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Detailed 2005 analysis of the collapse of the World Trade Center Buildings 1 and 2 (WTC1 & WTC2) by the National Institute of Standards and Technology (NIST)

The image is from:
http://www.nist.gov/el/disasterstudies/wtc/upload/Media_Public_Briefing_040505_final.pdf
http://fire.nist.gov/bfrlpubs/fire05/art119.html

Also see:
Sivaraj Shyam-Sunder, ”Final Report on the Collapse of the World Trade Center Towers”, National Institute of Standards and Technology (NIST). NIST NCSTAR 1; 298 p. September 2005.
Order number: PB2006-100819
ABSTRACT: This is the final report on the National Institute of Standards and Technology (NIST) investigation of the collapse of the World Trade Center (WTC) towers, conducted under the National Construction Safety Team Act. This report describes how the aircraft impacts and subsequent fires led to the collapse of the towers after terrorists flew jet-fuel-laden commercial airliners into the buildings; whether the fatalities were low or high, including an evaluation of the building evacuation and emergency response procedures; what procedures and practices were used in the design, construction, operation, and maintenance of the towers; and areas in current building and fire codes, standards, and practices that warrant revision. Extensive details are found in the 42 companion reports. The final report on the collapse of WTC 7 will appear in a separate report. Also in this report is a description of how NIST reached its conclusions. NIST complemented in-house expertise with private sector technical experts; accumulated copious documents, photographs, and videos of the disaster; established baseline performance of the WTC towers; performed computer simulations of the behavior of each tower on September 11, 2001; combined the knowledge gained into a probable collapse sequence for each tower; conducted nearly 1,200 first-person interviews of building occupants and emergency responders; and analyzed the evacuation and emergency response operations in the two high-rise buildings. The report concludes with a list of 30 recommendations for action in the areas of increased structural integrity, enhanced fire endurance of structures, new methods for fire resistant design of structures, enhanced active fire protection, improved building evacuation, improved emergency response, improved procedures and practices, and education and training.

The following text is from:
http://en.wikipedia.org/wiki/Collapse_of_the_World_Trade_Center
“The scope of the NIST investigation was focused on identifying ‘the sequence of events’ that triggered the collapse, and did not include detailed analysis of the collapse mechanism itself (after the point at which events made the collapse inevitable).[72][73][74] In line with the concerns of most engineers, NIST focused on the airplane impacts and the spread and effects of the fires, modeling these using the software program Fire Dynamics Simulator. NIST developed several highly detailed structural models for specific sub-systems such as the floor trusses as well as a global model of the towers as a whole which is less detailed. These models are static or quasi-static, including deformation but not the motion of structural elements after rupture as would dynamic models. So, the NIST models are useful for determining how the collapse was triggered, but do not shed light on events after that point.”

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