Influence of L-shaped deflector dimensions on the vortex-induced vibration of a closed-box girder: Experimental and numerical study

This study provides a comprehensive investigation into the influence of L-shaped deflector dimensions on the vortex-induced vibration (VIV) of a closed-box girder, based on synchronized wind tunnel tests with vibration and pressure measurements, spectral proper orthogonal decomposition (SPOD), and numerical simulations. Results indicate that vertical bending VIV occurs within a single response interval and is suppressed with the increasing horizontal plate size. In contrast, torsional VIV exhibits two distinct response intervals with increasing deflector dimensions and is generally amplified by the vertical plate. Vertical bending VIV is primarily governed by the horizontal plate, whereas torsional responses are dominated by the vertical plate. For vertical bending VIV, vortex-excited forces exhibit marked nonlinearity and frequency multiplication. In torsional cases, the first torsional interval exhibits smaller amplitudes but higher vortex-excited force moments, while the second shows stronger nonlinearity and more prominent higher harmonics. Across all vibration types, the upper surface consistently contributes most to the aerodynamic force, especially in the downstream region, while the inclined web exerts positive effects mainly under torsional conditions. SPOD analysis reveals that the first-order mode exhibits a streamwise-traveling structure in all cases, while the second torsional interval shows greater modal energy concentration and spatial coherence than the first. Flow field evolution further confirms that vertical bending VIV is governed by symmetric counter-rotating vortices, whereas torsional VIV arises from pronounced phase differences in vortex shedding between the upper and lower surfaces, leading to significant flow asymmetry.