## 6 Conclusions  
To study the wind characteristics over mountainous terrain, the Xiangjiang Bridge site was employed in this paper. The improved boundary transition sections were adopted to reduce the influence of the artificial cliffs on the edge of the terrain model on the wind characteristics at the bridge site over the mountainous terrain. The mean cross-bridge wind speed and wind attack angles at the main deck level, longitudinal wind speed profiles at L/4, L/2, and 3L/4 of the bridge length were investigated in detail with the assistance of numerical simulations and wind tunnel tests. The main conclusions are summarized as follows:  
1. The cross-bridge wind speeds and wind attack angles at the main deck level of the bridge at mountainous terrain site vary greatly along the bridge axis. Considering the span layout characteristics large-span bridges, it can be roughly divided into three parts along bridge axis, namely, mountain areas (I, III) and central canyon area (II). The changes in wind characteristics near the mountain areas (I, III) were relatively large, while the changes in wind speed and wind attack angles in the central canyon area (III) were relatively small. 2. Experimental and numerical results show that the cross-bridge wind speed at the main deck level of the mountainous terrain model with BTS was generally larger than that of the mountainous terrain model without BTS in the central canyon area (II) for most cases, which needs to be paid special attention in wind-resistance design of the bridge. If there is no improved BTS in front of the terrain model, the cross-bridge design wind speed of the bridge deck may be underestimated. 3. In general, the range of wind attack angles at the main deck level of the mountainous terrain model with BTS within 1/4 to 3/4 of the bridge length; namely, in the central canyon area (II), are smaller than the range of wind attack angles of the mountainous terrain model without BTS. It is recommended to use the improved BTS for terrain model boundary correction. 4. The longitudinal wind speed ratio at different positions; namely, L/4, L/2 and 3L/4 of the bridge length, generally increase with height. The longitudinal wind speed ratio of the terrain model with BTS at L/4, L/2 and 3L/4 of the bridge length are larger than that of the terrain model without BTS for most cases. 5. In general, there are some discrepancies between the numerical results and wind tunnel tests results of wind characteristics, namely cross-bridge wind speed ratios, wind attack angles, and longitudinal wind speed ratios at L/4, L/2, and 3L/4 of the bridge length, but the maximum relative error between numerical and experimental results for most cases is about 30%. Figure 22: Numerical results vs. experimental results of longitudinal wind speed ratio at 3L/4 under different cases. (**a**) Case 1 and 2; (**b**) Case 3 and 4. **Author Contributions**: Conceptualization, Z.C., Z.L. and X.C. ; methodology, Z.L. and X.C. ; software, X.C. ; validation, Z.L., X.W. and J.Z. ; formal analysis, H.X. ; investigation, X.C. ; resources, Z.L., X.W. and J.Z. ; data curation, H.X. ; writing--original draft preparation, X.C. ; writing--review and editing, Z.L. ; visualization, H.X. ; supervision, Z.C. ; project administration, X.W. and J.Z. ; funding acquisition, Z.L. All authors have read and agree to the published version of the manuscript. **Funding:** This research was funded by the National Natural Science Foundation of China, grant number 51478180 and 51778225 and China Railway Siyuan Survey and Design Group Co., Ltd.  
**Acknowledgments:** We deeply appreciate the assistance provided by [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] in the process of wind tunnel test and the administrative and technical support by the Hunan Provincial Key Lab of Wind Engineering and Bridge Engineering. **Conflicts of Interest**: The authors declare no conflict of interest.