· Wierzbicki, T., Xue, L., and Hendry-Brogan, M. (2002). "Aircraft Impact Damage", The Towers Lost and Beyond - A collection of essays on the WTC by researchers at theMassachusetts Institute of Technology, Ed. Eduardo Kausel, pages 31-63.
"The external columns were impacted at a very high speed and the process is controlled mainly by local inertia. As the fuselage and wings cut through the steel facade of the Towers, the affected portions of the column sheared off. It was found that the momentum transfer between the airframe and the first barrier of external columns was responsible for most of the energy dissipated in this phase. The energy to shear off the column constituted only a small fraction of that energy."
· Wierzbicki, T., Teng, X.(2003). "How the airplane wing cut through the exterior columns of the World Trade Center", International Journal of Impact Engineering, Volume 28, Issue 6, Pages 601-625, 10.1016/S0734-743X(02)00106-9.
"Using the exact dynamic solution in the membrane deformation mode, the critical impact velocity to fracture the impacted flange was calculated to be 155 m/s for both flat and round impacting mass. Therefore, the wing would easily cut through the outer column."
· Omika, Y., Fukuzawa, E., Koshika, N., Morikawa, H., and Fukuda, R. (2005). ”Structural Responses of World Trade Center under Aircraft Attacks.” Journal of Structural Engineering, Vol. 131, No. 1, Pages 6–15, 10.1061/(ASCE)0733-9445(2005)131:1(6).
"Based on the results of the analysis using a detailed finite element model, the damage situation of each structural component around impacted stories and the destroyed components were evaluated. As a result, the damage situation of the outer wall of WTC1 and WTC2 and the velocity reduction curve of the aircraft for WTC2 showed good agreement with the actual phenomena."
· Karim, M. and Fatt, M. (2005). ”Impact of the Boeing 767 Aircraft into the World Trade Center.” Journal of Engineering Mechanics, Volume 131, Issue 10, Pages 1066–1072, 10.1061/(ASCE)0733-9399(2005)131:10(1066).
"When the aircraft impacts the building at the top speed (240m/s) with a full fuel tank and the exterior columns have the original column thickness of 9.5mm., it is observed that all columns fail and the aircraft penetrates through the exterior wall. It was found that about 46% of the initial kinetic energy of the aircraft was used to damage columns. The minimum impact velocity of the aircraft to just penetrate the exterior columns would be 130m/s. It was also found that a Boeing 767 traveling at top speed would not penetrate exterior columns of the WTC if the columns were thicker than 20mm."