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Project Management 67 Dr. Emad Elbeltagi
CHAPTER 4
PROJECT PLANNING AND SCHEDULING
This chapter deals with preparing projects plans in terms of defining: work breakdown
structure, activities, logical relations, durations and activities direct cost. Terminology of
project planning will be presented and discussed. Project network representation using
different graphical methods including: activity on arrow and activity on node are
presented.
Scheduling is the determination of the timing of the activities comprising the project to
enable managers to execute the project in a timely manner. The project scheduling ids
used for:
- Knowing the activities timing and the project completion time.
- Having resources available on site in the correct time.
- Making correction actions if schedule shows that the plan will result in late
completion.
- Assessing the value of penalties on project late completion.
- Determining the project cash flow.
- Evaluating the effect of change orders on the project completion time.
- Determining the value of project delay and the responsible parties.
4.1 Introduction
Planning is a general term that sets a clear road map that should be followed to reach a
destination. The term, therefore, has been used at different levels to mean different
things. Planning involves the breakdown of the project into definable, measurable, and
identifiable tasks/activities, and then establishes the logical interdependences among
them. Generally, planning answers three main questions:
Project Management 68 Dr. Emad Elbeltagi
What is to be done?
How to do it?
Who does it?
In construction, for example, plans may exist at several levels: corporate strategic plans,
pre-tender plans, pre-contract plans, short-term construction plans, and long-term
construction plans. These plans are different from each other; however, all these plans
involve four main steps:
- Performing breakdown of work items involved in the project into activities.
- Identifying the proper sequence by which the activities should be executed.
- Activities representation.
- Estimating the resources, time, and cost of individual activities.
Planning requires a rigorous effort by the planning team. A planner should know the
different categories of work and be familiar with the terminology and knowledge used in
general practice. Also, the planning tem should seek the opinion of experts including
actual construction experience. This helps produce a realistic plan and avoids problems
later on site.
4.2 Project Planning Steps
The following steps may be used as a guideline, or checklist to develop a project plan:
1. Define the scope of work, method statement, and sequence of work.
2. Generate the work breakdown structure (WBS) to produce a complete list of
activities.
3. Develop the organization breakdown structure (OBS) and link it with work
breakdown structure o identify responsibilities.
4. Determine the relationship between activities.
5. Estimate activities time duration, cost expenditure, and resource requirement.
6. Develop the project network.
4.2.1 Work Breakdown Structure (WBS)
Project Management 69 Dr. Emad Elbeltagi
House
Civil Plumping Electrical
Foundations Walls/Roof Piping H/C Water Wiring Fittings
Figure 4.1: WBS and their description
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 smaller
elements of work at each lower level of the breakdown. At the lowest level of the WBS
the elements of work is called a work package. A list of project’s activities is developed
from the work packages.
Effective use of the WBS will outline the scope of the project and the responsibility for
each work package. There is not necessarily a right or wrong structure because what may
be an excellent fit for one discipline may be an awkward burden for another. To visualize
the WBS, consider Figure 3.2 which shows a house construction project.
As shown in Figure 4.1, level 1 represents the full scope of work for the house. In level 2,
the project is sub-divided into its three main trades, and in level 3 each trade is sub-
divided to specific work packages. Figure 4.2 shows another example for more detailed
WBS, in which the project WBS is divided into five levels:
Project Management 70 Dr. Emad Elbeltagi
Level 1: The entire project.
Level 2: Independent areas.
Level 3: Physically identifiable sections fully contained in a level 2 area, reflect
construction strategy.
Level 4: Disciplines set up schedule.
Level 5: Master schedule activities, quantity, duration.
4.2.2 Project Activities
An activity is defined as any function or decision in the project that: consumes time,
resources, and cost. Activities are classified to three types:
Production activities: activities that involve the use of resources such as labor,
equipment, material, or subcontractor. This type of activities can be easily
identified by reading the project’s drawings and specifications. Examples are:
excavation, formwork, reinforcement, concreting, etc. each production activity
can have a certain quantity of work, resource needs, costs, and duration.
