Smart work packaging for constraints management in prefabrication housing production

Abstract

The situation in the shortage of public residential housing (PRH) becomes more and more stringent in Hong Kong. According to the Housing Authority of Hong Kong statistics, there were more than 153,300 general applicants for PRH and the average waiting time for them was 5.5 years (at its highest in last two decades) at the end of December 2018. To expedite the supply of PRH, the PRH in Hong Kong has benefited and will continue to benefit significantly from prefabrication housing production (PHP). However, the supply of PRH is still plagued by the pathological schedule delay of PHP. For example, the government planned to construct 13300 flat units of PHP in the financial year of 2016-2017. However, the actual amount is 11276 units, and 15.22% delay occurred. The constraints (e.g., limited space, lack of collision-free path planning, skillful workers shortage) in the fragmented PHP process have been proved to be the primary drivers. The constraints are also the apparent bottlenecks and thus are more predictable than the uncertainties to be improved in the task executions. As such, reliable constraint-free workflows are vital for achieving an industrialized construction environment across design, manufacturing, logistics, and on-site assembly so as to reduce schedule delays and cost overruns. However, the current constraints management approaches are limited to offer smart solutions for achieving adaptivity, autonomy, and sociability in the workflows. e.g., automatic identification and analysis of constraints and their interrelationships, optimal constraints improvement planning in a dynamic manner, and real-time sensing and tracking constraints status. The primary aim of this research is to investigate the smart solutions and approaches for constraints management in PHP process to equip the workers with the capacity of modeling, optimizing, and monitoring in the task executions. The specific objectives of this research are as follows: (1) To define the concept and properties of smart work packaging (SWP), specify its functions and paradigm for constraints management (CM), develop its prototype representation and propose the framework for SWP-CM; (2) To develop the constraints modeling module in SWP for enhancing the sociability in the constraints identifying, mapping, and analyzing process; (3) To develop the constraints optimizing module in SWP for improving the adaptivity in the constraints improvement process; (4) To develop the constraints monitoring module in SWP for achieving the autonomy in the constraints tracking, updating and predicting process; (5) To develop a simulation game for disseminating the concepts of SWP-CM in the industry and education. This research first reviewed previous studies regarding constraints management and smartness in PHP to summarize the current challenges and opportunities in this field. The constraints in the on-site assembly process of PHP and the opportunities of smartness for constraints improvement in workflows were identified by literature review and interviews. The SWP was defined with the smartness properties, and a conceptual framework was established to demonstrate the functions of SWP for constraints management in the task executions. On the basis of this framework, three scenarios were developed to detailedly present the functions of SWP in constraints modeling, optimizing, and monitoring. The validations were also conducted in these separate demonstrations. Finally, a simulation game is proposed as a hand-on learning tool to disseminate the "SWP for constraints management (SWP-CM)" in the education and the industry. The key findings concluded from this research are from five perspectives. Firstly, a conceptual framework outlined the skeleton and elements for SWP-CM with three core characteristics and three primary functions. Secondly, the social network analysis and the hybrid system dynamic (SD)-discrete event simulation (DES) model were incorporated into the constraints modeling service to simulate and pick out the most critical constraint "Lack of collision-free crane path planning" in the on-site assembly process of PHP. Thirdly, the constraints optimization service was proposed to improve dynamic constraints in the crane path planning by prioritizing their importance and embedding decision-making mechanism. It is proved to be an adaptive approach of conducting the crane path re-planning by considering its necessity. Fourthly, the constraints monitoring service focused on tracking and updating the status of crane operator fatigue, which is an internal constraint of "Lack of collision-free crane path planning." The service performance showed excellent accuracy. Finally, the simulation game was developed, and it indicated an excellent learning effect on the concepts of SWP-CM. This research made original contributions to the constraints management in the on-site assembly process of PHP from both theoretical and practical perspectives. From the theoretical perspective, this study extended the body of knowledge in the project management of PHP by enriching the constraints management with the smartness and lean principles. Additionally, it is also innovative thinking from the theory of constraints perspective to reconsider the goal of PHP by transferring separated project-level targets (e.g., schedule, safety, quality) into the integrated task-level executions. From a practical perspective, this study developed three services to demonstrate the functions of constraints modeling, optimizing, and monitoring. It could not only help workers to execute the task in a more autonomous, adaptive, and sociable manner but also it made the workflow more smooth and reliable. Additionally, a simulation game was a practical learning tool to help students and practitioners know well about SWP-CM.