# Productivity Analysis of Documentation Based on 3D Model in Plant Facility Construction Project
## 2 Literature Review
### 3D-model-based Documentation  
A 3D model is created from a combination of various object libraries that contain shape and property information. In particular, the 3D model for prefabrication provides the function to create not only design drawings but also drawings required for manufacturing and construction. The drawings of the structural steel frame consist of general arrangement drawing, assembly drawing, single part drawing, and single plate drawing. The documentation method using the 3D model extracts various 2D views from the 3D model to create a drawing including information about plans, elevations, and sections. The biggest advantage of this method is that when the update of design change is reflected in the 3D model, the related 2D view is changed automatically. This can greatly reduce drawing modification time compared to 2D drawing-based documentation.  
Previous studies on BIM based documentation were investigated as follows. [PERSON] et al. (2013) [35] proposed a standard for preparing BIM-based structural drawings, and [PERSON] et al. (2016) [36] proposed a standard for drawing requirements information for preparing BIM-based architectural permit design documents. [PERSON] et al. (2018) [37] established criteria to distinguish what should be modified in the BIM model from what should be corrected in the CAD drawings in order to minimize inefficient duplication and additional work when creating a BIM-based detailed design drawing. [PERSON] et al. (2018) [38] proposed a process for utilizing information extracted from BIM for steel construction. [PERSON] & [PERSON] (2010) [39] studied the modeling automation of complex steel joints, and [PERSON] & [PERSON] (2011) [40] studied the development of interfaces to improve interoperability between design processes. [PERSON] & [PERSON] (2009) [41] proposed a construction drawing automatic process for steel structures. However, empirical research on the productivity of 3D-model-based documentation is lacking.  
Meanwhile, research on prefabrication, digital fabrication processes, and productivity for atypical buildings and complex parts is increasing in recent years. Prefabrication and digital fabrication, usually done in factories, are generally classified as additional manufacturing and is based on computer-based design and robotic-based production processes [42]. The Bilbao Guggenheim Museum project automatically generated approximately 50,000 2D drawings from 3D models and provided them to project participants [43]. [PERSON] and [PERSON] (2018) [44] analyzed the process, productivity, and economics of the pre-fabrication method for BIM-based MEP racks. [PERSON] and [PERSON] (2014) [45] proposed a 3D methodology for manufacturing quality control of pipe spools.  
However, these studies cannot provide the productivity analysis results of 3D-model-based documentation method compared to 2D-drawing-based documentation method. BIM handbook analyzed the time of modeling and reinforcement detailing drawing production through threereinforced concrete building projects [2]. The analysis showed higher productivity than 2D method. [PERSON] and [PERSON] (2012) [13] used BIM in the design phase to reduce input time to output for productivity analysis. [PERSON] et al. (2008) [46] analyzed the drawing work using the BIM and CAD methods as the time spent in drawing for the productivity analysis of drawing generation. In order to analyze the productivity of the documentation method, the number of engineers who worked on the drawing work, the working time, and the total number of drawings are needed. However, not many structural engineers can create drawings using 3D-model-based documentation. In addition, it is difficult to obtain productivity data on actual projects required for research. Therefore, this study is to compare existing 2D-drawing-based documentation method with 3D-model-based documentation method through case analysis of EPC project.