Primavera P6 Constraint Types

During the construction process, many real-life issues control an activity’s start or completion date. These issues are dealt with by the constraint feature of Primavera P6. Constraints are applied to the activities when relationships do not provide the required results and are often a result of external dependencies.

Objectives

1. The main objective of applying constraints is to observe real-world aspects of the project more precisely.
2. Duration restrictions are used to observe project requirements that can’t be drafted into network logic.

Constraints are recommended to apply after scheduling the whole project because they can override the logic and must be used with care. It is difficult to reschedule the constraint activities compared to rescheduling activities having no constraints.

The different types of constraints in Primavera P6 are discussed here:

Start On or After Constraints:

Start On or After constraints are used when we have to set the earliest date an activity can start. It will affect the early dates of the successor activities.

In a construction project, if the embedded part’s delivery is expected on a particular date and the pour is dependent on this part, it is not possible to start the pour before the delivery date.

Start On or After Constraint added to Activity B, the activity starts on 9th Sep instead of 7th Sep

Start On or Before Constraints:

Start On or Before constraints are used when we have to set the latest date an activity can start. It will affect the late dates of the predecessor activities.

Start On or Before Constraint (9^th Sep) added to Activity B, the activity starts on 7^th Sep Now. Network logic is retained in this case.

Finish On or After Constraints:

Finish On or After constraint is used when we have to set the earliest date an activity can finish. It will affect the early dates of the successor activities. Activity B is assigned to finish on or after the 24^th of Sep. So the float of 3 days is available in Activity A.

Finish On or Before Constraints:

Finish On or After constraint is used when we have to set the latest date an activity can finish. It will affect the late dates of the predecessor activities.

For example, the delivery of steel tendons should not delay by a particular date in Silos construction to keep the project completion date on time. Finish On or Before Constraint (21^st Sep) added. The total float is zero now. Network logic retained.

Mandatory Start or Finish Constraints:

This constraint forces early and late dates to be equal to the constraint date. It violates the network logic.

In piling works, it is possible to start the steel fabrication works in advance to free the steel laborers for steel fixing of pile caps. We can use the mandatory start constraint to start the work in advance. A mandatory start constraint was added on Activity B (2^nd Sep) and it is completed on 17^th Sep now instead of 21^st Sep.

Conclusion:

The constraints should be used carefully in the scheduling works. The start/ finish constraints prevent the schedule’s logic, and mandatory start/finish constraints will violate the network logic. The objective of applying constraints is to observe the real-world aspects of the project more precisely.

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