基于双向地震叠加输入的强度折减系数谱研究

Research on the strength reduction factor spectra based on the superposition of bi-directional earthquake excitations

针对双向水平地震动作用下结构的等效单自由度体系理论提出了一种思路,通过双向的振型参与系数关系将双向地震动进行叠加作为等效单自由度体系的激励输入,以此为基础建立了考虑双向地震动作用的等延性强度折减系数Rb谱理论.建议通过修正传统强度折减系数Rs谱的方法来考虑双向地震作用的影响.建立了Rb/Rs比值谱,分析了相关变量对Rb/Rs比值谱的影响.为了简化应用,分别按Rb/Rs在周期0.05～5 s内取“平均值-1.65倍标准差”和“最小值”两种方法给出了强度折减系数的修正系数α1和α2.通过选取的双向水平强震记录,分析了场地类别、延性系数、双向振型参与系数比对修正系数α1和α2的影响,最后给出了简化的、便于应用的强度折减系数修正系数表.

Considering the irrationality of equivalent single-degree-of-freedom system of a structure subjected to bi- directional earthquake excitations, a new idea is proposed as ： superposition of bi-directional earthquake motions, based on the relationship of modal participation factors of two directions, is regarded as the single-directional excita- tion of equivalent single-degree-of-freedom. The strength reduction factor Rb spectrum is presented based on the presented idea. The method is proposed to consider the influence of hi-directional earthquake excitations, in which the traditional strength reduction factor Rs is adjusted by the relationship between Rb and Rs. The Rb/Ra spectrum is established and its regularities are analyzed. The modification coefficients, α1 and α2, are given and the earthquake ground motion records are selected to analyze the influences of soil sites, ductility factor and modal participation fac- tor ratio on the modification coefficients. Finally, the advices on the simplified modification coefficient are given for the practical application.