Topic 7 Project Planning and Scheduling

Introduction

What is project planning and scheduling? Planning is deciding in advance the future course of action and it is a primary function of management.

There are five main steps in the process of planning and these are as follows;

1. Objective - Defining the objective of the project.
2. Forecasts - Making forecast to achieve goals.
3. Identify Course of Action - Identifying the alternative course of action for achieving goals.
4. Evaluation of Resource availability - Evaluating the resources available to organization.
5. Evaluating and Selecting available alternative course of action.

During the process of planning, the various operations involved in the project, their sequences and their logical inter relationships are established.

Project Scheduling

Project scheduling refers to the process of laying out all the actual activities of the project in the time order in which they are to be performed, keeping in view of the logical sequence of the activities. In most cases, the sequence of activities would be as follows;

• Company Registration first and in order.
• Obtaining necessary approval in term of licencing, government approval etc.
• Appointment of Consultants where necessary.
• Resources mobilization (Internally and Externally).
• Land Acquisitions and Site Development.
• Preparing civil work designs, plans, and estimates and tender for contractors.
• Prepare design specifications and placing orders.
• Transport of plant and equipment to the project site.
• Erection of machinery.
• Commissioning the plant and taking trial run.
• Commencing regular commercial production.

Scheduling Techniques

Any project would consist of many activities. In most cases these activities are listed under different programs etc. Remember all activities consumes resources of three kind; Time, Men and Materials. Project Scheduling is trying to optimise the use of these three resources.
 

Bar Charts

Bar Chart is a pictorial representation showing the various activities involved in the project. The Bar Chart would have two co-ordinate axes; one axis represents the activities and the other axis represents the time required for completion of the individual activities. Bar chart was first conceived and developed by Henry. L. Gantt and hence bar chart is also sometimes referred to as Gantt chart.

Let us look at the above Bar chart and try to understand the axis that represents activities. Activity A is expected to take 10 Days to complete and commences together with Activity B. Activity D and E commenced work when activity A is about to complete. Activity E finishes together with Activity B and activity C started when B, D & E where finishing off. If you look carefully at the activities on the bar chart, you will notice that some activities are simultaneously together.

Let us look at a simple example; A Construction of a Residential House

Activities	Time Required
Digging of foundation	3 Weeks
Pouring foundation Concrete	1 Week
Construction of Walls	10 Weeks
Construction of Roof Slab	3 Weeks
Fixing of doors and Windows	1 Week
Digging of Well	1 Week
Plastering and finishing of Walls	2 Weeks

The above activities can be depicted in a bar chart, after identifying their logical sequence. Let us assume that we need water for construction work to start. In this case, digging of well will start early together with digging of the foundation.

Programme-progress Chart – Is also a Bar chart however, it incorporates the actual progress of the different activities. Both the estimated time and the actual time taken for completion of different activities are incorporated in the programme – progress chart. This helps in knowing the time lag between the estimated and actual progress of work and also helps in controlling the progress of work during the implementation of the project.

Limitation of Bar Chart

·         Bar charts are difficult to update when there are many changes

·         When there are changes between the plan and the actual achievement, bar charts become quickly obsolete.

·         Bar charts do not equate time with cost; hence time-cost relationship can not be derived from them.

·         Bar charts do not provide methods for optimizing resource allocation.

·         In view of the above limitations, bar charts are useful only for small projects and cannot be effectively used for medium sized and large projects.

Net Work Based Scheduling

Bigger projects involving a large number of activities, project scheduling becomes very complex and the use of conventional methods of scheduling like bar charts will not be effective.

Large projects if not correctly scheduled can result in under estimation or over estimation of project implementation period either of which will or may have serious consequences.

Example: If there is over-run in time, that will lead to cost over-run. If over-run costs are not made available on time, this can have an impact on project completion time and there will be set back.

Net Work Based Scheduling of projects comes handy in solving complex projects scheduling problems. There are two techniques that can be used;

1.      Critical Path Method (CPM)

2.      Programme Evaluation Review Technique (PERT)

CPM was developed in the year 1957 by Morgan R. Walker of DU Pont and E. Kelly of Remington Rand.

PERT was developed in the year 1958 by the US Navy.

Activity – An activity is any identifiable job that has a beginning and an end. Activity consumes time, man power, and material resources. An activity is represented by a straight arrow with circles at both ends. The direction of the arrow indicates the direction of flow of the project. The circle placed at the beginning of the arrow represents the starting point of the activity, while the circle placed at the end of the arrow represents the finishing point of the activity.

The symbol of the activity and its duration are represented as under

Event – Also called node is the beginning or end of any activity. Event does not consume time, manpower, or material resources but represents a specific point in time and is represented by a circle.

Relationship among Activities – Is a network or graphical representation of logical sequence of all the activities of a project. Activities are inter-related among themselves.

