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Transcript of Chapter 5_ Scheduling and Resource Allocation
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CHAPTER 5
SCHEDULING and
RESOURCE ALLOCATION
MSc Bui Thu Hien
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CHAPTER OUTLINE
5.1 SCHEDULING
5.2 RESOURCE ALLOCATION
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Useful Abbreviations
CPM- Critical Path Method
PERT- Program Evaluation and Review
Technique
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Background
Schedule is the conversion of a project action
plan into an operating timetable
Basis for monitoring a project One of the major project management tools
Work changes daily, so a detailed plan is
essential
Not all project activities need to be scheduled at
the same level of detail
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Background Continued
Most of the scheduling is at the WBS
level, not the work package level
Only the most critical work packages maybe shown on the schedule
Most of the scheduling is based on
network drawings
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Network Scheduling Advantage
Consistent framework
Shows interdependences
Shows when resources are needed
Ensures proper communication
Determines expected completion date
Identifies critical activities
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Network Scheduling AdvantageContinued
Shows which of the activities can be
delayed
Determines start dates Shows which task must be coordinated
Shows which task can be run parallel
Relieves some conflict
Allows probabilistic estimates
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Network Scheduling Techniques: PERT(ADM) and CPM (PDM)
PERT was developed for the Polarismissile/submarine project in 1958
CPM developed by DuPont during the same
time Initially, CPM and PERT were two different
approaches CPM used deterministic time estimates and allowed
project crunching
PERT used probabilistic time estimates
Microsoft Project (and others) have blendedCPM and PERT into one approach
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Terminology
Activity- A specific task or set of tasksthat are required by the project, use upresources, and take time to complete
Event- The result of completing one ormore activities
Network- The combination of all
activities and events that define a project Drawn left-to-right
Connections represent predecessors
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Terminology Continued
Path- A series of connected activities
Critical- An activity, event, or path
which, if delayed, will delay thecompletion of the project
Critical Path- The path through theproject where, if any activity is delayed,
the project is delayed There is always a critical path
There can be more than one critical path
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Terminology Continued
Sequential Activities- One activity must
be completed before the next one can
begin Parallel Activities- The activities can
take place at the same time
Immediate Predecessor- That activitythat must be completed just before a
particular activity can begin
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Terminology Continued
Activity on Arrow- Arrows represent
activities while nodes stand for events
Activity on Node- Nodes stand forevents and arrows show precedence
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AON and AOA Format
Figure 8-3
Figure 8-2
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Constructing the Network
Begin with START activity
Add activities without precedences as
nodes There will always be one
May be more
Add activities that have those activities asprecedences
Continue
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Gantt (Bar) Charts
Developed by Henry L. Gantt
Shows planned and actual progress
Easy-to-read method to know the currentstatus
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Advantages and Disadvantage
Advantages
Easily understood
Provide a picture of the current state of aproject
Disadvantage
Difficult to follow complex projects
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Microsoft Project Gantt Chart
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Microsoft Project AON Network
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Solving the Network
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The AON Network from the previoustable
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Calculating Activity Times
2
2
2
6
6
4
ab
bmaTE
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The Results
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Critical Path and Time
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Critical Path and Time Continued
Exercise: How long will this project take?
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Exercise: How long will this project take?What is the critical path?
Task Time Dependency
A 5 days None
B 3 days A
C 8 days A
D 3 days B
E 4 days C, D
F 3 days C, D
G 9 days D, E
H 6 days B, E
I 3 days F, G
J 7 day H, I
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Revised time to completion
A key technical expert who is needed for
step D had to travel to fix a customer crisis
just as step D started. The expert will return in 7 days.
What is the impact on the projects
completion date?
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Slack
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Slack Values
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Precedence Diagramming
Finish to start
Start to start
Finish to finish Start to finish
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Precedence Diagramming Conventions
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Microsoft Projects
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Gantt Chart
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AON Network
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Microsoft Project Calendar
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Uncertainty of Project Completion Time
Assume activities are statistically
independent
Variance of a set of activities is the sumof the individual variances
Interested in variances along the critical
path
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Example
45.52645.1745.543
22.1745.5
7
33
4350)(
2
ZD
DZ
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Toward Realistic Time Estimates
Calculations are based on 1% chance of
beating estimates
Calculations can also be based on 5% or 10%
Changing the percentage requires changing the
formulae for variance
When using 5%, the divisor changes to 3.29
When using 10%, the divisor changes to 2.56
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5.2 RESOURCE ALLOCATION
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Critical Path MethodCrashing aProject
Time and costs are interrelated
Faster an activity is completed, more is
the cost Change the schedule and you change the
budget
Thus many activities can be speeded upby spending more money
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What is Crashing / Crunching?
