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Chapter 10 1. 1.Apply lag relationships to project activities. 2.Construct and comprehend Gantt charts. 3.Understand the trade-offs required in the decision.

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Presentation on theme: "Chapter 10 1. 1.Apply lag relationships to project activities. 2.Construct and comprehend Gantt charts. 3.Understand the trade-offs required in the decision."— Presentation transcript:

1 Chapter 10 1

2 1.Apply lag relationships to project activities. 2.Construct and comprehend Gantt charts. 3.Understand the trade-offs required in the decision to crash project activities. 4.Develop activity networks using Activity- on-Arrow techniques. 5.Understand the differences in AON and AOA and recognize the advantages and disadvantages of each technique. 2

3 The logical relationship between the start and finish of one activity and the start and finish of another activity. Four logical relationships between tasks 1. Finish to Start 2. Finish to Finish 3. Start to Start 4. Start to Finish 3

4 Most common type of sequencing Shown on the line joining the nodes Added during forward pass Subtracted during backward pass 0 A 6 Spec Design 6 6 B 11 Design Check 5 15 C 22 Blueprinting 7 Lag 4 days This lag is not the same as activity slack 4

5 Two activities share a similar completion point The interior construction cannot happen until wiring, plumbing, and HVAC installation are complete 31 S 33 Plumbing 2 33 T 39 HVAC 3 39 U 45 Interior Const R 36 Wiring 6 Lag 3 days 5

6 Often two or more activities must start at the same time 6 31 S 33 Plumbing 2 33 T 36 HVAC 3 36 U 42 Inspection 6 30 R 36 Wiring 6 Lag 3 Logic must be maintained by both forward and backward pass

7 Least common type of lag relationship Successors finish dependent on predecessors start 22 S 28 Plumbing 6 28 T 33 HVAC 5 33 U 34 Inspection 1 30 R 36 Wiring 6 Lag 3 7

8 A graphical representation of the project schedule that illustrates how work flows over time Shows activity start and end dates and durations Links project activities to a project schedule baseline Can be used as a tracking tool Benefits of Gantt charts 1. Easy to create, read, and comprehend 2. Identify the project network and schedule baseline 3. Allows for updating and control 4. Useful to identify resource needs and assigning resources to tasks 8

9 Create a Gantt chart based on the activities listed in the table. TaskTimePredecessor Z8-- Y5Z X8Z W4Y,X V5W U3W T6V S7U,T R9S 9

10 10 TaskStartDuration Z08 Y85 X88 W164 V205 U 3 T256 S317 R389

11 11 Critical path in red

12 Accelerating a project by committing more resources. Principal options for crashing Improving existing resources productivity Changing work methods used Increasing the quantity of resources 12

13 The initial schedule may be too optimistic. Market needs change and the project is in demand earlier than anticipated. The project has slipped considerably behind schedule. The contractual situation provides even more incentive to avoid schedule slippage. 13

14 1.Compute the crash cost per time period. If crash costs are linear over time: Crash cost per period = (Crash cost – Normal cost) (Normal time – Crash time) 2.Using current activity times, find the critical path and identify the critical activities. 14

15 3.If there is only one critical path, then select the activity on this critical path that (a)can still be crashed, and (b)has the smallest crash cost per period. 4.If there is more than one critical path, then select one activity from each critical path such that (a)each selected activity can still be crashed, and (b)the total crash cost of all selected activities is the smallest. Note: the same activity may be common to more than one critical path. 15

16 5.Update all activity times. 6.If the desired due date has been reached, stop. If not, return to Step 2. 16

17 ||| 123Time (Weeks) $34,000 $34,000 $33,000 $33,000 $32,000 $32,000 $31,000 $31,000 $30,000 $30,000 Activity Cost Crash Point Normal Point Crash Time Normal Time Crash Cost Normal Cost Crash Cost/Wk = Crash Cost – Normal Cost Normal Time – Crash Time = $34,000 – $30,000 3 – 1 = = $2,000/Wk $4,000 2 Wks How far do you need to speed up the process? 17

18 Formula Slope = crash cost – normal cost normal time – crash time Example – calculating the cost of crashing Suppose: Normal activity duration = 8 weeks Normal cost = $14,000 Crashed activity duration = 5 weeks Crashed cost = $23,000 The activity cost slope = 23,000 – 14,000 or, $9,000 = $3,000 per week 8 –

19 Determine activity fixed and variable costs The crash point is the fully expedited activity Optimize time-cost tradeoffs Shorten activities on the critical path Cease crashing when the target completion time is reached the crash cost exceeds the penalty cost 19

20 20 ActivityPredNormal TimeMin Time Normal Cost Crash Cost A BA CA DB, C ED FD GE, F HG

21 What is the lowest cost to complete this project in 53 weeks? Times are in weeks and costs in dollars. 21

22 Activities represented by arrows Event nodes easy to flag Forward and backward pass logic similar to AON Two activities may not begin and end at common nodes Dummy activities may be required 22 Event label Earliest Event Time (ES) Latest Event Time (LF) Task Description Duration

23 23 Figure 10.18

24 A H F E D C B K G 24

25 Activity onActivityActivity on Node (AON)MeaningArrow (AOA) A comes before B, which comes before C (a) A B C BAC A and B must both be completed before C can start (b) A C C B A B B and C cannot begin until A is completed (c) B A C A B C 25

26 Activity onActivityActivity on Node (AON)MeaningArrow (AOA) C and D cannot begin until both A and B are completed (d) A B C D B AC D C cannot begin until both A and B are completed; D cannot begin until B is completed. A dummy activity is introduced in AOA (e) CA BD Dummy activity A B C D 26

27 Activity onActivityActivity on Node (AON)MeaningArrow (AOA) B and C cannot begin until A is completed. D cannot begin until both B and C are completed. A dummy activity is again introduced in AOA. (f) A C DB AB C D Dummy activity 27

28 1.Please give examples of circumstances in which a project would employ lag relationships between activities using: 1.Finish to start 2.Finish to finish 3.Start to start 4.Start to finish 2.The advantage of Gantt Charts lies in their linkage to the project schedule baseline. Explain this concept. 3.What are the advantages in the use of Gantt charts over PERT diagrams? In what ways might PERT diagrams be advantageous? 4.Under what circumstances might you wish to crash a project? 28

29 5.In crashing a project, we routinely focus on those activities that lie on the critical path, not activities with slack time. Explain why this is the case. 6.What are some of the advantages in the use of AOA notation as opposed to AON? Under what circumstances does it seem better to apply AON methodology in network development? Explain the concept of a dummy variable. Why are they employed in AOA notation? Why is there no need to use dummy variables in an AON network? 7.Explain the concept of a dummy variable. Why are they employed in AOA notation? Why is there no need to use dummy variables in an AON network? 29


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