Seismic design of yielding structures on flexible foundations

This paper introduces a simple method to consider the effects of inertial soil-structure interaction (SSI) on the seismic demands of a yielding single-degree-of-freedom structure. This involves idealizing the yielding soil-structure system as an effective substitute oscillator having a modified period, damping ratio, and ductility. A parametric study is conducted to obtain the ratio between the displacement ductility demand of a flexible-base system and that of the corresponding fixed-base system. It is shown that while additional foundation damping can reduce the overall response, the effects of SSI may also increase the ductility demand of some structures, mostly being ductile and having large structural aspect ratio, up to 15%. Finally, a design procedure is provided for incorporation of the SSI effects on structural response. © 2015 John Wiley & Sons, Ltd.