Nonlinear analysis of an RC frame structure considering the effects of embedment on soil–structure interaction

The interaction between soil and structure, which merges geotechnical and structural engineering, plays a crucial role in seismic regions. Traditional structural design often assumes that buildings are fixed at their foundations, neglecting the influence of local soil conditions. However, accounting for soil–structure interaction (SSI) indicates greater structural flexibility, modified dynamic behaviour, and variations in the intensity and distribution of earthquake forces. These influences are especially notable in soft or moderately stiff soils, where foundation flexibility may cause increases or decreases in seismic demand. To account for these influences, American pre-codes provide detailed guidelines for incorporating SSI into structural analyses. In this study, these guidelines were applied in both nonlinear static (push-over) and nonlinear dynamic (time-history) analyses of a six-storey reinforced concrete frame structure. The analyses considered two different soil types, B and C, which were classified according to Eurocode 8, to evaluate the effect of different soil rigidity on structural behaviour. The findings, with a focus on kinematic interaction, highlighted how foundation embedment influences seismic behaviour. The results showed notable deformations in storey displacements and inter-storey drifts, as well as the formation of plastic hinges, indicating nonlinear response mechanisms. Reduced capacity curves under lower seismic forces confirmed the influence of SSI. This study underscores the necessity of incorporating SSI effects to improve seismic design accuracy and enhance the prediction of structural behaviour during earthquakes.