chapter 4 project planning and schedulingosp.mans.edu.eg/elbeltagi/ien314 ch4.pdf · chapter 4...

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:


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)


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:


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


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


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


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)


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


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


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.


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


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


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


- 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


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)


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


- 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


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


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


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


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)

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