Lean Construction has been developing in France since the 2010s, mainly under the impetus of specialized consultants for the largest general contractors. Most of the expectations regarding work coordination and deadlines management are still in their infancy but a few interesting development paths are emerging.
The Last Planner® System is by far the main tool used to develop collaboration and the involvement of companies in project planning. At the same time, other technical tools and principles were developed in connection with this collaborative planning approach: Time-Location Diagrams and Rhythm Driven (Takt) planning.
This article will answer the following questions from the perspective of the current implementation in France:
Why use Time-Location Diagrams and Takt Time?
How to use them?
What are the results?
1. Why use Location Based Diagrams and Takt-Time Planning?
Planning is the main tool of communication on the construction site. At the different stages, schedules meet multiple objectives: establishing a long-term vision, anticipating, coordinating interventions, measuring progress, etc.
In France, schedules are mainly designed according to a Gantt Charts where each line corresponds to a task. In my opinion, this schedule representation has two major drawbacks for representing the execution of construction sites.
First, an execution schedule can quickly integrate hundreds or even thousands of tasks, all with a lot of interactions. All these tasks correspond to an overwhelming amount of lines and links on the schedule, which makes it difficult to read and understand.
Then, a Gantt Charts does not allow to focus on what is, most of the time, the main constraint of a site: the occupation of a physical space.
Location based diagrams are designed by “slicing & dicing” the project areas. Each line represents a task sequence for a specific area. This schedule helps to visualize execution flow on site, we easily identify “critical phases” and “no-activity phases” which can be described as waste. In this kind of planning, colors are used to visually identify the different teams or companies and thus have a reading of the human resources load.
On many projects, we can identify repetitive elements or patterns. It could be areas such as hotel rooms, apartments, offices. It can also be a sequence of tasks that will be repeated in the same way but in different kinds of areas.
Then, location-based diagrams can be extended by standardized work phase. Rather than reasoning for each task, in each zone, it is possible to consider sequences of tasks.
We can then, in the same way as we could imagine for a production chain, define a work sequence standard that we would repeat at the same rate according to the time available. The benefits can be manyfolds.
First of all, it is an optimization lever by reducing waiting times and stocks of ongoing areas. It is a good way to balance loads and streamline activities. It also facilitates continuous improvement by integrating standard work. Finally, the notion of progression rate makes it possible to quickly identify differences and performance drifts in production.
Here is the link between these different concepts and the Last Planner® System. These different concepts, although complementary, act on separate elements and can be used independently.
| Last Planner® System | Location Based Diagrams | Takt-Time Planning |
|---|---|---|
| Method of planning: involvement of stakeholders. | Mode of representation of the planning by areas. | Planning optimization method. |
2. How can I use this approach?
Divide your project into areas
In order to draw up the Time-Location Diagram, it is necessary to carry out a geographical division of the project. This division must be carried out in line with the phasing of the work, the principle being that each area can be treated as a separate entity.
It is necessary to consider the following constraints:
• Area division must avoid co-activity constraints.
• Area division must be consistent regarding the equivalent working time by area (on most projects, it is not relevant to consider a level of detail lower than the day).
• Area division must correspond to the logic of carrying out the work (access constraints for example).
• Area division must integrate constructive constraints (continuity of networks for example).
This work can be carried out for the different projects phases and the areas sizes can change between different work phases.
Design a schedule with Takt-Time Planning
In order to achieve a Takt-Time Planning, it is necessary to identify potential repetitive "products" when dividing into areas. Indeed, this allows you to define a standard sequence that can be applied for all similar units. The work must then be carried out according to the calculation of Takt Time.
Takt Time can be defined as the production rate necessary to meet customer demand. The Takt Time calculation is widely used in industry with the following formula: \[Takt Time = {Operating Time \over Required Quantity}.\]
For example, most of the major car manufacturing factories usually produce a car every 60 seconds, so each workstation must perform activities at that pace.
This calculation is slightly different on construction sites because it is essential to consider the set up time, that is to say the crossing time required to achieve the first unit.
