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Topics: Scheduling
CPM and PERT
For a construction project, What do you think is necessary to put in place before you implement PERT and CPM techniques?

Muthu
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When I worked in construction projects the best way to communicate all related to project to engineering and others was to show schedules that were created/optimized/monitored using PERT or CPM. But in the last 5 years I am not working with that type of projects or a project where construction component has a great impact so perhaps it has changed in the last times.
Not sure I understand the question but here goes a simplistic approach.

You need to have a work break down structure to start building a schedule, PERT or CPM. You start by creating a list of tasks necessary to achieve the objective. I typically start at the end and repeatedly ask the question: "What is the final task and what do I need to complete before I can start that task?" You then work backwards until you get to the start. Keep in mind that some tasks may not start until a number of other tasks have been completed. This way you establish dependencies thus creat a network. The next step is to determine resources necessary and duration of each task. That will give you the required effort (cost) and project duration. If you can't live with these values you start crashing the schedule - adding resources, establishing concurrent tasks until you are comfortable with the result.

CPM is the common methodology in the construction industry and is usually presented as a bar chart which everyone can understand and follow.
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1 reply by Muthukrishnan Ramakrishnan
Feb 14, 2021 7:47 AM
Muthukrishnan Ramakrishnan
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That explains a lot.
In construction industry it is not rare when project resources are constrained. Both PERT and CPM do not take into account resource, supply, cost and space constraints creating project schedules that are not feasible.
So consider resource leveling for project scheduling.
Muthukrishnan -

If you are asking about the prerequisites for successful use of PERT and CPM techniques, then I'd suggest the following:

1. A WBS or similar decomposition of the scope to a manageable level of detail
2. Expert judgment from stakeholders on the durations, dependencies and constraints affecting the activities
3. Awareness and willingness on the part of stakeholders to use these tools

Kiron
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1 reply by Muthukrishnan Ramakrishnan
Feb 14, 2021 7:52 AM
Muthukrishnan Ramakrishnan
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Agreed. Thank you
Other than my own planning at the beginning or critical points in a schedule, I have have very little success using PERT. Getting one estimate from everyone is difficult enough. Getting 3 point estimates seems to create more pain than extracting teeth.

When using linked dependencies in a schedule network, in addition to the excellent input from Kiron, I would suggest finding a tool that reduces the required effort. In educational examples, I've done this manually but it can quickly become very labor intensive on a real project.

When working projects that have a very tight schedule and the critical path is changing daily, I have spent many extra hours each day updating my manually created network diagrams. With good software and a skilled user, I could cut that time by 90%. Linking up all the dependencies is all well and good, but when you start moving tasks around, you can easily wind up with errors like tasks need to finish before they start. Good software is the difference between getting a message that you have an error somewhere in hundreds of events and dependencies, and showing you exactly which dependencies caused an error.
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1 reply by Muthukrishnan Ramakrishnan
Feb 14, 2021 7:54 AM
Muthukrishnan Ramakrishnan
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Thank you for the explanation. Let me put to use
Feb 12, 2021 6:35 PM
Replying to Peter Rapin
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Not sure I understand the question but here goes a simplistic approach.

You need to have a work break down structure to start building a schedule, PERT or CPM. You start by creating a list of tasks necessary to achieve the objective. I typically start at the end and repeatedly ask the question: "What is the final task and what do I need to complete before I can start that task?" You then work backwards until you get to the start. Keep in mind that some tasks may not start until a number of other tasks have been completed. This way you establish dependencies thus creat a network. The next step is to determine resources necessary and duration of each task. That will give you the required effort (cost) and project duration. If you can't live with these values you start crashing the schedule - adding resources, establishing concurrent tasks until you are comfortable with the result.

CPM is the common methodology in the construction industry and is usually presented as a bar chart which everyone can understand and follow.
That explains a lot.
Feb 13, 2021 9:22 AM
Replying to Kiron Bondale
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Muthukrishnan -

If you are asking about the prerequisites for successful use of PERT and CPM techniques, then I'd suggest the following:

1. A WBS or similar decomposition of the scope to a manageable level of detail
2. Expert judgment from stakeholders on the durations, dependencies and constraints affecting the activities
3. Awareness and willingness on the part of stakeholders to use these tools

Kiron
Agreed. Thank you
Feb 13, 2021 1:33 PM
Replying to Keith Novak
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Other than my own planning at the beginning or critical points in a schedule, I have have very little success using PERT. Getting one estimate from everyone is difficult enough. Getting 3 point estimates seems to create more pain than extracting teeth.

When using linked dependencies in a schedule network, in addition to the excellent input from Kiron, I would suggest finding a tool that reduces the required effort. In educational examples, I've done this manually but it can quickly become very labor intensive on a real project.

When working projects that have a very tight schedule and the critical path is changing daily, I have spent many extra hours each day updating my manually created network diagrams. With good software and a skilled user, I could cut that time by 90%. Linking up all the dependencies is all well and good, but when you start moving tasks around, you can easily wind up with errors like tasks need to finish before they start. Good software is the difference between getting a message that you have an error somewhere in hundreds of events and dependencies, and showing you exactly which dependencies caused an error.
Thank you for the explanation. Let me put to use

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