Transcript CE 405 - SCHEDULING

CE 405 - SCHEDULING
Review: Three fundamental steps in
developing a Schedule are:
1. Identify the Activities
2. Determine the Durations
3. Establish the Logical Interrelationships
 Activities, Durations, Logic
CE 405 - SCHEDULING
Activities, Durations, Logic
None of these three is really a
single, stand-alone operation
Experienced Schedulers often
think of these three processes as a
single process – especially the
relation of durations to logic
CE 405 - SCHEDULING
What is Logic in the context of a
Construction Schedule?
CE 405 - SCHEDULING
Logic is the relationship(s) that any
given Activity has with all the other
Activities in the Schedule.
1. What interaction does this Activity
have with the other Activities?
2. If you change when or how this
Activity is done – what happens to
the other Activities? – ripple effect
CE 405 - SCHEDULING
When you are developing the Logic of
your Schedule –
What is the primary consideration
that you will be addressing if you
want to get the work done as
expeditiously as possible regarding
each and every Activity?
CE 405 - SCHEDULING
Expedited Logic?
1. What Activities must be completed
before I can Start work on this
Activity
2. What Activities can be worked on
at the same time that I am working
on this Activity.
CE 405 - SCHEDULING
The three terms that pertain to the
Logic of your Schedule are:
1. Dependencies
CE 405 - SCHEDULING
The three terms that pertain to the
Logic of your Schedule are:
1. Dependencies
2. Sequential work
CE 405 - SCHEDULING
The three terms that pertain to the
Logic of your Schedule are:
1. Dependencies
2. Sequential work
3. Concurrent work
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What is your definition of
Dependencies in a Schedule?
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Definition of Dependencies?
What work (Activities) must be
completed before I can start work
on this Activity [Predecessors]
What work (Activities) can not start
until work on this Activity is
completed [Successors]
• Predecessor - controls the start
or finish of another activity
• Successor - depends on the
start or finish of another activity
Predecessor
to Act. B
Successor to
Act. B
10-3
CE 405 - SCHEDULING
What is your definition of
Sequence?
CE 405 - SCHEDULING
Definition of Sequence?
A group (string or chain) of
Activities that proceed in a logical
order – the preceding Activity has
to be Substantially Complete
before the follow-on Activity can
start
• Sequence – A group of Activities
that logically follow one after the
other
10-3
CE 405 - SCHEDULING
Review:
The term Substantially Complete
was used on the preceding slide –
what does it mean in relation to a
Construction Activity (not the job
as a whole)?
CE 405 - SCHEDULING
Substantially Complete is when
work on a given Activity has
proceeded to the point that work
on following Activities can Start.
Work on a CMU block wall can
start even if the forms have not
been stripped off the footings
CE 405 - SCHEDULING
What would be the Activity
Sequence for a CMU foundation
wall?
CE 405 - SCHEDULING
Activity Sequence for foundation wall?
1. Survey/Layout
2. Excavate
3. Form/Place Footing
4. Lay CMU block
 Each Successor Activity logically
follows the Predecessor Activity
CE 405 - SCHEDULING
The third term associated with logic
is concurrent – what does this
mean?
CE 405 - SCHEDULING
Definition of concurrent?
What other Activities can be
worked on at the same time that
work is proceeding on this
Activity?
• Concurrent Activities –
Activities that can be worked on
at the same time
Concurrent
Activities
10-3
CE 405 - SCHEDULING
Definition of concurrent?
After a building is dried-in and the
interior is painted – what would be
some of the concurrent Activities
that could be worked on?
First of all – what does dried-in
mean?
CE 405 - SCHEDULING
Dried-in definition?
All work necessary to “waterproof”
the interior is complete
Shingles are on, doors and windows
are in, siding/fascia/soffits are done,
etc.
CE 405 - SCHEDULING
What concurrent Activities can be
accomplished after the building is
dried-in and the sheetrock/painting
are done?
CE 405 - SCHEDULING
Concurrent Activities after dried-in?
1. Interior finishes – baseboard, trim
2. Finish electrical work/fixtures
3. Finish mechanical/HVAC
4. Finish plumbing
5. Cabinetry
6. Flooring
CE 405 - SCHEDULING
What three Scheduling Network
Systems are most commonly used
for Construction Projects?
