Research On Wind-induced Vibration Characteristics And Influencing Factors Of H-Shaped Hangers With Moderate Side Ratio Under Large Wind Angles Of Attack

H-shaped hangers,as a common blunt section component in large span arch bridges and steel truss bridges,are distinguished by their high slenderness ratio,low damping ratio,and wide range of wind attack angles.In comparison to circular hangers,H-shaped hangers experience a more complicated and prominent wind-induced vibration problem.Currently,there is a dearth of research investigating the characteristics of soft flutter of the H-shaped hangers at large attack angles,and the commonly employed openings of the web or flange also require improvement as they are incapable of suppressing all potential wind-induced responses.To address this,this paper takes the H-shaped hangers with medium side ratio(width-to-depth ratio as B/D = 2.4)as the research object,and mainly conducts the following research:In order to identify the basic wind-induced vibration properties of the H-shaped sections,a three-degree-of-freedom coupled vibration test device was designed to perform the wind tunnel segment model force measurement and vibration test at attack angles ranging from 0° to90°.As a result,three force coefficients and wind vibration responses were obtained,and four kinds of turbulent wind fields were simulated by passive grids.The findings indicate that the H-shaped sections exhibit a flutter phenomenon within the attack angle range of 0° to 30°,and display strong axial vortex resonance at an attack angle of 65°.The influence of turbulent intensity on the vibration response of H-shaped sections is more pronounced than that of turbulent integral scale,as it not only changes the vibration mode of the H-shaped sections under turbulent wind fields but also induces vortex resonance and galloping resonance.Secondly,to evaluate the opening measures of the H-shaped hangers in actual bridges,vibration tests were carried out using an aeroelastic model with adjustable opening ratios,uncovering the influence of unopened and combined web/flange openings on the vibration response of H-shaped hangers.Moreover,an indicator function for evaluating the opening ratio was proposed,which proved to be an effective reference for performance evaluation of the combined opening of H-shaped hangers.The research shows that the vibration phenomena of the H-shaped sections with no opening are considerably intricate at 0° attack angle,and soft fluttering vibration emerges at 30° attack angle.The vibration modes of the H-shaped hangers with openings,on the other hand,undergo alterations.For a single opening,the flange opening should be selected when the opening rate is less than 20%,while the web opening would be more appropriate when it is higher than 20%.For combined openings,an optimal solution can be achieved by combining moderate flange openings and larger web openings.Finally,the vibrational characteristics and flow field mechanism when soft flutter occurs were analyzed by combining segment model test results and CFD numerical simulation technology.On the basis of verifying the reliability of the numerical simulation method,the static three force coefficients of the H-shaped section and dynamic mesh soft flutter simulation based on the free vibration method were calculated.The research reveals that distortion occurs when implementing the traditional vertical spring suspension system at large attack angles,thus indirectly affirming the superiority of the three-degree-freedom coupled vibrating device.During the limit cycle oscillations of the soft flutter,the degree of involvement of phase difference and vertical vibrations remains nearly constant.However,after the flutter divergence,the degree of involvement of phase difference significantly decreases,while the degree of involvement of the vertical bending significantly increases,leading to a weakened torsional coupling effect.