土层非线性非平稳有效应力动力响应可靠度分析

NONSTATIONARY PROBABILISTIC DYNAMIC RESPONSE ANALYSIS OF EFFECTIVE STRESS OF NONLINEAR SOIL PROFILE

在非平稳一致地震输入下对非线性土层进行了有效应力动力响应可靠度分析。通过虚拟激励法,将非平稳地震加速度功率谱密度作为基岩上的虚拟输入,并利用Hardin-Drnevich双曲线模型考虑土层的非线性特性,迭代计算得到土单元的剪切模量与阻尼比。在此基础上,运用有限元方法对土层进行了地震响应分析,通过比较4种方法获得等效峰值剪应力和剪应变来计算等效动力剪切模量和振动孔压。结果表明,采用基于概率平均法的插值方法与确定性分析所得的平均值较为接近,说明由于孔压的不断上升与土层有效应力的降低,可液化地基的地震响应变为非平稳随机过程。

The nonstationary probabilistic seismic response was carded out via pseudo excitation algorithm combined with finite element method under uniform nonstationary seismic environment. The evolutionary power spectral density （PSD） of acceleration at the engineering bedrock was handled as the nonstationary pseudo input. Shear modulus and damping ratio were obtained iteratively from the Hardin-Drnevich constitute relationship accounting for the nonlinearity of soil and the effect of pore pressure. Also, the performance of four techniques, using different approximations to estimate the equivalent peak value of shear stress and strain, were investigated for the purpose of determining the equivalent shear modulus, damping and excess pore water pressure induced by seismic loading, in which the equivalent peak value is computed in terms of its standard deviation and the corresponding peak factor. It is found that the interpolation method based on probabilistic average approach is appropriate compared to the deterministic method. The analytic results indicate that the dynamic response of liquefiable soil is time-dependent due to the cumulation of the excess water pore pressure and should be considered as nonstationary process.