The formula is as follows: \[Takt Time = {Lead Time Available - Lead Time Of One Unit \over Units Number-1}.\]
This Takt Time calculation can be performed several times for the same project, for different zones or between different milestones. It is also often a work done by iteration.
3. Case Study - a real “construction world” example:
Let us look at an example of how these principles are applied. Take the example of a typical apartment complex project. The project comprises 74 apartments divided into 2 buildings.
To make the example easily understandable, we will focus on the interior works phase. The same work was done with the structural works and enclosure trades.
1. Identify the different types of areas
We identify in this project 3 types of areas.
A. Apartments: The apartments vary in size, but the nature of the work to be carried out is similar.
B. Common landings: We consider these spaces which are repeated on each level separately from the apartments. Indeed, some work will be carried out in parallel with the apartments, but the finishing work will be carried out in a second phase once the apartments on the first floor are completed.
C. Stairwells and entrance hall: We consider these spaces as a third area. These have severe access constraints and will be carried out after the areas they serve.
2. Break down into micro-zones
It is then necessary to decompose the apartments into a number of work packages (by trades) which will correspond to our unitary volume of work.
To limit the variability and according to the level plans, we define work by set of about 2 apartments, which corresponds to a half-level for each stairwell. We then split the project into 40 apartment areas.
3. Map the tasks sequence
The apartment area corresponds to most of the work to be carried out in this phase. We therefore initially focus exclusively on this product.
We define the logical sequence of all the tasks to be carried out, integrating the different prerequisites or external needs.
From this work, we estimate that the crossing time, the minimum duration of realization of our unit is 62 days.
4. Calculation of Takt Time
In order to calculate the necessary rhythm, we define according to the prerequisites and the following phases (including a buffer period) the earliest start date of the first area and the latest end date of the last apartment area. We identify an available deadline of 110 working days.
Considering the 40 zones to be completed and 62 days of crossing time, we obtain a Takt Time equal to 1.23 day. It therefore was necessary to be able to find a way, together, to ensure everyone will progress by one zone each and every day.
This calculation then makes it possible to adjust certain task durations and to estimate the number of staff required.
5. Representation using a Time-Location Diagram
Areas order must be defined and the Time-Location Diagram can then be created by and for the people who will use it.
Note: This work was carried out by the general contractor’s foreman and all the subcontractors were actively collaborating. Weekly work plan meetings were also implemented throughout the project with these few tools and rituals. This simple approach allowed them to create their own “custom made” Location Based Management System.
4. Results
The project that served to illustrate this example went exceptionally well. The deadline, although very tight, was met with much less pressure (and claims) than usual. It was welcomed that the work was carried out smoothly and that there were none of the usual difficulties at the end of the project.
More specifically, the following benefits have been highlighted in connection with the application of the principles set out in the article:
- Takt Time Planning made it possible to quickly establish a first overall vision of the completion of the work.
- The companies involved were reassured during the negotiation phase by the fact that the organization had been relatively precisely pre-imagined.
- There has been extraordinarily little deterioration due to careful reflection with companies regarding the logical sequence of tasks.
- The use of standard areas encouraged improvement throughout the project and a reduction in crossing time was measured as the zones progressed.
- Monitoring progress is made easier by dividing it into zones, deviations could be quickly identified.
5. Points of Attention and Key Takeaways
Lean is a mindset that helps people learn together to improve their work and their performance.It is essential that the principles presented in this article be applied by the project team, in conjunction with a collaborative planning process.
In addition, here are some points of attention to deepen the process:
- It is necessary to integrate the upstream process (execution studies, validation, procurement). In fact, the Takt-Time Planning favours the completion of the first zones as soon as possible and therefore an early start of the finishing tasks compared to a more conventional organization.
- It is essential to use appropriate indicators to measure overall performance and identify gaps. Priority must also be given in the careful monitoring of blocking points.
- It may be appropriate to extend the process by also improving logistics flows. We can consider the pooling of supply, the use of logistics platforms, and kitting.
