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8 | Tree column in large swimming pool with glass cupola and spherical roof shell.

9 | Boundary beam details, scale moo and i:20. In centre: window to wall connection and facade columns; below: support with casting and plywood element, l Upper part of 85 x 1300 mm boundary beam, which was screwed into position after assembly of meridian ribs. 2 Lower part of 85 x 1300 mm boundary beam. 3 120 x 120 mm intermediate timbers, which are glued to the bottom boundary beam section. 4 205 x 200 mm glulam meridian rib. 5 140 x 120 mm ring rib, double boarding twice 24 x 100 mm. 6 Roof construction: 1.2 mm pvc sheeting, fabric-reinforced; separating layer; treadproof mineral wool board, three times 40 mm; vapour barrier with aluminium coating. 7 Spot fixing of insulation and roof skin: plastic plate fasteners; hard foam, 200 x 200 x 40 and 150 x 150 x 80 mm; wood disk diameter 120 mm. 8 Façade column head, aluminium casting. 9 Glass façade. 10 Gutter. 11170-mm-thick beech plywood.

12 60 mm glulam masking.

13 Support insert of cast steel. 14 Steel washer, diameter 130 x 20 mm.

15 Conical casting. 16 Steel ring with welded reinforcement. 17 Concrete support.

For the heads of the 108 façade columns a special aluminium construction was developed consisting of a support, ball-head bolts and an abutment. This allowed for the unproblematic and economical adaption of the columns to the varying slope of the roof. The facade columns themselves are hollow aluminium sections connected to the air-conditioning system and provided with ventilation holes to ensure a uniform temperature over the window surfaces.

Construction | Because of the large number of curved and twisted ribs and boundary arches a special works programme and production method were necessary. At intervals of some 80 cm the three coordinates and the two angles of twist of the cross-section had to be calculated for each individual rib and boundary beam. The result was up to 17-m-long glulam beams with 10 to 20, in some cases as many as 98, different cross-sections. The timber construction firm developed special steel production frames, which were appropriately assembled and adjusted on the shop floor.

Ten months were available from the beginning of production to the topping-out ceremony. The first step was the erection of the tree columns. These were each brought to the site in two sections and glued together on the spot. Then the bottom parts of the tree rings and the curved edges were fitted. At the facade columns the height and slope of the edges were exactly measured; tolerance compensation was possible at the supports. No other geodetic checks were necessary during the installation work. It sufficed to fix the meridian ribs at the top and bottom connecting points with a temporary screw and to support them with a strut. With the positioning of the annular ribs, which by their spread determined the spacing of the meridian ribs, the shape of the roof developed on its own.

Costs | The building costs of the whole complex amounted to 20 million DM. The building costs of the wooden shell roof were in the region of 1000 DM per m2 of ground area and thus not much higher than those of a conventional structure. The higher costs of the three-dimensionally curved glulam members were made up for by the lower amount of timber used. The planning costs were admittedly twice as high as usual, the project necessitating unusually intensive cooperation between the architects, construction engineers, geodetists and the timber construction company.

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