Project Planning & Scheduling
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Transcript of Project Planning & Scheduling
Project Planning & Scheduling
Yousaf Ali KhanDepartment of Management Sciences and HumanitiesGIK Institute of Engineering Sciences and Technology
What is a ―Project‖?― An individual or collaborative enterprise that is
carefully planned and designed to achieve a
particular aim‖
EXAMPLES:
• constructing a new road
• building a ship
• designing and marketing a new product
• moving to a new office block
• installation of a computer system.
Objectives and Tradeoffs
Meet the
specifications
Meet the
Deadline--schedule
Due Date!
Stay within
the budget
Management of Projects
Planning - goal setting, defining the project, team
organization
Scheduling - relates people, money, and supplies to
specific activities and activities to each other
Controlling - monitors resources, costs, quality, and
budgets; revises plans and shifts resources to meet
time and cost demands
Planning
Objectives
Resources
Work break-down schedule
Organization
Scheduling
Project activities
Start & end times
Network
Controlling
Monitor, compare, revise, action
Project Management Activities
Establishing objectives
Defining project
Creating work breakdown structure
Determining resources
Forming organization
Project Planning
Often temporary structure
Uses specialists from entire company
Headed by project manager
Coordinates activities
Monitors scheduleand costs
Permanent structure called ‗matrix organization‘
Project Organization
A Sample Project Organization
TestEngineer
MechanicalEngineer
Project 1 ProjectManager
Technician
Technician
Project 2 ProjectManager
ElectricalEngineer
Computer Engineer
Marketing FinanceHuman
Resources DesignQuality
MgtProduction
President
The Role ofthe Project Manager
Highly visibleResponsible for making sure that:
All necessary activities are finished in order and on time
The project comes in within budget
The project meets quality goals
The people assigned to the project receive motivation, direction, and information
Project Life Cycle
Concept
Feasibility
Planning
Execution
Closure
Man
agem
en
t
Work Breakdown Structure (WBS)
Level
1. Project
2. Major tasks in the project
3. Subtasks in the major tasks
4. Activities (or work packages)to be completed
Example Of WBS For Building a
House
Identifying precedence relationships
Sequencing activities
Determining activity times & costs
Estimating material and worker requirements
Determining critical activities
Project Scheduling
1. Shows the relationship of each activity to others and to the whole project
2. Identifies the precedence relationships among activities
3. Encourages the setting of realistic time and cost estimates for each activity
4. Helps make better use of people, money, and material resources by identifying critical bottlenecks in the project
Purposes of Project Scheduling
Gantt chart
Critical Path Method (CPM)
Program Evaluation and Review Technique (PERT)
Project Scheduling Techniques
• Gantt Charts– Shown as a bar charts
– Do not show precedence relations
– Visual & easy to understand
• Network Methods– Shown as a graphs or networks
– Show precedence relations
– More complex, difficult to understand and costly than Gantt charts
PERT and CPM
Network techniques
Developed in 1950‘s
CPM by DuPont 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
Six Steps 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
Questions PERT & CPM Can Answer
1. When will the entire project be completed?
2. What are the critical activities or tasks in the project?
3. Which are the noncritical activities?
4. What is the probability the project will be completed by a specific date?
5. Is the project on schedule, behind schedule, or ahead of schedule?
6. Is the money spent equal to, less than, or greater than the budget?
7. Are there enough resources available to finish the project on time?
8. If the project must be finished in a shorter time, what is the way to accomplish this at least cost?
Constant-Time Networks
Activity times are assumed to be constant
Activities are represented by Arcs in the network
Nodes show the events
Notations used in calculating start and finish times:
– ES(a) = Early Start of activity a
– EF(a) = Early Finish of activity a
– LS(a) = Late Start of activity a
– LF(a) = Late Finish of activity a
A Comparison of AON and AOA Network Conventions
Activity on Activity Activity onNode (AON) Meaning Arrow (AOA)
A comes before B, which comes before C
(a) A B CBA C
A and B must both be completed before C can start
(b)
A
CC
B
A
B
B and C cannot begin until A is completed
(c)
B
A
CA
B
C
Rules
1. One node has no arc entering and defines the starting
event.
2. One node has no arc leaving and defines the finishing
event.
3. Each activity should appear exactly once as an arc of
the network, and lies on a path from the starting event
to the finishing event. Dummy activities can also be
used.
4. There should be a path passing successively through
any two activities if and only if the first is a pre-
requisite for the second.
5. There should be at most one arc between each pair of
nodes of a network.
Drawing Project Networks
We consider an activity-on-arc approach.
We need a list of activities (constituent elements of a
project) and their prerequisites.
Example. Planting a tree
Description Activity Prerequisites
Dig hole A -
Position tree B A
Fill in hole C B
A B C1 2 3 4
Analysing Project Networks
Number the nodes so that each arc is directed
from a node i to a node j where i < j.
