Influence of dynamic soil-structure interaction analyses on shear buildings: Fid-Bau Portal

Influence of dynamic soil-structure interaction analyses on shear buildings

Renzi, Stefano

Despite extensive research there is still controversy regarding the role of SSI in the seismic performance of structures founded on soft soil. Neglecting SSI effects is currently being suggested in many seismic codes as a conservative simplification that would supposedly lead to improved safety margins. The interest in studying the seismic SSI is motivated by the necessity of computing the effective earthquake excitation to a structure (Foundation Input Motion) with respect to the free-field ground motion. The latter strongly influences the structure seismic demand as it takes into account both the soil-foundation coupling (i.e. the dynamic impedance function of the soil-foundation system) and the scattering effects caused by the motion of foundations (i.e. the kinematic interaction effects). A systematic application of complete SSI analyses to different types of buildings (up to twenty storeys), has been performed; the compliance of the ground has been evaluated by means of the computer program SASSI2000 (Lysmer et al., 1999). Concrete shear-type structures have been modeled as generalized Single Degree Of Freedom (SDOF) systems using the principle of virtual displacements, while different soil conditions (consistent with the EC8-I), foundation depths and seismic excitations are taken into account. SSI effect has been also evaluated in terms of maximum displacements/accelerations at the top of the buildings and a systematic comparison with the fixed-base solutions has been performed. The final goal is the set-up of simplified charts and tables that can be easily used by consultants who want to face the task of SSI in an immediate and simplified manner. Such tool could be very useful for engineers, especially concerning the design of medium-rise reinforced-concrete buildings and/or for pre-design stages, where the SSI effect must be estimated and cannot be excluded a priori.