基础刚度对砖石古塔地震响应影响研究

Impact of Foundation Stiffness on the Seismic Response of Ancient Masonry Pagoda

以西安万寿寺塔纠偏工程为研究背景,分别建立增加圈梁、圈梁-地梁组合以及圈梁-地梁-托盘组合模型下的塔体与基础协同工作模型。采用时程分析法,对不同基础刚度条件下塔体的地震响应进行分析及评估,结果表明:(1)增大基础刚度的同时结构的地震位移响应将会被放大,但应力时程曲线的波动范围随之缩小、幅值减小;(2)增设圈梁时由于塔底三向受力,塔底应力将被放大;(3)进行基础完全托换能够大幅改善塔底在地震作用下的受力状态。在塔体加固维修时应综合考虑地震作用下塔体的位移放大效应与塔体应力分布的影响,选取合适的基础刚度。

Using the Wanshou Pagoda restoration project in Xi＇an city as the research focus,this paper discusses the establishment of a cooperative work model for the pagoda body and foundations using three different types of foundation stiffnesses（setting ring beam,combination of ring beam and ground beam,and combination of ring beam,ground beam and tray）.Field tests are conducted to determine the dynamic characteristics of the pagoda body using the pulsating method,and results are used as a reference for verifying the reliability of the simplified numerical model.Seismic waves（EL-Centro）under the same site conditions are selected as the horizontal excitation acting on the foundation.With an understanding of the pagoda＇s brittleness,this paper analyzes only the dynamic response in the elastic stage.A time-history analysis method is used to analyze the stress and displacement response law under different foundation stiffness conditions,and during displacement analysis the top of pagoda and 1Feave are selected as displacement monitoring points.The maximum horizontal displacement is found to increase with an increase in foundation stiffness,and the dip angle of the pagoda correspondingly increases.For stress analysis,two points, ＂a＂ and ＂b＂,from the pagoda bottom are selected as monitoring points,and the first and third principal stress-time curves of the two points are analyzed with different foundation stiffnesses.With an increase in foundation stiffness,the first and third principal stress at point ＂a＂ drops significantly,and the stress change trend at point ＂b＂ is similar to that at ＂a＂.It should be noted that when only the ring beam is set,the peak stress at the pagoda bottom is about 40~50times that of the other foundation forms.The analysis results show that：（1）with an increase in foundation stiffness there is amplification of the seismic displacement response of the pagoda structure,but a reduction in the fluctuation range of the stress time-history curve;（2）the stress state of the pagoda bottom is sensitive to foundation stiffness,and as the pagoda bottom is in a tri-axial stress state when the ring beams are added its stress is magnified;（3）underpinning the entire foundations would significantly improve the stress state of pagoda bottom under seismic action,and also have a positive effect on the shear stress control of the pagoda body.However,when reinforcing the pagoda body and determining the appropriate foundation stiffness,it is necessary to comprehensively consider the displacement amplification effect of the pagoda body,and the stress distribution of pagoda bottom under seismic action.