AMERICAN SPORTS BUILDERS ASSOCIATION CRITICAL PATH METHOD SCHEDULING FOR SUCCESS

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AMERICAN SPORTS
BUILDERS ASSOCIATION
CRITICAL PATH METHOD
SCHEDULING FOR SUCCESS
December 6-8, 2008
New Orleans, Louisiana

Presented By: Bill Pronevitch

SCHEDULING- Is It Necessary?
• Effective Project Management involves
coordinating activities such as:
–
–
–
–

Planning
Organizing
Controlling Time (scheduling)
Cost

• The “Scheduling” process forces people to:
– Quantify their effort in discrete terms
– Place tasks in proper relationships

SCHEDULING- Methodologies
• Two of the most common methodologies:
– Bar Charts

– Critical Path
• ADM: Arrow Diagramming Method
• PDM: Precedence Diagramming Method
• Both scheduling methods are widely used for:
– Controlling
– Making optimal use of project time

SCHEDULING- Bar Charts
• Bar Charts (also called “Gantt Charts”) are
primarily for controlling Time elements:
– Analyze/ specify the basic approach to be used
– Segment the work into a reasonable number of
activities that can be scheduled
– Estimate the time required to perform each
activity (i.e.- activity duration)
– Place activities in “time-order” (logic)
– Adjust the chart until the specified completion
date, if one exists, is satisfied.

SCHEDULING- Bar Chart
A

Gantt Chart
(Bar Chart) shows:

B

•All Activities and

Status on a Single
Chart

C
D
E
F
0

1

2

3

4

5

6

7

8

9

10

11

12

SCHEDULING- Bar Charts
• Benefits:
– Plan, Schedule, and Progress on a single chart
– A simple, understandable way to schedule small
projects or undertakings

• Disadvantages:
– Activity-limited, can’t handle complex projects
– Doesn’t show logic ties (activity relationships)
– Insufficient detail to enable timely detection of
schedule slippages on long duration activities

SCHEDULING: Critical Path
• The Critical Path Method (CPM) was
designed for and is useful on projects where
the duration of each activity can be
with reasonable certainty
- it predicts project overall completion
- it identifies the (critical) activities that
control the overall length of the project
• CPM is widely used in: process industries
construction and plant outages/ shutdowns.

SCHEDULING: Critical Path

• Benefits:
– Determines shortest project completion time
– Identifies “critical” activities – that can not be
slipped or delayed (i.e.- “TOTAL FLOAT”)
– Shows allowable slippage for “non-critical”
activities (i.e.- “FREE FLOAT”)
• Disadvantages:
– Large number of activities required
– Difficult to read, understand, and maintain.

SCHEDULING: CPM/ADM
• ADM (Arrow Diagramming Method):
– Arrow (line): represents an Activity
– Tail (of arrow): shows an Activity’s start
– Head (of arrow): shows an Activity’s finish
– Node (or event): shown at each end
• The “Activity Number” consists of Head and Tail
numbers, commonly referred to as I-J nodes (i.e.- “IJ Method” of CPM)

SCHEDULING: CPM/ADM
ADM: Arrow Diagramming Method
Process Work

Requisition

Install

Order

Material

Pump

1

4

2

Assign
Crew

3

5

(Dummy Activity – shows
relationship, zero duration)

SCHEDULING: CPM/ADM
• Benefits:
– Allows use of “Dummy Activities” which:
• Have a “ZERO” time duration
• Can be used to show additional relationships
• Disadvantages:
– An Activity’s “Predecessor” must be complete
before the Activity can start!

– Neither the Activity’s “arrow length” or “arrow
direction” have any meaning

SCHEDULING: CPM/PDM
• PDM (Precedence Diagramming Method):
– Box/ Node: represents an Activity
– Line/ Arrow: represents a Precedence – with time
and direction properties

• Precedence consist of two parts:
– “Relationship”: a Predecessor or Successor
– “Lag”: the (positive or negative) number of work
periods by which a specified Activity will be
delayed (assumed to be “0” if not specified)

SCHEDULING: CPM/PDM
PDM: Precedence Diagramming Method
Process
Work
Order

Requisition
Material

Install
Pump

A

B

C

Assign
Crew

D

Pump
Installation
Completed

E

SCHEDULING: CPM/PDM
• Types of Relationships, Lags (aa,n):
– FS, 0: Finish-to-Start, With “0 units” of delay
– FF, 7: Finish-to-Finish, with “7 units” of delay
– SS, 5: Start-to-Start, with “5 units” of delay
– SF, 0: Start-to-Finish, with “0 units” of delay

SCHEDULING – PDM/ LOGIC
Relationships (Logic Ties, Lags
Finish -to- Finish
Finish –to- Start

A
(FS,0)

A

B

B

Start –to- Start

A
(SS,4)

(FF,5)

Start –to- Finish

B

B
A
(SF,0)

SCHEDULING: CPM/PDM
• “6” Major Types of Constraints
– Start On: a mandatory date
– Start No Earlier Than*: can start “later”
– Start No Later Than*: can start “earlier”

– Finish On: a mandatory date
– Finish No Earlier Than*: can finish “later”
– Finish No Later Than*: can finish “earlier”
* NOTE: Schedule logic drives “earlier” and “later”
start and finish dates

SCHEDULING- PDM/ OTHER
• Hammock Activity
– Spans many activities to show an “overall”
performance period (i.e.- a summary activity)
• Logic Loop
– One of the most common “scheduling errors”
– Occurs when a set of activities precede each
other in a “circular” fashion, (a group of activities
can never begin nor end)
– Must be eliminated prior to calculating the
schedule (i.e.- running a time analysis)

SCHEDULING- Hammock
PDM: Hammock (Summary) Activity

A

B

C

D

E

SCHEDULING – PMD/LOOP
LOOP: No beginning or end
(a circular path)

A

B

C
LOOP

F

E

D

SCHEDULING – PDM/ CALC’S
• Once a network has been created and the durations
estimated for each activity, both the “Total Time” to
reach project completion and each activity’s
“individual” start and finish times, can be calculated
– Manual computation is easy and logical (but
tedious & time-consuming on large projects)
• Forward Pass: calculates early start/finish, (ES/EF)

• Backward Pass: calculates late start/finish, (LS/LF)

SCHEDULING – CALC’S
• FORWARD PASS:
– Calculates “Earliest Start” and “Earliest Finish”
times, observing the following rules:
• Assign an “ES” time to the first activity
• Other activities start as soon as their
“predecessor” relationships have been satisfied
• Equations:
– ES = EF (Pred.) + 1
– EF = ES + Duration - 1

SCHEDULING – CALC’S
• BACKWARD PASS:
– Calculates “Latest Start” and “Latest Finish”
times, observing the following rules:
• Assign an “EF” time to the last activity.
• All activities finish as soon as their “Successor”
relationships have been satisfied.
• Equations:
– LF = LS (Succ.) – 1
– LS = LF – Duration + 1

SCHEDULING – CALC’S
• PDM ACTIVITY NOTATION:
–

–
–
–

Activity Number: unique number to an activity
Duration: number of “work periods” assigned
ES & EF: calculated in Forward Pass
LS & LF: calculated in Backward Pass
ACTIVITY NUMBER

ES
LS LF

EF

1

A

5

3

5

7

DURATION