Wollo University

Institute of Technology
Department of Construction
Technology and Management

Construction Planning and Scheduling

CoTM-4211

Ali H.
1
 Construction Planning and
Scheduling

Chapter Three: Construction Scheduling

Fundamentals

 Creating the Schedule

 Network Scheduling and PDM, PERT, CPM

 Scheduling with Resource Constraints

2
Project scheduling is the determination of the timing and sequence
of operations in the project and their assembly to give the overall
completion time.
 At this stage, managers decide how long each activity will take and
compute how many people and how much material will be needed
at each stage of construction.
Why scheduling???
 Shows the relationship of each activity to others and to the project
as a whole
 Identifies the precedence relationships among activities
 Encourages the setting of realistic time and cost estimates for
each activity
 Helps make better use of people, money, and material resources by
identifying critical bottlenecks.
3
 Construction Scheduling Fundamentals

• Principal use of scheduling for different phases:

1. Before Starting
• Provides an estimate of time required for each
portion of the project as well as for the total project
[in both rough and detail].
• Establishes the planned rate of progress in terms of
phases or operations
• Forms the basis for managers to issue instructions to
subordinates
• Establishes the planned sequence of operations for
the use of manpower, materials, machines and money.
4
Construction Scheduling Fundamentals
2. During Construction
• Enable the manager to prepare check list of key dates,
activities, resources, and soon.
• Provides a means of evaluating the effect of changes
and delays measurement
• Serves as the basis for evaluating progress
• Aids for coordination of resources.
3. After completion of construction
• Permits a review and analysis of the project as actually
carried out on the bases of plan
• Provide historical data for improving future planning
and estimating.
5
 Creating the Schedule

• Scheduling can be classified or created as

follows:

1. Construction schedule

2. Material Schedule

3. Labour Schedule

4. Equipment schedule

5. Financial Schedule
6
 Creating the Schedule
1. Construction Schedule
• It describes:
• the Quantity/Volume of work,
• rate of completing the work,
• number of manpower required (both skilled and
unskilled)
• number and type of equipment needed and
• interrelationship of various operations
• Therefore the sequence of various operations is
given the date of completion of each operation.
7
 Creating the Schedule
2. Material Schedule
• It is a schedule which shows the dates of delivery and
storing of each type of material at site.
• The materials should be delivered at the project site before
it is needed.
• An excessive and early delivery is not desirable.
Item Description of Unit Total Month of year
No. material quantity October November
Week
1 2 3 4
1 Cement bags 100 150 150 200

Material delivery schedule format

8
 Creating the Schedule

3. Labour Schedule
• It will indicate the nature and quantity of labour required for the
execution of different operations on different dates during certain
weeks.
• The Project Manager/Engineer should arrange the labour in such
away so that there are minimum labour fluctuations.

Item Activities Weeks

No 1 2 3 4 5 6 7 8
1 Excavation 15 10
Bar chart
2 Foundation 10 10 6
3 Walls 15 15 15 10
4 Roof Slabs 8
5 Plastering 8
Total 15 20 25 21 15 18 8
Labour requirement schedule format
9
 Creating the Schedule

4. Equipment Schedule:
• Equipment schedule shows the types and quantities of
equipment required on particular dates in the entire project
based on the planned productivity.

Item Type of Months of the year on which equipment required (2005)

No Equipment Sep. Oct. Nov. Dec. Jan. Feb.
1 Bulldozer 1 1 1
2 Grader 1 1 1 1
3 Dump trucks 3 3 4 3 3 3

Equipment Schedule Format

10
 Creating the Schedule
5. Financial Schedule
• Financial schedule shows the flow of money into a
project.
• A construction schedule may be used to estimate the
amount of funds that a contractor must provide in
financing a project during construction.

Weeks after Activities under construction Expenditure per Cumulative

starting week expenditures
1 Excavation $6000 $6000
2 Lean concrete, Rebar, formwork $10,000 $16,000
& concrete
Financial Schedule Format
11
Plans involve four main steps:
1. Performing breakdown of work items involved
in the project into activities.
2. Activities representation
3. Identifying the proper sequence by which the
activities should be executed.
4. Estimating the resources, time and cost of
individual activities.

12
The WBS is described as a hierarchical structure which is
designed to logically sub-divide all the work-elements of the
project into a graphical presentation.
 The full scope of work for the project is placed at the top
of the diagram, and then sub-divided in to smaller elements
of work at each lower level of the breakdown.
 Effective use of the WBS will outline the scope of the
project and activities.
 The following illustrative example shows the „whole to
part‟ relation between the project , sub- projects, tasks,
work packages and activities for the construction of a
house construction project.

