buildingSMART Forums

Confusion about IfcColumn, IfcBeam, and IfcMember

I would really appreciate some clarification on how to determine whether to classify IfcBeam, IfcColumn and IfcMember. Where the objects name matches the predefined types available for one of these, the case is simple, or whether it is obviously the primary structure of the building such as in a concrete frame building. However, there are cases which I am less certain.

For example: a steel frame for a glass lift. Would you call the vertical elements columns? They are primarily vertical, function in compression, but are not part of the primary structure of the building. What about the horizontal elements? Are they IfcBeam, or are they IfcMember with a type of BRACING?

One possible self-interpretation provided by a colleague is that any mostly vertical primary structure is a column, any mostly horizontal primary structure is a column, and everything remaining is a member. If you remove it, and the building falls down, then it is a column or beam. If you remove it, and cladding / awnings fall down, it’s a member.

Another example of ambiguity with my co-workers interpretation: in the following scenario you have blue concrete slabs, red concrete columns, and a white facade system of some kind. The green element is fixed from floor to underside of slab above, and is is, say, a 150mm square hollow steel section. It is obviously primarily vertical, it fixes to primary structural slab, but its function is to act as intermediary support for the facade framing (not shown for simplicity). In this case, is it an IfcColumn, or is it an IfcMember as it is part of “framing” and not primary structure?

Can somebody clarify the intention by buildingSMART?

I am not entirely sure if my method is right, but I tend to use the Entities I see fit and define in the propertyset if the entity is part of the primary structure of the building (LoadBearing = true). You can further specify the entity with a Type Enumeration-- which in some cases is neccesary to get full use out of the entity, like IfcCovering.CEILING. This in turn opens up a new Propertyset, in this case Pset_CoveringCeiling.

As for your situation, what I’d do is:

  • Blue = IfcSlab.FLOOR
  • Red = IfcColumn.COLUMN
  • Green = IfcColumn.COLUMN if stand-alone, or an IfcMember.MULLION (I suppose?) if part of an IfcCurtainWall.

Additionally, the hollow square profile could be defined by IfcRectangleHollowProfileDef.

Agree, assuming the facade system is not a curtain wall, I would also make this choice.