# Development of Railway Infrastructure BIM Prototype Libraries
## 3 Methods  
This study aimed to develop BIM prototype libraries that could be generally used for railway facilities, among other public infrastructures. Railway infrastructures are classified into various facilities, such as tunnels, bridges, tracks, stations, electricity, and signals. In this study, roadbeds, tracks, and tunnels, most of which change according to the linearity, as well as bridges, signals, and electricity, which are combinations of objects, were focused on. Stations were excluded because they have strong vertical elements and can thus be regarded as buildings. In this study, the following research was conducted to construct BIM libraries for railway facilities. The standardized drawings (roadbeds, tracks, electricity, and signals) provided by Korea Rail Network Authority (KR) were analyzed to select BIM library construction targets. As standard drawings were not available for tunnels and bridges, the target facilities were selected by analyzing two railway project cases. The various standards provided by MOLIT were analyzed to create the attributes and specifications to be included in the BIM libraries. The forms of the BIM libraries were modeled for the selected facilities, and the defined attributes and classification systems were entered. The constructed libraries were tested for certain roadbed and bridge sections. To construct the BIM libraries of railway infrastructures, it is important to identify the types of target facilities as well as the characteristics. Therefore, the characteristics, shapes, and uses of the target facilities were identified in this study by analyzing the drawings related to such facilities, and a library construction strategy that reflected the results was established. For railway facilities such as roadbeds, tracks, and tunnels, the libraries must consider the effects of the cant that occurs in a curved path. Therefore, the use of a software program capable of considering the effects of a cant as well as the linear path is essential, and 3D libraries alone cannot consider such effects. The parametric elements of 3D libraries alone cannot implement linearly changing shapes and cannot be utilized for various future projects. Therefore, it is necessary to create 3D libraries based on 2D cross-sections, which linearly change in connection to the path based on 2D cross-sections and thus can implement 3D models. 3D object libraries also cannot be applied to structures with certain shapes, such as retaining walls, gutters, and soundproof wall foundations, for which changes in the length direction must be considered, in addition to linearly changing facilities, because each project has different directions and lengths. Therefore, library types based on 2D profiles are necessary to implement the shapes required by the users for each project. In addition, there are single-object-type libraries without linear characteristics. Based on the results of such analysis, libraries can largely be divided into three types, as shown in Table 1. The first is the library type with 2D cross-sections, which can implement 3D models containing linearly changing shapes and quantity calculation. The second is the library type that implements 3D models based on 2D profiles for facilities changing in the lengthwise direction. The third is the library type that has a unique shape and quantity and that uses individual 3D models regardless of the linearity. All of these library types are consequently expressed in 3D forms. In addition, to construct these three library types without encountering problems, it is necessary to use both a software program capable of considering linearity and an object-based software program capable of constructing 3D models. The level of development (LOD) specification is very important for the construction of BIM libraries. As each railway construction project has specific site conditions, it is difficult to construct standard libraries that can be used in any construction. If libraries with a high LOD are constructed and used