Wind-induced Vibration Control Of Large Span Cable-stayed Bridge Under Construction

A cable-stayed bridge under construction has low structural damping and is not as stable as a completed bridge. The structure is easy to vibrate due to wind excitation, which may affect the comfort of workers during construction. Strong wind or earthquake may cause safety problems of structure and construction devices. Therefore, vibration control countermeasures, such as installing mass dampers or energy dissipating devices, are necessary especially for cable-stayed bridges under construction. A cable-stayed bridge is a flexible and spacial structure which has more complicate static and dynamical characteristics, so active control is more effective for mitigating structural vibrations with multiple modes. To improve control performance, more than one distributed control devices may installed on the structure. It is significant to investigate the vibration control methods and control algorithm for complicated structures, such as cable bridges under construction, subjected to strong wind loads. In this dissertation, the following research topics:1. A cable-stayed bridge model for active control design is established. The analysis was carried out on dynamic characteristics and response of cable-stayed bridge at cantilever state of construction phase subjected to wind loads, and the contribution of modes to vibration response at important structural sections was discussed. For investigating the control of wind-induced vibration, a model of system that combined cable-stayed bridge and distributed mass dampers was developed with considering the contribution of self-excited force to aerodynamic damping and stiffness. Three modal reduction methods, i.e. the Guyan reduction method (the improved reduced system (IRS) method), the model reduction method using internal balancing, and the reduction method based on modal superposition, were discussed. A reduced system modal was obtained and ultilized for design active control algorithm.2. By introducing H₂/H_∞performance index functions, a parameter optimization method for distributed TMD was proposed. The method can be used for the design of multi-distributed TMD at arbitrary positions of structure, and the designed TMD can be tuned to one mode or multi-modes of structure. The effectiveness of distributed TMD was illustrated by simulation on an example cable-stayed bridge.3. Vibration control for buffeting response of cable-stayed bridge by ATMD was studied. Controllers were designed by LQG control algorithm or H_∞, control algorithm. Considering the engineering limitations for actual application of ATMD, control effectiveness of multi-distributed ATMD which were located at different positions and tuned to one or multi- structural modes were discussed.4. Aiming at the characteristics of buffeting response of cable-stayed bridge, hybrid control systems that combine TMD and ATMD for the wind-induced vibration were proposed. TMD and ATMD can be tuned to rower structural modes and higher mode respectively. The simulation results shown that the effectiveness of hybrid control can efficiently suppress both displacement and acceleration response of bridge.5. For the vibration control of a steel bridge tower of large span cable-stayed bridge under construction, passive dampers including TMD and TLD were designed and implemented. The tests and measurement on response of tower shown that the dampers had good performance for mitigating vibrations induced by wind.