Aerodynamic force distribution and vortex drifting pattern around a double-slotted box girder under vertical vortex-induced vibration

Abstract

Double-slotted box girder is a novel type of main girder for long-span bridges. To investigate the vertical vortex induced vibration (VIV) performance and aerodynamic effect of double-slotted box girder, wind tunnel tests were conducted on a spring-suspended sectional model. The results showed that the aerodynamic forces on the upper and lower surfaces of upstream box, the upper surface of middle box, and the rear regions of upper and lower surfaces of downstream box contribute positively to the VIV, becoming the main excitation source. Compared with streamlined closed-box and central-slotted box girders, the regions with obvious contribution values on double-slotted box girder surface significantly increase. This indicates that double slots allow the aerodynamic forces acting on larger areas of girder surface to participate in VEF generation and potentially affect the VIV performance. A vortex-related flow pattern around the double-slotted box girder was described by combining the vortex drifting theory and simplified vortex model, which provide insight into the mechanism of vertical VIV. Periodic vortex drifting exists on the upper surface of downstream box. The aerodynamic forces from the windward side to the front area of the lower surface of middle box appear to be significantly affected by vortices in windward slot.