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NIST's investigation of the building's collapse was delayed until after reports were completed on the ] twin towers.<ref name="nist-questions">{{cite web |url=http://www.nist.gov/el/disasterstudies/wtc/faqs_wtc7.cfm|title=Questions and Answers about the NIST WTC 7 Investigation |publisher=NIST |accessdate=August 26, 2010}}</ref> In the meantime, NIST provided a preliminary report about 7 World Trade Center in June 2004, and thereafter released occasional updates on the investigation.<ref name="NIST-june2004">{{cite web |year = 2004 |url = http://wtc.nist.gov/progress_report_june04/appendixl.pdf | format = PDF | title = Interim Report on WTC 7 | work=Appendix L | publisher=National Institute of Standards and Technology |accessdate =August 20, 2007}}</ref> According to NIST, the investigation of 7 World Trade Center was delayed for a number of reasons, including that NIST staff who had been working on 7 World Trade Center were assigned full-time from June 2004 to September 2005 to work on the investigation of the collapse of the twin towers.<ref name="NISTFAQ">{{cite web |url=http://wtc.nist.gov/pubs/factsheets/faqs_8_2006.htm |title=Answers to Frequently Asked Questions |publisher=National Institute of Standards and Technology |month=August | year=2006|accessdate=February 17, 2008}}</ref> In June 2007, Shyam Sunder explained, "We are proceeding as quickly as possible while rigorously testing and evaluating a wide range of scenarios to reach the most definitive conclusion possible. The 7 WTC investigation is in some respects just as challenging, if not more so, than the study of the towers. However, the current study does benefit greatly from the significant technological advances achieved and lessons learned from our work on the towers."<ref name="NIST7STAT1">{{cite press release |url=http://www.nist.gov/public_affairs/releases/wtc_062907.cfm|title=NIST Status Update on World Trade Center 7 Investigation|last=Newman|first=Michael|date=June 29, 2007 |publisher=National Institute of Standards and Technology|accessdate=August 26, 2010}}</ref> | NIST's investigation of the building's collapse was delayed until after reports were completed on the ] twin towers.<ref name="nist-questions">{{cite web |url=http://www.nist.gov/el/disasterstudies/wtc/faqs_wtc7.cfm|title=Questions and Answers about the NIST WTC 7 Investigation |publisher=NIST |accessdate=August 26, 2010}}</ref> In the meantime, NIST provided a preliminary report about 7 World Trade Center in June 2004, and thereafter released occasional updates on the investigation.<ref name="NIST-june2004">{{cite web |year = 2004 |url = http://wtc.nist.gov/progress_report_june04/appendixl.pdf | format = PDF | title = Interim Report on WTC 7 | work=Appendix L | publisher=National Institute of Standards and Technology |accessdate =August 20, 2007}}</ref> According to NIST, the investigation of 7 World Trade Center was delayed for a number of reasons, including that NIST staff who had been working on 7 World Trade Center were assigned full-time from June 2004 to September 2005 to work on the investigation of the collapse of the twin towers.<ref name="NISTFAQ">{{cite web |url=http://wtc.nist.gov/pubs/factsheets/faqs_8_2006.htm |title=Answers to Frequently Asked Questions |publisher=National Institute of Standards and Technology |month=August | year=2006|accessdate=February 17, 2008}}</ref> In June 2007, Shyam Sunder explained, "We are proceeding as quickly as possible while rigorously testing and evaluating a wide range of scenarios to reach the most definitive conclusion possible. The 7 WTC investigation is in some respects just as challenging, if not more so, than the study of the towers. However, the current study does benefit greatly from the significant technological advances achieved and lessons learned from our work on the towers."<ref name="NIST7STAT1">{{cite press release |url=http://www.nist.gov/public_affairs/releases/wtc_062907.cfm|title=NIST Status Update on World Trade Center 7 Investigation|last=Newman|first=Michael|date=June 29, 2007 |publisher=National Institute of Standards and Technology|accessdate=August 26, 2010}}</ref> | ||
] helicopter captured footage of the south face of 7 World Trade Center, including a glimpse of a gash, extending approximately 10 stories.]] | ] helicopter captured footage of the south face of 7 World Trade Center, including a glimpse of a gash, extending approximately 10 stories.]]<!--Non free file removed by DASHBot--> | ||
