BIM Workflow: Data Exchange Using IFC Files

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In the BIM workflow, IFC files are frequently used as the basis for data exchange between CAD and structural engineering software. However, there is a fundamental problem with this approach. This article explains various types of IFC files, and provides an overview of the import and export options in the Dlubal Software programs.

Views of an IFC file

Generally, there are two different types of IFC files, the so-called views. The Coordination View describes a model with its physical properties as a solid element, whereas the Structural Analysis View describes components related to an axis as an analytical element. This is shown by a simple example of a wall in the following figure (relative to the center axis).

Figure 01 - Comparison of Coordination View with Structural Analysis View

Generally, CAD programs use the Coordination View to export your data to an IFC file because their components are treated as physical elements (usually solids). Structural analysis software, however, does not necessarily describe its elements as solids, because in structural engineering systems often have to or must be reduced to simpler models.
Thus, the first conflict arises between both views of an IFC file and the data exchange is not easily possible.

Differences due to business models

Another hurdle in the data exchange based on an IFC file is the necessity of the corresponding functional models for a building modeling. The Coordination View (physical model) is used to perform correct mass determinations or collision checks. The Structural Analysis View, on the other hand, is used in structural engineering. This will be illustrated by a simple example. The following figure shows this. It is a structure consisting of two walls and a ceiling.

Figure 02 - Example Structural System for Displaying Branch-Specific Models

Starting from the center axis model, the following models result for this system:

  1. architectural physical model - Coordination View
  2. analytical structural model - Structural Analysis View

Figure 03 - Comparison of Branch-Specific Models / Views of IFC File

Based on this representation, it can be seen that even for the Structural Analysis View, a predictable structural system is not easily created. Accordingly, you have to rework manually here as well.

Export of an IFC file (Structural Analysis View)

Based on the previous explanations, RFEM and RSTAB use the Structural Analysis View to export IFC files. The following shows the elements used in the Structural Analysis View (2x3).

Figure 04 - Elements of Structural Analysis View (2x3)

Furthermore, this IFC file contains:

  • Information and definition of load cases and load combinations
  • Information about cross-sections (names and properties)
  • Information about Materials (Name)

For the data exchange, it is therefore necessary to ensure that the importing program also supports the Structural Analysis View for importing an IFC file.

Import of an IFC file (Coordination View and Structural Analysis View)

If RFEM and RSTAB recognize during the import of an IFC file that the used file was written in the Structural Analysis View, the content is also automatically imported. Since RFEM and RSTAB do not have a physical model in principle, it is not possible to directly import IFC files in the Coordination View. In order to exchange data, an IFC file can be imported with the option "Enable CAD/BIM Model."

Figure 05 - Enabling Import of Physical Models

The subsequently imported solids are not yet Dlubal objects and have to be converted manually into corresponding members, surfaces or solids. For this, the position of the neutral axis and the preferred material can be edited.

Figure 06 - Dialog Box for Converting Architectural Solids

Summary

A continuous data exchange between CAD and structural analysis software based on IFC files is currently difficult to implement in practice, because the described different views and the mostly different philosophies of the software manufacturers could not yet be combined in any official guideline or standard. However, the described options also show that parts of the work process can be simplified using this file format and the corresponding interfaces.

Reference

[1]  buildingSMART International

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RFEM Main Program
RFEM 5.xx

Main Program

Structural engineering software for finite element analysis (FEA) of planar and spatial structural systems consisting of plates, walls, shells, members (beams), solids and contact elements

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RSTAB 8.xx

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The structural engineering software for design of frame, beam and truss structures, performing linear and nonlinear calculations of internal forces, deformations, and support reactions

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