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A stainless steel conical spire

The spire is 3m in diameter at its base; it tapers to 150mm in diameter at the tip, which is 120m above ground level. It is fabricated from Grade 316L rolled stainless steel plate with a shot-peened finish. The plate is 20mm thick, except for the lowest 4m of the spire, where it is 35mm thick, and the topmost section, which is 10mm thick.

The spire was fabricated in eight sections (frustums) of up to 20m in length. Each frustum was formed from a series of short sections, fabricated as follows. A stainless steel plate was cut to a curved template, rolled to form a half-section and welded with vertical joints to form a complete short section. A series of these were then welded together with circumferential joints to create a frustum.

The thicker frustums at the base of the spire were curved using a modern asymmetric plate-forming machine; the upper frustums, which were too small for conventional rolling, were formed using a 1,000tonne press brake.

The lowest seven frustums are connected by bolted flanges. The uppermost frustums have a threaded connection.

The tip of the spire is fitted with lighting and with aviation warning lights. These are maintained by means of a lift and lower mechanism - a pulley is housed at the very tip of the spire - and by ladder access with integral fall-arrest system.

The ladder is set in the central void of the spire and leads to an open grille platform at about 70m above ground level. The lighting unit is composed of light-emitting diodes and is 10m in overall length. The ladder access also allows the mass damper system to be adjusted.

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