Contents:

• Concept
• IFC import options
• Model Adjustments
  • Type Modification
  • Analytical Member Correction
  • Analytical Model Adjustment
  • Continuity Check

Concept

FEM-Design can read IFC models and create native and editable FEM-Design analytical model elements from the following types of structural building elements: IfcColumn, IfcBeam, IfcMember, IfcSlab, IfcWall, IfcPlate and IfcRoof. Other IFC types of IFC Building Elements (for example IfcStair, IfcFooting, IfcCurtainWall, IfcPile), or IFC Distribution Elements (MEP equipment), or IFC Furnishing Elements can be displayed as reference elements only in the model space.

The most important steps to get a correct, usable structural analytical model from the IFC input are:

Loading IFC file by applying conversion and mapping settings. As a result, FEM-Design creates editable analytical model members that are not properly connected to each other (the analytical model is not continuous). The non-recognized and non-structural elements can be displayed as reference elements in the model space.

Creating continuous and task-appropriate analytical model with numerous checking and automatic adjustment tools (model adjustments). Use unrecognized, non-convertible elements as reference elements when creating analytical members using the FEM-Design tools.

IFC import options

When loading an IFC file (with File > Open) a dialog pops up with the following conversion and general options:

Bar analytical axis position: select one option to set the axis position of the new FEM-Design Beam and Column analytical members generated from IfcBeams, IfcColumns and IfcMembers.

• Center of solid sets the position of the axis to the center of the recognized cross-section of the IFC physical body.
• Local coordinate system, centric sets the position to the axis as described (if available) for the IFC element and without considering eccentricity.
• Local coordinate system, eccentric sets the position to the axis as described (if available) for the IFC element and with considering eccentricity.

Shell analytical plane position: select one option to set the plane position of the new FEM-Design Plate and Wall analytical members generated from IfcSlab, IfcWall, IfcPlate and IfcRoof.

• Center of solid sets the position of the plane to the center of the recognized IFC physical body.
• Local coordinate system, centric sets the position to the plane as described (if available) for the IFC element and without considering eccentricity.
• Local coordinate system, eccentric sets the position to the plane as described (if available) for the IFC element and with considering eccentricity.

Filter for load bearing elements (if available): check that in order to convert only the structural elements (IfcBeam, IfcColumn, IfcMember, IfcSlab, IfcWall, IfcPlate and IfcRoof) that are classified as load-bearing elements in the IFC file ("LoadBearing" IFC boolean-type property with "True" value in the IFC exporter software).

Import original geometry as solid: check that option in onder to generate solids from the body of structural elements besides their automatic analytical member generation, and place them on "Imported solids" Drawing layer as reference. This option also provides a visual opportunity to check the success of the analytical member conversion, by coloring the solids:

• Green represents physical elements converted to analytical members without any problem.
• Orange represents physical elements converted to analytical members but with some issues (for example the physical body is too complex to convert,or cross-section cannot be identified).
• Red represents physical elements not converted to analytical members

Import as reference solid: check that option in order to generate solids from the body of non-structural IFC element types that are not supported for conversion, and place them on "Imported solids" Drawing layer as reference. The solid of these elements will be blue.

Comments:

The automatic conversion can be controlled by mapping the materials and cross-sections of physical IFC elements to proper FEM-Design data. Although the conversion process try to recognize valid cross-sections, the "Section" mapping can override them. If the cross-section is not recognizable and there is no mapping the cross-section of the default element is used (with a warning message).
 

Model Adjustments

Type Modification

The result of the conversion depends on the type of IFC element to be converted:

The IFC output type in modeling software is most often tool- or classification-driven. Thus, it may happen (typically in architectural practice) that, for example, a structural element that would be considered as a wall in a structural analysis was modeled with a column creator tool in a modeler and was exported as an IfcColumn. This is converted to a Column analytical member by the FEM-Design automatic converter. To solve this "modelling" issue, we can change the analysis and so the FEM-Design structural object type (here Column) with the CONVERT tool of the target element (here one of the wall commands). The following figure shows an example of its use.

The converted object keeps as much properties of the original one as possible; all other properties are derived from Default settings of the target object's tool. An examples: if the original object is a Wall, the converted Column gets its material from the Wall's material, its cross-section is set according to the Wall’s width and thickness, its length is equal to Wall’s height, but its analysis and design data, its Stiffness values and its End conditions are set according to Default settings of the applied Column command.

The following table shows all the conversion possibilities of the structural elements:
 

Multiple Beams or Columns can be converted into a single common Profiled panel, if the selected elements are connected to each other and their common geometry and position allows.

Analytical Member Correction

When converting physical elements, due to inaccurate physical modeling and differences between physical and analytical models, members with incorrect or distorted geometry can be created from the point of view of analysis and design.

These cases can be checked and resolved easily and quickly with the Correct model tool (Tools menu). The image shows examples of solutions to the following major and common problems:

1. There may be overlaps between the created members
2. Solid element operations (SEO) performed in physical modelers can cause small redundant elements and holes in 2D analytical members too.
3. Small parts unnecessary for analysis may remain around the openings.

Analytical Model Adjustment

The physical body geometries stored in IFC and their automatic conversion based on their parameters (lengths, heights, mid-planes etc.) do not give a continuous analytical model. As a post-process of the IFC import, we should connect the analysis members correctly by applying position and geometry modification rules (like axial or planar stretch, cutback and parallel offset). The Adjust analytical model tool provides tools to resolve such modelling issues.

Adjustments can be made between structural elements (for example "fit Beams to a Plate (plane)") or to the structural grid defined by Storeys and Axes. A Storey can be used as an infinite horizontal adjuster plane, while an Axis can be used as an infinite vertical adjuster plane.
 

Storeys and Axes can be easily and quickly allocated to analytical members generated from an IFC model. Just select (even faster with multi-selection) horizontal elements (Plates and Beams) for the Storeys, or Beams and Plate/Wall edges for the Axes. In case of Storey definition, if more objects are selected and their position is closer than a given Tolerance, Storey will be generated at the bottom-most object’s level.

Continuity Check

The correctness, so the continuity, of the model can be checked by the following:

• Run a quick finite element mesh generation without any error (Mesh tab > Prepare), or
• run a quick analysis for the self-weight after support definition, and check displacement with deformed shape.

Parent topic: BIM Integration > IFC 

Check also:

• Correct model tool
• Adjust analytical model
• Objects conversion
• Export to IFC