# Digital Twin for Supply Chain Coordination in Modular Construction
## 1 Introduction  
Recently, modular construction has emerged as a promising construction method in the construction industry because of its potential to reduce project scheduling and costs [1]. The benefits of modular construction come from prefabricating a building module at an offsite factory while onsite foundations and assemblies are simultaneously performed [2]. To achieve maximum benefits (e.g., avoiding idle time for concurrent work), the module should be manufactured and delivered to the construction site on time. Thus, modular construction requires effective supply chain coordination among offsite manufacturing, logistics, and the onsite construction process [3, 4, 5]. However, modular construction typically involves complicated, volumetric, and large building components which can cause schedule deviation risks in the supply chain process [5, 6]. Furthermore, since many modular construction projects take place in dense urban areas with limited space for module storage, such deviations exacerbate idle time [7]. For example, it a module arrives at the site earlier than planned, idle time occurs for the transporter; if it arrives late, idle time occurs for field workers and equipment. Therefore, it is essential that supply chain scheduling among project participants be certain in order to maximize the benefits of modular construction. Recent studies have noted that digital twin technology can be an effective team coordination tool for supply chain management [8, 9, 10, 11]. A digital twin can be described as a real-time digital replica of a physical asset that contains its current condition, properties, and dynamic behaviors [12]. In the supply chain process, a digital twin can represent manufacturing machines, module components, transportation, warehouses, delivery trucks,assembly workers, and cranes to visually monitor the project's current condition and progress. Also, a digital twin simulates diverse \"what-if\" real-world scenarios to accurately predict potential supply chain risks such as schedule deviation [8,9]. If the digital twin collects real-time sensor (e.g., global positioning system (GPS)) data, analyzes them accordingly, and provides all the useful insights (e.g., optimal delivery route, accurate delivery time, and optimal module order time) along the supply chain in modular construction, project participants may have effective coordination and subsequently, better project performance. Despite its promising potential for supply chain management, existing digital twin research is mainly found in the contexts of product operation and shop floor management [13,14]. There is thus untapped potential for using a digital twin for logistics, the process in which modules are produced in a factory, stored in a warehouse, and then delivered--one key component of supply chain management in modular construction. Recently, studies have indicated that a digital twin could enable efficient logistics management, but their application has been limited to logistics in factories and warehouses [9,15,16]. There is still a lack of knowledge about the digital twin's practical application in logistics for construction projects where materials are delivered from offsite to onsite through transportation. Many logistical uncertainties and risks have thus not been addressed, posing a major barrier to the widespread application of modular construction. To address this issue, we aim to develop and test a digital twin framework that enables real-time logistics simulation in modular construction. The digital twin uses building information modeling (BIM) and geographic information system (GIS) as its backbone because BIM can include detailed geometry, scheduling, quantities, and module properties while GIS provides geospatial data with transportation information (e.g., traffic and regulation), all of which are important for logistics simulation.