A Simple Numerical Tool for Dynamic Soil-Structure Interaction Analyses Including Non-Linear Behaviour of Both Structure and Foundation

In this paper a simple model to take into account dynamic non-linear soil-structure interaction is presented: it consists of a 1 degree-of-freedom (dof) superstructure and a 3 dof macro-element foundation. Both the superstructure and the soil-foundation system exhibit a non-linear behaviour. In particular the superstructure is characterized by an elastic perfectly plastic behaviour, 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 global model thus entails the following features: a) the coupling between the foundation and the superstructure when one or both of them enter into the non-linear range, b) the capability for the foundation and the superstructure to dissipate energy, c) a prediction of peak and residual displacements in both the superstructure and the foundation, d) the possibility to model the isolation effects for the structure due to the foundation non-linear behaviour and e) the possibility for the superstructure to reach a particular level of ductility demand. Therefore, 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 several case studies of bridge piers, 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