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Awarded Contracts for External Experts to Support the 

NIST World Trade Center (WTC) Disaster Investigation

Contract No. Awarded to Date Awarded

SB1341-03-Z-0022 Applied Research Associates, Inc. 

(ARA)

9/23/2003

ANALYSIS OF AIRCRAFT IMPACTS INTO THE WORLD TRADE CENTER TOWERS

Under solicitation number SB1341-03-Q-0334, an indefinite deliverable, indefinite quantity (IDIQ) 

purchase order has been awarded to APPLIED RESEARCH ASSOCIATES, INC. (ARA) of Albuquerque, 

New Mexico:

ARA is an engineering firm that specializes in the following areas: nonlinear structural dynamics under 

blast and impact loading, vehicle crashworthiness and impact behavior, aircraft impact analysis, dynamic 

fracture modeling and failure analysis, impact and penetration mechanics, probabilistic engineering 

mechanics, and structural engineering. ARA is well qualified to conduct the analysis of the aircraft impact 

into the WTC towers with active research programs in crash, impact, and blast damage of structures for 

over 20 years. ARA is selected by the Federal Highway Administration as a Center of Excellence in finite 

element crash analyses and is designated by Livermore Software Technology Corporation (the developer 

of the LS-DYNA software package) as a Research Collaborator. Specific examples of the team’s past 

work include:

Analysis of aircraft impact into nuclear power plant containment structures and storage 

containers. 

Analysis of a fighter aircraft impact into multiple reinforced concrete barriers. 

Fragmentation of aircraft components due to turbine rotor failure. 

Simulation of railcars in high-speed impacts. 

Studies of the effects of blast on buildings and their progressive collapse. 

The specific tasks that ARA will perform include:

1) Provide estimates of the damage to structural systems due to aircraft impact – including exterior walls, 

floor systems, and interior core columns.

2) Provide estimates of the aircraft fuel dispersal during the impact.

3) Provide estimates and contours of accelerations and deformations as a function of time in each of the 

two towers due to aircraft impact to be used for estimating damage to fire proofing.

4) Provide a database of the major fragments of the aircraft and destroyed structural components of the 

towers to be used for estimating damage to the mechanical and architectural systems inside the towers.

The impact analyses will be conducted at various levels 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. The analyses will also include simplified and approximate methods. Analysis of uncertainties 

using the component, subassembly, global, and simplified analyses will also be conducted to assess the 

effect of uncertainties associated with various parameters on the damage estimates.
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The team from ARA combines engineers from several branches of ARA with diverse background and 

experience in crashworthiness, dynamic fracture analysis, applied mechanics and nonlinear dynamics, 

probabilistic mechanics, constitutive modeling, and structural engineering. The team is led by the three 

engineers with relevant backgrounds and appropriate knowledge in impact and crashworthiness studies. 

Select experience of these key project personnel is summarized below:

Dr. Steven W. Kirkpatrick is the program manager for this project. Dr. Kirkpatrick is a senior 

engineer with 19 years of experience in vehicle crashworthiness, structural dynamics, finite 

element analysis, impact and penetration mechanics, and failure analysis. He has more than 80 

publications in these areas. His research experience includes a wide range of government and 

commercial projects for rail, highway, civil, military, and aerospace applications. He has been a 

program leader for many studies requiring close collaboration between experimental and 

computational efforts with emphasis on model validation. Dr. Kirkpatrick has a doctorate in 

mechanical engineering from Stanford University.

Dr. B. Samuel Holmes is the program supervisor for this project. Dr. Holmes is a principal 

engineer with 40 years of experience in vehicle crashworthiness, structural dynamics, failure 

analysis, and fluid mechanics. He has served as a program manager and group leader for a 

variety of projects combining analysis and experiments. He acted as principal investigator for 

studies of train crashworthiness and the design of a crashworthy locomotive cab, and automobile 

accidents including compatibility and structural design for high speed impact, train aerodynamics, 

and impact. His experience also includes studies of weapons and blast effects on large 

structures. He has more than 40 publications in these areas. Dr. Holmes has a doctorate in 

applied mechanics from Drexel University.

Dr. Justin Wu is the technical lead in performing the uncertainty analysis of this project. Dr. Wu is 

the director of probabilistic engineering at ARA. He is a renowned expert in probabilistic methods 

with 20 years of experience in the development and application of innovative physics-based 

probabilistic methods for a wide range of applications including structural reliability analysis and 

design of space shuttle, aircraft, offshore pipeline, power plant, and automotive; nuclear waste 

repository risk assessment, and hard target uncertainty analysis. Dr. Wu heads the development 

of ARA’s ProFES (Probabilistic Function Evaluation System) software package, previously 

supported by the Air Force and NASA. He also leads the development of methodologies and 

software tools for hard target uncertainty analysis for DTRA, reliability-based multi-disciplinary 

design for NASA, and rotorcraft probabilistic damage tolerance analysis for FAA. He has more 

than 100 publications. Dr. Wu has a doctorate in mechanical engineering from University of 

Arizona. 

Other key ARA team members include:

Dr. Robert Bocchieri, Senior engineer, will provide expertise in constitutive modeling, ratedependent material behavior, fracture mechanics and failure analysis, finite element analysis, 

structural dynamics, and crashworthiness. Dr. Bocchieri has a doctorate in aerospace 

engineering from the University of Texas at Austin.

Dr. Lawrence A. Twisdale, Principal Engineer/Scientist, will provide expertise in structural 

engineering and building performance. Dr. Twisdale is a licensed professional engineer and has a 

doctorate in civil engineering from the University of Illinois.

Mr. Robert Frank, Principal Engineer/Scientist, will provide expertise in structural mechanics, 

structural dynamics, finite element analysis, and development and application of simplified 

response models. Mr. Frank is a licensed professional engineer and has a Master of Science 

degree in civil engineering from the Massachusetts Institute of Technology. 

In addition, the ARA team is augmented by the following experts:
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Dr. P. V. Banavalkar, President of Ingenium Inc., will provide expertise in the analysis and 

behavior of high-rise steel structures. Dr. Banavalkar has over 40 years of project experience and 

ten of his building designs are listed in "100 of the World’s Tallest Buildings" published in 1998 by 

the Council of Tall Buildings and Urban Habitat. His experience includes design for all conditions 

including critical seismic regions, blast-resisting structures and systems for prevention of 

progressive collapse. His notable projects include Library Tower in Los Angeles, Fountain Place 

in Dallas, Chase Tower in Houston, and U. S. Bank Place in Minneapolis. As a leading expert in 

his field, Dr. Banavalkar has authored more than 40 publications and lectured extensively on 

subjects such as steel structures, seismic stress, and concrete. Dr. Banavalkar is a licensed 

professional engineer and has a doctorate in civil engineering from Cornell University.

Dr. Matthew H. Koebbe, independent consultant, will provide expertise in finite element modeling 

and automatic mesh generation, and nonlinear dynamics. Dr. Koebbe has a doctorate in 

Mathematics from the University of California, Santa Cruz.