Analysis of Aircraft Impacts into the World Trade Center

Analysis of Aircraft Impacts into the World Trade Center Towers Chapters 1, 2, 3, 4, 5, 6, 7 and 8. Federal Building and Fire Safety Investigation of the World Trade Center Disaster.

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Kirkpatrick, S. W.; Bocchieri, R. T.; Sadek, F.; MacNeill, R. A.; Holmes, S.; Peterson, B. D.; Cilke, R. W.; Navarro, C.

NIST NCSTAR 1-2B; 290 p. September 2005.


World Trade Center; high rise buildings; building collapse; disasters; fire safety; fire investigations; terrorists; terrorism; aircraft impact; impact; failure; aircraft fuels; dispersons; structural dynamics; uncertainty; damage; structural damage


The objective of this report was to analyze the aircraft impacts into each of the World Trade Center (WTC) towers to provide the following: (1) estimates of probable damage to structural systems due to aircraft impact, including exterior walls, floor systems, and interior core columns; (2) estimates of the aircraft fuel dispersal during the impact; (3) estimates of debris damage to the interior tower contents, including partitions and workstations. Thus, this analysis established the initial conditions for the fire dynamics modeling and the thermal-structural response and collapse initiation analysis. The impact analyses were conducted at various levels of complexity including: (1) the component level, (2) the subassembly level, and (3) the global level to estimate the probable damage to the towers due to aircraft impact. Simplified analyses were also used to support the development of the global finite element models. Analysis of uncertainties using the component and subassembly analyses were conducted to assess the effects of variability associated with various input parameters and identify the most influential parameters that affect the damage estimates using orthogonal factorial design. Based on the results of the sensitivity analyses, the most influential parameters identified were varied in the global models to provide a range of damage estimates for WTC 1 and WTC 2. As part of the tower and aircraft models, constitutive relationships describing the actual behavior of the structures under the dynamic impact conditions of the aircraft were developed based on test results of the tower steels and from the open literature for other materials. Various grades of steels used in the exterior walls and core columns of the towers, weldment metal, bolts, reinforced concrete, aircraft materials, and nonstructural contents were considered. The constitutive relationships included high strain-rate effects and failure criteria for the various materials. The tower models used in the global impact analyses were developed based on the original WTC drawings and the structural databases of the towers developed within the framework of the baseline structural performance analysis. The tower models included the primary structural components of the towers in the impact zone, including exterior walls, floor systems, core columns, and connections. A refined finite element mesh was used for the areas in the path of the aircraft and a coarser mesh was used elsewhere. The models also included the nonstructural building contents, such as partitions and workstations, in the path of the aircraft debris. The Boeing 767 aircraft model was developed based on information gathered from documentary aircraft structural information, and data from measurements on a Boeing 767 aircraft. The model included the aircraft engines, wings, fuselage, empennage, and landing gear, as well as nonstructural components of the aircraft. A detailed analysis was carried out to estimate the fuel distribution in the aircraft wings at the time of impact.

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