考虑倒塌储备的近断层区域RC框架结构抗震设计方法

Seismic design method of RC frame structures at near-fault region considering collapse margin

近断层脉冲型地震动通常会引发结构严重破坏甚至倒塌,但目前的设计方法仅通过修正设计谱来考虑近断层效应,并不能考虑结构的倒塌储备。为此,在使用近断层设计谱的基础上提出考虑倒塌储备的结构抗震设计方法。基于近断层设计谱和远场设计谱共设计了12个钢筋混凝土(RC)框架结构,分别采用20条近断层脉冲型地震动和远场非脉冲型地震动研究了RC框架结构的倒塌易损性,对比分析了近断层、远场区域结构的倒塌储备系数,发现近断层区域结构的倒塌储备系数小于远场区域结构。为实现近断层、远场区域结构倒塌储备等效,首先给出了以基本周期为变量的结构50%倒塌概率对应的谱加速度的预测公式,然后推导了结构倒塌储备等效方程,并结合设计谱进行数值求解,最后给出了倒塌储备等效条件下以远场区域结构基本周期为变量的近断层区域结构基本周期设计建议公式。结果表明,按照近断层设计谱进行抗震设计能够明显减小结构的倒塌概率,但大部分近断层区域结构的倒塌储备系数仍小于远场区域结构,且平均差别可达20%,综合使用该预测公式和近断层设计谱可以实现近断层、远场区域结构倒塌储备等效.

Near-fault pulse-like ground motions often cause serious damage or even collapse of structures.However,the current methods consider the near-fault effect just by revising design spectra,and the collapse margin cannot be considered.The seismic design method was proposed considering the collapse margin on the basis of using near-fault design spectra.Therefore,a total of 12 reinforced concrete(RC)frame structures were designed based on near-fault and far-field design spectra.The collapse vulnerability of RC frame structures was studied with 20 near-fault pulse-like and 20 far-field non-pulse-like ground motions,respectively.The collapse margin ratios of near-fault and far-field structures were compared and analyzed.It is found that the collapse margin ratio of near-fault structures is smaller than that of far-field structures.In order to realize the equivalent collapse margin of structures,the prediction equation of spectral acceleration of structure with 50%collapse probability was firstly proposed with the basic period as variable.Then the equivalent collapse margin formula was derived,and it was numerically solved with design spectra.The design formula of fundamental period of near-fault structure was proposed with fundamental period of far-fault structure as variable under the condition of equivalent collapse margin.The results indicate that using near-fault design spectra can clearly decrease the strctural collpase probability.However,the collapse margin of most near-fault structures is still smaller than that of far-fault structures,and the mean difference can reach 20%.The equivalent collapse margin of near-fault and far-field structures can be realized by using the prediction formula combined with near-fault design spectrum.