## 7 Results and Discussion
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**(a)**} \\ \hline
**Profile** & **Depth 1 (in)** & **Calculated Depth 2 (in)** & **Difference 3** \\ \hline
4-in & 2.50 & 2.92 & 17\% \\
8-in & 2.50 & 2.93 & 17\% \\
12-in & 2.50 & 2.94 & 18\% \\
16-in & 2.50 & 2.93 & 17\% \\
24-in & 2.50 & 2.94 & 18\% \\ \hline \hline \end{tabular}
\end{table} 
Table 2: (a) Top rebars’ depth for different GPR profile offsets; (b) top rebars’ horizontal spacing for different GPR profile offsets. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Calculated**} & **Calculated** & **Calculated Spacing** \\  & **Depth (in)** & **Horizontal Concrete Cover (in)** & **(in)** & **(in)** \\ \hline Minimum & 2.93 & 4.90 & 8.69 \\ \hline Maximum & 2.94 & 4.96 & 8.74 \\ \hline Variance & 0.01 & 0.06 & 0.05 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Top longitudinal rebar minimum and maximum calculated depth and spacing values. concrete would not be fully visible, potentially leading engineers to mistakenly believe that no voids exist. To ensure a more comprehensive assessment, using three longitudinal scans per beam is highly advisable, though the precise number of scans should be determined based on a thorough evaluation of the specific bridge conditions. This approach ensures a more complete understanding of the beam's internal features and improves the overall reliability of the detection process. Finally, the effects of profile line offsets on the bottom face of the concrete box beam were evaluated. Similar to the top transverse profile lines, different bottom profile line offsets consistently resulted in similar results for rebar spacing and depth, regardless of the offset between the profile lines. Table 6 summarizes the results of the average calculated depth and spacing values for the prestressed tendons. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{5}{c}{**(a)**} \\ \hline \hline \multirow{3}{*}{\begin{tabular}{c} **Profile** \\ **Spacing** \\ \end{tabular} } & \multirow{3}{*}{\begin{tabular}{c} **Depth 1** \\ **(in)** \\ \end{tabular} } & \multicolumn{2}{c}{**Calculated**} & \multirow{3}{*}{\begin{tabular}{c} **Spacing 2** \\ **(in)** \\ \end{tabular} } & \multirow{3}{*}{\
\begin{tabular}{c} **Calculated** \\ **Spacing 3** \\ \end{tabular} } & \multirow{3}{*}{
\begin{tabular}{c} **Difference 3** \\ **(in)** \\ \end{tabular} } \\ \hline
4-in & 2.0 & 1.82 & \(-9\%\) & 2.0 & 1.88 & \(-6\%\) \\ \hline
8-in & 2.0 & 1.86 & \(-7\%\) & 2.0 & 1.87 & \(-6\%\) \\ \hline
12-in & 2.0 & 1.86 & \(-7\%\) & 2.0 & 1.88 & \(-6\%\) \\ \hline
16-in & 2.0 & 1.83 & \(-9\%\) & 2.0 & 1.88 & \(-6\%\) \\ \hline
24-in & 2.0 & 1.83 & \(-8\%\) & 2.0 & 1.87 & \(-7\%\) \\ \hline \hline \end{tabular}
\end{table} 
Table 6: (**a**) Two sets of prestressed tendons’ depth and spacing for different GPR profile offsets; (**b**) center prestressed tendon depth and spacing values for different GPR profile offsets. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{\begin{tabular}{c} **Longitudinal Profile** \\ **Layout** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Depth 1** \\ **(in)** \\ \end{tabular} } & \multicolumn{2}{c}{**Calculated**} & \multirow{2}{*}{\begin{tabular}{c} **Depth 2** \\ **(in)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Depth 3** \\ **Diff. 3** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Spacing 1** \\ **(in)** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Calculated** \\ **Spacing 2** \\ **(in)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Space Diff. 3** \\ **(in)** \\ \end{tabular} } \\ \hline
1 Profile line (Center) & 2.0 & 2.35 & 18\% & 12.0 & 11.83 & 1\% \\
2 Profile Lines & 2.0 & 2.38 & 19\% & 12.0 & 11.89 & 1\% \\
3 Profile Lines & 2.0 & 2.37 & 19\% & 12.0 & 11.87 & 1\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Shear reinforcement spacing and depths for different numbers of GPR profile lines.