Two dimensional seismic responses of free field in typical seafloor site based on dynamic finite difference method
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摘要: 以我国近海海域工程场地为研究对象,充分考虑上覆海水的自重影响,构建典型的饱和海底自由场计算模型,运用动力有限差分法开展二维地震反应分析,探讨以不同幅值的SV波、P波作为基底输入条件下上覆海水厚度对海底地震动峰值和反应谱的影响,总结上覆有水和无水场地的地震动结果差异,并分析差异产生的原因。结果表明:当基底输入SV波时,上覆有水场地海床表面峰值加速度小于上覆无水场地地表峰值加速度,海水层厚度对峰值加速度的影响可以忽略;当基底输入P波时,上覆有水场地海床表面峰值加速度大于上覆无水场地地表峰值加速度,且随着海水层厚度的增大,海床表面峰值加速度逐渐减小。Abstract: Taking the engineering site in the offshore area of China as the research object, the typical calculation model of saturated submarine free field is constructed after fully considered the influence of self-weight stress of overlying sea water, and the dynamic finite difference method is implemented to carry out two-dimensional seismic response analysis. In this paper, we discussed the influence of the thickness of overlying sea water on the peak ground motion value and response spectrum of seafloor under the condition that SV and P waves of different amplitudes are used as the input of the basement, and systematically analyzed the causes of the differences. The results show that when SV wave is input into the sea floor, the peak acceleration of the sea floor surface is smaller than that of the overlying anhydrous site surface, and the effect of the thickness of the sea water layer on the peak acceleration can be ignored; when P wave is input into the sea floor, the peak acceleration of the sea floor surface is larger than that of the overlying anhydrous site surface, and the peak acceleration of the sea floor surface gradually decreases with the thickness of the sea water layer increase.
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图 2 基底输入地震动加速度时程及傅里叶谱
(a) Kobe波加速度时程;(b) El-Centro波加速度时程;(c) Kobe波傅里叶幅值谱;(d) El-Centro波傅里叶幅值谱
Figure 2. Acceleration time history and Fourier spectra of ground motion input
(a) Acceleration time history of Kobe wave;(b) Acceleration time history of El-Centro wave; (c) Fourier amplitude spectrum of Kobe wave;(d) Fourier amplitude spectrum of El-Centro wave
表 1 水平成层场地土层参数
Table 1 Soil layer parameters of horizontal layered site
计算参数 ρ/(kg·m−3) G/MPa K/MPa vS/(m·s−1) vP/(m·s−1) C/kPa Φ/° 第一层 1 700 97 478 240 1 700 10 30 第二层 2 000 226 6 130 360 1 800 10 30 第三层 2 250 951 9 330 650 2 170 6 500 45 表 2 以SV波作为输入形式下观测点A的峰值加速度
Table 2 PGA of point A in the stratified model under SV wave seismic inputs
输入幅值/g 峰值加速度/g Kobe波 El-Centro波 模型一 模型二 模型三 模型四 模型一 模型二 模型三 模型四 0.05 0.1068 0.0983 0.0983 0.0983 0.1650 0.1632 0.1632 0.1632 0.10 0.2135 0.1966 0.1966 0.1966 0.3293 0.3257 0.3257 0.3257 0.15 0.3209 0.2954 0.2954 0.2954 0.4949 0.4895 0.4895 0.4895 0.20 0.4208 0.3932 0.3932 0.3932 0.6586 0.6514 0.6514 0.6514 0.25 0.5344 0.4920 0.4920 0.4920 0.8253 0.8163 0.8163 0.8163 0.30 0.6462 0.5971 0.5971 0.5971 0.9897 0.9790 0.9790 0.9790 表 3 以P波作为输入形式下各工况下观测点A的峰值加速度
Table 3 PGA of point A in the stratified model under P wave seismic inputs
输入幅值/g 峰值加速度/g Kobe波 El-Centro波 模型一 模型二 模型三 模型四 模型一 模型二 模型三 模型四 0.05 0.0298 0.0307 0.0306 0.0306 0.0298 0.0321 0.0320 0.0319 0.10 0.0596 0.0613 0.0613 0.0611 0.0594 0.0640 0.0639 0.0636 0.15 0.0895 0.0921 0.0921 0.0919 0.0893 0.0962 0.0960 0.0956 0.20 0.1191 0.1226 0.1225 0.1223 0.1188 0.1281 0.1277 0.1277 0.25 0.1490 0.1534 0.1533 0.1530 0.1489 0.1605 0.1601 0.1601 0.30 0.1790 0.1842 0.1842 0.1842 0.1785 0.1924 0.1920 0.1911 -
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