Evolution characteristics of influence of slot width on aerodynamic performance for separate steel box girder

Objective Long-span cable-supported bridges are prone to significant wind-induced vibrations under strong winds, which severely compromise the structural safety and service performance. To address this challenge, this study systematically analyzes the influence of slot width on aerodynamic performance evolution and underlying mechanisms of separate steel box girders, aiming to provide a theoretical basis for the optimization on wind-resistant design. Method Five separate steel box girder sections with different slot widths were selected as study objects by using computational fluid dynamics numerical simulations. The aerodynamic response characteristics in both static and vertical forced vibration conditions were systematically investigated. The study examined the variations in aerostatic force coefficients, surface pressure distribution characteristics, and the evolution of flow field structures around the sections, thereby revealing the influence mechanism of slot width on aerodynamic performance of structure. Result With the increase of slot width, the girder cross-section in static state tends to generate stronger vortex shedding, while the fluctuations of lift force and lift moment exhibit a characteristic pattern, i.e., initial increase followed by stabilization. When subjected to vertical forced vibration, the flow-structure coupling effect intensifies significantly, resulting in overall amplitude amplification of both lift force and torsional load. However, a moderate increase of slot width could effectively mitigate this amplified vibration-induced aerodynamic response, and reduce aerodynamic force fluctuations. Conclusion Moderate slot widening not only mitigates lift fluctuations in static conditions, but also inhibits vertical bending and torsional responses during vibration. Considering both static and dynamic behaviors, a slot width-to-girder height ratio within a moderate range of 1.7-2.2 is recommended. This configuration ensures vertical stability while maintaining torsional safety, providing a reference for wind-resistant design of ultra-long-span cable-supported bridges.