## 2 Design Concepts and Features
### Design Features and Details  
The main arch rib is a Y-shaped box arch with variable sections. The arch axis in the elevation adopts the suspension chain line, in which the net span is 220 m, the net height is  
Figure 3: General layout of the main and secondary arch collaborative Y-shaped steel box arch bridge (unit: m). Figure 2: Main components of the main and secondary arch collaborative Y-shaped steel box arch bridge. 62.5 m, the arch axis coefficient is 1.347 and the height-to-span ratio is 1/3.52. The plane projection of the arch axis is Y-shaped, the single arch is arranged on the right bank side of Jinghe River, the double arch is arranged on the left bank side of Jinghe River and the angle of axis divergence is 12.42\({}^{\circ}\). The arch box section is 3.0-6.6 m high and 2.0-3.5 m wide along the top of the arch to the foot of the arch. The arch box top slab, bottom slab and web are designed with variable thickness from the top to the foot of the arch, the slab thickness is 16-30 mm. The stiffening ribs and diaphragms are set to enhance the stiffness of the arch ribs, with a diaphragm spacing of about 1.5 m and a slab thickness of 12-24 mm, as shown in Figure 4. The bridge has two wind braces between the double main arches, with a rectangular steel box section, equal height with the arch ribs, and slab thickness of 20 mm. The bridge is designed with a crossbeam at the intersection of the arch ribs and the main girder on each bank, and the main girder is supported by supports. The crossbeam on the right bank arch adopts a variable-height rectangular steel box section with a section size of 4.0 m \(\times\) 3.5-2.5 m. The crossbeam on the left bank arch adopts an equal-height rectangular steel box section with a section size of 4.0 m \(\times\) 3.5 m.  
The wall thickness of the steel box at the foot of the arch is relatively thin, and the steel box section is prone to distortion and out-of-plane deformation under the action of constant load and live load, so the setting of bearing slabs and diaphragms and stiffening ribs can effectively prevent excessive deformation of the section and improve the torsional deformation resistance of the thin-walled arch box. The single arch rib in the arch foot position sets longitudinal diaphragms, which consist of eight character slabs, as shown in Figure 5.  
The secondary arch ribs are symmetrically arranged and inclined 5\({}^{\circ}\) outward around the line of their axes, which is a three-dimensional structure in space. The setting of secondary arch ribs improves the aesthetic characteristics of the structure. When the secondary arch ribs are removed, the distance between the top of the arch and the bridge deck is reduced and the arch becomes flat, which greatly weakens the structural aesthetics (see Figure 6). The arch axis is a suspended chain line, in which the net span is 184.5 m, the net height is 43 m, the height-to-span ratio is 1/4.29 and the arch axis coefficient is 1.756. The secondary arch is made of a circular steel tube section with 1.4 m diameter and 24 mm slab thickness. The stiffening ribs are slab ribs with a thickness of 12 mm, and the diaphragm is 12 mm thick. The axis of the main and secondary arch connecting ribs is a circular curve, varying step by step, with the section size of 0.7 m \(\times\) 1.0 m and slab thickness of 20 mm. Figure 4: Characteristic sections of arch ribs (unit: cm): (**a**) Section A-A; (**b**) Section B-B; (**c**) Section C-C; (**d**) Section D-D. In the Jinghe Bridge section layout, to meet the requirements of connecting the roadbed and tunnel, as well as because the Jinghe Bridge is part of an important landscape of the Guanzhong Canyon tourism belt, the deployment of sidewalks is considered for sections on both sides. The Jinghe Bridge standard section width is 18 m, using two lanes in both directions. The width of the lane is 2 \(\times\) 3.75 m, and there are 2.75 m wide sidewalks on each side.