Numerical modelling methods for seismic soil-structure-interaction analysis

本研究旨在了解常用的土-结构-地震相互作用(SSI)分析数值模拟方法的准确性和局限性。为了准确地模拟地震SSI效应，需要对各种分量进行模拟，如地震波在非弹性土介质中从基岩到地表的传播、地基-地基界面的非弹性行为(缝隙开合、摩擦、土体屈服)、结构的动力响应以及结构动力响应引起的波的辐射。对所有这些组件进行建模需要大量的工作和计算时间。因此，到目前为止，对非弹性土-结构体系进行全面模拟的尝试还很少。在目前的抗震设计和性能评估实践中，地震SSI是通过简化的建模方法来考虑的。例如，基础的影响通常是使用基础最大响应处的割线刚度来近似建模的。在许多研究项目中，地基是通过将非线性弹簧指定为单个集总弹簧或温克勒型弹簧来建模的。有时，集中质量和阻尼元被指定为不同的构型，以模拟惯性相互作用效应。与综合数值模拟方法相比，这些模拟方法的精确度还不是很清楚。研究的主要范围是了解不同建模方法的精度，如1)考虑基岩到地表的非弹性波传播和非线性SSI效应的综合有限元模型，2)将自由场表面运动作为有效力施加于结构的有限元模型，以及3)采用非线性耦合宏单元考虑地基和地基的影响的SSI模型。研究结果将为简化建模方法提供依据。该项目的成功完成将导致在行业合作伙伴的产品中实施简化建模方法。

The research aims to understand the accuracy and limitations of commonly used numerical modelling methods for seismic soil-structure-interaction (SSI) analysis. To accurately simulate the seismic SSI effect, it is necessary to model various components such as seismic wave propagation from bedrock to surface through inelastic soil medium, inelastic behaviour at the soil-foundation interface (gap opening/closing, friction, soil yielding), dynamic response of the structure, and radiation of wave due to the dynamic response of the structure. Modelling all these components requires significant efforts and computing time. Thus, only a few attempts have been made so far in which the inelastic soil-structure system is modelled comprehensively. In the current seismic design and performance assessment practice, the seismic SSI is accounted for by using simplified modelling methods. For example, the effects of foundations are often approximately modelled using a secant stiffness at the maximum response of the foundation. In many research projects, the foundation is modelled by assigning nonlinear springs either as a single lumped spring or as Winkler-type springs. Sometimes lumped mass and damping elements are assigned in various configurations to simulate inertial interaction effect. The accuracy of these modelling methods in comparison with the comprehensive numerical modelling approach has not been clearly understood. The main scope of the proposed study is to understand the accuracy of different modelling methods such as 1) a comprehensive finite element (FE) model including inelastic wave propagation from bedrock to surface and nonlinear SSI effect, 2) an FE model in which the free field surface motion is applied as an effective force to a structure, and 3) a SSI model in which the effect of soil and foundation is considered using a nonlinear coupled macro element. The research results will provide confidence on the simplified modelling methods. Successful completion of the project will lead to implementation of the simplified modelling methods in the products of the industry partner.