Enhancing Structural Design with Parametric FEM Toolbox

Technical Article on the Topic Structural Analysis Using Dlubal Software

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Technical Article

Author: Diego APELLÁNIZ

B+G Ingenieure Bollinger und Grohmann GmbH; Alt-Moabit 103, 10559 Berlin; [email protected]

The Parametric FEM Toolbox is a plugin developed by the author in collaboration with Bollinger + Grohmann that implements the RF-COM API of the finite element software Dlubal RFEM in the visual programming environment of Grasshopper in order to establish a connection between these two platforms. Both the transfer of data from Grasshopper into RFEM and back from RFEM into Grasshopper are supported. Thus, new possibilities beyond the options of the conventional graphical user interface (GUI) of RFEM are enabled: the use of the Rhino 3D-Modelling tools to create NURBS curves and surfaces, the possibility to parametrically modify an existing FE-Model or part of it, the export and process of data of a FE-Model which sometimes is not even available through the program GUI such as the 3D shapes of beam elements, etc. Due to these functionalities and its object-oriented structure and compact graphical user interface, this tool can easily be adapted to numerous workflows and optimization processes.

1. Introduction

Since the late 1980s and 1990s there has been a paradigm shift in architecture characterized by a new building design approach, in which variable and adaptative forms are preferred to the traditional simple repetition of rigid forms. These new requirements, and not the other way around, have led to the development of algorithmic generative modeling techniques that fulfill this task more efficiently than explicit modelling techniques. Furthermore, design heuristics and analysis have become closely bound together in order to include performance optimization towards results (Schumacher [6]).

Although there are already parametric tools for structural analysis that are being successfully implemented in the design process, such as the plugin Karamba3D for Grasshopper (Preisinger [4]), they usually do not provide such a robust result as commercial FEM software and a reanalysis with commercial FEM software is therefore still necessary.

For these reason, a new Grasshopper plugin was developed by the author in collaboration with Bollinger + Grohmann in order to generate an effective parametric interface for the commercial FEM software RFEM 5. This plugin is called the Parametric FEM Toolbox (Apellániz [1]).

2. Workflow

It is possible to start a new RFEM application with the API, but the Toolbox is compiled in such a way, that there must be a running RFEM model to interact with. This section describes the workflows that are possible with the Toolbox depending on whether data is transferred from Grasshopper to RFEM, in the opposite direction, or they involve additional functionalities.

2.1. Workflow from Grasshopper to RFEM

Most of the Toolbox components refer to a particular RFEM object. Figure 3 shows the process to define a member object inside of Grasshopper and export it to RFEM. Most of the object components require as input grasshopper geometries and some basic information such as cross section number in this case. More advanced optional input parameters such as member type, hinges, etc. can be displayed through an extendable menu. The object is created inside of Grasshopper, so that no connection with RFEM is required at this step. Its properties can be displayed inside of Grasshopper panels and they can be also internalized inside of RFEM parameters.

In order to export data to RFEM, it is necessary to plug these objects into a “Set Data” component and set the “Run” parameter to true. The advantage of using an explicit component for the export process is the fact that this relatively more computationally expensive process of exporting the objects to RFEM is grouped in a single step. The outputs of the “Set Data” component are the same objects but with additional information about the index that RFEM has automatically assigned to them which can be very useful for modifying these objects in later steps, apply loads to them, etc.

2.2. Workflow from RFEM to Grasshopper

Similarly, data can be imported from Grasshopper to RFEM through the “Get Data” component by just specifying which kinds of objects shall be imported. In case that not all existing objects of a certain type should be imported, the user can use filter components with several available parameters in order to specify the exact objects to be imported and thus cut down the required execution time.

The imported objects can be analysed with the same object components but in “disassemble” mode, so instead of creating an RFEM object from certain input parameters, the object properties are obtained from a certain input object. It is also possible to directly convert RFEM objects into Grasshopper geometry by casting them into Grasshopper containers. This workflow will be further explored in sections 3.3 and 3.5.

It is also possible to import calculation results from RFEM into Grasshopper through the “Calculation Results” and the “Optimize Cross Sections” component. This might be interesting for using the visualization options of Rhino to display these results and also to carry out potential structural optimizations with any of the evolutionary solvers available in Grasshopper (Rutten [5]) by using the results as fitness function and the original input parameters as genes.

All the object components have a modify menu that make possible to modify the properties of RFEM objects within this optimization loop. Although this optimization workflow is more computationally expensive than similar approaches with FEM solvers compiled inside of Grasshopper plugins, such as Karamba3D, that do not require to export and import data from external applications, it might still be interesting when advanced calculation options and code-based checks are necessary.

2.3. Additional functionalities

There are currently a couple of functionalities of the toolbox that provide additional features beyond this object-based logic:

  • Extrude members: Through a single component, it is possible to obtain in Grasshopper the 3D shapes of member objects as it can be seen in Figure 4 and Figure 9. Output geometry in the form of both NURBS and Mesh elements is possible.

  • Input for LCA: Through a single component, it is possible to break down the masses and geometries of all RFEM objects according to assigned material, which can be used as input for running a Life Cycle Assessment out of an RFEM model as it is described in in section 3.5.

