Chapter-5-Scheduling-and-Resource-Allocation.ppt

CHAPTER 5
SCHEDULING and
RESOURCE ALLOCATION
MSc Bui Thu Hien

CHAPTER OUTLINE
5.1 SCHEDULING
5.2 RESOURCE ALLOCATION

Useful Abbreviations
 CPM - Critical Path Method
 PERT - Program Evaluation and Review
Technique

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

Background Continued
 Most of the scheduling is at the WBS
level, not the work package level
 Only the most critical work packages may
be shown on the schedule
 Most of the scheduling is based on
network drawings

Network Scheduling Advantage
 Consistent framework
 Shows interdependences
 Shows when resources are needed
 Ensures proper communication
 Determines expected completion date
 Identifies critical activities

Network Scheduling Advantage
Continued
 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

Network Scheduling Techniques: PERT
(ADM) and CPM (PDM)
 PERT was developed for the Polaris
missile/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 blended
CPM and PERT into one approach

Terminology
 Activity - A specific task or set of tasks
that are required by the project, use up
resources, and take time to complete
 Event - The result of completing one or
more activities
 Network - The combination of all
activities and events that define a project
– Drawn left-to-right
– Connections represent predecessors

Terminology Continued
 Path - A series of connected activities
 Critical - An activity, event, or path
which, if delayed, will delay the
completion of the project
 Critical Path - The path through the
project where, if any activity is delayed,
the project is delayed
– There is always a critical path
– There can be more than one critical path

 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 activity
that must be completed just before a
particular activity can begin

 Activity on Arrow - Arrows represent
activities while nodes stand for events
 Activity on Node - Nodes stand for
events and arrows show precedence

AON and AOA Format
Figure 8-3
Figure 8-2

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 as
precedences
 Continue

Gantt (Bar) Charts
 Developed by Henry L. Gantt
 Shows planned and actual progress
 Easy-to-read method to know the current
status

Advantages and Disadvantage
 Advantages
– Easily understood
– Provide a picture of the current state of a
project
 Disadvantage
– Difficult to follow complex projects

The AON Network from the previous
table

Calculating Activity Times
 
 
2
2
2
6
6
4









 




a
b
b
m
a
TE

Critical Path and Time Continued

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

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 project’s
completion date?

Precedence Diagramming
 Finish to start
 Start to start
 Finish to finish
 Start to finish

Precedence Diagramming Conventions

Uncertainty of Project Completion Time
 Assume activities are statistically
independent
 Variance of a set of activities is the sum
of the individual variances
 Interested in variances along the critical
path

Example
 
  45
.
52
645
.
1
745
.
5
43
22
.
1
745
.
5
7
33
43
50
)
(
2












Z
D
D
Z






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

Critical Path Method—Crashing a
Project
 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 up
by spending more money

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

Activity Slope
Crash Cost Normal Cost
Crash Time Normal Time
Slope




Activity Slopes—Cost per Period for
Crashing

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

The Resource Allocation Problem
 CPM/PERT ignore resource utilization
and availability
 With external resources, this may not be
a problem
 It is, however, a concern with internal
resources
 Schedules need to be evaluated in terms
of both time and resources

Time Use and Resource Use
 Time limited: A project must be finished
by a certain time
 Resource limited: A project must be
finished without exceeding some specific
level of resource usage
 System-constrained: A project has fixed
amount of time and resources

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 firm’s resources

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

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

Constrained Resource Scheduling
Heuristic
Approach
An approach, such as a
rule of thumb, that yields
a good solution that may
or may not be optimal
Optimization
Approach
An approach, such as
linear programming, that
yields the one best
solution.

Heuristic Methods
 They are the only feasible methods used
to attack large projects
 While not optimal, the schedules are very
good
 Take the CPM/PERT schedule as a
baseline

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

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

Heuristic Methods Continued
 These are just the common ones
 There are many more
 The heuristic can either start at the
beginning and work forwards
 Or it can start at the end and work
backwards

Optimization Methods
 Finds the one best solution
 Uses either linear programming or
enumeration
 Not all projects can be optimized

Multi-Project Scheduling and Resource
Allocation
 Scheduling and resource allocation
problems increase with more than one
project
 The greater the number of projects, the
greater the problems
 One way is to consider each project as
the part of a much larger project

Multi-Project Scheduling and Resource
Allocation Continued
 However, different projects have different
goals so combining may not make sense
 Must also tell us if there are resources to
tackle the new projects we are
considering

Standards to Measure Schedule
Effectiveness
 Schedule slippage
 Resource utilization
 In-process inventory

Schedule Slippage
 The time past a project’s due date
 Slippage may cause penalties
 Different projects will have different
penalties
 Expediting one project can cause others
to slip
 Taking on a new project can cause
existing projects to slip

Resource Utilization
 The percentage of a resource that is
actually used
 We want a schedule that smoothes out
the dips and peaks of resource utilization
 This is especially true of labor, where
hiring and firing is expensive

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

Heuristic Techniques
 Multi-projects are too complex for
optimization approaches
 Many of the heuristics are extensions of
the ones used for one project

Additional Priority Rules
 Resource scheduling method
 Minimum late finish time
 Greatest resource demand
 Greatest resource utilization
 Most possible jobs

Goldratt’s Critical Chain
1. Thoughtless optimism
2. Capacity should be equal to demand
3. The “Student Syndrome”
4. Multitasking to reduce idle time

Goldratt’s Critical Chain Continued
5. Assuming network complexity makes no
difference
6. Management cutting time to “motivate”
workers
7. Game playing
8. Early finishes not canceling out late
finishes

Chapter-5-Scheduling-and-Resource-Allocation.ppt

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