Upgrading Bridge Safety Using Seismic Isolation

Many damages to the structure of bridges occurred during the past earthquakes, are mostly the result of underestimation of seismic forces. For this reason, seismic isolation can be effectively used in designing or retrofitting the bridges in high seismic zones. The objective of this paper, along with the study of characteristics of electrometric isolator that can be manufactured in the country, is to briefly present design guidelines of these isolators and to investigate the effects of key parameters like elastic stiffness, inelastic stiffness and yielding force of isolators on seismic performance of five typical highway bridges.Based on the results obtained in this research, seismic isolators have a significant role in reduction of seismic forces and displacements of the typical bridges, protecting sub structural elements which are usually weak and brittle. The larger the bridge lateral stiffness, the more effective will be the seismic isolation. The primary elastic stiffness and yield force of isolators are the key factors in isolation efficiency and its hysteretic damping.By decreasing the elastic stiffness of isolators, the bridge response will decrease while the absolute displacement of the bridge deck will increase. This drawback can be compensated by increasing yielding force and damping of isolators by inserting other types of passive devices. Optimum design can be found through numerical investigation. It is eventually concluded that elastomeric seismic isolators can be effectively used in designing new bridges or retrofitting existing bridges, according to the performed design and analysis of bridges in this paper. Experimental studies on seismic isolators are recommended as a complementary to numerical procedure to ensure desired lateral performance of isolated bridges.