###### Abstract  
Large-span suspension bridges are susceptible to wind loads. Therefore, a more precise analysis of their wind-induced vibration response is necessary to ensure the structure's absolute safety. This investigation conducted wind tunnel tests for the construction and completion stages to reveal the vortex-induced vibration (VIV) phenomenon of a double-deck suspension bridge. The results showed that no VIV occurred during the construction stage. However, the inclusion of railings significantly deteriorated the aerodynamic performance of the suspension bridge, leading to significant VIV at \(+3^{\circ}\) and \(+5^{\circ}\) wind angles of attack. Additionally, reducing the railing ventilation rate can significantly suppress the VIV amplitude. A new analysis method based on computational fluid dynamics (CFD) simulation is proposed to investigate the VIV mechanism of the double-deck truss girder. Twenty-nine measurement points were used to explore the vortex that causes VIV. The numerical simulations found that the area above and aft of the upper deck dominated the vertical VIV, while the aft of the lower deck dominated the torsional VIV. Furthermore, the intensity of the vortex in these areas was significantly lower during the construction stage. Moreover, reducing the railing ventilation rate significantly suppresses the torsional VIV by reducing the intensity of the vortex in the region behind the lower deck. vortex-induced vibration; double-deck suspension bridge; railing effect; computational fluid dynamics simulation; wind tunnel test +
Footnote †: journal: Medical  
the bridge [14]. However, since it occurs at low wind speeds, persists for prolonged periods, and has a high probability of occurrence, long-term VIV can impact the comfort of traffic and pedestrians and can reduce the durability of the bridge [15; 16; 17]. Truss girders, unlike \(\Pi\)-girders and box girders, consist of numerous discrete components, with web members that change along the bridge axis, creating complex aerodynamic disturbances [18]. This leads to the generation of multi-frequency and multi-size vortex shedding after different members, making the evaluation of VIV performance more challenging. Therefore, analyzing VIV and studying measures to suppress vibration in large-span double-deck truss girder suspension bridges is of particular importance. Aerodynamic measures modifying the cross-sectional shape of components or adding appendages that alter airflow patterns (e.g., stabilizer plates, deflector plates, and wind fairings) represent the most commonly employed method for suppressing bridge VIV [19]. This approach involves making small, cost-effective, highly reliable structural changes, making it the preferred method for VIV suppression [20; 21; 22; 23]. Additional aerodynamic measures can be more effective at suppressing VIV but require more materials and can negatively impact bridge aesthetics. Optimizing bridge aerodynamic performance by changing the structural shape, such as adjusting the railing ventilation rate or modifying the dimension and location of the maintenance track, can address these issues and better align with the demands of sustainable development, even though it may result in slightly reduced vibration suppression. Furthermore, VIV can also be suppressed through structural and mechanical measures [24; 25; 26; 27]. Structural measures involve enhancing the stiffness or mass of the structure and increasing internal or external constraints, which can carry a higher cost. Mechanical measures entail incorporating various dampers to suppress vibration, which can lead to a more complex structural design. Therefore, these measures are more suitable for special cases where aerodynamic measures are ineffective. The VIV of double-deck truss girders has received relatively little attention. Only [PERSON] et al. [28] have studied the effect and mechanism of fairing and deflector plates on truss girder VIV. [PERSON] et al.