# The Bearing Performance and Sectional Design Method of Yielding U-Shaped Steel Support
## 3 Indoor Experimental Research on the Bearing Performance of Yielding U-Shaped Steel Support
### Analysis of Test Results
#### 3.2.1 Analysis of the Deformation and Yielding Process  
The overall and local deformation patterns of the three-section and four-section support are shown in Figures 6 and 7, respectively. The comparison of the maximum deformation amounts of the top and the straight legs is shown in Figure 8, and the comparison of the yieldable amounts of the support nodes is shown in Figure 9.  
Figure 8: Comparison of steel support deformation. Figure 7: Failure of the four-section compressed steel support. Figure 9: The comparison of the yieldable amounts of the support nodes. Analysis of Support Deformation  
The three-section U-shaped steel support as a whole presents an \"M\"-shaped deformation pattern with a top sinking. Obvious buckling failures occur in the middle of the top, such as bulging deformation and paint peeling, and bending deformation appears on the straight legs on both sides. After measurement, the deflection of the top is 183 mm and the inward deformation of the two straight legs is 47 mm and 51 mm in sequence. The top of the four-section U-shaped steel support settles, and the left and right straight legs do not have obvious deformation, while the whole is symmetrical left and right. After measurement, the deflection of the top is 76 mm and the inward deformation of the two straight legs is 9 mm and 11 mm in sequence. Compared with the three-section support, the deflection of the top corresponding to the maximum bearing capacity of the four-section support is reduced by 58.5%. Analysis of Node Yielding  
Before reaching the maximum bearing capacity, the three-section U-shaped steel support does not have obvious yielding deformation, and the slip amounts at the nodes on both sides are only 12 mm and 10 mm. The cable clamps at the lapped parts of the support turn outward, the screw rods are pulled and bent, mainly with an open-type rotation. The opening angles of the two lapped steel sections are 26\({}^{\circ}\) and 29\({}^{\circ}\), respectively. Before reaching the maximum bearing capacity, the nodes of the two straight legs of the four-section U-shaped steel support first generate yielding slip and keep increasing. The node slip amounts are 156 mm and 159 mm, respectively. The top node first generates slip and then turns outward. The node compression amount is 9 mm and the opening angle is 12\({}^{\circ}\). Compared with the three-section support, the node yielding effect corresponding to the maximum bearing capacity of the four-section support is significantly improved. Analysis of Support Bearing Capacity  
The bearing capacity-displacement relationship curves of the three-section and four-section support are shown in Figure 10, and a comparison of the peak bearing capacity and the peak deformation is shown in Figure 11. Among them, the bearing capacity is the sum of the loads of each cylinder and the displacement is taken at the position of the fourth cylinder where the deformation is the largest. Figure 10: Bearing capacity–displacement of steel support. It can be seen from Figure 10 that under the condition of a uniform load, the bearing process of the support can be divided into the elastic bearing stage, the yieldable bearing stage, and the post-peak bearing stage. Elastic Bearing Stage (OA1, OA2): The bearing capacity and displacement are basically in a linear relationship and the bearing capacity-displacement curves of the three-section and four-section support basically coincide, indicating that no slip occurs at the nodes in this stage. Yieldable Bearing Stage (A1B1, A2B2): The slope of the bearing capacity-displacement curve decreases and the bearing capacity-displacement curve of the four-section support tends to be flat. In this stage, the retractable nodes begin to play a yieldable role. The deformation amount of the four-section support in this stage is 51 mm larger than that of the three-section support. After this stage ends, the supports reach their respective ultimate bearing capacities.