11

EASTERN MEDITERRANEAN UNIVERSITYEASTERN MEDITERRANEAN UNIVERSITYFACULTY OF ENGINEERINGFACULTY OF ENGINEERING

DEPARTMENT OF CIVIL ENGINEERINGDEPARTMENT OF CIVIL ENGINEERING CIVL CIVL 449393 Construction Management Construction Management

Assoc. Prof. Dr. Ibrahim YITMEN

Project Scheduling

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Introduction to SchedulingIntroduction to Scheduling

Why We Need a Schedule:Why We Need a Schedule: Contractual obligationContractual obligation To establish a sequence of work and timeframe To establish a sequence of work and timeframe

for performance of construction activitiesfor performance of construction activities To provide a communication tool between To provide a communication tool between

contractors, owner, A/E, subs, and supplierscontractors, owner, A/E, subs, and suppliers To document modifications (“as-planned” To document modifications (“as-planned”

versus “as-built”)versus “as-built”) To show the impact of productivity-related To show the impact of productivity-related

problems on project completion (weather, problems on project completion (weather, strikes, delays)strikes, delays)

Determine when to order and deliver materials Determine when to order and deliver materials and equipmentand equipment

33

Types of SchedulesTypes of Schedules

Bar ChartBar Chart Often called Gantt ChartOften called Gantt Chart

Network DiagramsNetwork Diagrams Arrow DiagramArrow Diagram Precedence DiagramPrecedence Diagram Often called Critical Path Method (CPM)Often called Critical Path Method (CPM)

44

Formats of SchedulesFormats of Schedules

Summary scheduleSummary schedule Shows major work elements, such as sitework, Shows major work elements, such as sitework,

masonry, carpentry, electrical, plumbing, etc.masonry, carpentry, electrical, plumbing, etc.

Detailed scheduleDetailed schedule Work should be broken down into activities that Work should be broken down into activities that

comprise not more than 5% of total projectcomprise not more than 5% of total project

Short-interval scheduleShort-interval schedule Identifies work for upcoming 2-3 weeksIdentifies work for upcoming 2-3 weeks Usually prepared by superintendentUsually prepared by superintendent

55

Bar ChartBar Chart

Developed by Henry GanttDeveloped by Henry Gantt Often called a Gantt ChartOften called a Gantt Chart

DefinitionDefinition A graphical description of a project consisting of A graphical description of a project consisting of

well-defined collection of taskswell-defined collection of tasks

66

Activities are represented by bars in Activities are represented by bars in proportion to their durationproportion to their duration An activity is a task or closely related group of An activity is a task or closely related group of

tasks whose performance contributes to the tasks whose performance contributes to the completion of the overall projectcompletion of the overall project

Example: Excavate foundationExample: Excavate foundation

Activities are represented by bars in Activities are represented by bars in proportion to their durationproportion to their duration

Bar chart is usually graphed on a calendarBar chart is usually graphed on a calendar

Can be as simple or detailed as necessaryCan be as simple or detailed as necessary

Bar ChartBar Chart

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Example Bar ChartExample Bar Chart

June July August September October

Excavation & Backfill

Pilling

Abutment No.1

Abutment No.2

Steel girders

Concrete deckFinishing operations

Time

88

Constructing a Bar ChartConstructing a Bar Chart

When constructing a bar chart, the following When constructing a bar chart, the following questions must be answered:questions must be answered: What time units should be used? (days, weeks, What time units should be used? (days, weeks,

months)months) Should work days or calendar days be used?Should work days or calendar days be used? How do I schedule non-continuous work?How do I schedule non-continuous work?

