## 2 Materials and Methods  
### Data Collection  
The maintenance guidelines in South Korea mandate that various activities related to the serviceability and durability of bridges must be conducted at specific intervals [1,4]. These activities are classified into \"regular inspection\", \"precise inspection\", \"precise safety diagnosis\", and \"emergency inspection\". In general, visual inspections are conducted to determine whether any defects have emerged since the previous \"regular inspection\", and a summary of the new defects is recorded. In such cases, insufficient funding for bridge inspections results in the frequent use of junior technicians and the limited time allocated to inspections, leading to significant human-induced uncertainties, such as measurement errors or misinterpretations of damage. Conversely, \"precise inspection\" and \"precise safety diagnosis\" are performed to identify physical and functional defects as well as inherent risk factors through field surveys and various tests. Figure 1 shows examples of a slab defect map and quantity table recorded in an inspection report. This reporting method is essential for \"precise inspection\" and \"precise safety diagnosis\" to ensure that the types of defects, the year of occurrence, the volume of defects, and their locations can be accurately identified for each bridge component.  
Figure 1: Example of a slab defect map and defect quantity table from the inspection report used for data collection.  
Because the inspection results contain quantifiable and abundant objective data, this study analyzed the inspection reports generated from \"precise inspection\" and \"precise safety diagnosis\" to collect the deterioration data. A total of 856 inspection reports pertaining to 311 reinforced concrete (RC) slab bridges from nine regions (A-I) in South Korea were examined. The term \"region\" refers to 9 of the 17 administrative divisions in Korea, including the capital city, Seoul. This classification is necessary because bridge management agencies are designated based on administrative divisions, enabling the consideration of regional environmental factors, such as areas with high traffic volumes or regions prone to heavy snowfall. The reason for applying regional distinctions in this study is to enable the practical application of the model. If a deterioration model were constructed based on specific environmental factors, it would create a challenge in determining what values to input for these factors each time HI is used to evaluate a bridge in different regions. By using regional distinctions, however, these environmental factors are inherently included, simplifying the construction of the deterioration models.  
As the deterioration data in these inspection reports are categorized by components, individual data pertaining to slabs, piers, and abutments can be obtained. In total, 19,525 instances of 12 types of deterioration data were collected for each bridge component, as listed in Table 2, which are the most commonly observed deterioration factors in slab bridges and are essential evaluation factors specified in the Korean maintenance standards [1,4] This categorization enabled distinguishing training data, allowing us to construct different deterioration models for each component, as described in Section 2.2. All data were collected in terms of area, and for one-way cracks, a width of 0.25 m was assumed to calculate the area. Additionally, the instances wherein the same type of deterioration was recorded at multiple locations within a component were aggregated and processed into a single data entry. Figure 2 shows the average area for each deterioration according to bridge components. The slab exhibits significantly higher occurrences of microcracks, macroracks, crazing, spalling, efflorescence, and leakage than the other components, and it is evident that it experiences more damage owing to the direct impacts of moving vehicles.