Scheduling the Project
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Transcript of Scheduling the Project
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SCHEDULING THEPROJECT
Intro of Project Network
Language of PERT & CPM
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PERT & CPM Networks
PERT vs CPM
1. Developed by the U.S. Navy,a consulting firm & Lockheed
Aircraft
1. Developed by DuPont
2. Uses probabilistic estimatesof activity durations
2. Uses deterministic estimatesof both cost and time to allowcost/time trade-offs
It is used for non repetitive jobs Used for repetitive jobs
Makes use of the dummyactivities
Does not make use of thedummy activities
Deals with the concept ofcrashing.
Does not deal with crashing.
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Continued.PERT & CPM Networks
PERT & CPM similarities
1. Both methods employed networks to schedule and
display task sequences
2. Both methods identified activities a critical path of tasksthat could not be delayed without delaying the projects;
3. Both methods identified activities with slack (float)thatcould be somewhat delayed without extending the projecttime;
4. Anything that could be done with PERT can also be
determined through CPM
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The language of PERT/CPM
Activity-a set of tasks required by a project; use resources &time
Event-An identified state resulting from the completion of oneor more activities. Events consume no resources or time
Milestones- identifiable and noteworthy events markingsignificant progress on the project
Network-a diagram of nodes connected by directional arcs;
Path- a series of connected activities between any twoevents in a network
Critical path- the set of activities on a path from theprojects start to finish event, that if delayed, will delay thecompletion date of the project. Marked by events having a
zero slack.-
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Building the Network
Two ways to display a network: AON (CPM),AOA (PERT)
Example:Tasks Predecessor
a --
b --
c a
d be b
f c,d
g e
Start
a
b
d
e
c
f
e
Start
AON
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Example: Activity on Arrow
St
art
1
2
3
4
St
art
a
b
e
d
cf
g
A completed sample of AOA network showing the use of a dummy task:
Dummy task: It shows a technological linkage. These are used in
situations where two activities have the same start and finish nodes or
where a single activity connects to two or more nodes.
Start
1
2
3
5
Start
a
b
e
d
cf
g
4
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Critical Path & critical time
Activity Predecessor Duration
A - 5 days
B -- 4
C A 3
D A 4
E A 6
F B, C 4
G D 5
H D, E 6I F 6
J G, H 4
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Slack time
Slack/Float: It is the amount of time that anactivity can be delayed without delaying theproject;
Slack= LST-EST = LFT-EFT
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Problem
ImmediateActivity Predecessor(s) Time Taken
A 12B 9C A 10D B 10E B 24F A 10G C 35
H D 40I A 15J E,G,H 4K F,I,J 6
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Probabilistic Time Estimates
Pessimistic time (Tp): the maximum possible time
required to accomplish a task, assuming everything
goes wrong;
Most likely time (Tm): the best estimate of the time
required to accomplish a task, assuming everything
proceeds as normal.
Optimistic time (To): the minimal possible time required
to accomplish a task, assuming everything is in your
favour
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Construct a PERT Network
Activity Precedences Time Estimates (Weeks)
Optimistic Pessimistic Most Likely
A
None
2
4
3
B None 8 8 8C A 7 11 9D B 6 6 6E C 9 11 10F C 10 18 14G C, D 11 11 11H F, G 6 14 10I E 4 6 5J I 3 5 4K H 1 1 1
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Slacks/Floats Types
Total float
extra time available to complete an activity if itsstarted as early as possible and finished as late
as possible. (LF- ES) Free float
Extra time available to complete an activity whenits started at EOT of its preceding activity and
finished at EOT of its succeeding activity
Independent float
When an activity is started at LOT of preceding
activity and finished at EOT of succeeding
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PROJECT CRASHING
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Project Crashing
Crashing reducing project time by expending additional
resources
Crash time an amount of time an activity is reduced
Crash cost cost of reducing activity time
Activity Cost Slope: It indicates the additional costincurred per unit of time saved in reducing the durationof an activity.
Activity cost slope:
Goal
][
]cos[
TimeCrashTimeNormal
NormalCosttCrash
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Project Cost
Direct costs
Consists of labor, material, machine time, etc. andis associated with individual activities.
If the time duration of the activities are reduced,the direct cost increases.
Indirect Costs
Associated with the project not the activities
If the duration of the project is reduced/ crashed,the indirect costs decrease.
Administrative overhead, rent of equipment, etc.
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Time-Cost Tradeoff
Cost($)
Project duration
Crashing Time
Minimum cost = optimal project timeTotal project cost
Indirect cost
Direct cost
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Problem on crashing
For a network shown below, normal time, crash time,normal cost and crash cost are given in the table.Construct the network by crashing it to the optimumlevel and find out the optimal project cost. Indirectcost is given as Rs 100per day.
Activity NORMAL CRASH
Time (days) Cost(Rs) Time (days) Cost(Rs)
1-2 3 300 2 400
2-3 6 480 4 520
2-4 7 2100 5 2500
2-5 8 400 6 600
3-4 4 320 3 360
4-5 5 500 4 520
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Resource Leveling
Resource leveling is a projectmanagement technique used to examineunbalanced use of resources (usually people
or equipment) over time, and for resolvingover-allocations or conflicts
http://en.wikipedia.org/wiki/Project_managementhttp://en.wikipedia.org/wiki/Project_managementhttp://en.wikipedia.org/wiki/Conflicthttp://en.wikipedia.org/wiki/Conflicthttp://en.wikipedia.org/wiki/Project_managementhttp://en.wikipedia.org/wiki/Project_managementhttp://en.wikipedia.org/wiki/Project_management