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IFC Based OPEN BIM Workflow – Part 1

Emoke Csikos

How to prepare your model in ARCHICAD for collaboration in OPEN BIM

For every party collaborating in OPEN BIM it is crucially important to have a shared system of the project regarding: Identical Project Location settings, such as:
  • Project origin
  • North direction
  • Story system
Among the first steps of preparing your model you need to properly set the following:
  • Element Classification
  • Structural Function
  • Position
Let’s see these in details:

Element Classification

Each type of element in ARCHICAD has a default matching IFC type. In ARCHICAD 19:
The IFC based workflow is basically about sharing 3 dimensional model information along with some 2 dimensional information and some metadata assigned to the element that does not affect the element’s appearance but contains specific data. Most of the IFC types that are assigned to ARCHICAD elements by default are obvious, but there is one that is a bit different: GDL based objects’ IFC type is selected based on their place in the subtype hierarchy. For example the Armchair 01 20 object’s subtype is Seating, but since there is no IFC type named Seating, IFC type will be searched and defined by the program by moving upwards in the subtype hierarchy. In this case the next level (parent subtype) in the tree structure of subtypes that has a matching IFC type is Furnishing. So the object’s IFC type will be IfcFurnishingElement.
If there is no subtype under the Model Element subtype that matches an IFC type, the IFC type of the object will be set as a relatively simple type, named IfcBuildingElementProxy. Each ARCHICAD element has a default IFC type set by the program automatically. The IFC type assignment is based on the Element Classification that can be defined in the Settings dialog of the element. In ARCHICAD 19 there is a default classification for all elements called ARCHICAD Type, but you can also reclassify your model element by selecting another type in the roll-down list. (As of ARCHICAD 20 there is no ARCHICAD Type as classification since it caused some confusion, users did not always understand its meaning) The IFC type assigned to the element will follow the change you make in the classification of the element. For example a slab can be classified as a slab or as ceiling depending on its function in the building. The IFC type of the slab will be set accordingly:
Another example: the table on the image was modelled using the slab and the column tools. These were then converted to morph and the morph was classified as Furniture. Therefore, the IFC type was automatically set to IfcFurnishingElement.

Structural Function

The structural function of an element can be set by the structural engineer or by the architect. The structural function can be
  • Load-Bearing Element
  • Non-Load-Bearing Element or
  • Undefined
Setting the Structural Function of all elements properly makes it easier to filter the model. Non-load-Bearing elements are usually irrelevant for the structural engineer so they can be left out. Using the command View > Elements in 3D View > Filter and Cut Elements in 3D gives further options for selecting what model content to save in the IFC file. This is how e.g. windows can be eliminated when exporting the model for the structural engineer.
The Document > Partial Structure Display command offers yet another option to finetune what is included in the export based on what is visible:
  • Entire Model
  • Without Finishes
  • Core Only
  • Core of Load-Bearing Elements Only


Position of elements can also be set in the Settings dialog of the element as
  • Exterior
  • Interior or
  • Undefined
Structural Function, Element Classification and Position can be used as search criteria in Find & Select.
These ARCHICAD properties are of course schedulable and are editable in Interactive Schedules as well.

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