Vibration Control Of Stay-Cable Using Magneto Rheological Damper

Considering an extremely economic design and an aesthetic view to human being, cable-stayed bridges are practiced widely in longer spans. As the most important structural components in cable-supported bridges, stay cables, however, are vulnerable to vibrations with large amplitudes due to relate small mass, low internal structural damping and high flexibility. A number of methods have been proposed to mitigate cable vibrations, such as tying cables together, aerodynamic cable surface modification, passive and semi-active cable control have been used to dampen vibration. However, each has limitations in suppressing the longer cable vibration. As semi-active control devices, magneto-rheological (MR) dampers have significant potential to advance the acceptance of structural control as a viable means for dynamic hazard mitigation. This thesis focuses on the field of control of cable vibration by using MR dampers. Main conclusions are as follows:Considering that the field experimental study of bridge stay cables installed MR dampers is lack and different passive vibration controls have not compared in the same experiment, the discrete MR dampers were installed on the 154m-Iong cable near the anchorage in the 3rd QianJiang cable-stayed bridge. Vibration mitigation of the cable using MR dampers in a purely passive mode, where constant levels of current are supplied to the damper, is examined by a series of free vibration tests and compared to that of using oil dampers. The displacement signal is driven by harmonic planar loads, filtered through wavelet decomposition and transformed by Hilbert. The equivalent cable modal damping ratios attributed to MR dampers were measured and the relationship between the equivalent modal damping ratios, the system frequency, the voltage imposed and displacement responses at the point of cable was pursued. It is shown that MR dampers to the cable can more significantly reduce cable vibration than oil dampers do. There is optimum voltage on which the maximum modal damping ratio can be achieved.A theoretical model for the cable damper system is formulated by accounting for the cable inclination and sag effect based on the Hamilton's principle. The motion of the cable was computed by using a finite series approximation with the Galerkin method. A static deflection shape as an addition shape function improved the sine series convergence. The experimental cable is taken as an numerical example. A nonlinear hysteretic biviscous model is identified for MR dampers according to experiment. The results also show the similar phenomenon and conclusions from experiment.A stay cable incorporated with MR dampers exhibits pronounced nonlinearity. The dynamic response performances of a cable with MR dampers are explored indetail by using Spencer photometric model. The primary measure of damper performance considered is the root mean square(RMS) cable deflection integrated along the length of the cable and the whole time. A universal estimation approach has been configured to depict the relationship among the equivalent modal damping ratio, RMS cable deflection, the optimal parameter of MR dampers (marker, mounting position and voltage applied), the first frequency of cables (tensile force, length and mass per unit length), Irvine parameter, excited loads (type, frequency and amount). The mitigation effect of the first three modal vibration of the cable was compared to the optimal oil dampers do. Frequency shift also debated. The theoretical studies rich and perfect the experimental results, and supply an optimal method for passive MR damper in practice.Based on equivalent RMS cable deflection criteria, the simplifying model is established for MR damper passive control. The calculated results shown that the simplifying model not only has the similar effect of mitigation to the Spencer model but also reveal the laws of energy dissipation criteria for MR dampers much better. The equivalent viscous damping coefficient and the equivalent stiffness coefficient capture the salient features of M...