Spm Pert&Cpm Part1

Strategic Project Management 1SPM Basic PERT/CPM (Part 1)

A Look Ahead

We will now turn our attention to several tools and techniques associated with Project Time Management

First, we will consider: PERT & CPM Historical Perspective Overview of Sequencing Techniques ADM: Arrow Diagramming Method Determining the Critical Path

• download ADM_Class_Example.doc


A Look Ahead(continued)

After that, we will continue our exploration of tools and techniques by considering: The Concept of Float

download ADM_Float_Calcs.xls Probabilistic Activity Duration Estimates

download ADM_Mean_Variance.xls Probabilistic Project Completion

download ADM_Standard_Normal_Table.xls


PERT/CPMSome History

PERT was first used in the late 1950’s by the Navy for the Polaris Missile Program

PERT => Project Evaluation & Review Technique

Development was in conjunction with the consulting firm of Booz, Allen, and Hamilton

Development was designed to meet the needs of the “age of massive engineering”

The Navy was concerned with performance trends on large military projects.


PERT/CPMSome History (continued)

Virtually simultaneously CPM was developed by the duPont Company and Remington-Rand-Univac.

CPM => Critical Path Method For use on large construction projects Specifically targeted for process industries

The two groups were unaware of each other's existence until about 1960. By then, each stood on its own merits


PERT/CPMSome History (continued)

PERT’s strengths are in its use of probabilistic estimates of activity durations

CPM’s strengths are in its ability to do “time-cost trade-offs”

Today, PERT/CPM are widely recognized as comprising one set of techniques the differences are primarily viewed as only

of historical importance


Activity SequencingDisplay Techniques

There are many suitable techniques for displaying the sequence of activities involved in a project Gantt Charts Precedence Diagramming Arrow Diagramming Conditional Diagrams


Gantt Charts

Gantt charts use horizontal bars (or lines) to represent activities Gantt charts are more commonly used for

schedule display than activity sequencingsee BOK Figure 6-6 (1996 & 2000) for an examplelength of the bars show expected durationactivity inter-relationships are not explicitly shown

we will see Gantt Charts again when we consider Resource Loading & Leveling


The Precedence Diagramming Method

The Precedence Diagramming Method (PDM) uses boxes to represent activities and arrows to represent dependencies see BOK Figure 6-2 (1996 & 2000 for an

exampleThis technique is also known as the

Activity-on-Node (AON) Diagramming


More on PDM

Dependencies can include: Finish-to-Start Finish-to-Finish Start-to-Start Start-to-Finish

Dependencies are usually indicated by the placement of the arrow heads and tails relative to the nodes but no consistent approach has been universally adopted.

Looping and Conditional Branching is not allowed


The Arrow Diagramming Method (ADM)

The Arrow Diagramming Method (ADM) uses the following conventions: Arrows represent activities

"Regular" activities require time and resources"Dummy" activities show precedence relationships

Nodes represent eventsA point in timeSome nodes may represent milestone events

see BOK Figure 6-3 (1996 & 2000) for an example


More on ADM

Also known as Activity-on-Arrow (AOA)Each activity is represented by one and

only one arrow in the network.Nodes (events) are numbered uniquely.

Duplicate node numbers are not allowedNo two activities can be identified by

the same beginning and ending nodes. Dummy activities may be required


More on ADM (continued)

Before an activity can begin, all activities terminating at the activities beginning node must be completed.

Neither the length of an activity arrow nor its “compass” direction have any significance.

Networks should (must) have only one initial event and one terminal event.


An Example to Try:Draw an Arrow Diagram

A project consists of Activities A, B, C, D, E, F, G, H, I, J, K, and LA, B, and C, the 1st activities of the project,

can start simultaneouslyA and B precede DB precedes E, F, and HF and C precede GE and H precede I and JC, D, F, and J precede KK precedes LI, G, and L are terminal activities for the project


Let’s Examine the Example Solution

Solution to be shown in class.


Conclusion of Sequencing Techniques

We’ll return to ADM in just a few minutes but first let’s complete the set of sequencing techniques by considering Conditional Diagramming


Conditional Diagramming

Conditional Diagramming methods allow for probabilistic activities and looping neither of these are allowed in traditional PDM

or ADMConditional diagramming techniques

include Graphical Evaluation and Review Technique (GERT) and System Dynamics these are beyond the scope of this course


Activity Durations

The next logical step in Project Time Management is to determine activity durations.

We are going to defer a detailed discussion of estimating activity durations until later in the course.

At this point we need to introduce the concept of the Critical Path of a project.


The Concept of the Critical Path

The determination of the start and completion time of each activity on the network diagram requires a special calculation procedure.

This approach classifies each activity as either critical or non-critical. The approach is commonly known as

the Critical Path Method


The Concept of the Critical Path (continued)

A delay in the start or completion of a critical path activity will cause a delay in the completion of the entire project.

Non-critical path activities can absorb some delay in start or completion without impacting project completion. The amount of delay which can be

absorbed is known as slack or float.



There will always be at least one sequence of activities from the initial node to the terminal node that is made up entirely of critical activities.

This is known as the Critical Path of the Project.

Any delay of a critical path activity will delay the completion of the project.



The critical path defines the minimal completion time for the project.

Multiple critical paths are possible. Complete multiple critical paths

two or more critical paths exist from the initial node to the terminal node of the project.

• rare in uncrashed networks, common in fully crashed Partial multiple critical paths

two or more sets of parallel activities are critical over some segment of the project.

• relatively common


Determining the Critical Path

The critical path is found by a two phase methodology after activity durations have been determined. A “forward pass” is made through the

network diagram to determine the earliest start time for each node.

A “backward pass” is made through the network to determine the latest completion time for each node.


Determining the Critical Path (continued)

This is best illustrated through an example. Mathematical details in SPM_PERT&CPM_Math

An ADM diagram for a project is shown on the following page the activities themselves are not labeled, we

will use the (start node, end node) pair to uniquely identify activities (e.g., (0,1))

duration estimates are indicated


Class ExampleCritical Path Calculations

0

2

1

4

3

5 6

3

2

2

3

2

23

57

6


Forward Pass and Backward Pass



The Critical Path

An activity lies on the critical path if it meets the three following conditions: The earliest start and latest completion

for the activity’s terminal node are equal; The earliest start and latest completion

for the activity’s initial node are equal; The difference between the earliest start

of the terminal node and the earliest start of the initial node is the activity duration.


The Critical Path(continued)

Let’s re-examine the example for the critical path.


Spm Pert&Cpm Part1

Documents

Transcript of Spm Pert&Cpm Part1