Teaching by Doing: A Research Pavilion in Stuttgart
On the edge of the campus of the University of Stuttgart stands an unusual structure resembling a woven basket. This research pavilion has been there since the end of the summer term.
Institute for Computational Design (ICD): Achim Menges
Institute of Building Structures and Structural Design (ITKE): Jan Knippers
From the 10th floor of K2, one of two high-rise slabs on the campus, it is hard to make out its scale; only the people who stream into this filigree structure of thin timber strips provide an indication of its true dimensions. Its diameter is an impressive 10 metres, and it bulges upwards over a circular concrete base that had existed unnoticed on this site for some time. When illuminated at night, the pavilion is reminiscent of an outsized Danish designer lamp, causing passing motorists to do a double take. The structure is more than just a visually attractive piece of urban furniture, however. Used for scientific research, it is unrivalled in its innovative features and the manner in which it links various disciplines.
“The starting point of our deliberations was one of the properties of plywood, the potential of which has not been exploited for structural purposes up until now,” Manuel Vollrath explains at a press conference. “What I mean by that is its elasticity, resulting from the inherent stresses in the material.” In just a few sentences, the architectural student sums up the concept on behalf of his design team: “Initially, we had to determine the characteristics of the material by measurements made with experimental rigs; in other words, [we had to find out] to what radii the plywood sheeting could be bent, and what stresses this gave rise to. The second step was to find a geometry that would allow the potential of the material to be exploited in an optimal manner, which would also result in a cogent piece of architecture in terms of both function and design.
“The geometric basis of the structure is a pair of segmental arches. These are connected in such a way that the tension and bending functions are pided into separate sections, with each tensile segment elastically maintaining the form of the adjoining bending segment. Forty of these curved pairs – that is, 80 radial wood strips – were necessary to close a torus with an external diameter of 10 metres. This was fixed with vertical ribs in gravel-filled timber troughs. The filigree structure, with a span of 3.5 metres, is nevertheless efficient and intrinsically stable.”
The timber strips were produced in the institute building only a few hundred metres from the pavilion. There, the faculty’s own industrial robot, configured as a CNC milling machine, stands behind a glass safety screen waiting to be set in motion. The sight of this facility drives home the fact that it would have been inconceivable to implement the student design without the state-of-the-art research done at the university’s institutes, the ICD and ITKE.
Each of the more than 500 timber elements has its own inpidual geometry. In addition, the 10-metre-long plywood strips had to be cut into segments in order to be transported around tight corners in the institute building. Simple socket connections and bolts were used instead of the elaborate steel nodes commonly found in timber construction. The inherent stresses in the material increase the load-bearing capacity of the overall system considerably, thus making it possible to construct the entire pavilion from birch plywood strips only 6.5 millimetres thick. The computational design model was based on the bending behaviour and a script with roughly 6,500 lines of code, corresponding to about 170 A4 pages.
The structural analysis model forms the foundation for all further steps: the structural calculations in the process of “coiling up” the flat strips by means of finite element analysis (FEA), and the robotic production of the elements and their exact positioning on site. While it takes just a few minutes to run through the computational design model, an efficient computer needs a day and a half for the FEA simulation.
Finally, the researchers were able to measure the relaxation behaviour in the finished pavilion; that is, the slackening of the innate tension of plywood as a result of ageing. The results can be used as data for future virtual 3D models.
Concept and implementation: A. Eisenhardt, M. Vollrath, K. Wächter and T. Irowetz, O. Krieg, Á. Mahmutovic, P. Meschendörfer, L. Möhler, M. Pelzer, K. Zerbe Scientific development: M. Fleischmann, C. Robeller, K. Dierichs (ICD); S. Schleicher, J. Lienhard, D. D’Souza (ITKE)