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CRITICAL PATH ANALYSIS

CRITICAL PATH ANALYSIS. aka NETWORK PATH ANALYSIS. DESIGNED to help managers who are planning complex projects that involve many interrelated tasks.

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CRITICAL PATH ANALYSIS

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  1. CRITICAL PATH ANALYSIS aka NETWORK PATH ANALYSIS DESIGNED to help managers who are planning complex projects that involve many interrelated tasks The idea is to help identify which of these interrelated task are the CRITICAL ones. Any change in these ‘critical’ tasks will have a significant impact* on the overall project * “impact”, relates firstly to time delays in this context

  2. Lots of interrelated tasks eg To build the bridge you need both the passway and the base. The general idea BUILDING A BRIDGE They are in fact interrelated by by TIME. To build the passway you FIRST have to build the base. Any delay in the building of the base, is going to cause a delay in the building of the passway Building of the base is a critical activity

  3. Don’t copy any of these down !

  4. THE CRITICAL PATHWAY is made up of NODES. 2 3 A node for each independent activity/task On the very first node these will both be ZERO Earliest Start Time 1 2 Node number [in order of the network] 4 For this task Activity / task Latest Finishing Time 3 Duration of activity For the preceding task 5 The START node = EST of following node - Duration of current activity

  5. a MIDDLE node For node 5 the Latest Finishing Time [for activity D & E] is 10. They must both be finished by the 10th week or else the Final Finishing Time will be delayed. This makes sense because if the activity F cannot be started until the 11th week and takes 1 week itself, the Final Finishing Time will be week 12! Therefore all activities preceding Node 5 must be finished by week 10 at the latest. It can be calculated by the “EST of node 6 (11) – Duration of F (1) = 10”

  6. The LFT [for activity 4] recorded in Node 8 will be the same as the EST in Node 8 because there is no following node and no activity The activity of the final node is not shown as it is the ‘end’ The EST means ‘what is the earliest the ‘end’ can start’ and will be : the EST of node 7 + Duration of Activity 4 Earliest Start Time 8 Node number [in order of the network] 4 For this task Activity / task Latest Finishing Time Duration of activity For the preceding task 5 = EST - Duration The FINISH node

  7. Lets try a simple example You cannot leave the classroom until you have finished your work and tidied up a. Finish work b. Tidy up 37 30 3 0 2 1 37 30 mins 30 7 mins 0 ESTs & LFTs are the same because this is a simple example with no parallel tasks

  8. Lets try one that’s a little harder c. clear laptops a. Finish work 45 You cannot leave the classroom until you have all finished your work, girls should then tidy up and put up the chairs while guys put away the laptops 30 4 0 2 1 15 mins 45 30 mins 30 0 d. Put up chairs b. Tidy up 6 mins 7 mins 37 Duration of task is the next issue to identify… 3 39 1 : same as before = 0 2 : same as before = 30 3 : 30 + 7 = 37 4: 37 + 6 = 43 or 30 + 15 = 45 ? Always the LONGER therefore = 45 EST’s Go in reverse 4: 45, remember it’s the same. 3 :45-6 = 39 2 : 39 – 7 = 32 or 45 – 15 = 30 Always the SHORTER therefore 30 1. 0, remember it’s the same. LFT’s

  9. Task A must be started before Task B, but either could finish first A A B 1 Task B cannot be started before Task A is complete B B Task A will be divided up into two tasks : B & C A A 2 C Neither task B nor C can start until tasks A is completed B C Task D can be started when Task C is completed A A 3 Neither task B nor D can start until tasks A and C are completed D B B Neither task C nor D can start until tasks A and B are completed C

  10. BUT AT THIS STAGE WE HAVE NOT YET LOOKED AT THIS IDEA OF ‘CRITICAL’ “TASKS THAT CANNOT BE ALTERED WITHOUT AFFECTING THE WHOLE PRODUCTION PROCESS”

