Near optimum selection of module configuration for efficient modular construction
Introduction
Offsite construction systems vary depending on the size of prefabricated components which affect the need for onsite construction. These systems include many categories such as modular, panelized, prefabricated, and processed materials construction. Blending two or more of these categories results in a “hybrid” offsite construction system. Each category has its own unique configuration based on its own constraints such as transportation, manufacturing, and onsite lifting and positioning limitations. Choosing between the use of any offsite construction system depends on project characteristics and its targeted cost, schedule, and the scope of off-site manufacturing that can be used.
Modular construction provides a viable alternative to traditional (stick building) construction in view of enabling technologies developed earlier such as that used in the shipbuilding and automotive industries. The percentage of off- site manufacturing for modular construction ranges between 60 and 70%, comparing to 30 to 50% for hybrid construction and 15 to 25% for panelized construction [1].
This accounts for 50 to 60% of construction time reduction for modular construction compared to 30 to 40% for hybrid construction and 20 to 30% for panelized construction [1].
The advantages of modular construction were identified several decades ago [2] and more recently by O'Connor et al., [3]; investigating a set of critical success factors and enablers for optimum industrial modularization. Studying the critical success factors for modularization provided an overall idea highlighting needed changes in current engineering, procurement and construction (EPC) project delivery system to support optimal use of modularization. These studies, however, did not provide a systematic process to quantify the degree of modularity in construction projects. This quantification will enable the modular construction system to compete with the hybrid construction system. Since more manufacturers are beginning to use hybrid construction to eliminate some of the dimensional limitations that modular manufacturers currently face [4].
This paper provides a novel methodology for near optimum selection of module configuration. The methodology addresses the lack of knowledge by architects about the limitations of the manufacturing process of modules, which was identified in an earlier study [5]. In fact, architects should design modules as production designers to standardize the process of module manufacturing [6].
The developed methodology is accomplished by considering a set of practical constraints and factors that affect module configuration such as onsite connections limitation, transportation and weights limitations, crane cost limitation, and the required concrete quantities for project foundation.
Section snippets
Literature review
Modularization is a concept of mass customization for products that have been successfully adapted by various industries [7]. Product configuration focuses on structuring and standardizing products models to fulfill customer needs [8]. In the construction industry, the needs of customers have been identified based on building geometrical shapes; arranged in a manner that maximizes the Quality Function Deployment (QFD) in the design phase [9], [10].
The QFD analysis requires the input of customer
Methodology
The developed methodology utilizes five indices, which accounts for connections of modules onsite (CI), transportation of fabricated modules to construction jobsite (TDI and TSDI), crane operating condition and related cost (CCPI) and project concrete foundation (CVI). These five indices are integrated into one indicator (MSI) measuring the relative suitability of competing modular designs. These indices are described below.
Case study
This hypothetical case study is presented to illustrate the use of proposed indices and to validate the proposed methodology by comparing indices values for the manufacturing two projects in three different cities (e.g. Ottawa, Quebec City, and Kingston) by three different manufacturers. Each manufacturer develops one project as design A and one project as design B as shown in Fig. 6, while this project is constructed in Montreal after comparing the three manufacturers cost penalty indices and
Discussion
Offsite construction systems are competing currently to gain more share in the market place. This creates competition against traditional stick-built construction and invites construction managers to assess and evaluate these two competing alternatives with respect to project schedule, cost, quality, and project's unique constraints such as transportation, manufacturing, and craning limitations. This evaluation requires structured tools to assist in the selection process. Critical to the
Conclusion and future work
This paper presented a newly developed methodology to support the process of identification and selection of near optimum module configurations that account for project conditions. It assists developers and project stakeholders in delivering projects not only with accelerated schedules but also with cost reduction. The developed modular suitability index (MSI) provides a quantitative indicator for the suitability of module design configurations in building construction. It integrates the effect
Acknowledgements
The authors wish to thank Dr. Hany Elsawah and Dr. Ibrahim Bakry for their comments and review of the manuscript of this paper.
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