame,and seismic fragility curves for evaluating the moment magnifying factors of columns are produced.