Why Revit hates Steel Fabricator Models (DWG & IFC formats)

[JOfford_13]

I'm in curtainwall fabrication and we often interface with models from steel fabricators who don't use Autodesk products but can provide 3D DWG or IFC files.  For a very complex 10 story building the DWG file may be around 40-70 Mbs and the IFC maybe 150-400 Mbs, containing primarly structural framing, columns, and plate elements, all 100% accurate to what's being fabricated.  I'm assuming these are coming from Tekla but can't confirm.

When it comes time to update our Revit components to these files Revit a few bad things happen.

1.  Directly importing the DWG into the Revit project file works greaty but Revit cannot property cut the DWG in section/plan views.  This requires working with the entire file in wire-frame visual style and often turns into a blur of thousands of lines.  Autodesk, please address sectioning of 3D DWG files in Revit.

  --->  My usual workaround (and yes, it shouldn't really be required for another Autodesk file format) for this issue is to create a Mass family and link the DWGs into it, then load the mass into the project file.  However, if the DWG is too complex Revit simply rejects it.  I've attached example error messages of this procedure.  This "limitation" is completely absurd.  If Revit can't deal with the reality of complicated structures we can't continue to use Revit.  Please Autodesk, take off the any complexity limitations (including the 1/32" minimum line length) in Revit and let users manage their own content.  Sometimes reality is massive.

   At this point I have a perfectly accurate DWG that I cannot use.  Thus I turn to the IFC file.

2.  Converting IFC to Revit is very good once completed however it is extremely slow.  On average it's taking about 8 hours (on a decently powered computer) for Revit to open an 150 Mb IFC file and then save it as its own Revit project file, which will end up being around 200 Mbs.

Navisworks, Inventor, and Rhino have no issues importing the DWGs.  I've explored options of roundtripping via Rhino into Revit but not much success and lots of time wasted.  This issue is a major roadblock for Revit in AIA LoD 400-500 jobs out there in the world.  I feel I will never be able to understand why a precision CAD tool like Revit continues to limit precision to something other than what the user decides.

Has anyone else had better results with such files?

[Alfredo_Medina]

In regards to curtain walls, I know for sure that Revit can do all the work that a curtain wall detailer might need. As an example, my friend Dave Jones has been working with Revit sucessfully for five years and now he is doing all the work in Revit: he models everything in Revit, annotates the sheets, takes quantities, and makes his details. To overcome the 1/32" limit, he has developed a simpler way of drawing screws and other small objects. But if you are not a detailer but a fabricator, that simplication is, most likely, not possible. In that case I would agree that Revit is not the tool for the job. I would suggest working with Inventor, instead.

[JOfford_13]

Thanks for the reply.

My post however was not about Revit's ability to model curtainwall.  We do that all the time and extract quantities just fine.  The problem I was trying to point out was how to best interface with very large, complex, detailed, structural steel models, upon which curtainwall elements (anchors/plates/attachments) are dependent on.  Those models are what Revit struggles with.

[Alfredo_Medina]

The error message says that there are too many faces. Some programs have the option to export to solids instead of faces. Is that possible? Have you considered that option?

[JOfford_13]

I'd be interesting to see but I don't have much hope.  Geometry-wise, solids should have roughly the same number of faces as polyface meshes.  I may bug the provider and see what other options they have.

On a similar note my computer just finished chugging on an IFC model which is a 12 story steel structure.  It took 48 hours to open in Revit 2012 (with me occasionally clicking ok to numerous warnings of "Can't join elements"/"Can't keep elements joined"/"Can't create blend"/etc) and save as an .rvt.  See the attachment for the file size.  It's completely ridiculous.  Can anyone explain the extremely poor expansion of file size?

[Alfredo_Medina]

Don't know... but you would be saving lots of time if the structural models that you receive were modeled in Revit. I know that other applications such as Tekla can handle more detail in the model but having to wait 48 hours to open a model is outrageous. That's more than a week of work. Most likely, the building could be modeled from scratch in Revit in less time than that.

[LinasL]

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@JoeOfford wrote:

Thanks for the reply.

My post however was not about Revit's ability to model curtainwall.  We do that all the time and extract quantities just fine.

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A bit off topic but.. Are you only extracting quantities using Revit or also make fabrication drawings, etc.?