Modelling Nonlinear Static Analysis for Soil-Structure Interaction Problems

Nonlinear static analysis is a well-established seismic design method for structur-al systems. However, soil-structure interaction can significantly affect the earthquake-induced effects in the structural members. This is particularly evident for bridges with integral abutments, that imply the full transmission of the inertial effects developing in the soil to the entire structural system. In this view, this paper proposes an extension of the capacity spectrum method to soil-bridge systems as a simplified numerical procedure directly applicable in design. In the proposed method, the capacity of the system is evaluated through two different distributions of equivalent inertial forces applied to a computationally manageable soil-bridge domain, reproducing the deformation patterns associated with the dominant vibration modes. These modes are mainly controlled by the soil response and can be reasonably determined by a modal analysis of the soil deposit. The entire procedure is implemented in OpenSees and validated against the results of several dynamic analyses carried out on a reference case study.