Vortex-induced Vibration Performance Of ?-shaped Composite Girder And Its Aerodynamic Control Measures

With the advancement of science and technology,the modern bridge structure is constantly developing in the direction of slender,soft and low damping.On the basis of summarizing multiple wind-casued accidents,Bridge Wind Engineering is gradually grown up.As a kind of frequently happened wind-induced vibration at low wind speed,vortex-induced vibration?VIV?not only affects the comfort and safety of bridge driving,also may causes fatigue damage to the bridge structure.So,it is an important part of the research of Bridge Wind Engineering.This thesis takes a long-span cable-stayed bridge with ?-shaped composite girder and small side boxes,which is going to be constructed,as a practical research background.Firstly,a finite element model is built in ANSYS and the dynamic characteristics is calculated out.The 1^st symmetric vertical bending frequency of the main bridge is0.2445Hz and the 1^st symmetric torsion frequency is 0.4047Hz.Then,based on the result of dynamic characteristics calculation,a scaled section-model wind tunnel test of the girder is carried out.The static test gives out the aerostatic coefficients of Tri-component of the girder under wind attacking angle ranging from-12°to+12°.In the dynamic test,at an angle of attack of 0°and+3°,the vertical VIV is occurred at the wind speed between 16m/s and 24m/s.The largest vertical displacement is 144.3mm.After that,five different aerodynamic control measures are put forward into the test.Comparing the vibration suppression effect,No.3 wind fairing is the best.In the CFD part,a 2D square cylinder simulation model is established to verify the suitability of the FLUENT and the correctness of the parameter settings.In the static flow calculation,the result of both laminar flow model and SST k-?model is match the references in other documents well.By dynamic grid technology and loose coupling method,square cylinder with vertical vibration is simulated.It comes out the motion of square cylinder contains VIV and“Lock-on”phenomenon.Finally,a simulation model with the same scale of wind tunnel test model of the girder is established.The calculation of the aerostatic coefficients of Tri-component of the girder basically meets the tests'.Under dynamic mode,the girder suffers vertical VIV at the wind speed from 12m/s to 28m/s.The vibration's amplitude is 98mm and frequency is“Locked-on”2.3Hz,which is close to the setting value of girder's self-oscillation frequency2.296Hz.In summary,this thesis talking about the VIV of ?-shaped girder based on wind tunnel test and numerical Simulation.Although there is a certain gap between the results of two methods,the overall trend is consistent.This paper also gives out some aerodynamic control measures and chooses the bset by tests.It may has reference value and significance for the study of VIV and wind-resistent design of bridges with ?-shaped girder.