非一致激励下大跨度铁路斜拉桥地震响应规律

以一座主跨228 m的铁路钢桁梁斜拉桥为工程背景,采用有限元软件SAP2000建立了基于大质量法的动力分析模型,根据实际工程场地条件从NGA-West2数据库中选取了7条地震动记录作为地震激励对结构进行非一致激励分析,探讨桥梁结构地震响应与地震波到达两主塔时差(相位差)之间的内在联系。结果表明:大跨度铁路斜拉桥在非一致激励下塔顶位移响应峰值与墩底弯矩响应峰值均随相位差呈周期性变化,且变化周期与结构一阶自振周期基本一致;工程结构设计中可通过调整桥梁跨径与结构自振周期,使相位差接近结构一阶自振周期的(2 n+1)/2倍(n为整数)以降低非一致激励下结构地震响应;对于大跨度空间结构抗震设计,考虑行波效应的影响十分必要,应进行相位差为一阶自振周期整数倍的非一致激励分析。

Seismic Response Law of Large Span Railway Cable-stayed Bridge Under Non-uniform Excitation

Taking a steel truss cable-stayed bridge with main span of 228 m as engineering background,a dynamic analytical model based on large mass method was established by using f inite element software SAP2000.Seven seismic records were selected from NGA-West 2 database to analyze the non-uniform excitation of the structure according to the site conditions of the actual project.The internal relationship between the seismic response of the bridge structure and the time difference(phase difference)between the seismic waves reaching the two main towers was discussed.The results show that for large span railway cable-stayed bridges,peak values of displacement response and internal force response of the structure under non-uniform excitation vary in period along with phase difference and the variation period is generally the same with the f irst order natural vibration period.In engineering structure design,bridge span and natural vibration period could be modif ied comprehensively to make phase difference approach(2n+1)/2 multiple(n is an integer)of f irst order natural vibration in order to reduce structure seismic response under non-uniform excitation.For seismic design of large span space structures,it is necessary to consider the inf luence of traveling wave effect.Non-uniform excitation analysis should be carried out when the phase difference is an integral multiple of the f irst order natural vibration period.