Seismic-Isolation Study on Bridges with Variable-Frequency Friction Pendulum Systems (I)~(III)

In the past catastrophic earthquakes, isolated structures have been verified to have high seismic performance than conventional non-isolated structures. However, although the induced seismic loading is reduced through the elongated natural period, the unexpected larger response may occur during near-field ground motions. The objective of this project is to apply the new variable-frequency friction pendulum system (VFPS) to isolated bridges for avoiding the resonant response under near-field excitations. Additionally, the deck displacement can be decreased to avoiding the pounding effect at expansion joints and P-delta effect. The anti-lifting device is also installed with the VFPS in parallel to restraint the lift-off of the superstructure. In this poject, the target bridges are 2-D and 3-D bridges with regular columns and irregular columns. Numerical simulation is performed for the bridge with VFPS and anti-lifting device using the nonlinear dynamic time-stepping method. Shaking table testing is conducted to verify the isolation efficiency of the VFPS and the effect of the anti-lifting device. In this study, a simple, robust and highly efficient nonlinear dynamic time-stepping method is developed to analyze the complicated bridge with the VFPS and anti-lifting device which exhibit highly nonlinear behavior. The reasonable design parameters of the bearing system are suggested for practical implementation. It can be anticipated that the new bearing system is an excellent alternative scheme for the design of new bridges, the retrofit of the exiting bridges, and the reconstruction of bridges after earthquake disaster.