Nothing up my sleeve, presto!
GAITHERSBURG, Maryland -- The National Institute of Standards and Technology (NIST) has released its long-awaited report on the collapse of World Trade 7 following the attacks of Sept. 11, 2001. "Our take-home message today is that the reason for the collapse of World Trade Center 7 is no longer a mystery," NIST lead investigator Shyam Sunder told journalists at this morning's press conference in Gaithersburg, Md. "WTC 7 collapsed because of fires fueled by office furnishings. It did not collapse from explosives or from diesel fuel fires."
World Trade Center 7 Report Puts 9 11 Conspiracy Theory to Rest
office fires do not create a symmetrical collapses of steel framed hi-rise buildings at free fall speed
The link explains how it does. I guess you haven't read what you are replying to?
After 7 hours of uncontrolled fires, a steel girder on Floor 13 lost its connection to one of the 81 columns supporting the building. Floor 13 collapsed, beginning a cascade of floor failures to Floor 5. Column 79, no longer supported by a girder, buckled, triggering a rapid succession of structural failures that moved from east to west. All 23 central columns, followed by the exterior columns, failed in what's known as a "progressive collapse"--that is, local damage that spreads from one structural element to another, eventually resulting in the collapse of the entire structure.
The report clarifies a number of widely debated issues concerning the collapse, particularly the role of the building's many diesel fuel tanks and the importance of structural damage from falling WTC 1 debris. Both of those factors have been cited by investigators as possibly contributing to the collapse; the 2006
Popular Mechanics book
Debunking 9/11 Myths: Why Conspiracy Theories Can't Stand Up to the Facts mentions both hypotheses. However, the final NIST report downplays both scenarios...
.... In fact, the report concludes: "Even without the structural damage, WTC 7 would have collapsed from fires."
The report determines that the actual culprit in the collapse was the combustion of ordinary building furnishings: "These uncontrolled fires had characteristics similar to those that have occurred previously in tall buildings." If the sprinkler system in WTC 7 had been working, it is likely that "the fires in WTC 7 would have been controlled and the collapse prevented." The report also suggests that current engineering standards for coping with fire-induced thermal expansion need to be re-examined, particularly for buildings like WTC 7 that have long, unsupported floor spans. A key factor in the collapse, NIST concluded, was the failure of structural "connections that were designed to resist gravity loads, but not thermally induced lateral loads." According to Sunder: "For the first time we have shown that fire can induce a progressive collapse."
World Trade Center 7 Report Puts 9 11 Conspiracy Theory to Rest