Forums >> Revit Building >> Technical Support >> new slabs, existing slabs, and the nature of constraint(s)

dhoff13

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Joined: Tue, Apr 26, 2011
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I'm working on remodeling an existing warehouse. The existing floor slab is not even close to being level (as much as an 18" drop across the space). I have modeled the existing slab with a generic floor, which I then pulled down in one corner with a control point.

My plan is to pour new slabs on top of the existing slab in order to create level surfaces in the building. I need to keep quantities accurate, so is there anyway to model the new slab so that its bottom face is constrained to the shape of the exsiting slab?

I've attached a picture, but please let me know if the question doesn't make sense.

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WWHub

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For quantity purposes, the only way I can see to do this is to make a slab as deep as your deepest area then use an in-place void to cut the bottom away as you have described.

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dhoff13

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That would definitely work.

My walls can simply attach to the existing floor. they will continue to match the slope even if i change them (or the floor) after they are built. Is there not a way to make the new floor slab do the same? In a perfect world, the bottom surface of the new slab would by constrained to the top surface of the existing slab, can that be done?

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WWHub

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No.

I did an experiment creating a sloping slab then another flat slab taht filled the area to flat.  I looked at the volumn of both slabs then joined the two.  The flat slab alwyas stayed complete (no matter what creation order) and the sloping slab was cut to the bottom of the flat slab.  A worthy experiment but wrong results.

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AbsoluteBIM

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Joined: Fri, Jun 17, 2011
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i can't comment on your revit question but would like to warn you about your intended construction. If you intent to have a slab with a vanishing thickness; the thinner portions will be very fragile and will likely fall apart with just foot traffic. Usually a concrete topping will maintain a minimum thickness (consult the concrete contractor) to ensure durability. Just a note of warning. 

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