VIV Performance of a Railway Streamlined Box Girder Section and Its Aerodynamic Countermeasures

While streamlined box girders are widely adopted in railway bridges, their vortex-induced vibration (VIV) behavior and the effectiveness of aerodynamic countermeasures depend significantly on cross-sectional geometry. This study presents a case-specific experimental investigation into the VIV performance of a representative streamlined box girder section and evaluates the mitigation performance of two aerodynamic countermeasures (splitter plates and railing spoilers) against the peak vertical VIV response under a +3° wind attack angle. By simultaneously measuring vibration responses and surface pressures, this work offers a case-specific interpretation of the aerodynamic characteristics associated with the peak VIV response and its mitigation for the tested configuration. The main observations for this specific section and condition are as follows: (1) At a +3° wind attack angle, the original section exhibits noticeable vertical VIV, with a peak amplitude approximately 4.25 times the allowable amplitude. At the peak-response wind speed, the higher contribution values on the upstream top flange and lower surface lead to an increase in the total contribution values of the section, which may be related to the observed peak amplitude. (2) The splitter plate reduces the RMS values of pressure coefficients and the sectional contribution values. Despite the transition of the contribution values from negative to positive on the upper surface, the decrease on the lower surface leads to a 45.87% reduction in the total contribution values at the peak-response wind speed, corresponding to a reduction of the peak vertical VIV amplitude for this configuration. (3) The railing spoiler reduces the contribution values on both surfaces, thereby modifying the respective aerodynamic contributions of the upper and lower surfaces, yielding a 55.27% reduction in the total contribution values at the peak-response wind speed and a corresponding decrease in the peak vertical VIV amplitude under the tested condition. (4) For the tested section, the splitter plate alters the flow deflection at the windward fairing, modifies the reattachment patterns on the top and bottom flanges, and reduces surface aerodynamic loads, thereby possibly contributing to the suppression of the peak vertical VIV response. The railing spoiler increases the separation distance between the railing-induced vortex and the top flange surface, which may reduce fluid-structure interaction. These observed flow modifications may contribute to the effectiveness of the countermeasures in mitigating the peak vertical VIV response under the +3° attack angle. These results may provide a reference for similar sections, although the actual mitigation effectiveness may vary or prove limited depending on specific geometric and aerodynamic conditions.