Seismic performance improvement of continuous rigid-frame bridges with hybrid control system under near-fault ground motions

To improve the seismic performance of continuous rigid-frame bridges (CRFBs) in near-fault earthquakes, this study developed a hybrid seismic control system (HSCS) combining a three-dimensional hybrid seismic isolation bearing (3D-HSIB) with a longitudinal fluid viscous damper (L-FVD). The hybrid numerical model of the HSCS and the nonlinear numerical model of a CRFB prototype were simulated in OpenSees. The study comparatively analyzed the seismic responses of non-controlled bridges and HSCS-controlled bridges under near-fault ground motions, evaluated the seismic control effectiveness of the HSCS, and investigated the effects of vertical exci-tations on the seismic performance of the CRFB. The numerical results show that the proposed HSCS effectively reduces the three-directional seismic responses of the CRFB. When the PGA is 0.4 g, the seismic isolation ratios of displacement, internal force, and pounding force all exceed 0.4. The hysteresis behavior of the HSCS can be fully utilized under three-directional excitations with pulse-like effects. The girder-end uplift behavior under vertical excitation can be effectively controlled by the proposed 3D-HSIB with a seismic isolation ratio of at least 0.6. When vertical excitation exceeds a certain level, the bearing is tensioned upward while axial tension force may also occur in main piers. Furthermore, the seismic responses under pulse-like near-fault ground motions are significantly larger than those under non-pulse near-fault ground motions. This work may provide a useful reference for the seismic analysis and design of CRFBs.