A Digital Project Management Framework for Transnational Prefabricated Housing Projects

Abstract

Compared with an ordinary prefabricated housing project (PHP), a transnational PHP tends to involve more uncertainties, with major stakeholders residing in different countries. This study proposes a novel digital project management framework that integrates building information modeling to enhance information utilization. This framework also incorporates innovative design concepts of modulor, modulus, module, model, durability, and recyclability for enhanced user comfort, housing industrialization, and extended lifespan. It was demonstrated how planning, design, manufacture, and transportation processes can be streamlined in transnational PHP delivery. A case study was performed in a typical transnational PHP between the Kingdom of Saudi Arabia and China for validation. By applying the framework, this PHP could install a single house within 24 h, improve precast level by about 20%, and reduce project cost per square meter by 5.2%, because of integrated design concept, reduced labor cost, effective material cost control, and enhanced information management.

1. Introduction

The Belt and Road Initiative (BRI) involves a massive development of transnational construction among the countries along this trade route [1]. Construction firms with cutting-edge management concepts, advanced technologies, and standardized construction methods are playing an increasingly important role in the international engineering, procurement, and construction (EPC) market. These countries have a lot of investments in infrastructure and housing projects, providing a fertile ground for EPC contractors to strengthen their international marketing [2]. However, the unique cultural, political, and economic circumstances in these countries can cause huge challenges to the contractors. Many contractors have suffered from huge cost overruns and schedule delays in construction projects in these counties, with poor risk management as the root cause [3,4].

The dilemma may also be attributed to the construction firms’ reliance on traditional construction methods. Problems such as waste of resources, poor working conditions, environmental pollution, and labor-intensive service prevent the firms from maintaining competitiveness or acquiring a competitive edge in the international construction market. Prefabricated construction can overcome these shortcomings [5,6]. China’s green building revolution demonstrates how integrating sustainable technologies into large-scale construction projects can achieve both environmental and economic benefits, providing companies with greater competitiveness in the international market [7,8]. However, it also faces technological and management problems, such as fragmentation between design, manufacture, and construction phases. In the design phase, manufacture and construction requirements are not fully considered, which may easily lead to problems such as clashes and deviations during construction. Although prefabricated construction can shorten construction period, it can increase designers’ workload and reduce design flexibility [9].

The problem of transporting assembled components has also received extensive attention. The distances between component manufacturing factories and the construction site of a project may be too great, which would increase transportation cost and difficulty in maintaining factory–site connection. In addition, low usage rate of space in containers due to lack of scientific planning for component placement can also add transportation cost [10]. Currently, the combination of building information modeling (BIM) and prefabricated construction provides a good way for construction industry transformation and upgrading [11]. BIM improves information sharing and utilization among major stakeholders of different disciplines in different phases. Thus, the incorporation of BIM-based work processes into prefabricated construction can overcome the fragmentation among processes, and life cycle information management may optimize cost management [12].

Previous studies have explored implementation frameworks or platforms that integrate BIM with prefabricated construction. For example, Gao et al. developed a BIM and IoT-based smart tracking system for precast construction, which enables real-time tracking of components and uploads data to a cloud-based BIM platform. The platform can adjust construction plans based on real-time data, reducing delays caused by construction uncertainties [13]. Zhai et al. developed an IoT-enabled BIM platform for modular integrated construction projects, which consisted of smart construction objects for production, transportation, and on-site assembly processes [14]. The platform could address inconvenient data collection, less automatic decision support, and incomplete information facing independent stakeholders. However, the applicability of these platforms tended to be limited to prefabricated building projects in Hong Kong. Li et al. proposed a conceptual framework for integrating BIM and prefabricated construction, which created a gateway between smart BIM platform, smart work packages, and smart prefabricated production objects to facilitate communication and interaction with the central database, but is yet to be validated [15]. Therefore, little is known about how to apply these BIM-based frameworks to transform the delivery process and enhance the performance of transnational prefabricated housing projects (PHPs).

Compared with an ordinary PHP, a transnational PHP tends to involve more uncertainties, with its two major stakeholders, i.e., owner and contractor, residing in different countries and facing very distinct people management and respective culture and politics. This study aims to establish a novel BIM-based digital project management framework for transnational PHPs. The framework involves three components, including:

• Combining BIM and prefabricated construction to improve information exchange efficiency among stakeholders in different phases;
• Proposing a novel BIM implementation concept in transnational PHPs, namely modulor, modulus, module, and model (4M), to guide BIM uses in the design, manufacture, logistics and transportation, and construction phases for more efficient project management;
• Adopting work breakdown structure (WBS), risk breakdown structure (RBS), and model breakdown structure (MBS) to support implementation of the 4M concept in transnational PHPs. This study may inspire further developments to this framework and provide valuable information for academics and experience for practitioners in delivering transnational PHPs.

