Experimental Study On Buffeting Force Characteristics And Aerodynamic Admittance Of Double-sided Box Π-shaped Beams

With the wide application of double-sided box Π-shaped beams in long-span bridges,it is urgent to study its wind resistance performance.In this paper,the buffeting force characteristics and aerodynamic admittance of double-sided box Π-shaped beams are studied in detail.The main research contents are as follows:(1)The quality of flow field in wind tunnel is measured and analyzed.Two kinds of threedimensional turbulence fields with different characteristics are simulated by passive grid device,and the uniformity and isotropy of the two kinds of grid turbulence fields are analyzed,and the wind speed data and basic statistical parameters of the two kinds of grid turbulence fields are obtained.(2)Three pressure measuring models of double-sided box Π-shaped beam segments with different aspect ratio are designed.Force and pressure measurement experiments were carried out in uniform flow field.The static three-component coefficients of double-sided box Π-shaped beams with three aspect ratios are obtained.The surface pressure distribution characteristics,fluctuating pressure spectrum characteristics,buffeting force spectrum characteristics and buffeting force spanwise correlation of double-sided box Π-shaped beams under its own characteristic turbulence are analyzed.The effects of aspect ratio,wind attack angle and average wind speed on buffeting force spectrum of double-sided box Π-shaped beams under characteristic turbulence and the spanwise correlation characteristics of buffeting force of Π-shaped beams with different aspect ratio are studied.The results show that the aspect ratio of the model and the wind attack angle will affect the buffeting force energy distribution of double-sided box Π-shaped beams under the characteristic turbulence,and the average wind speed only affects the buffeting force energy at the vortex shedding frequency.Under the action of characteristic turbulence,the spanwise correlation of buffeting force of double-sided box Π-shaped beams will be significantly enhanced with the decrease of aspect ratio of double-sided box Π-shaped beams.The experimental value of spanwise coherence function of buffeting force of double-sided box Π-shaped beams under the action of characteristic turbulence fluctuates sharply in the middle and low frequencies,and the spanwise coherence function value of buffeting force will increase obviously at the vortex shedding frequency.(3)Three double-sided box Π-shaped beam models with different aspect ratios were tested in two kinds of grid turbulence fields.The characteristics of surface pressure distribution,fluctuating pressure spectrum,buffeting force spectrum and spanwise correlation of doublesided box Π-shaped beams in two kinds of grid turbulence fields are analyzed,and the effects of aspect ratio and wind attack angle on buffeting force spectrum and spanwise correlation of double-sided box Π-shaped beams are studied.The empirical models of spanwise coherence function of buffeting force of three double-sided box Π-shaped beams with different aspect ratios are established.The buffeting characteristics of double-sided box Π-shaped beams in grid turbulence and characteristic turbulence are compared and discussed.The results show that the buffeting force energy caused by characteristic turbulence in grid turbulence accounts for a small proportion of the total buffeting force energy.the spanwise coherence function of buffeting force of double-sided box Π-shaped beams will fluctuate in low frequency.Compared with spanwise coherence function of buffeting force of double-sided box Π-shaped beams under characteristic turbulence,the fluctuation is obviously slowed down,and it will be slowed down with the increase of the aspect ratio of the model.The spanwise coherence of buffeting resistance will be less than that of longitudinal fluctuating wind speed at low frequency,which will disappear with the increase of aspect ratio of the model.(4)Three-dimensional one-wavenumber aerodynamic admittance and two-dimensional aerodynamic admittance of double-sided box Π-shaped beams with different aspect ratios are identified and fitted into objective functions.The effects of turbulence field characteristics,aspect ratio and wind attack angle on the two-dimensional aerodynamic admittance of doublesided box Π-shaped beams are studied.The results show that the two-dimensional aerodynamic admittance of double-sided box Π-shaped beams will appear convex at low frequency,which is obviously different from Sears function.The two-dimensional aerodynamic admittance of double-sided box Π-shaped beams in the two types of grid turbulence fields is basically the same,and there are significant differences in the two-dimensional aerodynamic admittance of double-sided box Π-shaped beams under different aspect ratios and different wind attack angles.