© 2006 John Wiley Critical Path Method - Crashing a Project • CPM includes a way of relating the project schedule to the level of physical resources allocated to the project • This allow
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Project Management: A Managerial Approach
Chapter 9 – Resource Allocation
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Overview
• Critical Path Crashing
• Resource Leveling
• Resource Constrained Schedules
• Multiproject Resource Management
• Critical Chain
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Critical Path Method - Crashing a Project
• CPM includes a way of relating the project
schedule to the level of physical resources
allocated to the project
• This allows the project manager to trade time
for cost, or vice versa
• In CPM, two activity times and two costs are
specified, if appropriate for each activity
Chapter 9-1
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Critical Path Method - Crashing a Project
• The first time/cost combination is called normal,
and the second set is referred to as crash
• Normal times are “normal” in the same sense as
the ‘m’ time estimate of the three times used in
PERT
• Crash times result from an attempt to expedite the
activity by the application of additional resources
Chapter 9-2
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Critical Path Method - Crashing a Project
• Careful planning is critical when attempting to
expedite (crash) a project
• Expediting tends to create problems; and the
solution to one problem often creates several more problems that require solutions
• Some organizations have more than one level of crashing
Chapter 9-3
Trang 12• Because design is usually completed before
construction starts, overlapping the two activities will result in shortening the project duration
Chapter 9-4
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The Resource Allocation Problem
• A shortcoming of most scheduling procedures is that they do not address the issues of resource utilization and availability
• Scheduling procedures tend to focus on time rather than physical resources
• Time itself is always a critical resource in project
management, one that is unique because it can neither
be inventoried nor renewed
Chapter 9-5
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The Resource Allocation Problem
• Schedules should be evaluated not merely in terms of meeting project milestones, but also in terms of the timing and use of scarce resources
• A fundamental measure of the project manager’s
success in project management is the skill with which the trade-offs among performance, time, and cost are managed
Chapter 9-6
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The Resource Allocation Problem
• The extreme points of the relationship between time use and resource use are these:
– Time Limited: The project must be finished by a
certain time, using as few resources as possible But it
is time, not resource usage, that is critical
– Resource Limited:The project must be finished as
soon as possible, but without exceeding some specific level of resource usage or some general resource
constraint
Chapter 9-7
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The Resource Allocation Problem
• If all three variables - time, cost, specifications - are fixed, the system is “overdetermined”
• In this case, the project manager has lost all
flexibility to perform the trade-offs that are so
necessary to the successful completion of projects
• A system-constrained task requires a fixed amount
of time and known quantities of resources
Chapter 9-8
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Resource Loading
• Resource loading describes the amounts of
individual resources an existing schedule requires during specific time periods
• The loads (requirements) of each resource type are listed as a function of time period
• Resource loading gives a general understanding of the demands a project or set of projects will make
on a firm’s resources
Chapter 9-9
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Resource Loading
• An excellent guide for early, rough project
planning
• Because the project action plan is the source of
information on activity precedences, durations, and resources requirements, it is the primary input for both the project schedule and its budget
• The action plan links the schedule directly to
specific demands for resources
Chapter 9-10
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Resource Loading
• The PERT/CPM network technique can be
modified to generate time-phased resource
requirements
• The project manager must be aware of the ebbs and flows of usage for each input resource throughout the life of the project
• It is the project manager’s responsibility to ensure that the required resources, in the required amounts, are available when and where they are needed
Chapter 9-11
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Resource Leveling
• Resource leveling aims to minimize the
period-by-period variations in resource loading by shifting tasks
within their slack allowances
• The purpose is to create a smoother distribution of resource usage
• Several advantages include:
– Less hands-on management is required
– May be able to use a “just-in-time” inventory policy
Chapter 9-12
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Resource Leveling
• When resources are leveled, the associated costs
also tend to be leveled
• The project manager must be aware of the cash
flows associated with the project and of the means
of shifting them in ways that are useful to the
parent firm
