Class 107: Activity Constraints
What are Activity Constraints?
An activity constraint
is a restriction that is placed on an activity to control the activity’s start
date, finish date, and/or duration. Common examples of activity constraints include start-no-earlier-than,
finish-no-later-than, mandatory start, and as-late-as-possible.1
Activity constraints are
often utilized in construction schedules to identify the contractual completion
date. Often called “Substantial
Completion,” this activity is rarely the last activity in the schedule. However, placing a constraint on the
“Substantial Completion” activity prioritizes the work sequence for the project
and defines the schedule’s critical path. Activity constraints can also
be applied for financial restrictions, material delivery dates, or crew
availability.
Other constraints that
can be applied to the schedule include: “(1) minimum time constraints to create
a time buffer between two activities; and (2) minimum distance/location
constraints to denote the minimum physical distance between two activities to
allow for the proper or safe execution of linear construction activities.”2
These constraints apply more to project management rather than to project
scheduling, but they are often incorporated into a schedule by using activity
constraints.
Example of an Activity Constraint:
Why Constrain an Activity?
An activity constraint
can be applied to define a certain activity sequence to achieve a specific
milestone date. Large schedules can
often have multiple concurrent critical paths, so applying a constraint to one
or more milestone can help prioritize a particular activity sequence. Constraints are also helpful for documenting
impacts to the schedule, such as weather impacts and major changes.
Sometimes, the presence of an activity constraint, particularly a finish constraint on Substantial Completion, can cause a critical path to have negative float, meaning the critical path has been delayed to the extent that achieving the constrained activity on time is infeasible. In this case, the negative float value indicates the number of days that the critical path is behind schedule as defined by the activity constraint.
The most common activity
constraints are as follows:
• As Late as Possible
• Mandatory Start & Mandatory Finish
• Start On, Start On or Before, & Start On or After
• Finish On, Finish On or Before, & Finish On or After
Activity Constraint Summary:
1. An activity constraint is a restriction placed on an activity to control the activity’s start and/or finish date.
2. An activity constraint is most often used to define a contractual completion date that must be achieved and must be on the critical path.
Key Terms:
Activity Constraint – a restriction that is placed on an activity to control the activity’s start and/or finish date to indicate a date that will not change, regardless of other changes to the schedule
Critical Path – the longest continuous chain of activities which establishes the minimum overall duration
Float – amount of time an activity can be delayed without impacting the overall project
Resources:
1. 10S-90: Cost Engineering Terminology. https://web.aacei.org/docs/default-source/rps/10s-90.pdf?sfvrsn=60
2. Bramble, Barry B. , and Callahan, Michael T.
Construction Delay Claims. Wolters Kluwer Legal & Regulatory U.S.,
2017.
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