9/11 Allgemein
06.05.2015 um 17:28@kurvenkrieger
NIST NCSTAR 1
Federal Building and Fire Safety Investigation
of the World Trade Center Disaster
Final Report on the Collapse of
the World Trade Center Towers
Probable WTC 1 Collapse Sequence
Aircraft Impact Damage
• The aircraft impact severed a number of exterior columns on the north wall from the 93 rd to
the 98 th floors, and the wall section above the impact zone moved downward.
• After breaching the building’s perimeter, the aircraft continued to penetrate into the building,
severing floor framing and core columns at the north side of the core. Core columns were
also damaged toward the center of the core. Insulation was damaged from the impact area to
the south perimeter wall, primarily through the middle one-third to one-half of the core width.
Finally, the aircraft debris removed a single exterior panel at the center of the south wall
between the 94 th and 96 th floors.
• The impact damage to the exterior walls and to the core resulted in redistribution of severed
column loads, mostly to the columns adjacent to the impact zones. The hat truss resisted the
downward movement of the north wall.
• Loads on the damaged core columns were redistributed mostly to adjacent intact core
columns and to a lesser extent to the north perimeter columns through the core floor systems
and the hat truss.
• As a result of the aircraft impact damage, the north and south walls each carried about
7 percent less gravity load after impact, and the east and west walls each carried about
7 percent more load. The core carried about 1 percent more gravity load after impact.
Thermal Weakening of the Structure
• Under the high temperatures and stresses in the core area, the remaining core columns with
damaged insulation were thermally weakened and shortened, causing the columns on the
floors above to move downward. The hat truss resisted the core column shortening and
redistributed loads to the perimeter walls. The north and south walls’ loads increased by
about 10 percent, and the east and west walls’ loads increased by about 25 percent, while the
core’s loads decreased by about 20 percent.
• The long-span sections of the 95 th to 99 th floors on the south side weakened with increasing
temperatures and began to sag. Early on, the floors on the north side had sagged and then
contracted as the fires moved to the south and the floors cooled. As the fires intensified on
the south side, the floors there sagged, and the floor connections weakened. About
20 percent of the connections on the south side of the 97 th and 98 th floors failed.
• The sagging floors with intact floor connections pulled inward on the south perimeter
columns, causing them to bow inward.
Collapse Initiation
• The bowed south wall columns buckled and were unable to carry the gravity loads. Those
loads shifted to the adjacent columns via the spandrels, but those columns quickly became
overloaded as well. In rapid sequence, this instability spread all the way to the east and west
walls.
• The section of the building above the impact zone (near the 98 th floor), acting as a rigid block,
tilted at least 8 degrees to the south.
• The downward movement of this structural block was more than the damaged structure could
resist, and global collapse began. (S.150f des Reports, WTC 2 kommt gleich danach)
NIST NCSTAR 1
Federal Building and Fire Safety Investigation
of the World Trade Center Disaster
Final Report on the Collapse of
the World Trade Center Towers
Probable WTC 1 Collapse Sequence
Aircraft Impact Damage
• The aircraft impact severed a number of exterior columns on the north wall from the 93 rd to
the 98 th floors, and the wall section above the impact zone moved downward.
• After breaching the building’s perimeter, the aircraft continued to penetrate into the building,
severing floor framing and core columns at the north side of the core. Core columns were
also damaged toward the center of the core. Insulation was damaged from the impact area to
the south perimeter wall, primarily through the middle one-third to one-half of the core width.
Finally, the aircraft debris removed a single exterior panel at the center of the south wall
between the 94 th and 96 th floors.
• The impact damage to the exterior walls and to the core resulted in redistribution of severed
column loads, mostly to the columns adjacent to the impact zones. The hat truss resisted the
downward movement of the north wall.
• Loads on the damaged core columns were redistributed mostly to adjacent intact core
columns and to a lesser extent to the north perimeter columns through the core floor systems
and the hat truss.
• As a result of the aircraft impact damage, the north and south walls each carried about
7 percent less gravity load after impact, and the east and west walls each carried about
7 percent more load. The core carried about 1 percent more gravity load after impact.
Thermal Weakening of the Structure
• Under the high temperatures and stresses in the core area, the remaining core columns with
damaged insulation were thermally weakened and shortened, causing the columns on the
floors above to move downward. The hat truss resisted the core column shortening and
redistributed loads to the perimeter walls. The north and south walls’ loads increased by
about 10 percent, and the east and west walls’ loads increased by about 25 percent, while the
core’s loads decreased by about 20 percent.
• The long-span sections of the 95 th to 99 th floors on the south side weakened with increasing
temperatures and began to sag. Early on, the floors on the north side had sagged and then
contracted as the fires moved to the south and the floors cooled. As the fires intensified on
the south side, the floors there sagged, and the floor connections weakened. About
20 percent of the connections on the south side of the 97 th and 98 th floors failed.
• The sagging floors with intact floor connections pulled inward on the south perimeter
columns, causing them to bow inward.
Collapse Initiation
• The bowed south wall columns buckled and were unable to carry the gravity loads. Those
loads shifted to the adjacent columns via the spandrels, but those columns quickly became
overloaded as well. In rapid sequence, this instability spread all the way to the east and west
walls.
• The section of the building above the impact zone (near the 98 th floor), acting as a rigid block,
tilted at least 8 degrees to the south.
• The downward movement of this structural block was more than the damaged structure could
resist, and global collapse began. (S.150f des Reports, WTC 2 kommt gleich danach)
