۱- Introduction

۲- Literature review

۳- Approach

۴- Overview of case study

۵- Conceptual process mapping

۶- Simulation model

۷- Application of lean construction principles

۸- Conclusions

۹- Limitations and future research

References

Abstract

One way to encourage adoption of prefabrication and off-site manufacturing (OSM) techniques, such as modular construction, is to improve the efficiency of site operations, which makes the technology more attractive to non-adopters. Lean principles have been widely applied to improve the productivity and efficiency of construction operations, while simulation augments Lean theory by allowing its benefits and issues to be analyzed quantitatively before actual implementation. Thus, this study aims to conduct a detailed simulation study of modular construction operations, otherwise known as Prefabricated Prefinished Volumetric Construction (PPVC) in Singapore. In contrast with existing research, which are frequently focused on the barriers and drivers to the adoption of prefabrication, this study will provide and evaluate recommendations to improve modular construction efficiency through application of Lean concepts. A detailed baseline (As-Is) simulation model of an ongoing PPVC project case study was first developed. Lean Construction principles were then applied to the baseline simulation model. Key Lean Construction principles and concepts implemented includes Total Quality Management, E-Kanban based Just-In-Time deliveries, cross training and the use of construction robotics. Lean (To-Be) simulation models were developed based on the Lean Construction principles. The outputs from the baseline and Lean models were compared to assess the impact of the proposed improvements. The findings demonstrated that through the application of Lean concepts, reductions in cycle time and process time, and increases in process efficiency and labor productivity can be achieved. The case study also provides a detailed description of the simulation approach, which is a useful reference for future application of simulation in offsite construction research.

Introduction

With its ability to harness the efficiency of manufacturing processes, offsite construction, offsite manufacturing (OSM) or prefabrication, has long been seen as the way forward in enhancing productivity of the construction sector [1–۳]. It offers significant benefits, such as reduced project duration and defects, and improved health and safety [2,4]. Modular construction is a subset of OSM, where each prefabricated module is a volumetric component that can be a complete or partial room or unit (e.g. bathroom or lift) [5,6]. In contrast, non-volumetric offsite construction includes two-dimensional elements like walls and columns. Interest in OSM persisted across the years. In the United Kingdom, for example, the OSM sector has seen tremendous growth since the Egan Report (Egan 1999) [7], which recommended OSM as a solution to boost productivity and overcome labor shortages. OSM continues to be highlighted in the “Construction 2025” document [8]. Similarly, the US National Research Council has identified offsite construction as the key to improving the competitiveness of its construction industry [9]. Offsite construction has been used in Singapore since the 1980s. Efforts to increase the use of prefabrication have largely been spearheaded by the Building and Construction Authority (BCA). In 2014, BCA unveiled its Second Productivity Roadmap [10] which aimed to increase the prevalence of Design for Manufacturing and Assembly (DfMA), including the prefabrication of components that can be assembled on site. One of the key technologies promoted in Singapore is Prefabricated Prefinished Volumetric Construction (PPVC), in which building modules complete with internal finishes and fittings are manufactured off-site and assembled on-site in a Lego-like manner. PPVC is essentially modular construction using complete and pre-finished room units. Nonetheless, barriers to prefabrication such as perceived higher capital costs have impeded its adoption [11]. For instance, OSM only contributed to 2.1% of total construction value in the UK in 2007 [12].