Seismic fragility of tall buildings considering soil structure interaction (SSI) effects

Soil Structure Interaction (SSI) effects have been extensively studied for low-rise buildings, while less contributions considered tall buildings. In this regard, 3D numerical simulations were herein performed to evaluate the seismic performance of a 20-floor building founded on pile foundation. SSI effects have been studied with a probabilistic-based approach in order to develop analytical fragility curves. Opensees was applied to perform non-linear dynamic analyses in order to consider soil hysteresis and plasticity that cause non-linear mechanisms in the ground and are responsible for structural damage. The principal findings consist of considering both the cases where SSI helps reducing the vulnerability of the system and the mechanisms of site amplification that are driven by SSI effects (kinematic and inertial interaction). In particular, the developed fragility curves show the role of the mutual interaction of the soil and of the structure (in terms of period elongation, lateral deflections, roof accelerations and floor drifts). Therefore, neglecting the role of SSI was shown to be responsible of the increase of the vulnerability of the entire system (soil-foundation-superstructure).