A new modal pushover analysis approach for soil–structure interaction

Soil–structure interaction has been taken into account in performance-based seismic analysis of flexibly supported single-degree-of-freedom systems, but there has been less research for multiple-degrees-of-freedom structures. In a new complex modal pushover analysis developed in this study, the seismic demand for each mode is determined by regular pushover analysis method using modified modal inertia force distributions. Combining all modal demands then leads to the estimation of seismic demands of the soil–structure system. A set of generic frame models representing low-rise, mid-rise and high-rise structures was developed. The foundation flexibility was considered using a substructuring method and the soil–structure systems were subjected to a number of far-field and near-fault ground motions. The results indicated that the foundation flexibility could significantly change the response of the system and neglecting this phenomenon might lead to erroneous conclusions in the prediction of seismic performance of flexibly supported reinforced concrete frame structures.