2. Issues and Needs of Digital Project Management in Transnational PHPs

2.1. Need for Integrating Prefabricated Construction and BIM

BIM and prefabricated construction constantly evolve in the architecture, engineering, and construction (AEC) industry. Using this construction method, a building is constructed in the same way as a piece of flat-packed furniture is assembled. However, prefabricated construction is difficult to be widely used due to lack of skilled technicians [16]. To overcome the shortage and achieve maximum value, it is encouraged to integrate prefabricated construction with other tools, such as BIM. BIM implementation can solve many issues in prefabricated building project delivery, such as fragmentation among different phases, design workload, and reduced design flexibility [9,17]. To avoid these problems, Yuan et al. used BIM for manufacture and assembly to improve design efficiency and avoid unnecessary reworks [18].

2.2. Importance of Adopting the 4M Concept

The 4M concept represents modulor, modulus, module, and model, as shown in Figure 1. This comprehensive concept is suitable for the entire life cycle of PHPs and is committed to providing value-added services such as optimizing production, shortening construction period, reducing costs, and improving quality. Each “M” in the concept is interpreted.

Firstly, modulor is an attempt to use the human body to measure behavior and spatial scale, trying to make the design of a transnational prefabricated house more suitable for people’s habits. Modulor is a universal and anthropometric scale of proportions to measure and reconcile mathematics, human form, architecture, and beauty into a single system. The proportions are used to control the design from details to the whole [19]. The emergence of modulor provides designers with a standard for determining measurement data. When the measurement cannot be precisely defined, modulor provides a scale system with appropriate proportions [20].

Secondly, modulus is a selected standard unit of measurement scale, aiming to make building components fit with each other and be interchangeable. Establishing a scientific modulus standard system helps to achieve standardization of design and construction as well as industrialization of production [21].

Thirdly, module is the basis of modular design. This concept can be defined as a unit with a specific function and structure formed by a combination of standard modules and non-standard modules [14]. Modules can constitute a series of standardized models in the way of building blocks and meet diverse requirements of different users [22]. Modularization is an innovation that can transform scattered building components into integrated value-driven prefabricated modules after proper production and assembly. In a modular project, independent modules are manufactured in a prefabricated yard and then transported to the construction site for assembly [23]. In a modular prefabricated project, the various modules of a building (such as bedrooms, kitchens, bathrooms, etc.) are independently manufactured and preassembled in the factory. These modules are transported to the construction site, where they are quickly assembled like pieces of a puzzle to form a complete house. This method not only reduces on-site construction time but also ensures consistent building quality.

Lastly, model is not simply a building information model of the prefabricated house. Instead, it is a database that is essential for data sharing among all of the major stakeholders in the life cycle. When they work collaboratively on a shared platform and use a single unified data source, issues such as information fragmentation can be avoided [24].

However, previous studies have rarely attempted to adopt the 4M concept in their project delivery processes for enhanced project management efficiency, especially in transnational PHPs.

2.3. Risk Management in Transnational PHPs

Compared with a domestic project, a transnational EPC project is more susceptible to changes in social and environmental factors. As the project proceeds, there will be many uncertainties, which may be contractually transferred to the EPC contractor. Thus, it is particularly important to effectively identify the uncertain factors that affect the value-added of the project [25]. Lin developed a risk model for transnational EPC projects and proposed measures to avoid risks in the form of EPC contracts to reduce losses, thereby increasing the projects’ profits [3]. However, this previous study did not investigate PHPs and elaborate on risk identification in the projects, which was the basis of subsequent risk assessment and control. Enshassi et al. introduced a systematic methodology that employed Bayesian inference theory for key project stakeholders to dynamically assess and proactively manage excessive geometric variability risks in modular construction projects, such as lack of accurate data on modularization process capabilities for fabrication, transportation, and erection in the early design stage, but this methodology has not yet been tested in transnational PHPs [26].