Concurrent Activities – The activities that can be carried out concurrently are called concurrent activities. As we have seen earlier, digging a well and excavation of foundation are concurrent activities since they do not depend on each other.

Preceding Activities – For a given activity, the activity that occurs immediately before it, its preceding activity.

Succeeding Activities – For a given activity, the activity that follows immediately after it, is its succeeding activity.

Dummy Activities – A dummy activity is an imaginary activity included in a network. Since it is not a real activity, it does not consume time, manpower and material resources. It is included in a network to maintain the network logic and to avoid ambiguity. It is always represented by a dotted arrow.

Rules for drawing Network Diagram

1. All activities shall be represented by way of straight arrows pointing towards the right. This means that the flow of network shall be from the left towards the right.
2. There shall not be any criss-crossing of arrows. See the example below of which two arrows crosses each other. This is not permitted. The same can be drawn without any criss-crossing. See the same example with no criss-crossing.
3. The arrows of a network shall not form loops. In complex network problems, if the logical sequence of activities is not correctly followed, a loop network may be formed. See example below showing a loop network. (Page 230)
4. There shall not be unnecessary dummy activities in the network. Dummy activities shall be introduced only when it is absolutely necessary and without which the network diagram can not be completed. See example (Page 231 Fig 8.18 and 8.19)

See below examples of Diagram and Logic to understand the use of diagram well.

Numbering of Events (Fulkerson's Rule)

Every activity in a network is given a name or symbol. The events are represented by circles at the beginning and at the end of an activity and are assigned numbers. Numbering of events help in drawing the network correctly. Numbers should be assigned to the events so that they reflect logical sequences.

Fulkerson's Rule:

1. Identify the initial event and assign it a number 1. Initial event is the starting point of any project. Defining from angle of a network diagram, initial event is the event which has one or more arrows emerging from it and no arrow entering it. See example below.
2. Delete all the emerging arrows from the initial event (event 1). This will create one or more new initial events. Number these new events as 2, 3, 4......etc. (See example below)
3. Delete all the emerging arrows from the new initial events, which will create a new set of new initial event. Assign numbers to these initial events starting from the number next to the number that has so far been assigned. (See example below)
4. Follow the above procedure till the end of the network is reached. The last event of the network is the one from which no arrow emerges and into which one or more arrows enters. The last event is assigned with the highest number in the network. (See example below)

Skip Numbering - Large projects involves a large number of activities. Since all the activities can not be correctly foreseen and included in the network, the network for large projects may need modifications during execution of projects. The modification may be in the form of addition of a few new activities or deletion of few activities originally included. renumbering of events due to modifications will be a tedious task. This problem can be overcome if the events are numbered in steps of 10, 20, 30, 40 etc. instead of 1, 2, 3, 4. This method of numbering of events is called skip numbering and is used for large networks to facilitate additions/deletion of activities.

Critical Path Method

A network represents the logical sequence of activities contained in a project.

Characteristics of Critical Path

• A critical path is the longest path(time-wise) connecting the initial and final events
• A critical path may run through dummy activity/activities
• Since critical path is the path having the longest time duration, it does not mean that the critical path will have the maximum number of activities. The number of activities on a critical path may be less than the number of activities in other non-critical paths.
• It is possible that a network may have more than one critical path i.e., if two or more paths have the same time duration which is the maximum then all such paths.

Finding Critical Path In Large Network

The method of finding out the number of paths available in a given network connecting the initial and end events, finding the time duration of all the available paths and identifying the critical path is suitable for smaller networks. If the network is relatively larger in size, there will be a large number of paths available connecting the initial and the end events. 

 Finding critical path in large project

In such cases, it would be cumbersome to find out the entire possible path. The method uses two series of computation; the Forward pass computation and the backward pass computation. Let us look at this two series of computation;

Forward pass computation – This method of computation of starting time of events. The computation begins from the initial event and moves towards the final event. The series of computation is done to arrive at the Earliest Start Time of all the events. See the example below;

From the above explanation we can easily work out the Earliest Start Time for the other events;

Event -3 which is the start of activity C can commence immediately after activity B is completed. Thus the Earliest Start Time for event 3 is 10 days (7 days + 3 Days)

Therefore; TE (For event 3) = 10 days

Event - 4 is the last event. Though the network does not extend beyond event 4, for the purpose of computation of Earliest Start Time, the same logic is followed. Thus the Earliest Start Time for event 4 would be 20 days. (7 days + 3 days + 10 days)

Therefore TE (for event 4) = 20 days

Backward pass computation – This is a method of computation of the finishing time of events. The computation begins from the final events and moves towards the initial event. This series of computation is done to arrive at the Latest Finish Time (T1) of all the events. Latest Finish Time is also referred to as Latest Allowable Event Time or Latest Allowable Occurrence Time or Latest Completion Time. (Nagarajan, 2008)

Let us look at the network below to understand backward pass computations;

Event - 8 – Earliest Start Time of event 8 is 34. Since this is the last event, for completing the project without time delay the Latest Finish Time (TL) for the last event should be equal to the Earliest Start Time (TE) of that event.