To speed up, or expedite, a project
Of course, the resources to do this must be
available
Crunching a project changes the schedule for
all activities
This will have an impact on schedules for all the
subcontractors Crunching a project often introduces
unanticipated problems
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Activity Slope
Crash Cost Normal Cost
Crash Time Normal Time
Slope
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An Example of Two-Time CPM
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Activity SlopesCost per Period forCrashing
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Crashing the Project
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Seven Day Schedule
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Six Day Schedule
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Five Day Schedule
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Four Day Schedule
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Cost-Crash Curve
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Fast-Tracking
Fast-tracking is another way to expedite a
project
Mostly used for construction projects Can be used in other projects
Refers to overlapping design and build
phases Increases number of change orders
Increase is not that large
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The Resource Allocation Problem
CPM/PERT ignore resource utilization
and availability
With external resources, this may not bea problem
It is, however, a concern with internal
resources Schedules need to be evaluated in terms
of both time and resources
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Time Use and Resource Use
Time limited: A project must be finished
by a certain time
Resource limited: A project must befinished without exceeding some specific
level of resource usage
System-constrained: A project has fixedamount of time and resources
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Resource Loading
Resource loading describes the amount
of resources an existing schedule
requires Gives an understanding of the demands a
project will make of a firms resources
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Resource A
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Resource B
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Resource Leveling
Less hands-on management is required
May be able to use just-in-time inventory
Improves morale Fewer personnel problems
When an activity has slack, we can move
that activity to shift its resource usage
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Resource Leveling Continued
May also be possible to alter the
sequence of activities to levelize
resources Small projects can be levelized by hand
Software can levelize resources for larger
projects Large projects with multiple resources are
complex to levelize
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Constrained Resource Scheduling
Heuristic
Approach
An approach, such as a
rule of thumb, that yields
a good solution that mayor may not be optimal
Optimization
Approach
An approach, such as
linear programming, thatyields the one best
solution.
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Heuristic Methods
They are the only feasible methods used
to attack large projects
While not optimal, the schedules are verygood
Take the CPM/PERT schedule as a
baseline
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Heuristic Methods Continued
They sequentially step through the
schedule trying to move resource
requirements around to levelize them Resources are moved around based on
one or more priority rules
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Common Priority Rules
As soon as possible
As late as possible
Shortest task first Most resources first
Minimum slack first
Most critical followers Most successors
Arbitrary
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Heuristic Methods Continued
These are just the common ones
There are many more
The heuristic can either start at thebeginning and work forwards
Or it can start at the end and work
backwards
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Optimization Methods
Finds the one best solution
Uses either linear programming or
enumeration Not all projects can be optimized
M lti P j t S h d li d R
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Multi-Project Scheduling and ResourceAllocation
Scheduling and resource allocationproblems increase with more than oneproject
The greater the number of projects, thegreater the problems
One way is to consider each project as
the part of a much larger project
M lti P j t S h d li d R
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Multi-Project Scheduling and ResourceAllocation Continued
However, different projects have differentgoals so combining may not make sense
Must also tell us if there are resources totackle the new projects we areconsidering
St d d t M S h d l
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Standards to Measure ScheduleEffectiveness
Schedule slippage
Resource utilization
In-process inventory
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Schedule Slippage
The time past a projects due date
Slippage may cause penalties
Different projects will have differentpenalties
Expediting one project can cause others
to slip Taking on a new project can cause
existing projects to slip
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Resource Utilization
The percentage of a resource that is
actually used
We want a schedule that smoothes outthe dips and peaks of resource utilization
This is especially true of labor, where
hiring and firing is expensive
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In-Process Inventory
This is the amount of work waiting to be
processed because there is a shortage of
some resource
Similar to WIP in manufacturing
Holding cost is incurred
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Heuristic Techniques
Multi-projects are too complex for
optimization approaches
Many of the heuristics are extensions ofthe ones used for one project
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Additional Priority Rules
Resource scheduling method
Minimum late finish time
Greatest resource demand Greatest resource utilization
Most possible jobs
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GoldrattsCritical Chain
1. Thoughtless optimism
2. Capacity should be equal to demand
3. The Student Syndrome4. Multitasking to reduce idle time
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GoldrattsCritical Chain Continued
5. Assuming network complexity makes no
difference
6. Management cutting time to motivateworkers
7. Game playing
8. Early finishes not canceling out latefinishes