Experimental and Numerical Study on the Aerodynamic Admittance of Twin-Box Bridge Decks in Sinusoidal Gusts and Continuous Turbulence

Aerodynamic admittance functions (AAFs) of twin-box decks are particularly complex due to the presence of a central gap, so require the performance of dedicated studies to determine them. Two main approaches are available for this purpose, which consist of studying the aerodynamic forces produced by the section when impinged by sinusoidal gusts or continuous turbulence, respectively. However, owing to the difficulty in the generation of large-scale turbulence in traditional wind tunnel tests, the two aforementioned approaches often provide remarkably different results. To address this problem, this study aims to systematically investigate the admittance function of twin-box decks by comparing three approaches: active wind tunnel tests, and large eddy simulations (LESs) using both sinusoidal gusts and continuous synthetic turbulence. In particular, wind tunnel tests equipped with an active gust generator are conducted to generate a series of single-frequency vertical sinusoidal gusts. The effects of gust amplitudes and gap widths on the AAFs are experimentally investigated. In addition, LESs are performed aiming to provide valuable insights regarding the discrepancy between AAFs obtained in the two inflow conditions. Results obtained adopting all the aforementioned methodologies are compared, showing good agreement among the three approaches and values sometimes higher than the Sears function. It is also shown that buffeting forces are mainly produced by the upstream deck, so explaining the good agreement obtained between sinusoidal gust and continuous turbulent inflows.