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io I Isometric projection of upper roof construction for exhibition hall.

Structure Exhibition Hall | The exhibition hall is a timber-stud design without any metal connectors whatsoever. The 12 loadbearing 300 x 300 mm main columns are arranged in a circle and extend right up to the roof, a height of about 8.50 m. They are braced against each other horizontally by means of the wall cross-members and by grids of beams, one at the 5 m level and one at the eaves. A monopitch roof, supported on the main columns at the level of the first grid of beams, covers the enclosed ground floor gangway which encircles the whole building. The principle of the grid is that each beam is supported on the next one in the circle and mortised into the main columns. In each case, the beam then extends, cranked, beyond its support point on the next beam, past the next two columns and is then mortised into the next column, where it joins at the same level as the start of the next beam in the grid. The beams for the grid at the 5 m level are 140 x 180 mm; at roof level they are 300 x 360 mm. Here, the 180 x 330 mm roof beams, rising in a spiral, are supported on each of the high points of the grid. At the same height there is a 90 x 90 mm purlin right around the building which also serves as the uppermost purlin for the lowest roof surface. It is a system which looks extremely complicated but is in fact very simple structurally: each beam rests on the next one - in a circle, and with different inclinations, proportions and dimensions at the various levels. This type of construction caused the local authorities quite a headache and approval was finally granted only after they had examined a 1:30 model.

The roof construction is as follows: the conical roof surface is divided into three separate areas, each having a different pitch and each with its own rings of purlins. These 90 x 90 mm purlins carry the 40 x 105 mm rafters with the 12 mm boarding and the traditionally shaped clay tiles. Thermal insulation comprising 50 mm rockwool is fixed beneath the boarding and this is covered by fibreglass sheeting.

The external walls are supported by 90 x 90 mm battens mortised into the main columns. These carry the 75 mm boarding inside and outside which in turn provides a base for the 13-mm-thick rendering. Additional thermal insulation is not provided here.

11 | The 1:30 model of the exhibition hall structure.

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