## 3 Proposal of Bridge Maintenance Prioritization Model
### Risk Score Evaluation Criteria  
Using standard bridge data from Korea's Ministry of Land, Infrastructure, and Transport, four main factors were employed to determine the risk score: bridge service life, design load, seismic design presence, and safety grade [2]. However, these factors have varying impacts on each bridge, making analyses and the establishment of criteria challenging. Therefore, building on previously established weighting guidelines [16], as well as values proposed in earlier studies [17], we adopted those weights and multiplied them by the relevant evaluation criteria to compute each bridge's risk score. Specifically, the final weights were set as follows: safety grade (0.40), service life (0.30), seismic design status (0.20), and design load (0.10). These values reflect both the structural importance and the operational considerations generally recommended in risk-based maintenance practice. These weight values were initially derived through a structured Analytic Hierarchy Process (AHP) survey involving 35 civil engineering experts. While the AHP analysis yielded highly skewed values for the weight distribution safety grade (0.655), service years (0.24), seismic design (0.0651), and design load (0.0399), the relative importance ranking was preserved, and the numerical values were moderately adjusted to enhance practical applicability and interpretability. The final adjusted weights reflect a balance between theoretical rigor and field applicability, ensuring the model's usability in large-scale infrastructure evaluations. To verify the reliability of the AHP results, [PERSON]'s alpha analysis [30] was conducted using SPPS, confirming acceptable consistency among expert responses. Among the four identified risk factors, safety grade was thus confirmed to have the greatest overall influence, followed by service life, seismic design status, and design load. The final weighting results are summarized in Figure 3, which illustrates the relative impact of each factor. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Facility Type** & & **Description** \\ \hline Type 1 & (1) & Bridges with superstructures in the form of suspension bridges, cable-stayed bridges, arch bridges, and truss bridges. \\ Type 2 & (2) & Bridges with a main span length of 50 m or more (excluding single-span bridges). \\  & (3) & Bridges with a total length of 500 m or more. \\  & (4) & Cover structures with a width of 12 m or more and a total length of 500 m or more. \\ \hline Type 2 & (1) & Single-span bridges with a span length of 50 m or more. \\ Type 3 & (2) & Bridges with a total length of 100 m or more that do not fall under Type 1 facilities. \\  & (3) & Cover structures that do not fall under Type 1 facilities, with a width of 6 m or more and a total length of 100 m or more. \\ \hline Type 3 & (1) & Bridges installed on a road mentioned under Article 10 of the Road Act with an extension of 20-100 m. \\  & (2) & Bridges of least 20 m in length installed on a road other than roads mentioned under Article 10 of the Road Act. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Facility classification criteria [29]. The score for each element used to evaluate the risk factors was calculated as follows. Service life and design load were classified into four categories each. Service life was divided into less than 10 years, 10-20 years, and 20-30 years and over 30 years. The design load was categorized as DB-24, DB-18, DB-13.5, and unspecified. Seismic design was categorized as either present or absent. The design vehicle load (DB) used in Korea represents the load of an imaginary semi-trailer vehicle and follows the same procedure as the Load and Resistance Factor Design (LRFD) standards of the American Association of State Highway and Transportation Officials (AASHTO).