Research On Nonlinear Aerodynamic Characteristics Of Large-amplitude Vibration Bridge Decks Via Wind Tunnel Tests

With the rapid development of the country,the span of the bridge is increasing,the structural rigidity is getting smaller and smaller,and the Ultra-large span bridge is more prone to wind-induced vibration.The traditional theoretical framework is only applicable to micro-vibration,and the linear frequency domain analysis method can not solve all problems.The phenomena of limit-loop chattering,frequency multiplication,and frequency mixing observed in wind tunnel tests also indicate that nonlinear effects cannot be ignored.Therefore,it is very important to study the aerodynamic nonlinearity of the vibration of the bridge girder section.This paper focuses on two typical sections,a thin plate section and an H-section,and Uses a self-developed suspension device to perform a large-scale vibration wind tunnel test.Some main results are summarized as follows:(1)The thin plate model and the H-shaped section were subjected to single-degree-of-freedom vertical and torsional excitation at an angle of attack of 0° wind speed of 0°,and the frequency and damping ratios were investigated with amplitude changes.The results show that the vertical bending frequency and torsional frequency vary little with the amplitude,the mechanical damping ratio of the system changes little with the amplitude,and the system characteristics are stable.(2)When the initial attack angles are 0°,+5°,0°,and +5° in the uniform flow field and turbulent flow field,the initial excitation is not applied to the high wind speed interval and the fluttering process is observed.,Solve the instantaneous frequency and damping ratio.In the low wind speed range,after the initial excitation is applied,the model is attenuated and vibrated.The results show that with the increase of amplitude,the frequency decreases gradually.Under the same amplitude condition,the absolute value of the aerodynamic negative damping ratio increases with the increase of wind speed.Therefore,the higher the wind speed,the faster the model divergence.At the same wind speed,the absolute value of the damping ratio increases continuously,so the rate of occurrence continues to increase.In the low wind speed range,the model does decay vibration.Affected by positive aerodynamic damping.The lower the wind speed,the greater the aerodynamic damping and the faster the model decay rate.Through the H-section model,under the uniform flow field of 0°,the angle of attack of +5° and the angle of attack of the turbulence field of 0°,with different wind speeds,it can be seen that the model performs limit cycle vibration.With the increase of amplitude,the instantaneous frequency decreases gradually,and the damping ratio increases with the amplitude.In the low wind speed range,the model performs damped vibration.In the damping process,the damping work is gradually offset by the aerodynamic work,and the damping ratio gradually decreases until it decreases to around zero.