| Double-box composite beam has the advantages of light dead weight and convenient construction.However,due to the blunt aerodynamic shape,it is sensitive to wind load.Vortex-induced vibration occurs easily at low wind speed.It will have an impact on pedestrians and traffic.And cause fatigue to the structure.With social development,to meet the demand for traffic,the width of double-box composite beam is getting larger and larger.At present,the research on the aerodynamic force and vortex-vibration characteristics of double-box composite beam by scholars at home and abroad is mainly aimed at specific practical projects.The amplitude of double-box composite beam is not very wide and there is no influence law of different width-height ratio on aerodynamic and vortex vibration characteristics of the system.In order to ensure the wind-resistant safety of widewidth double-box composite beam,it is necessary to accurately determine their aerodynamic and vortex vibration characteristics.In view of this,the widest doublebox composite beam bridge in China is taken as the engineering background.Firstly,through the combination of model force test and numerical calculation,the aerodynamic characteristics of double-box composite beam under different wind attack angles and width-height ratio were studied.And the flow field mechanism was explored.Then,the vortex-vibration characteristics of double-box composite beam under different wind attack angle,damping ratio and width-height ratio were studied by model vibration test.The main work and conclusions of this paper are as follows:(1)The variation of aerodynamic characteristics of double-box composite beam with wind attack angle and width-height ratio was made clear: When the wind attack angle changes from-10° to 10°,the drag coefficient of double-box composite beam with width-height ratio of 12.8 decreases first and then increases.The minimum when the wind attack angle is 0° and the maximum when the wind attack angle is10°.The lift coefficient is positive at positive angle of attack and negative at negative angle of attack.And all of them show an increasing change law with the increase of wind attack angle.When the wind attack angle changes from-10° to 10°,the lifting moment coefficient increases first,then decreases and then increases again.The torque direction is always clockwise.With the width-height ratios increases,the drag coefficient and lift coefficient of double-box composite beam can be divided into two intervals.The drag and lift coefficients are about 1.29 and-0.26 for an aspect ratio of 9 to 15,and 1.61 and-0.13 for an aspect ratio of 15 to 19,respectively.With the width-height ratios increases,the coefficient of lifting moment decreases linearly in general.(2)The variation of vortex vibration characteristics of double-box composite beams with wind attack angle,damping ratio and width-height ratio is revealed:With the wind attack angle changes from-3°to 3°,vertical bending vortex vibration response increases in low wind speed region and decreases in high wind speed region.The change of torsional vortex vibration response with wind attack angle has no obvious change law.Damping can obviously restrain vortex vibration of doublebox composite beam.There are two vertical bending vortex vibration zones in double-box composite beam with different width-height ratios under horizontal inflow.In the low wind speed range,the amplitude first increases and then decreases with width-height ratios.In the range of high wind speed,the amplitude increases firstly and then decreases sharply with the width-height ratios.There are two torsional vortex vibration intervals in double-box composite beam with different width-height ratios under horizontal inflow.In the low wind speed range,the amplitude changes little with the increase of width-height ratios.In the range of high wind speed,the amplitude increases and then decreases with the increase of widthheight ratios. |
