Non-linear dynamic soil-structure interaction: application to seismic analysis of structures on shallow foundations

In this paper a novel macro-element formulation is introduced, specifically suited for the modelling of the non-linear dynamic soil-structure interaction of shallow foundations. After presenting the validation activity against a significant number of results from large scale experiments, the model is used to simulate non-linear dynamic soil-structure interaction by a simple model, consisting of a 1 degree-of-freedom (dof) superstructure and a 3 dof macro-element foundation. Both the superstructure and the soil-foundation system may exhibit a non-linear behaviour. In particular the superstructure can be characterized by different elasto-plastic hysteretic rules, while the foundation macro-element encompasses the two sources of non-linearity that arise in the soil-foundation interface: a) the one due to the irreversible elastoplastic soil behaviour (material non-linearity) and b) the one due to possible foundation uplift (geometric non-linearity). The model can serve as a numerical tool for assessing performance-based design approaches that wish to take into account non-linear soil-structure interaction. This is illustrated through a case study of a bridge pier, in which a comparison between the results obtained by dynamic analyses performed with different base conditions (fixed base, elastic base, elastoplastic base with uplift) emphasizes the role of the non-linear soil-structure interaction in design.