Chapter 5_ Scheduling and Resource Allocation

5/27/2018 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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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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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

Chapter 5_ Scheduling and Resource Allocation

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