Let A be the set of activities
dij be the duration of activity (i, j)n be the number of nodes.
Compute earliest event times, assuming that the
project starts at time zero and all activities are
scheduled as early as possible.
EET1 = 0EETj = max{EETi + dij} j=2,…,n
(i,j)A
Analysing Project NetworksNote that EETj is the length of a longest path from
node 1 to node j.
The project duration is EETn.
Compute latest event times, assuming that the
project finishes at time EETn and all activities are
scheduled as late as possible.
LETn = EETn
LETi = min{LETj - dij} i=n-1,…,1(i,j)A
Note that LETn - LETi is the length of a longest path
from node i to node n.
Determining the Project Schedule
Perform a Critical Path Analysis
The critical path is the longest path through the network
The critical path is the shortest time in which the project can be completed
Any delay in critical path activities delays the project
Critical path activities have no slack time
Slack is the length of time an activity can be delayed without delaying the entire project
Slack = LS – ES or Slack = LF – EF
Example
Activity DescriptionImmediate
Predecessors
A Lease the site —
B Hire the workers —
C Arrange for the Furnishings A
D Install the furnishings A, B
E Arrange for the phones C
F Install the phones C
G Move into the Office D, E
H Inspect and test F, G
Precedence and times for Opening a New Office
Determining the Project Schedule
Perform a Critical Path Analysis
Activity Description Time (weeks)
A Lease the site 2
B Hire the workers 3
C Arrange for the furnishings 2
D Install the furnishings 4
E Arrange for the phones 4
F Install the phones 3
G Move into the office 5
H Inspect and test 2
Total Time (weeks) 25
AOA Network For
Opening a New Office
H
(Inspect/ Test)
7Dummy Activity
6
5D
(Install the furnishings)
4C
(Arrange for the
furnishings)
1
3
2
Determining the Project Schedule
Perform a Critical Path Analysis
A
Activity Name or Symbol
Earliest Start ES
Earliest FinishEF
Latest Start
LS Latest Finish
LF
Activity Duration
2
ES/EF Network for Opening a New Office
Start
0
0
ES
0
EF = ES + Activity time
A
2
EF of A = ES of A + 2
2
ESof A
0
ES/EF Network for Opening a New Office
E
4
F
3
G
5
H
2
4 8 13 15
4
8 13
7
D
4
3 7
C
2
2 4
B
3
0 3
Start0
0
0
A
2
20
LS/LF Network for Opening a New Office
E
4
F
3
G
5
H
2
4 8 13 15
4
8 13
7
D
4
3 7
C
2
2 4
B
3
0 3
Start0
0
0
A
2
20
LF = EF of Project
1513
LS = LF – Activity time
LF = Min(LS of following activity)
10 13
Computing Slack Time
After computing the ES, EF, LS, and LF times for all activities, compute the slack or free time for each activity
Slack is the length of time an activity can be delayed without delaying the entire project
Slack = LS – ES or Slack = LF – EF
Computing Slack Time
Earliest Earliest Latest Latest OnStart Finish Start Finish Slack Critical
Activity ES EF LS LF LS – ES Path
A 0 2 0 2 0 YesB 0 3 1 4 1 NoC 2 4 2 4 0 YesD 3 7 4 8 1 NoE 4 8 4 8 0 YesF 4 7 10 13 6 NoG 8 13 8 13 0 YesH 13 15 13 15 0 Yes
Critical Path for Opening a New Office
E
4
F
3
G
5
H
2
4 8 13 15
4
8 13
7
13 15
10 13
8 13
4 8
D
4
3 7
C
2
2 4
B
3
0 3
Start0
0
0
A
2
20
42
84
20
41
00
ES – EF Gantt Chartfor Opening a New Office
A Lease the site
B Hire the workers
C Arrange for the furnishings
D Install the furnishings
E Arrange for the phones
F Install the phones
G Move into the office
H Inspect and test
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
A
B
C
D
E
F
G
H
CPM assumes we know a fixed time estimate for each activity and there is no variability in activity times
PERT uses a probability distribution for activity times to allow for variability
Variability in Activity Times
Three time estimates are required
Optimistic time (a) – if everything goes
according to plan
Most–likely time (m) – most realistic estimate
Pessimistic time (b) – assuming very
unfavorable conditions
Probabilistic Time Estimates
• Optimistic time
– Time required under optimal conditions
• Pessimistic time
– Time required under worst conditions
• Most likely time
– Most probable length of time that will be
required
Probabilistic Estimates
Activitystart
Optimistictime
Most likelytime (mode)
Pessimistictime
to tptm te
Beta Distribution
Expected Time
te =to + 4tm +tp
6
te = expected time
to = optimistic time
tm = most likely time
tp = pessimistic time
Variance
2 =(tp – to)
2
36
2 = variance
to = optimistic time
tp = pessimistic time
1-2-3
(H)7Dummy
Activity6
52-4-6
(D)
41-2-3
(C)
1
3
2
Optimistic
timeMost likely
time
Pessimistic
time
Computing Variance
Most ExpectedOptimistic Likely Pessimistic Time Variance
Activity a m b t = (a + 4m + b)/6 [(b – a)/6]2
A 1 2 3 2 .11
B 2 3 4 3 .11
C 1 2 3 2 .11
D 2 4 6 4 .44
E 1 4 7 4 1.00
F 1 2 9 3 1.78
G 3 4 11 5 1.78
H 1 2 3 2 .11
Probability of Project Completion
Project variance is computed by summing the variances of critical activities
s2 = Project variance
= (variances of activities on critical path)
p
Probability of Project Completion
Project variance is computed by summing the variances of critical activities
Project variance
2 = .11 + .11 + 1.00 + 1.78 + .11 = 3.11
Project standard deviation
p = Project variance
= 3.11 = 1.76 weeks
p
Probability of Project Completion
Standard deviation = 1.76 weeks
15 Weeks
(Expected Completion Time)
Probability of Project Completion
What is the probability this project can be completed on or before the 16 week deadline?
