A COMPREHENSIVE COMPUTATIONAL APPROACH FOR THE ANALYSIS OF NON-LINEAR SOIL-STRUCTURE SYSTEMS UNDER EARTHQUAKE LOADING

Abstract eng:
Soil-structure interaction (SSI) is one of the most classical topics in earthquake engineering analysis; nevertheless, most of the approaches and methods proposed in literature are based on simplified assumptions and are limited to linear or equivalent linear soil behaviour. Regarding simplified methods, the macroelement approach and the Beam-on-Winkler-Foundation model represent the most popular ones because of their extensive studies and feasibility of application. On the other hand, Finite Element (FE) analysis provide an efficient and robust tool for modelling SSI problem in a three-dimensional domain, properly accounting for nonlinearities of the materials. On this basis, a comprehensive three-dimensional finite element procedure is developed for evaluating nonlinear dynamic SSI effects under earthquake loading in case of deep and massive foundations. The attention is focused on the development of an efficient, rigorous and robust numerical approach able both to handle the numerical effort necessary for treating three-dimensional problems and to take the complexity of the soil mechanical behaviour into account. Regarding the latter, a proper constitutive model (Lagioia, Panteghini; 2014, 2016) is implemented in the FE formulation which is able to reproduce, with excellent computational efficiency, the nonlinear behaviour of the material. It is also acknowledged that dynamic SSI analysis are also influenced by the presence of adequate adsorbing boundaries to simulate radiation effects at the contour of the finite domain. Furthermore, accuracy of numerical analysis is based on restrictions of shape and size of elements as well as on the extension of the discretized domain, this leading to a large domain size. The problem is reduced by adopting the so-called Domain Reduction Method (Bielak et al., 2003), which is a twostep procure based on transferring the seismic input motion from application to the boundary to internal nodes of the domain. The method is also proposed in a modified version. All the aforementioned aspects are given proper consideration in the research and are exploited in a numerical procedure developed in the FE code Abaqus that allows investigating the effects of both inertial and kinematic interaction effects on the response of the structural system, which is represented by a nuclear power plant reactor building resting on an embedded foundation. The effect of the introduction of a base isolation system is also under investigation.

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