Additional information may be added to the Additional information may be added to the basic bar chart basic bar chart Cost of activity (“cost-loaded schedule”)Cost of activity (“cost-loaded schedule”) Labor required for each activity (“man-loaded”)Labor required for each activity (“man-loaded”) Materials required for each activity (“resource-Materials required for each activity (“resource-

loaded”)loaded”)

99

Steps to Construct a Bar ChartSteps to Construct a Bar Chart

Three basic steps to construct a bar Three basic steps to construct a bar chart:chart:

1.1. Break the job down into activitiesBreak the job down into activities

2.2. Establish the sequence of workEstablish the sequence of work

3.3. Estimate activity durationEstimate activity duration

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1. Break the Job Down Into 1. Break the Job Down Into ActivitiesActivities

Use the Work Breakdown Structure Use the Work Breakdown Structure (WBS) from the cost estimate(WBS) from the cost estimate

Add activities as necessaryAdd activities as necessary

Rule of thumb: Rule of thumb: no activity should no activity should comprise more the 5% of the total scope comprise more the 5% of the total scope of workof work

Rule of thumb: Rule of thumb: activity duration should activity duration should range from 1 day to 15 daysrange from 1 day to 15 days

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Sequencing needs to take into account the Sequencing needs to take into account the relationships between activitiesrelationships between activities

There are four types of relationships that There are four types of relationships that need to be taken into account.need to be taken into account.

1.1. Physical:Physical: Exists between two or more activities when one Exists between two or more activities when one

cannot start until another is partially or totally cannot start until another is partially or totally complete (i.e., cannot pour footings until they complete (i.e., cannot pour footings until they have been formed)have been formed)

2. Establish the Sequence Of 2. Establish the Sequence Of WorkWork

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2.2. Safety:Safety: Exists when simultaneous performance of two Exists when simultaneous performance of two

activities can result in a safety hazard (i.e., in activities can result in a safety hazard (i.e., in multi-story construction it is at times unsafe for multi-story construction it is at times unsafe for crews to be working under one another)crews to be working under one another)

3.3. Resource:Resource: Due to limited resource availability, two Due to limited resource availability, two

activities may not be able to use a resource at activities may not be able to use a resource at the same time (i.e., a crane cannot be used for the same time (i.e., a crane cannot be used for both pouring walls and erecting steel)both pouring walls and erecting steel)

4.4. Preferential:Preferential: How the contractor wishes certain activities to How the contractor wishes certain activities to

be sequencedbe sequenced

2. Establish the Sequence Of 2. Establish the Sequence Of Work (continued)Work (continued)

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3. Estimate Activity Duration3. Estimate Activity Duration

How to estimate duration:How to estimate duration:

From company’s historic recordsFrom company’s historic records

From asking superintendent or foremanFrom asking superintendent or foreman

From standard estimating guideFrom standard estimating guide

From calculation using the Labor Hour From calculation using the Labor Hour Productivity equationProductivity equation

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Labor-Hour Productivity MethodLabor-Hour Productivity Method

Total labor-hours required for an activity = Total labor-hours required for an activity = labor-hours /Unit x no. of unitslabor-hours /Unit x no. of units

Total days = Total days =

Total days =Total days =

total labor hourslabor-hours / day

total labor hourscrew size x hrs/day

3. Estimate Activity Duration 3. Estimate Activity Duration (continued)(continued)

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Using a Bar Chart for Planning Using a Bar Chart for Planning and Progressand Progress

Assume the progress of the activity as a Assume the progress of the activity as a direct linear function of the elapsed timedirect linear function of the elapsed time

Example:Example:Duration(Days) Amount Units 3/30 4/6 4/13 4/20 4/27 5/4 5/11 5/18 5/25 6/1 6/8 6/15 6/22 6/24 7/6 7/13 7/20 7/27 8/3

1 Move-in 5 -

2 Clear & Grub 20 SF

3 Earth moving 60 CY

4 Site Grading 45 SF

5 Subbase 45

6 Base 25

7 Paving 25

QuantityNo Acitivity

Week Ending

5/1R eporting

date

M em oria l dayholiday

W ork p lanned

W orkcom pleted

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Bar Chart Progress ScheduleBar Chart Progress Schedule

Bar chart progress schedule should satisfy Bar chart progress schedule should satisfy the following minimum requirements:the following minimum requirements:

Include activities that describe essential Include activities that describe essential features of the work.features of the work.

