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NIST World Trade Center Investigations
The Silicon Valley Office of ARA conducted analysis of the aircraft impacts into the World Trade Center (WTC) towers under funding from the National Institute of Science and Technology (NIST). Aircraft impact analysis was performed to obtain:
- Structural damage to the WTC towers produced by aircraft impacts.
- Estimates of jet fuel distribution.
- Estimates of debris distribution.
- Environment for fireproofing removal.
- Analysis of uncertainties in results.
Data from ARA's research was provided to established the initial conditions for the fire dynamics modeling and the thermal-structural response and collapse initiation analysis in subsequent NIST sponsored projects.
The WTC aircraft impact analysis is very complex, with large scale fracture and fragmentation of both tower and aircraft structures, nonlinear rate-dependent material behaviors, and the fluid-structure interaction of the aircraft fuel. The analyses of the aircraft impacts performed for this investigation are believed to be the highest-fidelity simulations ever performed for this impact behavior using state-of-the art analysis methodologies. Wherever possible, the models were validated against observables or supporting test data developed by the WTC Investigation.
To estimate the probable damage to the towers due to aircraft impact, the analysis was conducted at various levels of complexity including the component level, the subassembly level, and the global level.
Analysis of uncertainties using the component, subassembly, and global analyses were also conducted to assess the effect of uncertainties associated with various parameters on the damage estimates and to identify the most influential parameters that affect the impact response.
The nine floor building models were created with an internal core structure surrounded by the exterior structure. The model contains work stations and divider walls in locations where they were known to exist. Figure 2 below shows the complete building model.
All the significant components of the airplane were modeled, including the passenger seats. The airplane material densities were scaled to account for passenger and cargo weights. Figure 3 below shows the complete airplane model with (a) and without (b) the external shell. Movies 1 and 2 in the Results section below show the aircraft impacting WTC 1 and WTC 2, respectively.
The airplane impact conditions were obtained from analyzing video and photographic evidence. These impact conditions are given in the table below.
Table 1: Aircraft impact conditions for each building.
Figures 4 and 5 plot the damage incurred to the columns in WTC 1 and WTC 2, respectively. Figure 6 (below) shows the damage fringes and the thresholds for categorizing light, moderate, heavy, and severe damage producing failure.
Figure 6. Column damage fringes.
Released Reports:
Information can also be found at the NIST WTC Web site.
For inquiries or comments, please contact:
Dr. Steven Kirkpatrick
Principal Engineer
e-mail: skirkpatrick@ara.com
Dr. Robert T. Bocchieri
Principal Engineer
e-mail: rbocchieri@ara.com
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