# Research on the Tie Cable Replacement Method of Half-through Tied-Arch Bridge
## 1 Introduction  
The half-through tied-arch bridge is a bridge structure that uses flexible cables to connect the ends of the side arches to bear a horizontal thrust. Flexible tie cables often use cables composed of steel strands or parallel steel wires, and their materials and section forms are the same as those of arch-bridge suspenders and cable-stayed bridge cables. In recent years, there have been many instances of damage and fracture accidents of suspenders of arch bridges and cables of cable-stayed bridges [1, 2], and national specifications stipulate that these cables must be replaced after reaching their service life. In the existing research on cable replacement, the replacement life cycle of arch bridge suspenders is about 15 years [3], and the replacement cycle of the cables of cable-stayed bridges is about 20 years, but there is less research on the tie cable replacement of the half-through tied-arch bridge. In the existing research, the cable replacement methods are mainly divided into the non-substitution method and the temporary substitution method. The main difference between them is whether there is a temporary replacement structure to replace the old cable force. The non-substitution method directly removes and replaces the cables that need to be replaced. It is often used in cable-stayed bridges with dense cable systems and high structural redundancy [4, 5]. According to the redundancy of the structural system, multiple cables can be replaced at the same time. Because the non-substitution methoddirectly removes the cable force, it will cause large changes in internal force, which can be implemented only when the structure itself has sufficient bearing capacity. The temporary substitution method replaces the original cable force by installing temporary structures. The commonly used temporary substitution method is divided into the temporary susspender method, the arch-rib pocket-lifting method, the bridge-deck pocket-lifting method, etc. Due to the existence of the replacement device, it has little impact on the old structure. The temporary substitution method is widely used in cable replacement of cable-stayed bridges with thin cable systems [6], suspension-bridge susspender replacement [7; 8], and arch-bridge susspender replacement [9; 10; 11]. The temporary substitution method needs to solve the problem of the replacement numbers and replacement steps. The choice of replacement number and replacement steps is mainly related to the bearing capacity of the bridge structure. The main beam, bridge tower, and adjacent cables are involved in cable-stayed bridges, the bridge deck and adjacent suspenders are involved in suspension bridges, and the arch rib, bridge deck system, and adjacent suspenders are involved in arch bridges. When the bearing-capacity margin of the original structure is small, the single-cable-replacement method may be adopted. When the bearing capacity margin of the original structure is large enough, more cables can be replaced at the same time or in fewer replacement steps. By reasonably adjusting the cable-force-transformation process, the temporary replacement method can achieve equivalent replacement [9; 10], which is theoretically applicable to all cable-replacement scenarios. However, due to the need to install temporary replacement devices on the original structure, there is a risk of damage to the structure and high-altitude operation. Most existing research on the replacement of tie cables of arch bridges adopts the temporary substitution method, which gradually replaces the cable force of the old tie cables by adding temporary tie cables [12; 13]. The change in the cable force in the replacement process produces internal force distribution in the arch bridge, so it is necessary to ensure the safety of the original structure, such as the arch rib, adjacent tie cable, and foundation during the replacement of the tie cable [14].