2.4. Importance of Integrating BIM, WBS, and MBS

This study also presents some supporting tools that can be incorporated in the BIM-based work processes, including WBS and MBS. The work breakdown structure (WBS) is a tool in project management that decomposes a project into smaller, manageable tasks, each pointing towards a specific deliverable. WBS must be constructed in a way that each new level in the hierarchy includes all of the project work needed to complete its parent task. The model breakdown structure (MBS) is a systematic and structured approach similar to the WBS used in project management, but it is specifically suitable for detailed modeling of complex models within projects. Like the WBS, the MBS decomposes complex models into manageable parts. Each level of decomposition goes into greater detail, from a high-level overview down to individual components or elements. It continues down to specifying detailed materials (such as screws on a window) to respective workers, clearly presenting the overall situation of the existing building without missing any details.

For example, Han et al. introduced a classification mechanism that integrated construction sequencing rationale with BIM to infer project progress, and illustrated how this mechanism could augment 4D BIM in the case of low levels of development and less detailed WBS to assist visual progress assessment for occluded BIM elements [27]. Park and Cai proposed a WBS-centered database approach and created an automatic link mechanism between construction tasks and BIM objects based on WBS code to generate a multi-dimensional BIM database [28]. The method could incorporate construction records into the database for as-built document production without data duplication or omission. Similarly, MBS decomposes a building information model into smaller and manageable units. By applying 3D laser scanning, WBS, BIM-based secondary design, MBS, prefabricated construction, and other supporting technologies in a renovation project, Ding et al. achieved efficiency optimization of the renovation process by 15%. Thus, incorporating WBS and MBS into BIM-based project delivery is essential for completing PHPs. However, a BIM-based digital project management framework that incorporated WBS and MBS has not been developed for transnational PHPs [29].

3. Methodology

This study was divided into three stages. First, a literature search was conducted to establish the need for integrating the 4M concept, risk management, WBS, and MBS in the BIM-based work practices for more efficient transnational PHP delivery. Second, a digital project management framework was developed to demonstrate how project teams may streamline the planning, design, manufacture, and transportation processes at a high prefabrication rate in managing transnational PHP delivery. Finally, a case study was performed in a typical transnational PHP, which is located in the Kingdom of Saudi Arabia (KSA) and partly completed by a Chinese EPC contractor, to validate the proposed framework in terms of schedule compliance, cost saving, and quality assurance. For better readability, the methods of data collection, data processing, and data analysis are presented in the “Case study” section.

4. A Proposed Digital Project Management Framework for Transnational PHPs

This study developed a comprehensive BIM-based project management framework, which considers the characteristics of prefabricated buildings and provides effective information and managerial insights for transnational EPC PHPs, as shown in Figure 2. The framework integrates BIM and prefabricated construction and incorporates the 4M concept and risk management in transnational EPC projects. This echoed Ding et al., who found that an appropriate combination of BIM and other tools for specific projects can improve project management efficiency [29]. The current research focuses on the planning, design, manufacture, and transportation phases of prefabricated projects. This framework’s architecture, problems involved, solutions, and practices as well as their rationale are described in detail below.

4.1. Planning Phase

This phase focuses on the identification of risk factors from the perspective of the general contractor in a transnational EPC PHP. EPC contracting model is widely used in international building projects that involve digital information models, because the models’ timeliness, accuracy, and comprehensiveness in information transmission can play a much better role under this contracting model. However, this requires the EPC contractor to bear almost all external and internal risks of the project [30]. Thus, the risks that may occur throughout the project life cycle should be identified and avoided by an experienced EPC contractor during the planning phase to optimize delivery efficiency [31].

Moreover, it is necessary to use WBS to deliver information to the right people in the preparation stage of a transnational PHP. This method can offer a clear understanding of the requirements of estimated duration, cost, and resources, allowing all major stakeholders to understand and clarify their work contents, roles, and responsibilities to avoid any omissions and duplicate efforts and to be aware of accurate project information [29].

4.2. Design Phase

The adoption of the EPC contracting model in the design phase fully considers the difficulties in the production, transportation, construction, operations, and maintenance of prefabricated building projects and responds to them in advance. Figure 3 illustrates the design phase of the digital project management framework in detail, which can be divided into conceptual design, design modeling, and detailed design.

