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CPM History

The Critical Path Method (CPM) emerged in the mid-1950s.

US Navy- Polaris Missile System

DuPont & Remington Rand

Benefits of Scheduling & Evaluation

Without some kind of periodic and consistent measurement system--it's close to impossible to make critical judgments with confidence that the facts are in hand.

Better decision making

Better resource management

Better time management

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Managing Small Projects And Why Scheduling Still Matters

Multiple projects to manage

Higher risk

Limited resources

Short duration

Overtime?

Activity Priority

Requested Project Duration

Estimated Project Duration

Q: How long will it take?

We often neglect consideration of such factors as:

Mobilization

Paper Work

Material and Equipment Deliveries

Subcontractors Availability

A: We can handle it Attitude:

We typically respond with the time we think

it would take us to do the work, when

actually it will be done by others.

The Most Common Q&A:

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The Benefits: Decision Making

The Benefits: Decision Making

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The Benefits: Resource Management

The Benefits: Multi Project Management

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Advantages

Shows the Construction Logic Identifies the Critical Activities (80 20 Rule) Allows Management to set Priorities Shows the Effects of a Change Order or Delay Is Self-adjusting when updated Easy to Follow Visually See the Big Picture Potentially it is the most effective scheduling system Helps to Analyze Different Methods or Sequences Useful for Court Cases Keeps You Out of Court Serves as a Basis for Systems Control Forces the Management Team to Plan and Think in Detail Communicates the Process to Every Team Member Promotes Teamwork

Disadvantages

Can Become Complex - It is the Most Sophisticated Scheduling System

Requires Training to Become an Effective User

Due to Not Fully Understanding CPM and Its Complexity, It is Often Abandoned

88

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Network

Activity on Node (AON)

Activity A

Activity

B

Relationship

Successor Predecessor

Critical Path Method (CPM) Provides a timetable for performing the tasks which comprise

a project

Acts as a tool for examining activity relationships and resource utilization

Supplies data for reports and graphics that aid in decision making

The longest continuous path of activities through a project determines the project end date.

A delay in a critical activity delays other activities and the project as a whole

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A CPM Network

Name

ES EF

LS LF

TF FF

Duration

(TF, FF, IF, INDF)

Construction Flow Chart

Shows Preceding Activities

Shows Succeeding Activities

Shows Concurrent Activities

Shows the Critical Path Activities

Shows the Amount of Float

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How to Create a CPM Schedule

Review the Plans and Specifications

Get the Project into Your Head

Brain Storm the Project with the Project Team

Make Sure the Project Manager and Supervisors are involved Check with the Estimator

Discuss the Overall Job Approach

Discuss Problem Areas Anticipated

Any Special Conditions or Features?

Steps to Create A CPM Schedule

1) Breakdown the project into activities

2) Construct the Logic Diagram

3) Add the Durations

4) Calculate the Early Dates (forward pass)

5) Calculate the Late Dates (backward pass)

6) Calculate the Total Float

7) Mark the Critical Path

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Break the Project into Activities

Could use a Work Breakdown Structure (WBS)

Keep trades and contractual divisions separate

May even want to separate crews

Keep field work separate from shop or office work

Determine the level of Detail

Include submittal process?

Include procurement of material?

Include curing time for concrete?

Break the Project into Activities

Could Use a Work Breakdown Structure

WBS example:

1. Preconstruction Phase

1.1 Obtain Permits

1.2 Obtain Bonds

1.3 Obtain Insurance

2. Engineering Phase

2.1 Shop drawings

2.2 Review shop drawings

2.3 Fabrication

3. Job Mobilization Phase

3.1 Set up field office

3.1.1Locate Job Office Trailer

3.1.2 Construct Project Bulletin Board

3.1.3 Construct Deck and Roof Cover

3.2 Install temporary Power

3.3 Set up security Fence

3.4 Telephone Hookup

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Make Sure the Logic is Correct

Review Logic Diagram with ALL Team Members

Ask question #1 of every activity - Does this activity really have to be done before each of the following activities can start?

Ask question #2 What other activities need to be done before this activity can start?

How Do You Determine the Durations of the Scheduled Activities?

From Subs

Estimating or Productivity Manuals

Company Records of Productivity Rates

Flat out Guess

What was it we were trying to manage?

Add the Durations to the Logic Diagram

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Exercise

Activity

Immediate

Predecessor Duration

A H 2

B C 4

C H 1

D A,C 3

E A 1

F B 4

G E,D 2

H ~ 0

I F,G 0

Activity On Node Notation (typical)

ES = Early Start

EF = Early Finish

LS = Late Start

LF = Late Finish

TF = Total Float

FF = Free Float

Name

ES EF

LS LF

TF FF

Duration

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CPM -Definitions

Activity: The performance of a task required to complete the project, such as, design of foundations, review of design, procure steel contracts, or form concrete columns. An activity requires time, cost, or both time and cost.

Duration (D): estimated time required to perform an activity.

Early Start (ES): earliest time an activity can be started. Early Finish (EF): earliest time an activity can be finished.

Equal to the early start plus the duration. EF=ES+D Late Finish (LF): latest time an activity can be finished. Late Start (LS): latest time an activity can be started without

delaying the projects completion date. LS=LF-D

Early Start Calculation (Forward Pass)

ES = MAX {EFpredecessors}

A

B

C

D

EF=2

EF=6

EF=4

ES= 6

Name

ES EF

LS LF

TF FF

Duration

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Early Finish Calculation (Forward Pass)

EF = ES + Activity Duration

Framing

ES = 3 EF =

LS LF

TF FF

6

9

Late Finish Calculation (Backward Pass)

Successors

B

C

D 7

LF=

10

7

LS=

LS=

LF = MINIMUM {LSsuccessors}

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Late Start Calculation (Backward Pass)

Set Anchor Bolts

ES EF

4

LS= LF=16 12

LS = LF - Activity Duration

Total Float (TF): the amount of time an activity may be delayed without delaying the projects completion date.

TF=LF-EF=LS-ES

Free Float (FF): amount of time an activity may be delayed without delaying the ES time of the following activity or the projects completion date .

EFi=ESj-EFi,where the subscript i represents the preceding activity and the subscript j represents the following activity.

Critical Path: a series of interconnected activities through the network diagram, with each activity having zero, free and total float time. The critical path determines the minimum time to complete the project.

CPM -Definitions

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Total Float

0

LF EF ES

TF

TF = LS ES TF = LF - EF

LS

3 7 10

TF

Total Float

TF = LS ES

TF = LF EF

Activity

3

5

6

8 14

9

TF =

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Free Float

Minimum ES of all Successors

ES

FF

EF

FF = MIN {ES successors} EF activity

Free Float

FF = MIN {ES successors} EF activity

B

C

D

EF= 1

10

11

12

FF = Min{11,12} 10 = 1

FF=

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Time-scaled Network

From: Verzuh, E., (1999). The Fast Forward MBA in Project Management. John Wiley & Sons, Inc., New York, NY.

Types of Float

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Calculating Interfering & Independent Float

Managing the Float

Which Type of Float Would You Share with Subs?

Using Float to Hide Days in the Schedule

Sharing Shared Float in Order to Make the Schedule More Manageable

Use the Float to Manage Resources

Spring 2013-Lecture 02-CPM Time-Scaled Network

Documents

Transcript of Spring 2013-Lecture 02-CPM Time-Scaled Network