The magic mushroom: Pavilion at Stuttgart university

It looks elegantly simple, but this pavilion at Stuttgart university pushes to the limit what can be done with computing and structural design tools - and some sheets of 6.5mm plywood. According to the university, a conventional structure such as this would need an arch at least 100mm deep to stand up, but this 10m diameter building achieves the same result using a material usually considered useless for serious construction.

Instead of designing a structure and then finding a suitable material, the university’s computational design and building departments chose a material and then designed the structure around it. Ply was chosen as it is cheap, readily available and easy to cut, but crucially also bendy. Structurally the pavilion works in a similar way to an archer’s bow - a flexible material becomes stiff once bent and held in place with a length of string. In this building a flexible material is given stiffness by pre-stressing it in the same way.

The first job was to determine the maximum bending radius of the plywood. The team fed this information into a structural design tool to come up with the shape of the building. With the theoretical work done, the construction was relatively straightforward. The computer program controlled the machinery used to cut the plywood, which was done in the university. Then the strips were joined together. Slots in the plywood hold the curved sections in position, and theoretically the building would stand up without needing any glue or screws. Because the pavilion is in a public place the university played it safe and used screws on the joints for extra stiffness.

Could this building herald a new generation of plywood domes? Not at the moment: in just two months damp has reduced the bending pre-stress by half, with the result that the building has sagged. It has taken digital and structural design on a step, but proves that thin plywood is, for the moment, best left to the DIYers.