Parametric Vibration Of Cables For Long-span Railway Cable-stayed Bridges

In this paper, taking domestic long-span railway cable-stayed bridge as the background, and selecting some representative cables, the study about parametric oscillation for cables can be divided in two aspects-the theoretical analysis and numerical analysis.First of all, based on some basic assumptions, cable coupled and uncoupled theory analysis model is established and through the theoretical analysis method the vibration differential equation of cable will be derived. Through MATLAB using numerical analysis method, parametric excitation term、external excitation term and terms caused by end vertical displacement excitation can be further studied. In the case of coupling and uncoupling, one aim of the study which is oscillatory differential equation of stay-cable and tower or girder and exploring the influence on cable caused by the component of end vertical displacement excitation in the perpendicular direction of cable is implemented.Secondly, the finite element model of bridge and cable are established by means of the finite element software ANSYS, and then dynamic characteristics for the models are calculated. According to the calculation results, the possibility of cable resonance is confirmed. Next based on BANSYS in time domain buffeting and vehicle-bridge interaction, the displacement time history caused by wind load or vehicle load of cable in the end is calculated. Vibration response under different displacement excitations will be analyzed when the cable is imposed multiple displacement excitations(simple harmonic wave、white noise、wind load response or vehicle load response).The other aim of study the vibration response under the end vertical displacement excitation which is caused by simple harmonic wave、white noise、wind load or vehicle load is also implemented.Analysis of theoretical model for cable shows that, in the uncoupling vibration differential equation, the terms influenced by the component of vertical displacement excitation can be ignored. In the two-coupling vibration differential equation, if the terms influenced by the component of vertical displacement excitation is higher order, it can be ignored, otherwise should be retained; In the three-coupling vibration differential equation, all of the terms influenced by the component of vertical displacement excitation should be retained.Analysis of finite element model for cable shows that, simple harmonic excitation will cause cable vibration parameters; White noise excitation won’t cause parameter vibration lasso, but cable vibration amplitude should not be ignored; Under displacement excitation caused by the wind load, vibration response of the cable increases with the increase of wind speed, vibration response amplitude is smaller; Under displacement excitation caused by vehicle load, the shape of midpoint and end displacement time history curve to cable are analogous, they have the same development tendency, vibration response amplitude is smaller.