Procurement activities: activities that specify the time for procuring materials or
equipment that are needed for a production activity. Examples are: brick
procurement, boiler manufacturing and delivery, etc.
Management activities: activities that are related to management decisions such
as approvals, vacations, etc.
Gas development project
Recovery unit 300 Process unit 400
Level 1
Level 2
Train 2 Train 1 Gas treating Separation and stabilization Level 3
Instrumentation Structural steel Civil Piping Level 4
Piping
fabrication Level 5
Figure 4.2: Five levels WBS
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An activity can be as small as “steel fixing of first floor columns” or as large as
“construct first floor columns”. This level of details depends on the purpose of preparing
the project plan. In the pre-construction stages, less detailed activities can be utilized,
however, in the construction stages, detailed activities are required. Accordingly, level of
details depends on: planning stage, size of the project, complexity of the work,
management expertise.
Example 4.1:
Figure 4.3 shows a double-span bridge. Break the construction works of the bridge into
activities. The plan will be used for bidding purposes.
Figure 4.3: Double span bridge
A list of the double-span bridge activities is shown in Table 4.1
Table 4.1: Activities of the double-span bridge
Activity Description Activity Description
10
14
16
20
30
40
50
60
70
80
90
Set-up site
Procure reinforcement
Procure precast beams
Excavate left abutment
Excavate right abutment
Excavate central pier
Foundation left abutment
Foundation right abutment
Foundation central pier
Construct left abutment
Construct right abutment
100
110
120
140
150
155
160
170
180
190
200
Construct central pier
Erect left precast beams
Erect right precast beams
Fill left embankment
Fill right embankment
Construct deck slab
Left road base
Right road base
Road surface
Bridge railing
Clear site
Precast beams Deck slab
Road base left Road base right
Hand rail
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4.2.3 Activities Relationships
In order to identify the relationships among activities, the planning team needs to answer
the following questions for each activity in the project:
- Which activities must be finished before the current one can start?
- What activity(ies) may be constructed concurrently with the current one?
- What activity(ies) must follow the current one?
Example 4.2:
Determine the relationships between activities of the project studied in Example 4.1.
Table 4.2: Solution of Example 4.2
Activity Description Predecessors
10
14
16
20
30
40
50
60
70
80
90
100
110
120
140
150
155
160
170
180
190
200
Set-up site
Procure RFT
Procure P.C. Beams
Excavate left abutment
Excavate right abutment
Excavate central pier
Foundation left abutment
Foundation right abutment
Foundation central pier
Construct left abutment
Construct right abutment
Construct central pier
Erect left P.C. Beams
Erect right P.C. Beams
Fill left embankment
Fill right embankment
Construct deck slab
Left road base
Right road base
Road surface
Bridge railing
Clear site
---
---
---
10
10
10
14, 20
14, 30
14, 40
50
60
70
16, 80, 100
16, 90, 100
80
90
110, 120
140
150
155, 160, 170
155
180, 190
Project Management 73 Dr. Emad Elbeltagi
Logical relationship considering resource constraints
For efficient use of resources or in case of constrained resources, it might be beneficial to
consider the resources when determining the logical relationship among the activities that
use the same resources. For example, consider the case of construction a simple project
consists of three units and each unit has three sequential activities (logical relationship).
Table 4.3 shows the logical relationship among these activities assuming unconstrained
(resources are available with any quantities) and constrained resources (only one resource
unit is available from each resource type).
Table 4.3: Logical relationships considering constrained and unconstrained
resources
Activity description Predecessors
(unconstrained resources)
Predecessors
(constrained resources)
A1
B1
C1
A2
B2
C2
A3
B3
C3
Excavate unit 1
Concreting unit 1
Brickwork unit 1
Excavate unit 2
Concreting unit 2
Brickwork unit 2
Excavate unit 3
Concreting unit 3
Brickwork unit 3
-
A1
B1
-
A2
B2
-
A3
B3
-
A1
B1
A1
B1, A2
C1, B2
A2
B2, A3
C2, B3
Overlap or lag
Overlap between activities (negative lag) is defined as how much a particular activity
must be completed before a succeeding activity may start. The absence of overlap means
that the first activity must finish before the second may start. A negative overlap (lag)
means a delay is required between the two activities (Figure 4.4).
