BIM Workflow: Data Exchange Using IFC Files

Technical Article

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 IFC File

Generally, there are two different types of IFC files, the so‑called Views. Coordination View describes a model and its physical properties as a volume element, whereas the Structural Analysis View describes components with regard to an axis as an analytical element. This is illustrated on a simple example of a wall in Figure 01 (with regard to the central axis).

Figure 01 - Comparison of Coordination View with Structural Analysis View

In general, CAD programs use Coordination View for exporting your data to an IFC file because this concerns the structural components as physical elements (usually solids). However, a structural engineering software does not necessarily describe the elements as solids because structural designs often require reducing structural systems to simpler models.

This results in the first conflict between both Views of an IFC file so the data exchange is not straightforward.

Differences due to Branch-Specific Models

Another obstacle in the data exchange based on an IFC file is the need for models of the corresponding branch for structural modelling. Coordination View (physical model) applies to the determination of correct dimensions or collision checks. On the other hand, Structural Analysis View is used in structural design. This is illustrated by a simple example in the following figure, which shows a structure consisting of two walls and a ceiling slab.

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

Based on the central axis model, the following models result for this structural 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

This representation shows that even for Structural Analysis View, it is not easy to create a computable structural system. Here, it is also necessary to adjust the model manually.

Export of IFC File (Structural Analysis View)

Based on the facts mentioned above, RFEM and RSTAB use Structural Analysis View for exporting IFC files. The following figure shows the elements used in Structural Analysis View (2x3).

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

This IFC file also includes:

  • Information about and definition of load cases and load combinations
  • Information about cross‑sections (names and properties)
  • Information about materials (name)

Therefore, it is necessary to ensure that the importing program supports Structural Analysis View for the IFC file import.

Import of IFC File (Coordination View and Structural Analysis View)

If during the import of an IFC file RFEM and RSTAB detects that the used file was created in Structural Analysis View, the content is imported automatically. Since RFEM and RSTAB basically do not work with a physical model, it is not possible to import IFC files of type Coordination View directly. In order to exchange the data, select the “Enable CAD/BIM model” option to import an IFC file.

Figure 05 - Enabling Import of Physical Models

The solids imported subsequently are not yet “Dlubal” objects and must be converted manually into the corresponding members, surfaces, or solids. For this, it is possible to edit the neutral axis position and the preferred material.

Figure 06 - Dialog Box for Converting Architectural Solids

Summary

A continuous data exchange between CAD and structural engineering software based on IFC files is currently problematic, because of the different Views and mostly because the different software producers' philosophies have yet to be unified in any official guideline or standard. However, the options described in this article show that the process can be facilitated when using this file format and the corresponding interfaces.

Reference

[1]   buildingSMART - International. (2017). Retrieved 3 August 2017.

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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

RSTAB Main Program
RSTAB 8.xx

Main Program

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