• Resource leveling is a procedure that can be used for almost all projects, whether or not resources are constrained
Chapter 9-13
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Resource Leveling - Example
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Constrained Resource Scheduling
• There are two fundamental approaches to constrained allocation problems:
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Heuristic Methods
• Heuristic approaches to constrained resource
scheduling problems are in wide, general use for a number of reasons:
– 1 They are the only feasible methods of attacking the
large, nonlinear, complex problems that tend to occur in the real world of project management
– 2 While the schedules that heuristics generate may not be optimal, they are usually quite good- certainly good
enough for most purposes
Chapter 9-15
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Heuristic Methods
• Most heuristic solution methods start with the
PERT/CPM schedule and analyze resource usage period by period, resource by resource
• In a period when the available supply of a resource
is exceeded, the heuristic examines the tasks in that period and allocates the scarce resource to them
sequentially, according to some priority rule
• Technological necessities always take precedence
Chapter 9-16
Trang 26– Shortest task first
– Most resources first
– Minimum slack first
– Most critical followers
– Most successors
– Arbitrary
Chapter 9-17
Trang 27• Most heuristics use a combination of rules: a primary rule, and
a secondary rule to break ties
• As the scheduling heuristic operates, one of two events will
result:
– The routine runs out of activities before it runs out of resources
– The routine runs out of resources before all activities have been
scheduled
Chapter 9-18
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Optimizing Methods
• The methods to find an optimal solution to the
constrained resource scheduling problem fall into two categories:
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Optimizing Methods
• Linear programming is usually not feasible for reasonably large projects where there may be a dozen resources and thousands of activities
• In the late 1960s and early 1970s, limited
enumeration techniques were applied to the
constrained resource problem
• Tree search, and branch and bound methods were devised to handle up to five resources and 200
activities
Chapter 9-20
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Multiproject Scheduling and Resource Allocation
• The most common approach to scheduling and
allocating resources to multiple projects is to treat the
several projects as if they were each elements of a
single large project
• Another way of attacking the problem is to consider all projects as completely independent
• To describe such a system properly, standards are
needed by which to measure scheduling effectiveness
Chapter 9-21
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Multiproject Scheduling and Resource Allocation
• Three important parameters affected by project scheduling are:
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Multiproject Scheduling and Resource Allocation
• Schedule slippage, often considered the most important
of the criteria, is the time past a project’s due date or
delivery date when the project is completed
• Resource utilization is of particular concern to
industrial firms because of the high cost of making
resources available
• The amount of in-process inventory concerns the
amount of work waiting to be processed because there
is a shortage of some resource
Chapter 9-23
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Multiproject Scheduling and Resource Allocation
• All criteria cannot be optimized at the same time
• As usual, the project manager will have to make offs among the criteria
trade-• A firm must decide which criterion to evaluate its
various scheduling and resource allocation options
Chapter 9-24
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Mathematical Programming
• Mathematical programming can be used to obtain solutions to certain types of multiproject scheduling problems
• These procedures determine when an activity should
be scheduled, given resource constraints
• Mathematical programming, however, is rarely used
in project management to handle the multiproject
problem (mostly, heuristics are used)
Chapter 9-25
Trang 35– 2 Minimum total completion time for all projects
– 3 Minimum total lateness or lateness penalty for all projects
• These objectives are most appropriate for ‘job shop’ type solutions to resource constraints
Chapter 9-26
Trang 36well-– Resource Scheduling Method
– Minimum late finish time
– Greatest resource demand
– Greatest resource utilization
– Most possible jobs
Chapter 9-27
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Critical Chain
• Eliyahu M Goldratt’s “Theory of Constraints”
• Traditional Project Estimation Techniques Ineffective
– Time and Resource Constraints Usually Violated
– PMs Rely on “Padding” of Schedules and Budgets
– Unknown Nature of Event Interaction
• Fear, Uncertainty, Doubt
• Psychological, Organizational, and Physical
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Critical Chain - Approach
• Bottleneck Management
– Activities with Several Predecessors and/or Successors
– Add “Time Buffers” at Bottleneck Events
• “Safety Stock” Equivalent in Manufacturing
• Just-in-Time with “Just-in-Case”
• Statistically-derived “Path Buffers”
– Establish the Critical Chain for Scarce Resources
– Prioritization of Resources in Chain Events
• Communication of “Walt” Needs is Critical to Success
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