Figure 4.4: Overlap among activities
+ve overlap (-ve lag) -ve overlap (+ve lag)
Project Management 74 Dr. Emad Elbeltagi
Types of activities relationships
Four types of relationships among activities can be defined as described and illustrated
below (Figure 4.5). Typically, relationships are defined from the predecessor to the
successor activity.
a) Finish to start (FS). The successor activity can begin only when the current
activity completes.
b) Finish to finish (FF). The finish of the successor activity depends on the finish of
the current activity.
c) Start to start (SS). The start of the successor activity depends on the start of the
current activity.
d) Start to finish (SF). The successor activity cannot finish until the current activity
starts.
Figure 4.5: Types of relationships
4.2.4 Drawing Project Network
A network is a graphical representation of the project activities and their relationships. A
project network is a set of arrows and nodes. Before drawing the network, it is necessary
to ensure that the project has a unified starting and ending point. The need for this start
activity arises when there is more than one activity in the project that has no predecessors
and the end activity is needed when there is more than one activity that has no successors.
Also, networks should be continuous (i.e., each activity except the first and the last has
both preceding and succeeding activities).
a b
c d
Project Management 75 Dr. Emad Elbeltagi
In this method, the nodes represent activities and the arrows represent logical
relationships among the activities. If the arrow starts from the end side of an activity
(activity A) and ends at the start side of another activity (activity B), then A is a
predecessor of B (Figure 4.6). AON representation allows the overlap or lag
representation on the relationship arrows connecting activities.
Example 4.3:
Construct an AON network for the activities listed in Table 4.4.
Table 4.4: Data for Example 4.3
Activity Predecessors
A
B
C D
E
F
G
-
-
A, B C
C
D
D, E
10
A
Activity number
B depends on A
C depends on A and B
D depends on C
B depends on A
C depends on B
D depends on B
Figure 4.6: Basic patterns of AON diagrams
Activity name
20
B
10
A
20
B
10
A
30
C
20
B
40
D
10
A
20
B
40
D
30
C
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To understand the drawing of the AON, some ordering for the activities may be
necessary. This is done by placing the activities in a sequence step order. A sequence step
may be defined as the earliest logical position in the network that an activity can occupy
while maintaining the logical relationships. In this example, as there are two activities
(activities A and B) has no predecessor, then a start activity is added to have one unified
start activity (Start) for the project. Also, a finish activity (Finish) is added as there are
two activities without successors (activities F and G).
Considering the data given in Table 4.4, sequence step 1 is assigned to the Start activity.
Then, we take all activities on the list one by one and look at their immediate
predecessors and then assign a sequence step that equals the highest sequence step of all
immediate predecessors plus one as given in Table 4.5. After all sequence step numbers,
have been assigned, the AON diagram can be drawn.
Table 4.5: Determining the sequence steps
Activity Predecessors Sequence step (SS)
Start
A
B
C
D
E
F
G
Finish
-
Start
Start
A, B
C
C
D
D, E
F, G
SS(Start)=1
2=SS(Start)+1
2=SS(Start)+1
3=Highest of [SS(B), SS(A)]
4=SS(C)+1
4=SS(C)+1
5=SS(D)+1
5=Highest of [SS(D), SS(E)]
6= Highest of [SS(F), SS(G)]
AON representation is shown in Figure 4.7, including project start and finish nodes. Note
that dummy activities are not required for expressing precedence relationships in activity-
on-node networks.
