Construction Scheduling. Do you have a Schedule or a CPM Schedule?

Is what you’ve created a CPM schedule? Or is it a schedule with dates and activity bars?

Can you tell the difference?

First, CPM stands for Critical Path Method and is kind of a general term often used for Precedence Diagram Method, PDM schedule development.

Almost any schedule developed, using one the many current scheduling software programs, will be created based on the precedence diagram method. Most of the current scheduling software programs are set up for that.

Creating the WBS structure or summary bars and adding activities that model the work for the project in these programs will produce a schedule.

But is this really a useful schedule? Or is it a list of activities with dates assigned through the use of incomplete logic and date constraints? We get a list of activities with planned dates. That’s all we need, right? Isn’t that a schedule…?

Not really. That may be useful for conveying the basic plan for future work. But this is not a dynamic CPM schedule that can be used to model future work based on current progress, produce a Longest Path, or model the impact added or delayed work may have on future completion dates for the project.

I run into this a lot. A PM or someone on the project team will create a schedule and assume it is a CPM schedule. There are a few requirements to meet before a schedule can be considered a true CPM schedule.

Listed below are the minimum requirements for a CPM schedule.  

  1. Calendars.            

For your schedule to be reasonably accurate, calendars need to be created to allow activities to have durations based on planned work periods. This usually requires the development and use of multiple calendars to account for various work periods such as 5-day 8-hour workweeks; 4-day 10-hour workweeks; workweeks with specific holidays set as non-workdays; anticipated non-workdays due to anticipated weather impacts….

  • Logic.

The only activity without a predecessor should be the first activity in the schedule. Usually NTP. The only activity without a successor should be the last activity, usually Project Complete or CCD… To be a true CPM schedule, all activity dates should be driven by the predecessor activities durations and logic. Having only all the predecessors assigned is not enough. There must be activities that are driven by the start or finish of a predecessor activity. If the activity in fact, does not drive the start of any work except the end of the project, then the successor should the last activity.

  • Constraints.

There are valid uses for date constraints in any schedule. However, overuse creates multiple interruptions to the forward and backward passes which determine float values. This produces snippets of paths based on the types of date constraints. Just using a constraint to set a planned start date for an activity is not a valid use of a date constraint. An interim date constraint should represent an external driving force for an activity or milestone or the contractually required date for a milestone. Limiting the use of date constraints allows the activity durations and activity relationships, (logic) to drive finish dates and produce a Longest Path to the finish of the project. This gives us the Critical Path for completion of the project.

  • Relationships and lags.

There valid reasons for using SS and/or FF relationships to model the planned sequencing of activities. But they should not be used in lieu of decomposing the work. Using SS and /or FF relationships should only be used to model work which will run concurrently even when the work is broken down to a reasonably small duration. Lags should not be used to model work or a waiting period. Lags are not transparent and using a lag with SS or FF relationships results in the work being modeled to start or finish based on a set time after the driving relationship has been satisfied, not on actual measurable work being complete to a specific point.

These are the most basic requirements for a CPM schedule.

The idea is to end up with a schedule that will model the impact actual progress to-date has on remaining scheduled activity dates. A CPM schedule can be used by the project team to proactively manage current schedule slippage, more accurately manage resources, and project finish dates and time-scaled cost flow.

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I’d love to hear what you think!

Please visit https://conschmanservices.com to learn more about Construction and Schedule Management Services, LLC

Please visit my LinkedIn account to learn more about me.

Please visit my “The Blue Book” ProView.

Paul Epperson CCM, PMP, PSP, PMI-SP

Construction Scheduling. Milestones and Constraints.

From time to time, I hear a project team member refer to a constraint when what they are actually referring to is a milestone.

This is really a “jargon” issue. I’ve heard people refer to a milestone with the intention of the milestone being a constraint on the project. I’ve heard people describe a project constraint as a schedule constraint.

It gets a bit confusing.

