Tuesday, February 15, 2011

The 'I' in BIM - Concrete Beam Surface Area - Material Take off Problem

This is a post I have been meaning to put up since the back end of last year, for some reason I put it on the back burner and then never came round to writing it up.

I was asked if Revit can schedule the surface area of beams for the purpose of calculating how much paint would be required to cover the beams.

My simple response was of course Revit can do that....

So I quickly got to work and soon realised something wasn't quite right, when doing a test manually to calculate the surface area of the beams in a small portion of this model, the answer I was getting contradicted the schedule within Revit.

Back to the drawing board.

I soon worked out that the problem is when a beam was joining a wall or column. The 'surface' that joins that wall or column, in theory should not show up in the surface area schedule, because that face will not be painted, that surface will never be visible due to the nature of concrete construction - concrete 'joins' concrete.

Revit however doesn't recognise that (even though Revit does recognize that concrete joins concrete)

The images below, show a beam on it's own and the schedule for that beam.





The images below show the exact same beam, joining a wall, and the schedule for that beam.





There is a difference of 0.25m2.

While this isn't a huge different, if this was a large scale project and you were pushing the use of BIM, and giving the contractor / QS as much "accurate" BIM information as possible to assist in the pricing or value engineering process, this could cause quite a headache and perhaps some embarrassment.....

Below are images showing the same problem if a wall below is butting up against the underside of a beam.

Beam on it's own.

Schedule of the above beam.


Beam with wall butting up to underside.




Schedule of the above beam.


Once again, both schedules show the same result.

Basically, I am pointing out that a material take off schedule that schedules the surface area of concrete objects as if they are 'floating in space' rather than the actual, physical, visible, constructed surface area of the objects, has little to no use at all in a project / construction environment.

2 comments:

  1. Ive tried it with two beams crossing each other assuming it was the difference in families, but no change. The beams were of the same family, same material etc. Maybe something to highlight to Autodesk.

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  2. I swear this came up somewhere before where they were trying to do takeoffs for CIP concrete formwork.

    I thought they had a fix/solutions - but I'm drawing a blank in my search.

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