Characteristics Of Buffeting Force On Twin-box Birdge Girders

In this dissertation,the buffeting force characteristics of twin-box girders are studied in detail and in-depth by means of wind tunnel test and theoretical analysis.The main contents of this paper are as follows:1.referring to two-dimensional buffeting force theory and three-dimensional buffeting force theory of thin airfoil,the concepts of two-dimensional and three-dimensional AAF of bridge section are defined,and the fundamental reason of the change of bridge AAF with turbulence characteristics is pointed out.The concept of equivalent three-dimensional AAF and the quantitative analysis method of three-dimensional effect of turbulence are put forward.2.Three kinds of turbulenct wind fields with different turbulence integral scales are simulated in the wind tunnel,and the turbulence characteristics of the simulated turbulent flow field are analyzed.A vibrating grid device which can generate fully correlated harmonic wind field is independently developed to identify the two-dimensional AAF of the bridge section,and the characteristics of the simulated fluctuating wind field are analyzed.The accuracy of the wind field is vertified by measuring the AAF of airfoil section in the harmonic wind field.3.Using the pressure measurement system,the fluctuating pressures on the surface of several typical twin-box girder sections are obtained.According to the obtained mena pressure distribution characteristics,fluctuating pressure distribution characteristics,time history curve and frequency spectrum of fluctuating load,the influence of the central gap width on its overall flow pattern is analyzed.The spanwise correlation of buffeting force of the overall twin-box girder and the upstream-and downstream-box is also studied,respectively.It is pointed out that the spanwise correlation of the twin-box girder decreases because the downstream box girder is affected by the wake from the upstream box girder.Based on the test data,the empirical formula of the buffeting force spanwise coherence function of the twin-box girder is established.4.Based on the concept of equivalent three-dimensional AAF,the equivalent three-dimensional aerodynamic admittance of the twin-box girder section in turbulent flow is identified,the difference between the equivalent three-dimensional aerodynamic admittance of the twin-box girder section and the traditional closed box girder is investgated,the empirical formula of equivalent three-dimensional aerodynamic admittance of the twin-box girder section is established,and the influence of flow pattern on the aerodynamic admittance of twin-double box girder is also disscussed.5.The pressures of several groups of twin-double box bridge models are measured in the fully correlated harmonic flow field.The flow characteristics,buffeting force spatial distribution characteristics and two-dimensional aerodynamic admittance of the twin-box bridge model in the two-dimensional flow field are analyzed in depth.The two-dimensional aerodynamic admittance empirical model suitable for the twin-box is established,and the three-dimensional effect transfer function is established to link the equivalent three-dimensional and two-dimensional aerodynamic admittance of the twin-box girder.