## 5 Calibration of Structural Capacity  
### Introduction of Bridge-Condition Rating System  
In order to predict the response ratio, which is the ratio of the calculated deflection and the measured deflection response, the safety-diagnosis history reports for multiple bridges were collected. Given that this study focuses on bridge girders, the scope of the collected condition evaluation consists of the condition evaluation items for girders and bridge bearings. As the collected safety-diagnosis reports are based on safety diagnoses performed in South Korea, the Korean condition evaluation rating system was introduced. During the evaluation of the condition of the girders, the crack width, the amount of damage to the reinforcing bars, and, for PSC girders, the presence of filling defects and the corresponding chloride content are evaluated. In addition, bearings are divided into elastic bearings and steel bearings, cracks and shear deformation are evaluated, and the cracks, peeling, and exfoliation of the concrete supporting the bearings are evaluated. The aforementioned items do not require a separate field test; instead, only visual inspections  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **MLR** & **DT** & **SVM** & **BT** & **GPR** \\ \hline MAPE & 3.1\% & 2.3\% & 3.0\% & 4.5\% & 0.3\% \\ \(R_{adj}^{2}\) & 0.969 & 0.979 & 0.984 & 0.985 & 0.999 \\ \hline \hline \end{tabular}
\end{table}
Table 2: MAPE and \(R_{adj}^{2}\) results of five regression algorithms.  
Figure 7: Performance of each regression model. (**a**) MLR. (**b**) DT. (**c**) SVM. (**d**) BT. (**e**) GPR.  
are required. Tables 3 and 4 show the damage status according to the condition evaluation grading system for the girders and bridge bearings [24].  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Condition Rating**} & \multicolumn{4}{c}{**Bearing Plate**} \\ \cline{2-9}  & \multicolumn{2}{c}{**Elastomeric Bearing Plate**} & \multicolumn{2}{c}{**Steel Bearing Plate**} & \multicolumn{2}{c}{**Support Concrete**} \\ \hline A & – & Good & – & Good & – & Good \\ \hline B & – & Light deterioration such & – & & & & \\  & & as microcracks & – & & & & \\  & & & & & & & \\  & & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 4: Condition grading system for bearing plates.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Condition Rating**} & \multicolumn{4}{c}{**Girder**} & \multicolumn{4}{c}{**Prestressing Tendon**} \\ \cline{2-9}  & \multicolumn{2}{c}{**Crack Width**} & \multicolumn{2}{c}{**Deterioration and Damage**} & \multicolumn{2}{c}{**Tendon Exposure**} & \multicolumn{2}{c}{**Cement Grout**} & \multicolumn{2}{c}{**Sheath**} \\  & \multicolumn{2}{c}{**Cheath**} & \multicolumn{2}{c}{**Width**} & \multicolumn{2}{c}{**Deterioration and Damage**} & \multicolumn{2}{c}{**Tendon Damage**} & \multicolumn{2}{c}{**and Damage**} & \multicolumn{2}{c}{**Filling Defect**} & \multicolumn{2}{c}{**D Damage**} \\ \hline A & – & No & – & No & – & No exposure & – & No filling defect & – & No \\ \hline B & – & Less than & – & Surface damage & – & Exposure (1) & – & Filling defect & – & Damage (5) \\  & & 0.2 mm & & area less than 2\% & – & & & & \\ \hline C & – & & – & Surface damage & & & & & \\  & & & area 2\(\sim\)10\% & – & Surface & – & Chloride content (4) & & \\  & & & Over than 2\% & – & & & & 1.2\(\sim\)2.5 kg/m\({}^{3}\) on & & \\  & & & of rebar & & & & & \\  & & & & corrosion area & & & & \\ \hline D & – & & – & Over than 10\% & & & & & \\  & & & of surface & & & & & \\  & & & damage area & & & & & \\  & & & Over than 2\% & & & & & \\  & & & Over than 2\% & & & & & \\  & & & of rebar & & & & \\  & & & & corrosion area & & & & \\ \hline E & – & – & & Degradation of & & & & \\  & & & & member stability & & & & \\  & & & due to severe & & & & \\  & & 0.5 mm & & & damage at end & & & \\  & & & & concrete or & & & \\  & & & & anchorage zone & & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Condition rating system for girders.