Pub: Sydney Morning Herald
High-risk towers are here to stay
September 11 has slowed but by no means halted the rise and rise of skyscrapers, writes Elizabeth Farrelly.
Bouncing back is one of the things humans, like tiggers, do best. So anyone looking for an end to high-rise cities as September 11’s surprise silver lining can think again.
Them skyscrapers are tougher than that. But there is hope, just a shred, for the extinction of that global marketing scourge, the architectural icon.
Building-code changes are usually cataclysm-driven. So you might expect the odd post-September 11 amendment. But the causal link from cataclysm to code seldom bears the imprint of logic.
Sydney, July 10, 1901; 22-year- old Harry Clegg becomes an instant celebrity by teetering for an hour on an eighth-storey ledge in the Haymarket, before leaping to his death before lunchtime crowds, as the building is devoured by flame.
Four others died unseen in the basement, but it was Clegg’s spectacular end that captured public imagination. He made headlines for a week and his death led inexorably to Sydney’s 1912 legal ban on buildings higher than 150 feet (45.72 metres). Logic wasn’t even in the neighbourhood.
Sydney had seen worse fires; New York and Chicago worse still, mostly in smaller buildings like theatres and tenements. And it wasn’t a tall building. At 120 feet, Clegg’s final perch was well above Sydney’s longest fire ladder, but by 1912 our longest ladder was still only 80 feet.
The 150-foot limit would have done less than nothing for young Harry, but his death was a PR disaster that took the Sydney skyscraper 50 years to get over.
New York, as happens, got the fire bogey about the same time and with more reason, given its run of appalling tenement conflagrations.
Result? The NYC Height of Buildings Commission argued strongly against skyscrapers dirty, ugly, unsafe, unnecessary then allowed them anyway, drafting the 1916 zoning provision that shaped the much-loved Chrysler Building, and other attenuated ziggurats.
Meanwhile Sydney, with no fire problem to speak of, went for zero tolerance. No skyscrapers, period. Behind all this was sheer political pragmatism.
The crucial difference was that by 1916 New York already had many tall buildings. The city’s entire cultural superstructure land values, insurances, taxes rested on that basis and expectation.
In 1912 Sydney, by contrast, the tallest building was 150 feet. So that’s where the limit sat until, in 1957, the combination of architects’ agitation and abject fear of losing the Sydney-Melbourne race prevailed, and the height limit was scrapped.
It’s this pragmatism, good or bad, that provides the common thread, a century on, with September 11.
The World Trade Centre’s twin towers, it is now agreed, did not collapse because of cheap or inadequate construction, as several authorities averred at the time.
Structural engineers have declared the towers “superbly engineered”, and the official joint report, issued last month, of the on-site American Society of Civil Engineers (ASCE) and Federal Emergency Management Agency (FEMA) team found that :
* The ability of the two towers to withstand aircraft impacts without immediate collapse was a direct function of their design and construction characteristics.
* Many buildings with other design and construction characteristics would have been more vulnerable to collapse in these events.
Nor is it necessarily the case, as has been widely reported, that the towers would have survived had they been of concrete, rather than steel, construction.
At 110 storeys (411 metres) the WTC towers were the first super-tall buildings designed without structural masonry. This was unusual even in the United States, where steel construction is cheaper and more standard than in Australia or Europe.
Structurally, they were elegant beasts. A perimeter of close-spaced steel columns, giving the windowless look, also brought enormous lateral stiffness against wind loads, for instance, preventing routine seasickness in office workers and allowed column-free interiors.
In the event it was this lattice-structure that kept the twins standing as long as they did 105 and 56 minutes respectively despite gaping multistorey wounds in their sides.
Many concrete towers, fatally weakened by such structural depletion, would have suffered progressive collapse from this impact damage alone. And in the extreme, explosive heat of hydrocarbon fires, concrete is apt to “spall”, leaving reinforcing steel as exposed and vulnerable as in the WTC.
The twin towers would probably have withstood either the impact of a full-on Boeing 767 or the intense heat of a hydrocarbon-fuelled fireball. But not both.
As well as inflicting huge structural damage and flooding lift shafts with jet fuel, the planes’ impact disabled all three levels of systemic fire defence: sprinklers, firefighter access, and “passive” structural protection, stripping spray-on gunk
from joists and plasterboard from columns in one catastrophic blow.
Had any one of these systems remained intact the buildings, and many more of their inhabitants, may have survived.
Whether by luck or management, the event was every bit as superbly designed as the buildings. What could have been done? And what should be changed?
Not a lot, it turns out. There’s no sudden regulatory push against high-rise. The ASCE-FEMA report recommended little more than further study and a range of voluntary measures. Of course there is politics in this pussyfooting. No-one wants to talk things down, increase building costs or criticise the WTC before the litigation cloud settles.
So you might expect quicker changes elsewhere. But in Australia, where the direct political heat is much lower, it is the same story.
An independent report by Arup, engineers assisting the ASCE-FEMA exercise, tested 12 Australian (concrete-framed) towers against Britain’s more stringent building codes (since testing against direct aircraft impact seemed unnecessarily specific).
The main deficit identified here was in the joints, especially floor-column joints.
Under explosive impact, or where structure sags from heat, building joints are put in tension and can suddenly pull apart, producing catastrophic building failure.
The Arup solution is to make joints not stronger so much as more ductile lithe boxer rather than stolid wrestler in line with current earthquake thinking.
Remarkably, such changes can use less material, and can therefore reduce construction costs. So far, so good. What is really notable, though, is the ductility of the markets.
One American paper, The Christian Science Monitor, casts “the golden age of the American skyscraper” as a thing of the past. The latest proposed Trump tower, in Chicago, it reports, has shrunk since September 11 from 120 storeys (world’s tallest) to a diminutive 78. The Empire State has increased vacancy rates, despite halving its rent, and no super-tall buildings are under construction. Only in Asia, according to New York architect Stephen Goldberg, does “that sort of swashbuckling mentality” persist.
Generally, though, optimism prevails. Arup director Richard Hough notes that in its portfolio over Australia, Britain, Asia and America not a single tower project has been scrapped since September 11. Mark Quinlan, acting CEO of Australia’s Property Council, says, “public liability insurance is the only issue that is of any concern”. And there, of course, is the rub.
There are measures, as the Arup report notes, to increase building safety in extreme events; blast-resistant escape routes, separate fire-fighting lifts and so on. But in the end it’s all about risk, and responsibility. A building’s users, tenants, managers, owners and insurers can be guaranteed to have different views as to which risks are worth taking, and who should be responsible. Then there’s the public. Clearly, though, terrorist risk attaches not to building height per se, but to symbolic status. The twin towers were targets not for their size, but as imperial icons. In Australia, this makes the Opera House say a more credible target than the MLC Centre. Nonetheless, Grocon’s 120-storey “world’s tallest” in Melbourne docklands has shrunk into the 88-storey Eureka now under construction, snuggling down with Mr Trump.
So is this it, then, for world’s-biggest-erection cravings? Have we seen the end of hyperbole as a marketing tool? Will Sydney real estate buccaneers find some other term for architectural gimcrackery than icon?
It’s possible, just. And it’s possible, if unlikely, that architecture might return to the humble business of life-enhancement, rather than vying endlessly for celebrity. But my money’s on human nature.