2. Introduction
Schedule converts action plan into operating time table
Basis for monitoring and controlling project
Scheduling more important in projects than in production,
because unique nature
Sometimes customer specified/approved requirement.
Based on Work Breakdown Structure (WBS)
3. Graphical portrayal of activities and event
Shows dependency relationships between tasks/activities in a
project
Clearly shows tasks that must precede (precedence) or follow
(succeeding) other tasks in a logical manner
Clear representation of plan – a powerful tool for planning
and controlling project
Network
5. History Of PERT/CPM
Developed by
the US Navy for
the planning
and control of
the Polaris
missile program
The emphasis
was on
completing the
program in the
shortest possible
time.
PERT Developed by
Du Pont to solve
project
scheduling
problems
The emphasis
was on the
trade-off
between the
cost of the
project and its
overall
completion time
CPM
6. Why PERT/CPM?
Prediction of deliverables
Planning resource requirements
Controlling resource allocation
Internal program review
External program review
Performance evaluation
Uniform wide acceptance
7. Applications Of PERT/CPM Techniques
1
• Construction of a Dam or Canal
• Construction of a building or highway
2
• Maintenance or Overhaul of aircrafts
• Space Flights
3
• Designing a Prototype of a Machine
• Development of Supersonic Planes
8. Steps in PERT/CPM
4. Controlling
3. Allocation Of Resources
2. Scheduling
1. Planning
9. Need of PERT/CPM
Prediction of deliverables
Planning resource requirements
Controlling resource allocation
Internal program review
External program review
Performance evaluation
Uniform wide acceptance
11. PERT
Project Evaluation
and Review
Technique (PERT)
• U S Navy (1958) for the POLARIS
missile program
• Multiple task time estimates
(probabilistic nature)
• Activity-on-arrow network
construction
• Non-repetitive jobs (R & D work)
12. PERT is based on the assumption that an activity’s duration
follows a probability distribution instead of being a single value
Three time estimates are required to compute the parameters of
an activity’s duration distribution:
pessimistic time (a) - the time the activity would take if things
did not go well
most likely time (m ) - the consensus best estimate of the
activity’s duration
optimistic time (b) - the time the activity would take if things
did go well
Mean (expected time):te = a + 4m + b
6
Variance: V =
b- a
6
2
PERT
13. Use of PERT
In construction activities
Transportation activities
In oil refineries
Computer system-
For manufacturing electric generator machines
Medical and surgical sector
Library activities
14. Importance of PERT System
Reduction in cost
Saving of time
Determination of activities
Elimination of risk in complex activities –
Flexibility
Evaluation of alternatives-
Useful in effective control-
Useful in decision making
Useful is research work
15. Critical path
Those activities which contribute directly to the overall duration of the
project constitute critical activities, the critical activities form a chain
running through the network which is called critical path.
Critical event : the slack of an event is the difference between the latest &
earliest events time. The events with zero slack time are called as critical
events.
Critical activities : The difference between latest start time & earliest start
time of an activity will indicate amount of time by which the activity can be
delayed without affecting the total project duration. The difference is
usually called total float. Activities with 0 total float are called as critical
activities
17. Critical Path
Method (CPM)
• E I Du Pont de Nemours & Co. (1957)
for construction of new chemical plant
and maintenance shut-down
• Deterministic task times
• Activity-on-node network
construction
• Repetitive nature of jobs
CPM
18. Path
A connected sequence of activities leading from the starting
event to the ending event
Critical Path
The longest path (time); determines the project duration
Critical Activities
All of the activities that make up the critical path
CPM calculation
19. Critical path
Those activities which contribute directly to the overall duration of the
project constitute critical activities, the critical activities form a chain
running through the network which is called critical path.
Critical event : the slack of an event is the difference between the latest &
earliest events time. The events with zero slack time are called as critical
events.
Critical activities : The difference between latest start time & earliest start
time of an activity will indicate amount of time by which the activity can be
delayed without affecting the total project duration. The difference is
usually called total float. Activities with 0 total float are called as critical
activities
20. Useful at many stages of project management
Mathematically simple
Give critical path and slack time
Provide project documentation
Useful in monitoring costs
Benefits of CPM/PERT
21. Clearly defined, independent and stable activities
Specified precedence relationships
Over emphasis on critical paths
Deterministic CPM model
Activity time estimates are subjective and depend on judgment
PERT assumes a beta distribution for these time estimates, but
the actual distribution may be different
PERT consistently underestimates the expected project
completion time due to alternate paths becoming critical
Limitations to CPM/PERT
25. 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
Goal
reduce project duration at minimum cost
26. Time-Cost Relationship
Crashing costs increase as project duration decreases
Indirect costs increase as project duration increases
Reduce project length as long as crashing costs are less than
indirect costs
Time-Cost Tradeoff
time
Direct cost
Indirect
cost
Total project cost
29. The Resource Problem
Resources and Priorities
Project network times are not a schedule until resources have
been assigned.
The implicit assumption is that resources will be available in the
required amounts when needed.
Adding new projects requires making realistic judgments of resource
availability and project durations.
Resource-Constrained Scheduling
Resource leveling (or smoothing) involves attempting to even
out demands on resources by using slack (delaying noncritical
activities) to manage resource utilization.
33. A network analysis technique used in project management.
It allows probabilistic treatment of both network logic and
activity duration estimated.
The technique was first described in 1966 by Dr. Alan B.
Pritsker of Purdue University.
Compared to other techniques, GERT is an only rarely used
scheduling technique.
GERT
34. Contd..
Utilizes probabilistic and branching nodes
It represents the node will be reached if any m of its p
immediate predecessors are completed.
m
n
p
35. Contd..
It represents a probabilistic output where any of q
outputs are possible
Each branch has an assigned probability
When no probability is given, the probability is assumed
to be one for each branch.
1
2
q