The effect of three-dimensionality on the aerodynamic admittance of truss girders in turbulence

The influence and aerodynamic mechanism of three-dimensional (3D) effects on the aerodynamic admittance function (AAF) of truss girders remain unclear. This study investigates the effect of 3D effects on the AAF of truss girders using the 3D buffeting force theory and segment model force measurement wind tunnel tests. The 3D effects, arising from the spatial distribution of turbulence and spanwise information of AAF, are quantified through 3D effect factors. The influences of the ratio of turbulence integral scale to the structural width γ and the structural aspect ratio θ on the 3D effect factors for AAF are systematically compared and analyzed. Furthermore, the applicable boundaries of the “strip assumption” under 3D effects are explored. Research findings indicate that the AAF of the truss girder identified through experiments is significantly influenced by 3D effects in the low-frequency region, with its magnitude notably lower than the theoretical value for a thin airfoil. The γ and θ have substantial impacts on both the 3D effect factor and AAF. The 3D effect factor and AAF increase with increasing γ but decrease with an increasing of θ. The two-dimensional (2D) AAF can be derived by isolating the 3D effect from the 3D AAF, depends solely on the sectional shape of the girder and the reduced frequency and remains unaffected by γ and θ. When γ > 1.5 and θ > 6, the “strip assumption” demonstrates sufficient accuracy, and under these conditions, the 2D AAF of truss girder has sufficient precision to evaluate the buffeting force acting on the girder.