双向地震动作用弹塑性反应谱研究

在基于性能/位移抗震设计中,弹塑性反应谱在计算结构地震位移反应方面越来越受到重视.考虑实际地震动的多维性和结构非线性反应空间耦合特性,研究并建立了双向地震动作用弹塑性反应谱模型,将其定义为在两个相互垂直的主轴方向上分别具有水平平动自由度,恢复力特性满足二维屈服面模型的理想弹塑性单质点系统,分别承受双向和单向地震动作用,在同一主轴方向上的最大位移反应之比.给出了一种等强度折减系数的弹塑性谱.通过硬土场地10组双向地震动记录等强度折减系数谱的统计平均结果,分析了结构周期、强度折减系数和阻尼等因素对谱值及结构双向地震反应的影响.结果表明,双向地震动作用相对单向地震动作用主要增加结构较长周期方向的最大位移反应;若增加结构较短周期方向的设计强度,可在一定程度上降低双向地震动不利影响;因定义的谱为比值形式,阻尼对其影响不大.

Research on inelastic response spectra for bi-directional ground motions

More attention has been paid to inelastic design spectra with the development of performance/displacement based seismic design, because it can be used to estimate the maximum displacement demand of structures. The bi-directional inelastic response spectrum by considering the multi-component earthquake excitation and coupled characteristics of structural response is developed, which is defined as the ratio of the maximum displacement response in the same principal axes direction of a single-mass-system with two translational freedoms along its perpendicular principal axes when subjected to two- and one-dimensional ground motions respectively. Force-restoring characteristics of the two-degree-of-single-mass-system are determined by two-dimensional yield-surface plasticity theory. The inelastic spectra with constant strength reduction factors are given. The effects of periods, strength reduction factors and damping on spectra amplitude and bi-directional structural responses are discussed by statistic analysis of 10 recordings in two directions on hard-site. Bi-directional earthquake excitations will increase the maximum displacement response of structures in the direction with longer period mainly as compared with one-directional one. Increasing the design strength of structures in the direction with shorter period can reduce the negative effects of bi-directional ground motions on structural response. Damping has little influence on the inelastic spectra with constant strength reduction factors since it is defined by the ratio of the maximum displacement response.