## 6 Conclusions  
In accordance with the bridge location environment and functional requirements of the Jinghe Bridge, a new structural form of single and double combination of arch ribs and collaborative working of the main and secondary arches was proposed for the first time, and the innovative design details and mechanical behavior of the main and secondary arch collaborative Y-shaped thin-walled steel box arch bridge were studied. The significant conclusions obtained are as follows:  
1. The innovative design concept and design details have been discussed and verified by numerical calculations, showing that the structure meets the design requirements in terms of mechanical performance and has certain advantages in terms of static stability. 2. The traditional single arch rib design is mechanically and aesthetically slightly worse than the main and secondary arch collaborative system. The secondary arch rib bears a certain proportion of the load with a smaller cross-sectional area, which not only plays the role of structural bearing, but also meets the aesthetic needs of the landscape; therefore, the synergistic effect of the main and secondary arch rib collaborative system is outstanding and reasonably designed. 3. The maximum tensile and compressive stresses in the main girder all occur at 3/8 of the span; the maximum tensile stress in the arch ribs occurs at the main arch end of the main and sub-arch connecting ribs, and the maximum compressive stress occurs at the position of 1/4 arch rib on the single arch side. 4. As the shape of the arch rib is spatially Y-shaped, the vertical deformation of the structure is special, and the maximum vertical deformation of the arch rib is not in the middle of the span, but in the vicinity of 3 L/8 and 5 L/8, and the deformation trend is similar to a \"W\" shape. 5. The structural mode is mainly manifested as deflection and drift, and special attention should be paid to the deflection vibration problem in the design. The relatively good torsional stability performance of the structure is mainly due to the innovative design  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Load** & **Allowable** & \multicolumn{3}{c}{**Single Arch Rib**} & \multicolumn{3}{c}{**Double Arch Ribs**} \\ \cline{3-8}
**Combination** & **Stress** & **Top slab** & **Bottom slab** & **Web** & **Top slab** & **Bottom slab** & **Web** \\ \hline (1) & 320 & 0–128 & 0–117 & 0–128 & 0–151 & 0–137 & 0–151 \\ (2) & 320 & 0–155 & 0–172 & 0–172 & 0–173 & 0–192 & 0–192 \\ (3) & 320 & 0–144 & 0–104 & 0–144 & 0–167 & 0–122 & 0–167 \\ (4) & 320 & 0–151 & 0–164 of the three-part bifurcated arch ribs and the stiffness contribution of the secondary arch ribs and connecting ribs, and these design measures can be referred to by future bridge designs. 6. The shear lag effect was observed in any cross-section of unconventional thin-walled steel box arch ribs, and the shear lag effect was more noticeable in single arch ribs than double arch ribs. The shear lag coefficient decreased with the decrease in arch rib width, and the maximum shear lag coefficient was 1.4 under the design load combination. 7. In future bridge construction, the main and secondary arch collaborative Y-shaped steel box arch design may be widely used in urban landscape bridges, and the design concept and method presented in this paper may provide an effective reference for the construction of similar projects in the future. Conceptualization, Q.H. and X.W. ; methodology, Q.H. ; software, Q.H. ; validation, Q.H., X.W. and H.W. ; formal analysis, Q.H. and X.W. ; data curation, Q.H., H.W. and Q.C. ; writing--original draft preparation, Q.H. ; writing--review and editing, Q.H. and X.W. ; project administration, X.W. ; funding acquisition, H.W. and Q.C. All authors have read and agreed to the published version of the manuscript. This research was funded by Shaanxi Provincial Department of Transport Scientific Research Project (No. 21-62K). Not applicable.