## 5 Test-Result Analysis
### Fatigue Test Results  
After first completing 2 million fatigue loads, an additional 1 million fatigue loads of 1.5 times the fatigue amplitude were applied, and there was still no significant change in the stress values at each test point, with no cracks observed on the surface of the structure. Table 4 shows the von Mises equivalent stress-test values at some of the test points after the cyclic fatigue loading. Figure 16 shows the von Mises equivalent stress-test values at some of the test points as a function of the number of cyclic loading cycles.  
Figure 14: Stress-test-value diagram of support plate N1 (MPa).  
Figure 15: Stress-test-value diagram of pressure plate N7 (MPa). (a) Top surface of pressure plate N7; (b) bottom surface of pressure plate N7.  
By analyzing the data from the fatigue-test-verification stage, it can be seen that after 2 million fatigue cycles, the von Mises equivalent stress values of most of the measuring points remained unchanged. After repeated observations, no cracks were found on the test model, and no significant fatigue damage occurred in the structure. This shows that the fatigue resistance of the built-in double-fixed steel anchor cable-girder box was good. At the fatigue-failure-test stage, the stress law of the model's measuring point was essentially the same as that in the fatigue-verification stage after the model underwent an additional 1 million fatigue cycles. After the fatigue loading was completed, the main plates and welds in the test model were inspected using an ultrasonic flaw detector, and no abnormalities were found in the main stressed plates or welds. According to this analysis, the built-in double-fixed steel anchor cable-girder box had a sufficient fatigue-strength safety reserve.  
Prediction and Evaluation System of Mechanical Properties of Steel anchor Box Based on PSO-BP Neural Network  
The large number of plates and complex welds in the steel anchor boxes of cable girders and the large cable forces to which they are subjected to make the rational design of their structure essential. The analysis of the structure of the built-in double-fixed cable-girder steel anchor box showed that it was mainly through the pressure plate that the cable force was transmitted to the support plate, followed by the weld between the support plate and the web of the main beam in the form of shear force. Based on the experimentally  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Point**} & \multicolumn{8}{c}{**Measured Stresses**} \\ \cline{2-9}  & **0 m** & **0.50 m** & **1.00 m** & **1.50 m** & **2.00 m** & **2.50 m** & **3.00 m** \\ \hline F1–1 & 20.9 & 20.5 & 20.11 & 21.12 & 20.13 & 23.45 & 23.33 \\ F  
validated finite-element-calculation model, the influence of the changes to the geometric parameters of the key plates on the mechanical properties of the main transmission welds was investigated, and a prediction-and-evaluation system, based on a PSO-BP neural network, for the mechanical properties of the built-in double-fixed steel anchor box of the cable-girder was established. The system used the geometrical parameters of the key plates and the designed cable force as the input variables, and the shear-stress-inhomogeneity coefficient, force-transfer ratio, maximum shear stress, and total force-transfer ratio of the four main force-transferring welds as the output-evaluation parameters, with a view to providing a reasonable and effective supplementary verification-and-evaluation method for the design stage of the built-in double-fixed cable-girder steel anchor box.