Transcript Slide 1
Lecture by Junaid Arshad Department of
Engineering Management
Abridged and adapted by A. M. Al-Araki,
sept. 2013
OBS: Lowest level
WBS: Lowest level
1
Topics Covered
Network
Representation
Network Development
Dummy Activity
Network Scheduling
Practice Problems
CPM Network Calculations
Network Representation
Even though a linked Gantt Chart can include
precedence relationships between activities, it is an
unsuitable tool if these relationships grow beyond a
certain complexity.
In such situations, the scheduling should be carried
out by a network technique.
However, the presentation of the schedule to the
project participants may still be done in a Gantt
Chart format.
Arrows and nodes are used for construction
of Network.
Node
Arrow
Node
There are two types of network representations:
1. Activity on arrow (AOA)
2. Activity on node (AON)
1. Activity on arrow (AOA)
Event
Activity
Event
In AOA Arrow shows activity and precedence relationships
2. Activity on node (AON)
Node
Activity
In AON Arrow shows precedence relationships only
NB! Okto_arrowed-line & node
Network Development
Following information is required in order to
develop a network:
A list of all activities
A list of all precedence relationships
An estimated duration of each activity
(required for network scheduling)
For
structure
of
network
Problem 1
Activity on arrow (AOA)
Act- Immediate
ivity Predecessor
A
B
C
D
A
B
A
B
C
D
Dummy Activity
An activity inserted into the network to
maintain the logic of the network.
A dummy takes zero time and do not
consume any resources.
Dummy Activity
Correct Display
Incorrect
Display
A precedes B and C, B and C precede D
1
A
B
2
3
D
C
4
Add a Dummy as shown by dash line below.
3
B
1
A
2
C
4
D
5
Network Scheduling
The purpose of network scheduling is
o
o
To determine when the project will finish
To determine which activities directly
influence the project duration
Two techniques of network scheduling are:
1. Critical path method (CPM)
2. Program evaluation and review
technique (PERT)
PERT and CPM
Developed in 1950’s
CPM by DuPont Cooperation for chemical
plants (1957)
PERT by Booz Allen Hamilton with the U.S.
Navy, for Polaris missile (1958)
Consider precedence relationships and
interdependencies
Each uses a different estimate of activity
times
Questions which may be addressed by
PERT & CPM
Is the project on schedule, ahead of schedule,
or behind schedule?
Is the project over or under cost budget?
Are there enough resources available to finish
the project on time?
If the project must be finished in less than the
scheduled amount of time, what is the way to
accomplish this at least cost?
Six Common Steps to PERT & CPM
1.
Define the project and prepare the work breakdown
structure.
2.
Develop relationships among the activities. (Decide
which activities must precede and which must follow
others.)
3.
Draw the network connecting all of the activities
4.
Assign time (and/or cost) estimates to each activity
5.
Compute the longest time path through the network.
This is called the critical path
6.
Use the network to help plan, schedule, monitor, and
control the project
CPM Network Calculations
CPM calculates a network in several steps:
For each event:
o
Earliest possible time: The earliest possible
time the event can occur
o
Latest possible time: The latest possible
time the event can occur
For each activity:
o
Early start (ES): The earliest possible
start time for the activity
o
Early finish (EF): The earliest possible
finish time for the activity
For each activity:
o
Late start (LS): The latest possible start
time for the activity so as not to delay the
completion time of the entire project.
o
Late finish (LF): The latest possible finish
time for the activity so as not to delay the
completion time of the entire project.
Continue to
next lecture
17
Topics Covered
CPM
Calculations for AOA
and AON Networks
Slack Time / Float
Critical Path, Critical Activity
Practice Problems
CPM Calculations for AON Network
Provides activity information
Early
start (ES) & late start (LS)
Early finish (EF) & late finish (LF)
Slack (S) / Float (FL)
Identifies critical path
Forward and Backward Pass
Forward pass is a technique to move forward
through network diagram. Backward pass is its
opposite.
Early Start (ES) and Early Finish (EF) use the
forward pass technique.
Late Start (LS) and Late Finish (LF) use the
backward pass technique.
Note: If the float of the activity is zero, the two
starts (ES and LS) and the two finish (EF and
LF) are the same. Hence, If float of activity is
zero, ES = LS and EF = LF.
Early Start and Early Finish Steps
Begin at starting event and work forward
ES = 0 for starting activities
ES
EF = ES + Activity time
EF
is earliest start
is earliest finish
ES = Maximum EF of all predecessors for
non- starting activities
Late Start and Late Finish Steps
Begin at ending event and work backward
LF = Maximum EF for ending activities
LF
LS = LF - Activity time
LS
is latest finish; EF is earliest finish
is latest start
LF = Minimum LS of all successors for
non-ending activities
Gantt Chart for General Hospital
Early Start and Finish
ES
EF
LS
LF
1 2 3 4 5 6 7 8 9 10 1112 13 1415 16
A Build internal components
B Modify roof and floor
C Construct collection stack
D Pour concrete and install
frame
E Build high-temperature
burner
F Install pollution control
system
G Install air pollution device
H Inspect and test
Slack Time/Float
Slack Time is the amount of time an activity
may be delayed without affecting the project
deadline. This is also referred as float.
An activity having zero slack time is called
critical activity.
The concept of critical activities is that it draws
the attention of the project manager to the
activities that needs the closest monitoring.
Any delay of a critical activity leads to an
equivalent delay of the total project.
A path having longest duration (completion
time) in the network is called critical path.