IFC Data Exchange

From CAD model to FE mesh
From CAD model to FE mesh

The data exchange format IFC (Industry Foundation Classes) is a manufacturer-independent transnational interface, which supports the exchange of all geometric and alphanumeric BIM data.

buildingSMART International develops and establishes IFC as an open standard for the building industry. IFC is registered as an international standard in ISO 16739.

The IFC version IFC 2x3 is used. The data can be exchanged using the import or export function.

Coordinate System

In the IFC product model the z axis of the global coordinate system typically runs from below to above. This is counter to the convention used in InfoCAD. To avoid all objects standing on their heads after an export or import, they are turned 180° around the global x axis.

Import

The data import consists of two functional areas:

  • Importing Analysis Models (frames works or model objects)
  • Importing the Geometry of Building Elements

1. Importing Analysis Models

The import is carried out for the static calculation models (IfcStructuralAnalysisModel) saved in the transfer file and selected by the user.

 

Dialog for selecting the import data
Dialog for selecting the import data
Imported framework
Imported framework

Example

The following illustrations display the import of a framework from file 'gtstrudl_physical.ifc' (Source: NIST, National Institute of Standards and Technology).

The file contains a analysis model with the name 'Loads and Results Exported from GTSTRUDL' and also building elements of various types that have been deselected for import. To import frameworks, either the FEM or the RSW static mode must be active.

2. Importing the Geometry of the Building Elements

This functional area calls for construction model objects saved in the transfer file whose type is derived from IfcBuildingElement. They include, for example, IfcBeam, IfcColumn, IfcSlab and IfcWall(StandardCase). Only objects with the geometric display ‘SweptSolid', 'Clipping', 'Brep' and 'MappedRepresentation' are considered. In InfoCAD special drawing objects are generated from these that make it possible to continue to use the geometry of the building elements. The snap modes 'End', 'Middle' and 'Normal' allow you to use, for instance, characteristic points for measurements or for the design of model objects.

Imported building elements
Imported building elements
Properties of the IFC object
Properties of the IFC object

Example

Building elements from the 'gtstrudl_physical.ifc' file (Source: NIST, National Institute of Standards and Technology).

The figure above shows several further characteristics that are imported in addition to the geometry of the building elements. These include

  • GlobalId: identification of the building element
  • Name, Descrip.: description
  • Material: assossiated material description
  • LoadBe(aring): displays whether the element bears load (1) or not (0)

Transformation into Model Objects

Imported drawing objects whose geometric display is based on the extrusion of a base area (IfcExtrudedAreaSolid) and who originate from

  • IfcBeam
  • IfcColumn
  • IfcMember
  • IfcSlab
  • IfcWall(StandardCase)

 

can be transformed, with the help of the program, into model objects (select 'Transform' from the shortcut menu, FEM static mode). As part of this process, linear elements are turned into edges with the meaning 'Free beam'. The generated beam section corresponds to the profile definition used for the base area. Objects originating from IfcSlab and IfcWall whose base area consists of a traverse with exactly four points are converted into model surfaces.

The following illustration displays some of the building elements from the file 'AC-90Smiley-West-14-07-2005.ifc', as well as the resulting model surfaces
(Source: http://www.iai.fzk.de/www-extern).

Geometry of the building elements / Model objects, not joined jekte verschnitten / Generiertes Elementnetz
Geometry of the building elements / Model objects, not joined

Because the model objects are created based on the wall or plate axis surfaces, gaps usually exists between neighboring objects (see detail).

As a remedy, all objects are joined with one another during the transformation and, if necessary, marginally reduced or enlarged. If for walls standing on top of each other the wall axes do not match up, for instance due to differing wall thickness, it might be necessary to add transition surfaces that are not perpendicular. In addition, openings that are close to the edge are adjusted.

The described operations help to improve the continuity between the model objects. This can eliminate the need for manual corrections in many cases. The following illustrations show the joined model objects and the element mesh that has been created as a result.

Model objects, joined
Model objects, joined
Generated element mesh
Generated element mesh

Export

The function applies to model objects and frameworks. The following data will be exported:

Model objects

  • Model edges with meaning 'free beam'
  • Model faces

Framework, if no model objects exist

  • Static analysis model without results
  • Construction model of the 3D framework with the objects IfcBeam, IfcColumn
 
Framework exported with InfoCAD displayed in IfcViewer (Forschungszentrum Karlsruhe, Institut für angewandte Informatik)
Framework exported with InfoCAD displayed in IfcViewer (Forschungszentrum Karlsruhe, Institut für angewandte Informatik)