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IfcStructuralElementsDomain Schema types: IfcPile or IfcFooting vs IfcColumn or IfcSlab

#1

Hello,

Is there any main difference, from the perspective of geometry types, between some types of the IfcStructuralElementsDomain Schema, such as IfcPile of IfcFooting in comparison to similar types of the IfcSharedBuildingElements Schema, i.e. IfcColumn or IfcSlab. ?

A similar question could be related to IfcFooting.FOOTING_BEAM vs IfcBeam. Are there geometry behaviour differences?

Thanks

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#2

From my understanding IFC separates the concept of geometric representation from BIM data. Any type of IFC class can have any type (or even multiple) of geometric representation. In FreeCAD, for example, you can change any shape to be any IFC class. The shape can then be further tailored into the exact method of geometric representation (extruded profile, BREP, NURBS, etc).

Most other BIM authoring programs tend to have preset geometric controls for certain object types, and this may make people think that geometry and data type is related, but this is an artificial limitation and not present in IFC from my understanding.

#3

True, any geometry representation can be assigned to any element that can be related to an ifcRepresentation.
I can see some logic behind the typical representation of certain types of builiding elements with certain types of geometric representation, for example the fact that its permits the standardization of measurements for each type of building element…

#4

I agree with that logic of having different quantities regarding type.

http://www.buildingsmart-tech.org/ifc/IFC4/final/html/schema/ifcstructuralelementsdomain/qset/qto_footingbasequantities.htm

But it would be interesting to know which particular schema feature is not implemented, in particular in Autodesk Revit and Graphisoft ARCHICAD, that blocks those geometries converting into native elements, as they already do with IfcColumns or IfcSlabs. Even when you are creating those geometries in the same BIM authoring tool and mapping them to the right class (i.e. IfcFooting), they appear after importing as objects (non native).

#5

Archicad could create an ifc model classified as ifcFooting using IfcShapeRepresentation of a extruded profile. This element could potentially be created with the column tool, or may be with the slab tool.

Once exported the ifc, the info about wich archicad tool was used to create the footing element is lost.

Then, when importing back the ifc model to archicad, in the abscense of a specific tool for footing, archicad has re-created it as an generic Object, probably using a extrusion method in the GDL definition, and properly classifing it as a footing element

I´am just guessing, but this makes sense to me…

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#6

Revit is doing it similarly…

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