## 3 Test Overview
### Object and data Collection  
According to the previous research of our research team [39; 40; 41], a 1:30 model was constructed for Taohuayu Yellow River Bridge. A total of 52 C30 concrete deck slabs (\(1.16\times 0.45\times 0.2\) m) were prepared and laid on the steel box girder to simulate vehicles on the bridge and serve as the counterweight.  
The main cable is composed of 37 steel wire ropes with a diameter of 2 mm, an elastic modulus of 195 GPa and a \(f_{\text{tk}}\) of 1860 MPa. The suspender is composed of steel wire ropes with a diameter of 4 mm, an elastic modulus of 195 GPa, and a \(f_{\text{tk}}\) of 1860 MPa. The main tower adopts a thin-walled box made of steel plate with a thickness of 6 mm and Q345D material.  
The standard section of the main beam is shown in Figure 3 in which the top, web, and bottom plates are made of 2 mm thick steel plates. Owing to the strong axial force of the main beam, considering the stability of the box girder, the top and bottom of the girder have four solid steel stiffeners (\(\Phi\) 6 rebar), which are connected with the top and bottom plates of the box girder by spot welding.  
In order to fully simulate the geometric similarity between the suspender and the main beam, the rigid arm is extended from both sides of the main beam at the lifting point, and the anchor plate is set on the rigid arm so that the suspender can be connected with the stiffener. Steel is selected for the rigid arm. To ensure the local stability of the main beam, one diaphragm is set every 450 mm (i.e., the section of the lifting point) of the main beam model, and the diaphragm and the main beam can be connected with the steel box girder by welding. The diaphragm plate is made of Q345D steel with a thickness of 2 mm. As shown in Figures 4 and 5, respectively.  
Figure 3: The standard section diagram of a girder model (unit: Mm).  
Figure 2: The workflow of the intelligent NRS system.  
The rigid arm has 5 cm wide and 5 mm thick steel plates, which are arranged through the cross-section of the main beam. The rigid arm is connected to the top plate of the steel box girder through welding; the stiffener adopts a 3 mm thick steel plate, which is connected to the main beam and the rigid arm through welding. The main beam is processed in the factory. The total length of the main beam is 24.2 m, which is divided into 24 sections: \(1.3+6\times 3.6+1.3\) m. Figure 6 is a photo of the reduced-scale model.  
The intelligent NRS system was set up 5m away from the bridge facade. Then, a computer-controlled camera rotated at fixed angles to collect the images of specific sections of the bridge from fixed positions. The layout of the lab and the principle of image collection are shown in Figures 7 and 8, respectively.  
Figure 4: Section at lifting point of main beam (unit: Mm).  
Figure 5: Schematic plan view of the main beam (unit: Mm).  
Figure 6: The reduced-scale model.  
To verify the feasibility of the image collection method, 11 dial gauges were arranged along the axis of the bridge to capture the shape change while the camera took photos of the bridge, DH5902N is adopted for data acquisition equipment. The arrangement of the dial gauges is displayed in Figure 9 below.