In November 2008, NIST released its final report on the causes of the collapse of 7 World Trade Center.<ref name="ncstar1-a">{{cite book |url=http://wtc.nist.gov/NCSTAR1/PDF/NCSTAR%201A.pdf |format=PDF| publisher=NIST |title=NIST NCSTAR1-A: Final Report on the Collapse of World Trade Center Building 7 |month=November | year=2008 |accessdate=July 11, 2011}}</ref> This followed their August 21, 2008 draft report which included a period for public comments.<ref name="nist-questions"/> In its investigation, NIST utilized ] to model events leading up to collapse initiation and ] models to simulate the global response to the initiating events.<ref>{{cite web |url=http://wtc.nist.gov/media/WTC7_Approach_Summary12Dec06.pdf |format=PDF|title=WTC 7 Technical Approach and Status Summary |author=McAllister, Therese |publisher=NIST |date=December 12, 2006|accessdate=February 17, 2008}}</ref> NIST determined that diesel fuel did not play an important role, nor did the structural damage from the collapse of the twin towers, nor did the transfer elements (trusses, girders, and cantilever overhangs). But the lack of water to fight the fire was an important factor. The fires burned out of control during the afternoon, causing floor beams near Column 79 to expand and push a key girder off its seat, triggering the floors to fail around column 79 on Floors 8 to 14. With a loss of lateral support across nine floors, Column 79 soon buckled – pulling the East penthouse and nearby columns down with it. With the buckling of these critical columns, the collapse then progressed east-to-west across the core, ultimately overloading the perimeter support, which buckled between Floors 7 and 17, causing the entire building above to fall downward as a single unit. The fires, fueled by office contents, along with the lack of water, were the key reasons for the collapse.<ref name="ncstar1-a"/> | In November 2008, NIST released its final report on the causes of the collapse of 7 World Trade Center.<ref name="ncstar1-a">{{cite book |url=http://wtc.nist.gov/NCSTAR1/PDF/NCSTAR%201A.pdf |format=PDF| publisher=NIST |title=NIST NCSTAR1-A: Final Report on the Collapse of World Trade Center Building 7 |month=November | year=2008 |accessdate=July 11, 2011}}</ref> This followed their August 21, 2008 draft report which included a period for public comments.<ref name="nist-questions"/> In its investigation, NIST utilized ] to model events leading up to collapse initiation and ] models to simulate the global response to the initiating events.<ref>{{cite web |url=http://wtc.nist.gov/media/WTC7_Approach_Summary12Dec06.pdf |format=PDF|title=WTC 7 Technical Approach and Status Summary |author=McAllister, Therese |publisher=NIST |date=December 12, 2006|accessdate=February 17, 2008}}</ref> NIST determined that diesel fuel did not play an important role, nor did the structural damage from the collapse of the twin towers, nor did the transfer elements (trusses, girders, and cantilever overhangs). But the lack of water to fight the fire was an important factor. The fires burned out of control during the afternoon, causing floor beams near Column 79 to expand and push a key girder off its seat, triggering the floors to fail around column 79 on Floors 8 to 14. With a loss of lateral support across nine floors, Column 79 soon buckled – pulling the East penthouse and nearby columns down with it. With the buckling of these critical columns, the collapse then progressed east-to-west across the core, ultimately overloading the perimeter support, which buckled between Floors 7 and 17, causing the entire building above to fall downward as a single unit. The fires, fueled by office contents, along with the lack of water, were the key reasons for the collapse.<ref name="ncstar1-a"/> |
Revision as of 05:06, 23 November 2011
In May 2002, the Federal Emergency Management Agency (FEMA) issued a report on the collapse based on a preliminary investigation conducted jointly with the Structural Engineering Institute of the American Society of Civil Engineers under leadership of Dr. W. Gene Corley, P.E. FEMA made preliminary findings that the collapse was not primarily caused by actual impact damage from the collapse of 1 WTC and 2 WTC but by fires on multiple stories ignited by debris from the other two towers that continued unabated due to lack of water for sprinklers or manual firefighting. The report did not reach conclusions about the cause of the collapse and called for further investigation.
Responding to FEMA's concerns, the National Institute of Standards and Technology (NIST) was authorized to lead an investigation into the structural failure and collapse of the World Trade Center twin towers and 7 World Trade Center. The investigation, led by Dr S. Shyam Sunder, drew upon in-house technical expertise as well as the knowledge of several outside private institutions, including the Structural Engineering Institute of the American Society of Civil Engineers (SEI/ASCE), the Society of Fire Protection Engineers (SFPE), the National Fire Protection Association (NFPA), the American Institute of Steel Construction (AISC), the Council on Tall Buildings and Urban Habitat (CTBUH), and the Structural Engineers Association of New York (SEAoNY).
