Theoretical Analysis On Vibration Control Of Cables On Cables-stayed Bridges

Cables are very efficient structural members due to their high strength and lightweight. However, they are flexible and their inherent damping is typically small.Consequently, large vibrations of cables can be easily induced by external forces ortheir support motions, such as wake galloping, parameter resonance, vortex sheddingand wind-rain induced vibration. Large cable vibrations developed minor cracksaround the anchor joints of the cables in many cable-stayed bridges.Corrosion-protection systems were thus damaged, which might lead to failure of thecables, large-amplitude vibration of cables may threaten safe traffic. Therefore,investigation of mechanism and countermeasures of cable vibration is very importantfor construction and maintenance of the cable-stayed bridges. If cables are long，control of such vibration by the conventional passive or semi-active dampers is verydifficult. Active control is a possible alternative to control vibrations of small-sagcables by use the axial support motion, although it possesses many problems in itsimplementation at present.This dissertation，supported by the Natural Science Foundation of the nationalproject, is concerned with the vibration axial active control of small-sag cables.Simulation analysis is carried out. The main contents are as follow:(1) Based on the comprehensive plenty of domestic and foreign literature,conception of structural vibration control is introduced. Review andsummary of the research is given, on vibration and vibration control ofcables in cable-stayed Bridges.(2) This paper introduces the current common active control algorithm, forexample, pole assignment, classical linear optimal control, instantaneousoptimal control, independent modal space control, sliding mode control,H state feedback control and optimal polynomial control and so on.(3) In order to control the vibration of small-sag cables, the main idea is thecable employed throughout this study is attached at a fixed support at oneand at a time-varying support at the other end and the support moves in thecable axial direction. The support displacement is responsible for axialactive control force on cables. Single modal and multi-modal modelsin-plane of small-sag cables of axial active control are established through modal reduction theory and Lagrange equation.(4) Based on active control model of small-sag cables vibration in-plane, singlemodal and multi-modal controls under different load case are realizedthrough linear quadratic optimal control strategy. The control efficiency isanalyzed and compared, and finally find out optimal active control force.(5) Based on active control model of small-sag cables vibration in-plane, singlemodal and multi-modal controls under different load case are realizedthrough Bang-Bang control strategy. The control efficiency is analyzed.