The conceptual design is to determine design thinking, layout and elevations, and prefabrication rate of the transnational PHP. The 4M concept, durability, and recycling are integrated to put forward a new design philosophy, which is innovative and can be used in future PHPs. The design modeling process refers to the application of the integrated design philosophy for developing the project’s design model step by step. In addition, the detailed design process is to optimize the structure of prefabricated components, which is the most important part of prefabricated housing industrialization. The key to this process is to consider the needs of all of the primary participants and multi-disciplinary coordination. Specifically, the innovative design philosophy includes the following concepts:

(1) Modulor, which refers to humanized design. Modulor is an effective tool in terms of connecting ideas and results. The use of modulor in the design leads to arrangements of building components in a humane manner, so that residents’ items can be placed in comfortable areas. For each functional area, the length, width, and height are also controlled according to the golden ratio of modulor, making the residents comfortable in vision and daily use. Modulor is also essential in modular design at different levels, so that the modules at each level conform to the humanized design concept; For example, when designing a bedroom, the dimensions of length and width are set at 3.6 m and 2.2 m respectively, according to the golden ratio defined by the modulor system. These proportions not only optimize spatial efficiency but also meet the ergonomic needs for vision and use. Furthermore, the modulor principle is applied in the design and layout of furniture to achieve optimal ergonomics. For instance, the design of desks and chairs considers the average adult height and sitting posture depth, determining appropriate heights and distances to support correct sitting positions and reduce discomfort associated with prolonged use.

(2) Modulus, which refers to standard design and involves standardization of prefabricated building components and the whole design process. Standardization is the basis for promoting prefabricated building projects. The core process is the establishment of a set of adaptable moduli and their coordination principles. An important principle is to reduce specifications and varieties of prefabricated components and increase the reuse rate of standard components. This facilitates component processing, manufacture, assembly, and installation, and increases turnover rate and labor efficiency, ultimately reducing cost. Similarly, the design concept of the modulus should also be used in the modular design of each level, so that components meet standard requirements and can be mass-produced in factories.

(3) Module, which refers to modular design. Based on modulor and modulus, it splits the building into orderly basic units and combines them in an orderly manner to form a variety of building products. The modular design of a PHP combines modules (composition of basic units) with different functions into houses according to the residents’ needs. To realize free combination and interchange of modules, the modules need to be designed collaboratively, with interfaces being standardized and generalized. Various standard modules with different areas and functions are designed by selecting commonly used plane shapes and layout forms, considering factors such as modulor, modulus, and modeling, and conducting proper optimization.

(4) Model. The collaborative design of prefabricated modules using BIM has already received great attention from stakeholders. Design modeling requires cooperation between architecture; structure; mechanical, electrical, plumbing (MEP); and other disciplines as well as coordination between their models to ensure that forces are reasonable, connections are simple, and positions are accurate. Detailed design analysis is conducted based on a full understanding of the design philosophy.

(5) Durable design and recyclable design, which will not directly contribute to the reduction in time and costs and thus are often regarded by the general contractor as the least important design concepts. However, since good durability and recyclability of prefabricated components greatly increases the service life of prefabricated buildings and reduces the amount of construction waste generated, these two design concepts should be well recognized [32,33,34]. Durable design is often achieved by using new building materials to extend a building’s lifespan, whereas recyclable design tends to use detachable component connections instead of traditional concrete infill methods. This allows damaged components to be easily replaced, extending the building’s lifespan and enabling more environmentally friendly production and construction.

4.3. Manufacture Phase

In PHPs where prefabricated components are mass-produced in factories, reworks are expensive. Once reworks occur, large quantities of components need to be reprocessed or reproduced, which may also incur additional transportation costs. Thus, in the design phase, the integration of design, production, and construction based on BIM is often emphasized, which was introduced in depth earlier. For the manufacturing phase, this study will focus on the specific application of the 4M method and the model-based decomposition for enhanced production and reduced reworks.

In the component-manufacturing stage, after types and quantities of prefabricated components are statistically analyzed in a composite design model, the bill of quantities, preliminary budget, and bill of materials (BOM) can be extracted. The BOM is obtained based on MBS, as shown in Figure 4. The model is decomposed into basic units and finally into the smallest components that the factories can produce. Meanwhile, analysis of comprehensive attributes and standard specifications of main materials and auxiliary materials helps make most use of raw materials, scientifically cut materials, and reduce material waste.

The issues in the manufacturing phase are not limited to material selection and usage but also include production processes and quality control in finishing. For example, using inappropriate materials, inaccurate component measurements, and inadequate manufacturing processes will affect production efficiency and the final quality of components. Therefore, it is crucial to ensure that the manufacturing process for each component adheres to design and production standards.

This study focuses on the specific application of the 4M method and model-based decomposition. The MBS can accurately break down the BOM required for each component. By integrating the BOM with the BIM system, the factory is ensured to use only validated, appropriate materials, thus avoiding improper material selection. Additionally, MBS decomposes complex models into manageable units, each with detailed material, finishing, and manufacturing process requirements. Furthermore, MBS assigns specific responsibilities for each small unit to individual workers or teams on the assembly line, improving accountability and production efficiency.

