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As it came out of the events in the morning of September 11, 2001, the WTC twin towers - in certain aspects - a real pride of human engineering, were destroyed by a mere, but very intensive, fire caused by the fuel of the two airplanes that were flown into them
The popular perception is that the tragedy of these worldwide renowned landmark build-ings - as structures, and the irreparable human toll it took, has been caused only by those almost fully fuel-loaded commercial airplanes. Still, the "gut feeling" of many tells them that this cannot be the whole story Most of the unprofessional people ask themselves: How come the hits of two planes can destroy these two mastodons? The refusal to accept such a notion is reasonable! We saw how the planes cut through the buildings, and those remained firmly in their place for about hour-hour and a half The professional eye goes further on to explain that the stories affected by the fire melted down and the energy of the enormous weight above was sufficient to knock down both buildings like in a domino chain (but in vertical) True! We saw it very clearly when the northern tower was falling! It was indeed a series of knocking down stories one after another But still, one question remains unanswered: Why it didn't happen like this, for example, that only few floors below the melted ones be crushed by the falling ones above? These buildings have been designed to withstand such an enormous weight True [again]! But the connections between the structural elements, appears, have not been properly designed for the times-fold increase in vertical and--of greater significance--in horizontal dynamic loads ... While being a civilian volunteer at the "ground zero" site during the first 3-4 days and nights - when such people were still admitted there - besides the search for survivors and unfortunately dead, I was trying to find answers to the questions stemming from this surreal picture I saw cut off four- and six-bolt connections that were supposed to keep one over the other the vertical faηade column elements I saw cut off non-full penetration welds whose purpose has been to integrate in "one"--one over the other--the pieces of the huge in cross-section internal steel columns I saw cut off one- or two-line bolt groups, which apparently had the only purpose to keep in place one three-piece faηade steel column element to the other next to it One thing, though, I didn't see! A question: What is the purpose of the RINGS in an oil, a water, or whatever else barrel? The answer is that these RINGS keep the walls of the barrel from bursting out as a result of the horizontal pressure This is exactly what I didn't see in the rubble: Something resembling [or functioning as] those RINGS, which would keep the towers from bursting out in all horizontal directions In my opinion, precisely this missing element is what brought down the towers completely - not only part of them I do believe that two-thirds to three-quarters of the height of the buildings could have been spared, and only several stories smashed, given those "rings" Many human lives could have been saved! Yet, another measure - saving the structures and human beings, might have been a vertical and a horizontal (along the building's perimeter) damping system at each story level to dissipate the energy - of course at economy's expense Finally, those two buildings which have a special place not only in the American heart, but also in every heart in the world that is proud of human achievements, appears, would have come down after any fire of such a magnitude - even without the insignificant energy-wise hits of the airplanes Mario Behar - structural engineer New York, September 24, 2001 mbehar.geo@yahoo.com mbehar7@earthlink.net tel. (718)-728-4937 fax (718)-956-8873 JPEG images: The original (September 24, 2001): Page 1 ; Page 2 ; Download the opinion in MSWord-format The first e-mail (September 27, 2001): Page 1 ; Page 2 The e-mail to the ASCE Teams to Study the NY & DC Disasters (October 25, 2001): Page 1 ; P2 ; P3 LIST OF THE MEMBERS of the ASCE Teams to whom this opinion has been submitted: W. Gene Corley, PhD, PE Charles Thornton, PhD, PE Robert Smilowitz, PhD, PE Ronald Hamburger, PE, SE Paul Mlakar, PhD, PE Mete Sozen, PhD, PE James R. Harris, PhD,PE Donald Dusenberry, PE
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