BIM in Structural Engineering

Dlubal Software and Building Information Modeling

23 June 2014

Planning without data exchange between CAD software and structural analysis software is nearly impossible with regard to construction projects containing complex geometries. Example projects are the Bahá’í Temple in Chile and the roofs of the Frankfurt Trade Fair entrance gates.

For both projects the modeling was done in Rhinoceros, a 3D modeling software. Then, the geometry data was transferred to the structural analysis software RFEM/RSTAB. Both structural analysis programs provide a variety of powerful interfaces and program connections that allow for a BIM oriented planning. For example, they have direct interfaces with Tekla Structures, Revit Structure, Autodesk Structural Detailing and Bentley ISM.

Bahá’í Temple in Chile

The "Temple of Light" is currently being built in Chile and should be complete at the end of 2014. It is one of eight Bahá’í temples worldwide. The monotheistic Bahá’í religion has about seven million followers.

The German company Josef Gartner GmbH was given the job of planning, designing and constructing the entire structure above the foundation.

The shape of the temple resembles a nine-petalled blossom of a lotus flower. The building has a diameter of about 34 m and a height of 30 m. The substructure consists of a two-story concrete structure and a flat footing.

As the site is located in a Chilean region with a high seismic risk, it was necessary to uncouple the structure horizontally from the ground with regard to vibrations. That is why a total of ten friction pendulum bearings were arranged between the concrete columns and the second intermediate ceiling.

The steel supporting structure is a kind of space frame with an upper and lower chord layer consisting of rectangular cross-sections as well as round pipe diagonals serving as connecting elements. The nine petals that are identical in construction are closing with their leaf apices at the maximum point forming a light dome (oculus). The structural skeleton is formed, like for real plant petals, by an interior framework consisting of round pipes with thicker section walls of d = 323.9 mm.

Modeling in Rhinoceros

First, the temple was modeled in the design software Rhinoceros. Then, the 3D line model was transferred to RSTAB as well as to RFEM and optimized in close cooperation with the architect.

The analysis model of the steel structure was calculated by Gartner in RFEM and RSTAB considering the impact of earthquakes.

Roofs Above Gates of Frankfurt Exhibition Grounds

In 2008, the German company Messe Frankfurt GmbH organized an architectural competition for planning the redesign of the entrance leading to the exhibition center. The aim was to design roofs for the southern and northern gates, which should be developed as extraordinary structures with high recognition value.

The winning designer was the German architect Ingo Schrader from Berlin, who worked closely together with the German structural engineers Bollinger + Grohmann. In August 2013, the roof construction was finished on the northern gate.

Roof Structure of Northern Gate

The shape of the roof is oval. Its size is 42 m x 18 m with a maximum lamella depth of 60 cm. The roof cantilevers up to 10 m and is only 15 cm thick on its edge. It is supported by four columns that are placed in an irregular grid. Their pyramidal shapes visually represent the downward force distribution in the columns. Due to their triangular shape, they appear particularly slim and the roof has the illusion that it is floating.

Connection of Rhinoceros and RSTAB by VBA Script

The roof support structure was generated and optimized by means of a computational model. One may have the impression that the axes of the load-bearing lamellas are randomly arranged. But their arrangement is the result of a computerbased design process where structural, formal and manufacturing boundary conditions were brought in line.

Then, the heights and widths of the lamellas were optimized. In this optimization process RSTAB was connected with the design program Rhinoceros by using an individually created VBA script. A special algorithm iteratively reduced the cross-section dimension of the flat steel lamellas on the basis of the occurring equivalent stresses.

Interfaces of RFEM and RSTAB

The data exchange between Rhinoceros and Dlubal programs currently works with the exchange file format DXF which is the most common exchange file format in the CAD field. By using the DXF interface, it is possible to import, for example, the lines of the individual layers as members to RFEM/RSTAB.

Further exchange file formats which are available in RFEM/RSTAB, in addition to many others, are IFC, STP (for example for Intergraph, Advance Steel, SEMA, Cadwork, HSB-Cad etc.), and DSTV (for example for Bocad and Frilo).

Direct Interfaces Available in RFEM and RSTAB

As mentioned at the beginning, Dlubal Software programs have direct interfaces with Tekla Structures, Revit Structure, Autodesk Structural Detailing and Bentley ISM.

Design results of the RFEM add-on module RF-CONCRETE Surfaces including geometry can be transferred to Autodesk Structural Detailing. For example, it is possible to export the result values for the required top and bottom reinforcement calculated in RF-CONCRETE Surfaces. Then, in Autodesk Structural Detailing, the corresponding reinforcement drawings will be created.

The interfaces with Tekla Structures, Revit Structure and Bentley ISM are bidirectional, meaning that data can be transferred in both directions. The advantage is that changes in one model can be easily updated in the other by a click of a button.

The intelligence of objects won't get lost during the data transfer, members remain members, walls remain walls, etc. Information about cross-sections, supports and releases, if contained in the model, are transferred as well.

To provide the user with the possibility of BIM oriented planning, the Dlubal company adapts its interfaces continuously to the current versions of the other programs. Furthermore, the interfaces themselves are subject to continuous development.

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