Scheduling best practice generally discourages the use of constraints, or at least keeping them to an absolute minimum, but what if you have a project constraint date that cannot be ignored? In this case, you should know the process for creating a project level constraint in Primavera P6.
It is generally best to let your activity durations and associated activity relationships drive the end of the project. However, sometimes there are external factors that could have a binding effect on the project. As an example, a river dredging project in Canada that must complete before the river freezes over in November. Regardless of your project schedule, you absolutely cannot dredge a frozen river.
Another example could be the Environmental Protection Agency prohibiting certain types of construction projects taking place near and during fish spawning or eagle nesting seasons. Primavera P6 allows you to create a project constraint, so that you can know the impact on your schedule imposed by the external constraint.
This article describes how to create a project level constraint for the entire project in Primavera P6, so that nothing can slip past the constraint date without Primavera P6 calculating negative float in the schedule.
Project Level Constraint
In the following example we have a pipe repair and improvement project. Because the piping system services a hospital and its computer center, we are given a small window of opportunity to make the repairs and improve the piping system. If the project does not end on time it could impact the scheduling of hospital operations.
The doctors also will not be able to access patient information stored in the computer center; the computer center will be shut down during the construction. Delayed operations due to shut down of facility service or inaccessibility to patient data could produce a potentially life threatening situation. The bottom line is that the pipe repair and improvement project absolutely must complete during the small window of opportunity afforded your construction project by the hospital.
Figure 1 displays the schedule for the Piping System Repair and Improve construction project.
The project commences on June 1, 2015. Based upon the activities required to complete the project, activity duration estimates, and the relationships between activities the project will finish on Thursday, June 18th at the close of business. Note the total float of all activities is zero, indicating that all activities for this project are on the critical path. No activity may be delayed without delaying the entire project.
The hospital, however, has stipulated that the project may commence on June 1st and must complete no later than Tuesday, June 16th close of business. This is a mandatory project constraint. Failure to adhere to this constraint will upset the hospital schedule and possibly result in a life threatening situation. In an effort to ensure that the Piping System Repair and Improve project stays within the specified time frame you set a Must Finish By constraint on the project of June 16th close of business, Figure 2.
Select Edit | User Preferences and set the preferences to display the hour and minutes, Figure 3.
Adjusting the Schedule
Your schedule with the Must Finish By constraint is as displayed in Figure 4.
Note the total float of all activities is minus 2 days. You therefore are aware that you have 2 days to make up in your schedule. Inspecting the schedule you realize you have two possible options.
- You could decrease the scope by removing the thrust block, which is being installed to improve the piping system. You therefore would only do the repairs for the piping system and leave the thrust block installation for another day.
- As the project manager you could work overtime on the weekend to write the Quality Assurance report and complete it by the close of business Monday, June 15th.
Obviously, the best choice with the least impact is option 2, work overtime to complete the quality assurance report. However, this is an exercise in how to apply a project Must Finish By constraint, and how to go about adjusting the schedule accordingly. With the must finish by constraint and total float column you see the affect the constraint has on the entire project.
You may also display a curtain on everything that occurs after the constraint date. To add a curtain right click on the Gantt chart select Attachments | Curtain | Add Curtain. Enter the respective curtain dates and select OK. You now can graphically view the effects of the constraint, Figure 5, in addition to your tabulated total float values.
When you have a completion date that is absolutely imperative the Must Finish By project level constraint will allow you to see the impact this will have on the schedule without the need to place constraints directly on activities.
Display the total float so you have a tabulation of the constraints effect on each activity. The curtain will help you visually see the constraints impact. With these items in place you now have the knowledge necessary to weigh options for making up time on the schedule. So the project constraint is generally discouraged, but nevertheless helpful for understanding an unforgiving completion dates impact on the schedule.