Z = – /p
= (16 wks – 15 wks)/1.76
= 0.57
due expected datedate of completion
Where Z is the number of standard deviations the due date or target date lies from the
mean or expected date
Probability of Project Completion
What is the probability this project can be completed on or before the 16 week deadline?
Z= − /sp
= (16 wks − 15 wks)/1.76
= 0.57
due expected datedate of completion
Where Z is the number of standard deviations the due date or target date lies
from the mean or expected date
.00 .01 .07 .08
.1 .50000 .50399 .52790 .53188
.2 .53983 .54380 .56749 .57142
.5 .69146 .69497 .71566 .71904
.6 .72575 .72907 .74857 .75175
From Appendix I
Probability of Project Completion
Time
Probability(T ≤ 16 weeks)is 71.57%
0.57 Standard deviations
15 16Weeks Weeks
What Project Management Has Provided So Far
The project‘s expected completion time is 15 weeks
There is a 71.57% chance the equipment will be in place by the 16 week deadline
Five activities (A, C, E, G, and H) are on the critical path
Three activities (B, D, F) are not on the critical path and have slack time
A detailed schedule is available
Advantages of PERT/CPM
1. Especially useful when scheduling and controlling large projects
2. Straightforward concept and not mathematically complex
3. Graphical networks help highlight relationships among project activities
4. Critical path and slack time analyses help pinpoint activities that need to be closely watched
5. Project documentation and graphics point out who is responsible for various activities
6. Applicable to a wide variety of projects
7. Useful in monitoring not only schedules but costs as well
Trade-Offs And Project Crashing
The project is behind schedule
The completion time has been moved forward
It is not uncommon to face the following situations:
Shortening the duration of the project is called project crashing
Factors to Consider When Crashing A Project
The amount by which an activity is crashed is, in fact, permissible
Taken together, the shortened activity durations will enable us to finish the project by the due date
The total cost of crashing is as small as possible
Steps in Project Crashing
1. Compute the crash cost per time period. If crash costs are linear over time:
Crash costper period =
(Crash cost – Normal cost)
(Normal time – Crash time)
2. Using current activity times, find the critical path and identify the critical activities
Steps in Project Crashing
3. If there is only one critical path, then select the activity on this critical path that (a) can still be crashed, and (b) has the smallest crash cost per period. If there is more than one critical path, then select one activity from each critical path such that (a) each selected activity can still be crashed, and (b) the total crash cost of all selected activities is the smallest. Note that the same activity may be common to more than one critical path.
4. Update all activity times. If the desired due date has been reached, stop. If not, return to Step 2.
Crashing The Project
Time (Wks) Cost ($) Crash Cost CriticalActivity Normal Crash Normal Crash Per Wk ($) Path?
A 2 1 22,000 22,750 750 Yes
B 3 1 30,000 34,000 2,000 No
C 2 1 26,000 27,000 1,000 Yes
D 4 2 48,000 49,000 1,000 No
E 4 2 56,000 58,000 1,000 Yes
F 3 2 30,000 30,500 500 No
G 5 2 80,000 84,500 1,500 Yes
H 2 1 16,000 19,000 3,000 Yes
Crash and Normal Times and Costs for Activity B
| | |
1 2 3 Time (Weeks)
$34,000 —
$33,000 —
$32,000 —
$31,000 —
$30,000 —
—
Activity Cost
Crash
Normal
Crash Time Normal Time
Crash Cost
Normal Cost
Crash Cost/Wk =Crash Cost – Normal Cost
Normal Time – Crash Time
=$34,000 – $30,000
3 – 1
= = $2,000/Wk$4,000
2 Wks
Figure 3.16