People can see overview about this history
here"If you want to take a look at the construction methods and the design, that's in this day and age what computers do. Just looking at a piece of metal generally doesn't tell you anything"
Mayor Bloomberg
See also this interesting article:
December 25, 2001
THE TOWERS
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In calling for a new investigation, some structural engineers have said that one serious mistake has already been made in the chaotic aftermath of the collapses: the decision to rapidly recycle the steel columns, beams and trusses that held up the buildings. That may have cost investigators some of their most direct physical evidence with which to try to piece together an answer.
Officials in the mayor's office declined to reply to written and oral requests for comment over a three- day period about who decided to recycle the steel and the concern that the decision might be handicapping the investigation.
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Interviews with a handful of members of the team, which includes some of the nation's most respected engineers, also uncovered complaints that they had at various times been shackled with bureaucratic restrictions that prevented them from interviewing witnesses, examining the disaster site and requesting crucial information like recorded distress calls to the police and fire departments.
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"This is almost the dream team of engineers in the country working on this, and our hands are tied," said one team member who asked not to be identified. Members have been threatened with dismissal for speaking to the press.
"FEMA is controlling everything," the team member said. "It sounds funny, but just give us the money and let us do it, and get the politics out of it."
A spokesman for FEMA, John Czwartacki, said the agency's primary mission was to help victims, emergency workers and to speed the city's recovery, and added, "We are not an investigative agency."
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Dr. Frederick W. Mowrer, an associate professor in the fire protection engineering department at the University of Maryland, said he believed the decision could ultimately compromise any investigation of the collapses. "I find the speed with which potentially important evidence has been removed and recycled to be appalling," Dr. Mowrer said
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Some experts have suggested that the only way to definitively determine the sequence and cause of the collapse is to recover large amounts of steel from the areas near where the planes struck, and possibly reassemble sections of the towers
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911research.wtc7.net/cache/wtc/groundzero/urge_inquiry.html