Das Kapitel präsentiert eine umfassende Analyse der Entwurfsstrategien für Permanent Modular Construction (PMC), die sich auf schnelles Bauen konzentrieren, wobei das Aurora-Projekt von Solar Decathlon China 2021 als Fallstudie herangezogen wird. Aurora, ein solarbetriebenes Haus, das für das Zusammenleben mehrerer Generationen konzipiert wurde, ist ein Beispiel für die Integration von Vorfertigung und Montage vor Ort, um extreme Bauzeitpläne und finanzielle Zwänge einzuhalten. Das Kapitel behandelt die innovativen
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Abstract
Solar Decathlon establishes a platform for students to demonstrate their study and research outcomes. This paper discusses a project of SDC2021, Aurora, to illustrate the adoption of design strategies for Permanent Modular Construction (PMC) oriented to rapid construction. Through the off-site prefabrication and on-site assembly procedures, this work investigates the feasibility of deploying rapid construction and simultaneous collaboration of multi-participants to realize a modular volumetric house.
Through systematic empirical research and data analysis, the paper also explores the potential contributions of PMC in enhancing industrialization levels in construction, reducing on-site waste, and promoting environmentally friendly architectural design. Finally, it provides insights into future research directions and trends in the PMC field to innovate further and apply rapid construction technologies.
1 Introduction
Solar Decathlon establishes a platform for higher education institutes to demonstrate their latest research outcomes and allows architectural students to lead in actual practices [1‐3]. Solar Decathlon China 2021 (SDC2021) was held in Desheng Village, Zhang Jiakou. As shown in Fig. 1, Aurora is a single-story residence designed by the joint team of Denmark Technical University and Soochow University (DTU-SUDA). The 3-weeks construction period has posed a challenge to each team [1]. Therefore, under an extreme construction schedule and financial pressure, the DTU-SUDA team chose design strategies oriented to rapid construction, focusing on off-site prefabrication and on-site assembly to realize Aurora.
Fig. 1.
Aurora in SDC 2011 (taken by authors)
Aurora is a solar-powered house based on the popular Nordic concept of “one and a half home” [4]. “One and a half” represents one unit containing a family of three, and the “half” unit is designed for grandparent generations. Also, the small unit might be turned into a multi-purpose room, including a workspace, fitness, or entertainment room (Fig. 2). As a residential building that can be fully powered by solar energy, Aurora pursues comfort housing and functional flexibility in the design of layout and advocates low-carbon technical concepts in terms of sustainability.
Fig. 2.
The plan of Aurora for multi-generation cohabitation (drawn by authors)
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Without changing the design concept and building form, rapid construction demands the building details to accommodate easy fabrication procedures. The traditional design-to-build procedures typically follow a top-down workflow where building manufacturing and assembly must follow design schemes and requirements [5, 6]. However, due to the multi-type participants involved in pre-fabrication and always slow feedback, this workflow cannot meet Aurora's requirement for rapid construction [7]. The team adopted the idea of detailed design alteration dominated by manufacturing and assembly requirements [7, 8]. During the design and build workflow of Aurora, the authors aimed to clarify and validate the strategies of rapid manufacturing and assembly. It stimulated a multi-disciplinary simultaneous implementation and multi-participant collaboration for the Permanent Modular Construction (PMC) house [9]. Meanwhile, as a practical application of the rapid construction-oriented PMC design strategy, the Aurora project once again proved the advantages of PMC and gradually explored solutions to existing problems.
2 Literature Review of PMC
PMC, also called Prefabricated Prefinished Volumetric Construction (PPVC), is an alternative construction method utilizing offsite and lean manufacturing techniques to prefabricate buildings in deliverable modules [10‐12]. Compared to temporary container buildings, PMC is indistinguishable from conventional construction and is characterized by easy assembly, structure safety, low carbon, and site adaptability [8, 13]. Smith et al. (2017) analyzed the construction performance of 17 PMC cases and concluded the PMC method could save 16% on construction cost and 45% on construction time [14]. Zhang et al. (2020) verified PMC's advantages, such as construction speed, building performance, and comfort, for example, in the COVID-19 hospital project of Xiao Tangshan [15]. Hou et al. (2020) summarized strategies of volumetric building systems for emergency construction projects through Huo Shenshan Hospital, which must be constructed in only ten days [16].
