CE 405 – SCHEDULING
CRITICAL 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 – SCHEDULING
CRITICAL 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/Time
Final Day that the Owner will accept
bids/proposals
A 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 Bid
After 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 - Proposals
After 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 Date
The 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 Date
For 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 – SCHEDULING
COMBINATION 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 – SCHEDULING
COMBINATION CONVENTION
BOTD + EOTD Conventions
When 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
Forward Pass:
• 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
11-4
Scheduling Concepts
Forward Pass:
• 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.
11-4
A
ES 1
5
EF 5
C
ES 11
B
ES 1
15
EF 25
10
EF 10
Forward pass
11-4
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 Pass
This 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.
Backward Pass:
• 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
11-5
Backward pass
LS 6
LF10
A
ES 1
5
EF 5
LS11
LF 25
C
LS1
LF 10
B
ES 1
15
ES 11 EF 25
10
EF 10
11-5
CE 405 - SCHEDULING
Total Float
The 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 Float
To 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 - SCHEDULING
Total 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 Float
The 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 Sequence
What does bifurcate mean?
CE 405 - SCHEDULING
Total Float – Continuous Sequence
What 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.
Backward pass
LS 6
LF 10
A
ES 1
5
EF 5
LS 11 LF 25
TF =5
C
LS 1
LF 10
15
ES 11 EF 25
TF =0
B
ES 1
10
EF 10
TF = 0
Forward pass
11-7
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.
11-3
Critical Path Review
• 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.
11-3
Critical Path Review
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.)
11-3
Critical Path Review
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.
11-3
CRITICAL PATH REVIEW
Critical 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 Path
It’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 Summary
The forward pass calculates
early start and finish dates.
The backward pass calculates
late start and finish dates.
11-15
Scheduling Summary
Total 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 – ES
TF = LF – EF
11-15