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WTC report highlights key areas for further study

News special

THE REPORT INTO the World Trade Center disaster has identified key areas which need further analysis, the engineer who led the American Society of Civil Engineers (ASCE) investigation said this week.

'We have identified a number of things which might suggest changes to professional design practice, but we can't quantify these because we don't have studies done, ' ASCE team leader Dr Gene Corley told NCEI.

'For example, does putting stairwells further apart make things better or worse? There is no data on this, so we do not know. We need to look at the robustness of stairwells and how it can be improved, ' said Corley.

He also identified fire resistance and protection of structural members to avoid disproportionate collapse as key areas for study.

'We need research on how to provide fire resistance for bolted connections. There is no comprehensive guidance anywhere, yet this is a major issue in a building, ' said Corley.

Protection of elements or members vital to the survival of a building needed to be assessed, while the use of buildings must also be considered.

'If you have a library in a building, the fireload can be extremely large.

Recent thinking was that more money had been put into fireproofing than was necessary, but that doesn't take into account what could happen, ' said Corley.

He also warned that where active and passive fire protection systems were used, the consequences of one failing or underperforming needed to be assessed.

He added that facilities for some of the material tests needed did not exist, and that around $40M to pay for the studies lasting between two and four years would be granted by the US government.

'The tests to be carried out by the National Institute of Science & Technology are effectively starting right now, ' he said.

Other leading engineers broadly welcomed the report.

'As horrific as the event was, around 55,000 people got out of that complex who are alive today because of the inherent strength of the building. The report shows that 99% of the people who were in the buildings below the level of impact survived, ' said Parson Brinckerhoff chairman Bob Prieto.

But he added: 'It's a wake up call.

In a heavily engineered environment like New York, it shows that engineers must be part of the first response team in the event of disaster.'

Consultant to Babtie Harris & Sutherland James Sutherland also welcomed the report, but cautioned against trying to codify from its findings. 'I would be completely opposed to that. These are issues that you can't deal with by codes or regulations, ' he said. Fulfilling codes would replace independent engineering thinking, he said, and he recommended a third party approach to such complex problems on projects.

He added that engineers must think about what the next hazards might be.

Yolles director Richard Thiemann said that UK practice was ahead of the US regarding design against disproportionate collapse.

'But there are certain things to learn about fire protection - the whole team must be involved - not just fire experts, ' he said.

Atkins head of structures Mike Otlet said: 'The report is right not to impose anything immediately, but sensibly is asking engineers to carry out more studies of the implications of collapse of buildings in our designs.'

However, Pell Frischmann group chairman professor Wilem Frischmann said that the analysis of the twin towers collapse contained 'nothing new' and was written in a cautious 'legalistic' way.

'What is most interesting is the performance of the other buildings. It showed that in WTC7, a serious fire in a steel framed building could cause progressive collapse.

'We never thought that would have happened. It also showed that fire was helped by tanks in the buildings - many office buildings today have fuel tanks for generators for emergency lighting. This is very dangerous, ' said Frischmann.

All the UK engineers pointed to the need for study into adhesion of fire resistant materials on structural elements. Arup's Peter Bressington said that the report could have included more recommendations on small, low cost measures that building owners could implement quickly.

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