Effects of nonlinear soil-structure-interaction on seismic damage of 3D buildings on cohesive and frictional soils

The present paper investigates the impact of nonlinear soil-foundation-structure-interaction (NLSFSI) on the damage response of 3D R/C buildings supported on different soil types with varying flexibility. The main goal of the paper is to present a first approach towards the possible quantitative differentiation, with respect to fixed base conditions, on the overall damage level when NLSFSI effects are accounted for. To accomplish this purpose nine buildings with various heights and structural systems are studied. For the foundation of the buildings two different soil types are considered, namely cohesive and frictional ones. Moreover, the soil flexibility is taken into account by using two different values of the soil's shear wave velocity. The buildings are subjected to 65 bidirectional earthquake records, for which nonlinear time history analyses are conducted. The accelerograms of each record are scaled to two different seismic intensities corresponding to certain performance levels using appropriate scaling factors. The damage state of the buildings is expressed through the maximum interstorey drift ratio. The assessment of the results revealed that the role of soil-foundation-structure-interaction (SFSI) is not necessarily beneficial. In order to assess the SFSI effects a number of parameters are important as the frequency content of the earthquake ground motion, the building's structural system, the foundation soil flexibility as well as the earthquake intensity.