动剪切模量比对反应谱影响的定量分析

动剪切模量比的不确定性会对场地地震反应计算的结果产生较大的影响,而目前对这种影响的研究多限于定性分析,笔者利用渤海海域典型场地对这一影响进行定量分析。首先,建立了土层地震反应计算模型;然后,在不改变影响土层地震反应计算结果其他参量的前提下,赋予了原动剪切模量比一系列偏差并求得了场地反应谱的变化;最后,得到了反应谱对动剪切模量比的敏感度。结果表明:1)在动剪切模量比曲线增大(或减小)后,在基准反应谱的特征周期附近,存在一个反应谱相对于基准反应谱由增大转变为减小(或由减小转变为增大)的转变点。2)在概率水准2和3下:反应谱平台段对动剪切模量比的敏感度最高,其值基本上分布在1.0~3.0;反应谱下降段的敏感度绝对值随着周期的增大先迅速增大后逐渐趋于0,最大值达1.0以上;反应谱上升段的敏感度分布平稳,其值多分布在1.0~2.0。

Quantitative Analysis of Dynamic Shear Modulus Ratio's Effect on Response Spectra

The uncertainty of dynamic shear modulus ratio has a large impact on the site seismic response analysis results.Most studies on the influence are qualitative at present.The authors try to quantitatively study the influence on the engeering sites in Bohai Sea.Firstly,The authors builted the site seismic response calculation models;secondly,by adding a series of deviations to the original dynamic shear modulus ratio with maintaining other parameters unchanged,the anthors calculated the change of response spectra,and then got the sensitivity values of response spectra on the dynamic shear modulus ratio.According to the research,the conclusion is drown as below:1)With the dynamic shear modulus ratio curves going up and down,a turning point appears near the characteristic period of the datum response spectrum;2 )Under probability level 2 and 3,the platform segments of the response spectra show the highest sensitivity values which are basically between 1.0 and 3.0.The absolute sensitivity values on the decending segment are mostly larger than 1.0,and increase quickly at first;and then decrease slowly to zero with the increase of period;but relatively stable between 1.0 to 2.0 on the ascending egment with the increase of period.