Download - Pert, cpm & gert
Network Scheduling, Planning & Controlling
Techniques
By Pranava Krishna
IntroductionSchedule converts action plan into operating time
tableBasis for monitoring and controlling projectScheduling more important in projects than in
production, because unique natureSometimes customer specified/approved
requirement.Based on Work Breakdown Structure (WBS)
Graphical portrayal of activities and eventShows dependency relationships between
tasks/activities in a projectClearly 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
Networking Techniques
CPM
GERT
PERT
History Of PERT/CPMDeveloped 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
Why PERT/CPM?Prediction of deliverablesPlanning resource requirementsControlling resource allocationInternal program reviewExternal program reviewPerformance evaluationUniform wide acceptance
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
Steps in PERT/CPM
4. Controlling
3. Allocation Of Resources
2. Scheduling
1. Planning
Need of PERT/CPMPrediction of deliverablesPlanning resource requirementsControlling resource allocationInternal program reviewExternal program reviewPerformance evaluationUniform wide acceptance
PERT
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)
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 wellmost likely time (m ) - the consensus best estimate
of the activity’s durationoptimistic time (b) - the time the activity would
take if things did go wellMean (expected time):te = a + 4m + b
6
Variance: V =b- a
6
2
PERT
Use of PERTIn construction activities Transportation activitiesIn oil refineriesComputer system-For manufacturing electric generator machinesMedical and surgical sectorLibrary activities
Importance of PERT SystemReduction in costSaving of timeDetermination of activitiesElimination of risk in complex activities –FlexibilityEvaluation of alternatives-Useful in effective control-Useful in decision makingUseful is research work
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
CPM
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
PathA connected sequence of activities leading from
the starting event to the ending eventCritical Path
The longest path (time); determines the project duration
Critical ActivitiesAll of the activities that make up the critical
path
CPM calculation
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
Useful at many stages of project managementMathematically simpleGive critical path and slack timeProvide project documentationUseful in monitoring costs
Benefits of CPM/PERT
Clearly defined, independent and stable activitiesSpecified precedence relationshipsOver emphasis on critical pathsDeterministic CPM modelActivity time estimates are subjective and depend
on judgmentPERT 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
Activity
Predecessor activity
A noneB noneC AD AE BF CG D & E
1
3
2
5
4
6
A
B
C
D
E
F
G
Example
Activity
Predecessor activity
A noneB AC AD BE CF D ,E
Example
1 2
3
4
5 6A
B
C
D
E
F
Project CrashingCrashing
reducing project time by expending additional resources
Crash timean amount of time an activity is reduced
Crash costcost of reducing activity time
Goalreduce project duration at minimum cost
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 costsTime-Cost Tradeoff
cost
time
Direct cost
Indirect cost
Total project cost
Activity Normal(Wks)
Crush(Wks)
Cost Slope(K$)
Tn Cn Tc Cc
A 9 10 6 16 2B 8 9 5 18 3C 5 7 4 8 1D 8 9 6 19 5E 7 7 3 15 2F 5 5 5 5 -G 5 8 2 23 5
Crashing Example
AD
G
FC
B E
98
87
55
5
0 22
149
178
22
10
0
9 17
17
Critical Path A-D-G=22wks
The Resource ProblemResources 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.
PeopleMaterialsEquipmentWorking Capital
Kinds of resource
GERT
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
Contd..Utilizes probabilistic and branching nodesIt represents the node will be reached if
any m of its p immediate predecessors are completed.
m
n
p
Contd..It represents a probabilistic output where any
of q outputs are possibleEach branch has an assigned probabilityWhen no probability is given, the probability is
assumed to be one for each branch.
1
2
q
Example
Thank you