After the first modular construction project in Korea in 2003, the scope and demand for modular systems have gradually increased. However, modular producers in Korea utilize spreadsheets to manage the process, manpower, and materials required for modular construction. This is inadequate compared to other countries that are more advanced in modular construction such as Japan and the United Kingdom. The management system in Korea decreases the effectiveness of modular construction in reducing construction time and cost. There is no formal system for managing modular production in Korea. Although some construction management programs utilized in the traditional construction industry are available, they do not reflect the flow of modular production, that is, to simultaneously produce several types of modules in accordance with demand in a factory. This research develops a modular-construction-specific production management system that has three overall functions: factory setup, project creation, and result analysis. These functions can link all the relevant data for managing modular production and can help manage several types of modules. The production management system is verified through simulation of the existing processes observed for a completed project and comparing the results to an alternative process. Through such comparisons, an optimized process design can be achieved.
Recently, the construction industry has experienced a paradigm shift from a site-centered, labor-intensive industry to a mechanized, automated, and information-technology-dependent industry [
Interest for local and international modular housing systems is driven by the automation of the construction industry, and domestic companies and research centers are now increasingly studying and developing modular systems. After the first modular construction project for the Singi Elementary School in Korea in 2003, the scope and demand for modular systems have gradually increased. Modular systems refer to houses or buildings that are constructed by erecting a frame from steel, wood, and/or concrete (module) at an offsite location and completing the internal and external finishing on-site [
Studies related to improving modular system production have been performed by other researchers [
The objective of this research was to examine the manufacturing process for the completed Jinju-Hamyang build-transfer-lease (Build-Transfer-Lease) project and to analyze problems with the existing factory processes. The input and output data such as manpower, time, materials, and productivity were determined, and the framework for the software program was established based on the analyzed data. The input data related to the modular construction of the Jinju-Hamyang BTL project was applied to this developed program. Moreover, using the developed program, the optimized process was simulated by evaluating different conditions, such as manpower and time, from the existing process. Finally, the productivity results of the existing process were compared to the optimized process. Figure
Research flow chart.
We monitored and analyzed the current factory manufacturing processes for a private investment facility project for the Korean military constructed by a local modular construction company. The first monitoring period was from July 8 to July 9, 2015, and the second was performed on July 21, 2015. The project was then authorized by the Ministry of National Defense. The entire construction project covered two regions for the air force (Jinju) and two regions for the army (Hamyang and Yeosu). However, the modular systems were only constructed in the two regions for the army. The overall project duration was 105 days from June 3 to September 15, 2015, but the modular manufacturing period for the required 288 units was only 55 days [
The factory manufacturing process observed during the monitoring periods, with corresponding photos (Figure
Factory manufacturing process. (a) Manufacturing of the floor frame. (b) Manufacturing of the concrete floor slab. (c) Assembly of the structural frame. (d) Installation of light-weight steel structures. (e) Installation of plumbing and electrical equipment. (f) Installation of inner walls and insulation. (g) External work and open storage.
By monitoring the modular factory manufacturing process in Korea, we were able to identify that the entire process was being delayed owing to inefficient management. In particular, the manufacturing durations were not uniform, resulting in specific processes being delayed, which in turn delayed the entire process. The delays were caused by inefficient manpower allocation. Ideally, once a single process concludes, the workers proceed to the next process. However, it was observed that workers from the previous process who were unable to finish their work before being scheduled for the next process continued into the time allocated for the following process. This prevented the workers in the following process from starting their work on time. Kim et al. [
Generally, to reduce the required construction time, more manpower and equipment can be added at a typical construction site. However, increasing manpower and equipment for factory manufacturing can have adverse effects owing to overlapping manpower, bottlenecks, and rework. Therefore, unlike on-site work, subassembly lines need to be added and optimized in the factory, and the construction period can be reduced by increasing manpower in conjunction with integration and subdivision of work. However, there is currently no analytical tool for predicting the effect of implementing a method for reducing construction time or for optimizing this method.
Factory manufacturing processes are broadly categorized in three stages: (1) prestation stage, where the individual modular components are formed; (2) station stage, where the module is assembled and manufactured while moving along a rail; (3) poststation stage, where the completed modular unit is packaged and prepared for transport. The prestation stage can be distinguished by floor, wall, ceiling, and structure assembly activities. The station stage is where work is carried out in a continuous manner; hence, it is distinguished by subprocesses that occur sequentially. Finally, the poststation phase is subdivided into water-related processes and packaging process (Figure
Subdivided manufacturing process flow.
The work, work time, and number of workers per process are arranged as shown in Table
Work, work time, and number of workers per process.
