Non-linear dynamic analysis of buildings founded on piles: Simplified modelling strategies for soil-foundation-structure interaction

The paper investigates the problem of Soil-Foundation-Structure Interaction (SFSI) for buildings supported on piles through the comparative analysis between the fixed base and the compliant base assumptions. The structure, a nine-storey residential building (with or without infills), is modelled in non-linear regime while the piled foundation is idealized by means of independent lumped parameters models, either linear or non-linear. In this last case, the soil-foundation system is replaced by an assembly of viscous-dampers, fictitious masses and non-linear springs modelled according to the classical Bouc-Wen formulation, so as to account for the hysteretic behaviour of the foundation. A detailed calibration procedure for both linear and non-linear foundation models is also presented and discussed. Two different natural soil deposits are considered, a pyroclastic deposit and a deep layer of lacustrine clay. The results undertaken in the context of a probabilistic analysis show that SFSI may lead to a significant reduction of the seismic demand in infilled buildings at low and intermediate earthquake intensity levels. Conversely, at higher intensity earthquakes the seismic demand is not affected by the non-linear springs. It is shown that a proper modelling of radiation mechanism at foundation level is crucial for a reliable and sustainable prediction of SFSI effects.