# BIM-Based Management System for Off-Site Construction Projects
## 1 Introduction  
Recently, the construction industry has been plagued with various difficulties. The productivity of the construction industry is developing gradually, unlike the rapid development trend of other industries. The stagnation of labor productivity in the construction industry has lasted for a considerable period, and productivity growth has averaged only 1% worldwide for the past 20 years [1]. The shortage of skilled workers in the construction industry has emerged as a significant problem [2]. According to an existing report, a notable risk to the construction industry is the shortage of skilled craftsmen [3], and 64% of regions worldwide announced that they are experiencing difficulties in supplying skilled workers for various reasons, such as COVID-19 [4]. In addition, the construction industries of nearly all countries are under pressure to adopt carbon-neutral practices to address climate change problems such as global warming. The industries are attempting to decrease the environmental load for sustainable development [5]. Considering that the carbon emission of the construction sector in 2020 was 38% of the total [6], the construction industry must respond more actively to climate change [7, 8]. Furthermore, occupational accidents are more prevalent in the construction industry compared to other industries worldwide [9]. In particular, 44% of fall accidents--which are most likely to lead to death--in the last three years (from 2019 to 2021) occurred in the construction sector [10]. Accordingly, strategies for preventing safety accidents in the construction industry must be actively identified [9, 11]. Offsite construction (OSC) has emerged as a promising alternative to address the abovementioned problems [12]. In the OSC frameworks, the mechanical, electrical, andplumbing (MEP) elements, including the structural and nonstructural elements of a building, are produced offsite and then transported and installed onsite. Compared to the conventional production method, the construction period, cost, and workforce requirements in the OSC frameworks are 30-50% [13], approximately 50% [14], and approximately 5% [15] lower, respectively. OSC can respond more flexibly to changes in the construction industry. By producing the components, approximately 85-90% of the project work, in specialized plants, this method can minimize simple onsite production activities, reducing inefficient energy and material consumption [16]. Moreover, owing to reduced onsite work, the projects are less dependent on human resources [17]. Workers can work safely and more comfortably in indoor spaces [18; 19] and standardized production can help to enhance the finishing level of building projects [20]. The effectiveness and flexibility of the OSC approach are driving countries worldwide to adopt it [21]. The UK and Australia have implemented mid- to long-term policies to revitalize OSC projects since the early 2000s [22]. Moreover, the National Institute of Standards and Technology of the US has selected permanent modular construction as one of the innovation factors for the future construction industry [23]. Since the 1970s, Japan has steadily increased the proportion of OSC activities in factory-built housing projects, and the focus areas at present are the marketability and quality [24; 25]. China is also concentrating its national capacity on raising the proportion of OSC projects to 30% over the next decade [19]. The global OSC market size was USD 820 billion in 2020 and is expected to reach USD 1.9 trillion in 2025, considering the future growth rate [26]. The implementation of OSC projects requires appropriate management techniques and systems. Supply chain management (SCM) plays a vital role in OSC projects. Because OSC projects are concurrently produced, transported, and installed at different locations, SCM is required to organically connect these processes. Additionally, OSC projects require careful management of the production and logistics stages in addition to the installation stage.