The twin towers of the World Trade Center collapsed on September 11, 2001, as a result of al-Qaeda's September 11 attacks, in which terrorists affiliated with al-Qaeda hijacked four commercial passenger jet airliners, flying one into the North Tower (1 World Trade Center) and another into the South Tower (2 World Trade Center). The South Tower collapsed at 9:59 a.m., less than an hour after being hit by the hijacked airliner, and at 10:28 a.m. the North Tower collapsed. Later that day, 7 World Trade Center collapsed at 5:21 p.m. from fires that had started when the north tower collapsed. As a result of the attacks to the towers, 2,752 people died, including all 157 passengers and crew aboard the two airplanes. The collapse of the twin towers also caused extensive damage to the rest of the complex and nearby buildings. Debris from the collapsing towers severely damaged or destroyed more than a dozen other adjacent and nearby structures.
The Federal Emergency Management Agency (FEMA) completed its performance study of the buildings in May 2002. It declared that the WTC design had been sound, and attributed the collapses wholly to extraordinary factors beyond the control of the builders. While calling for further study, FEMA suggested that the collapses were probably initiated by weakening of the floor joists by the fires that resulted from the aircraft impacts. According to FEMA's report, the floors detached from the main structure of the building and fell onto each other, initiating a progressive "pancake" collapse.
The towers were designed as "tube in tube" structures, which provided tenants with open floor plans uninterrupted by columns or walls. Numerous, closely-spaced perimeter columns provided much of the strength to the structure, along with gravity load shared with the steel box columns of the core. Above the tenth floor, there were 59 perimeter columns along each face of the building, and there were 47 heavier columns in the core. All of the elevators and stairwells were located in the core, leaving a large column-free space between the perimeter that was bridged by prefabricated floor trusses.
The structural engineers working on the World Trade Center considered the possibility that an aircraft could crash into the building. In July 1945, a B-25 bomber that was lost in the fog had crashed into the 79th floor of the Empire State Building. A year later, another airplane nearly crashed into the 40 Wall Street building, and there was another near-miss at the Empire State Building. Leslie Robertson, one of the chief engineers working on the design of the World Trade Center, has since claimed to have personally considered the scenario of the impact of a jet airliner�a Boeing 707�which might be lost in the fog and flying at relatively low speeds, seeking to land at JFK Airport or Newark Airport. However, Robertson has provided no documentation for this assertion.
Did the Twin Towers Collapse
The collapse of the Twin
Twin Towers Collapse?
Twin Towers disintegrating in
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Twin Towers Collapse
the twin towers collapse,
the Twin Towers Collapse
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How did the WTC towers
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The twin towers were the
Why Did the World Trade Center
Why did the World Trade Center
World Trade Center // Tower
attack on the Twin Towers:
The Federal Emergency Management Agency (FEMA) completed its performance study of the buildings in May 2002. It declared that the WTC design had been sound, and attributed the collapses wholly to extraordinary factors beyond the control of the builders. While calling for further study, FEMA suggested that the collapses were probably initiated by weakening of the floor joists by the fires that resulted from the aircraft impacts. According to FEMA's report, the floors detached from the main structure of the building and fell onto each other, initiating a progressive "pancake" collapse.
The towers were designed as "tube in tube" structures, which provided tenants with open floor plans uninterrupted by columns or walls. Numerous, closely-spaced perimeter columns provided much of the strength to the structure, along with gravity load shared with the steel box columns of the core. Above the tenth floor, there were 59 perimeter columns along each face of the building, and there were 47 heavier columns in the core. All of the elevators and stairwells were located in the core, leaving a large column-free space between the perimeter that was bridged by prefabricated floor trusses.
The structural engineers working on the World Trade Center considered the possibility that an aircraft could crash into the building. In July 1945, a B-25 bomber that was lost in the fog had crashed into the 79th floor of the Empire State Building. A year later, another airplane nearly crashed into the 40 Wall Street building, and there was another near-miss at the Empire State Building. Leslie Robertson, one of the chief engineers working on the design of the World Trade Center, has since claimed to have personally considered the scenario of the impact of a jet airliner�a Boeing 707�which might be lost in the fog and flying at relatively low speeds, seeking to land at JFK Airport or Newark Airport. However, Robertson has provided no documentation for this assertion.
Did the Twin Towers Collapse
The collapse of the Twin
Twin Towers Collapse?
Twin Towers disintegrating in
the Twin Towers to fall?
Twin Towers Collapse
the twin towers collapse,
the Twin Towers Collapse
But how did a car all of a
How did the WTC towers
Twin Towers. yet it did
The twin towers were the
Why Did the World Trade Center
Why did the World Trade Center
World Trade Center // Tower
attack on the Twin Towers:
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