CE 405 - SCHEDULING
3 Scheduling Network Systems?
1. Activity-on-Node (AON) [Chptr 6]
2. Activity-on-Arrow (AOA) [Chptr 7]
3. Precedence Diagramming Method
(PDM – leads, lags) [Chapter 17]
 All three use the Critical Path
Method (CPM)
CE 405 – SCHEDULING
CRITICAL PATH
Critical Path Method (CPM) handout
- Logic Boxes – numerous layouts
- Combination Convention
- BOTD + EOTD [Primavera]
CE 405 – SCHEDULING
CRITICAL PATH
Primavera Combination Logic:
BOTD and EOTD combined
Forward Pass: EF = ES + Dur – 1
Backward Pass: LS = LF – Dur + 1
Total Float: TF = LS – ES
or TF = LF – EF
Critical Path: Sequence where TF = 0
CE 405 - SCHEDULING
Network Model Characteristics:
1. Discrete Activities
2. Deterministic (vs Probabilistic)
Durations
3. Deterministic Logic
4. Activities “Flow” from Start to
Finish
CE 405 - SCHEDULING
What is the definition of
“deterministic”?
CE 405 - SCHEDULING
Definition of “deterministic”?
You have “pre-supposed” (i.e.
made your mind up) that things will
proceed in a preconceived manner
to an all ready decided end result
(i.e. a foregone conclusion)
Contrasted with “probabilistic”?
CE 405 - SCHEDULING
Definition of “probabilistic”?
The likelihood (statistical) that a given
alternative or option will happen
Construction Schedules require fixed
Start and Finish dates to enable all the
participants to Plan the progression of
their work
Deterministic = Reasonable Certainty
CE 405 - SCHEDULING
Network Elements:
1. Activities
2. Milestones
3. Activity Relationships (Logic)
CE 405 - SCHEDULING
Review:
What is a Milestone?
CE 405 - SCHEDULING
Review:
What is a Milestone?
A Milestone marks a “point-intime” – but unlike an Activity, it
does not consume any time within
a Construction Schedule
CE 405 - SCHEDULING
What are some examples of
Milestones that you might build
into your Schedule?
CE 405 - SCHEDULING
Examples of Milestones?
1. Notice to Proceed (NTP)
 Usually considered to be the first
day of your Schedule (Day 1)
CE 405 - SCHEDULING
Examples of Milestones?
1. Notice to Proceed (NTP)
2. Building “Dried-in”
CE 405 - SCHEDULING
Examples of Milestones?
1. Notice to Proceed (NTP)
2. Building “Dried-in”
3. Contract Substantial Completion
 Work on all Activities has progressed
to the point that the Project could be
used for its intended purpose
 Liquidated Damages not assessed
CE 405 - SCHEDULING
Examples of Milestones?
1. Notice to Proceed (NTP)
2. Building “Dried-in”
3. Contract Substantial Completion
4. Project Complete
 The Owner has accepted the work
and will make Final Payment
CE 405 - SCHEDULING
Activity-On-Node (AON) Networks:
AON Networks are normally
displayed as “boxes” connected
with “lines”. The “lines” indicate
some form of relationship between
the “boxes” at each end.
Red logic boxes
= Critical Path
“X-ed” boxes
means Activity is
complete.
CE 405 - SCHEDULING
Primavera software is based on the
generic Precedence Diagramming
Method (PDM).
CE 405 - SCHEDULING
Activity-On-Node (AON) Networks:
By definition – preceding
[Predecessor] Activities in an AON
network must Finish before the
following [Successor] Activity can
Start. This is described as a
“Finish-to-Start” relationship.
CE 405 - SCHEDULING
REVIEW:
What were the four types of Activity
Relationships that we covered
during the Bar Chart discussion?
CE 405 - SCHEDULING
Four types of Activity Relationships:
1. Physical
2. Safety
3. Resource
4. Preferential
CE 405 - SCHEDULING
What is a Constraint in a Scheduling
context?
CE 405 - SCHEDULING
What is a Constraint in a Scheduling
context?
 Something that controls the
accomplishment of an Activity
CE 405 - SCHEDULING
Were the four Activity “relationships”
that were just discussed potential
constraints (physical, resource,
safety, preferential)?
