大跨度斜拉立体桁架的水平地震反应分析

Horizontal seismic response of a long span cable-stayed space truss

大跨度斜拉立体桁架是一种频谱密集周期较长的杂交结构体系,以该结构的两塔三跨和一塔两跨两种体系为对象,研究了通过控制振型参与质量贡献率来确定采用振型分解反应谱法分析时参与组合所需的振型数,探讨了水平地震反应分布规律,并进行了时程分析。研究表明:地震反应振型组合需取前20阶振型具有足够的精度,桁架最大竖向位移和塔顶水平位移及桁架和索的内力反应不大,而塔根的内力反应较大,设计时应给予足够重视。对一塔两跨体系,时程分析结果比振型分解反应谱法分析结果普遍偏大,该结构体系在设计时应采用时程分析法进行多遇地震下的补充计算。

A long span cable-stayed space truss is a hybrid structural system with a denser frequency spectrum and longer periods.Here,the required mode numbers determined using modal mass contribution ratio to horizontal seismic response of two models of two spans with one tower and three spans with two towers for a cable-stayed space truss and its horizental seismic response distribution law were studied by using the mode superposition response spectrum method.Time history analyses were performed for two models.Results showed that the first 20 modes participating earthquake responses have enough accuracy;the maximum vertical displacement of the space truss,the horizontal displacement of the tower top and internal forces of members of the space truss and the cables are not big,but internal forces of the tower roots are relatively great;in process of design,tower roots should be regarded;for the model of two spans with one tower,the results using time history analysis method are bigger than those using the response spectrum method.Therefore,complementary calculations using the time history analysis procedure under multi-earthquake should be performed for systems of two spans with one tower.