Millennium dome-architectonic drama.

At first sight of the architects' drawings, the great Dome of Greenwich, Britain's main celebration of the Millennium, seems conventional. In fact, it is immense, and incorporates many new structural and environmental engineering ideas.

The unique qualities of the Millennium Dome, its size, its significance and the speed required to get it going, called in the combined expertise of a multidisciplinary Buro Happold team of structural engineering and building services, geotechnical, civil and facade engineering, environmental engineering, fire engineering and access consultants working with the New Millennium Experience Company (NMEC), Richard Rogers Partnership, the McAlpine/Laing Joint Venture and specialist works contractors.

In concept, the structure of the dome is innovative yet apparently simple. In shape the roof surface is a spherical cap. Twelve 100m high steel masts support a tensioned net of steel cables, arranged radially on the surface of the Dome and held in space by hangar and tie-down cables at 25m intervals. A 30m diameter cable ring restrains the centre of the cable net. A compression ring beam and vertical ground anchors at the perimeter restrain tension forces. Between the cables, panels of tensioned PTFE-coated glass fibre fabric, in all 80 000[m.sup.2] (the size of 13 football pitches) enclose the Dome. An inner liner reduces solar gain and improves thermal and acoustic performance. The central 30m diameter area of the roof is fitted with 36 mechanically opening vents to allow natural ventilation.

geotechnical problems

Formerly a gasworks, the Dome site at Greenwich was heavily polluted, requiring installation of a gas-tight membrane beneath the building. Site investigations found fill and silty clay sub-soil; consequently a grid of piles, more than 8000, was installed. The Blackwall Tunnel runs under the site; and continuous flight auger piles into the clay had to be used in places adjacent to it.

inside the dome

The engineering services team envisaged the Dome as an umbrella, like a grand railway station, which visitors would enter dressed according to the external climate. What makes the Dome different is its physical scale and the requirement to house exhibitions inside it. The aim is a tempered environment. Fresh air is introduced by natural ventilation at the perimeter and air-handling units in the service cores; they will slightly cool or warm the air according to season.

Exhibitions are provided with power, water, chilling and communications by 12 drum-like service pods set around the perimeter of the Dome. On legs, they comprise three floors of chillers, plantrooms, tanks, pumprooms and generators. They supply exhibits through a network of trenches and pipework laid in the ground slab. Just as at any public event when 30 000 or more people come together, careful planning of entrance and exit strategies is required; pedestrian flow patterns around the exhibitions were visualized by means of EXODUS, a specialist pedestrian flow programme.

the macrobert award

Thirty years after the engineers of the original Severn Bridge won the first MacRobert Award for engineering innovation, the Millennium Dome has won Buro Happold the most sought after prize in British engineering; this is only the second time a construction project has won the [pounds]50 000 prize and coveted gold medal.

Buro Happold will be presented with the 1999 Royal Academy of Engineering MacRobert Award at Buckingham Palace on 24 November. For the winning team (Ian Liddell [below], Paul Westbury, Dawood Pandor and Gary Dagger), it crowns four years' involvement from the first concept of the Dome.