## 5 Conclusions  
This article investigates the influence of railing ventilation rate on VIV in a double-deck truss girder through wind tunnel tests and CFD simulations and presents the following principal conclusions.  
1. The construction stage sectional model did not exhibit any VIV during the wind tunnel tests. Conversely, the completion stage sectional model demonstrated significant VIV at +3\({}^{\circ}\) and +5\({}^{\circ}\) wind angles of attack, with one vertical VIV locking range and two torsional VIV locking ranges. The maximum vertical VIV amplitude was 98 mm, while the maximum torsional VIV amplitude was 0.21\({}^{\circ}\). Moreover, the vertical VIV frequency was locked at 2.23 Hz, while the torsional VIV frequency was locked at 4.29 Hz.
2. Wind tunnel tests demonstrate that decreasing the railing ventilation rate has a suppressing effect on VIV, with the maximum suppression effect occurring at the railing ventilation rate of zero. Among them, the suppression effect on vertical VIV is weak, with maximum suppression rates of 22.7% and 24.8% at +3\({}^{\circ}\) and +5\({}^{\circ}\), respectively. The suppression effect on torsional VIV is significant. At +3\({}^{\circ}\) and +5\({}^{\circ}\), the maximum suppression of minor torsional VIV is 78.5% and 78.7%, respectively, and the maximum suppression of major torsional VIV is 71.3% and 71.6%, respectively.
3. Comparing the vorticity contours of the construction stage and completion stage sections, it is evident that the wake vortices' intensity and range are significantly higher in the completion stage section, leading to VIV occurrence. Various vortices with different frequencies and sizes were generated after each discrete member of the completion stage section. It is plausible that the vortex shedding above the upper deck or in the wake area of the upper deck leads to vertical VIV, whereas the vortex shedding in the wake area of the lower deck leads to torsional VIV.
4. Numerical analysis of the truss girder cross-section with different railing ventilation rates found that minor torsional VIV may be related to vortex shedding from the railing gap and the top of the railing, and major torsional VIV may be related to vortex shedding from behind the lower chord. Decreasing the railing ventilation rate reduces vortex intensity and volume in the wake region of the lower deck significantly, thereby suppressing VIV.  
Figure 21: Variations in the wind speed characteristic frequency recorded at measurement point P22.  
**Author Contributions:** Conceptualization, G.Y.; methodology, G.Y., Y.C. and Y.Y.; software, Y.C. and H.D.; validation, G.Y. and Y.C.; formal analysis, G.Y.; investigation, G.Y. and Y.Y.; resources, Y.Z.; data curation, Y.C. and L.W.; writing--original draft preparation, Y.C.; writing--review and editing, G.Y. and Y.Y.; visualization, Y.C. and L.W.; supervision, Y.Y. and Y.Z.; project administration, Y.Y.; funding acquisition, Y.Z. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Chongqing City Infrastructure Construction Investment Co., Ltd., grant number CQCT-JSA-GC-2021-0140.  
**Data Availability Statement:** Not applicable.  
The authors declare no conflict of interest.