Network analysis & cpm


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Network analysis & cpm analysis

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Network analysis & cpm

  1. 1. Slide 1Project Management Project is defined as a huge (mammoth) task which for convenience of management is broken down into smaller elements such that, for each of the smaller elements, one can identify the finite requirements of resources and finite requirements of time. These smaller elements are referred as activities of the project i.e. project essentially comprises of a number of activities e.g. construction of building is a project and electrical work is one of the activities of the project. Contd…
  2. 2. Slide 2Project Management Like the electrical activity, a project will have a number of activities. The first task of the project manager is to define all the activities of the project in terms of time and other dimensions like cost etc. The second task is to establish the inter relation & interdependence of the defined activities. The following are some examples to explain small projects.
  3. 3. Slide 3Example 1Christine Philips is in charge of planning and coordinating nextspring’s sales management training program for her company.Christine has listed following activities information for this project. Immediate Duration Activity Description predecessors (weeks) A Select location - 2 B Obtain speakers - 3 C Make speaker travel plans A, B 2 D Prepare and mail brochure A, B 2 E Take reservations D 3Draw the network diagram; find the critical path and the durationalong the critical path.
  4. 4. Slide 4 Example 2 A research and development department is developing a new power supply for a console television set. It has broken down the job into the following form: Immediate Duration Activity Description predecessors (days) A Determine output voltages - 5 Determine whether to use solid B A 7 state rectifiers C Choose rectifiers B 2 D Choose filter B 3 E Choose transformer C 1 F Choose chassis D 2 G Choose rectifiers mounting C 1 H Layout chassis E, F 3 I Build and test G, H 10Draw the critical path schedule, indicate the critical path. What is the time required forcompletion for the project?
  5. 5. Slide 5Categories of ProjectThe following is an illustrative list of categories of project:i. Complex projects with unknown elements for e.g. Construction of nuclear power plantsii. Large projects with standard elements for e.g. Construction of an automobile factoryiii. Intermediate project for e.g. layout of machine, implementing TQM programme, developing new markets etc.iv. Small projects for e.g. installing a new machine, conducting a market survey etc.v. Turnkey project is one which starts from zero to proceed to a finished ‘product’. Concept of turnkey is that when the project is finished one turns a key to set the facility in operation, for e.g. Reliance refinery project at Jamnagar is a turnkey project.
  6. 6. Slide 6Session Objective Given the activities, their duration and their inter relation, our objective in this session is: i. to represent these relation of activities in the form of a network diagram ii. to analyze the network diagram using CPM (Critical Path Method)
  7. 7. Slide 7Network Diagram Network diagram is a graphical / pictorial representation of a series or a sequence of activities in the logical order of their performance, such that we establish the inter relation and interdependence of one activity on all other activities of the project. Network Diagram comprises of two basic elements:(i) Activity(ii) Event (Node)
  8. 8. Slide 8Elements of Network Diagrami. Activity: An activity is denoted by an arrow Tail Head It signifies the deployment of finite resources over a finite period of time. The tail of the arrow signifies the commencement of the activity and the head signifies the completion of the activity.ii. Events or Nodes: An event is denoted by a circle i where, i={1,2,3,4…. and so on} It signifies the status of the project at a point of time. It indicates the start & completion of an activity.
  9. 9. Slide 9 A-O-A Convention (i-j convention) Activity A or Activity i-j A i j tij Tail Event Head Event i<jTail event signifies commencement status of the activity.Head Event signifies completion status of the activityArrow signifies deployment of finite resources over a finite period of time.tij is the duration of the activity
  10. 10. Slide 10Good practices of drawing a NetworkDiagrami. Drawing a network diagram is a trial and error procedureii. The starting event is always one event, irrespective of the number of starting activities. This event signifies the commencement status of the projectiii. The completion event is always one event, irrespective of the number of final activities. This event signifies the completion status of the project.iv. The length of the arrow is the convenience of drawing the network diagram. It is no indication of the duration of activity.v. The arrows must be drawn in the forward direction. Avoid crossing of The numbering of events starts with the first event and progressively moves from the left to the right of the network diagramvii. There is no uniqueness in the final picture of the network diagram.
  11. 11. Slide 11Good practices of drawing a NetworkDiagram These Guidelines are explained with the following five illustrations of network diagram:
  12. 12. Slide 12Analysis of Network Diagram There are two popular tools used for analysis of Network Diagram CPM (Critical Path Method) PERT (Program Evaluation & Review Technique)In the following slides, CPM is explained with examples.
