软土场地地震动效应概率化模型

Probabilistic model for seismic effects on soft soil sites

软土场地对地震动响应有强烈的非线性放大作用,不同国家和地区抗震设计规范普遍的做法是给出一套与各自场地分类标准相一致的调整系数来考虑地震动的场地效应。基岩输入地震动具有显著的不确定性,给出具有不同超越概率水平的场地调整系数能更好地符合基于性态的抗震设计要求。以50个覆盖土层厚度在50~150 m的Ⅲ,Ⅳ类软土场地为研究对象,从ESM数据库中筛选了43个参考场地在73次地震事件中记录到的100条强震记录并分别调幅至25,50,100,150 gal作为输入,采用一维等效线性化程序SHAKE2000开展了共20000种组合的土层地震响应计算。给出了不同强度地震动作用下峰值加速度、峰值速度和峰值位移的放大系数FPGA,FPGV和FPGD以及短周期(T=0.2 s)和中长周期(T=1 s)加速度反应谱放大系数F_(a)和F_(v)的分布形态及特征参数,并给出了超越概率为2%,16%和50%时不同放大系数的建议取值。

The seismic response exhibits strong nonlinear amplification on soft soil sites.The common practice in different countries and regions for the seismic design codes is to provide a set of adjustment coefficients that are consistent with their respective site classification criteria to consider the local site effects.Given the significant uncertainties in bedrock input motions,putting forward the site adjustment factors with different levels of exceedance probabilities better meets the performance-based seismic design requirements.50 typeⅢandⅣsoft soil sites with covering soil layer thicknesses ranging from 50 to 150 m are collected as numerical models.100 strong seismic records are selected from 43 reference sites recorded during 73 earthquake events in the ESM database and their peaks are adjusted to 25,50,100 and 150 gal as inputs.Using the one-dimensional equivalent linear program SHAKE2000,a total number of 20000 site response calculations are carried out.The distribution features and characteristic parameters of the peak acceleration,peak velocity and peak displacement amplification coefficient,as well as the short-period(T=0.2 s)and medium-to-long period(T=1 s)acceleration response spectrum amplification coefficients,namely FPGA,FPGV,FPGD,F_(a) and F_(v),under different intensities of input motions are given.The recommended values for various amplification coefficients are also provided for the exceedance probabilities of 2%,16%and 50%.