When using glass-fibre concrete – at the time a new development – the minimum thickness of the reinforced concrete shells required for structural reasons (6 to 8 centimeters) can be reduced to the thickness necessary to avoid buckling. In this way, large prefabricated and light-weight sections with a thickness of 10 to 12 millimeters can be produced. This method was tested with the prefabricated sections for the National Garden Festival 1977 in Stuttgart.
The shell is composed out of eight hypar-units with an average thickness of 15 mm. They were subsequently gunnited against one formwork. Since the weight of one unit was 2500 kg only, a standard crane was sufficient to lift and place it. After placing the units into their final position, their joints were cast using glass-reinforced concrete (GRC)-Mix. The eight prefabricated sections were constructed using one and the same formwork and were brought into position using a normal building crane. To emphasize the lightness of the roof and to facilitate erection it is supported on eight stainless steel balls serving as bearings. These permit local rotation in any direction and thus reduce the stresses caused by expansion and contraction of the roof following temperature changes. The shell proved so successful that the authorities allowed it to stand for five years rather than the originally planned six months. In 1982 the shell was badly damaged by hooligans. By this time it has also suffered appreciable creep deformation and the glass-reinforced concrete was becoming brittle – unfortunately, in those days glass fibres were not sufficiently alkali-resistant. It was therefore decided not to spend money on repairing it, but to carry out a few final wind load tests and demolish it.
