Effect of foundation flexibility on response of concrete frame structures under near-fault ground motions

Currently, it is understood that seismic responses of building structures could be changed, owing to the foundation flexibility. The present study is limited to evaluate such phenomenon on non-linear responses of reinforced concrete structures, emphasising their ductility demand distributions. To accomplish this objective, a set of three dimensional reinforced concrete generic frames were modeled as an assemblage of beam/column elements. Utilising substructure method, a set of linearly elastic spring-dashpot model was used to characterise the supporting soil. To estimate ductility demands, non-linear time history analyses as well as pushover analyses were conducted. The foundation–structure system was subjected to an assemblage of ‘ordinary' and ‘near-fault' ground motions. The results indicated soil-structure interaction effects mostly increase ductility demands of the flexible base structures. Consequently, neglecting this phenomenon may lead to erroneous conclusions in the prediction of seismic performance of flexibly supported reinforced concrete frame structures, especially when subjected to near-fault ground motions.