苏通大桥初设阶段主桥场地地震反应计算

Computation of Site Seismic Response for Sutong Bridge in Preliminary Design Phase

本文计算了苏通大桥初设阶段主桥近300 m深场地的地震反应。将三种地震波从基岩输入,并考虑了行波效应,从而得到不同计算工况下8个桥墩所在场地的地震反应结果,列出了工程场地地表的部分绝对加速度和绝对位移的计算结果。从计算结果来看,土层的地震反应受到以下几个因素的影响:土层计算模型、土层的地质地形条件、行波效应。当有倾斜河谷地形时,采用一致输入下水平均匀分层土层的简单模型后,计算所得的工程场地地震动参数与实际场地精细化模型的计算结果有较大的差距。是否考虑基岩面上地震波的行进过程,也会对场地地表的地震动参数产生较大的影响。

The seismic responses of the site with about 300-meter deposit are computed for Sutong Bridge in preliminary design phase.SR2D software package is used as the computational tool that is developed by our team.Traditional method analyzing the problem is one dimensional wave theory.Because the site on the Sutong Bridge is very complex and the span of the bridge is very long,the one-dimensional method cannot fully reflect the seismic response character of the site.The site seismic responses at eight bridge piers are found under the excitation of three seismic waves input at the bedrock for different cases.The effect of the seismic waves traveling along the bedrock surface is considered in the analysis.Some results of absolute accelerations and displacements at the site surface are listed in this paper.Furthermore,by using the response spectrum theory,the response spectra of seismic waves inputted is researched.Comparisons between the response spectra of seismic waves inputted and response spectra at bridge piers show that the peak values of response spectra become increasingly larger filtered by soil layer.From the computational results,it can be seen that the following factors have important effects on the site seismic responses： computational model of soil layer,geological and topographic condition of soil layer and traveling velocity of wave.If there is sloping river valley,the results are obtained from the simple model in which the site is simulated by horizontal layered uniform soil layer with coincident excitation are different obviously from the ones obtained from the precise model of the site.The seismic responses at some bridge piers are larger and others are smaller.As the effect of seismic wave traveling along the surface of bedrock has important influence on the ground motion at surface of site,for long-span structure,such as long-span bridge or giant gymnasium,it is essential to consider multi-supported excitation to get accurate seismic response.