Response of an isolated cable-stayed bridge under bi-directional seismic actions

This paper investigates the effectiveness and limitations of seismic isolation for the earthquake protection of a cable-stayed bridge under bi-directional seismic actions. A simplified lumped mass finite element model of the Quincy Bay-view Bridge at Illinois is developed for the investigation. The deck of the bridge is isolated from the towers by using elastomeric and sliding isolation systems. For the non-linear isolation systems, the interaction between the restoring forces in two orthogonal horizontal directions is duly considered in the response analysis. The seismic response of the bridge is obtained by solving the governing equations of motion in the incremental form using an iterative step-by-step method. A parametric study is also performed by varying important parameters of the isolation systems. The seismic response of the isolated cable-stayed bridge is compared with the corresponding response of the bridge without isolation systems. The results of the investigation indicate that the peak base shear response of the towers and deck accelerations are significantly reduced by the isolation. The displacement response of the hysteretic isolation systems is found to be increased when the bi-directional interaction of the bearing force is considered in the response analysis. Furthermore, it is also found that the response of the bridge is significantly affected by the variation in the parameters of the isolation systems.