考虑弹性应变阈值的频率相关等效线性化方法

Frequency-dependent equivalent linear method considering elastic strain threshold

传统等效线性化方法由于原理简单、参数获取方便而广泛应用于工程场地非线性地震反应分析中.实际工程应用中发现,这种方法由于对各个频率分量采用了等效剪应变水平,使得地面最大峰值加速度和高频段计算结果明显偏低.若干实验表明,应变幅值对土的力学行为起着关键性作用,当应变低于弹性应变阈值时,土体处于线弹性状态,弹性应变阈值主要与土的塑性指数有关.本文在对各种频率相关等效线性化理论方法分析的基础上,结合弹性应变阈值理论,建立了考虑弹性应变阈值的频率相关等效线性化方法.运用本文方法对海口某实际场地进行了土层地震反应分析,对比了与传统等效线性化方法的差异;同时对不同覆盖层厚度遭遇不同地震动强度的地震动进行了计算分析,总结了不同覆盖层厚度下本文方法和传统等效线性化方法计算结果的差异及规律.

One-dimensional equivalent linear method is widely used in estimating seismic ground re- sponse due to its simple theory and easily obtainment of parameters. However, in practical application, it is found that the Fourier spectrum amplification ratio at high frequency is underestimated because the artificial value of the equivalent shear strain is quite larger than the real shear strain in high frequency ban. Furthermore, tests results show that shear strain threshold plays an important role in soil behav- ior. For shear strains below elastic shear strain threshold, soil behaves essentially as a linear elastic ma- terial. To consider the effect of elastic shear strain threshold and frequency-dependent soil behavior on wave propagation, the shear strain threshold and frequency-dependent equivalent linear method is pro- posed. Site response is performed for Haikou site. Also, for the sites with different soil deposit depths, a series of analyses are performed from relatively weak to strong input motion, and results show that the effect is more .pronounced as input motion goes from weak to strong.