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CH6: Developing a Project Schedule - Coggle Diagram
CH6: Developing a Project Schedule
Learning Objectives
06-01 Understand the linkage between WBS and the project network.
06-02 Diagram a project network using AON methods.
06-03 Calculate early, late, and slack activity times.
06-04 Identify and understand the importance of managing the critical path.
06-05 Distinguish free slack from total slack.
06-06 Demonstrate understanding and application of lags in compressing projects or constraining the start or finish of an activity.
6.1 Developing the Project Network
The Project Network Defined
Is a graphic flow chart depicting the project activities that must be completed, the logical sequences, the interdependencies of the activities to be completed, and the times for the activities to start and finish along with the longest path(s) through the network—the critical path.
Provides the basis for scheduling labor and equipment.
Enhances communication among project stakeholders.
Provides an estimate of project duration.
Provides the basis for budgeting the cash flow.
Identifies which activities are “critical” and should not be delayed.
Highlights which activities to consider for compressing the project duration.
Helps managers get and stay on the project plan.
6.2 From Work Package to Network
6.3 Constructing a Project Network
Terminology
Activity: an element of the project that requires time but may not require resources
Parallel activities: activities that can take place at the same time, if desired.
Burst activity: an activity that has more than one activity immediately following it (more that one dependency arrow flowing from it)
Merge activity: an activity that has more than one activity immediately preceding it (more than one dependency arrow flowing to it)
Path: a sequence of connected, dependent activities
Critical path: the path with the longest duration through the network
Two approaches
Activity-on-Node (AON) uses a node to depict an activity.
Activity-on-Arrow (AOA) uses an arrow to depict an activity.
Basic Rules to Follow in Developing Project Networks
Networks flow typically from left to right.
An activity cannot begin until all preceding connected activities have been completed.
Arrows on networks indicate precedent and flow and can cross over each other.
Each activity should have a unique identification number.
An activity identification number must be greater than that of any activities that precede it.
Looping is not allowed.
Conditional statements are not allowed.
Where there are multiple starts, a common start node can be used to indicate a clear project beginning on the network. Similarly, a single project end node can be used to indicate a clear ending.
6.4 Activity-on-Node (AON) Fundamentals
Network Information (Automated Warehouse) 實例
Automated Warehouse—Partial Network 實例
Automated Warehouse—Completed Network 實例
6.5 Network Computation Process
Forward Pass—Earliest Times
How soon can the activity start? (early start—ES)
How soon can the activity finish? (early finish—EF)
How soon can the project finish? (expected time—TE)
Backward Pass—Latest Times
How late can the activity start? (late start—LS)
How late can the activity finish? (late finish—LF)
Which activities represent the critical path? (critical path—CP)
How long can the activity be delayed? (slack or float—SL)
Network Information (Automated Warehouse) 實例
Activity-on-Node Network 實例
Activity-on-Node Network Forward Pass 實例
Forward Pass Computation
Add activity times along each path in the network (ES + Duration = EF).
Carry the early finish (EF) to the next activity where it becomes its early start (ES) unless…
The next succeeding activity is a merge activity, in which case the largest early finish (EF) number of all its immediate predecessor activities is selected.
Activity-on-Node Network Backward Pass 實例
Backward Pass Computation
Subtract activity times along each path starting with the project end activity (LF – Duration = LS).
Carry the late start (LS) to the next preceding activity where it becomes its late finish (LF) unless…
The next succeeding activity is a burst activity, in which case the smallest late start (LS) number of all its immediate successor activities is selected.
Forward and Backward Pass Completed with Slack Times實例
Determining Slack (or Float) Times
Total Slack
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Free Slack
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The Critical Path
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6.6 Using the Forward and Backward Pass Information
6.7 Level of Detail for Activities
6.8 Practical Considerations
Network Logic Errors
Activity Numbering
Use of Computers to Develop Networks (and Gantt Chart)
Calendar Dates
Multiple Starts and Multiple Projects
Network Logic Errors—Illogical Loop 實例
Automated Warehouse Picking System Network 實例
Automated Warehouse Picking System Gantt Chart 實例
6.9 Extended Network Techniques to Come Closer to Reality
Laddering
Activities are broken into segments so the following activity can begin sooner and not delay the work.
Use of Lags to Reduce Schedule Detail and Project Duration
A lag is the minimum amount of time a dependent activity must be delayed to begin or end.
Lengthy activities are broken down to reduce the delay in the start of successor activities.
Lags can be used to constrain finish-to-start, start-to-start, finish-to-finish, start-to-finish, or combination relationships.
Example of Laddering Using Finish-to-Start Relationship
Use of Lags 實例
Finish-to-Start Relationship
Start-to-Start Relationship
Use of Lags to Reduce Project Duration 實例
New Product Development Process 實例
Use of Lags (Continued) 實例
Finish-to-Finish Relationship
Start-to-Finish Relationship
Combination Relationships
Network Using Lags 實例
Hammock Activity
Spans over a segment of a project.
Has a duration that is determined after the network plan is drawn.
Is very useful in assigning and controlling indirect project costs.
Is used to aggregate sections of the project to facilitate getting the right level of detail for specific sections of a project.
Hammock Activity Example 實例
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