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Dear Gregory from Oz:

Thank you for taking the time to make your comments below. I like to offer the following:

1. Our findings with regard to the structure of the collapsed WTC towers not complying with the code is not just about these buildings not following a certain code, but also with regard to the fact that these buildings did not use , for the most part, the known and well tested structural systems that our codes are based upon. Specially, searching through the published literature as much as we could, we could not find other applications of these steel bearing wall systems and floors nor the use of their unique connections and splices. Nor we could find considerable amount of research data and testing on performance of these systems and their components in the published literature. There is almost no indwependent testing of critical yet unique systems and components of these structures.

2. As you know, code provisions have evolved over the years and continue to evolve through the efforts of code committees and approval agencies utilizing data resulting from analysis and testing, observations on actual behavior of these systems and components under the realistic service and ultimate load conditions, as well as collective understanding of their behavior coming from the structural engineering community of the known systems used in the past as well as any new system that has emerges. Recent examples are development of the new seismic code provisions for welded moment frames (a traditional system) and provisions for design of base-isolated structures and unbound braced systems (both new and innovative systems). In both of these new systems and all other innovative system in the past , when there was a major deviation from the traditional system, there has been extensive research and trial applications, mostly independent of the inventors and developers, as well as independent peer reviews and discussions of the structural performances of the systems at professional gatherings and in the pages of journal and conference papers and other publications which are publicly available. As a result of this lengthy, elaborate and careful process, the final code provisions are truly representing the best information that our profession can offer at the time of their adaptation to be used in design of these systems to produce safety level that is targeted by the codes , again based on the consensus of the profession, yet economical structures. Even then, when there in new information either from the researchers or from the actual performance of our structures as they go through their service life, we incorporate such new data into our codes, again going through the same lengthy but reliable process delibrations and consensus-based process. A recent example is the case of overhaul of almost entire code provisions regarding seismic design of steel welded moment frames after the Northridge-94 earthquake. Such was not the case for the uncommon structural systems and their components used in the WTC towers. One even wonders if applying the code provisions that are developed for systems that we have known and used in design of these unusuall and almost totally different systems of the WTC towers could be justified. In my humble opinion, doing so would be similar to someone applying the provisions that are in the code for traditional concentrically braced frames to design a braced frame with unbound braces and its components.

3. The issue of code compliance and whether or not all building structures, and indeed all structures, need to be designed according to the governing code, or certain buildings should be exempt from the code , as were the WTC towers, is a very important question and has many safety, economic, social and legal aspects and I do not feel qualified at all to offer an expert opinion on it. But, regardless of how highly I regard the owners, designers and contractors who fund, design and construct our structures, as a citizen who lives and works in these structures, I rather see that everyone follows the governing codes of design and construction and uses systems that are covered by these codes. This , in my opinion will guarantees that I am living and working in a building that is designed based on the consensus of the structural and construction engineers, past and present, instead of living and working in a building that the only assurance of safety I have is coming from only a single team of owner, designer and contractor which was the case for the WTC towers.

4. Point of Information: Some have called the exterior "steel bearing walls" of the WTC towers a 'tube system" . This seems not to be quite correct since the exterior steel walls did not have a framing system with beams and columns framing into each-other and normally connected to each other with moment connection as the traditional tube system is. The exterior walls did not have horizontal girders or vertical columns forming a frame. The walls consisted of steel plates, with penetrations for window opening where, the plates were stiffened with vertical 3-plate channels every 3'-3". I have seen the structural drawings of the World Trade Center, issued by Skilling, Helle, Christiansen, Robertson, Structural & Civil Engineers with Mr. Leslie E. Robertson's seal on them refer to the exterior walls as "bearing walls". After studying the structural system of the WTC towers, it seems to me that the structure of the WTC towers, above the 10th floor or so to be a steel version of the masonry bearing wall system that were used in buildings prior to the invention (or development?) of the steel skeletal framing system in late 1800's by William Le Baron Jenny.. some calling him the father of skyscrapers.

5. as for "flimsiness" the Oxford Dictionary online has the following entry:


• *adjective* (*flimsier*, *flimsiest*) *1* weak and insubstantial. *2* (of clothing) light and thin. *3* (of a pretext or account) weak; unconvincing.

• *noun* (pl. *flimsies*) Brit. *1* very thin paper. *2* a copy of a document, made on very thin paper.

If you study the structural drawings of the WTC towers in depth, which I have done, you may also find the definition "1" above to be applicable to the exterior bearing walls of the towers in the context of the events of 9/11 (i.e. impact of the airplanes, entry of the plane almost intact inside the building delivering thousands of gallons of jet fuel and ensuing fire) , as you have already concluded for the one case that you have mentioned in your e-mail that you are aware of which I assume is the connection of floor joists to the exterior bearing walls as I discussed with you in my earlier personal e-mail.

6. In the aftermath of this horrible tragedy caused by 19 murderers and their organizers and supporters, the public and specially victims families were asking our profession why these buildings collapsed so fast and so completely and is there a lesson that we could learn to apply to future designs or modifications of current designs to prevent these murderers from using our structures to murder us?. Instead of having at least an open discussion on what exactly these structures were and why never before a steel structure that has caught fire collapsed so fast and so completely while trapping more than 1500 people on floors above the fire region, a few in our profession, some of them or their firms directly or indirectly involved in design of these unusual systems, have embarked on a campaign of defending the design of these structures and without any analysis, declaring, in public as well as in the pages of publicly funded reports, to the effect that there was nothing wrong with these systems , again in the context of 9/11 events, and any building hit by an airplane, as happened in 9/11/01, will end up with the same fate. More unfortunate is that others in the profession, quite knowledgeable and honorable individuals, relying on the trust that naturally we all have in each other in our profession, blindly and again without any facts in their hands, have continued and still continue defending these structures and repeating the same line that " there was nothing wrong... " as evidenced by some comments in these pages and other places.

7. I like to use this opportunity and call on the Port Authority of New York and New Jersey as well as Mr. Leslie E. Robertson, the structural engineerof the record and Mr. Jon Magnusson, the CEO and Cahirman of the Board of the Magnusson Klemencic Associates ( the firm that was Skilling , Helle, Christiansen, Robertson at the time of the design of the WTC and designed the structures) to post the structural drawings of the WTC towers publicly on the Internet and allow structural engineers and researchers to study these structures and learn lessons from their performance to see if anything that is learned from this tragedy and performance of these towers can be used in their practice to protect public against future murderer or even against accidental airplane impact and fires. If such studies , such as ours, help save even a single life in the future we have done our moral obligation to ourselves, our profession and our fellow human beings.

Best wishes as always and thank you again for your time.
Hassan Astaneh, Ph.D., P.E., Professor (
Member of Professional Advisory Panel of the Skyscraper Safety Campaign (Sally Regenhard, Chairperson)

From: "ASC" <ggg(--nospam--at)>
To: "Struct EngAssoc" <seaint(--nospam--at)>

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BlankWith respect to WTC he had a point:
If the building were constructed according to the Code, it would have a reserve of strength, or, in other words, would=20
not be so flimsy.

Of course, his criticism of the official investigators of the collapse was too strongly worded. But, if he is right, then someone who knows it too,
but doesn't mention it in the report, is wrong, isn't he?

I am more of an analyst than a designer and my familiarity with codes is minimal. But I am aware of at least one 'flimsiness' aspect, that was the most =
likely contributing cause to WTC collapse.

Sometimes circumstances work in unexpected manner. That's why we need a reserve of strength.

As for a public vs private criticism I agree, it would be more professional to stick to the latter. But who would listen then?

Sincerely, Gregory from Oz

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