Aerodynamic Force Distribution Characteristics around a Double-Slotted Box Girder of a Long-Span Bridge during Vortex-Induced Vibration

Vortex-induced vibrations (VIVs) remain a key issue for slotted box girders. To clarify the influence of additional structural elements on the aerodynamic characteristics of a double-slotted box girder for highway and railway hybrid bridges, wind tunnel tests involving the pressure distribution, VIV responses, and wake measurements were performed. The wind pressures and vortex-shedding frequency characteristics of a bridge were compared under different additional structural element combinations of balustrades, wind barriers on highways and railway deck surfaces, maintenance rails, and so on. The results indicated that the maintenance rails had a limited influence on VIV characteristics and distributed pressures of the double-slotted box girder. However, owing to the stronger disturbance of the wind barriers and balustrades on the highway deck surface, unsteady shear flow separating from the wind barrier top acts on the middle and leeward girders, resulting in large-amplitude torsional VIVs to generate considerable excitation forces. Moreover, because wind flow across the slotted parts interacted with the girder and additional structural elements, stronger torque forces were generated. Consequently, correlation and contribution were enlarged, which corresponded to large-amplitude torsional VIVs. This provides a reasonable explanation for the considerable influence of wind barriers on highway decks on torsional VIVs. Moreover, with regard to the double-slotted box girder [especially the upper surface of the windward girder, upper and lower surfaces of the leeward girder, and windward gap of the three girders (Regions II to IV, VI, and X to XI, respectively)], the distributed wind pressures acting on the characteristic parts of bridge decks further contributed to the generation of torsional VIVs.