The Dutch pavilion at the EXPO 2000 in Hannover

The Dutch pavilion for the world exhibition EXPO 2000 in Hannover is not a typical timber structure. However, the structural use of thirteen oaks and one beech, which are used including bark, is exceptional. The building consists of six storeys and the structure of the fourth storey is carried out with the trees. Storeys five and six, with a lake and six (small) windmills on top, are supported by these trees, which are loaded at serviceability limit state level up to 3000 kN. Besides the ‘tree-storey, all storeys have a hybrid steel-concrete structure. The trees were cut in the Netherlands and in Denmark. High quality requirements were specified. Since fungi may have seriously affected even healthy looking oaks and beeches, a non-destructive research programme was developed to determine the integrety of the internal structure of the trees. Part of this research was carried out while the trees were still standing in the forest. Furthermore, bending and compression tests on (green) oak and beech were carried out at the Delft University of Technology. The research and the results are discussed in this paper. To avoid bending moments in the trees, special attention was paid to the connection between the hybrid steel-concrete structures and the trees. The structural design of the ‘tree-storey’ is also discussed in this paper. Expo 2000 will be open to the public from the first of June till the end of October. Forty million people are expected to visit the exhibition.