PMC buildings employ modular design, standardized components, and industrial production [17], and their modules can be used alone or combined horizontally or vertically [18]. Conventional PMC projects contain only a few modular types designed for easy assembly but cannot meet various requirements of form and function. Hwang et al. (2018) concluded relevant international trends of PMC and pointed out problems such as monotonous form caused by module standardization [11].
3 Methodologies
Issues such as project delay cost overrun, and low quality will be reduced by integrating knowledge and experiences from multi-participants into the design team [12]. The goal is to promote seamless collaboration and to eliminate barriers among different participants and stages of the project. Therefore, this work investigates an innovative application of PMC and validates the design strategies for rapid construction. The steps of the methodology are as follows:
1.
Identifying the requirements of the manufacturing and assembly processes.
2.
Coordinating conflicts among multi-disciplinary implementors.
3.
Integrating existing technological solutions.
4.
Selecting off-the-peg components.
5.
Design alteration for PMC.
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As a design-build demonstration house, Aurora was used to validate the process, and the construction data for each step was collected and calculated through phased assignments. The team planned to adopt a manufacturing-driven approach, which was organized into two sections: the design strategy for manufacturing and the design strategy for assembly.
4 Rapid Construction Strategy for PMC
4.1 Section 1: The Design Strategy for Manufacturing
Subsystem Design of “Fixed - Flexible” Layer.
The design strategy for manufacturing pursues a seamless workflow from off-site prefabrication to on-site construction. It optimizes collaboration between various links through multi-party concurrent engineering and collaborative intelligence, achieving uninterrupted, efficient, and smooth work. Since manufacturing and assembly deviations are inevitable, a set of well-designed subsystems would maximize the manufacturability of building parts and the efficiency of the concurrent prefabrication mode. As shown in Fig. 3, the team divided Aurora into five subsystems, including the concrete foundation, the steel structure foundation, the modular volumetric building, the laminated bamboo rooftop structure, and the photovoltaic roof. Five sup-pliers prefabricated the five subsystems, each following a unified module size. The team designed the connection joint and prefabricated process to improve the manufacturability of different subsystems.
Fig. 3.
Five subsystems of Aurora according to “Fixed–flexible” (drawn by authors)
To solve the deviation accumulation of multi-disciplinary subsystems, the team designed a “fixed-flexible” layer. It defined the subsystems with minimal error tolerance during manufacturing and assembly as the “fixed layer.“ The concrete foundation and the modular volumetric building were challenging in eliminating deviation in their subsystems, so they were “fixed layers.” Comparatively, it describes the subsystems made of components with some degree of error tolerance as the “flexible layer.“ During on-site assembly, the component assembly of the steel structure foundation and laminated bamboo rooftop structure permitted a degree of deformation to rectify errors from the lower subsystem. This characteristic designates them as the “flexible layer.“ By adjusting joints and processing components of the steel structure foundation and laminated bamboo rooftop structure on site, the construction team reduced the errors of the concrete foundation and the modular volumetric building in their upper layers. The design strategy used the error tolerance of on-site assembly and made the interval arrangement of subsystems according to the “fixed-flexible” layer [19].
A Collaborative Process Design for PMC.
The subsystem of modular volumetric building was crucial to the off-site factory manufacturing. This process integrates various components, such as architecture, structure, water supply and drainage, electricity, heating, ventilation, and air conditioning (HVAC) [10]. In this case, the design strategy for manufacturing achieved the simultaneous construction of multiple building modules and multi-disciplinary operations within a single building module.
The production-driven layout for module prefabrication helped the workers and students to carry out simultaneous tasks, achieving synchronized manufacturing of multiple building modules. For each building module, the team designed a manufacturing process based on the requirements of multi-disciplinary operations. Multi-type installations can be synchronized in the single building module, including façade, ceiling, lighting, sanitary ware, pipeline, door, and window. Due to the close integration of parametric design and prefabrication of the facade, the exterior building facade was fully prefabricated and assembled by inexperienced students. This not only allowed students to participate in actual practice but also allowed the professional workers to focus on operations demanding more expertise (Fig. 4). In this rapid assembly working mode, Aurora can realize the collaborative and sequential construction of different subcontractors and students.
Fig. 4.
Simultaneous installation for students and workers in the factory (taken by authors)
4.2 Section 2: The Design Strategy for Assembly
Module Partition Design for Efficient Transportation and Lifting.
