Exercise caution when using multiple calendars in Primavera P6 on a schedule. Not all calendars play well together.
In Primavera P6 Professional it is possible to assign calendars at the activity level. An activity can therefore have a unique calendar. And a project schedule can then have more than one calendar definition assigned to activities.
This article provides a quick tip to demonstrate that not all calendars work well together on a Primavera P6 Professional schedule, in particular when calendars have different shift start and end times.
We have in Figure 1 our demonstration project.
This is a brief underground pipe installation project. It consists of site preparation, excavation, installation, and backfill & repave deliverables. All activities are assigned a standard 8-hour day and 5-day workweek calendar, Figure 1. We want to explore differing calendars for the excavation deliverable.
We first consider a non-standard 8-hour day and 6-day workweek calendar for the excavation work crew. Figure 2 displays the workweek and detailed work hours/day for the 6×8 calendar.
In Figure 3 the excavation effort is assigned a 6×8 calendar.
Well, the schedule still looks good. After inserting the 6-day workweek calendar for the excavate effort and recalculating the schedule, all activities still start work in the morning at 8-am and finish work at 4-pm. We also observe, Figure 4 that the install shoring activity begins on Saturday as allowable on our 6-day workweek calendar.
Next we explore a non-standard 10-hour day and 4-day workweek calendar for the excavation work crew, Figure 5.
This is a 4 day workweek, which is fine. The issue we may have though is that the day shift for the excavation effort is different from the day shift of all other activities. The 4×10 workweek calendar begins the day at 7-am and not 8-am, like the 8-hour day calendars. In Figure 6 we assign the 4×10 calendar to the excavation effort and recalculate the schedule.
The schedule then appears similar to Figure 6. This updated schedule has some problems. The major project suspending issue is that our schedule now has a discontinuity, as evidenced by the 0.2-days total float on the excavation activities.
Yes, multi-hundred-million dollar projects have been suspended until schedulers could resolve the schedule discontinuities. Further, inspection shows a start of backhoe excavation at 4-pm, which is not our intention. In fact all the excavation activities begin at 4-pm and conclude at 4-pm, which is not a realistic work schedule.
Schedulers attempting to resolve this discontinuity could, for example, insert a 0.2-day lag between mobilize and backhoe excavation activities. This appears to eliminate the total float and the discontinuity, as displayed in Figure 7, but our schedule still as issues.
The start and finish time of the excavation activities is 9:36-am, which is not our intention. So it may be possible to eliminate total float and discontinuities by inserting lag. But this at best is a jerry-ridged approach. The start and finish times are still off. And the scheduler will have difficulty providing a reasonable explanation for inserting the lag.
Most schedules are agreeable with multiple calendars that have a different number of days in the workweek. However, the caveat is that the resources must work the same shift, either all 8-hours per day, or, perhaps, all 10-hours per day.
Serious schedule problems surface when multiple shifts are implemented in the same schedule if activities that share them have a relationship. In other words if activity A is using an 8am – 4pm calendar, and its successor is using a 7am – 5pm calendar, there will be issues.
And there really is no good patch for meshing these differing shifts together. So avoid assigning linked activities a different shift calendar. Again, multiple calendars with identical shift start and end times are acceptable.