Man of steel

Vicky Richardson talked to Glyn Trippick, the engineer who has overcome all of the political foot-dragging to help make the Millennium Dome a technical wonder of our age

Just 18 months ago the largest structure on the north Greenwich peninsular was the New Millennium Experience site office. Now the prefab - no garden shed itself - is a speck on a horizon dominated by the Dome. When I talked to Trippick it became clear that 1998, not 2000, was the year he will remember.

Like the Dome, Trippick is not fashionable or postmodern. But his unshakeable confidence in the project is a nice change from the defensiveness of his client, the New Millennium Experience Company. He sees the Dome for what it is: a tremendous technical achievement. And this confidence in the technology has carried him through the pessimism and political foot-dragging that surrounds the structure, and which has caused unnecessary panics and placed needless obstacles in his way.

For example, in September the headline 'Dome risks collapse into Blackwall Tunnel' appeared on the front page of the Observer, causing great hilarity in the Greenwich site office. Rather than getting on the phone to reassure the client that the ground was indeed still there, Trippick pinned the cutting on the wall with other Dome memorabilia. Two weeks later the paper printed an apology, but on the same day the Sunday Telegraph filled its Dome slot with the same recycled story ('It'll be ready...when', 4 October). The problem of supporting the ground above the Blackwall Tunnel had indeed been an issue for Trippick, but that was several months previous to the Observer's revelation. The solution turned out to be a straightforward system of reinforced foundations to bridge the tunnel and support the spirit zone above.

The first thing you notice about the Dome is its sheer size: my quick site visit took three hours. The inside is still a cavernous empty space, apart from pavilions housing catering facilities and services. It is so big that walking around the perimeter hardly feels like walking in a circle, until you find yourself back where you started. This month all 13 zones will go on site, each one a substantial building in its own right.

Standing underneath the world's largest covered structure it is easy to get carried away with symbolism, since the only things to compare it to are mountains and canyons. But the Dome is very much a man-made achievement, the result of a genuine collaboration between architects and engineers. There are up to 1000 builders on site at any time and Trippick himself admits he is amazed by the technology every time he walks round to check on progress. 'Somebody I'm employing knows how all this stuff works', he says, 'but I don't!'.

Many critics have said that the form of the Dome and its grand scale symbolises oppressive authority (namely Peter Mandelson's). In the recent memorial issue of Marxism Today, critic Jonathan Glancey writes, 'dictators and their architects have chosen domes because domes represent the last word in control...The Millennium Dome is thus a disturbing symbol of social control'. Presumably Glancey believes that Eskimos are the biggest control freaks on the planet.

By contrast Trippick sums up the Dome, magnificent though it is, as 'an engineering response to indecision'. 'The job has gone ahead because we didn't sit back and wait for the arguments to reach a conclusion', he says. Ironically it is precisely the building team's isolation from the political debate on the Dome that has allowed it to get built.

The Dome was the product of an undefined client-brief. 'This was commissioned by the previous government, so we had to design something that would allow flexibility', says Trippick. So while the 13 zones planned by Mandelson may have their problems there are actually no limits to what could go inside the Dome. 'It's unconstrained. Basically it's a big umbrella designed to keep out the wind, rain and sun.' Cables are raised off the ground on masts - each one twice the length of Nelson's Column. Each mast is supported on four legs, spaced widely enough for articulated lorries to pass underneath. When politicians had no idea what to put in the Dome, the designers were already thinking of the possibilities. 'At the back of our minds we pictured the Dome housing an eight-lane, 400-metre running track in the middle with space for several football pitches around the outside.'

One major consequence of the political indecision surrounding the Dome was the government's decision to change the fabric of the roof, born out of its capitulation to the green lobby. In August 1997 critics of the Dome found a new cause for complaint, arguing that its PVC roof was a sign of our throwaway consumer culture. This row threatened the ethical credibility of the project, and clearly the government could not bear to have the Dome equated with a disposable (non-biodegradable) plastic bag. PTFE, or Teflon-coated glass fibre, became the sustainable alternative and the life expectancy of the Dome increased from 10 to 25 years.

For Trippick and his team of engineers the u-turn must have seemed entirely irrational. For a start, changing the roof fabric meant redesigning almost every detail of the building from scratch, and by the time of the decision the contract for the steel and cables had already been awarded. These contracts had to be torn up since the fixings for PVC and PTFE (Teflon-coated glass fibre) are completely different; polyester fabric can be folded and unfolded, but when glass fibre material is folded the fibres break. Trippick himself is reticent about the environmental benefits of polyester v glass fibre. 'We could have used cotton canvas [as Greenpeace suggested]. But we would have had to soak it in some pretty awful chemicals.'

Technologically, the Dome is absolutely of our time and, says Trippick, 'could not have been built five years ago'. It is an extremely minimal and cost-effective structure, consisting of a net of steel cables supported by 100-metre masts which pull huge panels of fabric taut. Strictly speaking it is not actually a dome - that would involve materials held in compression (pushing together) - but a tent with the fabric stretched in tension. Both the cables and the fabric are pushed to their absolute limits to create a structure that is cheaper per square metre than a B&Q shed. Cables and fabric have been used before, but the Dome puts them together in a unique and novel way. A computer program called Tensyl, first developed by Buro Happold in the 1970s, has made this possible by calculating the cutting patterns for the fabric, the length of cables and the forces pulling them in different directions.

Stylistically, the Dome is not complex enough for some architectural critics. Many of them wish we could have had a variation on Bilbao's crashed spaceship (the Guggenheim Museum designed by Frank Gehry) - a flashing image that has become familiar all over the world. As postmodern writer Charles Jencks puts it, 'architectural fashion demands something that is jumping and organic'.

But the Dome's geometric rigour, which Trippick and the other designers have fought for, transcends fashion and captures a humanist spirit that is not easily reproduced on t-shirts or fridge magnets. However vapid the contents of the Dome may turn out to be, the building that will house them is an inspiration.

Vicky Richardson is a senior reporter on RIBA Journal, a monthly architectural magazine, and co-author of In Defence of the Dome, with Penny Lewis and James Woudhuysen. Copies are available from the Urban Research Group; email: vickyr@easynet.co.uk

Dome facts

• One kilometre circumference
  
• 80 000 square metres of ground space
  
• 13 Albert Halls could fit inside
  
• 12 steel masts, each 100 metres long
  
• £758 million total cost
  
• 12 million visitors expected during the year 2000
  

Glyn Trippick's Dome is second to none