基于OpenSees的饱和土场地中地下结构地震反应研究

Study on Seismic Response of Underground Structure in Saturated Soil Deposit Based on OpenSees

应用OpenSees有限元计算程序,选取某地铁车站结构为主要分析对象,构建了饱和土-地下结构体系地震反应运算模型,并利用该模型进行系统的地震反应计算。将现场饱和土动力反应视为饱和两相介质近场波动问题,选取时域显式数值算法进行计算,同时考虑了土体的弹塑性。研究结果显示:(1)因选取弹塑性土体本构,土体-地下结构的位移反应时程和输入地震动的位移时程体现出了显著性差异。(2)对于两层三跨地下结构,在以剪切波形式输入的地震动作用下,顶板的峰值加速度和侧向位移最大,中板次之,底板最小,场地土体对地震波具有放大效应,顶层的层间位移大于底层。(3)在地震动作用下,地下结构不同区域应力时程的改变规律存在非常显著的差异。中柱底部与底板节点处的应力峰值最大。地震动输入结束时,结构存在残余应力。

Using the finite element calculation software OpenSees,this study focuses on a subway station structure as the primary analysis object while establishing an operational seismic response model for a saturated soil-underground structural system.This model enables a systematic calculation of the seismic response.The study considers the dynamic response of the saturated soil on site as a nearfield fluctuation problem of a saturated two-phase medium.A time-domain explicit numerical algorithm is employed for calculations,incorporating the elastic-plastic dynamic response characteristics of the soil.The results of this study indicate several key findings:(1)The elastic-plastic dynamic response characteristics of the site soil are accounted for during the simulation analysis.This consideration reveals a significant difference between the displacement response time histories of the soil and underground structures compared to the displacement time histories of the input ground motion.(2)In the case of a two-story,three-span underground structure subjected to ground motion in the form of shear waves,the roof exhibits the highest peak acceleration and lateral displacement,followed by the middle plate,while the bottom plate shows the smallest values.Additionally,the inter-story displacement of the top layer is greater than that of the bottom layer.(3)Under earthquake loading,there are pronounced differences in the stress time history patterns across various regions of the underground structure.The stress peak at the joint between the bottom of the center column and the bottom plate is the highest observed.Furthermore,when ground motion input ceases,residual stresses remain in the structure.