activity sequencing
TRANSCRIPT
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Project Scheduling: Lagging,
Crashing and Activity Networks
Chapter 10
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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
1. Finish to Start
2. Finish to Finish3. Start to Start
4. Start to Finish
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Finish to Start Lag
Most common type of sequencing Shown on the line joining the modes
Added during forward pass
Subtracted during backward pass
0 A 6Spec Design
6
6 B 11Design Check
5
15 C 22Blueprinting
7
Lag 4
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Finish to Finish Lag
Two activities share a similar completion point
The mechanical inspection cannot happen until
wiring, plumbing, and HVAC installation are complete
10 A 16
Plumbing
6
16 B 21
HVAC
5
21 C 22
Inspection
1
15 D 21
Wiring
6
Lag 3
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Start to Start Lag
31 A 33
Plumbing
6
33 B 36
HVAC5
36 C 37
Inspection1
30 D 36Wiring
6
Lag 3
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Start to Finish Lag
Least common type of lagrelationship
Successors finish dependent onpredecessors start
22 A 28
Plumbing
6
28 B 33
HVAC
5
33 C 34
Inspection
1
30 D 36
Wiring
6
Lag 3
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Gantt Charts
Establish a time-phased network
Can be used as a tracking tool
Benefits ofGantt charts
1. Easy to create and comprehend
2. Identify the schedule baseline network
3. Allow forupdating and control
4. Identify resource needs
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Create a Gantt chart based on the
activities listed in the table.
Task Time Pred Task Time Pred
Z 8 -- U 3 W
Y 5 Z T 6 V
X 8 Z S 7 U,T
W 4 Y,X R 9 S
V 5 W
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Gantt Chart With Resources in MS Project
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Crashing Projects
Accelerating a project by committing more
resources than initially planned
Principal methods for crashing
Improving existing resources productivity
Changing work methods
Increasing the quantity of resources
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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 crash cost exceeds the penalty cost
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What is the lowest cost to complete thisproject in 53 weeks? Times are in weeks
and costs in dollars.Activity Pred NormalTime
Min
Time
Normal
Cost
Crash
Cost
A -- 14 9 500 1500
B A 5 2 1000 1600C A 10 8 2000 2900
D B, C 8 5 1000 2500
E D 6 5 1600 1900
F D 9 6 1500 3000
G E, F 7 4 600 1800
H G 15 11 1600 3600
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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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1. Use AOA to sketch the network that represents the
project as described in the table.
2. Calculate early and late start and finish times for allactivities.
Activity Time Pred Activity Time Pred
A 4 -- F 4 D
B 2 A G 15 D
C 10 A H 7 E,F,G
D 3 B,C K 11 G
E 15 B
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Controversies in the Use of Networks
Networks can be too complex
Poornetwork 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