Category | Process | Precedence | Work description | Time (min) | No. of workers |
---|---|---|---|---|---|
Prestation | PS-OS-2 | — | Processing of beam & column member | 60 | 3 |
PS-M-1 | — | Processing of plate/bracket | 60 | 1 | |
PS-M-2 | PS-OS-1 |
Welding of column framework with plate/bracket | 60 | 1 | |
PS-A-F-1 | PS-OS-1 |
Painting and curing of beam/column framework | 180 | 2 | |
PS-A-F-2 | PS-M-2 | Welding of floor slab material and assembly of floor frame | 120 | 2 | |
PS-A-F-3 | PS-A-F-1 | Installation of deck and wire mesh | 60 | 3 | |
PS-A-W-1 | PS-A-F-2 | Pouring concrete in the floor frame | 60 | 2 | |
PS-A-C-1 | PS-M-2 | Manufacturing of short-span outer wall (welding/bolting) | 15 | 2 | |
PS-A-C-2 | - | Manufacturing of plumbing/electrical wiring | 120 |
2 | |
PS-MA-1 | PS-M-2 |
Manufacturing of ceiling frame (welding/bolting) | 120 |
4 | |
PS-MA-2 | PS-A-F-3 |
Assembly of module frames and installation of brace | 120 |
1 | |
|
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Station | S-1 | PS-MA-1 | Regular welding of modular unit and repair of fireproof painting | 130 | 2 |
S-2 | PS-MA-2 | Installation of runner and stud | 120 |
2 | |
S-3 | S-1 | Installation of gypsum board/insulation and embedded plumbing pipe at long span | 90 |
2 | |
S-4 | S-2 | Installation of gypsum board/insulation and internal stud at short span | 90 |
2 | |
S-5 | S-3 | Installation of vertical plumbing pipe, inner insulation, and A/C box | 120 |
2 | |
S-6 | S-4 | Installation of inner gypsum board, Tyvek, and electrical outlet | 80 |
2 | |
S-7 | S-5 | Installation of windows and doors | 50 |
2 | |
S-8 | S-6 |
Installation of external wall frame, installation parallel sliding door, and arrangement of electric conduit | 120 |
2 | |
S-9 | S-7 | Installation of ceiling support | 120 |
2 | |
S-10 | S-8 | Installation of ceiling gypsum board | 130 | 2 | |
S-S-1 | S-9 | Other finish work and transportation | 120 |
1 | |
|
|||||
Poststation | WP-1 | - | Manufacturing of external panel frame using jig and installation of external materials | 60 | 1 |
WP-2 | S-10 | Apply urethane waterproofing in bathroom and installation of buffer material | 30 | 2 | |
WP-3 | WP-1 | Pouring and curing of autoclaved light-weight concrete | 90 | 1 | |
WP-4 | WP-2 | Installation of bathroom wall/floor tiles and installation of ceiling panels | 60 | 1 | |
WP-5 | WP-3 | Installation of bathroom ceramics (toilet bowl, water basin, and mirror) and electrical outlet/switch/light | 30 | 3 | |
EP-1 | WP-4 | Installation of finishing materials on bathroom floor, baseboard, and ceiling molding/finishing materials | 240 | 1 | |
EP-2 | S-10 |
Installation of bathroom light and furnishings and quality inspection | 60 | 4 | |
|
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Manpower ∗ total hours | 5,710 minutes (including the manpower standby time (total 580 minutes) marked with a star ( |
PS : prestation, S : station, OS : outsourcing, M : member, A : assembly, F : floor, W : wall, C : ceiling, MA : modular assembly, WP : wet process, EP : end process.
The system developed for analyzing the modular factory manufacturing process in this study is referred to as the integrated management system, and it is equipped with three broad functions, as shown in Figure
Software framework.
The factory length and width are configured through the workspace creation function, as shown in Figure
Roof frame after configuring the factory size.
Process line after configuring the workspace and arranging the process line.
The detailed manufacturing line setup function allows the input of relevant information for configuration. The location, length, and rotation angle of the line can be established similar to the factory setup. The workspace area and free space that will be utilized to manufacture the modular unit can be set in this stage.
Additionally, when configuring the manufacturing line, the default setting is static production, but this can be changed to continuous production. For static production, since space is required for materials to be transported and for manpower to carry out operations, the width of the workspace and moving space need to be configured. Since the module moves along a rail in continuous production, there is a limitation in the workspace and the moving space for manpower. Therefore, they need to be set up in accordance with their respective requisite characteristics.
Finally, once the manufacturing line is set up, the manufacturing process is input (Figure
Manufacturing line with process code, process name, and time for continuous production line.
Manpower breakdown sheet.
The results analysis function can calculate and show the daily work hours, weekly work days, process, manufacturing method, module output (calculated per day, week, month, and year), and manpower inputs based on the entered data. Moreover, a productivity comparison between alternative processes and the existing process is possible for evaluating any improvement from the existing process. Additionally, the factory layout setup can be saved in DWG format.
The information collected from monitoring the Jinju-Hamyang BTL construction project was applied to the program (Figure
Simulation setup.
The existing process created through the program and the optimized process integrating the manpower rearrangement and process were compared using the productivity index. The standard for changing the existing process was accelerated using manpower input for the process type on the critical path. The required time was standardized by changing the manpower input and work integration of the process type that were assigned to the continuous production line. Moreover, when a fixed daily workforce was required (i.e., when there is a minimum daily workforce), the daily average manpower input was lowered so that the spare time could be utilized to the extent that the process type on the critical path was not greatly changed.
