| The study presented in this thesis concerns the open-loop and closed-loop vibration control of bridge stay cables using semi-active magneto-rheological (MR) dampers. Theoretical investigations and in-situ experiments are carried out in this study.; The open-loop vibration control of flat taut cables is first investigated. A mathematical model based on complex modal theory is formulated to evaluate the damping ratio of the cable-damper system in the open-loop control mode, which takes into account the damper coefficient, damper stiffness, damper mass, stiffness of the damper support, and nonlinearity of the damper. Both asymptotic and numerical solutions are obtained. With the formulated model, a parametric study is conducted to investigate the effect of various damper parameters on the effectiveness of the vibration control.; Next, the proposed model for flat taut cables is extended for inclined sagged cables. The effects of cable sag and inclination are included in the formulation in terms of the sag-extensibility parameter. Making use of an asymptotic solution, a 'generalized universal formula' is proposed for the damper design, taking into account the sag and inclination of the cable as well as the abovementioned damper parameters. A parametric study is conducted to investigate the effects of cable sag and inclination on the control effectiveness. It turns out that the effect of the sag and inclination is independent of the damper parameters and, therefore, the parametric study carried out for taut cables is also valid for sagged cables. A case study is conducted for a 536 m long stay cable on Stonecutters Bridge to quantify the influence of the sag and inclination in extremely long bridge cables. The theoretical study concludes with the formation of guidelines for the design and implementation of MR dampers for open-loop cable vibration control, either in a multi-mode suboptimal control pattern or in a single-mode optimal control pattern.; For the purpose of in-situ experimental verification, the modelling of a full-scale MR damper and its application to the open-loop vibration control of a 114 m long stay cable in Dongting Lake Bridge are accomplished. The concept of an optimal voltage/current input that achieves maximum system damping is proven, and a multi-switch open-loop control strategy is developed.; In-situ experiments in the Dongting Lake Bridge site are then conducted to verify the effectiveness of MR dampers for the open-loop vibration control of stay cables under rain-wind excitation and artificial sinusoidal-step relaxation excitation, respectively. (Abstract shortened by UMI.)... |
