Seismic Control Of A Multi-Tower Cable-Stayed Bridge Subjected To Near-Fault Ground Motions

The seismic performance and control of multi-tower cable-stayed bridges has become one of the most important research issues in domestic and foreign academia and engineering. In order to guarantee the seismic safety of multi-tower cable-stayed bridges, the deep research should be focused on both the mechanical properties of multi-tower cable-stayed bridges and ground motion characteristics. In this paper, focusing on the seismic safety of multi-tower cable-stayed bridges subjected to near-fault ground motions, the seismic control method of multi-tower cable-stayed bridges subjected to near-fault ground motions is investigated with respect to five aspects, i.e., ground motion intensity indices, seismic performance of multi-tower cable-stayed bridges, characteristics of seismic control of multi-tower cable-stayed bridges, passive seismic control method and hybrid seismic control method. The main contents and achievements in this paper are as follows.1. The ground motion intensity indices subjected to near-fault ground motions are investigated. The applicable intensity indices for medium and long period structures subjected to near-fault ground motions are put forward. And the most unfavorable design ground motions applicable to medium and long period structures are further proposed combined with the concept of the most unfavorable design ground motion, based on which 7 groups of the most unfavorable design ground motions are determined for the seismic analysis of structures with different site conditions and vibration periods.2. The seismic performance of multi-tower cable-stayed bridges subjected to near-fault ground motions is investigated. The characteristics of seismic responses of multi-tower cable-stayed bridges using partially constrained system and full floated system subjected to near-fault ground motions are discussed in detail, on the basis of which the main control objectives of multi-tower cable-stayed bridges are determined. The analysis results reveal that the objective of seismic control for multi-tower cable-stayed bridges using partially constrained system subjected to near-fault ground motions is to reduce the longitudinal internal forces on the bottom of bridge towers due to the partially constraint between the bridge tower and girder, and the objective of seismic control for multi-tower cable-stayed bridges using full floated system is to reduce the longitudinal bending moments on the bottom of bridge towers, longitudinal top displacements of bridge towers and longitudinal relative displacements between bridge towers and girder (piers).3. The characteristics of seismic control of multi-tower cable-stayed bridges subjected to near-fault ground motions are investigated. The seismic effects of multi-tower cable-stayed bridges using partially constrained system and full floated system subjected to near-fault ground motions are discussed in detail using viscous damper and elastic cable, based on which the applicable passive control devices are determined. The analysis results reveal that the viscous damper is found to be more effective than elastic cable in controlling the seismic responses of multi-tower cable-stayed bridges using partially constrained system, and the viscous damper and elastic cable are both effective in controlling the seismic responses of multi-tower cable-stayed bridges using full floated system.4. The passive seismic control method for multi-tower cable-stayed bridges subjected to near-fault ground motions is investigated The optimization control method using the combination of the response surface method and genetic algorithm is put forward for multi-tower cable-stayed bridges subjected to near-fault ground motions. The passive seismic control method using viscous fluid damper is established for the multi-tower cable-stayed bridges using partially constrained system considering the contradiction of longitudinal internal force control of bridge towers. And the comprehensive control system using both viscous damper and elastic cable and the corresponding two-stage optimization control method are proposed for the multi-tower cable-stayed bridges using full floated system.5. The hybrid seismic control method for multi-tower cable-stayed bridges subjected to near-fault ground motions is investigated. The semi-active control effect of multi-tower cable-stayed bridges using MR dampers is diseussed using the combination of the classical linear optimal control algorithm and Hrovat optimal control algorithm, on the basis of which the optimal semi-active control schemes are put forward for multi-tower cable-stayed bridges using partially constrained system and full floated system. The hybrid seismic control strategy with mainly passive control and secondarily semi-active control is proposed for multi-tower cable-stayed bridges, on the basis of which the hybrid seismic control methods are put forward for multi-tower cable-stayed bridges using partially constrained system and full floated system.