scheduling. putting the activities in chronological order –chicken or the egg allows the pm to...

Scheduling

Scheduling

• Putting the activities in chronological order– Chicken or the egg

• Allows the PM to determine the time required to complete a project

Types of Schedules

• Depend on Viewer– Simple bar chart (Gantt chart)

• Tells owner progress– Activity on Node (AON)– Activity on Arrow (AOA)

• Used by PM, supers, foremen– Short term schedules

• Monthly , allows for close-up look at schedule

Developing Activity Sequence

• Physical Relationship• An activity cannot start until a previous one is complete

• Safety Relationship• Performing activities which cause a safety hazard to other

activities

• Resource Relationship• The amount of resources available at any time

• Preferential Relationship• Contractors preference on activity order

Constructing Bar Chart

• How should bar chart be laid out– Time on horizontal axis– Activity on vertical axis– Time of activity start based on position– Duration of activity based on length of line

• Day = start of day to start of day


• What time unit should be used– Work days– Hours– Weeks– What makes sense for your project– Bar chart size may dictate time units– Time unit dictates activity size


• Additional Info– Activity Value– Activity Cost– Activity Resource requirements


• Work days or Calendar days– Work days harder to follow

• No weekends or holidays– Calendar days allow you to see concrete curing

Gantt Chart

• Looks like a horizontal bar chart• Good for linear work• Good for providing an overview of the

project• Not good for complex projects

Gantt ChartID Task Name Duration1 Excavate foundation 2d

2 Form footings 1d

3 Pour footings 2d

4 strip footings 1d

5 Form foundation walls 1d

6 Pour foundation walls 3d

7 Strip forms 1d

8 Frame 1st floor 2d

9 Backfill foundation 1d

10 Frame 1st floor walls 2d

11 Frame 2nd floor 2d

12 Frame 2 floor walls 2d

13 Frame 2nd floor ceiling 1d

14 Frame roof 3d

15 Shingle roofing 4d

16 Rough plumbing 3d

17 Rough electric 3d

18 Insulation 2d

19 Drywall 3d

20

21

22

23

24

F S S M T W T F S S M T W T F S S M T W T F S S M T W T F S S M T W T F S S M T WApr 7, '02 Apr 14, '02 Apr 21, '02 Apr 28, '02 May 5, '02 May 12

Owner’s Chart

Activity Network Development

• Network Models• Activity on Node• Precedence Diagram Method• Activity on Arrow

• Network Characteristics• Discrete Activities• Deterministic Durations• Deterministic Logic• Activity Flow

Network Elements

• Activities• Basic building block• Represent tasks• Must consume time and resources

• Milestones• Notice to Proceed• Building Enclosed• Substantial Completion• Project Complete

• Activity Relationships• Physical, Safety, Resource, Preferential

Precedence

• Succeeding activities cannot start until preceding activities finished

• Changes in duration of one activity affect all succeeding activities

Activity on Node

• All activities occur at nodes• Arrows connect nodes and show

relationships

Activity on Node

• Basics:• Unique Alphanumeric identifier• Unique description• Estimated Duration• Succeeding activity cannot start until preceding

activity is finished• Need beginning and ending milestone to tie project

together

Constructing an AON Network

• Sequential logic– All activities preceding

must be finished before next activity can start

• Concurrent Logic– 2 or more activities can

be worked at one time

100Excavate Footings

2

110Form & Reinforce Ftg

2


2


2

120Install floor drains


• Multiple Successor Logic– 2 or more activities can be

worked at one time after common predecessor is finished

• Multiple Predecessor Logic– 2 or more activities need to

be finished before next activity starts


2


2



2


2



• Combinational Logic– 2 or more activities can

be worked at one time after multiple predecessor activities are finished


2


2

120Install f loor drains

115Trench for f loor drains

Logic Errors and Problems

• Incorrect Logic• Activities MUST have a logical connection• Paint color does not control the roofing application

