In order to study the seismic isolation mechanism of different seismic isolation devices on the long-span extradosed cable-stayed bridge of high-speed railway,an extradosed cable-stayed bridge with span arrangement(90+180+90)m was taken as the research background.Based on nonlinear time history analysis,a finite element model was established to study the damping effect of friction pendulum bearing,viscous damper and seismic isolation hybrid device as well as the seismic performance of the bridge.The results show that the combination of friction pendulum bearing and viscous damper at the main tower of the whole bridge can effectively solve the seismic problem under rare earthquakes.After parameter combination optimization,it is recommended to select the friction pendulum bearing with a friction coefficient α of 0.06 and a curvature radius of 2 m.Besides,the viscous damper with damping coefficient of 12,000 kN·(m·s-1)-αand damping index of 0.8 are recommended.Compared with the use of friction pendulum bearing and viscous damper alone,the hybrid seismic isolation device can greatly reduce the internal force of each key section of the bridge,the displacement of pier and the rotation angle of beam,and significantly improve the seismic performance of the bridge.Besides,the damping rate of shear force and bending moment is 70.85％and 76.94％,respectively,and the damping rate of pier top displacement is 76.08％.The safety factor of each key section is greater than 1,and the structure is in the elastic state,which can well meet the seismic performance requirements of the bridges.
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