## 5 Wind Fatigue Tests
### Test Parameters and Results  
Two groups of test parameters were used for the tests. In group A, the purlin distance was 1000 mm, and the design wind pressures were 4.5, 3.6 (repeated twice), and 3.0 kPa (repeated twice). In the other group, the design wind pressure was 4.5 kPa, and the purlin distances were 600 and 800 mm. Seven working conditions were included in the two groups. The failure stages of the two groups of test results are summarized in Table 4.  
The effects of different wind pressures and purlin distances on the fatigue damage of metal roof claddings were observed in the tests. The wind-induced fatigue failure processes of metal roof panel were divided into four stages according to the observation and records of the test processes. First, the fastener holes of the roof specimen became larger due to reciprocating cyclic loading, thus complete and effective constraints are impossible to form. Obvious uplift deformations near the fastener holes were observed with continuous loading. Then, the locations with maximum deformations developed into cracks. When cyclic loading was continued, multiple cracks were generated near the fastener holes, which gradually deepened and merged to form cracks with the loading process. The failure process is shown in Figure 13. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Group**} & \(\mathbf{P}\) & **Span** & **Failure Stage** & **Damage Estimation** \\ \cline{2-5}  & **/kPa** & **/mm** & & **1.0** \\ \hline \multirow{5}{*}{I} & 3.0 & & Stage B of the second round of loading & 0.67–1.0 \\ \cline{2-5}  & 3.0 & & Stage C of the second round of loading & 0.67–1.0 \\ \cline{2-5}  & 3.6 & & Mid-stage G of the first round of loading & 1.0–1.3 \\ \cline{2-5}  & 3.6 & & End-stage G of the first round of loading & 1.0 \\ \cline{2-5}  & 4.5 & & Stage F of the first round of loading & 1.0–2.0 \\ \hline \multirow{2}{*}{II} & \multirow{2}{*}{4.5} & 800 & End-stage G of the first round of loading & 1.0 \\ \cline{2-5}  & & 600 & No damage observed in the three rounds of test & 0–0.33 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Summary of the test results. Figure 13: Wind-induced fatigue failure process of metal roof: (**a**) uplift deformation; (**b**) rack generation; (**c**) three cracks; (**d**) cut-through cracks. The damage estimation in Table 4 was obtained based on the estimated results according to the cycle stage of roof failure. When P = 3.0 kPa in the group I working condition with a purlin distance of 1000 mm, two tests showed that fatigue cracks appeared on the roof panes in stages B and C of the second round of loading. There was no fatigue failure in the first round of loading. It could be concluded that the damage value of single round loading was less than 1. In the second round of loading, fatigue failure occurred before half of the loading was completed. Therefore, the single round loading damage was greater than 1/1.5, which means that the damage for a single round loading ranges between 0.67 and 1. When P = 3.6 kPa, the fatigue cracks of the roof panels in the two tests occurred in the middle and end of stage G of the first round of loading. Fatigue failure occurred before the first round of loading was completed. As a result, the damage value of single-round loading was considered to be greater than 1. The damage caused by each loading cycle in stages B-F is greater than that in the A and G stages. If the single loading cycle damage in stages B-F is divided into two parts, one of them is defined as D, which is equal to the single loading cycle damage value in stage A and G. The sum of the remaining damage in the B-F loading stages is defined as D\({}_{\text{others}}\). Then, the cumulative damage in the process of one round of loading is 8653 D + D\({}_{\text{others}}\), since fatigue failures occurred in the middle and late G stage of the two tests.