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Stadia Use of circular hollow sections makes individual “We were involved in discussions on design, The roof slopes down towards the pitch to members inherently resistant to lateral buckling. All manufacture and programme for two years. By the maximise light. the trusses are three-dimensional with a triangular time we had to submit a final price we’d already cross-section, which gives them built-in stability solved most of the problems,” he says. The contract Fact File against lateral-torsional buckling. was then signed as a fixed lump sum. client: “When built, the roof members stabilise each To illustrate the benefit Mr Miller cites the main Arsenal Football Club architect: other,” Werran continues. “The secondaries stabilise trusses. “Working with McAlpine we identified 16 HOK Sports Architecture the primaries, and even the tertiaries contribute to possible erection methods. We weren’t sure which Structural engineer: stability.” was the optimum. We developed a programme and Buro Happold Werran adds that “huge investment” in producing cost details and a list of pros and cons for each, then Main contractor: Sir Robert McAlpine Ltd a 3D X-Steel fabrication model of the entire structure agreed which would be best for the project as a Steelwork contractor: has paid off: “Producing the model can be quite whole. Watson Steel Structures Ltd a painful process — you can’t do it in a piecemeal “The one chosen was one of the most expensive Steel tonnage: 3000t in roof way, you have to have everything detailed for it to from the steelwork aspect but saved many months Project cost: work, but it paid off in fit-up.” on the overall programme. We wouldn’t have £357M Watson Steel Structures director Peter Miller offered that on a normal lump sum tender because Due for completion: July 2006 says: “We do a 3D X-Steel model for every project we may not have won the job.” now. All the cutting, drilling and burning is done Highbury is renowned for having the best pitch electronically. But on this particular job it would in the Premiership and much thought has gone into have been very difficult if not impossible to resolve emulating this in the new stadium, with comparative Tripods 11m high support the geometry in any other way.” studies being undertaken between the existing the main trusses This is partly because the roof structure is curved and new pitch microclimates. The low overall roof in two directions, but also because of progressive height, allowing plenty of light through, will be the deflection as it is built. biggest contributor to the pitch quality. The expert “As we build the roof it changes shape. We have view is that the natural microclimate of the new to predict the change of shape as we build it so each pitch will not quite match that of the old, because element will fit.” This consequently means that the the existing stadium has open corners, but that it model has to be set up knowing the sequence of will be as close as possible. construction. “We spent a long time working with Meanwhile work continues towards the target the architect and engineer to get information up- of opening in time for the start of the 2006 season. front before starting the manufacturing process.” Even after the structure is finished, commissioning Mr Miller says this will pay dividends again later the complex IT and ticketing systems and training because all the necessary brackets for loudspeakers Arsenal staff in using them will be considerable and ancillary components are already detailed and tasks. fitted, avoiding possible delays and the additional So the collaborative spirit on the project, and the cost of having to go back and retrofit brackets 40m fact that Mr Miller expects the second half of the above ground after the structure has been erected. main trusses will be ready to lift by Easter, with a Mr Miller adds that collaboration was facilitated probable mid-April lift date, can only be good news. by a two-stage tender process by which Sir Robert He says: “We set out to try and beat the target on the McAlpine was appointed but did not have to confirm north end and put ourselves in the position that if the a final price until the design was almost complete. civils work was ahead we could take advantage of it. The same applied to subcontractors. We’re hoping to do the same with the south end.” NSC April 2005 19


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