The Response And Aerodynamic Charictaristic Of Vortx-Induced Vibration Of Rectangular And Streamlined Box Girder In Turbulent Flow

Vortex-induced vibration(VIV)is wind-induced vibration often occurring on long-span bridges under common wind speed.Continuous vibration affects the driving safety and pedestrian comfort,and even leads to fatigue failure of components of bridge.At present,in the wind-resistant design of long-span bridges,the section model wind tunnel test under smooth flow field is usually used to evaluate the VIV performance by comprehensively considering the structual damping,vibration mode,and three-dimensional(3-D)characteristics of vortex-induced force(VIF).However,the actual bridge is at the atmospheric turbulence field,and the influence of turbulence on the VIV characteristics is highly uncertain.The current VIV evaluation methods may misjudge the VIV performance of the bridge.In this thesis,the classical 5:1 rectangular and streamlined box girder sections are selected as the research objects,and then the VIV performance and aerodynamic characteristics of them are studied in different turbulence field by using the wind tunnel test.Moreover,the VIF model of long-span bridge girder under turbulence field is constructed by theoretical derivation.Finally,an analysis method for evaluating the VIV amplitude of the actual bridge using the section model wind tunnel test is proposed.The specific research results of this thesis include:(1)The VIV events of long-span bridges recorded in the literature are summarized,and the wind parameters of the wind field are emphasised.Then,the research history of wind resistant design and VIV of long-span bridges is reviewed.Finally,the analysis method of VIV of long-span bridges is introduced.(2)The Scanlan’s semi-empirical VIF model and the identification method of related aerodynamic parameters are introduced.Based on this model,the influence of longitudinal fluctuating wind is introduced,and the concept of average VIF parameters is proposed.The VIF model of blunt body section in turbulence field is constructed.Three calculation methods of VIV response of long-span bridge girder based on Scanlan’s model are introduced and discussed.Finally,a method for predicting the VIV amplitude of the actual bridge in the atmospheric turbulence field using section model wind tunnel test is established.(3)The section model wind tunnel tests of 5:1 rectangular and streamlined box girder were carried out in the grid turbulence field,and the VIV performance and aerodynamic characteristics of these two sections in the different turbulence fields were systematically studied.The results showed that the turbulence field significantly reduced the maximum fluctuating pressure coefficient on the surface of the 5:1 rectangular in the primary “lock-in”region,and weaken the aerodynamic correlation along the flow direction and the span direction,thereby reducing the VIV amplitude,but the influence on the VIV performance in the secondary “lock-in” region is not obvious.When the turbulence intensity is lower than a certain value,the effects of turbulence field on the VIV performance of streamlined box girder section is not obvious,which may be due to the vortex shedding at the wake region,and the turbulence has little effect on the wake flow characteristics of the section.(4)Based on the section model wind tunnel tests,the aerodynamic characteristics and distribution characteristics of the VIV of the 5:1rectangular and streamlined box girder sections are analyzed.Then,the VIF parameters of the harmonic force model and the Scanlan’s nonlinear model in the turbulence field are identified by pressure measurement and vibration measurement,respectively.Finally,the obtained VIF parameters are corrected to obtain the‘pure two-dimensional’ VIF parameters.(5)The taut strip model is a typical slender flexible structure,which can simulate the structural characteristics of long-span bridge girder.Based on the 3-D VIV calculation method of long-span bridges in turbulence field established in this thesis,the VIV responses of a taut strip model in different turbulence fields are calculated,and the influence tendency of turbulent parameters on VIV is further explored,which lays a theoretical foundation for the VIV response analysis of actual long-span bridges in turbulence flied.