Chapter 6 - Network Analysis

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Chapter 6 – Network Analysis 1. After completion of this chapter, you should be able to: 

To identify or define: - Critical Path - AOA Networks - Forward and backward passes - Variability in Activity times - Cost and Networks



To describe or explain: - Describe how a PERT network analysis works - Critical path method (CPM) - Variability in Activity times - Determining the Project Schedule.

2. Managing projects with networks usually involves four steps: -

Describing the project Diagramming the network Estimating time of completion Monitoring project progress

3. Objectives of network analysis -

Minimization of total project cost Minimization of total project duration. Minimization of idle resources Minimize production delays, interruptions and conflicts.

4. Management of large projects -

Planning – goal setting, project definition, team organization Scheduling – relating people, money, and supplies to specific activities and activities to one and other Controlling – monitoring resources, costs, quality, and budgets; revising plans and shifting resources to meet time and cost demands.

5. Project planning Project planning is the process of identifying all the activities necessary to successfully complete the project. It consists of: - Establishing objectives - Defining project - Creating work breakdown structure - Determining resources - Forming organization

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6. Project Scheduling Project Scheduling is the process of determining the sequential order of the planned activities, assigning realistic durations to each activity, and determining the start and finish dates for each activity. - Identifying precedence relationships - Sequencing activities - Determining activity times and costs - Estimating materials and worker requirements - Determining critical activities

7. Purposes of Project Scheduling -

Shows the relationship of each activity to others and to the whole project. 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 in the project.

8. Describing the project 

Activity - the smallest unit of work effort consuming both time and resources that the project manager can schedule and control.



Precedence Relationship - determines a sequence for undertaking activities; it specifies that one activity cannot start until a preceding activity has been completed.

9. Diagramming the Network 

Activity-On-Arc (AOA) network It uses arcs or arrows to represent activities and nodes to represent events.



Event – is the point at which one or more activities are to be completed and one or more other activities are to begin - an event consumes neither time nor resources. - A-O-A emphasizes activity connection points. - Here, precedence relationships require that an event not occur until all preceding activities have been completed.

10.Activity – On – Node (AON) Network

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  

Nodes represent activities and the arcs indicate the precedence relationships between them. The approach is activity oriented. Here the precedence relationships require that an activity not begin until all preceding activities have been completed.

11.Project Management Techniques   

Gantt chart Critical Path Method (CPM) Program Evaluation and Review Technique (PERT)

12.Gantt Chart A Gantt Chart is a simple technique that can be used to attach a time scale and sequence to a project. Gantt charts, also known as milestone plans, are a low cost means of assisting the project manager at the initial stage of scheduling. They ensure that:  All activities are planned for,  The sequence of activities is accounted for,  The activity time estimates are recorded; and  The overall project time is recorded.

13.PERT and CPM -

 Network techniques  Developed in the 1950’s CPM by DuPont for chemical plants (1957) PERT by Booz, Allen and Hamilton with the U.S Navy, for Polaris missile (1958)   

Consider precedence relationships and interdependencies. Each uses a different estimate of activity times. Method to analyse the tasks involved in completing a given project, especially the time needed to complete each task, and identifying the minimum time needed to complete the total project.

14.Program Evaluation and Review Technique (PERT) -

A flowchart diagram that depicts the sequence of activities needed to complete a project and the time or costs associated with each activity.

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Events: Endpoints for completion Activities: time require for each activity Slack time: the time that a completed activity waits for another activity to finish so that they can begin jointly another activity. 3

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Critical path: the longest path of activities that allows all tasks to be completed.

15. Critical Path Method – CPM The Critical Path Method, abbreviated CPM, is a mathematically based algorithm for scheduling a set of project activities. It is a very important tool for effective project management. It was developed in the 1950’s in a joint venture between DuPont Corporation and Remington Rand Corporation for managing plant maintenance projects. Today, it is commonly used with all forms of projects, including construction, software development, research projects, product development, engineering, and plant maintenance, among others. Any project with interdependent activities can apply this method of scheduling.

16.The six steps common to PERT and CPM      

Define the project and prepare the work breakdown structure. Develop relationships among the activities. Draw the network connecting all the activities. Assign time and cost estimates to each activity. Compute the longest time path through the network. This is called the critical path. Use the network to help plan, schedule, monitor, and control the project.

17. Errors and logical sequence Three types of errors in logic may arise when drawing network, particularly when it is a complicated one. These are known as 

Looping: Normally in the network, the arrow points from left to right. This convention is to be strictly adhered, as this would avoid the illogical looping, as shown wrongly below.



Dangling: The situation represented by the following diagram is also at fault, since the activity represented by the dangling arrow 7-8 is undertaken with no result.

18. Dummy arrows 

Dummy arrows are used to transfer logic from one event node to another in the net work. They are represented by broken arrows.

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 

A dummy arrow has zero duration and does not represent an activity. These symbols are used to represent the relationships amongst the activities.

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