B10 Lecture Project Scheduling Omar El-Anwar, PhD, PMP Network alculations The purpose of conducting network calculations is to know more about the scheduling of activities: When will each activity start? When will each activity finish? When will the project finish? an I delay an activity without delaying the project? 1
Scheduling Process 0 Start Forward pass Early times Total Duration End The forward pass starts from start to end. The total project duration is calculated from this pass. During this pass early times are calculated. This includes: Early Start (ES): The earliest time an activity can start if all preceding activities start on time Early Finish (EF): The earliest time an activity can finish if all preceding activities start on time Scheduling Process Start End 0 Late times Backward pass Total Duration During this pass late times are calculated. This includes: Late Start (LS): The latest time an activity can start without delaying the project Late Finish (LF): The latest time an activity can finish without delaying the project
Representing Activity Information: AON TF FF ES Description EF LS Duration LF 0 A 1 8 10 18 The Forward Pass The early start of the initial activities is always taken = 0 Initial activities are those activities that do not have a predecessor, that is they can start at the beginning of the project as they do not depend on other activities The Early Start of an activity = Maximum Early Finish of all preceding activities 0 0 B H 8 H cannot start until both and B have finished, since B will finish after (on day ) then the earliest possible start for activity H is day
The Forward Pass The early finish of an activity is calculated as follows: EF = ES + Duration 0 0 B H 8 Overall project duration is the largest possible EF of all activities. Note All times are denoted as end of day End of day End of day 0 0 End of day H 8 0 B 4
Example 1 Perform PM alculations B E G 9 START A 4 F 11 H L END D 8 I 8 K J The Backward Pass During this pass we calculate Late Times (LS, LF) The last activities in the schedule are assigned a LF = Project Duration The Late Finish of an activity = Minimum Late Start of all succeeding activities 1 B 4 4 7 8 4 4 E 9 10 7 7 The latest time that B can finish without delaying the project depends on its succeeding activities. The latest possible start for is 8 and for E is 4, hence B should not finish later than day 4 if the project is not to be delayed.
The Backward Pass The late start of an activity is calculated as follows: LS = LF - Duration 1 B 4 1 4 7 9 8 10 4 E 7 4 7 Activity Float Represents the amount of flexibility available in executing an activity. Types of float: Total Float (TF) Free Float (FF)
Total Float (TF) It is the amount of time a particular activity can be delayed from its early execution time without affecting the project completion date. Float = 0 à No flexibility à Any delay in the activity will delay the project Float > 0 à Some flexibility à Some delay in the activity is possible without delaying the project It is calculated as: TF = LS act. ES act. 7 9 8 10 TF = 1 OR TF = LF act. EF act. 4 E 7 4 7 TF = 0 Free Float (FF) It is the amount of time a particular activity can be delayed from its early execution time without affecting the early execution time of any of its succeeding activities. It is calculated as: FF = smallest ES of all succeeding activities EF of this activity 7
Free Float (FF) - Example 10 B 1 1 18 17 G 0 For activity B: FF = Min (14,17) 1 = 1 14 H 0 18 4 Importance of float If Total Float = 0 à ritical Activity If Total Float > 0 à Non-critical Activity In all cases TF FF 8
ritical Path Method (PM) Using the procedure described above we now are able to identify all activities in the project that are critical. ritical activities will always form a continuous chain from the start to the end of a project. This chain is called the ritical Path. The ritical Path is the longest of all paths in the network. A network can have more than one critical path. A network must have at least one critical path. Example 1 Solution Perform PM alculations 0 0 0 A 0 7 0 9 9 B 4 7 14 0 0 0 0 7 0 D 10 8 17 7 0 7 1 7 E 1 1 G 1 14 19 19 9 8 F 17 17 H 11 17 8 0 17 I 17 8 10 J 1 0 L 8 1 0 0 0 0 10 10 K 1 1 End 9
Example Activity IPA Duration A ---- 4 B ---- A D A E F,D,G 4 G B H G I G J E 4 K H 4 L K M K,I N F.J 9 O L,M 4 P L,M 10