Development of a frequency- and amplitute-dependent macro element for seismic SSI analysis of shallow and deep foundations

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The objective of the proposed research is to develop a computationally efficient numerical element which can capture both the inelasticity and the frequency dependency of shallow and deep foundations for seismic soil-structure-interaction analyses. One of the challenges in explicitly modelling a soil-foundation system is the complexity of the system's response under dynamic load. In reality a soil-foundation system is a large semi-infinite continuum with inelastic material. The nonlinearity at the interface between the soil and the foundation (i.e. rocking and sliding) also influences the hysteretic behaviour of the foundation. In addition, the dynamic response of the soil-foundation system is frequency dependent. Depending on the relative impedance of the soil-foundation and the structural system, both the inelasticity and the frequency dependent characteristics need to be represented in a numerical model. In a simplified models, such as lumped or Winkler spring models, however, it is difficult to capture these characteristics. In the proposed research, a generalized macro element will be developed with which the inelastic behavior of near-field soil and the frequency dependent characteristics of the soil-foundation system can be modelled. The PI and the industry partner has developed a framework in which a macro element can be integrated with a recursive parameter model. The macro element is based on a plasticity theory and captures the inelasticity of near field soil while the recursive parameter model captures the frequency dependent characteristics. The framework was applied to a two-dimensional shallow foundation. In this proposed research, the framework will be generalized such that it can be applied to both shallow and deep foundation for both two- and three-dimensional problems. The element will be calibrated and validated against available experimental test results and sophisticated finite element analyses. The element will reduce the modelling efforts and computational time while providing practically accurate response of soil-foundation system for seismic assessment of structures. The development of the element will lead to safe and optimized buildings and bridge structures.