By José Luis Ponz-Tienda, PhD

This is the example of implementation of the algorithm for takt-time, cycles and repetitive activities proposed by Ponz Tienda et al (2015), in which is mainly based the algorithms used by Plexos project, useful to show some of the differences between Lean project scheduling and the traditional method.

We wish that this example will be useful for all the Plexos´ fanatics.

The example consists of a 15 floors building, in which the first three floors are underground and the remaining 12 are above ground. The “water drainage” must work without interruption until at least the sixtieth floor is started to offset the water pressure with its weight. This fact implies that the duration of the “water drainage” is unknown and depends on the times of the followers and especially of the structure.

The concrete of the foundations is scheduled in three phases and overlapped with the reinforcement bars. The structure is an activity of 15 repetitive sub-activities overlapped with the activities of masonry, facades, and basements with an additional lag of 12 days for removal of formwork to ensure the proper hardening of the concrete.

The project has been scheduled following the Lean way and the traditional one to show the differences between both approaches.

 

In both cases, the duration of the activity “water drainage” has been solved by selecting “conditional duration” in the scheduling properties panel.

The requirements for introducing this capability is that the activity should be of at least 2 days of duration, and a finish-to-finish relationship with production levels or work days greater than zero. Additionally, must be unselected the “continuity” restriction in the scheduling properties panel.

The first difference that can be observed between both schedules is that with the lean way, only 18 activities and 26 relationships are required, instead of the traditional algorithms that require 78 activities and 139 relationships.

The project has been scheduled with the continuous condition unselected for all the activities, and the obtained times are the same with both approaches, but the lean way provides more compact and legible schedules, and we can introduce additional conditions to the schedule with the aim of guarantee a harmonious flow along the project:

1. Analyzing in just one line, several sub-activities of an activity
2. Changing the continuity condition of activities with just one click.
3. Testing the effect that produces changing the duration of several sub-activities of an activity with just one click.
4. Analyzing how modifying the condition of continuity, changes the times, the criticality, and providing sometimes a greater project duration, as with the activity “Masonry works”.

References:

Ponz-Tienda, J. L., Pellicer, E., Benlloch-Marco, J. and Andrés-Romano, C. (2015), The Fuzzy Project Scheduling Problem with Minimal Generalized Precedence Relations. Computer-Aided in Civil and Infrastructure Engineering, 30: 872-891. doi:10.1111/mice.12166

García-Nieves, J. D., Ponz-Tienda, J. L., Salcedo-Bernal, A. and Pellicer, E. (2018), The Multimode Resource-Constrained Project Scheduling Problem for Repetitive Activities in Construction Projects. Computer-Aided Civil and Infrastructure Engineering. doi:10.1111/mice.12356