CE 405 - SCHEDULING
Review: Three fundamental steps in developing a Schedule are:
1. Identify the Activities
2. Determine the Durations
3. Establish the Logical Inter-relationships
Activities, Durations, Logic
CE 405 - SCHEDULING
Activities, Durations, LogicNone of these three is really a
single, stand-alone operationExperienced 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
CE 405 - SCHEDULING
What is your definition of Dependencies in a Schedule?
CE 405 - SCHEDULING
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 Predecessor to Act. Bto Act. B
Successor to Successor to Act. BAct. B
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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
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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 Concurrent ActivitiesActivities
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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 completeShingles 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, trim2. Finish electrical work/fixtures3. Finish mechanical/HVAC4. Finish plumbing5. Cabinetry6. 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 – SCHEDULINGCRITICAL PATH
Critical Path Method (CPM) handout
- Logic Boxes – numerous layouts
- Combination Convention
- BOTD + EOTD [Primavera]
CE 405 – SCHEDULINGCRITICAL PATH
Primavera Combination Logic:BOTD and EOTD combined Forward Pass: EF = ES + Dur – 1Backward Pass: LS = LF – Dur + 1Total Float: TF = LS – ES
or TF = LF – EFCritical 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 happenConstruction 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-in-
time” – 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 “necks-down” (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 Busts2. 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.
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10 70
80 9030 50 6020
40
Open Ends continued:
START
FINISH
NOTE: Recommend that each project have only two
open ends, the NTP activity and the Project Complete
activity.
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10 70
80 9030 50 6020
40
Open Ends continued:
START
FINISH
Notice the relationship between activity 30 and 50 is missing, creating two additional open ends. What will happen when this network is scheduled?
Oops! 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.
Open Ends:
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10 70
80 9030 50 6020
40
Open Ends continued:
START
FINISH
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.
Oops! Open ends!
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 “Successors-to-the-immediate-Successor”
• Redundant Logic – When an Activity is a Predecessor more than once for an Activity that occurs later in the Project
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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
• Loops indicate circular logic between
two activities.
• Scheduling Software will not calculate a
schedule until the loop is eliminated.
Circular Relationships (Loops):
SA100SA10000
SA102SA10200
SA101SA10100
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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 NumberingSureTrak 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 NumberingDon’t waste your time trying to
group your Activities by number – there are much easier ways to do it
CE 405 - SCHEDULING
Activity NumberingWork 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 SystemsThese 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 Manager2. Superintendent3. Carpentry Foreman4. Mechanical Subcontractor5. 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.