  11. To identify the critical tasks Lets assume a universal small change of 1 minute ? task A: c. clear laptops a. Finish work 45 Now last 31 minutes. That will affect the EST of Node 2 – & push it up to 31 min. 30 4 0 2 1 15 mins 45 30 mins 30 0 d. Put up chairs task B: b. Tidy up 6 mins Now last 8 minutes. That will affect the EST of Node 3 and push it up to 39 min. 7 mins 37 3 task C: 39 Now last 16 minutes. That will affect the EST of Node 4 and push it up to 47 min. The Critical Tasks are A and B, so the Critical Path is shown by the route connecting Nodes 1, 2 and 3 task D: Now last 7 minutes. That will affect the EST of Node 4 and push it up to 46 min. ALL CRITICAL tasks WILL HAVE E.S.T.s THAT ARE EQUAL TO THEIR L.F.T.s

  12. Common Error 2 tasks starting at the same time, with the same follow-on task. You cant draw it as we see because this would indicate that task a & b are the same duration c a 3 2 1 c b 1 A It would need to be as we have drawn before [see left] C 4 3 B 2

  13. 1. Draw the NETWORK Diagram 2. Identify the Critical Path 3. How long should you allow yourself to get to the interview on time?

  14. B E 26 51 3 5 15 26 51 25 A 0 10 1 2 10 D 10 10 0 C 16 4 16 6 We also talk about a FLOAT Is an activity which has an amount of time by which it can be extended and not affect the overall project time frame Which task here has a float? And how large is this float? Activity B! 1 minute

  15. P719 -722 readingp723 Q5.8.1 A C 7 9 2 4 E 7 7 10 2 13 3 6 0 1 13 0 F B 5 D 10 3 3 5 5 5 5 10

  16. P723 readingp724 Q5.8.2 E. House ID&F B. Construction 7 4 F. Final Testing 7 6 weeks 11 A. foundation 3 weeks 10 0 1 5 5 1 2 11 10 1 0 1 week 1 week D. Pool T&S C. Pool E&F 3 3 2 weeks 8 2 weeks Explain why its important?..... 4 marks

  17. P724 -726 readingp727 Q5.8.3 FREE FLOAT = EST (of next) – Duration (of current) – EST (of current) The amount of time that an activity can be delayed without affecting the EST of the next activity TOTAL FLOAT = [ LFT (of next) – Duration (of current) – EST (of current) ] You then add up all the Total Floats The amount of time a sequence of tasks can be delayed without affecting the whole process FF = ActB = 8-4-4 = 0 ActE = 16-5-8 = 3 E. 16 H 21 8 5 5 4 B. 16 21 11 5 5 4 A. 0 4 1 2 G 2 TF = ActB = 11-4-4 = 3 ActE = 16-5-8 = 3 = 6 4 0 4 C. D F 14 7 11 5 3 5 3 14 7 11 4 3

  18. P727 -728 readingp729 Q5.8.4

  19. P729 - 730 reading

  20. 2. continued The revised times are: Recalculate the network diagram and show the new time for the whole project. State whether the critical path has changed [3 marks] 3. Using this information and evidence from the case itself evaluate whether Max should go ahead and build the cottages [6 marks] [6 marks] MAXS COTTAGES [revised] QUESTION

  21. Assume you need to B.Build Access Road in order to bring in the cement needed to C.Lay Foundation ie Task C is preceded by A&B Assume also that you need to B.Build Access Road in order to bring in the materials needed to C.Lay Cables + Water Pipes ie Task D is preceded by A&B too 215 7 F H 215 20 I J 20 255 260 E 195 G 235 8 9 10 6 105 C 5 195 255 260 235 20 5 105 90 30 A 45 60 0 K 15 3 1 D 45 0 30 275 75 11 30 4 B 275 105 45 0 2 0 MAXS COTTAGES [revised] ANSWER

