Transcript Chapter 1

Allocating Resources
to the Project
Expediting a Project
Fast-Tracking a Project
Resource Loading
Allocating Scare Resources
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Introduction
• Projects Compete With One
Another for Resources
– resources that are not consumed
– resources that are consumed
• Goal of Resource Allocation is
to Optimise Use of Limited
Supply
• Requires making trade-offs
– time constrained
– resource constrained
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EXPEDITING A PROJECT
• The Critical Path Method
• Probabilistic Activity Durations
• Fast-Tracking a Project
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The Critical Path Method
• Normal Duration
Estimates
• Normal Costs
• Crash Duration Estimates
• Crash Costs
• Crash Cost Per Day
Normal Duration - Crash Duration
Crash Cost - Normal Cost
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Probabilistic Activity Durations
• Three time estimates
made for both normal
resource loading and
crash resource loading
• Variance of normal
activity may be different
than variance of crash
time
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Fast-Tracking a Project
• Used Primarily in
Construction Industry
• Building phase started
before design and
planning phases
completed (Scottish
Parliament)
• Particularly appropriate
when large proportion of
work is routine
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Resource Loading
• Amount of specific
resources that are
scheduled for use on
specific activities or
projects at specific times.
• Usually a list or table.
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Use of Software
• Begin with Pert/CPM
Schedule
• Activities examined
period by period and
resource by resource
• In cases where demand
for resource exceeds
supply, tasks considered
one by one and resources
assigned to these tasks
based on priority rules
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Some Priority Rules
• As soon as possible
• As late as possible
• Shortest task duration
first
• Minimum slack first
• Most critical followers
• Most successor
• Most resources first
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Resource Loading/Leveling
and Uncertainty
• What about
– Workers getting sick?
– Task not ready when
worker is ready?
– Change orders?
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Pseudo activities
• Used to link several
project together
• Have duration but do not
require any resources
• This approach allows a
set of projects to be dealt
with as though it were a
single project
– use of MSP’s resource
loading and leveling charts
and tables
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Bottle Necks
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•
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Identify the constraint
Exploit the constraint
Subordinate everything
else
Elevate the constraint
Go back to step 1
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Goldratt’s Critical Chain
What is it?
• Tackles the inherent
uncertainty in managing
projects
• Systems approach
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Goldratt’s Critical Chain
• Similar issues that trouble people
about working on projects
regardless of type of project
–
–
–
–
unrealistic due dates
too many changes
resources and data not available
unrealistic budget
• These issues/problems related to
need to make trade-offs
• To what extent are these problems
caused by human decisions and
practices?
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Observations
• Average Completion
Times
• Implications of Assuming
Known Activity Times
• Worker Time Estimates
• Impact of Inflated Time
Estimates
• Student Syndrome
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Common Chain of Events
• Underestimate time needed to
complete project
• Project team members inflate time
estimates
• Work fills available time
• Safety time misused
• Misused safety time results in
missed deadlines
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Common Chain of Events
concluded
• Poor multitasking
increases task durations
• Uneven demand on
resources also results
due to poor multitasking
• More projects undertaken
to ensure all resources
fully utilized
• More projects further
increases poor multi
tasking
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Reversing the Cycle
• Reduce number of projects
assigned to each individual
• Schedule start of new
projects based on availability
of bottleneck resources
• Reduce amount of safety
time added to individual
tasks and then add some
fraction back as project buffer
– activity durations set so that
there is a high probability the
task will not be finished on time
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The Critical Chain
• Longest chain of
consecutively dependent
events
– considers both precedence
relationships and resource
dependencies
• Project Buffer
• Feeding Buffer
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Critical Chain Rules
1. Projects should not be
started ASAP
2. Tasks and resources
should not be precisely
scheduled during planning
3. Adding explicit buffers into
projects makes them run
faster
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Buffer Management
Taking the appropriate action
No action needs to be taken,
consumption of the buffer is
expected
Identify the tasks consuming the
buffer, develop a recovery plan
Implement recovery plan Use
information on task performance
for future improvement activities
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Why not start projects ASAP?
All three projects started ASAP
• Constant resource shuffling
• Priorities not synchronised
• All projects are delayed
Start dates are staggered
• Resources stay focused
• Tighter synchronisation
• All projects finish faster
• More projects can be done
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Why not schedule precisely?
Schedules set in planning
• Uncertainties are
unavoidable
• Wanting to be reliable,
people add safeties into
estimates
• Safeties get wasted in
execution
Schedules set in Execution
• Estimates are used only to
plan projects
• Task schedules determined
in execution, when tasks are
closer to being started
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How safety or contingency
time is wasted
• Task dependency
– Gains are wasted and delays are
passed on
• Student Syndrome / Cherry Picking
– Starting work is delayed
• Parkinson’s Law
– “Work expands to fill the time available”
• Multi Tasking
– A resource has to divide its time
between two or more tasks
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Benefits
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PROJECTS:
coming in on-time
completing within budget
completing without cutting
scope
reduced project lead-times
Improved efficiency
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A resource allocation example
Looking at the example of Breakfast in Bed there can be seen a
number of different tasks to perform, all of which have a resource
implication.
Activity
Effort
Duration
(person-minutes)
(minutes)
Butter toast
1
1
Pour orange juice
1
1
Boil egg
0
4
Slice bread
1
1
Fill pan with water
1
1
Bring water to boil
0
3
Toast bread
0
2
Take loaded tray to bedroom
1
1
Fetch tray, plates, cutlery
1
1
Time resource estimates for "Breakfast in Bed" project
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Often estimates of the time taken are quite inaccurate
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Plan with Resource Allocation
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Revised Plan with Resource Allocation
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Plan with Levelled Resources and Warm Toast
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