Include start, duration, and completion date for Include start, duration, and completion date for each activity.each activity.

Include quantity and the estimated daily Include quantity and the estimated daily production rate for controlling items of work.production rate for controlling items of work.

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DefinitionDefinition A network consists of two basic elements, A network consists of two basic elements,

nodes and links between these nodesnodes and links between these nodes

Activities on arrows (arrow diagram)Activities on arrows (arrow diagram) Activities are represented by two nodes Activities are represented by two nodes

and one linkand one link

Activities on nodes (precedence diagram)Activities on nodes (precedence diagram) Activities represented by nodes and links Activities represented by nodes and links

represent the relationshiprepresent the relationship

Network DiagramsNetwork Diagrams

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Clear and grub

Cut and fill

Arrow Diagram

Excavate and form culvert

Place base

Construct culvert

Pave

Excavate and form

culvert

Pave

Constructculvert

Placebase

Cut and

fill

Clear & grub

Precedence Diagram

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Example: Retaining Wall Example: Retaining Wall Precedence DiagramPrecedence Diagram

Wall 1

Wall 2

Footing 1

Footing 2

10

Footing 1

20

Footing 2

40

W all 2

30

W all 1

2020

Basic Rules of Network Logic Basic Rules of Network Logic (Precedence Diagram)(Precedence Diagram)

20

A

30

B

40

C

(a) Incorrect Representation

20

A

30

B

40

C

(a) Correct Representation

Rule 1Rule 1: Eliminate redundant linkages: Eliminate redundant linkages

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Rule 2Rule 2: Close the network to give single : Close the network to give single beginning and ending nodesbeginning and ending nodes Networks may have only one Networks may have only one initialinitial event (with no event (with no

predecessor) and only one predecessor) and only one terminalterminal event (with no event (with no successor).successor).

Basic Rules of Network LogicBasic Rules of Network Logic

A

B

D

C E

InitialEvent

Correct Representation

Terminal Event

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Rule 3Rule 3: Before an activity may begin, all : Before an activity may begin, all activities preceding it must be completed activities preceding it must be completed (activities with no predecessors are self-(activities with no predecessors are self-actuating when the project begins).actuating when the project begins).

Rule 4Rule 4: All relationships are assumed to be : All relationships are assumed to be finish to start. finish to start.

Rule 5Rule 5: Event numbers must not be : Event numbers must not be duplicated in a network.duplicated in a network.

Rule 6Rule 6: No two events may be directly : No two events may be directly connected by more than one arrow.connected by more than one arrow.

Basic Rules of Network LogicBasic Rules of Network Logic

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a) Finish-to-start relationshipa) Finish-to-start relationship(Start of B must lag 5 days after the finish of A)(Start of B must lag 5 days after the finish of A)

b) Start-to-start relationshipb) Start-to-start relationship(Start of B must lag 3 days after the start of A)(Start of B must lag 3 days after the start of A)

Activities RelationshipsActivities Relationships

A BL = 5or FS =5

A

BL = 3

or SS =3

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Activities RelationshipsActivities Relationships

c) Finish-to-finish relationshipc) Finish-to-finish relationship(Finish of B must lag 3 days after the finish of A)(Finish of B must lag 3 days after the finish of A)

d) Start-to-finish relationshipd) Start-to-finish relationship(Finish of B must lag 45 days after start of A)(Finish of B must lag 45 days after start of A)

A

B

L = 3or FF =3

A B

L = 45or SF = 45

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Sequencing and NumberingSequencing and Numbering

10

A

15

D

25

E

20

C

30

F

5

Start

35

Finish

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Constructing a Precedence Constructing a Precedence DiagramDiagram

1.1. Create activity list and eliminate Create activity list and eliminate redundanciesredundancies

2.2. Construct precedence diagramConstruct precedence diagram

3.3. Arrange activities in a sequential order.Arrange activities in a sequential order.

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Time Values Associated With Time Values Associated With Each ActivityEach Activity

1.1. ESDESD Early Start Date Early Start Date

2.2. EFDEFD Early Finish Date Early Finish Date

3.3. LSDLSD Late Start Date Late Start Date

4.4. LFDLFD Late Finish Date Late Finish Date

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Scheduling ComputationsScheduling Computations(Forward Pass Rules)(Forward Pass Rules)

Rule 1:Rule 1: The initial project event is assumed to occur The initial project event is assumed to occur

at time zero.at time zero.

