Identification of two-dimensional aerodynamic admittance of a central-slotted box girder based on force-balance measurements

Abstract

This paper presents an experimental investigation of buffeting lift forces on a central-slotted box girder in turbulent flow, and aims to identify the corresponding generalized aerodynamic admittance (generalized-AAF) and two-dimensional aerodynamic admittance (2D-AAF). The generalized-AAF is obtained using the one-wavenumber spectra of lift and wind fluctuations, while the 2D-AAF is obtained using an improved method based on force-balance measurement. The key to this improved method is separating out the three-dimensional effect of turbulence (3D-effect) from the generalized-AAF while considering the segment length of the force measurement and turbulence integral scale. The results indicate that the generalized-AAF of the central-slotted box girder is much less than the Sears function, which is consistent with most previous studies. However, the values of 2D-AAF decay more slowly in comparison with the Sears function. An empirical formula for the 2D-AAF of the central-slotted box girder is given based on the experimental data. Additionally, the study finds that the ratio of the turbulent integral scale to the characteristic dimension of the model plays a significant role in determining the 3D-effect of turbulence, resulting in the difference between the generalized-AAF and 2D-AAF. Therefore, the 2D-AAF is particularly useful for estimating the buffeting force of a bridge deck when the turbulence scale does not match the size of the model.