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考虑非线性特征的局部复杂场地地震反应分析,一直是工程场地地震动预测中需解决的关键问题。借鉴目前一维成层场地地震反应分析中广泛使用的频域等效线性化思想,将其推广至时域及二维问题,提出了可用于考虑非线性特征的时域显式有限元方法,适用于复杂工程场地地震反应分析。本方法内域主要采用可实现显式算法的低阶有限元格式,人工边界处采用与显式算法相匹配的透射边界模拟无限域,单元内先通过求取平面应变状态下的最大切应变替代一维模型中的最大切应变,再依据整个时间过程的切应变求取等效切应变。每次整体求解采用时域中心差分的递推过程,并通过迭代完成非线性特征分析。为了验证本方法,选取水平成层场地及二维盆地两个典型场地模型进行模拟分析,将计算结果与传统的一维等效线性化模型及二维差分非线性计算结果做了对比,计算结果显示本文解与参考解非常吻合,证明了本文方法的可靠性。进一步采用该方法对美国Turkey Flat试验场地进行地表地震动模拟,计算结果与应用广泛的一维等效线性化模型及实测记录比较,探讨该方法的可靠性及与现有分析模型的差异,并阐述了非线性特征对地震动影响的规律。
The seismic response analysis of local complicated sites considering nonlinear characteristics has been the key problem to be solved in the earthquake prediction of engineering site. Based on the idea of equivalent linearization in frequency domain widely used in the seismic response analysis of one-dimensional stratified formation at present, this method is generalized to the time-domain and two-dimensional problems. A time-domain explicit finite element method, which can be used to consider nonlinear characteristics, It is suitable for seismic response analysis of complex engineering sites. The inner domain of the method mainly adopts the low-order finite element method which can realize the explicit algorithm. The artificial boundary adopts the transmissive boundary which matches the explicit algorithm to simulate the infinite domain. In the unit, the maximum shear strain in plane strain state One-dimensional model of the maximum shear strain, and then according to the whole process of time-dependent strain to obtain the equivalent shear strain. Each global solution adopts the recursion process of the time-domain center difference, and completes the non-linear feature analysis through iteration. In order to validate this method, two typical site models of horizontal stratigraphic site and two-dimensional basin are selected for simulation analysis. The results are compared with the traditional one-dimensional equivalent linearization model and two-dimensional differential nonlinear calculation results. The calculated results It shows that this solution is very consistent with the reference solution, which proves the reliability of this method. This method is further used to simulate the surface ground motion of Turkey Flat Flat in the United States. The calculated results are compared with the widely used one-dimensional equivalent linearization model and measured records to explore the reliability of the method and the differences with the existing analytical models. The influence of nonlinear characteristics on ground motion is expounded.