1. Project Scheduling: Lagging, Crashing and Activity Networks
Chapter 10
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2. Lags in Precedence Relationships
The logical relationship between the start and finish of one activity and the start and finish of another activity.
Four logical relationships between tasks
Finish to Start
Finish to Finish
Start to Start
Start to Finish
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3. This lag is not the same as activity slack
Finish to Start Lag
Most common type of sequencing
Shown on the line joining the modes
Added during forward pass
Subtracted during backward pass
This lag is not the same as activity slack A
Spec Design 6 B
Design Check 5 C
Blueprinting 7
Lag 4
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4. Finish to Finish Lag Two activities share a similar completion point
The mechanical inspection cannot happen until wiring, plumbing, and HVAC installation are complete A
Plumbing 6 B
HVAC 5 C
Inspection 1 D
Wiring
Lag 3
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5. Start to Start Lag
Logic must be maintained by both forward and backward pass A
Plumbing 6 B
HVAC 5 C
Inspection 1 D
Wiring
Lag 3
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6. Start to Finish Lag Least common type of lag relationship
Successor’s finish dependent on predecessor’s start D
Wiring 6
Lag 3 A
Plumbing 6 B
HVAC 5 C
Inspection 1
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7. Gantt Charts Establish a time-phased network
Can be used as a tracking tool
Benefits of Gantt charts
Easy to create and comprehend
Identify the schedule baseline network
Allow for updating and control
Identify resource needs
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8. Create a Gantt chart based on the activities listed in the table.
Task
Time
Pred Z 8 -- U 3 W Y 5 T 6 V X S 7
U,T 4
Y,X R 9
Task ES EF LS LF Z Y X W V U T S R
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9. Gantt Chart With Resources in MS Project
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10. Principal methods for crashing
The process of accelerating a project
Principal methods for crashing
Improving existing resources’ productivity
Changing work methods
Increasing the quantity of resources
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11. Managerial Considerations
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 crashing cost exceeds the penalty cost
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12. What is the lowest cost to complete this project in 53 weeks
What is the lowest cost to complete this project in 53 weeks? Times are in weeks and costs in dollars.
Activity
Pred
Normal Time
Min Time
Normal Cost
Crash Cost A -- 14 9
500
1500 B 5 2
1000
1600 C 10 8
2000
2900 D
B, C
2500 E 6
1900 F
3000 G
E, F 7 4
600
1800 H 15 11
3600
Initial early and late start and finish times
Task ES EF LS LF Slack A B C D E F G H
Project 63
Reduce A by 5 days at $200/week = $1000 Project length is now 58 weeks
Reduce G by 3 days at $400/week = $1200 Project length is now 55 weeks
Reduce C by 2 days at $450/week = $900 Project length is now 53 weeks
Total cost to finish project in 53 weeks is $3100
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13. Activity on Arrow Networks
Activities represented by arrows
Widely used in construction
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
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14. Calculate early and late start and finish times for all activities.
Use AOA to sketch the network that represents the project as described in the table.
Calculate early and late start and finish times for all activities.
Activity
Time
Pred A 4 -- F D B 2 G 15 C 10 H 7
E,F,G 3
B,C K 11 E
Task ES EF LS LF A B C D E F G H K
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15. Activity on Arrow NetworkB H A F C D K G
Task ES EF LS LF A B C D E F G H K
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16. Controversies in the Use of Networks
Networks can be too complex
Poor network construction creates problems
Networks may be used inappropriately
When employing subcontractors
The master network must be available to them
All sub-networks must use common methods
Positive bias exists in PERT networks
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17. Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall