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Building owners won't retrofit unless they have to by law

Cover Story: After 9.11

Mass retrofits of tall buildings against progressive collapse are unlikely in the United States, reports Antony Oliver

TALL BUILDING owners in the US are unlikely to retrofit structures against progressive and disproportionate collapse, say US structural engineers.

They claim such work would be too expensive.

There is widespread acceptance in the structural engineering community that much of the US commercial building stock is vulnerable to such collapse.

But landlords and owners are unlikely to act without legislation, engineers say.

The potential cost and complexity of beefing up structures to resist terrorist attack mean the focus is more likely to be on improving security and emergency procedures in vulnerable locations.

'There are people who are considering how to improve the performance of buildings and that includes the mitigation of progressive collapse, ' says Tod Rittenhouse of New York based Weidlinger Associates.

Rittenhouse, an expert in designing terrorist resistant structures, advised the US government on structural design after the 1995 Oklahoma City bomb.

'But at this stage we are more likely to see improvements in security to prevent access by vehicles, measures to protect people against flying glass and improvements in emergency procedures and equipment.'

Rittenhouse says recession in the US means few tall buildings have begun construction over the last 12 months, but it is clear that developers are now taking the whole progressive collapse and structural robustness issue much more seriously.

'Developers are certainly now looking into what can be done to improve the design of buildings, ' he says. 'You are seeing high profile tenants demanding security improvements - and getting them.'

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