远场长周期地震动下基础隔震结构非线性减震分析与控制

Mitigation and Control on Nonlinear Responses of Base-Isolated Structures under Far-field Long-period Ground Motions

为研究远场地震动中长周期成份、尤其类谐和成份对基础隔震结构非线性减震性能与损伤演化的影响,分别选取普通地震动与远场长周期地震动进行频谱特性对比.考虑隔震层上部结构梁柱的塑性性能,采用集中塑性铰模型,建立一幢钢筋混凝土基础隔震结构有限元模型,通过非线性分析探讨地震动中长周期成份,特别是类谐和成份对基础隔震结构减震性能的影响.提出在隔震层增设黏滞阻尼器,形成组合隔震方案,控制罕遇地震甚至中震作用下隔震层产生的超限水平位移.结果表明:对减震系数和层间位移而言,远场长周期地震动尤其是类谐和地震动作用下的隔震效果较差,类谐和地震动下层间位移出现放大效应且隔震层上部结构产生塑性损伤变形;远场长周期罕遇地震甚至中震下隔震层位移的增大尤其明显,严重超过隔震支座的允许变形限值.组合隔震能有效地控制远场长周期地震动,尤其类谐和地震动作用下隔震层的超限水平位移,减小隔震层上部结构非线性反应,防止隔震支座损伤破坏.

In order to examine the effect of long-period components,especially harmonic-likecomponents in far-field ground motions on the nonlinear shock absorption performanceand damage evolution of base-isolated structures,some far-field long-period groundmotions and common ground motions were selected,and the comparative analysis onspectral characteristics of these ground motions were performed.Then,a finite elementanalysis model of a base-isolated reinforced concrete structure was established,in whichthe plastic behavior of the beams and columns in the upper structure above the isolationlayer was considered by using the lumped plastic hinge model.The impact of the long-period components,especially harmonic-like components in far-field ground motions onthe nonlinear shock absorption performance were investigated by using nonlinear time-history methods.Further,a combined isolation scheme by the addition of viscousdampers in the isolation layer was proposed to control excessive displacement of theisolation layer caused by rare earthquake or even moderate earthquake.The results showthat the shock absorption performance on damping coefficients and interstory driftswhen subjected to far-field long-period,especially harmonic-alike ground motionsbecomes worse.The interstory drifts in the base-isolated structure are enlarged underharmonic-alike ground motions when compared with that in the aseismic structure,andplastic deformation occurs in the structure above the isolation layer.Furthermore,thedisplacement of the isolation layer increases extraordinarily and is far beyond theallowable displacement of isolation bearings.It is also indicated that the combinedisolation can effectively reduces the excessive displacement of the isolation layer andnonlinear responses of the supper structure,preventing the destruction of the isolationbearings.