Development of a macro element for seismic SSI Analysis of shallow foundations

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The objective of the proposed research is to develop a macro element for a soil-shallow foundation system that can take into account the inelastic behaviour of near-field soil as well as the frequency-dependent dynamic impedance of far-field soil. The element will greatly simplify the modelling method for a soil-shallow foundation system and will increase the accuracy of the evaluation of structural responses under earthquake excitation. It has been well acknowledged that the soil-structure interaction (SSI) influences the response of a structure that is subjected to earthquake excitation, but the consideration of SSI is not straightforward due to the complexities in the dynamic behaviour of soil-foundation systems. In the proposed research, an element will be developed that can capture the inelastic behaviour of near-field soil as well as the frequency-dependent dynamic of far-field soil. The development will be based on the integration of gyromass-spring-damper assemblies and a plasticity-based macro element. The inelastic macro element can take into account the interaction of multi-axial loads (axial force, shear force, and moment). The gyromass-spring-damper assemblies can capture the frequency-dependent dynamic response of far-field soil. Integrating these two elements and calibrating model parameters for typical soil types and foundation configurations will lead to a computationally efficient yet sufficiently accurate model for shallow foundations. The proposed main research tasks are 1) integration of two modelling approaches for near- and far-field soil, 2) calibrating lumped model parameters for inelastic macro spring element against a sophisticated finite-element model, 3) verifying the developed model against finite element analyses, and 4) applying the element to a typical low-rise building structure and a bridge structure. The use of the computationally efficient yet accurate numerical element will allow engineers to develop an optimized design for a structural system and accurately evaluate the performance of a structure in the event of an earthquake, which will lead to a resilient society against seismic hazard.