Two-Dimensional Aerodynamic Admittance of a Flat Closed-Box Bridge

Abstract

Wind tunnel tests were carried employing two different free-stream turbulent flow fields and one harmonic vertical gust profile conditions, and pressure measurements of the buffeting force on six separated strips of a flat closed-box bridge-deck section model were recorded. Two-dimensional aerodynamic admittance functions (2D-AAF) were obtained using one- and two-wavenumber computational theory, respectively. An empirical expression for determining the 2D-AAF for flat closed-box bridge decks in free-stream turbulence was proposed based on the extensive results of the experimental data. This study indicates that the 2D-AAF of the flat closed-box bridge deck is higher than the Sears function in the low-frequency range, and the aerodynamic admittance remains almost constant for reduced frequencies in the range of 0–0.145. For a given bridge section, its 2D-AAF is unique and related only to the geometry of the deck cross section, regardless of whether or not the strip assumption is valid. The fluctuating pressure near the leading edge of the bridge deck in the harmonic vertical gust was obviously much larger than that obtained in free-stream turbulent wind fields, which significantly affects the magnitude of the lift force.