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Collapse
See also: Collapse of the World Trade Center
7 World Trade Center on fire after the collapse of the Twin Towers on 9/11
As the North Tower collapsed on September 11, 2001, debris hit 7 World Trade Center, causing heavy damage to the south face of the building.[3] The bottom portion of the building's south face was heavily damaged by debris, including damage to the southwest corner from the 8th to 18th floors, a large vertical gash on the center-bottom extending at least ten floors, and other damage as high as the 18th floor.[3] The building was equipped with a sprinkler system, but had many single-point vulnerabilities for failure: the sprinkler system required manual initiation of the electrical fire pumps, rather than being a fully automatic system; the floor-level controls had a single connection to the sprinkler water riser; and the sprinkler system required some power for the fire pump to deliver water. Also, water pressure was low, with little or no water to feed sprinklers.[27][28]
After the North Tower collapsed, some firefighters entered 7 World Trade Center to search the building. They attempted to extinguish small pockets of fire, but low water pressure hindered their efforts.[29] A massive fire burned into the afternoon on the 11th and 12th floors of 7 World Trade Center, the flames visible on the east side of the building.[30][31] During the afternoon, fire was also seen on floors 6–10, 13–14, 19–22, and 29–30.[3] In particular, the fires on floors 7 through 9 and 11 through 13 continued to burn out of control during the afternoon.[32] At approximately 2:00 p.m., firefighters noticed a bulge in the southwest corner of 7 World Trade Center between the 10th and 13th floors, a sign that the building was unstable and might collapse.[33] During the afternoon, firefighters also heard creaking sounds coming from the building.[34] Around 3:30 pm FDNY Chief Daniel Nigro decided to halt rescue operations, surface removal, and searches along the surface of the debris near 7 World Trade Center and evacuate the area due to concerns for the safety of personnel.[33][35] At 5:20 p.m. EDT on September 11, 2001, 7 World Trade Center collapsed. There were no casualties associated with the collapse.
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. According to FEMA, structural elements were exposed to high temperatures for a sufficient period of time to reduce their strength to the point of collapse[6]; nevertheless, it has since been determined that the fires burned out in 20 minutes at any given location as they moved from point to point.[15]
Plan view of collapse progression, with structural failure initiating on lower floors, on the east side of the building and vertical progression up to the east mechanical penthouse
The report did not reach final conclusions about the cause of the collapse and called for further investigation:
Loss of structural integrity was likely a result of weakening caused by fires on the 5th to 7th floors. The specifics of the fires in WTC 7 and how they caused the building to collapse remain unknown at this time. Although the total diesel fuel on the premises contained massive potential energy, the best hypothesis has only a low probability of occurrence. Further research, investigation, and analyses are needed to resolve this issue. [Ch. 5, p. 31.][6]
In response 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.[36] The investigation, led by Dr S. Shyam Sunder, drew not only upon in-house technical expertise, but also upon 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).[37]
The bulk of the investigation of 7 World Trade Center was delayed until after reports were completed on the collapse of the World Trade Center twin towers.[32] In the meantime, NIST provided a preliminary report about 7 World Trade Center in June 2004, and since then has released occasional updates on the investigation.[3] According to NIST, the investigation of 7 World Trade Center has been 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.[38] 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."[39]
Few photos and video clips exist that show the damage sustained to south face of 7 World Trade Center on 9/11. From a news helicopter, ABC News captured footage of the south face of 7 World Trade Center, including a glimpse of a gash, extending approximately 10 stories.
In its progress report, NIST released a video and still-photo analysis of 7 World Trade Center before its collapse that appears to indicate a greater degree of structural damage from falling debris than originally assumed by FEMA. Specifically, NIST's interim report on 7 World Trade Center displays photographs of the southwest facade of the building that show it to have significant damage. The report also highlights a 10-story gash in the center of the south facade, toward the bottom, extending approximately a quarter of the way into the interior.[3][40] A unique aspect of the design of 7 World Trade Center was that each outer structural column was responsible for supporting 2,000 sq ft (186 m²) of floor space, suggesting that the simultaneous removal of a number of columns severely compromised the structure's integrity.[41] Consistent with this theory, news footage shows cracking and bowing of the building's east wall immediately before the collapse, which began at the penthouse floors.[3] In video of the collapse, taken from the north by CBS News and other news media, the first visible sign of collapse is movement in the east penthouse 8.2 seconds before the north wall began to collapse, which took at least another 7 seconds.[3][42]
The working hypothesis, released in the June 2004 progress report and reiterated in a June 2007 status update, was that an initial failure in a critical column occurred below the 13th floor, caused by damage from fire and/or debris from the collapse of the two main towers. The collapse progressed vertically up to the east mechanical penthouse. The interior structure was unable to handle the redistributed load, resulting in horizontal progression of the failure across lower floors, particularly the 5th to 7th floors. This resulted in "a disproportionate collapse of the entire structure."[3][39][43]
On August 21, 2008, NIST released its draft report on the causes of the collapse of 7 World Trade Center, beginning a period for public comments.[32] 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.[44] NIST determined that diesel fuel did not play an important role, nor did the structural damage from the collapse of the twin towers. But the lack of water to fight the fire was an important factor. The fires burned out of control during the afternoon, including on floor 13, where a critical interior column buckled. With the buckling of that column, adjacent columns also failed along with the floor structure above. This triggered a vertical progression of floor failures to the roof. The collapse then progressed east-to-west across the structure, and ultimately the entire structure collapsed. The fires, fueled by office contents, along with the lack of water, were the key reasons for the collapse.[45]
BMCC's Fiterman Hall was heavily damaged from the collapse of 7 World Trade Center, and is undergoing deconstruction.
When 7 World Trade Center collapsed, debris caused substantial damage and contamination to the Borough of Manhattan Community College's Fiterman Hall building, located adjacent at 30 West Broadway, to the extent that the building was not salvageable. In August 2007, Fiterman Hall was scheduled for deconstruction.[46] A revised plan called for demolition in 2009 and completion of the new Fiterman Hall in 2012, at a cost of $325 million.[47][48] The adjacent Verizon Building, an art deco building constructed in 1926, had extensive damage to its east facade from the collapse of 7 World Trade Center, though it was able to be restored at a cost of US$1.4 billion.[49]
7 World Trade Center housed SEC files relating to numerous Wall Street investigations, as well as other federal investigative files. All the files for approximately 3,000 to 4,000 SEC cases were destroyed. While some were backed up in other places, others were not, especially those classified as confidential.[50] Files relating Citigroup to the WorldCom scandal were lost.[51] The Equal Employment Opportunity Commission estimates over 10,000 cases will be affected.[52] The Secret Service had its largest field office, with more than 200 employees, in WTC 7 and also lost investigative files. Says one agent: “All the evidence that we stored at 7 World Trade, in all our cases, went down with the building.”[53]
The collapse of 7 World Trade Center is remarkable because it was the first known instance of a tall building collapsing primarily as a result of uncontrolled fires.[54]
World Trade Center controlled demolition conspiracy theories say that the building collapses on September 11, including that of building seven, were the result of controlled demolition.[55][56][57][58] The draft NIST report rejected this hypothesis, as the window breakages and blast sound that would have occurred if explosives were used were not observed.[59] The use of thermate instead of explosives is discarded by NIST on the basis that it is unlikely the necessary 100 pounds of thermate for each steel column could have been planted without being discovered. [60]
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Techious Star Community Member 2009/2010.
Voted for and funded by Scottie UK Ltd.
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. well i read some of it, and it all makes perfect sense I guess.
