With new tools come new methods. There are numerous examples of this when it comes to Lean Construction and BIM, where new BIM tools require new processes that very often encompass several lean principles. I tend to say that Lean is the right leg and BIM is the left leg, and although you could stand on either one, in a fiercely competitive market that constantly shifts, it is easier for a construction company to maintain balance by standing on both.
4D scheduling is one example of synergy where BIM can be used to achieve lean effects, either to support traditional planning methodology or to complement the Last Planner™ System. This blog post is meant to give an introduction to 4D scheduling and how some projects at Skanska achieve lean effects from using 4D in projects.
4D means adding the dimension of time to the 3D model by linking plan activities to corresponding BIM objects (figure 1). The schedule can be created directly in the 4D software or be imported (e.g. MS Project, Primavera).
Figure 1: Activities and BIM objects merged in Synchro 4D
It’s worth noting that the BIM model itself, just like 2D drawings, essentially is a representation of the finished design and therefore a fixed point in time (the completed project). 4D softwares (e.g. Navisworks, Synchro, VICO) however, provide an interactive timeline that allows us to represent the construction project at any point in time. In other words, you can build the entire building virtually before actual construction starts to find the optimal schedule.
4D ensures a better schedule in terms of constructability and workflow, where project participants and clients better communicate and collaborate. Instead of traditional sub-optimal information flow by verbally explaining current state and future work sequences, 4D enables projects to do this visually. This is especially beneficial in very complex projects (figure 2).
Figure 2: 4D model of a Norwegian water treatment facility in Navisworks
Instead of drawings and Gantt charts, with 4D we can now bring the schedule to site and present it in a much more understandable way than ever before. Furthermore, by equipping crews with 4D software on mobile devices or stationary BIM units, they can mark completion statuses of objects or the model spaces themselves, so-called KanBIM1 to visualize workflow, which is especially useful in location based planning.
Not only objects of the construction itself can be represented in 4D, but also elements such as site objects and material deliveries. Beyond 4D, other dimensions to include are project costs (5D), operational and maintenance cost (6D) and health and safety factors (7D), although these terms have not yet fully reached consensus within the industry.
INTEGRATING 4D AND THE LAST PLANNER™ SYSTEM
The most common form of 4D I have encountered and have performed myself as a 4D specialist is documenting a traditionally planned Gantt schedule for a planner. Fortunately, the trend seems to be moving towards using 4D actively with more modern planning concepts, such as location based planning and the Last Planner™ System.
Figure 3: Using Solibri Model Checker in a Skanska pull-planning session
For years we have known that using BIM in pull-planning sessions (figure 3), regardless of 4D functionality, can contribute to achieving better plan reliability, specifically by ensuring quality regarding the 4 quality criteria for assignments2:
Size – quantities with a single click from the BIM can tell a concrete crew how many cubic feet of concrete they are committing to produce and whether it is a realistic amount.
Sequence – by rotating the model, using sectioning planes and transparency tools, crews can better find the best work sequence to construct to design conformance.
Soundness – BIM helps communicate the soundness of assignments through object parameters. Some example parameters are “material ordered” or “material delivered to site” statuses and design statuses.
Definition – is the actual work correctly represented by the activity’s description in the plan? Since BIM “gets people on the same page” the potential of misunderstanding is reduced, so that project management and workers are aligned on what work is planned.
BIM-supported planning has proven beneficial, and 4D functionality should further improve the planning process as it additionally increases our understanding of what we are planning. With the Last Planner™ System as the planning framework for creating and maintaining the schedule in Skanska projects, 4D is a tremendous functionality to check and communicate this schedule throughout the project.
More and more construction projects are benefitting from 4D scheduling, and experience that it ensures higher plan quality and better communication of the schedule between project stakeholders and production crews. Having seen projects use 4D in various extent, I think there is much potential in not just using 4D to support existing processes, but adjusting these processes for 4D to play an active part in project planning and execution, for instance integrated with the Last Planner™ System.
1. Sacks, R., Barak, R., Belaciano, B., Gurevich, U. & Pikas, E. (2013) KanBIM Workflow Management System: Prototype Implementation and Field Testing
2. Ballard, H. G. (2000) The Last Planner System of Production Control
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