| In recent years,with the development of China’s transportation industry,the spanning capacity of arch bridges becomes increasingly large,and the span of arch ribs also increases.Large-span steel arch ribs are sensitive to wind loads due to their lightweight and small stiffness.At the same time,it will also be prone to vortex-induced problems at low wind speeds.It is of great significance to grasp accurately the aerodynamic force and vortex-induced vibration characteristics of long-span steel arch ribs for wind-resistant design.At present,the domestic and foreign scholar’s research on long-span steel arch ribs is mainly aimed at the conventional equal section of the aerodynamic force and vortex-induced vibration characteristics.However,to better meet the overall aesthetics of the bridge and other functional requirements,some irregular variable cross-section steel arch ribs appear from time to time,and their aerodynamic force and vortex-induced vibration characteristics are significantly different from those of conventional steel arch ribs.To ensure the wind resistance safety of irregular variable cross-section steel arch ribs,it is necessary to conduct in-depth research on its aerodynamic force and vortex-induced vibration characteristics.In this thesis,a large-span irregular variable cross-section steel arch rib was taken as the research background.Firstly,under different wind attack angles(α)and spacing ratios(L/B),the aerodynamic force characteristics of the arch rib were analyzed by the two-dimensional section model in the middle span.Then,under different wind attack angles and turbulence intensity(I_u),a series of analyses on the vortex-induced vibration characteristics of the arch rib were analyzed by the two-dimensional section model in the middle span.On this basis,under different wind attack angles and turbulence intensity,the three-dimensional aero-elastic model test was used to further study the vortex-induced vibration characteristics of the arch ribs.The main conclusions of this thesis are as follows:(1)Based on the mid-span two-dimensional segment model indicate that the aerodynamic force coefficient of double arch ribs has an obvious critical spacing effect.The critical spacing ratio is(L/B)cr=2.0～2.5 when wind direction angle is-5°and(L/B)cr=2.5～3.0 under other wind direction angles.The aerodynamic force coefficient of the upstream arch rib shows an obvious reduction effect at L/B<(L/B)cr,while the interference effect is not obvious at L/B>(L/B)cr.The absolute value of the drag and torque coefficient of the downstream arch rib shows an obvious reduction effect,and the interference effect of the lift coefficient is closely related to wind direction angles.The Strouhal number of double arch ribs mainly reveals a reduction effect.(2)Based on the two-dimensional section model test and the three-dimensional aero-elastic model test,the variation of the vortex-induced vibration characteristics of the arch ribs with the wind attack angle and the turbulence degree is consistent:as the wind attack angle changes from-3°to 3°,the vortex-induced vibration amplitude of the double arch ribs gradually increases,and the vortex-induced vibration performance continues to deteriorate.With the increase of turbulence intensity,the vortex-induced vibration amplitude of the double arch ribs decreases gradually,and the vortex-induced vibration performance continuously improves..(3)Compared with the results of the three-dimensional aeroelastic model test,although the results are consistent for the variation of the vortex-induced vibration characteristics of the arch rib with the wind attack angles and turbulence,which based on the mid-span two-dimensional segment model test,the amplitude is larger,and the results are conservative.For variable cross-section arch ribs,the results of three-dimensional aero-elastic model test should be used as the basis for the final vortex-induced wind resistance design. |
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