CE 405 - SCHEDULING
Were the four Activity “relationships”
that were just discussed potential
constraints (physical, resource,
safety, preferential)?
 Absolutely.
 What are some other common
constraints you will encounter?
CE 405 - SCHEDULING
Other common constraints?
1. Financial
 Does the Owner have sufficient
funding to pay for the work
 Do you (Contractor) have enough $
to buy materials and pay labor?
 Are your subs financially solvent?
CE 405 - SCHEDULING
Other common constraints?
1. Financial
2. Environmental –
 Spawning/Nesting periods
 Monsoon/Runoff periods
 Daily Noise Restriction timeframes
CE 405 - SCHEDULING
Other common constraints?
1. Financial
2. Environmental
3. Contractual –
 Required completion of one phase
before starting on another
CE 405 - SCHEDULING
Other common constraints?
1. Financial
2. Environmental
3. Contractual
4. Regulatory –
 Compliance with local, county,
state, or federal requirements
CE 405 - SCHEDULING
What are the impacts of these
common constraints?
1. Reduce Scheduling Flexibility
2. Lengthen Project Duration
3. Increase Project Cost
4. Complicate/Confuse your basic
Scheduling Logic
CE 405 - SCHEDULING
Every Baseline Schedule overlooks
some of these fundamental, basic
common constraints.
 One of the reasons that Schedules
have to be continuously updated.
CE 405 - SCHEDULING
What will be the Predecessor for
most of your initial Procurement
Activities (i.e. Prepare Shop
Drawings for Windows)?
CE 405 - SCHEDULING
Predecessor for most of your initial
Procurement Activities?
 Notice to Proceed
 The only initial constraint for most
Procurement Activities is having
the Owner tell you to start work
 Oftentimes you will start on your
Submittals before receiving NTP
ACTIVITY RELATIONSHIPS
Other Relationship Terminology
 Multiple Successors – “Merge”
 Multiple Predecessors – “Burst”
 Combinational Logic
MERGE
ACTIVITY RELATIONSHIPS
Think of a “Merge” as a “funnel”
where the whole Project “necksdown” (i.e. a bottleneck) and has
to flow through a single Activity.
 A “Merge” is also referred to as
“Multiple Predecessor Logic”
BURST
ACTIVITY RELATIONSHIPS
A “Burst” is just the opposite of a
“Merge” – once the Predecessor
Activity is substantially complete,
numerous other Successor
Activities can start.
 A “Burst” is also referred to as
“Multiple Successor Logic”
ACTIVITY RELATIONSHIPS
Logic Busts
1. Incorrect
2. Open-Ends
3. Redundant
4. Loops
ACTIVITY RELATIONSHIPS
Logic Busts
1. Incorrect – When your Schedule
shows that you will be painting a
wall before you hang and tape the
drywall – the Predecessor is not a
realistic constraint on the
Successor activity
ACTIVITY RELATIONSHIPS
Logic Busts
2. Open-Ends – Your Schedule
should always Start with one
single Activity (normally NTP);
and should always Finish with
one single Activity (normally
Project Complete).
ACTIVITY RELATIONSHIPS
Logic Busts
2. Open-Ends – When an Activity
does not have a Predecessor, the
Scheduling software default
assumption is that the Activity
starts on Day 1. This creates
unrealistic durations and does
not link Predecessor Activities.
ACTIVITY RELATIONSHIPS
2. Open-Ends – When an Activity does
not have a Successor, the Scheduling
software assumes that the required
Finish date is the last day of your
Schedule. This creates an unrealistic
duration and does not constrain
Successors that are dependent on
this Activity’s completion.
Open Ends continued:
10
70
FINISH
START
20
30
50
60
80
90
40
NOTE: Recommend that each project have only two open ends,
the NTP activity and the Project Complete activity.
11-10
Open Ends continued:
Oops!
Open
ends!
10
70
FINISH
START
20
30
50
60
80
90
40
Notice the relationship between activity 30 and 50 is missing,
creating two additional open ends.
What will happen when this network is scheduled?
11-10
Open Ends:
No predecessor - activity uses
Project start date as its early start
No successor - activity uses
project finish as its late finish
• Open ended activities can portray an
unrealistic amount of total float.
