Numerical modelling methods for seismic soil-structure-interaction analysis

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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.