# Research on Damage Localization of Steel Truss-Concrete Composite Beam Based on Digital Orthoimage
## 3 Static Test of a Steel Truss-Concrete Composite Beam
### Accuracy-Verified Data Acquisition  
#### 3.4.1 Deflection Gauge Measurement  
The deflection gauge is a traditional deformation measurement instrument that is often used as a basis for verifying the accuracy of experimental data because of its high accuracy [27].The conventional displacement measurement method of this test uses the deflection electric measurement system, which includes deflection gauge (range 0-30 mm, accuracy 0.01-mm) and DH5902N test and analysis system. The DH5902 acquisition frequency is set to 1 time in 2 seconds. Seven deflection gauges are installed directly below the vertical rod of the test beam at \(L/8\), \(L/4\), \(3L/8\), \(L/2\), \(5L/8\), \(3L/4\) and at the two supports, and the data acquisition system is arranged as shown in Figure 19.  
The deflections of different load classes for each damage condition measured by the deflection gauge are summarized in Table 4. The process of collecting deflection data under no-damage conditions is shown in Figure 20.  
From Table 4, it is found that in some positions, the damaged bars increase but the deflections decrease. The reason is that the steel joint-concrete combination beam has a complex internal support bar system, and the difference of structural deflection before and after the damage is not significant, which indicates that the deflection is not sensitive to the damage of the complex structure. Conventional single-point measurement damage identification methods are not ideal for this type of structure. Compared with the conventional damage identification methods, using this type of specimen as the test object can fully demonstrate the innovation and efficiency of structural holographic morphological data in the damage identification problem.  
Figure 18: Test beam image after perspective transformation process.  
Figure 19: Deflection gauge layout.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multicolumn{2}{c}{**Number of**} & \multicolumn{2}{c}{**Working**} & \multicolumn{2}{c}{**Load**} & \multicolumn{6}{c}{**Deflection Gauge Values (mm)**} \\ \cline{3-11} \multicolumn{1}{c}{**Damaged Rods**} & \multicolumn{1}{c}{**Conditions**} & \multicolumn{1}{c}{**(kN)**} & \multicolumn{1}{c}{**S1**} & \multicolumn{1}{c}{**L/8**} & \multicolumn{1}{c}{**L/4**} & \multicolumn{1}{c}{**3L/8**} & \multicolumn{1}{c}{**L/2**} & \multicolumn{1}{c}{**5L/8**} & \multicolumn{1}{c}{**3L/4**} & \multicolumn{1}{c}{**7L/8**} & \multicolumn{1}{c}{**S2**} \\ \hline \multirow{3}{*}{0} & O\({}_{1}\) & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\  & O\({}_{2}\) & 150 & 0.717 & 3.884 & 6.101 & 8.696 & 9.514 & 8.725 & 6.33 & 2.696 & 0.732 \\  & O\({}_{3}\) & 250 & 0.844 & 5.751 & 9.875 & 14.194 & 15.539 & 14.32 & 10.15 & 4.101 & 0.913 \\ \hline \multirow{3}{*}{1} & A\({}_{1}\) & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\  & A\({}_{2}\) & 150 & 0.689 & 2.401 & 5.949 & 8.541 & 10.693 & 8.921 & 6.198 & 2.001 & 0.694 \\  & A\({}_{3}\) & 250 & 0.828 & 4.213 & 9.668 & 13.871 & 16.815 & 14.103 & 10.104 & 3.319 & 0.851 \\ \hline \multirow{3}{*}{2} & B\({}_{1}\) & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\  & B\({}_{2}\) & 150 & 0.704 & 3.356 & 5.959 & 8.764 & 10.61 & 8.923 & 6.358 & 2.603 & 0.688 \\  & B\({}_{3}\) & 250 & 0.813 & 5.336 & 9.62 & 14.107 & 16.67 & 14.521 & 10.14 & 4.288 & 0.843 \\ \hline \multirow{3}{*}{3} & C\({}_{1}\) & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\  & C\({}_{2}\) & 150 & 0.655 & 4.155 & 6.479 & 9.246 & 10.583 & 9.524 & 6.384 & 3.139 & 0.664 \\ \cline{1-1}  & C\({}_{3}\) & 250 & 0.805 & 6.102 & 10.234 & 14.589 & 16.631 & 14.782 & 10.134 & 4.558 & 0.822 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Deflection measurement results.  
Figure 20: Deflection meter measurement process under no-damage conditions.