Assessment of the effect of the soil deformability on the peak response of base-isolated buildings under seismic excitations

This paper presents selected results from the numerical investigation of the potential effect of soil deformability on the peak seismic response of base-isolated buildings of various numbers of floors, under both near-fault and far-fault earthquake excitations. The dynamic simulations are conducted parametrically with the SAP2000 Open Application Programming Interface, through a custom-made software developed using the Python programming language. The motivation is twofold: firstly, to examine whether the common assumption that the soil deformability can be ignored in dynamic analyses of base-isolated buildings, assuming that it would be always beneficial to the peak seismic response; and, secondly, to assess the abilities of the provided interface in combination with a modern programming language to effectively and efficiently perform parametric analyses of base isolated buildings. Specifically, three different soil types are considered in the parametric analyses: rock, sand, and clay, using simplified soil springs to model the deformability of the supporting soil. Base isolated buildings with various numbers of stories are considered, while two sets of strong seismic excitations, near-fault and far-fault, are used in the conducted dynamic analyses, to assess the influence of soil deformability, as well as the earthquake characteristics, on the peak seismic responses of the simulated base isolated multi-story buildings. The computed results indicate that neglecting the soil deformability may lead to underestimation of the peak seismic responses, particularly in case of near-fault seismic excitations. That would be very crucial especially for the proper estimation of the required minimum width of the seismic gap that should be provided as clearance around a base isolated building to accommodate the maximum relative displacements that are expected at the seismic isolation level.