  22. Assume you need to B.Build Access Road in order to bring in the cement needed to C.Lay Foundation ie Task C is preceded by A&B Assume also that you need to B.Build Access Road in order to bring in the materials needed to C.Lay Cables + Water Pipes ie Task D is preceded by A&B too 255 7 F H 255 20 I 20 J 295 300 E 225 G 275 30 8 9 10 6 105 C 5 225 295 300 275 20 5 105 90 30 A 45 60 120 0 K 15 3 1 D 45 0 30 315 75 11 30 4 B 315 45 105 45 0 2 0 MAXS COTTAGES [revised] ANSWER

  23. QUANTITATIVE You originally reduced the Project Time by 90 days, to 275 days. Which is a 25% reduction. He then, in his re-estimations, bought it back up again by 55 days. Which is 20% increase (in relation to your New Project Time.) However 15 of those 55 days where part of the Float in Activity D so the Project Time only went up by 40 days which represents a 15% increase (in relation to your New Project Time). The Final Revised Project Time is now 315 days, which is still 50 days less than originally quoted. Or 14% less. He has bought his final prices down by $30 000 which represents 20%. His prices have gone from $411/day to $381/day (although this ignores material costs) QUALITATIVE He seems to be an over-charger, and requires careful watching. Do we want to get into a relationship with him? HOWEVER Do we have other options? Will they be any better. What is the likelihood of getting the Planning Permission? On time? If there is delays not caused by the Builders, what will be their overtime charge rates? Significant saving possible with Just-in-Time, provided motivation sand weather remain predictable Conclusion : We seem to have got a more competitive prices now and if we are willing to commit time to building a positive relationship with our supplier then I would recommend we go ahead. We should of course bear in mind that the CPA has limitations and numerous unforeseen factors might extend the actual task time. MAXS COTTAGES [revised] ANSWER

  24. 2. continued The revised times are: Recalculate the network diagram and show the new time for the whole project. State whether the critical path has changed [3 marks] 3. Using this information and evidence form the case itself evaluate whether Max should go ahead and build the cottages [8 marks] MAXS COTTAGES [original] QUESTION

  25. Assume you need NOT B.Build Access Road in order to C.Lay Foundation 200 5 F H 200 20 I J 20 240 245 E 180 G 220 5 5 5 90 7 C 5 180 240 245 220 20 5 90 90 30 A 30 60 0 K 15 2 1 D .. 0 30 260 60 5 30 6 260 B 60 45 45 3 260 MAXS COTTAGES [original] ANSWER

  26. Assume you need NOT B.Build Access Road in order to C.Lay Foundation 240 5 F H 240 20 I J 20 280 285 E 210 G 260 30 5 5 5 90 7 C 5 210 280 285 260 20 5 90 90 30 A 30 60 120 0 K 15 2 1 D 30 0 30 300 75 5 30 6 300 B 45 60 45 45 3 300 MAXS COTTAGES [original] ANSWER

  27. QUANTITATIVE You originally reduced the Project Time by 105 days, to 260 days. Which is a 29% reduction. He then, in his re-estimations, bought it back up again by 55 days. Which is 21% increase (in relation to your New Project Time.) However 15 of those 55 days where part of the Float in Activity D so the Project Time only went up by 40 days which represents a 15% increase (in relation to your New Project Time). The Final Revised Project Time is now 300 days, which is still 65 days less than originally quoted. Or 18% less. He has bought his final prices down by $30 000 which represents 20%. His prices have gone from $411/day to $400/day (although this ignores material costs) QUALITATIVE He seems to be an over-charger, and requires careful watching. Do we want to get into a relationship with him? HOWEVER Do we have other options? Will they be any better. What is the likelihood of getting the Planning Permission? On time? If there is delays not caused by the Builders, what will be their overtime charge rates? Conclusion : We seem to have got a more competitive prices now an dif we are willing to commit time to building a positive relationship with our supplier then I would recommend we go ahead MAXS COTTAGES [original] ANSWER

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