scheduling the project

8/3/2019 Scheduling the Project

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SCHEDULING THEPROJECT

Intro of Project Network

Language of PERT & CPM


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3/19

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

scheduling the project

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