Skyscraper design will change - or people will stop building skyscrapers

The Obayashi Corporation must be thinking twice about proceeding with Norman Foster's Millennium Tower in Tokyo, after seeing what happened to the twin towers of the World Trade Centre; as a sitting duck for kamikaze-style terrorist attack, this conical tower would surely be an all-too obvious target.

Designed in 1989 as a "timely solution to the social challenges of urban expansion", the tower is the world's tallest projected building. Rising 840m (2,772 ft) from its own artificial island in Tokyo Bay, it was to be 170 storeys high and would have contained 104 million sq m (1,119 million sq ft) of space.

The idea was that offices and "clean" industries would occupy the lower levels with enough residential space above to accommodate 60,000 people, topped by communications systems interspersed with restaurants and viewing platforms - all served by a vertical "metro", featuring cars with a capacity of 160.

Recession in Japan had delayed this ambitious, supremely arrogant project and it is now almost certainly doomed. Though its conical form had been engineered to withstand earthquakes and typhoons, nobody foresaw or could have imagined the apocalyptic fate that lay in store for New York's World Trade Centre.

Ironically, the Millennium Tower - billed as "inherently stable" because of its helical steel-cage structure - is illustrated in Norman Foster's latest catalogue by an aerial perspective that also features a Goodyear-style airship. And we all know what happened to the Hindenberg, just across the Hudson River in New Jersey.

The 110-storey towers of the World Trade Centre also had load-bearing external skeletons, consisting of a lightweight steel lattice structure. Columns on 1m centres provided wind bracing to resist overturning forces; the central core, where the liftshafts were located, took only the gravity loads of each tower.

In 1993, after a van containing 1,200 lb of explosives was driven into its basement and failed to topple the twin towers, one expert fatuously claimed that the complex was so structurally sound that it could withstand a plane impact. Six people were killed on that occasion, and 1,041 injured.

What Minoru Yamasaki, the Japanese-American architect, could not have foreseen was the fireball impact of two fuel-laden planes crashing into his towers. The steel structure and steel-trussed concrete floors melted in temperatures of 1,000 degrees Celsius, ultimately causing each tower to collapse like a house of cards.

Yamasaki, born in Seattle in 1912 to Japanese parents, was an unlikely architect for what were briefly the world's tallest buildings when they were completed in 1973. Barely more than five feet tall, he suffered from vertigo; one of the reasons why the columns were so close was to reassure the centre's 50,000 occupants.

The most innovative features of his design - which no doubt greatly appealed to his clients, the New York Port Authority - was the use of a "skylobby" system of express and local elevators, to minimise the size of the central core. This increased the net lettable space from 50 per cent to an unprecedented 75 per cent.

With a plaza at ground level from which one could appreciate the sheer scale of the towers and an enclosed observation deck offering views extending 45 miles on a clear day, the complex was consciously designed to make a big impact - even if it never supplanted the Empire State Building in terms of popular appeal.

Seven years before his death in 1986, using words that now seem very poignant, Yamasaki wrote that the World Trade Centre "should become a living representation of man's belief in humanity, his need for individual dignity, his belief in the cooperation of men and, through this cooperation, his ability to find greatness".

In New York, not surprisingly, there is a consensus that this potent symbol of the city's financial power should be rebuilt "bigger and better", as Bernard Tschumi, dean of the Columbia University school of architecture, put it. Whatever else, this would be perfectly in tune with the mood of defiance among New Yorkers.

"Once we get over the grieving, we should realise that this . . . could be like Chicago after the fire in 1871, when they invented the skyscraper and changed the ways cities have grown all over the world. We should build an even greater and more innovative skyscraper", said Terence Riley, architecture curator at the Museum of Modern Art.

Other views canvassed by the New York Times magazine included those of Richard Meier, the leading "white architect". What he wants to see built on the site is "an ensemble of buildings that are as powerful a symbol of New York as the World Trade Centre towers were" - with people living as well as working in the new complex.

Architecture critic Hugh Pearman believes there are two possible outcomes of the disaster in New York. "The most obvious and immediate is that skyscraper design will change. The other is that people will stop building skyscrapers," he wrote recently in Gabion. And that includes Foster's "visionary" project in Tokyo.

"Corporate pride may be hurt by this, but logically there is no reason why centralisation of people should be necessary anyway. Electronic communications, we have been told for years, should make large office buildings unnecessary. This seems in part to be coming true as more and more people work from home.

"The long-term effects of the September 11th terror attacks on America may affect the way every city in the world is built, and even threaten the whole notion of the dense urban centre: adherents of the loose net of small nodes will find themselves being listened to with increasing attention," according to Pearman.

This is likely to prove true in Dublin, too, putting a brake on the impetus to build landmark buildings as symbols of corporate power. With the city's latest high-rise complex being topped out at George's Quay and plans in the pipeline for still taller buildings, even gung-ho developers must now have their doubts.

If the public loses confidence in the safety of high-rise buildings as a result of the World Trade Centre apocalypse, the knock-on effects are likely to be profound. Indeed, developers may find financial institutions less willing to lend money for such projects unless they receive guarantees on their long-term security.

A discussion forum on the Irish architecture website - www.archeire.com - has focused on such practical issues as means of escape in the event of a disaster. "Something more radical than staircases has to be thought of," said one contributor. "All I can think of . . . is some form of escape chute like a helter-skelter," said another.

Yet another, using "Wasp" as a handle, commented: "It'll probably sound ridiculous, but some kind of parachute system akin to basejumping would be most appropriate for the evacuation of buildings such as these". Not so ridiculous, really, if you had been working in an office on the upper floors of the World Trade Centre.

Thousands of people occupying offices in the world's tallest buildings - notably the Petronas Towers in Kuala Lumpur, the Sears Tower in Chicago and the Kin Mao Tower in Shanghai - will want reassurance. At the very least, much more sophisticated fire protection is needed so workers can escape when disaster strikes.

Nobody will need to escape from the Monument of Light (aka The Spike) in Dublin's O'Connell Street, unless it topples. Foundations are currently being laid for this stainless steel needle, which will rise to a height of 120m (nearly 400ft): perhaps it could be dedicated to all the victims of terrorism both at home and abroad.