## 1 Introduction
[23] investigated the dynamic characteristics and mechanical responses of a long-span steel-box basket \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**No.** & **Bridge Name** &
\begin{tabular}{c} **Country of** \\ **Affiliation** \\ \end{tabular} & **Build Year** & **Span (m)** \\ \hline
1 & Rainbow Bridge & USA & 1942 & 290 \\
2 & Fremont Bridge & USA & 1973 & 383 \\
3 & Roosevelt Lake Bridge & USA & 1990 & 329 \\
4 & Kizugawa Bridge & Japan & 1993 & 305 \\
5 & Lupu Bridge & China & 2003 & 550 \\
6 & Wuyuan Bridge & China & 2004 & 208 \\
7 & Caiyuanba Bridge & China & 2008 & 400 \\
8 & Nanning Bridge & China & 2009 & 300 \\
9 & Mingzhou Bridge & China & 2011 & 450 \\
10 & Nan-Guang Railroad Xijiang Bridge & China & 2014 & 450 \\
11 & Yibin Jinsha River Highway–Railway & China & 2017 & 336 \\  & Dual-Use Bridge & China & 2018 & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Some steel box arch bridges built at home and abroad (arch ribs and main girder are steel structures). handle railway arch bridge under combined longitudinal and transverse seismic forces, and provided design recommendations. [PERSON] et al. [24] simulated the wide steel box girder of an arch bridge using a shell unit and calculated the stress distribution characteristics of the wide steel box girder under different loading conditions, and the results showed that the maximum stress inhomogeneity coefficients of the bottom and top plates of the wide steel box girder in the same section were 1.89 and 1.73, respectively. [PERSON] et al. [25] calculated the stability factor for the Nanning Bridge and conducted the characteristic buckling analysis and nonlinear buckling analysis of thin-walled steel box arch ribs, and the calculation results provided parameters for the construction and operation of the bridge. [PERSON] et al. [26] studied the shear lag effect of the steel box arch ribs of Zhongshan I Bridge by means of real scaled-down model tests, and the results showed that the bridge was correctly designed. [PERSON] et al. [27] analyzed the seismic damage characteristics of the structure and the influence of thickness of the arch rib steel plates on the seismic response by a non-hinged half-through steel arch bridge. [PERSON] et al. [28] built a hybrid finite element model for a combination bridge with a rigid frame and single-ribbed steel box arch and performed its eigenvalue stability and elastoplastic stability analysis. [PERSON] et al. [29] studied the spatial mechanical behavior of the structure, dynamic properties and stiffness relationships among the members taking a steel box butterfly arch bridge as the object and using a model test method. [PERSON] et al. [30] investigated the mechanical characteristic and actual bearing capacity of a convex steel box arch rib section by using scaled-down model tests and the nonlinear finite element method, and they revealed the regularity of the effect of stiffening ribs on the section. Although the research on thin-walled steel box arch bridges has made some progress at home and abroad, there are still few studies on steel box arch bridges with a collaborative system of main and secondary arches. Although many scholars have achieved fruitful results in the study of the shear lag effect, the research objects are mainly focused on the box-shaped concrete girders and high-rise barrel structures, and there are few investigations on the shear lag effect of the unusually shaped thin-walled steel box arch ribs. Therefore, in this paper, for a large-span main and secondary arch collaborative arch bridge designed with new Y-shaped thin-walled steel box ribs, the innovative design concept and design features are firstly introduced and discussed in terms of design details. Then, different finite element software is used to simplify the actual structure into a numerical model based on reasonable assumptions to numerically verify the innovative design of the structure.