TAKT TIME PLANNING AS A WORK STRUCTURING METHOD TO IMPROVE CONSTRUCTION WORK FLOW
- Author(s): Frandson, Adam Gene
- Advisor(s): Tommelein, Iris D
- et al.
Work structuring is critical to project production system design because it helps to define who is doing what work, when, what the handoffs are, how they are doing the work, how long it will take, which buffers are required, and what construction work should flow continuously without time buffers. Takt time planning is a work structuring method that aims to achieve the lean principle of continuous flow. Successful Takt time planning on a construction site results in trades working on activities at the same rate to release work areas at standardized times. Current planning practices in construction fail to account for continuous flow for trade activities. This phenomenon has several causes: complexity of design, focusing on productivity maximization, contracting methods, lack of production system design, lack of resources, lack of a method to follow, and tradition.
The objective of this research is to develop a method for Takt time planning and improve understanding of work structuring for all construction phases in repetitive and non-repetitive construction. To meet the objective, the research will focus on non-repetitive interior construction because if a method of Takt time planning is effective there, it follows that the method can also work for construction phases in which the work is less complex and more repetitive. In order to show that the method is effective, the research must a) identify barriers to structuring work for continuous flow in interior construction, the most challenging phase, and how those barriers are overcome, and b) demonstrate the effectiveness of the method regarding project performance, time, cost, reliability, and resource utilization.
Continuous flow requires and releases workspace for trade activities at even intervals. An activity, defined as a combined set of smaller tasks, is repetitive in that it has the same installation duration for the same activity in every location. The actual work contents within the tasks themselves may be non-repetitive. The distribution in work contents is defined as the work density. This research focuses on the duration of each activity given a set of constraints: work method (e.g., offsite prefabrication versus on-site stick building), crew size, methods and tools for performing elemental tasks, etc.
This dissertation is structured as follows: an introduction to the topic and explanation of the intended contribution, a review of the relevant literature, and a description of the research method. The dissertation continues with a description of the instance of Takt time planning that motivated this research, followed by three case studies and a discrete event simulation to model key elements observed in the case studies. The research concludes with a proposed framework for Takt time planning, a discussion section, and conclusions with recommendations for future research.
This research uses design science (in particular, case study research) and simulation to accomplish the objective and answer the research questions. Each case study instantiates the Takt time planning method for different types of work, different phases of work, and with different team members to understand the current state of the project, test the method in different conditions, and advance production theory.
Case Study 1 examines the development and execution of a Takt time plan during interior construction of a 7,000 ft2 urgent care unit at an existing hospital. The average percent planned complete (PPC) during the overhead MEP phase was 95% and the average PPC during the inwall MEP installation phase was 85%. Results from the overhead MEP phase of construction showed that structuring the work around continuous flow through small areas helped expose production problems and allowed the construction activities to improve upon the initial contract schedule duration by 12 days on a 44-day schedule (27% improvement). The inwall MEP installation phase of construction improved upon the contract schedule duration by 8 days on a 37-day schedule (24% improvement). The project concluded with trade partners earning a bonus, in addition to their full contractual profit.
Case Study 2 used Takt time planning to build the interiors of a two-story, 26-bed 19,000 ft2 psychiatric care facility. The project team used Takt time planning during two phases of the project with varying Takt times, spaces, team members, and work structuring constraints. The project finished with a 65% PPC and was delivered three months after the contractual completion milestone. Though the project did not complete on time, the project was a good case study for Takt time, as it provided valuable lessons on the method and application of Takt time that this dissertation discusses.
Case Study 3 focused on how Takt time developed in planning the production of the interior construction of a medical office building. The project is a two-story build out at an existing wood-framed, 14,000 ft2 facility. The project was delivered with a GMP general contract and hard-bid subcontracts. This presented an opportunity to test Takt time planning in a new environment with a team unfamiliar with Lean Project Delivery practices. The project team used Takt time planning during three phases (overhead MEP rough-in, inwall MEP rough-in, and above ceiling close-up), completed successfully on time with an average PPC of 76%, and consumed 23% of its planned overtime budget, saving 20 days of Saturday work on a 144-day schedule.
The discrete event simulation demonstrates three work structuring methods: Takt time planning, a CPM schedule allowing early starts, and a location-based approach using time buffers. Each method has four trades working through four zones, in the same order, with finish-to-start network logic. The Takt time planning method resulted in faster completions with less variability in the completion time. If the daily indirect costs multiplied by the difference in completion times exceed the costs of the capacity buffer, then Takt time planning is the preferred method on cost and time. However, if the work is not being made ready, then the capacity buffer quickly becomes a cost sink to the project, and time buffers are preferred.
The contributions from achieving the research objective are fourfold. (1) A tested method of work structuring for continuous flow in interior construction, called Takt time planning. The method requires a paradigm shift from scheduling with 100% utilization of crews with buffers in time, to using capacity buffers to accommodate variation and produce reliable, timely handoffs. (2) Contributions to knowledge on the challenges of designing continuous flow into interior construction. (3) A simulation providing new insight into the trade-offs of using capacity buffers versus time buffers in work structuring on the overall project cost. (4) Questions for future research for Takt time planning in practice and for simulation.