11-10
Open Ends continued:
Oops!
Open
ends!
10
70
FINISH
START
20
30
50
60
80
90
40
Activity 30 “thinks” it has until the end of the job to get done.
Activity 50 “thinks” it can start at the beginning of the job.
Both have an unrealistic amount of float.
11-10
ACTIVITY RELATIONSHIPS
Logic Busts
2. Open-Ends – Fortunately for you,
SureTrak provides an Error
Report that lists the Activities in
your Schedule with Open-Ends
ACTIVITY RELATIONSHIPS
Logic Busts
3. Redundant – Usually develops in
Sequential Activities where a
Predecessor is shown to not only
constrain the immediate
Successor, but also “Successorsto-the-immediate-Successor”
• Redundant Logic – When an
Activity is a Predecessor more
than once for an Activity that
occurs later in the Project
10-3
ACTIVITY RELATIONSHIPS
Logic Busts
3. Redundant – This becomes a
problem when you have to revise
your Schedule and you are
unaware or overlook the
secondary constraint
ACTIVITY RELATIONSHIPS
4. Loops – The infamous “Do Loop”
 As in “He’s stuck in a Do Loop.”
ACTIVITY RELATIONSHIPS
4. Loops – The infamous “Do Loop”
 It goes back to the Basic and
Fortran 4 programming languages
and “If-Do” commands.
 A common error caused the
computer to “run in a circle” that it
could not progress out of
Circular Relationships (Loops):
• Loops indicate circular logic between
two activities.
• Scheduling Software will not calculate a
schedule until the loop is eliminated.
SA1000
SA1010
SA1020
11-9
ACTIVITY RELATIONSHIPS
4. Loops – The infamous “Do Loop”
 Eventually the computer would
“Time-Out” and reject your program
 Then you would go thru your box of
computer cards, one-by-one, and try
to figure out where your error was
ACTIVITY RELATIONSHIPS
4. Loops – “Logic Loops” (Circular
Logic) are the same phenomenon,
but SureTrak again gives you an
Error Report that tells you which
Activities are the problem
 The computer is essentially just like
a dog “Chasing-its-tail”.
CE 405 - SCHEDULING
Activity Numbering
SureTrak automatically assigns
numbers to your Activities as you load
them into your Schedule. The default
spacing is an increment of 10.
Other than the fact that each Activity
will have a unique number, these
numbers are meaningless.
CE 405 - SCHEDULING
Activity Numbering
Don’t waste your time trying to
group your Activities by number –
there are much easier ways to do it
CE 405 - SCHEDULING
Activity Numbering
Work Breakdown Structures (WBS) –
many companies have elaborate,
extensive numerical coding systems
used primarily for accounting or to
develop historical estimating info.
Each company has its own “twist” on
these – we will not use them.
CE 405 - SCHEDULING
Activity Coding Systems
These are what we will use in
SureTrak to group, sort, organize,
prioritize – whatever you want to
do to select certain groups of
Activities for the purpose that you
need.
CE 405 - SCHEDULING
Activity Coding Systems
 You can assign Activity Codes at
any time to as many Activities that
you select – organizing your
Schedule this way gives you
infinite flexibility.
CE 405 - SCHEDULING
Activity Coding Systems
 SureTrak provides you with
numerous Activity Code groups and
you can also create your own
specialized Activity Codes
At the end of the Semester, we will
develop reports sorted and prioritized
by Activity Code
CE 405 - SCHEDULING
Activity Coding Systems
 Some common Activity Codes are:
1. Responsibility
2. Area/Phase
3. Trade
4. Department
CE 405 - SCHEDULING
Activity Coding Systems
 Each Activity Code can be broken
down further (SureTrak “Values”)
 Department could include:
1. Construction
2. Planning and Design
3. Purchasing
CE 405 - SCHEDULING
Responsibility could include:
1. Project Manager
2. Superintendent
3. Carpentry Foreman
4. Mechanical Subcontractor
5. Soil Testing Firm
 Whatever you need for the Job
CE 405 - SCHEDULING
Closing Comment
For your Schedule to be the effective
communication tool that it needs
to be, the logic has to be complete
and appropriately detailed so it
“flows” in a coherent manner for
everyone who uses it.