## 9 Conclusions  
This study aimed to determine the best transverse and longitudinal GPR profile line spacing offset. The method involved calculating the depth and spacing of rebars on each face of the beam by measuring the travel time of electromagnetic waves. This was achieved by conducting a series of GPR scans at different offsets and analyzing the hyperbolas recorded by the GPR. A custom computer code was created to automatically determine the depth and location of the rebar based on these hyperbolas.  
This study concluded that GPR profile line offsets do not significantly affect the results. Transverse profile line spacings ranging from 4 in. to 24 in. produced nearly identical results. Similarly, the number of longitudinal profile lines did not affect the stirrup depths and spacing results. However, it was found that the voids inside the concrete could not be determined with a single GPR profile line. Therefore, to ensure a thorough and accurate assessment of the prestressed concrete box beams, bridge inspectors must conduct multiple longitudinal profile scans, with a minimum of three scans being essential for a complete understanding of the internal features.  
The consistency in the study results provides a strong foundation for the study's reliability. The findings can enhance the efficiency and accuracy of bridge evaluations by  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**Two Sets of Prestressed Tendons**} & \multicolumn{2}{c}{**Center Prestressed Tendon**} \\
**Structure** & **Depth (in)** & **Spacing** & **Depth** & **Spacing** \\  & & **(in)** & **(in)** & **(in)** \\ \hline Minimum & 1.82 & 1.87 & 1.54 & 5.50 \\ Maximum & 1.86 & 1.88 & 1.59 & 5.54 \\ Variance & 0.04 & 0.01 & 0.05 & 0.04 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Bottom prestressed tendons’ minimum and maximum calculated depth and spacing values.  
helping bridge inspectors determine internal characteristics of prestressed concrete box beams, including rebar spacing, depth, sizes, and internal deficiencies. The study's findings offer valuable advancements and empower state departments of transportation with the knowledge to assess in-service concrete bridge box beams accurately, enabling them to make informed decisions about their bridge maintenance and repair strategies.  
Conceptualization, W.Z., F.M.R. and H.N.; methodology, F.M.R. and H.N.; software, H.N.; validation W.Z., F.M.R. and H.N.; formal analysis, F.M.R.; investigation, F.M.R.; resources, W.Z.; data curation, F.M.R.; writing--original draft preparation, F.M.R. and H.N.; writing--review and editing, W.Z.; visualization, W.Z.; supervision, W.Z.; project administration, W.Z.; funding acquisition, W.Z. All authors have read and agreed to the published version of the manuscript.  
Not applicable.  
The data presented in this study are available on request from the corresponding author (due to restrictions from the funding agency).  
The authors would like to express their sincere gratitude for the financial support provided by the West Virginia Department of Transportation, Division of Highways (WVDOH), for funding this research project. This support was instrumental in completing the study and is greatly appreciated. It is essential to clarify that the findings, conclusions, and recommendations presented in this study reflect the authors' perspectives and do not necessarily represent the views of WVDOH.  
The authors declare no conflicts of interest.