Study Of New Techniques For Suppressing Cables Vibration On The Cable-Stayed Bridges

Stay cables of the long-span cable-stayed bridges are susceptible to vibration under wind loading, or wind incorporated rain excitation, or deck motion due to high flexibility, relatively small mass and very low inherent damping, such as vortex shedding, wake galloping, parameter resonance and wind-rain induced vibration. Large-amplitude vibration of cables may reduce the life of cables and threaten safe traffic, and has been considered today as one of the most critical problems for this type of bridge. Therefore, investigation of mechanism and countermeasures of cable vibration is very important for construction and maintenance of the cable-stayed bridges.Increasing the damping of cables is the most direct and effective way of suppressing cable vibration. Since the damping of long cables tends to be naturally very low, the addition of relatively small amounts of damping at or near cable ends can provide dramatic improvements in stability. Traditional approach to raise damping is installing passive damper between cable and deck, such as viscous (oil) dampers. The viscous dampers have been successfully used on a number of existed bridges in the world, however it is difficult to acquire optimal effect due to inherent disadvantages of this type dampers. In addition, the way to determine optimal parameter need to be improved and perfected. In the recent years, a new smart damper, magnetorheological (MR) damper, is developed for vibration control, which is made of smart MR fluid. MR damper has an excellent variable damping property and its damping force can be changed by adjusting voltage applied to damper. Therefore, semi-active control can be implemented with the damper. Mitigating cable vibration using MR damper can be considered as a new research item, many problems in theory and application are remained to research and solve. Base on review of existed study and application in suppressing cable vibration in the world, technique of mitigating cable vibration with viscous damper and MR damper has been investigated in this dissertation, and the main contents and progresses in form of summary are as following:1 The motion differential equations of the cable-damper system are formatted, which take into account these factors, such as the inclined angle, sag, stiffness etc. Coupling motion between cable and deck is studied with analytical and numerical method. Numerical results show that large amplitude vibration of cable with beat rhythm will occur when exciting frequency of deck equals two times modal frequency of cable.2 A modification approach of the dynamic model of cable-damper system is proposed. The approach is employed to modify parameters of cable-damper modal using cable system's first a few of modal frequencies which is obtained by field test. Results show that analytical frequencies of modified cable model are close to field test's one with very small errors.3 A method identifying the structural parameter using the neural network is proposed. Simulation results show that the method is very simple to application and has also a good precision. Non-parameter neural network model of the cable-damper system is formatted. Based on the damping force and responses for past time steps, responses at the next time step can be predicted accurately with the non-parameter model.4 Dynamic characteristics of cable incorporated viscous damper are investigated. The relationships ofmodal damping versus the stiffness of cables, the attachment height of damper and damping constant are obtained. With the optimal structural control method, a new approach to determine the optimal damping constant of viscous damper is presented. The first a few modal damping can be optimized simultaneously under the optimal damping constant of damper, which is more convenient than the existed design method.5 Numerical simulations for dynamic characteristic of cable-MR damper system are conducted. Relationships of the first three modal damping ratios versus the excitation amplitude, height attaching damper to cabl...