Excerpt that mentions the reinforced-concrete core of each WTC tower: "We studied the Trade Towers extensively when I was in school. They were one of the first examples of an innovative and efficient structural concept called "tube" restraint. The Sears Towers are a variation called "bundled tube construction" and the idea is based on a minimum of interior columns, with the exterior facade having more numerous exterior perimeter columns. In the case of the WTC, there are no interior columns. Only a central concrete core roughly 60-80 feet square comprised of several vertical voids that house exit stairs, hoistways for the elevators, utility raceways and mechanical chases; and also, significantly, the sprinkler system main lines. The floors were prefabricated broad cellular panels of parallel trusses and main decking that had a light weight concrete topping applied after they were installed. They spanned a distance of roughly 60 feet from the concrete core to the exterior gridwork of columns and horizontal beams." ************************************************************ Message-ID: <3BAD5E05.F5A92E1E@aol.com> From: The Wizard of Oz Reply-To: wizard@wiz.mailshell.com Organization: abuse@wiz.mailshell.com X-Mailer: Mozilla 4.51 [en] (Win98; U) X-Accept-Language: en MIME-Version: 1.0 Newsgroups: dfw.singles Subject: The Letter Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 19 Date: Sun, 23 Sep 2001 04:07:51 GMT NNTP-Posting-Host: 65.1.47.166 X-Complaints-To: abuse@home.net X-Trace: news1.rdc1.tn.home.com 1001218071 65.1.47.166 (Sat, 22 Sep 2001 21:07:51 PDT) NNTP-Posting-Date: Sat, 22 Sep 2001 21:07:51 PDT As many of you know, I have a brother who lives in Birmingham, Ala who is an architect of some stature in his community. He has never let his successes go to his head, and is still the nice guy I grew up with. Just a day or two ago, my parents got a letter from him regarding the recent national tragedy in New York and Washington DC. He gave some technical details about the construction methods used in the WTC Towers which are very interesting, and also talks about his own thoughts on effects of the destruction on the country and himself. I found it extremely interesting, even if he is my brother, and, with his permission, will post it here in the NG for you to read if you care to. The technical aspects of the constructions get a little detailed, but he wrote it aiming at our parents who are non- professional in his field, but learned a little from him when he was in school. His own thoughts are interesting, to me, but I may be just prejudiced. Read it if you wish, or just move on to the next one. -- Regards, Wiz Reply to: wizard (at) wiz dot mailshell dot com Complaints to: abuse@wiz.mailshell.com ======================================================= Message-ID: <3BAD6303.DD312279@aol.com> From: The Wizard of Oz Reply-To: wizard@wiz.mailshell.com Organization: abuse@wiz.mailshell.com X-Mailer: Mozilla 4.51 [en] (Win98; U) X-Accept-Language: en MIME-Version: 1.0 Newsgroups: dfw.singles Subject: Re: The Letter References: <3BAD5E05.F5A92E1E@aol.com> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 120 Date: Sun, 23 Sep 2001 04:29:09 GMT NNTP-Posting-Host: 65.1.47.166 X-Complaints-To: abuse@home.net X-Trace: news1.rdc1.tn.home.com 1001219349 65.1.47.166 (Sat, 22 Sep 2001 21:29:09 PDT) NNTP-Posting-Date: Sat, 22 Sep 2001 21:29:09 PDT The following is his letter in its entirety, without any editing by me: +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ September 17, 2001 Dear Mom and Dad, I had just started a letter to you folks when I checked my voice mail and had a message from Dad to call him back. I enjoyed our brief call, and thanks for the stock update. I am still shaken over what has happened. I keep replaying that day over and over in my head. We studied the Trade Towers extensively when I was in school. They were one of the first examples of an innovative and efficient structural concept called "tube" restraint. The Sears Towers are a variation called "bundled tube construction" and the idea is based on a minimum of interior columns, with the exterior facade having more numerous exterior perimeter columns. In the case of the WTC, there are no interior columns. Only a central concrete core roughly 60-80 feet square comprised of several vertical voids that house exit stairs, hoistways for the elevators, utility raceways and mechanical chases; and also, significantly, the sprinkler system main lines. The floors were prefabricated broad cellular panels of parallel trusses and main decking that had a light weight concrete topping applied after they were installed. They spanned a distance of roughly 60 feet from the concrete core to the exterior gridwork of columns and horizontal beams. the floor trusses restrained the exterior walls and prevented them from buckling outward. The exterior structural system was prefabricated in panels of multiple columns (steel tubes only 14 inches square) that spanned vertically through 2 or three floors. This was a fast way to erect the building and helped enclose the building faster. At the upper floors, the winds are so high at times that no other work can begin (including pouring the floor topping) until the exterior is in place. Once the building was closed in, the underside of the floor assemblies were sprayed with a cementitious mineral fiber coating for fire resistance. Then the sprinkler lines were run, along with ductwork laterals from the main ducts built into the floor assemblies. A ceiling