Critical Path Method - R1
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Transcript of Critical Path Method - R1
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Critical PathMethod
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History
The critical path method (CPM) is a project
modeling technique developed in the late
1950s by Morgan R. Walker of DuPont and
James E. Kelle Jr. of Remin ton Rand.
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Application
CPM is commonly used with all forms of
projects, including
Construction Aerospace and defense
Software Development
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esearc ro ects Product Development
Engineering, and Plant maintenance,
among others. Any project with interdependent activities can
apply this method of mathematical analysis.
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Basic Technique
The essential technique for using CPM is to
construct a model of the project that includes the
following:
A list of all activities required to complete the
pro ect typ ca y categor ze w t n aWork Breakdown Structure),
The time (duration) that each activity will take
to completion, and The dependencies between the activities.
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Basic Technique
Using these values, CPM calculates
The longest path of planned activities to the
end of the project The earliest and latest that each activity
can start and finish without makin the
project longer.
This process determines which activities
are "critical" (i.e., on the longest path) and
which have "total float" (i.e., can be delayedwithout making the project longer).
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Basic Technique
In project management, a critical path is the sequenceof project network activities which add up to the
longest overall duration. This determines the shortest time possible to
complete the project.
An l n ivi n h ri i l h ir l
impacts the planned project completion date (i.e.there is no float on the critical path).
A project can have several, parallel, near critical
paths. An additional parallel path through the network with
the total durations shorter than the critical path is
called a sub-critical or non-critical path.
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PERT Chart
Activity-on-arrow diagram ("PERT Chart") is
where each activity is shown as a box or node
and the arrows represent the logicalrelationships going from predecessor to
successor as shown here in the "Activity-on-
no e agram .
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ES EF
LS LF5
A
ES EF
LS LF12
B
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Activity Relationships
Finish-to-Start (FS):
A relationship between activities in which the start of a successoractivity depends on the finish of its predecessor activity.
Start-to-Start (SS)
A relationship between activities in which the start of a successoractivity depends on the start of its predecessor.
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Activity Relationships
Finish-to-Finish (FF):
A relationship between activities in which the finish of asuccessor activity depends on the finish of its predecessor.
Start-to-Finish SF :
A relationship between activities in which a successor activitycannot complete until its predecessor starts.
Lags (or Leads):
An offset or delay from an activity to its successor. A Lag can bepositive or negative
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Activity Box
ES EF
LS LF5
A
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ES = Early StartEF = Early FinishLS = Late StartLF = Late FinishA = Activity Name
5 = Duration Of Activity
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Activity Network Diagram
ES EF
5A
ES EF
LS LF
10B
ES EF
LS LF
8C
ES EF
7E
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LS LF ES EF
LS LF
12D
LS LF
Activity NameA. Ordering of PumpB. Pump ManufacturingC. Pump TransportationD. Pump Foundation
E. Pump Erection
Assumptions 7 day work week FS Relationships No Lag or Leads
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Forward Pass
ES=6 EF=15
10B
ES=16 EF=23
8C
In Forward Pass Early Dates are calculated
Forward Pass
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ES=1 EF=5
LS LF
5A
LS LF LS LF
ES=6 EF=17
LS LF
12D
ES=24 EF=30
LS LF
7E
Early Finish = Early Start + Duration - 1
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Backward Pass
ES=1 EF=5
A
ES=6 EF=15
LS=6 LF=1510
B
ES=16 EF=23
LS=16 LF=238
C
ES=24 EF=30
E
In Backward Pass Late Dates are calculated
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LS=1 LF=5ES=6 EF=17
LS=12 LF=23
12D
LS=24 LF=30
Late Start = Late Finish - Duration + 1
Backward Pass
Assuming LF = 30
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Total Float
ES=1 EF=5
ES=6 EF=15
LS=6 LF=15
10B
ES=16 EF=23
LS=16 LF=23
8C
ES=24 EF=30
Total Float = The amount of time the activity can be delayed before delayingthe Project Finish Date
= =
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LS=1 LF=5
5A
ES=6 EF=17
LS=12 LF=23
12D
LS=24 LF=30
7E
Total Float = Late Finish Early Finishor Late Start Early Start
Assuming LF = 30
TF=0
TF=6
TF=0
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Critical Path Scenario-I
ES=1 EF=5
ES=6 EF=15
LS=6 LF=15
10B
ES=16 EF=23
LS=16 LF=23
8C
ES=24 EF=30
Activities with Total Float =< 0 are on the Critical Path
= =
Scenario I Late Finish of the project = 30
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LS=1 LF=5
5A
ES=6 EF=17
LS=12 LF=23
12D
LS=24 LF=30
7E
Activities A, B, C and E are on the Critical Path (Longest Path)Activity D can be delayed by 6 days before delaying the finish date of the Project
Assuming LF = 30
TF=0
TF=6
TF=0
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Critical Path Scenario-II
ES=1 EF=5
ES=6 EF=15
LS=16 LF=25
10B
ES=16 EF=23
LS=26 LF=33
8C
ES=24 EF=30
Activities with Total Float =< 0 are on the Critical Path
= =
Scenario II Late Finish of the Project is greater than 30 i.e. 40
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LS=11 LF=15
5A
ES=6 EF=17
LS=22 LF=33
12D
LS=34 LF=40
7E
There is no critical activittesBut the Longest path is Activities A, B, C and EFor Activity E, C is a driving activity as Finish Date of C determines the Start Date of EAnd D is Non Driving
Assuming LF = 40
TF=10
TF=16
TF=10
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Critical Path Scenario-III
ES=1 EF=5
ES=6 EF=15
LS=0 LF=9
10B
ES=16 EF=23
LS=8 LF=17
8C
ES=24 EF=30
Activities with Total Float =< 0 are on the Critical Path
=- =-
Scenario III Late Finish of the Project is Less than 30 i.e. 24
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LS=-5 LF=-1
5A
ES=6 EF=17
LS=6 LF=17
12D
LS=18 LF=24
7E
All the activities are critical
Assuming LF = 24
TF=-6
TF=0
TF=-6
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Total Float
Positive Total Float
We can delay the activity
Zero Total Float
Negative Total Float
The activity is already delayed
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Crashing Of Project
It is a project Schedule Compression, which is
performed for the purpose of decreasing total
Period of the project.Different Methods of Crashing of the Activities: First Crash Activities on the Critical (Longest) path.
Change the lags between activities Reduce the Duration of activities Increase the Resources
Change the Working time : 5 day workweek to6/7 day workweek