The geometry becomes evident internally when one looks vertically upwards (ill. 3). It is the outcome of the optimization method used in the unconventional fabrication process. The shell consists of fibres that are adhesively fixed together – so-called “rovings” – and that comprise thousands of individual filaments.
A tool at the tip of an industrial robot winds the rovings tautly over a framework consisting of linear-steel templates, the notches in which determine the geometry. Synchronized with the robot arm, which can be moved about six axes, the supporting structure is rotated, together with the templates, about its own axis. The seven axes of the overall system that are generated in this way allow the complex sequences of movement to be executed that are necessary for the winding process (ill. 4). The pentagonal form is the outcome of the regularity of this operation.
“It soon became apparent that the robot could end the winding process at the point where it began only if there were an uneven number of angles,” says Fréderic Waimer, one of four project managers and the person responsible at ITKE for material technology and structural design. Using a 1:5 model, the simulations were tested prior to the ultimate resin-based winding operation (ill. 5). In the final fabrication stage, the robot first dips the rovings in epoxy resin, then winds them round the temporary frame, where they can harden overnight. In all, 120 machine hours were required for this. The finished construction was tempered with hot-air equipment at 60 °C to harden the resin. After removing the template, the 3.60-metre-high structure with a diameter of 8 metres was complete.
The light weight of the pavilion – only 320 kg – meant that it could be carried by just a few people to the nearby exhibition site, where steel shoes wrapped in the feet of the supports were bolted to the foundation slab.
The use of different materials is based on their individual properties and above all on their load-bearing behaviour. Seventy per cent of the pavilion consists of the more flexible translucent glass fibres, These sections were first wound on to the framework to create the shell that defines the spatial form. Thirty per cent of the structure consists of more rigid, opaque carbon fibres, which (together with load-bearing glass fibres) were finally wound on to stiffen the translucent shell. The combination of materials, the various diameters of the rovings, the different numbers of layers and the orientation of the fibres allow the fabrication of shell structures that possess individual degrees of rigidity at various points. Using a 3D model, the planning team calculated the orientation and configuration of the rovings and the material thicknesses for the relevant loading (ill. 6). The aim was to achieve a structure that would be as thin as possible with a maximum exploitation of the material, while keeping deformation to a minimum (ills. 7, 8). For the pentagonal load-transmitting bracing ring in the roof and the five supports, the strongest available carbon-fibre rovings were used with a thickness of up to 2.246 mm and with 50,000 filaments (ill. 9). The thickness of (at most) six layers is only 4.594 mm. The maximum deformation of the structure is 395 mm.
The pavilion is a prototype that can be varied in many ways to meet the needs of other locations. In the cold winter months in Stuttgart, when there was a lot of snow, students were only sporadically able to take advantage of this striking object. All the more impressive was the way the translucent, reflecting skin caught the light of the winter sun shining at a low angle through the leafless trees.
