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Time Constraints vs Date Constraints

6 replies [Last post]
Rafael Davila
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Joined: 1 Mar 2004
Posts: 4977

In some jobs I need to model no-earlier/no-latter than time constraints separate or in combination to date constraints but most software do implement date constraint mixing it with time.

For example because of hot whether conditions some concrete pouring shall start after 4pm but not latter than 7pm no matter on what day, that would be a pure time constraint. In other occasions the constraint can be; do not start before certain date because of access limitations by Owner but also the time constraint about the start hour shall be satisfied. Maybe the activity because of some driving logic that moves it beyond the date can theoretically start on next day satisfying the date constraint but at an hour that breaks the time constraint.

How can I model the following scenario:

  • Date Constraint: Start no earlier than next Wednesday
  • No Earlier Time Constraint: Start no earlier than 4pm
  • No Latter Time Constraint: Start no latter than 7pm

Best regards,

Rafael

Replies

Rafael Davila
User offline. Last seen 5 hours 59 min ago. Offline
Joined: 1 Mar 2004
Posts: 4977

It works,

Photobucket

I run a second scenario for activities whose predecessor ends at mid day but must start on next day, perhaps the most common requirement, it also worked flawlessly. Better than limit your model to a day planning unit, I got the best of both worlds, and more, at the activity level.

Best regards,

Photobucket

...................... will thank you as soon as I hammer that milestone.

Rafael,

I do not understand the problem.

If you will define 6 hours work day calendar (from 3pm to 9pm) for concreting activities and will define them as continious, they will start no earlier than 3pm and if their expected finish will be after 9pm their start will be delayed to 3pm next day.

No milestones are needed.

Is there any other reason for their start not later than 6pm?

Best Regards,

Vladimir

Mike Testro
User offline. Last seen 9 weeks 20 hours ago. Offline
Joined: 14 Dec 2005
Posts: 4407

Hi Rafael

Set up different work patterns and apply them to different calendars.

I once did a delay analysis for external cladding in Siberia and each week had a different work period through the winter - from 8 hrs at the start to 3 hrs in the middle and back again.

Best regards

Mike Testro

Rafael Davila
User offline. Last seen 5 hours 59 min ago. Offline
Joined: 1 Mar 2004
Posts: 4977

As for example.

Date Constraint: Start no earlier than next Wednesday ==>> this is easy and modeled by any software

No Earlier Time Constraint: Start no earlier than 4 pm and No Latter Time Constraint: Start no latter than 3 am of next day or of same day-if possible ==>> a start milestone with the appropriate calendar can drive it but each pair requires an update to the extra milestone.

The issue is about ease of use, transparency and the efficiency in creating the schedule and keeping the updates when hundreds of activities have such requirement. We have hundreds of activities with such similar requirement, for some makes sense to start before noon but not latter for others it is just the contrary. The extra milestone and the updating overhead it adds is unnecessary.

It is like modeling lag using an activity instead of lag duration, can do the job but is very inefficient.

On some jobs we schedule walls pouring shall start no earlier than 3 pm but not latter than 6 pm but work can continue until 9 pm under normal conditions, again the start milestone can solve it but adding unnecessary scheduling overhead. This is a planning requirement related to the use of cranes. We use during regular hours the available cranes for the work with big crews and leave overtime for work that can be performed with small crews and no specialized expensive labor.

500% in favor of continuous PDM, any split shall be a management decision no single computer algorithm shall make.

Best regards,

Rafael

Start No Earlier Than constraint shall be applied if to start no earlier than next Wendesday (Date constraint).

Start No Earlier Than 4pm is modeled through activity calendar.

Start No Later Than is usually applied when you need to finish an activity same day when it was started - an activity performance shall not be interrupted. It is better just to define an activity as Continious. In this case if an activity will not finish the same day its start will be delayed to the beginning of the next day.

Rafael Davila
User offline. Last seen 5 hours 59 min ago. Offline
Joined: 1 Mar 2004
Posts: 4977

Perhaps if No Earlier Time Constraint > No Latter Time Constraint then No Latter Time Constraint shall be interpreted as a next day time constraint or same day constraint if possible, otherwise would be mutually exclusive.

As for example.

Date Constraint: Start no earlier than next Wednesday

No Earlier Time Constraint: Start no earlier than 4pm

No Latter Time Constraint: Start no latter than 3am of next day or of same day-if possible

Essentially a start range that can span two consecutive work days.

Think of it as an electrical timer that will triger the start of the activity, once started it will follow the calendars.

PhotobucketPhotobucket

Best regards,

Rafael

P.S. Emergency Generators do have a weekly timer, maybe time of day is not enough ... LOL