13
To the level that estimates and forecasts about the resources
required, durations and activity relationships are realistically
estimated for each activity;
– Project level
– Sub-project level: Sub projects are derived by dividing a
large project, usually termed a program, into independent
large-volume mini projects.
– Task level: A task is an identifiable and deliverable major
work which can be performed without major interference
from other tasks.
– Work package level: A work package contains a sizeable,
identifiable, measurable, cost able and controllable package
of work.
– Activity level: An activity is a sub division of a work
package and is defined as a work which has a definite start
and end and consumes resources.
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 Real Estate Development Mega project
(Program)

Residential Buildings Service Buildings Recreation Centers

Sub projects

Educational Buildings Health Centre Shopping centre

Tasks
Sub structure Super Structure Roofing Finishing

Excavation and
Earth work Footing Con Plinth wall Con Ground floor Con Work package

Excavation Earth work

Activities

Bulk excavation Pit Excavation Trench Excavation

15
  Pictorially
Text Indention House project
 A house project
 Civil work Civil work Plumbing Electrical

 Sub structure Sub

Super structure
» Site Clearing structure

» Excavation Site clearing

» Foundation
work Excavation

 Form Work
Foundation
 Rebar fixing work
Form work
 Concert
casting Concrete work

 Super structure
Rebar Work

16
Activity
• Production activities:
 Activities that involve the use of resources such as labor, equipment or
material. (e.g.: excavation, formwork, reinforcement, concreting, etc.)
 Each production activity can have a certain quantity of work, resource
needs, costs, and duration.
• Other activities are:
– Procurement activities
– Management activities
Activity relationships
Is determining
 Which activities must be finished before the current can start?
 What activity(ies) may be constructed concurrently with the current one?
 What activity(ies) must follow the current one?

17
Relationships are defined from the predecessor to the successor
activity. Four types of relationships exist:
A) Finish to start (FS)
The successor activity can begin only when the current activity
completes.
Example: the plaster must be finished before the tile can start.

Plaster Tile

18
 Types of activities relationships
B) Finish to finish (FF)
 The finish of the successor activity depends on the finish
of the current activity.
 Can be used where activities can overlap to a certain
limit.
Erect Remove
scaffolding Old paint

Smoothing
FF
/1
FF Dismantle
painting
/2 inspect scaffolding

19
C) Start to Start (SS)
 The start of the successor activity depends on the start of
the current activity.

Clean Spread
surface grout

SS

Set Clean floor

tile area

20
D) Start to Finish (SF)
 The successor activity cannot finish until the current
activity starts .
 Not Common
 Typically used with delay time or lag.

Erect Steel Pour

formwork reinforcement concrete

SF
Order
concrete

21
 Scheduling Techniques
• A variety of Scheduling techniques are available of
which only three are to be outlined indicating the
advantages and disadvantages and the most application
in practice.
 The Bar Charts
 The Networking Schedule Technique
1. The Critical Path Method (CPM),
2. The Precedence Diagramming Method
(PDM)
3. The Performance Evaluation & Review
Technique (PERT)

22
 Gantt or bar chart is a popular tool for planning and
scheduling simple projects.
 They give an idea of duration of activities / project
and hence can be useful in preparing strategy for
working.
 In a bar chart the activities are shown as horizontal
bars on a horizontal time scale, where the start and end
locations of the bars coincide with the start and finish
dates of the activities.
 A bar chart representation of the illustrative example
given in Figure below
 Gantt charts, though, do not adequately illustrate the
interrelationships between the activities and the
resources. 23
 Gantt (Bar) Chart structure:
tas
Tk 1

T 2

T 3

T 4

T 5

T 6

T 7

T 8

T 9

day 0 day 1 day 2 day 3 day 4 day 5 day 6 day 7 day 8 day 9 day 10

tim
Task and its duration e

24
 Gantt (Bar) Chart structure:
tas
Tk 1

T 2

T 3

T 4

T 5

T 6

T 7
T 8

T 9

day 0 day 1 day 2 day 3 day 4 day 5 day 6 day 7 day 8 day 9 day 10

tim
Phases, tasks groups: e

25
 Gantt (Bar) Chart structure:
tas
Tk 1

T 2

T 3

T 4

T 5

T 6

T 7
T 8

T 9

day 0 day 1 day 2 day 3 day 4 day 5 day 6 day 7 day 8 day 9 day 10

tim
e

26
 Gantt (Bar) Chart structure:
tas
Tk 1 100% complete
T 2 80%

T 3 100%

T 4

T 5 0%
T 6

T 7
T 8

T 9

day 0 day 1 day 2 day 3 day 4 day 5 day 6 day 7 day 8 day 9 day 10

tim
e
Project performance analysis

27
Draw the Gantt (bar) chart and estimate the total
duration for the following activities:
Activity description Duration predecessors
A Site clearing 1 -
B General excavation 2 A
C Excavation for utility 2 B
trenches
D Placing formwork and 3 B
reinforcement bars
E Installing sewer lines 3 C
F Installing other utilities 3 C
G Pouring concrete 2 D,E

