Principles and Performance of Roller Seismic Isolation Bearings for Highway Bridges

Keywords: Seismic performance.  Roller seismic isolation bearings.  Seismic isolation systems.  Highway infrastructure.  Bridges.  Cylindrical rollers.  Self-centering capabilities.  Constant spectral acceleration.  Ground motions.

Abstract: This report presents a new roller seismic isolation bearing for use in highway bridges.  This new bearing uses rolling motions of cylindrical rollers between sloping surfaces to achieve seismic isolation. The bearing is characterized by a constant spectral acceleration under horizontal ground motions and by a self-centering capability, which are two desirable properties for seismic applications. The former ensures that resonance between the bearing and horizontal earthquakes will not occur while the latter guarantees the bridge superstructure can self-center to its original position after an earthquake. Analytical models for the bearings under vertical loading and horizontal and vertical ground motions are derived and validated with results from finite element analyses and experimental studies. To decrease the displacement responses of the bearing and to maintain a constant spectral acceleration response while keeping the cost of the bearing low, sliding friction devices are integrated into a roller bearing. The seismic behavior of this new seismic isolation bearing with different design parameters under various ground motions is analytically studied. The parameters include the sloping angle, the sliding friction force and the PGA levels. Two prototype roller seismic isolation bearings have been developed and their design details are presented in this report. The first prototype bearing does not have any built-in friction devices, while the second prototype bearing has a unique built-in feature to achieve supplemental energy dissipation through sliding friction. The last part of the report presents a design example of the second prototype roller seismic isolation bearing to be used in a bridge in a region of high seismicity.