• Redundant Logic– Not incorrect– Can cause errors


2


2

120Pour Footing

2

Logic Errors and Problems

– Logic Loops


2


2

120Pour Footing

2

Activity Numbering

• Numbering Activities can make it easier to use schedule

• Group like activities under the same general numbers– Activity Category

• WBS can make it easy to categorize resources used to each activity

– Work Classification• Numbers refer to a class of activity

Activity Numbering

– Location• Number activity based on location on project

– Responsibility• Numbers refer to who is responsible for work

Activity Numbering

• Numbering Conventions– Directional

• Numbers increase from start to finish of project– Numbering gaps

• Leave gaps between numbers to allow for additions to schedule

– Even/Odd Numbering• Even # = part of base contract• Odd # = additional work

Constructing a AON

• Determine the relationships between the activities

• Forward Pass– Determine when each activity can start based on

the finish of the predecessor activities• Backward Pass

– Determine when each activity can start based on when the successor activities start

Constructing a AONActivity Duration PredecessorsA 6B 4 AC 10 BD 10 CE 1 D,G,IF 6 AG 8 FH 10 AI 6 H

Constructing a AON

• Critical Path– Path through schedule which provides the shortest time

to complete project• Total Float

– Amount of time that activity can float without impacting CP

• Free Float– Amount of time an activity can be delayed without

effecting the early start date of the successor activity

Reviewing the Schedule

• Is Schedule complete• Are Activity Duration Reasonable• Are Activity Relationships Complete• Are Activity Relationships Valid• Is Project Calendar Correct• Is Schedule Duration within Contract Time• Are Contractual Milestones Met

Analyzing the Schedule

• Is Critical Path Reasonable• Are there Multiple Critical paths• What Activities are Near Critical• How does Work Flow• Are there Conflicts Among Concurrent

Activities• Is there an Excessive amount of Work at

any Time

Value Engineering

• Provides alternatives to the proposed design– Save Owner $$– Must be as good or better than original design– Must save enough $$ so that contractor can

recover his cost of doing VE– Usually comes from contractor’s or engineer’s

previous experience

Value Engineering

• Can save $$ either due to savings in time or materials– Ex: Composite Wall and roofs – Material cost per sf is higher than regular roof– Labor cost is lower– Requires a crane

Value Engineering

• Ex:– Replace infiltrators with Eljen In drains

• System size is reduced to 50%• Also reduces amount of sand, clay, topsoil• Reduces dozer time and installation time • In-drain costs about 2x infiltrator

Updating Schedule

• Frequency– Depends on

• Complexity– More complex -> more updates

• Unexpected events– Update after event to determine new completion date – Helps team evaluate strategies to mitigate impacts

• When specified– By contract documents

Updating Schedule

• How– Gather Activity Status Info

• Update Date – when the info is gathered• Activity status

– Actual start date – meaningful work begins– % complete

» Work in place -> work in place/planned work quantity» Time expended -> time expended/ planned duration (only

good for time dependent activities like concrete curing)» Cost Incurred - >cost incurred/planned cost (depends on

actual resource productivity being constant and resource costs not varying)

» Resource used -> Resource Used/Planned resource amount

Updating Schedule

• How– Activity status

– Remaining duration – Remaining Work quantity/Anticipated Productivity

– Actual finish date – all completed activities» Provides data for future jobs

– Gathering Data• Direct observation, Update meetings, field reports,

turnaround reports, photos and videotape

Analyzing Schedule Status

• What is the basis for evaluating schedule status?– Usually the original schedule is the baseline

• What is planned completion date– Is updated schedule completion date same as

baseline• If not – why not (is there an error)

Analyzing Schedule Status

• Has the critical path shifted?– If so – why– Are CP activities really “critical”

• Has the float changed on any activities?• Has weather become a factor for any

activity• Are there trends worth watching• Any changes since last update?

Modify and Revise Schedule

• Revise network logic– Change duration to meet contracted completion– Reflect changes in planned means and methods

for completing activity– Shift activity to better time (summer for

concrete)

Modify and Revise Schedule

• Revise Activity Durations– Planned quantity of work has changed– Amount of resources has changed– Productivity is either higher or lower than

planned• Add & Delete Activities

– Scope of work changed– Activities divided into smaller activities

Review and Analyze Schedule

• Make sure new schedule does not contain errors

• Implement updated schedule

Out of Sequence Work

• Why?– Keep crews busy– Preparatory work starts early

• Gives crew a chance to test means and methods

• Preserve Schedule Logic– Shorten successor activity caused by out of sequence

work– Keep all other logic intact

scheduling. putting the activities in chronological order –chicken or the egg allows the pm to...

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