O R cpm and pert

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Network analysis

Introduction:

A project is composed of a number jobs, activities, or task that are related to each other and all of these should be completed in order to complete the project.

A network is a combination of activities and events of a project.

Objective of network analysis

Minimization of total cost of a project. Minimization of total time of a project. Minimization of cost of a project for a given

total time. Minimization of time of a project for given cost. Minimization of idle resources. Minimization of production delays, interruptions

and conflicts. Planning, scheduling and controlling projects.

Network techniques

Different network techniques are PERT, CPM, UNETICS, LESS, TPS and SCANS.

The man network techniques are CPM and PERT.

These two network techniques help to managers to plan, schedule, monitor and control large and complex project.

Applications of N T

Constructing building, bridge, factories and irrigation projects.

Administration. Manufacturing. Maintenance planning. Research and development. Inventory planning. Marketing.

Different phases in the application of N T

Important managerial functions for any project on the application of CPM and PERT are,

(1) Planning(2) Scheduling(3) Controlling

Planning

Planning is the most important project management, in which the jobs or activities to be performed, are formalized.

Gross requirements of material, equipment and manpower in addition to the estimates of costs and durations of various activities of the project, are also determined in the phase.

Scheduling

Scheduling is the determination of time required for executing each operation and the order in which each operation has to be carried out to meet the plan objectives.

Controlling

Controlling is the process in which difference or deviation between the plan and the actual performances are reviewed after the project has started.

The analysis and correction of these deviations form the basic aspects of control.

Activities and Events

An activity is a task associated with a project. It is a physically identifiable part of a project

which consumes time and resources. Activity is the work to be undertaken to

materialize a specific event. Therefore an activity is he actual performance

of a task.

Start and Terminal activities

Activities which have no predecessors are called start activities.

Activities which have no successors are called terminal activities.

Dummy Activity

Usually a job or a task requires time and cost, but there is a certain activity which do not take time or resources. They are known as dummy activities.

These are used to represent a situation where one event cannot take place until a previous event has taken place, although this requires no time or resources.

They are used to maintain a proper precedence relation between two events and is denoted by dotted arrows.

Event

Events represent instants in the time when certain activities have been started or completed.

An event or node in a network diagram is a junction of two or more arrows representing the activities.

Event is a point in time and does not consume any resources.

Tail Event

A tail event is the one which marks the beginning of an activity.

Head Event

All the activities have an ending marked by an event. Such an event is known as head event.

Successor Event

The events that are follow an event are called successor events.

Predecessor

The events that occur before an event are called predecessor.

Rules for constructing a network diagram

Each activity is represented by one and only one arrow in the network.

No two activities can be identified by the same head and tail events.

Except for the nodes at the beginning and at the end node must have at least one activity preceding it and at least one following it.

Only one activity may connect any two nodes.

Problems

Start and finish times of an activity

Earliest start time (EST) Earliest finish time (EFT) Latest start time (LFT) Latest finish time (LST)

Earliest start time (EST)

The earliest time by which it can commence. This is naturally equal to the earliest event time associated with the tail event of the activity.

The EST of an activity = Earliest occurrence of the tail event of the activity. So, for the activity 2---3, EST is E2

Earliest finish time (EFT) If the activity proceeds at its early time and

takes the estimated duration for completion, then it will have an early finish.

Hence Earliest finish time (EST) for an activity is defined as the earliest time, by which it can be finished.

EFT = EST + Activity duration.

Latest start time (LFT)

The latest finish time for an activity is the latest time by which an activity can be finished without delaying the completion of the project.

LFT of an activity = Latest expected time of head event. So, for an activity 2-----3, LFT = L3.

Latest finish time (LST)

Latest start time of an activity is the latest time by which an activity can be started without delaying the completion of the project.

LST = LFT – Activity duration.

Critical path

While analyzing a network of activities, it is often necessary to estimate the total project time.

The total project time is the maximum of the elapsed times among all paths originating from the initial even and terminating the terminal event, indicate the completion of the project.

Earliest event time( TE )

The earliest occurrence time or earliest event time(TE) is the earliest at which an event can occur.

Earliest occurrence of an event say ‘2’ is denoted by E2.

Latest event time (TL)

The latest allowable occurrence time or the latest event time (TL) is the latest time by which an event must occur to keep the project on schedule.

Latest occurrence of an event, say ‘2’ is denoted by L2.

CRITICAL PATH METHOD (CPM)

It was originally discovered for the applications to industrial situation like construction, manufacturing, maintenance etc.

Since then it was fond wide acceptance by construction industry with application to bridges, dams, tunnels, building, highways, power plants etc.

Steps involved in Critical Path Method List of all activities (task) and draw a network diagram. Find the Earliest event time (TE) and latest event time

(TL) of each event and show in the network diagram. Calculate Earliest start time, Earliest finish time, Latest

start time and latest finish time foe each activity. Determine the float for each activity. Identify the critical activity Draw double lines in the network diagram passing

through critical activities. The double lines show the critical path.

Calculate the total project duration which is the sum of duration of critical activities.

Problems

PERT Programming Evaluation review technique PERT is a management technique in which we

try to exercise logical disciplines in planning and controlling projects.

The main assumption in PERT is that activity durations are independent. That is, time required for one activity has nothing to do with the time for another activity.

Time Estimates in PERT

The Optimistic Time Estimate(to) The pessimistic Time Estimate (tp) The Most Likely Time Estimate(tm)