Investigation on the influence of railing layout on vortex-induced vibration performance and suppression mechanism of double-layer steel truss bridge

Double-layer steel truss suspension bridges, leveraging their excellent traffic capacity and advantages in efficient utilization of route resources, have become a preferred bridge type in complex topographical environments. However, the complexity of their cross-sectional configuration, coupled with the diverse turbulent aerodynamic characteristics exhibited by numerous discrete appurtenances such as bridge deck railings, significantly influences airflow separation and reattachment, thereby complicating their vortex-induced vibration (VIV) performance. This study combines wind tunnel tests and numerical simulations to investigate how the layout positions of the upper maintenance walkway railing and the lower pedestrian railing affect VIV performance and surrounding flow field characteristics. The results indicate that at +3° and +5° wind angles, moving the upper maintenance walkway railing inward significantly suppresses vertical bending VIV, with optimal suppression rates of 42.9% and 47.0%, respectively, achieved at an inward shift of 0.60h1. The underlying mechanism involves altering the deck's local geometry to weaken flow separation at the leading edge, thereby limiting vortex generation and shedding in the wake and attenuating periodic vortex-induced forces. Conversely, moving the lower pedestrian railing inward proves more effective for torsional VIV. Optimal suppression is achieved at a 0.60h2 shift, where at +3°, suppression rates for minor and major torsional VIV reach 70.3% and 76.9%, respectively, while at +5°, the rates are 68.7% and 72.2%. This suppression is attributed to the railing's adjusted position, which modifies wake vortex dynamics from the lower deck, compresses vortex development space, and creates a “force-relief effect” that consumes flow energy, thereby reducing overall wake vorticity.