Millennium engineer reveals some dome truths

One of the world's biggest cranes will lumber into action in North Greenwich, London, in the next few weeks to lift the first of 12 100-metre masts that will support the giant Millennium Dome.

In a lecture at the Royal Academy of Engineering next week, Ian Liddell of Buro Happold, the dome's consulting engineer, will hail the structure as the biggest of its kind in the world. The masts, each weighing 100 tonnes, will be raised into position one by one and held in place by more than 70km of high-strength cable. The masts will support the spherical Teflon-coated fibreglass roof.

A major problem the engineers have had to overcome is "ponding", Mr Liddell says. Ponds of rain or snow could destroy the structure, making it look like a poorly put-up tent after a storm. To help avoid the problem, the dome skin will be under very high tension - around 100 times that of a tent.

Mr Liddell says the Pounds 750 million National Lottery-backed dome, designed by Richard Rogers and due to be completed in late 1998, "will cover an area the size of Trafalgar Square. And it should be visible from space". It will be 320 metres in diameter and 50 metres high at its centre. The dome's circumference will be 1km and it will have a ground floor of over 80,000 square metres, twice the size of the Georgia Dome in the United States, currently the largest in the world. It will house the "Millennium Experience", an exhibition of the best of British products and services. The British Tourist Authority estimates the exhibition could generate Pounds 500 million in total.