grid would have been hung and minor interior partitions fastened to the floor and ceiling grid and covered with gypsum board panels. A building that size, 10 million square feet, would have each floor (roughly 40,000 square feet each) separated by fire/smoke barriers and exit corridors that prevented the migration of smoke and fire throughout a given floor. The stairs would have been considered an absolutely safe haven to leave a fire-envolved floor to an area of safety. In high rise construction, the stair towers are required to have the capability of being pressurized by large fans so that, in a fire emergency, smoke will be kept out of the stair; even with a number of the stair doors open. Otherwise it makes a perfect chimney. That is why you should never use an elevator in a fire. There are hose connections and hose cabinets at each floor so the firemen can fight the blaze where ever it may occur without hauling hose up the building. I'm no structural engineer, but the impact of the planes must have severely damaged the center core. They were designed to handle a Boeing 707; a typical plane in use in the late 60's. But no one imagined the thousands of gallons of fuel that poured into the structure. With essentially every fire barrier breached, the fuel must have flowed everywhere, and poured down the cavities between floors. They say the fuel combined with all of the furnishings produced fire temperatures in excess of 1000 degrees. Building beams and columns are protected with the fire proofing to prevent structural failure at temperatures of 1500 degrees for 1-hour. That is the way we design them per the requirements of the various building codes. Combined with the automatic sprinkler systems, the fire proofing in a structural steel building is intended to give firemen enough time to contain the blaze. With the sprinkler risers severed, and the cascading flood of fuel, the firemen would never have been able to save the building's structure from thermal failure in time. Ironically, Building 2 survived exactly one hour before it collapsed. Building 1 lasted close to 1 3/4 hours. When the high temperature caused the first few floor trusses to sag and pull away from the exterior wall, the wall buckled outwards, causing a chain reaction of dropping floor trusses, and buckling walls all the way to the bottom. The center core would have been only designed to accommodate gravity loads, vertically imposed loads. The falling floors must have created so much lateral force that the core disintegrated in the same chain reaction. As each floor pancaked, a shockwave blew out the windows and expelled the dust cloud of pulverized concrete, gypsum dust, and the cementitious fiber fireproofing. It was one of the first buildings constructed without asbestos fireproofing, so there should have been no danger of that in the dust cloud. In the last week, I have moved from shock and disbelief, through grief, and have settled into an anger that won't go away. I keep thinking of those now 5,400 innocent people looking themselves in the mirror for the last time, getting dressed for the last time and going to work. I can't imagine how those firemen searching through the debris must feel. People of my generation, as I mentioned to you before, never had a Great Depression, or a Pearl Harbor to galvanize us and crystallize our beliefs; to bring us together as one nation. We were just a pampered, unappreciative, self-centered bunch of self important egos; wondering how best to get ahead. I don't think that is the case any more. I still don't think the seriousness and gravity of this tragedy has hit us; those of us without your WW II perspective. September 18, 2001 I saw David Letterman last night; his first broadcast since Tuesday. He will probably never have a re-run of it, and if you didn't see it, it would be hard to describe. Last week I wondered how his show and Leno's would be able to come back with their usual irreverent "make-fun-of-everything-that-moves" brand of humor. Letterman's show opened with no music or monologue. Just him sitting at his desk with scattered quiet applause. He said that he didn't now if this show would work, doubting whether he could pull it off. Then he proceeded to convey his thoughts for about twenty minutes. His hands were shaking and his voice wavered. He lavished Giuliani with praise, saying he was "the definition of courage..." He used profanity, un-edited but somehow appropriate. It was riveting. His first guest was Dan Rather, who has always seemed to me too cool and professional to the point of being dull. Well he made it clear by the way he spoke and the things he said, that he had been waiting a long time to unload his thoughts and speak his mind. He broke down twice; too emotional to finish what he was saying. It was an incredible sight. I don't know what is going to happen next. Does anybody? I can't believe how astonishingly unbelievable this all has been. I think I know now how you all might have felt on December 7th. But look where we are 60 years later. I'm glad we have the experienced folks in there. Cheny, Powell, Rumsfeld. And the young frat boy Bush doesn't seem that way any more. He has really risen to the horrible occasion. I can't bring myself to think what Gore, Reno, and Albright would do to muster confidence in the country. I know we'll get through this. Those buildings will be built back like they were, only taller. And we'll leave your grandchildren a safer world. God bless America. You folks take care. Love, Phil