Using the BIM system allows for real-time monitoring and simulation of the production process, ensuring that materials, processing, and manufacturing procedures at each stage comply with design specifications. This approach effectively reduces quality issues that may arise from inadequate finishing or manufacturing processes.

Moreover, labor costs associated with prefabricated component manufacture must be fully considered in transnational PHPs. For example, the countries along the BRI trade route often rely heavily on the petroleum industry, and local contractors may lack sufficient experience in producing prefabricated building components, which increases the cost of manufacturing components and the time required for delivering prefabricated projects.

4.4. Transportation Phase

In transnational PHPs, prefabricated components often come from the factories all over the world. The complexity of logistics services becomes a significant characteristic. Hong et al. stated that transportation cost accounts for about 10% of the total cost of prefabricated components, and high cost is a critical obstacle to the widespread use of prefabricated materials [9]. Yi et al. reported that the difficulty in transporting prefabricated components as well as high damage ratios also prevent the practitioners from adopting prefabricated construction [35]. A transnational PHP usually has a very large logistics network for transporting components, which involves cumbersome procedures for successful transportation. Figure 5 presents an international logistics node diagram of transporting prefabricated components from the factories to the construction site. Three loading and unloading processes are generated in the whole process, which may easily cause damage to components.

Alternatively, integrating storage and transportation of modular components is an effective solution. It puts components on specific shelves in the factories in an orderly manner. The specific shelves serve as storage racks in the factories and can be directly moved to trucks. Thus, without the process of unloading and loading, components are directly transported to the construction site by sea and land transportation, which greatly reduces damage to components during multiple loading and unloading processes. The shelves for storing prefabricated components are designed based on the 4M method. According to the dimensions of international shipping containers and utilizing BIM technology, the stacking positions of the components within the containers are simulated and optimized to minimize displacement during transportation. This not only reduces the damage rate but also improves space utilization.

5. Case Study

5.1. Background of Case Project

To explore how the proposed BIM-based digital project management framework could be applied in transnational PHPs, this study took a transnational affordable PHP, which is owned by the KSA’s Ministry of Housing, as an example. This project aimed to deliver a total of 2.8 million houses, as rendered in Figure 6a. There were four types of prefabricated houses in this project, with different gross floor areas (GFAs), as shown in Figure 7. They are spliced by unified functional modules. It should be noted that Phase II of the transnational PHP served as the case project, which used EPC contracting. The EPC contractor was a Chinese joint venture of Company A (an experienced general contractor in international construction projects) and Company B (specialized in the integration of BIM and prefabrication). The primary supplier (Company C) was also based in China. This project used a combination of precast concrete and autoclaved lightweight concrete (ALC) when manufacturing the modules. The EPC contractor actively implemented the proposed framework live during the project execution, integrating it into their daily operations to enhance management efficiency and decision-making. They purchased prefabricated components, decoration raw materials, and other items from the Chinese supplier.

The difficulties faced by the project mainly included:

• The PHP was too large and its cost was high. The contract required that 80,000 houses should be delivered in Phase II of the project. Any delay occurring in the processes of design, off-site prefabrication, transnational transportation, and installation would affect the schedule. Thus, the project’s internal risks were difficult to control;
• The Chinese EPC contractor bore most risks. Apart from the internal risks, external risks, such as political risks, economic risks, and cultural differences, should also be fully considered and well managed. If setting up a new factory in the KSA to prefabricate building components, its material and labor costs would go far beyond the project’s limitation;
• The contractors from various countries had been customized with different standards in their past projects;
• Difficult transportation. The prefabricated components were transported from the factory in China to the KSA. To maximize freight volume within transportation cost constraints, the size of international shipping containers and the height of the tractors for transporting the standard containers should be carefully considered;
• Language barriers. During on-site installation, technical instructors and local workers used different languages, making it difficult to communicate.

The Chinese EPC contractor followed the digital project management framework established in this study to undertake the project’s design, manufacture, and construction work. Thus, this transnational PHP between the KSA and China could well serve as a case project.

5.2. Data Collection and Presentation

To validate the proposed digital project management framework, six out of ten AEC professionals in Company B were interviewed to solicit their feedback on the implementation process and results of the transnational PHP. They had good theoretical and practical knowledge of BIM and prefabricated construction and were actively involved during the execution of the transnational PHP. Semi-structured interviews were conducted with the experts because this approach has maximum flexibility and allowed them to provide new insights. The personal interviews were undertaken face to face, which was convenient to clarify ambiguous issues. Regarding each personal interview, an interview guide that indicated the aim of this study and interview questions were emailed to these experts ahead of time. They were then asked to provide information about the project. Finally, the experts were invited to provide opinions on the proposed digital project management framework and its application in this transnational prefabricated project. The interviews lasted from 40 to 60 min, with an average duration of 50 min. All interviews were recorded and transcribed. The answers provided by the six professionals were consistent.

