强震动作用下场地土的非线性对地震动反应特征影响明显。场地土的非线性效应首先是由岩土工程学家在室内试验中发现的,继而地震学家在强震动记录分析中亦发现了场地土的非线性效应。一般来讲,随着地震动输入强度增加,场地土非线性效应越明显。但对于不同场地类型,相同地震动水平作用下,场地土非线性效应是不同的。针对这一问题,选择了几个典型场地,采用等效线性化方法分析了不同地震动强度作用下各类场地土的非线性效应,并提出了一种以场地等效剪切波速随地震动输入水平变化为依据的场地土非线性效应确定方法,且定义当等效剪切波速变化率不足20%时,场地地震反应分析可不计入场地土的非线性效应。
The characteristics of surface ground motion are apparently affected by the nonlinear behavior of site soil under strong motion input. The soil nonlinear behavior is firstly discovered by geotechnical engineers in laboratory tests; and then the seismologists confirm it by analyzing record data from the strong motion observation. Generally speaking, the site soil nonlinear behavior becomes more significant while the earthquake excitation increases; however, for different site types and same excitation level, there would be different site soil nonlinear behaviors. A method is proposed to determine the corresponding earthquake motion input thresholds for typical sites based on the relationship of shear wave velocity variation ratio and earthquake excitation.