## 5 Conclusions  
In this paper, taking the Huangjietuo Yangtze River Bridge as the engineering background, the characteristics of the VIV of the double-deck truss girder suspension bridge and the vibration suppression mechanism of deflector plates were studied through wind tunnel tests and numerical analysis methods and the conclusions are as follows:  
1. At a +3\({}^{\circ}\) attack angle, it was found that the vertical VIV of the truss girder occurred in the wind speed range of 5.24 m/s\(\sim\)6.72 m/s, and the torsional VIV of the truss girder occurred in the wind speed ranges of 8.13 m/s\(\sim\)9.52 m/s and 12.27 m/s\(\sim\)18.06 m/s. At a +5\({}^{\circ}\) attack angle, it was found that the vertical VIV of the truss girder occurred in the wind speed range of 5.01 m/s\(\sim\)6.669 m/s, and the torsional VIV of the truss girder occurred in the wind speed ranges of 8.53 m/s\(\sim\)10.01 m/s and 13.75 m/s\(\sim\)19.49 m/s;
2. After the right-angled upper chord deflector plate was added to the original section of the double-deck truss girder, the onset wind speed of VIV was advanced at +3\({}^{\circ}\) and +5\({}^{\circ}\) wind attack angles. The vertical and torsional peak amplitudes of VIV also increased at +3\({}^{\circ}\) and +5\({}^{\circ}\) wind attack angles;
3. The right-angled lower chord deflector plate can well suppress vertical and torsional VIV at +3\({}^{\circ}\) and +5\({}^{\circ}\) wind attack angles, greatly reduce the peak amplitude of VIV, and shorten the length of the VIV locking range. The right-angled web deflector plate can slightly suppress the vertical and torsional VIV, reduce the peak amplitude of the VIV, and shorten the length of the VIV locking range. However, the vibration suppression effect of the web deflector plate is not as good as that of the lower chord deflector plate;
4. After adding right-angled lower chord and upper chord deflector plates on the original section of the double-deck truss girder, the peak amplitude of VIV and the locking range of VIV wind speed at +3\({}^{\circ}\) and +5\({}^{\circ}\) wind attack angles had no apparent changes. The right-angled lower chord deflector plate and web deflector plate can sufficiently suppress the vertical and torsional VIV, greatly reduce the peak amplitude of the VIV, and shorten the length of the locking range;
5. The length of the separation zone generated at the lower chord deflector plate is significantly smaller than that of the original section, and the vorticity at the exact position of the section is significantly lower than that of the original section. Similarly, although the degree of flow separation is weakened at the web deflector position compared with the original section, a weaker Karman vortex street is still formed. Therefore, this is how the lower chord deflector plate and the web deflector plate can suppress the VIV responses.  
Conceptualization, G.Y.; methodology, G.Y., L.W. and Y.Y.; software, L.W. and Y.C.; validation, L.W. and Y.Y.; formal analysis, G.Y.; investigation, G.Y. and Y.Y.; resources, M.L.; data curation, L.W. and H.D.; writing--original draft preparation, L.W.; writing--review and editing, G.Y. and Y.Y.; funding acquisition, M.L.; supervision, Y.Y. and M.L.; project administration, Y.Y.; visualization, L.W. and H.D. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Chongqing City Infrastructure Construction Investment Co., Ltd., grant number CQCT-JSA-GC-2021-0140, and the National Key Research and Development Program of China [2021 YFC3100300].  
Not applicable.  
The authors declare no conflict of interest.