Float | Total Float | Free and Interfering float

Monday, September 24, 2012 11:29
Posted in category Civil Engineering Practice
Views: 6,575 views


Float

Float is an additional time available to complete an activity beyond the activity’s work duration.

For example having 6 days available to do 4 days worth of work. Activities on the critical path have no float.

Total Float

Total float is the amount of time that an activity can be delayed without delaying the project’s estimated completion time.

Total float assumes that

  • all preceding activities are finished as early as possible.
  • All succeeding activities are started as late as possible.

Total float for an activity can be determined either :

Total float activity n = Late start activity n – Early start activity n

Total float activity n = Late finish activity n – Early finish activity n

Where n denotes the nth activity.

Both equation will yield the same answer.

Free float

Free float is the duration of time, that an activity can be delayed without delaying the project’s estimated completion time and without delaying the start of any succeeding activity.

Free float is the property of an activity not a network path. Free float can be determined by :

Free float n = Minimum early start of all successor activities – Early finish n

Where n denotes the nth activity.

Interfering float

Interfering float is the time available to delay an activity without delaying the project’s estimated completion time, but delaying an activity into interfering float will delay the start of one or more following non-critical activities.

Interfering float n = late finish n – Smallest early start of succeeding activity

The aggregate of free float and interfering float is equal to the total float.

Total float n = Free float n + interfering float n  

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