Performance-based design (PBD) involves designing structures to achieve specified performance targets under specified levels of seismic hazard. This involves analyzing the entire soil-structure system and requires structural and geotechnical expertise. This paper is focused on soil-foundation-structure interaction (SFSI) in relation to PBD. A Beam-on-Nonlinear-Winkler- Foundation (BNWF) model is developed to incorporate important SFSI aspects into structural analysis software. The model accounts for: nonlinearity due to soil yield and/or footing uplift; cyclic degradation of stiffness and strength due to variable-amplitude loading; distribution of soil resistance underneath the footing for different loading conditions; reduction in radiation damping with increased nonlinearity; and coupling effects between different responses of the foundation. The coupling between different responses is achieved by appropriate mathematically derived bounding surfaces. The model utilizes a rotation hinge governed by a bounding surface to model coupling between rocking (in two directions) and vertical responses, and a shear hinge governed by another bounding surface to couple the horizontal responses. These models are implemented in readily available structural packages, and hence allow structural engineers to properly account for SSI effects when performing PBD. The application of the developed models to analysis of experiments on model foundations showed good agreement between the calculated and observed behavior
