## 4 Experimental Verification
### Damage Identification Results  
The model cable force was adjusted to about 350 N, and the south hanger cable force is shown in Figure 11. The cable force is uniform, and this state can be regarded as the completed state of the bridge. The complete damage (the cable force is reduced by 100%) of each hanger on the south side was simulated by removing the damaged hanger itself. The difference of deflection at the anchorage point of hanger and tie-beam under healthy state and various damage conditions was obtained, and the results are plotted in Figure 12. Then, the deflection difference influence matrix of the model bridge in this state was also obtained. Figure 11: Cable force of south hangers. Figure 10: Illustration of the deflection sensor locations (S1:S9, N1:N9) on the bridge deck. \begin{table}
\begin{tabular}{c c c c} \hline
**Damage Type** & **Damage Case No.** & **Damage Hanger No.** & **Damage Degree** \\ \hline \multirow{3}{*}{**Single hanger failure**} & EDC 1-4 & S2 & 12.5\% 25\% 37.5\% 50\% \\  & EDC 5-8 & S3 & 12.5\% 25\% 37.5\% 50\% \\  & EDC 9–12 & S4 & 12.5\% 25\% 37.5\% 50\% \\  & EDC 13–16 & S5 & 12.5\% 25\% 37.5\% 50\% \\  & EDC 17–20 & S4 \& S5 & 12.5\% 25\% 37.5\% 50\% \\  & EDC 21–24 & S4 \& S6 & 12.5\% 25\% 37.5\% 50\% \\ \hline \end{tabular}
\end{table} 
Table 5: Twenty-four damage conditions considered by the test model. It can be seen from Figure 12 that the influence matrix obtained by the model bridge has the same characteristics as that obtained by the numerical example, and there is a peak in the deflection difference at the location of the damaged hanger. When simulating each damage condition, the model test is realized by removing the corresponding number of springs. When the damage degree of the simulated hanger is 12.5%, 25%, 37.5%, and 50%, 1-4 springs need to be removed accordingly. This method is also the essence of this model, making it can accurately control the preset degree of damage and repeatedly simulate various damage scenarios. The damage condition EDC1-EDC16 simulates the damage of a single hanger, and the identification result is shown in Figure 13. Figure 13a shows that the hanger S2 is damaged by 12.5%, 25%, 37.5% and 50%, respectively. In the test, the damage is simulated by removing the spring at the lower end of hanger S2. By making a difference in the static deflection of the healthy state and damaged states, the deflection difference vectors \(\{\Delta W\}\) at each anchorage point under different damage degrees are obtained. Figure 12: Deflection difference at each anchorage point when the hanger on the south side of the model bridge is wholly damaged. Figure 13: Damage identification results for EDC1–EDC16: (**a**) the preset damage hanger is S2; (**b**) the preset damage hanger is S3; (**c**) the preset damage hanger is S4; (**d**) the preset damage hanger is S5. The deflection difference vector and the influence matrix are brought into Equation (9), and the change vector of the cable force of the damaged hangers is obtained, and the result is plotted in Figure 13a. As shown in Figure 13a, the ratio change of cable force at the damaged hanger is much larger than that at the undamaged, and the identification result is not a vector with only one non-zero element, which is slightly different from the numerical results because there are inevitable measurement errors in the test process. However, it is easy to locate the damaged hanger from the figure. It can be seen from Figure 13b-d that the damaged hanger is S3, S4, and S5, respectively. Therefore, when a single hanger is damaged, this method can well locate the damage. Another observation can be made that the identified results increase with the increase of the degree of damage, so the proposed method can also relatively quantify the degree of damage.