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Staying power

Skyscape: Another dramatic cable stayed fabric roofed building graces the Greenwich peninsula but this one definitely will be gone in less than a year. NCE reports.

A ticket for the Dome also entitles visitors to see the specially commissioned Blackadder film, which is screened outside the Dome in the Skyscape building. Architect Richard Rogers Partnership and temporary events structure specialist Edwin Shirley Staging collaborated on the design of the Skyscape, which replaced the proposed 'Baby Dome' when the costs of the latter turned out to be unacceptably high.

Although it will be dismantled at the end of the Millennium Experience, the 120m by 53m single storey portal framed building is designed to conform with the building requirement for permanent structures. It houses two 2,500-seat cinemas which can show the film simultaneously, with a bar and lobby area in between. One of the cinemas can be converted into a fully seated venue that can hold 3,500 people for a pop concert or theatrical performance.

A range of five different ESS-developed standard tubular steel trusses are used in the structure. 'Working in the temporary structures world we try to keep things as light as possible because we need to be able to get them on the back of a truck,' explains ESS director OllyWatts.

'The architecture had a massive impact on why we decided to do what we did. There was a lot of collaboration between us, but in the end it was mainly dictated by pragmatism based on the engineering,' Watts adds.

The company proved this by being on site in December 1998 - just four months after being appointed. 'Often design time and the design co-ordination part can take longer than actually putting a building up,' says Watts. Once the concrete pad foundations had been cast, the frame went up in just 12 weeks.

Designed and fabricated by Landrell, the 10,000m2 fabric roof - silver on the outside, black underneath - is claimed to be the first PTFE-coated glassfibre fabric structure to be colour-coated with different colours on each site (see box).

For a temporary building , says Landrell architectural design principal Martin Hall, a more flexible PVC-coated polyester fabric would have been more appropriate, as it could be easily folded, stored and re-erected many times. However, there is a total NMEC-imposed ban on the use of PVC on the site, so Landrell used essentially the same fabric as the Dome itself.

Good acoustic performance is fundamental to the Skyscape's success. Planning permission was granted with a requirement that the entire building envelope must attenuate sound to a level of 30dB. 'This is the sort of noise attenuation that you would normally get from a solid oak door,' explains Hall.

Landrell had to develop a completely new lining system for the roof that met these requirements, while at the same time being flexible enough to follow the highly curved roof profile. The resulting liner is a quilt made of Rockwool mineral fibre wrapped in glass cloth, with a dense polymeric layer in the middle. The panels are joined by

tongue and groove joints in the polymeric layer - which is extended out beyond the panel edges - and a strong form of Velcro.

Walls are made of proprietary Kingspan sandwich panels with an aluminium skin filled with a dense foam core. This construction alone achieves a noise attenuation level close to 30dB, and the remaining acoustic insulation comes from a glass cloth quilt with a mineral fibre filling. The main internal wall between the two cinemas is built traditionally out of I- beams and plasterboard with the cavities filled with Rockwool insulation.

Sealed with a kiss

Applying a pigmented PTFE coating to woven glassfibre fabrics is not a particularly easy operation at the best of times, but producing a fabric with a different coloured PTFE coating on each face is a real challenge. Ireland-based fabric specialist Taconic has managed to achieve this using the 'kiss-coating' technique. Taconic supplied bi-coloured PTFE-coated glassfibre fabrics for a range of applications at Greenwich, including both the black/silver Skyscape roof and the Self Portrait Zone, which used both silver/white and silver/silver combinations.

Kiss coating involves passing the 2m wide fabric panels through a series of rollers, with a slight lessening of the tension between two of the rollers to allow the fabric to sag very slightly and just 'kiss' the surface of a bath containing the pigmented PTFE coating material. This technique allows a fabric with a different colour on each side to be produced economically for the first time ever, Taconic claims.

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