# Bridge Health Monitoring via Displacement Reconstruction-Based NB-IoT Technology
## 3 Bridge Health Monitoring Experiment
### Small-Scale Bridge with Vibration Induced by Passing Vehicle  
#### 3.1.1 Experiment Setup  
The experiment setup is shown in Figure 10, where the bridge has a 5.6 m span. During the testing, the excitation of the bridge is induced by a moving cart on the bridge span, as indicated in Figure 10. MEMS accelerometer with a sampling rate of 125 Hz and LVDT with a sampling rate of 200 Hz is equipped at the first quarter, middle, and the third quarter of the bridge as shown in Figure 10.  
For bridge frequency, the span length of small scale bridge is set so that its first three mode frequencies are 3.7 Hz, 15 Hz, and 30 Hz, respectively. As shown, these three frequencies are reasonable compared to those of a real bridge. For the mass ratio, two different types of ratios are used: light and heavy. The bridge weight is 291 kg, and the weights of vehicles are 30 kg and 47 kg, respectively. The mass ratio for the light case is around 10%, and the mass ratio for the heavy case is 16%. The heavy case is intended to model two consecutive trucks or a trailer truck with full loading. For the length ratio, the light case is 7%, and the heavy case is 16%. For the speed ratio (\(\alpha\)), the similarity ratio adopted is described in Equation (13), where \(v\) is the vehicle speed (m/s), \(f\) refers to the fundamental frequency (Hz), and \(I_{b}\) is bridge span length (m). Assuming the real bridge has 40 m in span and 3.7 Hz of the fundamental frequency, in this case, the small scale vehicle speeds of 0.4, 0.8, and 1.2 m/s are equivalent to 10, 20, and 30 km/h for a real bridge  
\[\alpha=\frac{v}{(2.f.l_{b})} \tag{13}\]  
To simulate various conditions of bridge and passing vehicle, 12 different scenarios are designed as indicated in Table 5. Two different bridge conditions are used, namely the original and the stiffened ones. The stiffened bridge refers to a stiffener is attached to one of the bridge spans to increase its stiffness, as shown in Figure 11b. Figure 10a indicates the location of the stiffened span. Two vehicles with different weights are used, namely heavy and light carts. The weights are 30.4 kgf and 47.3 kgf for the light and heavy carts, respectively. Three different speeds are used, and they are 0.4, 0.8, and 1.2 m/s, respectively. In total, 12 different scenarios are considered as listed in Table 5. For each scenario, the test will be repeated 10 times; each time, the cart will run back and forth once, as shown in Figure 10a. Figure 9: Illustration of Level 2 damage indicator. Figure 11: (**a**) Small scale bridge experiment; (**b**) a bridge span with a stiffened plate. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**No** & **Scenario Name** & **Bridge Type** & **Vehicle Mass** & **Vehicle Speed (m/s)** \\ \hline
1 & LVB0S1 & Original & Light & 0.4 \\
2 & LVB0S2 & Original & Light & 0.8 \\
3 & LVB0S3 & Original & Light & 1.2 \\
4 & HVB0S1 & Original & Heavy & 0.4 \\
5 & HVB0S2 & Original & Heavy & 0.8 \\
6 & HVB0S3 & Original & Heavy & 1.2 \\
7 & LVB1S1 & Stiffened & Light & 0.4 \\
8 & LVB1S2 & Stiffened & Light & 0.8 \\
9 & LVB1S3 & Stiffened & Light & 1.2 \\
10 & HVB1S1 & Stiffened & Heavy & 0.4 \\
11 & HVB1S2 & Stiffened & Heavy & 0.8 \\
12 & HVB1S3 & Stiffened & Heavy & 1.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: List for small scale bridge experiments. Figure 10: (**a**) General scheme of a small-scale bridge with passing vehicles; (**b**) cross-section of section A-A. Table 6 shows the dynamic bridge properties, such as the first three frequencies for the original and stiffened bridges. It is seen that although this is a small scale bridge, its dynamic property is adjusted so that it is similar to an actual bridge condition. In Table 6, frequency is measured under free vibration 5 times. It is shown that the stiffened bridge only slightly increases its frequency from 3.733 to 3.867 Hz. Table 6 also displays the coefficient of variation (cov) among 5 testing data. It is shown that covs are very small, indicating the measurement is very accurate.