中硬场地下两种土层地震反应方法与精确解的对比

基于谐波入射下的波动理论频域精确解,导出线性时域精确解,并在Matlab环境中编制相应的计算程序;选取8个简化的中硬场地剖面,用LSSRLI-1、精确解和SHAKE2000三种方法计算各场地在不同输入条件下的地震反应。结果表明:程序计算所得地表反应谱和土体剪应变分布与SHAKE2000结果一致;LSSRLI-1方法得到的地表反应谱与前二者结果一致;LSSRLI-1方法在某些情况下得到的土体剪应变分布与另外二者结果存在较大偏差,该偏差对地表反应谱有着不可忽略甚至非常显著的影响。

Contrasting Study of Two Seismic Response Methods and the Exact Solutions for Moderately Stiff Soil Sites

Earthquake ground motions can significantly affect buildings when they are amplified in surface soil layers.Therefore,in order to estimate the behavior of buildings during severe earthquakes,it is essential to evaluate those characteristics of amplification.Although investigations have been carried out,many problems remain unsolved with regard to those characteristics.Ground response analysis typically involves predictions of surface ground motions,developing a spectrum of design responses,determining dynamic stress and strain,and evaluating the potential for liquefaction.Methods used to calculate the ground response are commonly divided into linear,nonlinear,and equivalent linear concepts.The linear analysis assumes that the shear modulus as constant.However,soils often exhibit nonlinear behavior,even at low levels of strain.The nonlinear method is time consuming.The equivalent linear method,represented by the SHAKE model,is one of the most frequently used methods for analysis of ground responses to earthquakes.This method is used primarily for approximations because it uses effective strain to define the material property for analysis.However,the equivalent linear method remains the most popular method of seismic response analysis.It has been 20 years since the safety evaluation program LSSRLI-1 was developed and was used for seismic response analysis.At the time,LSSRLI-1 represented the most advanced method and contributed greatly to earthquake preparedness and disaster reduction for China.However,some deficiencies in the model were identified.Based on its focus in the frequency domain with a harmonic wave incident,the exact linear solution was deduced in the time domain,and compiled into a program in the Matlab environment.For the study,eight sites with medium-hard soils were chosen.Seismic responses were calculated using three different methods:the LSSRLI-1,exact solution,and SHAKE2000.The results show that the ground response spectrums and distribution of soil shear strain,calculated using the exact solution and SHAKE2000 methods,are in agreement with each other.The ground response spectrums,calculated using LSSRLI-1,were consistent with the other two methods.However,in some cases,the distribution of soil shear strain,calculated using LSSRLI-1,showed a relatively large deviation from the SHAKE2000 and exact solution methods.The extent of these differences may significantly affect the estimates of ground motion,and cannot be ignored.