The Research On Aerodynamic Test Techniques Based On The Force And Pressure Composite Segment Model

For long-span and slender bridge,the vortex-induced vibration(VIV)and buffeting phenomenon of the main girder are the most common forms of wind vibration,controlling the amplitude of the two kinds of vibration are very important in the wind resistant design to bridge,how to reveal the mechanism of VIV and accurately to predict the buffeting response are the important topic in the field of wind-resistance study of long-span bridges,which is based on exactly understanding and expressing the vortex induced force(VIF)and buffeting force.Given all this,wind tunnel tests of typical section model were carries out on the basis of a developed three-segment sectional device,then the test techniques and characteristics of VIF and buffeting force were researched,which lay a foundation for the research of exact expression of VIF and accurate identification of aerodynamic admittance.The main contents of this article are as follow:(1)The current VIV and buffeting anslysis theory were explained,then the test methods for aerodynamic force in wind tunnel test were discussed,and the research contents were proposed.(2)Designed and developed a three-segment sectional force and pressure device,which can get aerodynamic force of the model by internal balance and surface pressure integration synchronously.What’s more,access method for forces of the model and how to take out disturbing force such as inertia force were studied.(3)With the wind tunnel test of uniform convection field,the VIF in locked-domain of typical rectangular section and bridge section was tested and charateristics of VIF was analyzed based on VIF work and the offset between VIF and displacement response.It was found that variation curve of VIF with reduced wind speed was similar to the variation curve of displacement response with reduced wind speed.But the lag between VIF and displacement kept changing in the VIV domain,and VIF do positive work in the whole domain,which increased with the increase of reduced wind speed berore the wind speed correspondent to the maximum amplitude,then the lag between VIF and displacement were changed,and the work done by VIF decreased with the increase of reduced wind speed,finally VIV would fade when the work done by VIF was going to be zero.(4)With the VIF of tunnel tests for rectangular section and bridge section,On the basis of consistency of inverse displacement and measured displacement by Newmark-β method,the force capabilities was verified.Then the VIF time history would be further used to recognize parameters of Scanlan empirical nonlinear model,which was used to be compared with the result recognized by Ehsan-Scanlan displacement parameter identification method.The result shows an obvious gap between the two sources.(5)The aerodynamic lift could be acquired by pressure integration and force banlace,the result show that VIF tested by balance is a little too large in comparasions.Then aerodynamic lifting force correlation were studied according to the data of surface pressure,found that the span wise correlation of vortex-induced lift force decreased with the increase of system damping ratio,while span wise correlation of vortex-shedding force in fixed model tests is obviously lower than the correlation of vortex-induced lift force,which indicated that self-excited aerodynamic force has significantly effect on span wise correlation of VIF.(6)Compared and studied characteristics of different harmonic wind fields generated by along-wind active turbulence generater,and aerodynamic force of rectangular section model adopted elastic hanging style and fixed style in the wind field was tested by pressure integration and force banlace,.After that,the difference of correlation analysis between aerodynamic force and the coming wind were discussed,results shows that,the span wise correlation of both buffeting lifting forces and buffeting torque were obviously higher than the values of the coming wind speed in the same position,while span wise correlation of elastic aerodynamic force was higher than span wise correlation of buffeting force,which indicated that self-excited force could increase span wise correlation of aerodynamic force in stochastic wind field.