Table 1. Profile of the interviewees.

Interviewees	Work Experience in BIM and Prefabrication	Duties
1	20 years	Chief executive officer
2	15 years	BIM consultancy and project management
3	10 years	MEP design
4	9 years	BIM consultancy
5	9 years	Structural design
6	6 years	Architectural and decorative design

shows the profiles of the six interviewees, including a chief executive officer, project manager, BIM manager, and designers in Company B. All of them had more than five years’ experience of implementing BIM and prefabricated construction. The number (six) of interviewees accounted for 60% of the AEC professionals in this company. Some previous construction management research used similar numbers of experts to validate their frameworks or systems. For example, Imriyas validated an expert system for insurance premium rating by five experts and one case [36]. Liao et. al. validated a BIM implementation readiness evaluation model by five experts. Thus, the number of the interviewees in this study was considered adequate [37].

5.3. Application of the Proposed Digital Project Management Framework

The project’s workflow was based on a BIM platform. With the use of the proposed digital project management framework, all project-related information was managed and flowed smoothly. The transnational PHP’s risks were not only related to the political and economic situation, foreign relation, labor-related regulations, and foreign exchange management act of the KSA, but were also subject to different technical specifications, standards, and geographical and climatic conditions. By discussing project-related issues with experienced experts of the primary stakeholders, the project leadership team obtained the risk classifications and factors facing the project.

Measures were developed to control the risks. For example, it was suggested that the Chinese EPC contractor engaged Chinese workers rather than the local workforce due to cultural differences. The reasons included, but were not limited to the following:

• Working days in the KSA and China are different;
• Additional taxes. Hiring local workers would require paying religious taxes;
• Language. It was difficult for both the management and workers to communicate the construction intentions with the local workers due to language differences.

Company A studied the local AEC industry specifications and standards in the preparation and planning phase to avoid problems such as design discrepancies and failure to obtain regulatory approvals. Apart from its own standards, the KSA construction industry also uses European or North American standards, which are different from Chinese standards. Figure 8 presents the standard differences. During the design phase, all building systems were designed and finalized by the EPC contractor in accordance with the local regulations.

After analyzing and responding to the risks, the design team applied WBS to decompose the life cycle work of the prefabricated houses. To assign tasks to designated workers, some tasks were subdivided until they were broken down into work packages that could be assigned to specific workers.

After the decomposition, the proposed design concepts were applied. Specifically, the designers established a standardized, humanized, and collaborative building information model for the transnational PHP based on the work packages assigned to them, which adopted the integrated design concepts described in Figure 3. This mainly included the development of the model and the production of construction drawings after detailed design. Among the design concepts (modulor, modulus, module, model, durability, and recyclability), modular design served as the basis in the design modeling process. The 144 m² house type (see Figure 7) was used as an example. Figure 9a shows the traditional 2D design drafting method, with the water supply and drainage module depicted in detail. It is often difficult to coordinate and update all relevant drawings when small design changes occur. As a comparison, Figure 9b illustrates the 3D design model of the house type based on the proposed design framework. The 2D drawing in Figure 9a shows that the prefabricated house is composed of many identical modules. The living room, kitchen, dining room, four bedrooms, and two bathrooms in this house adopt a standardized and unified modular design. Specifically, the modules only need to be modeled once and can be applied to other house types. Consequently, the prefabricated houses of different GFAs are integrated by unified functional modules, which greatly shortens the duration required in the design phase. Take the bathroom module as an example. As shown in Figure 9c, the bathroom is made up of standardized functional units, including a wash basin, bath unit, toilet, and pipelines. Thus, the modular design concept from low level to high level achieves a diversity of house types. The integration of the proposed design concepts helps improve user comfort and housing industrialization.

In the process of the modular design, the designers also followed the proposed design concepts of modulor, modulus, model, durability, and recyclability. As shown in Figure 10, in the KSA–China PHP, 150 mm × 150 mm was the minimum modulus, and all of the modules were controlled in multiples of 150 mm. This was because the spacing among steel bars in slabs was 150 mm × 150 mm, and the moduli of all slabs were controlled in multiples of 150 mm. Connectors and longitudinally arranged connecting steel bars were also in multiples of 150 mm. The adoption of modulor and modulus ensured that all of the functional modules were standardized and parameterized, facilitating the streamlined production of prefabricated components in the factories.

