Studies focused on constructing an effective construction information classification system continue to be conducted separately from international standardization efforts. However, all classification systems are designed for the integrated management of substantial construction information, surpassing a simple arrangement of construction data
[31][32]. Although the developed classification systems are designed to conform to existing systems and enhance usability through careful analyses of requirements, design and construction work remain disconnected. Therefore, an information classification system that is widely used throughout construction projects is necessary. Some cite the lack of publicity and voluntary participation as reasons for low utilization in the early stages
[33]. Nevertheless, the fundamental cause lies in the lack of integrated development for construction information classification systems.
Research was conducted to expand the model breakdown structure under the component classification system of the construction information classification system, which is based on the WBS used in road construction projects in South Korea. The primary aim was to develop an information classification system incorporating the existing facet-based and object-oriented classification systems
[38][39]. It is feasible to develop a BIM that aligns with widely used construction information classification systems and organizes construction information based on an object-oriented approach. However, further research is necessary to address the flexible handling of construction information during its generation and adaptation to meet specific requirements at individual construction sites.
4.1. Object-Oriented Construction Information Classification System
The existing construction information primarily serves as a tool for delivering concepts and terminology to experts. However, digitally transformed road construction information is represented as a 3D construction information model using digital data, enabling the conveyance of additional information through spatial representation. Therefore, to ensure efficient utilization, construction information should be classified based on the construction objects represented in 3D models.
Road facilities can be designated as a single construction object or divided into segments. Additionally, the individual facility elements constituting the road can be designated as separate construction objects. The designation of construction objects can take various forms, depending on the most suitable form for delivering the required construction information. The construction objects that must be represented in three dimensions are defined by their shape, location, and attribute information, as shown in Figure 2.
Figure 2. Information related to construction objects.
Linking information concerning the individual works performed during the design and construction phases of a road project to individually defined 3D construction objects enables the classification of information. This classification allows users to intuitively understand and convey the information.
4.2. An Information Classification System That Separates Construction Objects and Activities
As road facilities are created through design and construction, it becomes challenging to entirely segregate the associated activities. Therefore, most existing information classification systems define construction information by linking construction objects with activity details, as shown in Figure 3. While this approach maintains flexibility for partial changes in construction objects or activity information, it cannot adequately accommodate significant modifications in the scope of construction objects or activity content. To address this issue, scholars developed a construction information classification system for each information type. This allows for independent modifications of construction objects, such as splitting or merging, and the replacement of all the activities assigned to construction objects without modifying the other data (Figure 4). The connection between construction objects and activities is established by referencing the unique IDs assigned to each of them.
Figure 3. Composition of existing construction information classification systems.
Figure 4. Configuration of proposed construction information classification system.
4.3. Information Classification System for Construction Objects
Construction objects are discrete 3D units within road facilities; they possess engineering significance. These objects can be identified independently, allowing for their classification as singular construction units for the entire road facility or as distinct portions. This enables a hierarchical classification of all construction objects. For example, an entire road facility can be designated as one object, while the portion constructed as a bridge can be designated as a bridge construction object. Furthermore, detailed elements, such as piers, copings, abutment concrete, and bridge supports, can also be identified as separate construction objects using the same method. These construction objects are classified within a hierarchical structure that falls under the infrastructure facilities category.
In construction, facility objects represent the structure of a facility, either in its entirety or in part. They are implemented as 3D models corresponding to the final products after the construction process. However, it may not be appropriate to rely only on facility objects to represent all construction activities throughout the construction lifecycle. To address this limitation, different types of objects have been defined. Element objects refer to specific components, such as reinforcing bars and concrete. These elements are subdivided to a level where functional aspects, which are necessary to achieve the purpose of the facility, are not considered. Construction-related components, such as temporary facilities, are collectively designated as temporary objects. These temporary objects are then assigned as sub-elements under the main facility object, enabling hierarchical structuring. Intangible objects cover construction elements not explicitly assigned to 3D visible facility objects but rather associated with higher-level facility objects.
Each construction object within the hierarchical structure carries distinct associated information that should be inheritable based on the hierarchy. If the information does not follow an inherited relationship, separate branches must be defined for construction objects.
4.4. Information Classification System for Activities
Road construction projects involve various activities contributing to the design and construction of facilities. Figure 5 illustrates how these activities constitute a collection of unit works focused on constructing the components of the road. Each unit is further subdivided to achieve certain objectives, such as safety, quality, and process management, providing detailed information. Moreover, these activities specify the necessary resources and conditions for their execution. These activities are interconnected with the construction objects, presenting independent information that can be classified hierarchically and facet-wise. They can be grouped based on similarities or hierarchically arranged by dividing or merging unit activities.
Figure 5. Definition of activity (proposed).
When an activity is linked to a construction object, it modifies the attribute information of the construction object, indicating the allocation of resources and ongoing on-site construction processes. Therefore, information regarding which activities are connected to specific objects becomes a critical aspect of the construction information model, providing insights into the execution of construction projects.
Infrastructure is managed and constructed by national or public institutions, each with its own distinct method for overseeing construction objects and activities. Consequently, the volume of construction information to be produced and managed may differ significantly. It is unfeasible to implement a universal regulation system for construction information models across various facilities managed by different public institutions. Therefore, an information classification system that permits flexible adjustments to be made to the construction information model is necessary.
In principle, construction objects must be associated with one or more activities. While some objects may not be directly linked to any activity, one or more intermediate objects between the top- and bottom-level objects must have assigned activities.
The unit construction cost is assigned to activities classified as billable, while activities of the same type but applied differently based on conditions are grouped as billable activities. These defined activities comprise multiple smaller unit activities grouped together to facilitate process management and progressive billing. Various types of construction information, including the materials, equipment, and personnel, define these activities. Time information related to the duration of unit activities can also be included. If a specific unit activity requires special management, such as safety or quality control, it was classified as an elementary activity. General management activities that could not be specifically identified in the construction process were classified as intangible.
4.5. Unit Works Defined by Construction Objects and Activities
Road construction projects encompass various works during the design and construction phases. Notably, the specifications of the target facility may undergo changes, and the content of activities can change throughout the construction lifecycle owing to advancements in engineering technology, the development of new construction methods, and fluctuations in social conditions. Therefore, effectively managing construction information involves maintaining continuity between stages, ensuring that the changes occurring in each stage are recorded and traced back to the preceding stages.
In cases where construction plans are modified, the hierarchical structure of the construction objects enables the easy selection and modification of objects that need revision. Simultaneously, associated activities can be modified concurrently or at a later stage. During the execution of the unit work, activities can be assigned or newly specified.