竖向地震动对地表最大剪应变的影响

Effects on maximum shear strain of soil layer surface of vertical seismic motion

提出以土剪应变幅值增量的变化作为基本指标来反映竖向地震动对土动力特性影响的分析方法,通过数值计算,在对不同地震波平均后,建立考虑竖向地震动与地表最大剪应变幅值相对增量之间的简化计算公式.简化公式中包含了场地类别、竖向和水平峰值加速度比、输入水平加速度峰值和土层厚度等主要影响因素,便于工程应用.同时,依据公式的参数分析表明,地表最大剪应变相对增量与输入水平加速度峰值成指数递增关系,与土层厚度成线性递增关系,与竖向和水平峰值加速度比成抛物线递增关系.

A simplified method for considering the effects of vertical seismic motion on the soil dynamic characteristics is presented by taking the relative shear strain increment on the soil surface as a basic parameter. A simplified formula for calculating effects of the vertical seismic motion on the shear strain increment on the surface of soil layers is obtained by averaging six different incident waves. The effects of four main parameters including site type, vertical - to - horizontal ratio of the peak acceleration, peak value of inputted horizontal acceleration and depth of soil layers on the shear strain increment have been considered in the formula. The parameter analysis results indicate that the shear strain increment increases exponentially with increasing of the horizontal acceleration amplitude, increases linearly with increasing of the soil layer depth and increases in the parabolic form with increasing of the vertical - to - horizontal ratio of the peak acceleration.