The model design concept was adopted, as shown in Figure 11. Specifically, the collaborative design concept among various disciplines was adopted in the creation of functional modules, such as the structural system, MEP system, water supply and drainage system, and door and window system. This design approach greatly improves the efficiency of project integration, reduces the conflicts among various professions, and ensures project quality.

The concepts of durability and recyclability were also applied in the design phase according to the KSA’s actual circumstances. Since the KSA has a tropical desert climate, the PHP would be built under high-temperature conditions. Cracks would inevitably occur in cast-in-situ reinforced concrete (RC) floor slabs. During the cast-in-situ process, the high temperature would reduce strength and volume stability of the RC. Moreover, this temperature condition would limit admixtures to be mixed, easily leading to collapse. Therefore, to enhance the durability of RC slabs, a new material type, namely a combination of precast concrete and ALC was used in the design. ALC slabs with small holes were made of materials such as fly ash, cement, and lime and cured by high-pressure steam. The key advantages of the ALC slabs included light weight (550–625 kg/m³), high strength, and high adaptability to high temperature and drought, which would effectively improve the durability of prefabricated houses and extend their lifespan to about 100 years.

In addition, to increase the service life of the prefabricated buildings and reduce the amount of construction waste, the designers also included the concept of recyclability in the design. Recyclable design emphasized the importance of removability and material recyclability. The recyclability of materials was an issue that every primary stakeholder needed to consider. Meanwhile, because some building components may be prone to damage in the operations phase, the use of a detachable design would facilitate component replacement for extended service life of the buildings. For example, when designing staircases, prefabricated stair components are usually bolted to the head or end of the stairs. This allows the components to be disassembled and replaced. The detailed design part in the proposed digital project management framework (see Figure 3) was not the research focus and thus is not elaborated in detail here.

Subsequently, the design model developed by SolidWorks in the detailed design process was used to guide the manufacture of the building components. The BOM was obtained after using MBS, which was then converted into a standard file format and imported to processing equipment. The factory’s manufacturing execution system could collect the production data for further management, scheduling, and control. Figure 12 shows the production process of wallboards from design modeling, BOM extracting, to manufacturing.

Finally, it was essential to apply the proposed digital project management framework in the transportation phase. Specifically, long-distance transportation across the Indian Ocean would greatly increase the project cost. This is because:

• The prefabricated components produced by the supplier in Shanghai, China (Company C) must be transported to Jeddah by sea, as shown in Figure 13;
• During transportation, the components are often damaged due to unreasonable placement, which would easily cause instability of their supporting points, resulting in wasted space and collisions.

To solve these problems, the project team used the proposed framework to reduce the transportation cost. Figure 14a,b represent the design of different storage racks. Their sizes fit the house components as well as the containers in trucks and ships. The racks could also help hold the components in place. Figure 14c shows that the storage racks are placed in the containers according to the concept of modulus. The application of the integration of storing and transporting the modular components ensures that the components are correctly placed in the trucks and ships as soon as they are produced in the factories. During the land and sea transportation, the components no longer leave the storage racks. Compared with the traditional method requiring multiple loading and unloading processes, the new approach saves time and reduces the damage rate. Thus, the placement of the storage racks in the international shipping containers is optimized based on the principle of modulus, reducing wasted space.

6. Results and Discussion

The application of the proposed digital project management framework in the case project enhanced time, cost, and quality performance. Firstly, all six interviewees reported that overall, risks were well identified, evaluated, and controlled in the transnational PHP between the KSA and China, except during the Coronavirus pandemic of 2019, which caused a delay in the project delivery. Thus, enhanced performance was reported subsequently in terms of the prefabricated houses delivered in Phase II, as shown in Figure 6b. Secondly, following the proposed framework, a single prefabricated house of the four types mentioned earlier could be installed within 24 h. Thirdly, compared with the precast level of 65% in a typical prefabricated residential building project in Shenyang, China [38], about 85% of the components in this transnational PHP were manufactured in the factory. These components were also well integrated with coating, doors, windows, and pre-embedded water and electricity pipelines where necessary.