3. Projects

3.1. Tondo Bridge

The following footbridge in the city of Brussels is a steel structure that is made up of interconnected steel plates. The modelling process of this complex geometry took place not in the actual calculation program RFEM, but in Rhinoceros, due to the more powerful tools of this modelling software regarding the definition of curved lines and the intersection of surface elements among other features. In order to avoid the duplicity of boundary lines of adjacent surfaces, the model geometry was also examined in Grasshopper so that these boundary lines have the exact same defining control points.

Even though there are standard functionalities in RFEM for importing geometry files from a Rhino model, the Toolbox made it possible to import not just geometry elements, but actual structural elements with mechanical properties and even loads attached to them.

3.2. My-Co Pavilion

The structural system of this research project is a plywood gridshell. The definition of the calculation model of this free-formed structure took place in Grasshopper, which offered several advantages that ended up drastically speeding up the modelling process:

  • The calculation of a gridshell requires the definition of the structural members as linear elements in contrast to the surface and volume elements of the architectural model. This conversion task was automatically carried out through a parametric algorithm in grasshopper, so the input geometry for the RFEM model was already defined in Grasshopper.

  • This made possible to analyze and preprocess the imported geometry. The orientation of the members was also automatically defined within the Grasshopper algorithm.

  • The definition of the wind loads was also carried out in Grasshopper, in order to automatically define the load sectors and even the load values. The toolbox also takes the future orientation of the member local axis of the member elements in RFEM into consideration, so that load values are defined either with a positive or negative value depending on the right orientation (notice applied loads in different blue and purple colors in Figure 8).

  • The orientation of the nodal supports was also automatically defined in Grasshopper, so that reaction forces along the right axis could be used to design the connections of the baseplates.

3.3. ArcelorMittal headquarters

The structure of the ArcelorMittal headquarters is mostly made up of architecturally exposed structural steel. In this project, the Toolbox was also used in direction RFEM to Grasshopper (see section 2.2) in order to analyse and filter the calculation results of such a large structure and also to properly visualize not only the calculation results but also the extruded steel members in order to design the connection elements and also to produce a render visualization for the calculation report (see section 2.3).

3.4. Expansion of the Red Bull Arena in Leipzig

The expansion of the Red Bull Arena in Leipzig was a complex operation due to the fact that the new building elements had to be planned with consideration of the already existing structure (see Fig. 6). The foundation of the new addition was therefore designed in the form of micropiles, almost all of them with different inclinations, in order not to affect the existing foundation elements and tunnels.

The micropiles were defined in a Rhino model which also included the existing structure and then imported into RFEM with the toolbox. The toolbox allows the custom orientation of nodal supports through a Grasshopper plane, which is an arguably much more user-friendly approach than the standard workflow of defining them through the orientation angles.

3.5. Multi-modal optimizations

Finally, there must be pointed out that this Grasshopper plugin can be combined with other existing grasshopper plugins in order to carry out multi-modal designs and optimizations. Figure 11 shows a multi-modal optimization in terms of both structural performance and embodied carbon of the structural system of an office building in Berlin by combining the Parametric FEM Toolbox with the Grasshopper integration of One Click LCA (Apellániz, Pasanen and Gengnagel [2]).

4. Conclusion

The implementation of structural analysis tools in a visual programming environment has already been successfully implemented in the design process as calculation tools in the form of Grasshopper plugins. The Parametric FEM Toolbox, however, does not provide Grasshopper with a Finite Element Solver, but it establishes a connection with the finite element program RFEM, where the structural analysis is carried out. Although this approach is more computationally expensive, it allows the use of the extensive possibilities of robust commercial finite element software. Furthermore, engineering peer review processes benefit from the use of well-established and widely used analysis software. To this day, there is no other plugin for grasshopper to the knowledge of the author that implements the API of a finite element program to the extent that the one presented in this paper does.

The Parametric FEM Toolbox has proven to be able to enhance the design process of numerous projects since its release. Not just those characterized by algorithmically generated geometries (Preisinger et al [3]), but it has also been implemented in a wide range of projects made up of non-standard structural systems. Since its release, the feedback of the users has made a great impact into the further development of this tool. Furthermore, the software producer of RFEM, Dlubal, also got in contact to obtain feedback for the development of the future versions of the API of RFEM. These coordination efforts between software manufacturer and third-party developers are fundamental in order to ensure a stable development and provide the users with a reliable and robust design tool.


Irena Kirova, M.Sc.

Irena Kirova, M.Sc.

Marketing & Customer Support

Ms. Kirova is responsible for creating technical articles and provides technical support to the Dlubal customers.


Parametric FEM toolbox Parametric design


[1]   Apellániz, D. and Vierlinger, R., 2022. Enhancing structural design with a parametric FEM toolbox. Steel Construction, 15(3), pp.188-195
[2]   Apellániz D., Pasanen P., Gengnagel C., 2021. A holistic and parametric approach for life cycle assessment in the early design stages, SimAUD 2021
[3]   Preisinger C., Heimrath M., Orlinski A., Hofmann A., Bollinger K., Moderne Parametrik in der Tragwerksplanung - Werkbericht. Stahlbau, 2019, vol. 88, 184-193
[4]   Preisinger C., Linking Structure and Parametric Geometry. Architectural Design, 2013, vol. 83, 110-113
[5]   Rutten D., Galapagos: On the logic and limitations of generic solvers. Architectural Design, 2013, vol. 83, 132–135
[6]   Schumacher P. et al, The Politics Of Parametricism. Digital Technologies In Architecture, Bloomsbury Publishing, 2015

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  • Updated 11/23/2022

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