Table
Productivity comparison between existing process and optimized process.
Category | # | Existing | Optimized | Remark and optimization plan | ||
---|---|---|---|---|---|---|
Time (min) | Manpower | Time (min) | Manpower | |||
Prestation | PS-OS-2 | 60 | 3 | 60 | 3 | |
PS-M-1 | 60 | 1 | 60 | 1 | ||
PS-M-2 | 60 | 1 | 60 | 1 | ||
PS-A-F-1 | 180 | 2 | 60 | 6 | Add manpower | |
PS-A-F-2 | 120 | 2 | 60 | 4 | Add manpower | |
PS-A-F-3 | 60 | 3 | 60 | 3 | ||
PS-A-W-1 | 60 | 2 | 60 | 2 | ||
PS-A-C-1 | 15 | 2 | 15 | 2 | ||
PS-A-C-2 | 120 |
2 | 240 | 1 | Downsize manpower | |
PS-MA-1 | 120 |
4 | 60 | 8 | Add manpower | |
PS-MA-2 | 120 |
1 | 60 | 2 | Add manpower | |
|
||||||
Station | S-1 | 130 | 2 | 60 | 4 | Add manpower |
S-2 | 120 |
2 | 60 | 4 | Add manpower | |
S-3 | 90 |
2 | 60 | 3 | Add manpower | |
S-4 | 90 |
2 | 60 | 3 | Add manpower | |
S-5 | 120 |
2 | 60 | 4 | Add manpower | |
S-6 | 80 |
2 | 60 | 4 | Integrate process | |
S-7 | 50 |
2 | ||||
S-8 | 120 |
2 | 60 | 4 | Add manpower | |
S-9 | 120 |
2 | 60 | 4 | Add manpower | |
S-10 | 130 | 2 | 60 | 4 | Add manpower | |
S-S-1 | 120 |
1 | 120 | 1 | ||
|
||||||
Poststation | WP-1 | 60 | 1 | 60 | 1 | |
WP-2 | 30 | 2 | 30 | 2 | ||
WP-3 | 90 | 1 | 90 | 1 | ||
WP-4 | 60 | 1 | 60 | 1 | ||
WP-5 | 30 | 3 | 30 | 3 | ||
EP-1 | 240 | 1 | 60 | 4 | Add manpower | |
EP-2 | 60 | 4 | 60 | 4 | ||
|
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Manpower ∗ Total time | 5710 | 5070 | 11.2% reduction |
PS : prestation, S : station, OS : outsourcing, M : member, A: assemble, F : floor, W : wall, C : celling, MA : modular assemble, WP: wet process, EP : end process.
Productivity comparison.
Category | Existing process | Optimized process |
---|---|---|
Days spent manufacturing (days) | 32 | 24 |
Daily average manpower input (number of workers) | 9.37 | 10.82 |
Daily average labor cost input (KRW) | 1,176,180 | 1,009,511 |
Total manpower input (number of workers) | 299.81 | 259.57 |
Total labor cost input (KRW) | 37,637,768 | 32,304,364 |
Manpower comparison between existing and optimized processes.
We analyzed the process data collected from monitoring an existing modular manufacturing project and subdivided it into 31 processes. We then arranged the manpower, work hours, and materials according to the associated processes. A total of 5,710 minutes were required to manufacture a single modular unit. The main problem of the modular manufacturing process was the inefficient workforce management. Manpower arrangements were inconsistent with the manufacturing requirements and caused the manufacturing process durations to be irregular, which delayed the entire process. To resolve this problem, subassembly lines were added and manpower was increased in addition to work integration and subdivision, contrary to the strategy used in a typical on-site construction scenario. However, there is no way to predict the effect of this change prior to implementation. To resolve this issue, this research utilized information and data related to modular factory manufacturing and identified the productivity of the current process. An integrated management system was developed with three overall functions: factory setup, project creation, and result analysis. Using this integrated management system, existing conditions were changed (e.g., change of process, change of manpower, and fluctuation of process arrangement) to create an optimized process. Subsequently, the integrated management system was refined to enable simulation through the system. This study configured a modular assembly process for manufacturing a total of thirty modular units in the developed program. In order to draw comparisons between possible processes, a process integrating manpower rearrangement was created through the integrated management system. If the manufacturing times are compared using the product of manpower input and time, the alternative manufacturing process requires 5,070 minutes, which is a 11.2% decrease in manufacturing time.
We developed an integrated management system that can manage the process, manpower, and materials for manufacturing modular components and assembling a finished module. Through the integrated management system, we can compare alternatives and design an optimized process. This integrated management system is being continuously developed and expanded to include a process rate management function and process table creation function in the future. Moreover, there are plans to add an optimization function that can automatically derive alternatives.
The data used to support the findings of this study are included within the article.
The authors declare that they have no conflicts of interest regarding the publication of this paper.
This research was supported by grant no. 19RERP-B082884-06 from the Housing Environment Research Program funded by the Ministry of Land, Infrastructure and Transport of the Korean government.