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Context of '(9:21 a.m.-9:59 a.m. September 11, 2001): Exterior Wall of South Tower May Bow Outwards or Inwards before Collapse'

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The exterior wall on the east side of the World Trade Center’s South Tower apparently bows before the building collapses. The first inquiry into the collapse, by the Federal Emergency Management Agency and the American Society of Civil Engineers, states that the perimeter walls bow outward. “Expansion of floor slabs and framing results in outward deflection of columns and potential overload,” the investigation concludes. [Federal Emergency Management Agency, 5/1/2002, pp. 2-25] However, a subsequent report by the National Institute of Standards and Technology states that the east wall of the South Tower bows inward. In places the wall is said to bow inward by between seven and nine inches at floor 80, and NIST interprets this bowing to mean that the floors must be sagging. NIST will find that the sagging and bowing are two of the seven major factors that led to the collapse of each tower, as the bowing walls are no longer able to support their share of the buildings’ weight, causing the buildings to tilt and the upper sections to fall. [National Institute of Standards and Technology, 9/2005, pp. 43-46, 87] A wall in the North Tower also apparently bows before the building collapses (see 10:23 a.m. September 11, 2001).

Entity Tags: Federal Emergency Management Agency, World Trade Center, National Institute of Standards and Technology

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

The exterior wall on the south side of the World Trade Center’s North Tower apparently bows before the building collapses. The first inquiry into the collapse, by the Federal Emergency Management Agency and the American Society of Civil Engineers, states that the perimeter walls bow outward (see (9:21 a.m.-9:59 a.m. September 11, 2001)). However, a subsequent report by the National Institute of Standards and Technology states that the south wall of the North Tower bows inward. In places the wall is said to bow inward by approximately 55 inches at floor 97, and NIST interprets this bowing to mean that the floors must be sagging. NIST will find that the sagging and bowing are two of the seven major factors that led to the collapse of each tower, as the bowing walls are no longer able to support their share of the buildings’ weight, causing the buildings to tilt and the upper sections to fall. [National Institute of Standards and Technology, 9/2005, pp. 32-34, 87]

Entity Tags: World Trade Center, National Institute of Standards and Technology, Federal Emergency Management Agency

Timeline Tags: Complete 911 Timeline, 9/11 Timeline


Several small fires burn inside World Trade Center Building 7.
Several small fires burn inside World Trade Center Building 7. [Source: New York City Police Department]World Trade Center Building 7 is reported to be on fire. [CNN, 9/12/2001]

Entity Tags: World Trade Center

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

May 30, 2002: WTC Recovery Efforts End

Recovery efforts end at the World Trade Center site. [Associated Press, 5/31/2002]

Timeline Tags: Environmental Impact of 9/11

By this time, 358 New York City firefighters and paramedics are on sick leave or light-duty because they have the “World Trade Center cough” (see November 26, 2001). [Newsday, 9/10/2002]

Timeline Tags: Environmental Impact of 9/11

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