The design strategy for assembly aims to promote the ability to assess Aurora by developing and adjusting an original design adaptively. The key is a reasonable partition scheme for the modular volumetric building subsystem. Matters such as packaging, shipping, and handling should be valued by module partition for rapid assembly. The team divided the modular volumetric building into five modules where: modules A and E with a width of 3 m, modules B and D with a width of 1.8 m, and module C with a width of 3.6 m. As shown in Fig. 5a, the module partition scheme aimed to make the most of transportation capacity. Modules A and E were loaded on two 3-m-wide trailers, modules B and D were combined and loaded on one 3.6-m-wide trailer, and another 3.6-m-wide trailer was used for module C with other components. In total, the team used four trailers with a length of 17 m to transport all the modules and elements from the factory to the site, traveling a total of 1500 km.
The building envelope of the roof and wall has already integrated waterproofing during the prefabrication in the factory, so the packaging of five building modules only required simple waterproof cloth (Fig. 5b). Each module had four standard container corner fittings compatible with the crane. The weight of each module was below the hoisting weight limit of the 25-ton crane provided by the general contractor, enabling swift and accurate lifting from the trailers to the foundation (Fig. 5c).
Fig. 5.
The shipping and lifting of building modules (drawn and taken by authors)
Facade Assembly Based on Mixed Reality.
The challenge left to the construction team, mostly college students with no on-site experience, is the realization of a non-standard building envelope made of flipped panels. To realize the complex building facade with a relatively simple construction method, The team used Mixed Reality (MR) technology for on-site assembly to ensure high quality and speed [20]. The team used a parametric method based on visual programming to design an undulating facade that required different lengths and angles of laminated bamboo boards. The on-site assembly process was challenging since the facade contains various components and a standing pad needing careful positioning, numbering, and material stacking management [21]. Eventually, with the help of Fologram, the team was able to project the digital model of the façade onto the building elevation in real-time via HoloLens, achieving an interactive yet immersive virtual-actual construction experience [20] (Fig. 6). Finally, students used HoloLens to identify various components of the undulating façade quickly. They installed them in the designated position with precision.
Fig. 6.
The immersive virtual-actual construction experience (taken by authors)
5 Results and Discussion
It only took five professional workers and ten undergraduate students to build Aurora in just 20 days, demonstrating a practical application of the design strategy for PMC oriented to rapid construction. To explain its advantage, the team cross-compared the construction periods between PMC and the traditional component assembly. As shown in Fig. 7, the team calculated and analyzed the construction period, including off-site manufacturing and on-site assembly for multi-type construction. Using the PMC method, the team spent 34 days on manufacturing, three days on packaging and shipping, 20 days on assembly, and 58 days on total. The team consulted all the subcontractors to estimate the period data of the component assembly strategy, which needed 16 days for manufacturing, three days for packaging and shipping, 51 days for assembly, and 70 days in total. Compared to the component assembly strategy, the on-site assembly period and total construction period of PMC were reduced by 64.7% and 21.4%, respectively.
Fig. 7.
Construction period comparison between PMC and component assembly (drawn by authors)
The goal of applying the design strategy for PMC oriented to rapid construction is to shorten construction time, reduce cost, and assure the quality of the project [22]. For the design-build team, a reasonable selection of prefabrication systems is the priority during the design phase, as well as the estimation of the capacity of each profession during the manufacturing and assembly stages. To achieve the goal of rapid and high-quality construction under extreme construction periods and financial pressures, the team rationally distributed construction tasks both off and on-site according to project characteristics. It matched corresponding technologies, manpower, schedule, materials, and equipment, which is the key to Aurora's success.
6 Conclusion and Future Work
This research achieved rapid construction, suggesting pragmatic value for promoting the use of modular construction in highly customized building projects [23]. The innovation of this research lies in the application of design for manufacturing and assembly processes and guidelines to detached houses. This research combines detailed design strategies for rapid construction, including pre-fabrication type, subsystem classification, collaborative process, module partition, and MR-based installation technology. The high-quality and fast construction of Aurora was achieved through the adaptation of design alteration to meet manufacturing and assembly requirements. This is an extension of the practical application of customized PMC.
Future research will continue to investigate the multi-story model utilizing PMC and its workflow of off-site manufacturing and on-site assembly as it advances rapid construction for PMC through multi-technology integration and interdisciplinary collaboration.
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