## 4 Experimental Verification  
### Test Model  
In order to further verify the effectiveness and accuracy of the proposed method, a 1:6 scale-down model test was designed according to the numerical simulated orthotropic steel box girder model, which consisted of a deck, U-rib, and diaphragm. The model is 270 cm long, 83 cm wide, and 20 cm high, with six U-ribs under the deck and six diaphragms with a spacing of 54 cm. The diaphragms are truncated vertically, so the model has no bottom plate, and all diaphragms are connected by two steel bars. The model is made of Q235 hot-rolled steel plate, and the thickness of all steel plates is 2 mm. The steel beam model is simply supported by a cushion at the bottom of the first and last diaphragm. To ensure that the test vehicle can pass the steel box beam model at a uniform speed, lead and tail beam were installed at the beginning and end of the steel box beam. The lead and tail beams are located as close as possible to the steel box girder but disconnected from the steel box girder.  
It should be noted that the designed experimental model does not strictly meet the similarity ratio criterion. However, the study does not focus on the absolute force condition of the structure. For different scale models, the measured strain response maybe different with practical engineering structures. However, the local force characteristic of the orthotropic deck is similar, and the strain influence line is short. We can identify the strain influence line and the optimized parameters corresponding to different scale models using the proposed method, and then we can verify the proposed method based on the identified results.  
Six axle weight sensors are placed on the lower edge of the span of each of the U-ribs in the middle section of the model, and ten FDA sensors are placed on the lower edge of the deck between adjacent U-ribs. Detailed dimensions and layouts of measurement points are shown in Figure 10.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Case**} & \multicolumn{4}{c}{**Identified Error (\%)**} \\  & **A1** & **A2** & **A3** & **GVW** \\ \hline
1 & 0.68 & 1.20 & 0.95 & 1.00 \\
2 & 0.66 & 0.17 & 0.37 & 0.40 \\
3 & 1.84 & 0.82 & 0.42 & 0.94 \\
4 & 2.31 & 2.03 & 0.87 & 1.52 \\
5 & \(-\)0.22 & 0.21 & 2.46 & 1.02 \\ Mean & 1.14 & 0.87 & 1.01 & 0.98 \\ \hline \hline \end{tabular}
\end{table}
Table 6: The identified result of the three-axle vehicle.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Case**} & \multicolumn{4}{c}{**Identified Error (\%)**} \\  & **A1** & **A2** & **A3** & **A4** & **A5** & **GVW** \\ \hline
1 & 0.70 & \(-\)0.26 & 2.08 & 2.32 & 0.54 & 1.06 \\
2 & 0.26 & 0.02 & \(-\)0.85 & 1.53 & \(-\)0.78 & \(-\)0.04 \\
3 & 1.22 & \(-\)2.50 & \(-\)0.41 & \(-\)0.22 & \(-\)2.90 & \(-\)1.01 \\
4 & 0.89 & \(-\)0.81A two- and three-axle vehicle was designed to simulate a vehicle's load. The vehicle's tread was 28 cm, the wheel width was 2 cm, the wheelbase can be adjusted, and the axle weight and gross weight can be changed by adding mass blocks to the vehicle. In order to ensure that the experimental trolley drives through the steel beam model in a straight line as much as possible, two limit holes are set on the experimental trolley, and two steel wires that can move laterally are fixed above the steel beam model. The wires pass through the limit holes of the trolley. A motor was fixed at the end of the tail beam, and the motor dragged the trolley through the experimental steel box beam at a uniform speed. The entire experimental model is shown in Figure 11.  
Figure 11: The entire experimental model.  
Figure 10: Model and layout of strain measurement points: (**a**) plan view and (**b**) elevation view.