Therefore

TL (of event 8) = TE (of event 8) = 34

Event -7 – There is only one activity emanating from event 7 (activity K). Activity K takes 11 days for completion. Since the Latest Finish Time (TL) for event 8 is 34, event 7 can occur as late as on the 23^rd day (34 – 11). If the Latest Finish Time of event 7 is delayed beyond 23, the project completion time will also extend beyond 34.

Hence TL (of event 7) = TE (for event 8) – duration of activity K.

= 34 – 11

= 23

Event - 6 – Again, there is only one activity emanating from event 6 (Activity H), which would take 11 days for completion. As per logic applied to event 7, the Latest Finish Time of event 6 is given by,

TL (for event 6) = TL (of event 7) – duration of activity H

= 23 – 11

= 12

Event – 5:  There are two activities emanating from event 5. Hence there will be two time estimates for finish times out of which the minimum of the two time estimates will represent the Latest Finish Time.

Activity –J takes 12 days for completion. Since the Latest Finish Time of event -7 is 23, event -5 can start as late as on the 11^th day (23 – 12)

Activity –I takes 2 days for completion. Since the Latest Finish Time of event -6 is 12, event -5 can start as late as on the 10^th day (12-2).

The Latest Finish Time of event – 5 is given by the minimum of the two time estimates, viz 10

TL (of event -5) = 10

Event – 4: There is only one activity emanating from even -4. Therefore the Latest Finish Time of event 4 is given by

TL (of event -4) = TL (of event-8) – duration of activity –G

= 34 – 8

= 26

Event -3: There are three activities emanating from event -3 (activity –D, E & F). Hence three times estimates of finish times are available out of which the minimum time represents the Latest Finish Time of event -3.

TL (of event -3) is the minimum of

a)      TL (of event -4) – duration of activity –D

= 26 – 7

= 19

b)      TL (of event -6) – duration of activity –E

= 12 – 8

= 4

c)      TL (of activity -5) – duration of activity –F

= 10 – 5

= 5

Therefore TL (of event -3) = 4 (being the minimum of the three time estimates).

Event -2: There is only one activity emanating from event -2.

Therefore: TL (of event -2) = TL (of event -4) – duration of activity –C

= 26 – 7

= 19

Event -1: There are two activities emanating from event -1. Hence TL of event -1 is the minimum of the following two times estimates.

a)      TL (of event -2) – duration of activity –A

= 19 – 5

= 14

b)      TL (of event -3) – duration of activity –B

= 4 – 4

= 0

Therefore TL (of event -1) = 0

If the backward pass computation are done correctly, the Latest Finish Time of the start event (event -1) will be equal to its Earliest Start Time.

In this example, we have arrived at TE (of event -1) = TL (of event -1) = 0

Slack Time and Critical Path

We have calculated the Earliest Start Time (TE) of all events by doing forward pass computations. We have also calculated the Latest Finish Time (TL) of all events by doing backward pass computation. Thus TE and TL of all the vents of the network is known.

Slack Time (or Slack) of an even is the difference between the Latest Finish Time (TL) and the Earliest Start Time (TE) of the event. The path connecting events with zero is the critical path.

The following Table reproduces the TL, TE and Slack of all events in the net work that we have considered in the examples.

Event	TL	TE	Slack (TL – TE)
1 2 3 4 5 6 7 8	0 19 4 26 10 12 23 34	0 5 4 12 9 12 23 34	0 14 0 14 1 0 0 0

From the above table, you will note events 1, 3, 6, 7 & 8 have zero slack. The path connecting these events is the critical path. Critical path is denoted in the network by bold line. (See network below)

What does Critical Path Signify?

The activities that lie on the critical path are called critical activities. Thus, in the examples provided by Nagarajan (2008), activities B, E, H and K are the critical activities.

Since the two time estimates of all the nodes in the critical path are the same, it means that a succeeding activity in a critical path shall commence immediately after its proceeding activity is completed.

In the above example, Activity –K shall start immediately after activity –H is completed; activity –H shall start immediately after activity E is completed and activity –E shall start immediately after activity –B is completed. If there is any delay in either starting a critical activity or if the time taken for a critical activity exceeds the estimated time, the project implementation period will get extended.

Given this understanding, the critical activities deserve more attention and control by the management. Any delay in critical activities will lead to time-overrun of the project. Since every time-overrun invariably results in cost-overrun, delay in critical activities will also more likely to result in cost-overrun of projects.

All paths in a network other than the critical path are called non-critical paths. A non-critical path may have only non-critical activities or a combination of both critical and non-critical activities.

Please note all the illustrations and examples are taken from Project Management 3^rd Edition, Nagarajan (2008) Chapter 8. Students are encouraged to read through this chapter 8.

Source: Project Management 3^rd Edition, Nagarajan (2008) (New Age)