Complex Wind-Induced Vibration Of Hangers In The Wake Of A Long-Span Suspension Bridge Tower

Taking advantage of high tensile strength of cable structures,suspension bridges are suitable to construct super-span bridges.However,hangers connecting the main cable and the girder have a small aspect ratio and low damping,sensitive to wind load.In the field observation,it is found that the long hangers near the bridge tower suffered a large amplitude vibration induced by wind,resulting in the collision between hangers.Therefore,it is necessary to study the wind-induced vibration characteristics and the vibration mechanism of long hangers near the bridge tower,which will provide the theoretical basis for the vibration reduction of the hanger.The main contents of this paper are as follows:First of all,since the hanging point and the surrounding flow field is closely relate to the vibration of hangers,the characteristics of flow field around the bridge tower should be studied first.The CFD model around the tower without hangers is established and wind velocity is monitored at the hanging points.By analyzing the relationship between aerodynamic force of the tower and the velocity at the hanging points,which are found to be basically identical in the main frequency components.Secondly,factors contributing to wind induced vibration of two groups of hangers near the tower is studied.The vibration of hangers is influenced by the tower wake,interference and collision between each other,which is very complex.The dynamic mesh method is used to control the deformation and reconstruction of the mesh around the hangers,whose vibration and collision are controlled by the User Defined Function.The hanger will resonate when the vortex shedding frequency of the tower is close to its natural frequency.In different wind yaw angle,the tower wake affects the movement of first group of hangers,hangers interfere with each other in the second group of hangers more obviously.Finally,the motion of the three-dimensional hanger in the tower wake is predicted based on the simulation results.Thirdly,we adapt to set the jet pipe outside the hanger to suppress the vibration in the tower wake.The holes on the jet pipe are evenly arranged along the circumference to accommodate different incoming flow yaw angle.When the sling movement is intense,the velocity of the airflow blown out of the holes can reduce the hanger wake width,thus reducing the drag of the hangers.The lateral vibration of the hanger is also weakened by a certain degree since the contribution of the jet pipe.