Simplified design method for energy dissipating devices in retrofitting of seismically isolated bridges

Abstract

Abstract: This paper presents an innovative simplified method for the optimum design of seismically isolated bridges incorporating energy dissipating devices. For an isolated bridge subjected to an earthquake, the deformation is concentrated in the isolators, which greatly reduces the seismic base shears transmitted from the superstructure to the substructures. However, some factors such as space limitations, stability requirement etc. limit the allowable deformation taking place across an isolator. To control the deformation of the isolators, supplemental energy dissipating devices can be introduced into the isolation system. This may nevertheless increase the total structure base shear and the merit of adding dampers has to be evaluated properly. In this study, a simplified approach is developed in order to optimize the performance of the isolated structure. This method is based on a simplification of the system and by setting objectives for displacement reduction as well as acceptable base shear increase. Based on this approach, damper stiffness and damping is determined as a function of pier and isolator stiffness. The method provides a range of added stiffness and damping that will be needed to reduce the total displacement of the structure while controlling the increased structural base shear. To verify the robustness of the method, response spectrum analysis of a typical isolated bridge has been performed. The numerical simulations showed a close relation with the proposed simplified method. It is concluded that the proposed simplified approach has the potential to optimize the performance of isolated bridges incorporating energy dissipating devices.