construction project scheduling - the critical path and calculating project duration
The critical path is the series of activities, that if delayed, delay the completion of the entire project. These activities have no float. That means, every extra day one of these activities takes to complete, is an extra day the project will take to complete. That is of course unless an appropriate treatment is applied.
You will hear the term that activities are on the "critical path" often on construction projects. These are the activities everybody will be paying attention to. They will have the most attention and resources devoted to completing them. When critical path activities are delayed, everybody will want to know why and what can be done to get them back on track.
Identifying and analyzing the critical path is a way to determine the minimum project duration. The time taken to complete all the project critical path activities will be the minimum project duration. Non-critical path activities still need to be completed, but they should not affect project duration unless they are delayed sufficiently. The amount a non-critical path activity can be delayed before it falls onto the critical path is referred to as its float.
CRITICAL PATH ANALYSIS
Critical Path Analysis is the process we use to identify the project critical path and hence determine project duration. For each activity, we first need to determine the early start/early finish, late start/late finish, free float, and total float. The early start/early finish is the earliest an activity can start/finish; i.e. when all the proceeding activities were completed as planned. The late start/late finish is the latest an activity can start/finish before that activity will fall on the project critical path; i.e. delay project completion. Free float is the amount an activity can be delayed before it delays its successor activity and total float is the total amount an activity can be delayed before it falls on the critical path.
We do this by completing a forward and backward pass of the network schedule. The network schedule is a diagram showing all the project activities with their logical links.