The Clay Rotunda is a free-standing earth-based cylindrical structure that serves as the outer, soundproof shell of the SE MusicLab, a high-fidelity music auditorium constructed inside Bern’s renovated Gurten Brewery. The structure has a diameter of nearly 11 meters and a height of 5 meters using only 15 centimeters of unreinforced clay. Over 50 days, a mobile robotic system collected over 30.000 soft clay bricks in situ.
The extreme slenderness of the Clay Rotunda is made possible by its undulated design, which increases the footprint and stabilizes the structure to avoid buckling effects. The computational model that controls the geometry of this thin shell was created by taking the engineers’ structural models, clay material properties, and building process sequencing into consideration.
Indeed, due to the robotic arm’s restricted reach and the material shrinking while drying, complicated strategies for horizontal and vertical segmentation of the structure into matching trapezoids were required. The computational model also allowed for the calculation of the building order within each segment, as well as the location of each of the 30’000 clay cylinders.
The developed clay mix is extruded into soft bricks, which are cylinders with a diameter of 9 cm and a height of 15 cm that is grabbed by the robotic arm from a picking station, exactly oriented, and sequentially pressed into their ultimate position by the robotic arm. The compression of approximately 60% of the initial height ensures a strong interlocking aggregation, resulting in a soft bond that reflects both the material’s plasticity and the dynamic forces of the fabrication process.
To handle the full scale of the structure, the custom robot – the in-situ fabricator – had to be moved for every single segment. This robot relocation, as well as the deformation of the fresh material induced by shrinkage, necessitated a regular capture of the as-built geometry via 3D scanning. The inevitable cracks caused by the drying process were constantly monitored and filled on a regular basis with the same clay mix.
Client: SE MUSICLAB – Jürgen Strauss, Manuel Frick, Filippo Melena, Anna Imfeld-Aebischer, Markus Imfeld
Team: Coralie Ming (Projektleitung), David Jenny, Hannes Mayer (Senior Researcher-in-Charge), Edurne Morales, Anton Johansson, Indra Santosa, Jomana Baddad, Nicolas Feihl, Selen Ercan Jenny, Jesus Medina, Karol Wojtas
Support: Mike Lyrenmann and Philippe Fleischmann (Robotic Fabrication Laboratory, ETH Zurich), Andi Reusser (Institute for Building Materials, ETH Zurich)
Selected experts: Seforb Sàrl – Joerg Habenberger, Gotham design studio
Selected Entrepreneurs: LEHMAG AG – Felix Hilgert
Industrie Partner: Brauchli Ziegelei AG, Wirz AG Bauunternehmung
Sponsor: Wirz AG Bauunternehmung, Welti Furrer, Eberhard, Siemens, Geberit, ETH Zürich Foundation