## 3 Analysis of Test Results
### Strain Analysis  
All unreinforced steel angle specimens were subjected to bending instability failure, and their load strain curve morphology is similar. LS1-1-1 and LS1-2-1 have been used as examples to illustrate, as shown in Figure 9. At the beginning of loading, the strain at all measuring points is compressive strain, and the strain values are similar, indicating that the additional bending moment of the specimen is small and the cross-sectional stress is basically uniformly distributed. Subsequently, a bifurcation point appeared in the curve, and the compressive strain at some measuring points began to decrease until they were completely in a tensile state, indicating that the specimen had already flexed and the second-order effect began to appear. Under the action of secondary bending moments, \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Bearing** & & **Bearing** & & **Calculation of** & **Calculation of** \\
**Retrofitted** & **Capacity** & **Steel** & **Capacity** & **Capacity** & **Bearing Capacity for Weak** & **Bearing Capacity** \\
**Specimens** & **of Retrofitted** & **Angles** & **of Steel** & **Enhancement** & **Axis of** & **for Strong Axis of** \\  & **Specimens/kN** & & **Angles/kN** & & **Steel Angles/kN** & **Steel Angles/kN** \\ \hline LR1-1-1 & 437.18 & LS1-1-1 & 314.09 & 39.19\% & 270.87 & 378.35 \\ LR1-2-1 & 345.33 & LS1-2-1 & 136.39 & 153.19\% & 146.42 & 323.49 \\ LR1-3-2 & 339.45 & & & 174.66\% & & \\ LR1-3-1 & 312.26 & LS1-3-1 & 113.69 & 169.26\% & 97.59 & 291.74 \\ LR1-3-3 & 306.45 & & & 166.91\% & & \\ LR2-1-1 & 547.03 & LS2-1-1 & 275.38 & 98.65\% & & \\ LR2-1-2 & 539.22 & & & 95.81\% & 228.68 & 458.37 \\ LR2-2-1 & 459.59 & & & 118.48\% & & \\ LR2-2-2 & 469.27 & LS2-2-1 & 210.36 & 127.68\% & 157.55 & 417.03 \\ LR2-2-3 & 478.95 & & & 109.36\% & & \\ LR2-2-4 & 440.41 & & & 164.67\% & & \\ LR2-3-1 & 425.01 & & & 151.28\% & & \\ LR2-3-2 & 403.51 & & & 155.86\% & & \\ LR2-3-3 & 410.86 & LS2-3-1 & 160.58 & 139.48\% & 101.96 & 373.44 \\ LR2-3-4 & 384.55 & & & 145.55\% & & \\ LR2-3-5 & 394.31 & & & 145.55\% & & \\ LR2-3-6 & 418.19 & & & 160.42\% & & \\ LR3-1-1 & 746.68 & & & 106.48\% & & \\ LR3-1-2 & 757.13 & LS3-1-1 & 361.63 & 109.37\% & 380.27 & 736.40 \\ LR3-2-1 & 709.69 & & & 130.18\% & & \\ LR3-2-2 & 702.65 & & & 127.90\% & & \\ LR3-2-3 & 642.44 & LS3-2-1 & 308.32 & 108.37\% & 263.16 & 670.81 \\ LR3-2-4 & 687.04 & & & 122.83\% & & \\ LR4-1-1 & 1126.65 & LS4-1-1 & 688.96 & 63.53\% & 618.38 & 1148.19 \\ LR4-1-2 & 1071.64 & LS4-1-1 & 688.96 & 55.54\% & & \\ LR4-2-1 & 1032.59 & & & 132.67\% & & \\ LR4-2-2 & 1002.37 & LS4-2-1 & 443.80 & 125.86\% & 432.81 & 1049.17 \\ LR4-2-3 & 977.92 & & & 120.35\% & & \\ LR5-1-1 & 1540.69 & & & 73.98\% & & \\ LR5-1-2 & 1513.52 & LS5-1-1 & 885.56 & 70.91\% & 832.78 & 1547.69 \\ LR5-2-1 & 1295.01 & & & 125.91\% & & \\ LR5-2-2 & 1242.33 & LS5-2-1 & 573.23 & 116.72\% & 579.64 & 1412.26 \\ LR5-2-3 & 1361.17 & & & 137.46\% & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Summary of bearing capacity. tensile stress appeared on one side of the cross-section. It can be seen that the biggest characteristic of the load-displacement curve of the unreinforced steel angle specimen is its symmetry; that is, the strain at the two measuring points symmetrical about the y\({}_{0}\) axis is basically the same. The strain data at the measuring points SP1, SP4, SP2, and SP3 in the figure are basically consistent, indicating that the deformation of the steel angle is symmetrical about the y\({}_{0}\) axis. In addition, the slenderness ratio of the LS1-1-1 specimen is 50. The slenderness ratio of the LS1-2-1 specimen is 90, so the deflection of the LS1-1-1 specimen is smaller, and the influence of the secondary bending moment is not significant. This is manifested in the load strain curve, where SP2 and SP3 measuring points do not transition to a tensile state until the curve descends, which is in stark contrast to LS1-2-1.