Experimental Study on Spanwise Aerodynamic Control Measures for Vortex-Induced Vibrations of a Narrow Π-Shaped Girder of a Large Span Railway Cable-Stayed Bridge

Large-span bridges with bluff body girders are susceptible to vortex-induced vibration (VIV) due to their low frequency, light mass, and relatively low damping ratio, affecting fatigue life and serviceability. While research progress has been made on VIV mechanisms and control measures, systematic investigations on the application of vortex generators (VGs) to narrow Π-shaped railway girders remain scarce, and the potential synergistic effect of combining VGs with conventional aerodynamic measures has not been explored. To address this gap, wind tunnel tests were conducted on a 1:50 scale sectional model of a narrow Π-shaped steel girder for a railway cable-stayed bridge. The experimental program systematically investigated the VIV response of the original girder and evaluated the suppression effectiveness of conventional aerodynamic measures (vertical stabilizers, deflectors, modified fairings) and spanwise control using VGs. Parametric optimization of VG height (0.1 H–0.2 H, where H is the girder height), spacing (2/3 L0 and L0, where L0 = 12.5 m is the standard segment length), and installation position (upper fairing, lower fairing, girder bottom) was performed. Results show that under wind angles of attack from −5° to +5° and a damping ratio of 0.36%, the original girder exhibits pronounced vertical VIV with a maximum RMS amplitude of 0.025 m, approximately 3.15 times the code limit. Conventional measures alone fail to adequately suppress VIV. However, the optimal combination of VGs (height 0.2 H, spacing L0, installed on the lower fairing) with a 0.5 m wide, 15° inclined deflector effectively suppresses VIV under wind AOAs of 0°, ±3°, and –5°, achieving suppression below the measurable threshold. This study contributes the first comprehensive parametric investigation of VGs for narrow Π-shaped railway girders, reveals a synergistic effect when combining VGs with deflectors, and incorporates practical engineering constraints (such as aesthetic requirements) into the optimization process.