A PM may consider a required completion date of a phase of the project as a milestone. To a scheduler, this is an interim milestone and may or may not be date constrained, (Constrained with a schedule constraint assigned in the CPM schedule software program). If this milestone has a contractually required date, a scheduler may assign the appropriate date constraint. If the milestone is just for reporting purposes, the scheduler need only make sure the appropriate activities drive and are driven by the milestone activity.

A PM may refer to a project constraint, like the coordination with an owner delivery or requirement from outside of the project scope and control of the contractor. A scheduler will consider this an external constraint and may assign an appropriate date constraint. (If the date constraint would be a “start no earlier than”, I sometimes prefer to use a lag to NTP… I like to avoid the use of date constraints….).

A scheduler shouldn’t assign date constraints to every “milestone” or “constraint” referenced by the project team. The use of date constraints should be minimized and only applied when necessary.

The PM should understand that they may need to clarify when they really need a date constraint applied. The scheduler may not pick up on the requirement based on discussions among the project team.

The communication between the project team and the planner / scheduler is critical to the successful development and management of the project schedule. The different “jargon” we use can make this more difficult. We need to be aware of this and be sure to clarify when we’re unsure.

I’m sure many of you have comments or additional insight into this subject. Please share!

I’d love to hear what you think!

Please visit https://conschmanservices.com to learn more about Construction and Schedule Management Services, LLC

Please visit my LinkedIn account to learn more about me.

Please visit my “The Blue Book” ProView. Paul Epperson CCM, PMP, PSP, PMI-SP

Construction Scheduling. Including Inspection, Testing, and Commissioning Activities in the Construction CPM Schedule?

Are you including activities for the testing of equipment and systems, inspections for acceptance of systems and areas, and the commissioning of systems when you develop your baseline schedule?

People often focus on the “construction” activities when developing the schedule.

But the construction activities are only a part of the plan to execute the project. There are submittals and procurement, permits, and the closeout process.

One of the areas often overlooked is the inspection, testing, and commissioning process. There will be all kinds of inspections for the acceptance of specific work and entire systems. While it’s not a good idea to try and add all the specific installation inspections and tests that occur on an almost daily basis. We should include the inspections and tests for systems.

It makes sense to include an inspection and pre-operational test for the fire alarm system, fire suppression system, elevator, security system, electrical system, and mechanical system for a specific area or structure. There may be more for your specific project… Unfortunately, I see schedules that only have an activity at the end of the schedule named “commission” or “punch list inspection”. These activities are vague and can’t really address the need to test the systems individually and as necessary, in conjunction with each other. (Think Fire Alarm and Elevator or Fire Alarm and HVAC system zone controls).

Sometimes, the schedule specifications will include specific requirements for the inspection, testing and commissioning processes. Usually, the specification requirements are more general. Regardless, it is in the best interest of the project to include activities for these quality assurance activities in the schedule.

Not having a series of activities for the development, submittal, review, and approval of a fire alarm test plan or mechanical system commissioning plan creates a large risk for the schedule. While everyone may understand these plans are necessary and the testing is required before substantial completion can be obtained, many project teams don’t include the entire process in the project schedule. We also need the actual start-up and pre-operational inspection and testing work, the commissioning of the system, and the performance testing in the schedule. Depending on the size of the project and system, these may or may not occur at the same time. For a smaller renovation project, it’s not unreasonable to expect the inspection, testing and commissioning of a system will all happen at the same time over the course of a couple of days. On a larger more complex project, there may be a third-party commissioning agent and the system may be large and complex enough that the inspection and pre-operational testing will take several days with additional coordination with other systems.

Not including activities for this work will create a delay situation at the back end of the project, when you can least afford it.

We need to put a lot of effort into looking at the end of project QA and closeout work to make sure we include everything we need. If we do not have the time for this work allocated at the beginning of the project, we will certainly not have any room to execute this work at the end of the project.

I’m sure many of you have comments or additional insight into this subject. Please share!

I’d love to hear what you think!

Please visit https://conschmanservices.com to learn more about Construction and Schedule Management Services, LLC

Please visit my LinkedIn account to learn more about me.

Please visit my “The Blue Book” ProView.

Paul Epperson CCM, PMP, PSP, PMI-SP