长周期随机地震作用下超大跨斜拉桥的行波效应分析

从各个国家和地区的地震记录库中寻找出一些具有良好记录质量和基本场地资料的强震记录,并从中挑选出较为典型的长周期地震波,对比分析了不同场地条件下长周期地震波和普通地震波的平均加速度反应谱及其规范形式的分段拟合曲线.选取软土场地拟合反应谱作为目标反应谱,用迭代方法求取与目标反应谱相对应的功率谱密度函数,分析了基于长周期地震动加速度功率谱密度的特点.在此基础上,以某超大跨斜拉桥结构为背景,利用ANSYS软件建立三维有限元分析模型,分别以文中拟合的长周期地震动功率谱密度和普通地震动功率谱密度作为输入,采用直接求取位移的改进虚拟激励法,对超大跨斜拉桥结构进行了不同视波速下的行波效应分析.结果表明:长周期地震动功率谱密度的卓越频率明显低于普通地震动功率谱密度的卓越频率.长周期地震动功率谱作用下的桥梁左桥塔顶、右桥塔顶和桥面板跨中节点的位移响应功率谱值均明显大于普通地震动功率谱作用下的结果,桥梁塔顶位移响应功率谱均呈双峰分布.在本文算例中,考虑行波效应使超大跨斜拉桥结构的位移响应和弯矩响应结果有所减小.

Traveling Wave Effect Analysis of Super-long-span Cable-stayed Bridge under Long-period Stochastic Seismic Excitation

Strong motion records with high recording qualities and basic site data were sought out from seismic records in various countries and regions, from which some typical long-period seismic waves were selected for analysis. Then, both the mean acceleration response spectrum and the fitted response spectrum based on long-period and general seismic records on different sites were analyzed and compared. After that, the fitted spectrum of seismic waves on soft sites was taken as the target, and its power spectrum density was iteratively calculated. The characteristics of acceleration power spectrum densities based on long-period seismic records were also analyzed. On this basis, with a super-long-span cable-stayed bridge as the background by applying ANSYS software to establish three-dimensional finite element model of the bridge structure, using power spectrum densities based on long-period seismic records and general seismic records as input, and utilizing the direct displacement pseudo-excitation method, the travelling wave effect of the super-long-span cable-stayed bridge under different apparent wave velocities was studied. The results have shown that the predominant frequency of power spectrum densities based on long-period seismic records is apparently lower than those based on general seismic records; the displacement response power spectrum values at the left tower top, the right tower top and the mid-deck under long-period seismic power spectrums are significantly larger than those under general seismic power spectrums, and the distribution of the displacement response power spectrum at tower tops is bimodality; and in this case, the travelling wave effect reduces the displacement and bending response values of the bridge structure.