28
Activity

A

B

C

D

E
F

G

day 0 day 1 day 2 day 3 day 4 day 5 day 6 day 7 day 8 day 9 day 10

time

29
 The Network Diagram is essentially a flowchart of the project
tasks.
 A project network is asset of arrows and nodes.
 Network diagrams are the preferred technique for showing
activity sequencing.
 The critical path method (CPM) and program evaluation and
review technique (PERT) are two of the most widely used
network techniques.
 When task durations are uncertain, the Network Diagram is
often a better technique to use than the Gantt (bar) chart.
 The Network Diagram shifts the focus for uncertain tasks from
arbitrary start and end dates to completion of the work and a
handoff to the next task/activity.
 There are two ways that are commonly used to draw a network
diagram for a project 30
 AOA: Activity on Arrow

 AON: Activity on Node



31
 Also called arrow diagramming method (ADM)
network diagram or (I‐ J) method (because activities
are defined by the form node, I, and the to node, J)

 Activities are represented by arrows.

 Nodes or circles are the starting and ending points of

activities.

 It can only show finish‐ to‐ start dependencies

32
33
34
35
36
Information required for drawing networks

 List of individual activities

 Activity interdependencies

 Activity time estimates.

Ground rules for developing a network :

 Each event should have preceding and succeeding

event

 Commencement completion

 Events should have a distinct number 37

 The dummy activity is an activity with zero duration,
consumes no resources, drawn as dashed lines, and used to
adjust the network diagram.

 A dummy activity is also used when one activity depends

upon two preceding activities and another activity depends
only upon one of these two preceding activities.

38
A B
A must finish before either B
C or C can start

A
C both A and B must finish
B before C can start

A C both A and B must finish

before either of C or D can
B D start

A B
Dummy A must finish before B can
start; both A and C must finish
C
D
before D can start
39
 The Network must have definite points of beginning and
finish.

 There should not be a loop formation in a network, No

activity should lead back to previous activity “No looping”

wrong

40
Not more than one activity should have the same preceding
and succeeding events, i.e. only one activity may connect any
two events.
wrong

 To ensure that each activity is uniquely numbered, it may

be necessary to introduce dummy activity

41
42
 Draw the arrow network for the project given next.

43
44
 Draw the arrow network for the project given next.

45
46
47
AON: Activity on Node

 A matter of preference which one to use

 Each activity labeled with Identifier (usually a

letter/code) and duration (in std. Unit like days)

 There is one start & one end event

 Time goes from left to right

48
Activity A B C D E F G H I J k

Predecessor - - A B B A C D A G, H, E J, F, I

I

A F K

Start C G Finish

B D H J

E

Activity on Node(AON) Network

49
Draw a network by using both AON and AOA.
Activity description Duration predecessors
A Design house and obtain 3 -
financing
B Lay foundation 2 A
C Order and receive 1 A
materials
D Select paint 1 B,C
E Build house 3 B,C
F Select carpet 1 D
G Finish work 1 E,F

50
AOA Project Network for House
3
Dummy
B
2 0
3 1 E G
1 2 4 6 7
A C 3 1
D1 1 F

5
AON Project Network for House
B E
2 3
G
Sta A 1
rt 3
C F
1 D 1
1

51
Critical path method
(CPM)

52
Critical activity:
Any delay on the start or finish of a critical activity
will result in a delay in the entire project.
Critical path:
 It represents a series of activities for which each
activity is a Critical activity (zero float time).
 longest time for the project from start to its
completion and decides the time of complet
ion of the project

53
 Major steps in CPM
CPM includes four main steps:
1. Determine the work activities:
 project breakdown
 Project must be divided into smaller activities or tasks (WBS)
 Prepare a list of all activities.
2. Determine activity duration
 Durations are calculated in workdays, (calendar) (“a 5 or 6-work day
/week”)
 The time required to complete an activity should depend not only on the
quantum of work to be executed (Q) but also the resources allocated (R)
and the (unit) productivity of the resources (P).
 Sources of crew productivity data
 From company‟s record
 From standard estimating guide
 Interviewing field personnel
 Consider non-work days, such as holidays, rain (weather) days
54
 Simply put, the time required (T) to complete an
activity can be calculated using the following
relationship, provided care is taken to ensure proper
units for all the quantities.
T = Q / (RxP)
 For example, the time taken to paint 100m2 (Q) using
2 painters (R) and assuming each painter can do 5 m2
in an hour (P), is simply 10 hours (T).
 Life in real projects is however, not as simple, and
there could be uncertainties involved in the estimation
of quantities, resources, and the productivity of a
resource.
55
3. Determine the logical relationships:
 Determine which activity must precede, succeed or
maybe done concurrently.
 Consider resource (labor, equipment) limitation
4. Draw the logic network and perform the CPM
calculations:
 Finish date of the project, the critical path, and the
available float for non-critical activities.
 CPM network using one of the commercially available
computer software programs, such as primavera project
manager or Microsoft (MS) project.
56
5. Review and analyze the schedule
a) Review the logic
b) Make sure the activity has the correct predecessor
c) Make sure there is no redundant activity
6. Implement the schedule:
 Take the schedule from the paper to execution
7. Monitor and control the schedule
 Comparing what is planned to what is actually done
8. Revise the database and record feedback
 Cost and time estimates for activities are based on past
experience
9. Resource allocation and levelling 57
  Forward Pass
 Earliest Start Time (ES)
 -Earliest time an activity can start without delaying
the project
 -ES = maximum EF of immediate predecessors

