Recent investigations have shown that the influences of Soil-Structure Interaction (SSI) may be detrimental to the seismic response of structure, and hence neglecting this phenomenon in analysis and design may lead to an un-conservative design. The objective of this paper is to quantify the effects of nonlinear soil-structure interaction on the seismic response of a low-rise special moment frame subjected to a family of ground motions with three hazard levels. To this end, seismic behavior of a 5-story special steel frame founded on linear and nonlinear flexible-base foundations are compared to the conventional fixed-base frame counterpart. The well-known Beam-on-nonlinear-Winkler-foundation approach is utilized to model nonlinear soil-shallow foundation. Nonlinear static and time history dynamic analyses have been conducted using the OPENSEES platform to examine the effect of modeling and ground motion parameters on their seismic performance. The results indicate some degrees of inaccuracy in the fixed-base and linear SSI assumptions when compared to its nonlinear flexible-base counterpart. It is also observed that disregarding the foundation flexibility effect may lead to over prediction of the force, drift and ductility demands of the low-rise steel structure.
