Study On The Allowable Amplitude Of Vortex-induced Vibration Of Free-standing Steel Tower

Suspension bridges and Cable-stayed bridges are the most important type of long-spanbridges which are commonly adopted in these situations when across the gorges, bays, rivers.Bridge tower is one of the members of suspension bridge or cable-stayed bridge, with thespan getting larger, the height of tower becomes higher, also with the developing of design,theory of computing, structural style and the material of bridge, steel bridge tower willbecome more and more common in long-span bridges.We can consider the pylon is slim-lined construction, because of the ratio of height andlateral dimension is lager. At free standing stage, tower is of low stiffness and small dampingwithout stay-cables system constraints, wind-induced vibration will becoming one of the keyfactors in the design scheme, especially for steel pylon, the characteristic of low damping ismore notability, and effected by lateral wind more easily, is prone to vortex-inducedresonance. Large amplitude of vortex not only impact the security of workers, constructionmachinery and the comfort of the workers, but also affect the strength and fatigue. So, it isnecessary to limit the amplitude of pylon which is in vortex-induced resonance region. Whenvortex vibration occurs, the value of acceptable amplitude of vortex (allowable amplitude) isnot defined in specification.The paper sets out from the resistance of structure, make sure when the allowableamplitude happens the stree of the section is not larger than maximum allowable stress, itmeans we can acquire the simplification calculation formula of allowable amplitude throughallowable stress of sections. Taking the pylons of Hongkong-Zhuhai-Macao River-seaDirect Navigation Bridge and third Nanjing Yangtze River Bridge as examples, usingsimplification calculation formula to get the allowable amplitude, and add the displacement tothe ANSYS model according to the oscillating curve of tower, also the forces due to vortexshedding should considered in the ANSYS model. Then we can get the maximum strees of the unfavorable section, and compared it with maximum allowable stress to make sure thesimplification calculation formula is right. Besides, modified the formula of first bendingand torsional vortex vibration in terms of calculation results, and get the relation ofallowable amplitude and the height of pylon. Inadditon, simplification calculation formula ofhigher bending and torsional vortex vibration of allowable amplitude are also given, furthermore, validity of the formulas are verified through engineering cases.Then, after wind-induced response of pylon is calculated under different wind directionand speed and wind direction, wind-induced fatigue life of pylon is estimated in theory ofcumulative damage in fatique. Also comparing the effects of fatigue life with or withoutvortex-induced vibration, and it turns out vortex-indcued vibration has effect on fatigue life, itcan not be ignore. Then, a brief accouts of comfort of workers is given base on dynamicsensitivity parameterK D.In the end, the effects of damping ratio and aerodynamic figuration to the vortexvibration are discussed based on the wind tunnel test ofaeroelastic model.