Semiactive Control of Seismically Isolated Bridges

This paper describes the application of semiactive devices for controlling the earthquake response of two highway bridges of different cross sections and pier heights. Each of the bridges consists of a three-span continuous deck supported on the piers and abutments. Semiactive devices such as the magnetorheological damper, the variable friction damper and the variable stiffness device are considered as the control devices. These devices are inserted between the deck and piers or abutments of the isolated bridge. The semiactive device changes its properties according to the structural response and adds control forces to the system. Each pier supporting the bridge is modeled as a linear lumped mass system. The optimum parametric values of the semiactive dampers are evaluated and considered in analysis of the bridge. A comparative study is performed for different semi-active devices installed on the bridges under different seismic loadings in the longitudinal direction. The behaviors of the bridges with different semiactive isolation devices are compared with the corresponding nonisolated ones. The semiactive dampers are observed as an effective protective device in reducing the displacements of the isolation bridges as well as the base shear of the piers.