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

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 Concurrent ActivitiesActivities

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 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.

11-10

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.

11-10

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:

11-10

11-10

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

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

• 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

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 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.