Project Management 77 Dr. Emad Elbeltagi
Figure 4.7: An AON Network
4.3 The Critical Path Method
The most widely used scheduling technique is the critical path method (CPM) for
scheduling. This method calculates the minimum completion time for a project along
with the possible start and finish times for the project activities. Many texts and managers
regard critical path scheduling as the only usable and practical scheduling procedure.
Computer programs and algorithms for critical path scheduling are widely available and
can efficiently handle projects with thousands of activities.
The critical path itself represents the set or sequence of activities which will take the
longest time to complete. The duration of the critical path is the sum of the activities'
durations along the path. Thus, the critical path can be defined as the longest possible
path through the "network" of project activities. The duration of the critical path
represents the minimum time required to complete a project. Any delays along the critical
path would imply that additional time would be required to complete the project.
There may be more than one critical path among all the project activities, so completion
of the entire project could be delayed by delaying activities along any one of the critical
paths. For example, a project consisting of two activities performed in parallel that each
requires three days would have each activity critical for a completion in three days.
Formally, critical path scheduling assumes that a project has been divided into activities
of fixed duration and well defined predecessor relationships. A predecessor relationship
implies that one activity must come before another in the schedule.
Sequence step 1 2 3 4 5 6
Project Management 78 Dr. Emad Elbeltagi
The CPM is a systematic scheduling method for a project network and involves four main
steps:
- A forward path to determine activities early-start times;
- A backward path to determine activities late-finish times;
- Float calculations; and
- Identifying critical activities.
4.4 Calculations for the Critical Path Method
Precedence Diagram Method (PDM) is the CPM scheduling method used for AON.
Forward Path
Forward path can proceed from one activity to the other; the process is as follow (Figure
4.8):
- At activity A. It is the first activity in the network. We give it an early-start (ES) of 0
in the left top box. Adding the activity duration, we determine the EF time of the
activity and we put it in the top right box.
Figure 4.8: Forward Path in PDM Analysis
- Then, move forward to the succeeding activities B, C, and D. These three activities
have only A as a predecessor with time 3 as its EF. As such, all the three activities
A (3)
0 3
D (6)
3 9
C (4)
3 7
E (5)
9 14
B (3)
3 6
Name (duration)
Late start Late finish
Early start Ealry Finish
6, 7, or 9
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can start as early as time 3 (ES = 3). Each activity, accordingly, has its own EF time
based on its duration.
- Moving forward to activity E. This activity has 3 predecessors (3 head arrows) of
activities B, C, and D with their largest EF time being 9. The ES of activity E, thus,
with becomes time 9. Adding its duration, the EF becomes time 14.
To generalize the calculations, consider Figure 4.9, of two activities i and j with
relationship finish to start and overlap between them. Overlaps will have a positive sign,
while lags will have a negative sign. The forward path calculations are as follows:
Figure 4.9: Activities times in PDM Analysis
ESj = EFi - overlapij (4.1)
In case of more than one activity precedes activity j then consider the maximum.
Backward Path
Once the forward path is finished, the backward path can start, moving from the last
activity to the first, putting the calculations in the bottom two boxes of each activity, as
shown in Figure 4.10. The process is as follows:
Figure 4.10: Backward path in PDM analysis
A (3)
0 3
0 3
D (6)
3 9
3 9
C (4)
5 9
3 7
E (5)
9 14
9 14
B (3)
6 9
3 6
Name (duration)
Late start Late finish
Early start Early Finish
6, 5, or 3
i (di)
LSi LFi
ESi EFi
j (dj)
LSj LFj
ESj EFj overlapij
Project Management 80 Dr. Emad Elbeltagi
- Start at the last activity E and we transfer the early-finish value to become the
activity's late-finish (LF) time. Then, subtracting the activity's own duration, the late-
start (LS) time is calculated as time 9 and put in the bottom left box of the activity.
- Moving backward to activities B, C, and D all have one successor (activity E) with
LS time of 9. The LF of all these activities becomes time 9. Each activity then has its
own LS time, as shown in Figure 4.10.
