Project ManagementA Managerial Approach

Chapter 9

Resource Allocation

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

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

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

Fast-Tracking

Another way to expedite a project is known as “fast-tracking”

It refers to overlapping the design and build phases of a project

Because design is usually completed before construction starts, overlapping the two activities will result in shortening the project duration

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

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

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

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

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

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

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

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

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

Constrained Resource SchedulingThere are two fundamental approaches to

constrained allocation problems: Heuristic Methods Optimization Models

Heuristic approaches employ rules of thumb that have been found to work reasonably well in similar situations

Optimization approaches seek the best solutions but are far more limited in their ability to handle complex situations and large problems

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

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

Heuristic MethodsCommon 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

Most priority rules are simple adaptations of the heuristics used for the traditional “job shop scheduling” problem of production/operations management

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

Optimizing MethodsThe methods to find an optimal

solution to the constrained resource scheduling problem fall into two categories: Mathematical programming

Enumeration

Mathematical programming can be thought of as liner programming (LP) for the most part

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

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

Multiproject Scheduling and Resource Allocation

Three important parameters affected by project scheduling are: Schedule slippage

Resource utilization

In-process inventory

The organization (or the project manager) must select the criterion most appropriate for its situation

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

Multiproject Scheduling and Resource Allocation

All criteria cannot be optimized at the same time

As usual, the project manager will have to make trade-offs among the criteria

A firm must decide which criterion to evaluate its various scheduling and resource allocation options

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)

Mathematical Programming

The three most common objectives of mathematical programming are: 1. Minimum total throughput time (time in the shop)

for all projects

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

Heuristic Techniques

There are scores of different heuristic-based procedures in existence

They represent rather simple extensions of well-known approaches to job-shop scheduling: Resource Scheduling Method Minimum late finish time Greatest resource demand Greatest resource utilization Most possible jobs

Summary

The critical path method (CPM) is a network constructed in the same manner as PERT but considers the possibility of adding resources to tasks to shorten their duration

The resource allocation problem is concerned with determining the best trade-offs between available resources, including time, throughout the duration of the project

Summary

Resource loading is the process of calculating the total load from project tasks on each resource for each time period of the project’s duration

Resource leveling is concerned with evening out the demand for various resources required in a project by shifting tasks within their slack allowances

Chapter 9-29

Summary

There are two basic approaches to addressing the constrained resources allocation problem: Heuristic methods Optimizing methods

For multiproject scheduling, three important measures of effectiveness are schedule slippage, resource utilization, and level of in-process inventory

Summary

When a new project is added to a multiproject system, the amount of slippage is directly related to the average resource load

Mathematical programming models for multiproject scheduling aim to either minimize total throughput time for all projects, minimize the completion time for all projects, or minimize total lateness for all projects

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Questions?

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