The PHP’s cost performance was appealing in comparison with the typical prefabricated project in Shenyang, China. The project cost in Shenyang was 2418 CNY/m² [38]. The figure for the transnational PHP in the present study was 2523 CNY/m². Instead, if excluding sea transportation fees from China to the KSA and retaining land transportation cost to ensure comparability and consistency, the case project’s cost was 2292 CNY/m², achieving a reduction by 5.2%. The reasons for this good cost performance included:

• Adoption of the 4M concept. During the design phase, the philosophy of modulor and modulus was strictly followed, which reduced building component types and specifications but increased their reusage. This facilitated the component manufacture and assembly processes;
• The labor cost accounted for 4% of the total project cost, as the design fully considered subsequent assembly and installation processes, and 85% of the components were prefabricated, reducing manpower;
• Effective control of material costs. Hong et al. reported that material costs in prefabricated projects usually accounted for 30% to 55% of total project costs, and labor cost and transportation cost constituted 14% to 24% and 6% to 11%, respectively. In the case project, due to the climatic factors of the KSA, the durability of the materials and the roof’s insulation were fully considered in the design [9]. The price of using precast concrete and ALC was higher than that of ordinary concrete, which was not reflected in the reduced project cost.

The enhanced performance was analyzed and is discussed below. The efficiency of prefabricated construction mainly depended on the planning and preparation phase and the design phase. The design phase determines most of the project cost, so good design concepts are particularly important for prefabricated buildings [39]. Subsequently, due to excessive amounts of information in the project life cycle, it was necessary to prevent work or component losses. Thus, the EPC contractor proposed the MBS approach, which demonstrated the sequences and details of the detailed design model and decomposed it into accurate components. This ensured accurate component production and avoided losses and reworks. In this case study, minimizing the types of prefabricated components effectively reduced the difficulty in the design, compressed the factory production time, and shortened the duration of on-site installation. The use of connectors effectively simplified the design, manufacture, and assembly processes, reducing time and cost.

This was consistent with Hong et al. that precast rate, connections of component nodes, and types of prefabricated components adopted are important factors for enhanced efficiency and cost-effectiveness [9]. However, although previous studies also used a parametric design for manufacture and assembly, they tended to emphasize design standardization and the suitability for industrial production and assembly. In other words, these studies somewhat ignored the ability of the housing to enhance user comfort and did not pay much attention to the design concepts of recyclability and durability, which is very important for household needs and social attributes [40]. The interviewees also highlighted the importance of following the design concepts suggested in this present study.

Moreover, previous studies provided little experience for contractors planning to undertake building projects in the countries along the BRI, and did not provide a digital project management framework that combined BIM, prefabricated construction, and the 4M concept. For example, El-Adaway et al. stated that Islam tended to serve United States contractors, aiming to enhance their competitiveness in undertaking projects in the KSA [41]. Therefore, in response to the problems facing transnational prefabricated projects, the present study developed a new digital framework with new distinctive design concepts to improve the use of prefabricated building technologies in transnational projects.

7. Conclusions and Recommendations

This research has studied how transnational PHPs could improve their delivery efficiency through an innovative approach. Through the literature review, the need for using prefabricated construction instead of the traditional project delivery in transnational housing projects was established. It was advocated that project teams should combine prefabricated construction with BIM to overcome inefficiencies such as information fragmentation. Following this, this study developed a novel BIM-based digital project management framework for transnational PHPs. This framework integrated the innovative design philosophy, including the 4M method and durable and recyclable design, and incorporated other methods such as MBS. The applicability of the framework was verified in a transnational PHP located in the KSA and mainly completed by a Chinese EPC contractor.

The main solutions and findings are summarized as follows. Firstly, in the planning and preparation stage, risks should be properly identified and proactively managed in transnational projects. Secondly, since reworks would be expensive, design optimization should be done early to ensure the completion of the project with high quality and within a limited time and cost. Thus, this study proposed the novel design concepts of modulor, modulus, module, model, durability, and recyclability. These concepts would be better implemented on the BIM platform due to enhanced information utilization. Collaborative multidisciplinary design is extremely important for the subsequent manufacture and installation stages. Production of prefabricated components is based on the design model in which their types and quantities can be statistically analyzed. To ensure accuracy and high-quality management, MBS is used to decompose the composite model until the smallest components fitting for production in the factory are reached. To prevent the components from being damaged in multiple loading and unloading processes, this study proposed the integration of storing and transporting the modular components. This facilitates correct placement of the components in the trucks and ships after they are manufactured. During the land and sea transportation, the components would no longer leave the storage racks. Specifically, the storage racks are designed based on the 4M principle, which caters to the requirement of international shipping containers.

In conclusion, this study is the first to build a universal BIM-based digital project management framework for transnational PHPs, with support from the novel concepts of modulor, modulus, module, model, durability, and recyclability, which provides valuable information for EPC firms to undertake building projects overseas, expanding literature related to comfortable design and prefabricated construction.