- Moving to activity A. The activity is linked to 3 tail arrows (i.e., has 3 successors) of
activities B, C, and D. The LF of activity A, thus, is the smallest of its successors' LS
times, or time 3. Activity A then has LS equals zero.
Considering Figure 3.9 again, the backward path calculations are as follows:
LFi = LSj + overlapij (4.2)
In case of more than one activity succeeds activity j then consider the minimum.
Notice that by the end of the backward path, all activity times can be read directly from
the boxes of information on the activity, without additional calculations. This also, makes
it simple to calculate the total float of each activity using the same relationships used in
the AOA analysis.
Identifying Critical Activities
Critical activities can also be easily determined as the ones having zero float times,
activities A, D, and E. The critical path is then shown in bold as Figure 4.10. The PDM
analysis, as explained, is a straight forward process in which each activity is considered
as an entity that stores its own information.
4.5 Schedule Presentation
After the AON calculations are made, it is important to present their results in a format
that is clear and understandable to all the parties involved in the project. The simplest
Project Management 81 Dr. Emad Elbeltagi
form is the Bar chart or Gantt chart, named after the person who first used it. A bar chart
is a time versus activity chart in which activities are plotted using their early or late times,
as shown in Figures 4.12 a and b. Early bar chart is drawn using the ES times of
activities, while the late bar chart is drawn using the LS times.
Figure 4.12: a) Early bar chat b) Late bar chart
The bar chart representation, in fact, shows various details. Float times of activities,
critical activities can be shown in a different color, or bold borders, as shown in Figure
4.12. The bar chart can also be used for accumulating total daily resources and / or costs,
as shown at the bottom part of Figure 4.13. In this figure, the numbers on each activity
represent the number of labors needed.
d=3
ES = 0 d=3 TF=3
ES=3 d=4 TF=2 ES=3 d=6 ES=3
d=5
ES=9
d=3
LF=3 TF=3 d=3
LF=9 TF=2 d=4 LF=9 d=6 LF=9 d=5
A
B
C
D
E
Activity
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Time
A
B
C
D
E
Activity
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Time
LF=14
a)
b)
Project Management 82 Dr. Emad Elbeltagi
Figure 4.13: Using bar chart to accumulate resources
One additional benefit of the bar chart is its use on site to plot and compare the actual
progress in the various activities to their scheduled times. An example is shown on Figure
4.13, showing actual bars plotted at the bottom of the original bars of the schedule.
4.6 Criticisms to Network Techniques
The CPM analyses for network scheduling provide very important information that can
be used to bring the project to success. However, some drawbacks that require special
attention from the project manager. These drawbacks are:
- Assume all required resources are available: The CPM calculations do not incorporate
resources into their formulation. Also, as they deal with activity durations only, it can
result in large resource fluctuations. Dealing with limited resources and resource
leveling, therefore, has to be done separately after the analysis;
- Ignore project deadline: The formulations of CPM method do not incorporate a
deadline duration to constrain project duration;
- Ignore project costs: Since CPM method deal mainly with activities durations, they
do not deal with any aspects related to minimize project cost;
2 2 2
2 2 2
1 1 1 1
3 3 3 3 3 3 1 1 1 1 1
2 2 2 6 6 6 4 3 3 1 1 1 1 1 Total labors
A
B
C
D
E
Activity
Profile of the labor resource demand
6
5
4
3
2
1 1
2
3
4
6
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Time
Project Management 83 Dr. Emad Elbeltagi
- Use deterministic durations: The basic assumption in CPM formulations is that
activity durations are deterministic. In reality, however, activity durations take certain
probability distribution that reflect the effect of project conditions on resource
productivity and the level of uncertainty involved in the project.
4.7 Solved Examples
Example 1
Perform PDM calculations for the small project below and determine activity times.
Durations are shown on the activities.
