## 2 Project Background  
In this paper, a cross-sea bridge with weathering steel used in the steel anchor boxes is selected as a research case. The bridge is a double-tower steel-box-girder cable-stayed bridge with a span layout of 110 + 236 + 458 + 236 + 110 = 1150 m. The middle and secondary side spans are equipped with stay cables. The cables are arranged in the shape of a fan with double cable planes and anchored on the outside. The tower adopts a horizontal H-shaped frame with a bridge deck width of 33.1 m. The layout of the bridge is shown in Figure 1.  
In order to reduce maintenance work during the operational period, the main structure of the steel anchor box, the steel anchor box diaphragm, the steel anchor box segment connecting plate, and the steel anchor box stay-cable sleeve of the cross-sea bridge are made of Q355 NHD weathering steel. The steel anchor boxes are uncoated and generate a stable protective rust layer on their own to achieve effective anti-corrosion within the operational period. Steel anchor boxes are divided into 12 sections, and their numbers correspond to the cable numbers. For example, the stay cables S14 and M14 correspond to the No. 14 steel anchor boxes. Steel anchor boxes are divided into types A, B, and C: the type-A steel anchor box is suitable for the No. 14 steel anchor box, which corresponds to stay cables S14 and M14 at the highest anchoring position; the type-B steel anchor box is suitable for the No. 4 to 13 steel anchor boxes, which correspond to stay cables S4-S13 and M4-M13 that are positioned in the middle; the type-C steel anchor box is suitable for the No. 3 steel anchor box corresponding to the stay cables S3 and M3, with the lowest anchoring position. There are 28 steel anchor boxes on the two towers, with 56 pairs of stay cables connected to them.  
The steel anchor boxes are all 5.2 m long and 1 m wide. The height of the type-A and -B steel anchor boxes is 2.5 m, and the height of the type-C steel anchor box is 3 m. The steel anchor box is a box-shaped structure composed of side pull plates, end bearing plates, webs, anchor plates, transverse diaphragms, connecting plates, and stiffening ribs. The side pull plate mainly bears the horizontal pulling force of the stay cable; the plate thickness is 40 mm, the two sides are equipped with a vertical manhole, and the outer side is equipped with vertical stiffeners that also serve as connecting plates. The end bearing plate has a thickness of 30 mm and a width of 1300 mm; shear keys are set on its outer side to connect to the concrete of the tower. The web plays an important role in transmitting the cable force to the side pull plate, for which the thickness is 40-60 mm, the height varies with the angle of the stay cable, and stiffeners are provided on both sides. The transverse  
Figure 1: Bridge layout.  
diaphrag is set horizontally between pull plates; it is a ribbed stiffened-steel plate with a thickness of 16 mm and with a manhole, which is used as a construction platform when the stay cable is stretched. The anchor plate is 40 mm thick, and the anchor pad is 80 mm thick. Since the tension in it is provided by the stay cable varies, there are two specifications for the anchor pads: 740 mm \(\times\) 740 mm and 640 mm \(\times\) 640 mm.