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场地土层结构对地震动的影响一直备受关注。针对含有一层软弱土层的匀质场地展开非线性地震反应分析,研究了软弱土层的几何分布特性和剪切波速变化对地表反应谱的影响。结果表明:1软弱层使得场地反应谱特征周期延长,长周期段曲线升高并出现多峰值现象,含软弱层场地的反应谱与无软弱层场地的反应谱差值比远大于工程可接受的误差范围。2软弱层所引起的最大反应谱差值比随软弱层厚度和埋深的增加而近似线性增大,随软弱层剪切波速的减小而非线性增加,在本文算例中,最大反应谱差值比接近12倍。3反应谱最大差值比所对应的敏感周期随着软弱层厚度、埋深和输入加速度幅值的增加而增大,随剪切波速的减小而增大。分析表明,软弱层中的剪应变远大于邻近正常土层中的剪应变,这是引起地表加速度反应谱发生改变的主要原因。
The influence of site soil structure on earthquakes has been drawing much attention. A nonlinear seismic response analysis is carried out on a homogeneous site containing a layer of soft soil. The effect of the geometrical distribution of soft soil layer and the variation of shear wave velocity on the surface response spectrum is studied. The results show that: 1 the weak layer makes the characteristic period of the response spectrum of the site prolong, the curve of the long period increases and the phenomenon of multi-peak appears. The difference between the response spectrum of the site containing the weak layer and that of the site without the soft layer is much larger than that of the engineering acceptable tolerance scope. The maximum response spectrum difference caused by the weak layer increases linearly with the increase of the thickness and depth of the weak layer and increases nonlinearly with the decrease of the shear wave velocity of the weak layer. In this case, the maximum response spectrum The difference is closer to 12 times. 3 Sensitivity cycle of the maximum difference ratio of response spectrum increases with the increase of thickness, depth and input acceleration amplitude of weak layer, and increases with the decrease of shear wave velocity. The analysis shows that the shear strain in the weak layer is much larger than the shear strain in the adjacent normal soil, which is the main reason that causes the change of the surface acceleration response spectrum.