| Cable-stayed bridge become more longer with the development of bridge technology and the increasing demand for bridge functions.In recent years,the phenomenon of high-order vortex-induced vibration has been observed on cable-stayed bridges with ultra-long cables.Traditional viscous dampers are generally designed for low-order wind and rain-induced vibrations,and it is difficult to effectively control high-order vortex-induced resonances.So this brings new challenges to the traditional viscous damper design of stay cables.In this paper,a new viscous inertial mass damper(VIMD)is formed by adding inertial mass into the viscous damper to improve the ability of the damper to simultaneously control the low-order wind-rain-induced vibration and highorder vortex-induced resonance of the stay cable.Taking the cable A30 on the Sutong Yangtze River Bridge as a background,the vibration damping effect of VIMD and the factors affecting the vibration damping effect of VIMD were carefully studied by the taut string model and the three-dimensional continuous model of cable stays of considering sag effect.The main contents are as follows:(1)The free vibration analysis of the cable-VIMD system and the vibration damping effect of VIMD on stay cables were investigated by using the taut string model.Firstly,the composition and vibration damping mechanism of VIMD are introduced,and then the differential equations of free vibration of stay cable-VIMD system are numerically solved by finite difference method.Secondly,the influence of VIMD installation position and inertial mass on the optimal dimensionless damping ratio of stayed cable-VIMD model is analyzed,and the numerical solution method is compared with the analytical solution method.Meanwhile,the influence of inertial mass on system frequency is also researched.Finally,the optimal inertial mass required for each modes of the stayed cable-VIMD system to reach the optimal damping ratio is calculated.The results show that the modal damping ratio of the stay cable is obviously enhanced by adding inertial mass into the viscous damper,and this is useful for vibration control of the stay cable.The magnitude of inertial mass required to achieve the optimal damping ratio is different for each modes.(2)The effect of various parameters on VIMD vibration reduction effect is studied.Firstly,by the taut string model establishing a stay cable-VIMD system model with stiffness,the effects of bracket stiffness and damper internal stiffness on the vibration damping effect of stayed cable-VIMD system were studied.Secondly,through the three-degree-of-freedom model of the stay cable,the influence of the inclination and sag of the stay cable on the vibration damping effect of the three-dimensional stay cable-VIMD system are analyzed.Meanwhile,the influence of the sag on the system frequency is analyzed.Lastly,the optimal inertial mass of the three-dimensional stay cable-VIMD model to achieve the optimal damping ratio of the system under different sags is analyzed.The results show that the modal damping ratio of the cable-VIMD system sharply decreases with the decrease of the support stiffness.The stiffness in the damper will also reduce the vibration damping effect of VIMD.Meanwhile,the damping ratio and dynamic characteristics of the first mode of the cable-VIMD system is decreases with the increase of the cable sag.(3)The damping effect of VIMD on wind-induced vibration of stay cables is studied.The studies show that when VIMD increases a small inertial mass,it has a good control effect on the cable stayed rain-wind induced vibration.VIMD has more advantage than VD when multiple vibration types of the cable need to be controlled. |
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