  13. 13. Slide 13Manager’s View of Critical Path Method Inputs Outputs (What information must (What information results be supplied to CPM) from CPM that provides for better project management)1. a complete list of 1. Estimated duration of project activities C project2. Precedence P 2. Identification of critical relationship among activities activities M 3. Amount of Float for3. Estimate of each each activity activities duration
  14. 14. Slide 14Critical Path Method It was developed in 1956 / 1957 by Remington Rand and Du- pont to help schedule maintenance projects in chemical plants and construction projects. Critical Path Method is a systematic scientific method based on principle of time estimates to perform a detailed analysis of Network in an application of Project Management Time estimates in CPM relate to estimating the time for the events of the network diagram. Since the event signifies the status of the project at a point of time, the time estimates in turn signify the status of the project at different points of time. There are two important time estimates; (i) Earliest starting time & (ii) Latest finishing time.
  15. 15. Slide 15Guidelines for Earliest Start Time (EST) Earliest Start Time (EST): It signifies the earliest that an activity can start with reference to the commencement status of the project. The following are the guidelines to obtain EST.i. Earliest starting time for event 1 is taken as zero because event 1 signifies the commencement status of the project i.e. status of the project corresponding to time ‘t = 0’.ii. For the calculation of EST we start from event 1 and progressively move from left to right in the network diagram (referred as forward pass)
  16. 16. Slide 16Guidelines for Earliest Start Time (EST)iii.Consider two adjacent events Ei Ej i j tij Tail Event Head Event Ej = Ei + tijEST of the head event = EST of the tail event + the duration of the activity
  17. 17. Slide 17Guidelines for Earliest Start Time (EST)iv. Consider a merging event (in case more than one activity is merging towards an event). Ea Ed = Ea + tad a tad Ed = Eb + tbd Eb Ed tbd b d Ed = Ec + tcd tcd Ec Take the maximum value c
  18. 18. Slide 18Guidelines for Latest Finish Time (LFT) Latest Finish Time (LFT): It is the latest time by which an activity should finish, otherwise the project completion time will be delayed. The following are the guidelines to obtain LFT.i. For the last event of the network diagram, LFT = EST (because the last event signifies the project completion status and both EST / LFT signify the project completion time)ii. For the calculation of LFT, we start with the last event of the network diagram & we proceed progressively from the right to the left of the network diagram (referred as backward pass).
  19. 19. Slide 19Guidelines for Latest Finish Time (LFT)iii. For two adjacent events Tail Event Head Event i j tij Li Lj Li = Lj – tijLFT of the tail event = LFT of the head event – the duration of that activity
  20. 20. Slide 20 Guidelines for Latest Finish Time (LFT)For a bursting event (If there are more than one subsequentactivities busting from an event), calculate LFT for each ofthe head events and take the minimum value 2 t12 L1 = L2 – t12 L2 t13 L1 = L3 – t13 1 3 L1 t14 L3 L1 = L4 – t14 4 Take the minimum value L4
  21. 21. Slide 21Note: Both EST and LFT for starting event (event 1 of the network diagram) are always zero
  22. 22. Slide 22 Total Float of an Activity  Total Float signifies the maximum permissible delay in performing the activity without delaying the project completion time. The following is the mathematical relation for Total Float E Head Event i i j tij Tail Event Lj Total Float of Activityi-j = Lj – Ei – tijTotal Float of Activity = LFT (Head Event) – EST (Tail Event) – Duration of Activity
  23. 23. Slide 23Free Float of an ActivityFree float signifies the maximum permissible delay incommencement of an activity without affecting the commencementof the succeeding activity Ei Ej Tail Event i j Head Event tij Li LjHead Event Float = Lj – EjFree Float = Total Float – Head Event Float
  24. 24. Slide 24Definition of Critical Path If total float of an activity is zero, it means there is no permissible delay in performing the activity i.e. any delay in performing the activity will result in a corresponding delay in the project completion time. Such activities are referred as critical activities. Path of network is a continuous series or sequence of activities that joins the first event with the last event of the network diagram. In a network one can enumerate many sequences of activities from starting event to end event. Each sequence will contain different combination of activities with different duration.
  25. 25. Slide 25Definition of Critical Path To know the possible time by which the project can be completed, we determine the critical path i.e. the sequence of activities with longest duration. It is known as critical path and any delay in activities lying on this path would cause a delay in the whole project. Alternately, Critical Path is a continuous series or sequence of critical activities that joins the first event with the last event of the network diagram. To quicken the process, the activities lying on the critical path should be taken first. The activity lying on non-critical path has some flexibility in their starting time and their delay in start is not likely to affect the final completion date. These are known as slack activities and should be given priority in order of their float value.