Longitudinal combined seismic mitigation systems and optimal control for long span triple-tower suspension bridges

Abstract Compared with the two-tower suspension bridge, the seismic response of the middle tower is crucial for the seismic design of triple-tower suspension bridges. A finite element model was developed for a suspension bridge. The seismic responses of a triple-tower suspension bridge with an elastic cable (EC) or a fluid viscous damper (FVD) installed between the tower and the deck were analyzed, and the application of an energy dissipation central buckle (EDCB) which was composed of multiple buckling-restrained braces (BRBs) installed at the mid-span in the triple-tower suspension bridge was discussed. Several novel seismic mitigation systems, such as the combination of EDCB and FVD, and the combination of EDCB and EC, were implemented to control the seismic responses of triple-tower suspension bridges. The effects of different seismic mitigation systems on the seismic responses of suspension bridges were studied. Additionally, the seismic performance of triple-tower suspension bridges was evaluated using the analytic hierarchy process (AHP) method, and the selection of parameters for seismic mitigation systems in suspension bridges was discussed. The results show that the longitudinal displacement (LD) of suspension bridges can be effectively controlled by using EC or FVD; however, the internal forces of the middle tower significantly increase due to the use of EC. Applying an energy dissipation central buckle (EDCB) is an effective measure to reduce the internal forces of the middle tower in triple-tower suspension bridges. The combination of EDCB and traditional seismic mitigation devices is highly beneficial for improving the seismic performance of triple-tower suspension bridges. The analytic hierarchy process (AHP) method can be used to select the optimal parameters for seismic mitigation systems. The results indicate that Case 23 is the optimal solution for controlling the seismic responses of the triple-tower suspension bridge.