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Dear Mr. Quilala: Thank you for your thoughtful comments and time. Our studies focused on answering primarily one question that to me and victim's families was worth finding an answer for: "If these structures were designed and built following the prevailing code and using systems and components that were in use for such structures at the time, such as moment frames , braced frames, tube systems, and shear walls instead of using the unusual systems and components that were used in the towers, would the outcome of 9/11 attacks by terrorists and murderers would be any different?"
After doing the necessary analysis, the results, which can be easily replicated by anyone who has the drawings, the software for such analysis and the knowledge of structural modeling, indicate that indeed the outcome would be different. The issue of code is not just following a certain code or not, but the issue is that whether you can apply the code provisions that are developed for known systems to a system that is almost totally different than the systems that the code provisions are developed for? To me the question was whether or not it was justified to use so many untested systems and components in a structure of this importance with 110 stories? I could be wrong, but, my own feeling is that if these buildings were not exempt from the code, no city planning department would allow such untested systems, which were not the result of evolution through the structural engineering community's consensus, to be used. The main goal for us was to learn lessons from this tragedy to apply to existing and future skyscrapers and hopefully to save lives in the future if such intentional or accidental impact of airplanes and/or fire events happen again which can happen. This goal of "learning lessons from the structural collapses to save lives" was also the goal of our honorary sponsor , the Skyscraper Safety Campaign ( In addition, when in May of 2002 I testified before the Committee on Science of the House of representatives on the results of mu NSF sponsored project 2001-2002), Chairman Boehlert of the Committee asked me to the effect that " Professor Astaneh; what do you need to continue your WTC studies, I responded that I need the drawings and upon receiving the drawings from FEMA based on his direction, I felt that I have an obligation to do the studies that we did for the goal that we set at the outset. This is what I, and many researchers and engineers have done for many years for earthquakes, fires, hurricanes and other catastrophes involving structural failures and loss of lives due to falling debris or release of water or hazardous material. As for your comments on Sears Tower, although we have not analyzed Sears Tower for airplane impact, in order to find out whether or not if it is hit by an airplane what will happen to, you do not need to actually take an airplane and attack it, but, to simulate the scenario realistically , which we can do today to great confidence, and see how it would respond. That is what we do day-in and day-out in structural engineering and research community today. What we did in our studies was to re-design the WTC Towers using known and common systems , which was perimeter tube moment frame and core reinforced concrete shear walls with no special consideration for airplane impact. This is a typical system in high -rises. The results indicated that in this case the airplane could not enter the building almost intact, as was the case on that tragic day and for the "as-built" WTC towers, delivering thousands of gallons of jet fuel to the core of the building which did not have much firewalls or protection walls around the staircases, igniting intense fire inside th "bearing wall" structure, quite vulnerable to fire, and in a relatively short period of time collapsing it while more than 1500 people were trapped in floors above the impact floors and more than 350 firefighters were trying to reach them to evacuate them pancaked to their death.
Abolhassan Astaneh-Asl, Ph.D., P.E., Professor
Principal Investigator for the World Trade Center Studies-Structural Aspects, an independent and  self-supported study,  and Member of the Professional Advisory Panel of the Skyscraper Safety Campaign (, Chairperson: Sally Regenhard.
"The truth that makes men free is for the most part the truth which men prefer not to hear" -Herbert Agar (1897-1980)
From: Alfonso Quilala <asqengg2(--nospam--at)>
To: seaint(--nospam--at)

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The bottom line is, are the WTC buildings collapsed because of the normal forces required to design the buildings per code?  To think that the building had been in service for about 40 years was a good indication that the building had been subjected to the actual forces in that particular location. =0A =0AIt's easy to analyze and comment in hindsight. And all those analysis are only theories.   How about let's try to test the Sears Tower if it can take the unexp=
ected fuel bombs that the WTC had been subjected to.  This way you will be able to find out if you are correct or not.  S. Quilala Jr
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