 Earliest finish time (EF)

 -Earliest time an activity can finish without delaying
the project
 -Earliest start time plus activity time

EF= ES + t
58
 Backward Pass
 Latest finish time (LF)
 Latest time an activity can be completed without
delaying the project
 LF = minimum LS of immediate successor
 Latest Start Time (LS)
 Latest time an activity can start without delaying the
project
 Latest Finish minus activity time

LS= LF - t
59
 CPM calculation with AON
(example 1)
Draw the logic network and perform the CPM
calculation:

60
Solution

61
 Graphical Solution

Project completion time = 23 days

CPM (ES = LS, EF = LF, & TF = FF = 0)

62
 Float calculations
Total float (TF): the maximum amount of time an activity
can be delayed from its earliest start time without delaying
the entire project.
TF = LS – ES
OR
TF = LF – EF OR
TF = LF – D – ES
Free float (FF): The maximum amount of time an activity
can be delayed without delaying the early start of the
succeeding activities.
FFi = min(ESi+1) - EFi

63
 Tabular solution for Example 1
In the previous example, for example:
Activity C’s free float, FF = 11 – 11 = 0 days
Activity C’s total float, TF = 16 – 11 = 5 days

 Critical Activity
 Note: We must always realize that FF ≤ TF

64
 The preceding logic is similar to that of the forward and
backward passes:
 The early event time, TE, is the largest (latest) date
obtained to reach an event (going from start to finish).
 The late event time, TL, is the smallest (earliest) date
obtained to reach an event (going from finish to start).

65
Perform the CPM calculations, using the arrow network
diagram:

Activity IPA Duration

A - 10
B - 5
C - 7
D A 8
E A,B 9
F C 4
G D,E,F 5
H D,E,F 8

66
 Solution
The arrow network shown below:

67
Solution

68
 The Precedence Diagramming Method (PDM)

• Besides the usual FS relationship, PDM permits the

relationships of:
Start-to-Start (SS),
Finish-to-Finish (FF), and
Start-to-Finish (SF).
• It also allows for time lags in these relationships, such
as lags between two starts, two finishes or a start and a
finish.
• These special relationships in PDM are described
hereunder using the AON networks.

69
 The Precedence Diagramming Method (PDM)
• Start-to-Start, SS
• In an SS relationship between two activities A and B, the
start of B can occur „n‟ days, at the earliest, after the
start of its immediate predecessor, A.
• Example:

• Suppose that a “ stone masonry work” can start no

sooner than 5 days after the start of “ trench
excavation”.
70
 The Precedence Diagramming Method (PDM)
• Finish-to-Finish, FF
• In an FF relationship between two activities A and B, B
will finish “n” days, at the latest, after A finishes.
• Example:

• An illustration is given above where “paint parking

lines” (B) must be finished within 5 days after “Asphalt
lay” (A) has been finished.

71
 The Precedence Diagramming Method (PDM)
• Start-to-Finish, SF
• In an SF relationship, the finish of activity B must occur “n”
days at the latest, after the start of activity A.
• For example:

• “phase out old system‟ (B) cannot be finished until 25 days

after “test new system” begins.
72
 The Precedence Diagramming Method (PDM)
• Finish-to-Start, FS
• In an FS relationship, the start of activity B can occur
“n” days, at the earliest, after the finish of activity A.
• For example:

• “tear down scaffolding” (B) can start no sooner than 5

days after “plaster walls” is finished.

73
 The Performance Evaluation & Review Technique (PERT)

• In PERT the line connecting the circles represents activities

and the circle itself represents an event, which marks
completion of activity.
• PERT uses three time estimates, i.e. Optimistic, Most
probable and Pessimistic.
• To find a single expected time the three time estimates can be
compounded together as follows.
te = O + 4M + P
6
• Optimistic: confidence in the achievement of expectation
• Most Probable: the likely be achieve the expectation
• Pessimistic: lack of confidence in the achievement of
expectation
74