NIST's investigation of the building's collapse was delayed until after reports were completed on the collapse of the World Trade Center twin towers. In the meantime, NIST provided a preliminary report about 7 World Trade Center in June 2004, and thereafter released occasional updates on the investigation. According to NIST, the investigation of 7 World Trade Center was delayed for a number of reasons, including that NIST staff who had been working on 7 World Trade Center were assigned full-time from June 2004 to September 2005 to work on the investigation of the collapse of the twin towers. In June 2007, Shyam Sunder explained, "We are proceeding as quickly as possible while rigorously testing and evaluating a wide range of scenarios to reach the most definitive conclusion possible. The 7 WTC investigation is in some respects just as challenging, if not more so, than the study of the towers. However, the current study does benefit greatly from the significant technological advances achieved and lessons learned from our work on the towers."
]
In November 2008, NIST released its final report on the causes of the collapse of 7 World Trade Center. This followed their August 21, 2008 draft report which included a period for public comments. In its investigation, NIST utilized ANSYS to model events leading up to collapse initiation and LS-DYNA models to simulate the global response to the initiating events. NIST determined that diesel fuel did not play an important role, nor did the structural damage from the collapse of the twin towers, nor did the transfer elements (trusses, girders, and cantilever overhangs). But the lack of water to fight the fire was an important factor. The fires burned out of control during the afternoon, causing floor beams near Column 79 to expand and push a key girder off its seat, triggering the floors to fail around column 79 on Floors 8 to 14. With a loss of lateral support across nine floors, Column 79 soon buckled – pulling the East penthouse and nearby columns down with it. With the buckling of these critical columns, the collapse then progressed east-to-west across the core, ultimately overloading the perimeter support, which buckled between Floors 7 and 17, causing the entire building above to fall downward as a single unit. The fires, fueled by office contents, along with the lack of water, were the key reasons for the collapse.
The NIST report found no evidence supporting conspiracy theories that 7 World Trade Center was brought down by controlled demolition. Specifically, the window breakage pattern and blast sounds that would have resulted from the use of explosives were not observed. The suggestion that an incendiary material such as thermite was used instead of explosives was considered unlikely by NIST because of observations of the fire and the building's structural response to the fire, and because it is unlikely the required quantity of material could have been planted without discovery.
The old 7 World Trade Center was the first tall building known to have collapsed primarily due to uncontrolled fires. Based on its investigation, NIST reiterated several recommendations it had made in its earlier report on the collapse of the twin towers, and urged immediate action on a further recommendation: that fire resistance should be evaluated under the assumption that sprinklers are unavailable; and that the effects of thermal expansion on floor support systems be considered. Recognizing that current building codes are drawn to prevent loss of life rather than building collapse, the main point of NIST's recommendations was that buildings should not collapse from fire even if sprinklers are unavailable.
- National Construction Safety Team Advisory Committee. "Transcript: Meeting of the National Construction Safety Team Advisory Committee, December 18, 2007" (PDF).
- "NIST's World Trade Center Investigation". NIST. Retrieved August 26, 2010.
- "World Trade Center Investigation Team Members". National Institute of Standards and Technology (NIST). Retrieved November 21, 2011.
- "Commerce's NIST Details Federal Investigation of World Trade Center Collapse". National Institute of Standards and Technology (NIST). 2002. Retrieved November 21, 2011.
{{cite web}}
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ignored (help) - ^ "Questions and Answers about the NIST WTC 7 Investigation". NIST. Retrieved August 26, 2010.
- "Interim Report on WTC 7" (PDF). Appendix L. National Institute of Standards and Technology. 2004. Retrieved August 20, 2007.
- "Answers to Frequently Asked Questions". National Institute of Standards and Technology. 2006. Retrieved February 17, 2008.
{{cite web}}
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ignored (help) - Newman, Michael (June 29, 2007). "NIST Status Update on World Trade Center 7 Investigation" (Press release). National Institute of Standards and Technology. Retrieved August 26, 2010.
- ^ NIST NCSTAR1-A: Final Report on the Collapse of World Trade Center Building 7 (PDF). NIST. 2008. Retrieved July 11, 2011.
{{cite book}}
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ignored (help) - McAllister, Therese (December 12, 2006). "WTC 7 Technical Approach and Status Summary" (PDF). NIST. Retrieved February 17, 2008.