超大跨斜拉桥地震行波效应分析

Effects of Traveling Wave Excitation for Super Longspan CableStayed Bridges

摘要:

对多点激励下的振型方程进行了推导，简化成类似于一致激励下的振型方程形式，导出多点激励下的振型参与系数和振型等效地震波，从而可由反应谱判断多点激励对结构振动的影响.以一座试设计的主跨1 400 m斜拉桥为例，采用振型分析法分析了考虑行波效应的超大跨斜拉桥振动机理。通过拟静力法分析了行波效应引起的各支承点地震动位移的差异对超大跨斜拉桥结构变形的影响，同时，利用位移输入法，对超大跨斜拉桥进行了地震时程分析，研究了行波效应对超大跨斜拉桥顺桥向耗能体系地震损伤的影响.研究结果表明：行波效应减小了耗能辅助墩的耗能作用，增大了桥塔的地震损伤，对超大跨斜拉桥顺桥向耗能体系地震反应的影响是不利的.视波速为1 000~3 000 m?s-1范围内的长周期地震动作用下行波效应的影响尤为显著，因此在超大跨斜拉桥地震反应分析时必须考虑.

关键词:大跨度斜拉桥; 地震动; 行波效应; 振型分析法; 位移输入法

Abstract:

The equation of motion under nonuniform excitation of supports was derived in the form under uniform excitation. Through the modal analysis, the modal participation factors and the equivalent modal ground accelerations with consideration of traveling wave excitation were obtained, so that the influence of traveling wave excitation on dynamic responses could also be judged in a response spectrum of this equivalent modal ground acceleration. Vibration mechanism analyses with consideration of traveling wave excitation by mode analysis method were carried out for a trial designed symmetrical cablestayed bridge with a central span of 1 400 m. The deformation of the cablestayed bridge under different support displacements due to traveling wave excitation was analyzed by pseudostatic analysis. Effects of traveling wave excitation on seismic response for super longspan cablestayed bridges with energy dissipating system in longitudinal direction, were researched by the displacement timehistory method. The results show that traveling wave excitation decreases energy dissipating of the piers so that seismic damage of the pylons aggravates. Effects of traveling wave excitation on seismic response for longspan cablestayed bridges with energy dissipating system were disadvantageous, especially under longperiod ground motion with the wave velocity within 1 000~3 000 m?s-1. Therefore, traveling wave excitation should be taken into consideration in seismic response analysis of longspan cablestayed bridges with energy dissipating system.

Key words:longspan cablestayed bridges; earthquake ground motion; traveling wave excitation; mode analysis method; displacement timehistory method