AMERICAN SPORTS BUILDERS ASSOCIATION CRITICAL PATH METHOD SCHEDULING FOR SUCCESS

SCHEDULING- Methodologies• Two of the most common methodologies: – Bar Charts – Critical Path • ADM: Arrow Diagramming Method • PDM: Precedence Diagramming Method • Both scheduling metho

AMERICAN SPORTS BUILDERS ASSOCIATION

CRITICAL PATH METHODSCHEDULING 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

SCHEDULING- Bar Chart

•All Activities and Status on a Single

Chart

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.- “I-J Method” of CPM)

Install Pump

Assign

Crew

(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)

Pump Installation Completed

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

Start –to- Finish

Finish -to- Finish Finish –to- Start

Start –to- Start

(FS,0)

(FF,5)

(SS,4) (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

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

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)

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

10

1

5 5

20 6

5 24

40 6

14

19

30 5

5 9

Legend Activity ID ES

What is the Scheduling Process?

Report/ Status

Scheduling

Planning

IDENTIFY MILESTONES

• Project Start

• Project Phase Start and Finishes

• Equipment and/ or Long Lead Item

Delivery

• Project Finish

DEVELOP ACTIVITY LIST

(EXAMPLE: HOUSE CONSTURCTION)

ASSIGN DURATION TO ACTIVITES

(EXAMPLE: HOUSE CONSTRUCTION)

SEQUENCE ACTIVITIES

ASK THREE QUESTIONS!

• What activity must come before this one?

• What activity must come after this one?

• What activities can I perform at the same time?

REVIEW AND FINALIZE

• Review Relationships

• Review and Finalize Durations

• Review Resource Usage

• Review and Finalize Project End Date

– Does this achieve the desired date?

– If it does not… What is the plan NOW?!?

SCHEDULING- CONCLUSION

• Planning and scheduling functions are

usually performed iteratively in order to

provide for accomplishing all required

tasks within the specified time frames

• Both Critical Path Methods (ADM & PDM) create networks showing activity durations and total time for project completion

• “Failing to Plan is Planning to Fail”, hence

“Plan the Work, Work the Plan”