# Bridge Displacements Monitoring Method Based on Pixel Sequence
## 3 Experimental Structure Composition
\begin{table}
\begin{tabular}{c c c} \hline \hline  & Sensor size & 36 \(\times\) 24 mm (3:2) \\ Canon 5 DsR & \begin{tabular}{c} Effective pixels \\ Sensor type \\ \end{tabular} & 50.6 MP \\ \hline  & & Focal length & 24–70 mm \\ EF 24–70 mm f/2.8L II & \begin{tabular}{c} Convert focal length \\ in APS-C format \\ \end{tabular} & 38–112 mm \\ (Canon Limited, Tokyo, Japan) & \begin{tabular}{c} Maximum diameter \\ and length \\ \end{tabular} & 88.5 \(\times\) 113 mm \\  & & Lens structure & 13 groups of 18 pieces \\ \hline  & DH#5G103 & & \\ (Jiangsu Donghua Testing Technology Co., Ltd., Taizhou, China) & \begin{tabular}{c} Sensitivity \\ Effective itinerary \\ \end{tabular} & 0.4 mV/mm@2 V \\ Output parameters & \
\begin{tabular}{c} Effective itinerary \\ \end{tabular} & 50 mm \\ \hline  & Images & 8868 \(\times\) 5792 \\ Output parameters &
\begin{tabular}{c} Videos \\ \end{tabular} & 1920 \(\times\) 1080 (25 FPS) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Conditions of instruments. In the laboratory setting, the experiment is arranged according to the specific layout depicted in Figure 9:  
In the experiments described in this paper, simulating the structural stress response of a bridge under working conditions requires applying loads to the structure. To verify the basic feasibility and practicality of the proposed algorithm, the load tests are divided into static load tests and dynamic load tests. The static load test serves as a fundamental test to evaluate the edge extraction effect of the DoG algorithm. By applying image-to-space scale transformation to obtain the algorithm's displacement and comparing it with LVDT data, the accuracy of the DoG algorithm can be analyzed. The dynamic load test aims to simulate the structural response of the bridge under working conditions [25], thereby assessing the applicability of the DoG algorithm proposed in this paper. To avoid any forward or backward movement of the vehicle caused by the applied load during the static load experiment, the vehicle is firmly secured in position prior to incremental loading and recording. Therefore, the weight of the vehicle does not need to be considered. The weights used in the laboratory are 10 kg, 5 kg, and 2 kg. The configuration of the loaded vehicle and supplementary weights is depicted in Figure 10:  
Figure 8: Schematic diagram of the DoG monitoring system. Figure 9: Experimental layout diagram. In the static load experiment, the vehicle is secured in place before incremental loading and recording to prevent the vehicle from sliding forward or backward due to the applied load. To avoid structural displacement fluctuations caused by impact effects during loading, which may lead to significant fluctuations in displacement measured by displacement sensors and extracted by the algorithm, the structure is allowed to settle for one minute after loading. Subsequently, the mechanical condition of the bridge is captured through photography, and displacement sensor data are collected (Table 2). During the dynamic load experiment, it is necessary to simulate the mechanical performance generated by a car passing over the bridge under normal working conditions. Therefore, after loading the vehicle, it is propelled at a constant speed over the bridge. During the experiment, a motor generates traction force to propel the vehicle steadily. Concurrently, the structure is monitored by a camera, and data are gathered (Table 3).