Calculation of Forward Pass | Early start/Early finish time

Saturday, September 22, 2012 9:17
Posted in category Civil Engineering Practice
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Forward Pass

Forward pass is a schedule calculation that determines the earliest start and early finish time of the activities and the minimum project duration.

A forward pass through the logic network will yield this information:

  • The earliest time each activity in the network can start and finish.
  • The minimum overall duration of the project.

In performing forward pass calculation, all successor activities are started as early as possible. And Each activity is postulated to finish as soon as possible. This finish requirement yields the following equation:

Early finish of nth activity = Early start of nth activity + Duration of nth activity

Early start/Early finish time

Early start time (ES) of an activity is the earliest point in time, that an activity may start.

The starting point for performing a forward pass is the first activity in the network. In the case of first activity of the project, the earliest time they may start is zero ( the end of day 0 or beginning of day 1).

Calculation of early start/early finish

┬áIf only one precedence arrow leads into an activity, then that activity’s early start time is the same as the previous activity’s early finish time. It means the early start time of the next activity will be the same as that of the early finish of the previous activity.

To determine the early start time, when more than one arrow leads in to its node. Select the largest early finish time of all activities at the tail of arrows. Logically, an activity cannot be start until all previous activities are completed. In this case, the equation of early start will be:

Early start of nth activity = Maximum early finish of all previous activities

Early finish time

The early finish time is the earliest time the activity may finish.

Add the duration of each activity to the early start time to compute early finish time.

Using this systematic procedure, compute all the early start and early finish times from the beginning activities to the finish of the project. This sequence will complete the forward pass.

Overall duration of the project

The overall duration of the project is the Early Finish (EF) of the last activity in the network.

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