CE 405 – SCHEDULINGCRITICAL PATH

In order to be an effective Scheduler/ Project Manager – and realizing that you will have too many things demanding your attention:

How will you decide which Activities you are going to focus on and intensively manage to make sure your Job gets done right?

CE 405 – SCHEDULINGCRITICAL PATH

Being able to calculate the Critical Path allows you to determine which Activities have to be complete when (Late Finish) in order to complete the Job within the time allocated.

CE 405 - SCHEDULING

Scheduling software allows you to calculate the Critical Path

What is your definition of a Critical Path?

CE 405 - SCHEDULING

Critical Path the sequence of Activities that will

have to be done chronologically – and on time – in order to complete the Project within the scheduled time.

CE 405 - SCHEDULING

Review:

What time units are you most likely to be working with when you are Scheduling a Construction Project?

CE 405 - SCHEDULING

Time units on a Construction Project?Whole Work Days – if it’s less than a

full day, you round it up (5½ = 6)Unless specifically noted, for the

remainder of the Semester, we will be talking about full work days.

CE 405 - SCHEDULING

If you have various subcontractors working on your Job – what two important pieces of Scheduling information are they going to be very interested in?

(not how much they are going to be paid)

CE 405 - SCHEDULING

If you have various subcontractors working on your Job – what two important pieces of information are they going to be very interested in?

When can they Start?When do they have to be Finished?

CE 405 - SCHEDULING

How do you determine when work on every Activity in your Schedule is planned to Start (i.e. what calendar date)?

CE 405 - SCHEDULING

Determine when work on every Activity is planned to Start?

You make a Forward Pass thru the Schedule

CE 405 - SCHEDULING

What is a Forward Pass?The process of calculating the

earliest time that each Activity on a Project can Start and Finish; thereby determining the minimum total duration [i.e. the longest sequence] of the Project.

CE 405 - SCHEDULING

Review:

What would be the beginning (Day 1) of your Forward Pass?

CE 405 - SCHEDULING

Review:What would be the beginning (Day 1)

of your Forward Pass?The normal beginning for most

Construction Projects is referred to as the Notice to Proceed (NTP) – when the Owner notifies the Contractor to start work.

CE 405 - SCHEDULING

What is the difference between the following three dates?

1. Bid Opening Date (or Submission of Proposal Date for RFP contracts)

2. Contract Award Date

3. Notice to Proceed Date

CE 405 - SCHEDULING

Bid/Proposal Opening Date/TimeFinal Day that the Owner will accept

bids/proposalsA Time (i.e. 2:00 P.M.) is usually

also stipulated, after which bids/ proposals will not be accepted

After bids are publicly opened, the apparent low bidder is identified

CE 405 - SCHEDULING

Contract Award Date – Hard BidAfter all the bids are checked for

compliance with the bid submission requirements, and arithmetic checked/mistakes corrected, the contract is awarded to the low bidder that survives this review.

CE 405 - SCHEDULING

Contract Award Date - ProposalsAfter all the proposals are reviewed

and evaluated – and the Owner has determined which is the Best Value, the proposing companies are told which Company was selected

CE 405 - SCHEDULING

What is the difference between a Hard Bid and a Best Value contract?

CE 405 - SCHEDULING

What is the difference between a Hard Bid and a Best Value contract?

Hard Bid – primarily public entities awarding to lowest price

Best Value – specific criteria used to evaluate/reject proposals – award to highest evaluation point value

Don’t confuse with “pure arbitrary”

CE 405 - SCHEDULING

Back to the original question - difference between the following three dates?

1. Bid Opening Date (or Submission of Proposal Date for RFP contracts)

2. Contract Award Date

3. Notice to Proceed Date?

CE 405 - SCHEDULING

Notice to Proceed DateThe Contractor receiving the Award

has to submit Performance and Payment bonds (Miller Act bonds on a Federal Government contract), as well as other “paperwork” (Minority Subcontracting Plan, etc.) before it is allowed to start work on the Job.

CE 405 - SCHEDULING

Notice to Proceed DateFor the sake of time allocated to

complete the contract (i.e. 400 days), the date of the Notice to Proceed (NTP) is the first day of the contract performance period – this is when the clock starts.

CE 405 – SCHEDULINGCOMBINATION CONVENTION

Combined Beginning-of-the-Day (BOTD) and End-of-the-Day (EOTD) conventions.

In order to conform Workdays into Calendar Days, Scheduling Software makes the math a little fuzzy

(Day 5 – Day 1 = 5 days), because Day 1 starts at 8:00 A.M. and Day 5 ends

at 5:00 P.M.

CE 405 – SCHEDULINGCOMBINATION CONVENTION

BOTD + EOTD ConventionsWhen you are making your Forward

Pass, you take the Start day, add the Activity duration (workdays), and then subtract one to get the Early Finish day.

Scheduling Concepts

• Calculates an activity’s early dates.

• Early dates are the earliest times an activity can start and finish once its predecessors have been completed.

