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Engineers fear overreaction to WTC report

LEADING US structural engineers warned against an overreaction to the final official report on the 2001 World Trade Center collapses following its publication in New York last month.

Others expressed doubts that recommendations in the report would lead to the construction of safer high rise buildings.

The 43 section, 10,000 page report is the result of a $17M, three year investigation by the US National Institute for Standards & Technology (NIST).

Engineers in New York welcomed several of the report's 30 recommendations on improving tall building safety.

These included:

designing to prevent progressive collapse

ruling out the need to design for aircraft impact

ensuring that an uncontrolled fire could burn out without causing structural collapse.

Other recommendations were more controversial:

calls for a 'structural frame' approach to fire safety under which all structural elements would have the same presecribed fire resistence.

No further use of performance based fi e design until more research is completed.

'At the moment we can't be sure that the NIST recommendations would produce significantly safer building codes, ' said Weidlinger Associates associate principal Dr Najib Abboud.

'We still don't have enough fi re research and testing results.

NIST is proposing that all structural elements have the same specified fire resistance, instead of the current practice of columns having double the fire resistance of beams, ' he said.

'But we have no proof that this would have any real effect on building performance, ' said Abboud.

Arup risk consulting principal Dr Brian Meacham said it was important not to take building specifi c and event specific failure information out of context.

'We need to realise that not all factors that contributed to the WTC collapse may be applicable to other building designs, ' he said.

Performance based fire engineering techniques as pioneered in Europe have been given an effective thumbs down from NIST, which says that new test methods and software have to be developed before a performance based design route can be adopted.

But even the prescriptive 'structural frame' option recommended by NIST is not underpinned by meaningful research, said Skidmore Owings & Merrill partner Carl Galioto. 'There are a lot of unproven assumptions about the fire performance of real structures in the prescriptive approach.' 'What exactly does a three hour fire resistance for a column mean, for example- We need more research badly, at federal or even international level.' (see feature p17)

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