Numerical investigation on vortex-induced vibration characteristics and vortex shedding mechanism of the triple-box girder

Box girders are increasingly utilized in extensive-span bridges due to their favorable aerodynamic stability and excellent traffic capacity. Nevertheless, the presence of gaps between these girders renders them highly sensitive to vortex-induced vibrations (VIV). This study utilized numerical simulation approach to explore the induced mechanism and vibration characteristics of vertical VIV of a triple-box girder with linear webs at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> <mml:mo>°</mml:mo> </mml:mrow> </mml:mrow> </mml:math> attack angle. By using the numerical model verified with the wind tunnel data, the aerodynamic characteristics of the triple-box girder are detailed analyzed from the aspects of fundamental flow features, vortex shedding mechanism, force coefficients, vibration response and transient pressure coefficient distribution at various reduced wind speeds and vibration stages. The results indicate that the flow states and vortex structures differ significantly across different reduced wind speeds. The vortices shed from the upstream and middle box girders impact the windward side of the middle and downstream box girders in different forms, then separate and reattach, resulting in a significant pressure difference between the upper and lower surfaces of the middle and downstream box girders, thus driving the vortex-induced vibration of the triple-box girder. In the process of vortex-induced vibration, the lift force and lift contribution of the downstream box girder increase rapidly, which exceeds the increase of the upstream and middle box girder, and is the main cause of vortex-induced vibration of the triple-box girder. Control measures should be carried out for the downstream box girder to suppress vortex-induced vibration. Moreover, during the ascent of VIV, the phase between aerodynamic lift and displacement responses is closely aligned, whereas during the descent phase, the phase difference sharply increases, ultimately stabilizing at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mn>180</mml:mn> <mml:mo>°</mml:mo> </mml:mrow> </mml:mrow> </mml:math> .