• Early Start + Duration - 1 = Early Finish

Forward Pass:

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Scheduling Concepts

• For the following example, we will assume that reinforcing steel work (A) takes 5 days to complete, that the concurrent formwork (B) takes 10 days to erect, and that the concrete (C) must cure for 15 days before the forms and falsework can be removed.

Forward Pass:

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Forward pass

A

C

B

5

15

10

ES

EF

EF

ES

ES EF

55

1010

1111 2525

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11

11

CE 405 - SCHEDULING

Forward Pass After you complete the Forward

Pass thru your entire Schedule, the Early Finish Day for your last Activity (normally Project Complete) will be the minimum total duration for your Project.

CE 405 - SCHEDULING

Backward Pass If you have completed your

Forward Pass thru the network and know when each Activity should start and finish – why would you want to perform a Backward Pass thru your network?

CE 405 - SCHEDULING

The Backward Pass calculation allows you to determine the latest that an Activity can start without delaying the finish of the Project.

CE 405 - SCHEDULING

Backward PassThis is just the opposite of the

Forward Pass - when you are making your Backward Pass, you take the Finish day, subtract the Activity duration (workdays), and then add one to get the Late Start day.

• Calculates an activity’s late dates.

• Late dates are the latest times an activity can start and finish without delaying the end date of the project.

• Late Finish - Duration + 1 = Late Start

Backward Pass:

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A

C

B

5

15

10

ES 1

EF 25

EF 5

ES 11

ES 1 EF 10

LS LF

LFLS

LS LF

Backward pass

25251111

101011

101066

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CE 405 - SCHEDULING

Total FloatThe last calculation that you will

perform is the determination of the Total Float.

Total Float is the number of days that you have flexibility in starting or finishing an Activity without delaying the programmed finish date.

CE 405 - SCHEDULING

Total FloatTo determine the Total Float, you

take the information from your previously performed Forward and Backward Passes, and then determine the differences between either your Early and Late Start days, or your Early and Late Finish days.

CE 405 - SCHEDULINGTotal Float (TF) is computed by subtracting either the Early Start (ES) from the Late Start (LS) or the Early Finish (EF) from the Late Finish (LF):

TF = LS – ES

TF = LF – EF

CE 405 - SCHEDULING

Total FloatThe Critical Path is defined as the

continuous sequence of Activities that stretches the entire length of the Network where the Total Float for those Activities in that sequence is equal to zero.

CE 405 - SCHEDULING

Total Float – Continuous SequenceWhat does bifurcate mean?

CE 405 - SCHEDULING

Total Float – Continuous SequenceWhat does bifurcate mean?“To divide into two branches”

Critical Paths will occasionally bifurcate and you will then have parallel critical paths for a portion of your schedule.

A

C

B

5

15

10

ES 1

EF 25

EF 5

ES 11

ES 1 EF 10

LS 11 LF 25

LF 10LS 6

LS 1 LF 10

Backward pass

TF =

TF =

TF =

Forward pass

00

00

55

Critical Path

Critical Path

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Critical Path Method (CPM) Scheduling Review

• CPM software uses activity durations and relationships to calculate schedule dates – you will not “fix” an Activity’s start date.

• This calculation requires two passes through the activities within a project.

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Critical Path Review

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• The critical path is the longest continuous path of activities through a project that determine the project completion date

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

• Establishes the minimum total time to compete the contract.

Critical Path Review

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In order to compute the Critical Path, the two terms that you will need to understand are:

• Beginning of the Day (BOTD)

• End of the Day (EOTD)All Activities Start at the BOTD

and Finish at the EOTD (Activity Durations will be Whole Days.)

Critical Path Review

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In order to compute the Critical Path information for each Activity, you have to perform a Forward Pass thru the entire Schedule Network Diagram first, and then perform a Backward Pass thru the entire Schedule Network Diagram.

CRITICAL PATH REVIEWCritical Path Definition:The Sequence (Chain) of Activities that extends (unbroken) through the entire Project Schedule where the Total Float for all of the Activities is ZERO.

CRITICAL PATH SCHEDULING

Critical Path Definition:It is not unusual for portions of the Schedule to have more than one Critical Path (parallel Critical Paths) – it can “split” for awhile and then “rejoin” back into a single Critical Path again.

CRITICAL PATH SCHEDULING

Don’t try to be “smart” and submit a Schedule where all the Activities are shown as being on the Critical PathIt’s not unreasonable to have as many as 20% of the Activities on the Critical Path(s)

CRITICAL PATH SCHEDULING

If an Activity is shown to have zero Total Float, but the Activity is not in the Critical Path sequence – then there is a bust in the Contractor’s Critical Path computation

Scheduling SummaryThe forward pass calculates

early start and finish dates.The backward pass calculates

late start and finish dates.

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Scheduling SummaryTotal Float (TF) is the number of

workperiods that an activity’s early start can be delayed without delaying the end date of the project.

Late Dates – Early Dates TF = LS – ESTF = LF – EF

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