SEISMIC BEHAVIOR OF HIGHWAY BRIDGES WITH BASE ISOLATION

A study was made on the seismic behavior of highway bridges with lead-rubber base isolation. The system of base isolation is considered as a bilinear spring. Single- and two-span highway bridges subjected to representative strong earthquake ground motion records were analyzed. The effect of various parameters such as the isolator's stiffness, pier stiffness, and pier eccentricity on the system response was evaluated. It was found that the use of base isolation shifts the fundamental frequency of the bridge system towards the longer period. Proper design of the base isolation tends to reduce the design forces on the bridge piers and is accompanied by larger displacements. The increased forces at the abutments are accompanied by reduction in the shear force transmitted to the pier. Increased displacements and forces may also result when the location of the pier departs from the center and unequal spans are created. In this case, the maximum displacements and forces occur at the abutment adjacent to the long span.