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How to Use Constraints in Primavera P6 V 8.2 Software

Project Planning and Control Using Oracle Primavera P6 - Version 8.2 EPPM Web

Using Constraints in P6 Version 8.2

Constraints are used to impose logic on activities that may not be realistically scheduled with logic links. This article will deal with the following constraints in detail:

  • Start On or After
  • Finish On or Before

These are the minimum number of constraints that are required to effectively schedule a project.

Start On or After (also known as an “Early Start” or “Start No Earlier Than” constraint as it only affects the Early dates calculation) is used when the start date of an activity is known and does not have a predecessor. Primavera will not calculate the activity early start date prior to this date.

Finish On or Before (also known as “Late Finish” or “Finish No Later Than” constraint as it only affects the Late dates calculation) is used when the latest finish date is stipulated. Primavera will not calculate the activity’s late finish date after this date.

The following table summarizes the methods used to assign Constraints to Activities or how to add notes to activities:

Topic Notes for Creating a Constraint
  • Setting a Primary and Secondary constraint with the Activity Details form.
Open the Status tab on the Activity Details form.
  • Setting Constraints using columns.
The following columns may be displayed and the constraints assigned or edited:

  • Primary Constraint
  • Primary Constraint Date
  • Secondary Constraint
  • Secondary Constraint Date
  • Expected Finish Date
  • Dragging an Activity in the Gantt Chart.
  • Dragging an Activity in the Gantt Chart.
Dragging an Activity in the Gantt Chart will open the Confirmation form where the user is able to confirm the setting of a Start On or After constraint.
  • Adding Notes, these could be about constraints or other activity information.
The Activity Details form has a Notebook tab, which enables Notes to be assigned to Notebook Topics.

Primavera P6 software will permit two constraints to be assigned to each activity. Asta Powerproject, P3, and SureTrak also allow two constraints but Microsoft Project only permits one except when a Deadline constraint is applied.

A full list of constraints available in Primavera:

  • <None>
This is the default for a new activity. An activity by default is scheduled to occur As Soon As Possible and does not have a Constraint.
  • Start On
Also known as Must Start On and sets a date on which the activity will start. Therefore, the activity has no float. The early start and the late start dates are set to be the same as the Constraint Date.
  • Start On or Before
Also known as Start No Later Than or Late Start, this constraint sets the late date after which the activity will not start.
  • Start On or After
Also known as Start No Earlier Than or Early Start, this constraint sets the early date before which the activity will not start.
  • Finish On
Also known as Must Finish On, this constraint sets a date on which the activity will finish and therefore has no float. The early finish and the late finish dates are set to be the same as the Constraint Date.
  • Finish On or Before
Also known as Finish No Later Than or Late Finish, this sets the late date after which the activity will not finish.
  • Finish On or After
Also known as Finish No Earlier Than or Early Finish, this sets the early date before which the activity will not finish.
  • As Late As Possible
Also known as Zero Free Float. An activity will be scheduled to occur as late as possible. It consumes Free Float only and does not have any particular Constraint Date. The Early and Late dates have the same date.
  • Mandatory Start
This relationship prevents float being calculated through this activity and effectively breaks a schedule into two parts. This is also sometimes called a Hard Constraint.
  • Mandatory Finish
This relationship prevents float being calculated through this activity and effectively breaks a schedule into two parts. This is also sometimes called a Hard Constraint.
  • Expected Finish
An Expected Finish sets the Early Finish to the Expected Finish constraint date and calculates the Remaining Duration from the Early Start date for an un-started activity, or Data Date if the activity is in-progress to the Expected Finish date.

Earlier Than constraints operate on the Early Dates, and Later Than constraints operate on Late Dates. The following picture demonstrates how constraints calculate Total Float of activities (without predecessors or successors) against the first activity of 10 days’ duration:

An activity assigned an As Late as Possible constraint in Primavera P6, Primavera Contractor, Primavera P3, and SureTrak software will schedule the activity so it absorbs only Free Float and will not delay the start of any successor activities, this is normally called a Zero Free Float constraint. In Microsoft Project, an activity assigned with an As Late as Possible constraint will be delayed to absorb the Total Float and delay all its successor activities which have float, not just the activity with the constraint.

Eastwood Harris Supplies Project Management Training Manuals, Project Management Training Presentations and Consulting on Primavera P6 and Microsoft Project 2010 across Australia.


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