5 | Detail of crown joint, plan, scale moo. The steel tube, 500 mm dia., 15 mm wall thickness, 600 mm high, is stiffened internally by means of two welded rings and X-bracing made from steel flats. Flat plates are welded onto the outside for mounting and positioning the incoming ribs and wind girders. As the wind girders are erected first, only these connections have the V-shaped retainers in order to prevent slippage.

Each rib is fixed using one _

stud which is welded onto a steel flat incorporated in the end of the rib and tightened from inside the tube of the crown hinge.

The dome itself, outside diameter 43 m and inside radius of curvature 35.76 m, is formed by 16 No. goo x 180 mm curved main ribs, all of which are propped against a steel joint at the crown of the dome. Between each of the main ribs is a 550 x 180 mm intermediate radial beam which, however, only extends as far as a peripheral 550 x 160 mm trimmer beam stiffening the upper half of the main ribs. In addition to this trimmer beam there are further purlins between all radial beams, thus subdividing each sector of the dome into nine bays up the slope of the roof, i.e. the purlins are at approx. 2.50 m centres. Owing to their different lengths, the purlins range from 120 x 120 mm to 190 x 120 mm; they are fixed vertically so the upper edge is cut to match the respective curvature of the dome.

Further bracing is provided by the four main bays at go┬░ around the dome which are designed as wind girders with 120 x 120 mm timber bracing. Each of these four bays is a single prefabricated unit. Two opposing bays, including the joint at the crown, were erected first using four mobile cranes. Having checked the correct positioning of these, the pair of bays at right-angles to this first pair were then lifted into position. The basic framework was now stable and the remaining main ribs could be positioned. The trimmer beam and purlins were added afterwards.

Part of one of the main bays of the dome can be removed for servicing and inspecting the tank. The frame of this bay consists of 550 x 80 mm members with the same purlin arrangement as the other bays. Of course, diagonal wind bracing is also provided here by means of 120 x 120 mm members - like the wind girders. In addition, a framework to brace the lower part of this bay is formed by a curved 300 x 120 mm bottom boom in conjunction with the third purlin from the base. Four lifting eyes are provided for lifting out the element which rests on 250 x 80 mm timbers glued-nailed onto the sides of the main beams.

Special attention was devoted to the timber connections which, due to the dampness and the aggressive vapours, had to be realized with the minimum number of structural steel parts. However, all steel parts which are indispensable are in rustproof V2A steel, including screws and bolts. All timber members are fabricated from larch and are given a coat of protective lacquer. In order to reduce the steel in the connections to a minimum, the purlins, for example, were provided with U-shaped brackets consisting of 320 x 210 x 40 mm glulam members which were glued-nailed onto the main and auxiliary ribs. So generally, the purlins are fixed with one M8 x 160 hexagon head woodscrew per connection.

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