Rule 2:Rule 2: All activities are assumed to start as soon All activities are assumed to start as soon

as possible, that is, as soon as all the as possible, that is, as soon as all the

predecessor activities are completed.predecessor activities are completed.

Rule 3:Rule 3: The early finish time of an activity is merely The early finish time of an activity is merely

the sum of its early start date and the the sum of its early start date and the

estimated activity duration.estimated activity duration.

EFDI= ESDI + TI

Four rules of completing a Forward Pass:Four rules of completing a Forward Pass:

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Scheduling ComputationsScheduling Computations(Forward Pass Rules) – cont.(Forward Pass Rules) – cont.

Rule 4:Rule 4: At merge points, the early start is the largest At merge points, the early start is the largest

value of the preceding early finish time.value of the preceding early finish time.

2

EFD=6

4

EFD=9 6

EFD=9

Forward

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Scheduling ComputationsScheduling Computations(Backward Pass Rules)(Backward Pass Rules)

Rule 1:Rule 1: The late finish date of the last activity is The late finish date of the last activity is

equal to its early finish date.equal to its early finish date.

Rule 2:Rule 2: The late start date for any activity is found The late start date for any activity is found

by subtracting the activity duration from its by subtracting the activity duration from its

late finish date.late finish date.

LSDI= LFDI - TI

Three rules of completing a Backward Three rules of completing a Backward

Pass:Pass:

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Scheduling ComputationsScheduling Computations(Backward Pass Rules) – cont.(Backward Pass Rules) – cont.

Rule 3:Rule 3: In the backward pass, the late finish date of In the backward pass, the late finish date of

an activity is the smallest late start value of an activity is the smallest late start value of

the following activities.the following activities.

12

LSD=37

14

LSD=42

10

LFD=37

Backward

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The Float ConceptThe Float Concept

What is “float”?What is “float”? Float or slack is the amount of scheduling Float or slack is the amount of scheduling

leeway that a network activity hasleeway that a network activity has

What is “total float”?What is “total float”? That time span in which the completion of an That time span in which the completion of an

activity may occur and not delay the activity may occur and not delay the completion of the projectcompletion of the project

Equation for total float (TF):Equation for total float (TF):

TFTFII = LFD = LFDII - EFD - EFDII

= LSD= LSDII - ESD - ESDII

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What is “free float”? What is “free float”? The time span in which the completion of an The time span in which the completion of an

activity may occur and not delay the finish of activity may occur and not delay the finish of the project or delay the start of any following the project or delay the start of any following activityactivity

What is a link lag?What is a link lag? The difference between the early start date of The difference between the early start date of

an activity and the early finish date of the an activity and the early finish date of the preceding activitypreceding activity

The Float Concept (cont.)The Float Concept (cont.)

Lagij= ESDj - EFDi

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How to determine free float:How to determine free float: Free float is the minimum value of the link lags Free float is the minimum value of the link lags

of the link that follows an activity.of the link that follows an activity.

FFFF2020 = Min = Min

= Min= Min

= 1= 1

FloatFloat20-2520-25

FloatFloat20-3020-30

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1 1

{ }{}

The Float Concept (cont.)The Float Concept (cont.)

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Critical Path ExampleCritical Path Example

10

B

4 8 12

124

15

C

9 3 12

74

25

E

12 7 19

1912

20

D

10 2 12

64

30

F

14 5 19

127

5

A

0 4 4

40

35

G

19 1 20

2019

1

7

6

5

1 2 3 4

Sequence Step

FF=0T F=0

FF=1T F=6

FF=0T F=5

IN T F=5

FF=0T F=0

FF=0T F=0

FF=7T F=7

FF=0T F=0