Seismic Evaluation of Flexible-Base Low-Rise Steel Frames Using Beam-On-Nonlinear-Winkler-Foundation Modeling of Shallow Footings

Recent investigations have shown that the influences of Soil-Structure Interaction (SSI) can be detrimental to the seismic behavior of structure, and hence ignoring this phenomenon in analysis and design may result in to an un-conservative design. The aim of this paper is to quantify the effects of nonlinear SSI 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 (BNWF) approach is utilized to model nonlinear soil-shallow foundation. Nonlinear static and time history dynamic analyses were conducted using the OPENSEES platform to examine the effect of modeling and ground motion parameters on their seismic performance. The results demonstrate some degrees of inaccuracy in the fixed-base and linear SSI assumptions when compared to its nonlinear flexible-base counterpart. It is also found that disregarding the foundation flexibility effect may lead to over prediction of the inter-story drift, force and ductility demands of the low-rise steel structure.