Solution
A
(1)
I
(2)
J
(7)
H
(1)
D
(1)
B
(4)
C
(1)
E
(2)
F
(2)
G
(1)
L
(2)
K
(4)
C (1)
6 7
1 2
J (7)
7 14
7 14
Name (duration)
LS LF
ES EF
9 or
9 or 14
L (2)
14 16
14 16
H (1)
9 10
4 5
A (1)
0 1
0 1
B (4)
1 5
1 5
G (1)
6 7
6 7
E (2)
7 9
2 4
K (4)
10 14
5 9
F (2)
8 10
2 4
I (2)
12 14
7 9
D (1)
5 6
5 6
Critical path
12 or 7
1 or 6
7 or 8 5 or 4
Project Management 84 Dr. Emad Elbeltagi
Example 2
Perform PDM calculations for the small AoN network shown here. Pay special attention
to the different relationships and the lag times shown on them.
Solution
4.8 Exercises
1. Select the right answer:
I. The elements of construction project planning are:
a. Time b. Resources
c. Cost d. All
II. Which of the following is not a typical activity category?
A
(3)
D
(6)
B
(3)
C
(4)
E
(5)
SS=2
FF=2
D (6)
4 10
3 9
B (3)
4 7
2 5
C (4)
3 7
3 7
Name (duration)
LS LF
ES EF
A (3)
0 3
0 3
E (5)
7 12
7 12
12-2=10
4 or
3 or (4-2+3)
SS=2
FF=2
5, 7 or
(9+2-5)
0+2=2
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a. Production b. Procurement
c. Administrative d. None of the above
2. In developing the WBS for a project, level of details depends on: …..,……,……..
3. Draw a PDM network for a project with the following activities. Show all steps
including removing redundant relations; and sequence steps.
- Activity B depends on A;
- Activity G follows E, F & D;
- Activity E depends on B and A;
- Activity F can start when D & B are completed;
- Activity C is followed by F and follows A;
- Activity D is dependent upon A and B.
4. Consider the following set of activities:
Code Description
A
B
C
D
E
F1
F2
G1
G2
H
I
J
K
Layout foundation
Excavation
Obtain concrete materials
Place concrete
Obtain steel reinforcement
Cut and bend reinforcement (part 1)
Cut and bend reinforcement (part 2)
Place reinforcement (part 1)
Place reinforcement (part 2)
Obtain formwork
Erect formwork
Remove formwork
Clean up
Project Management 86 Dr. Emad Elbeltagi
A gang of steelfixers is used to cut and bend reinforcement and another gang is
used for placing reinforcement. The first part of reinforcement can be placed
during formwork erection while the second part should wait for completion of
formwork erection. Tabulate the predecessors of each activity and draw AON
network.
5. The free float is defined as:
a. The amount of time an activity can be delayed without affecting the following
activity.
b. The amount of time an activity can be delayed without affecting total project
duration.
6. Total float equals:
a. Late finish minus early finish c. Late start minus early start
b. Late finish minus (early start + duration) d. All of the above
7. State True (T) or False (F):
a. The critical activities can be determined easily when using the bar chart.
b. The network must have definite points of beginning and end.
c. The network must be continuous from start to end.
d. There’s no dummy activities in the arrow networks,
e. A forward pass is used to determine late start and late finish times.
f. The time for completing a project is equal to the sum of the individual activity
times.
8. For the Following project data, answer the following questions:
Activity Duration (days) Predecessor
Project Management 87 Dr. Emad Elbeltagi
A
B
C
D
E
F
G
2
6
3
1
6
3
2
--
A
A
B
B
C, D
E, F
a. Draw an AOA network and perform forward and backward pass calculations?
b. Draw an AON network and perform forward and backward pass calculations?
c. Draw a time-scaled diagram of the project?
d. Tabulate activities ES, EF, LS, LF, TF, and FF.
e. What is the effect of delaying activity D by 3 days?
9. Perform PDM calculations for the project below and determine activity times.
Durations are shown on the activities
A
(1)
I
(2)
J
(7)
H
(1)
D
(1) B
(4)
C
(1) E
(2)
F
(2)
G
(1)
L
(2)
K
(4)