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| Building Const. For Fire Service (Was: Some WTC Thoughts) (348053) | |||
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Building Const. For Fire Service (Was: Some WTC Thoughts) |
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Posted by JayZeeBMT on Tue Aug 26 15:08:50 2008, in response to Some WTC Thoughts...., posted by JournalSquare-K-Car on Tue Aug 26 12:22:21 2008. Before I begin my comments, let me establish my qualifications on this topic: I am a 20 year veteran of the New York City EMS as well as a "fire medic" cross-trained in firefighting principles and operations. (Those days are behind me but I haven't forgotten what I've learned.) The material I discuss below is directly from in-service training, instructional courses taught by faculty from the National Fire Academy in Emmitsburg, MD, and by the FDNY EMSC's own expertts, including 9then) Capt. Stephen Holliday. The textbook I refer to the most is "Building Construction For The Fire Service", by Frank Brannigan, SFPE, who is recognized by most in the emergency services community as one of the fathers of modern structural firefighting.WTC 1 and 2 were constructed using "core-frame construction", which was compliant with new-law (post-1967) building codes for NYC. To maximize available office space, as well as enhance the mechanical live load-bearing strength of the towers, 47 columns comprised the inner core of the structure. Within this inner core, were the elevators, HVAC ductwork, plumbing and electrical conduits, and communications wiring. The central core of each tower carried about one third of the live load to the ground. The outer core of the towers were ringed with columns carrying the remaining live load and the window glass, some 200 additional tones of live load for each tower. The core construction concept, as built, performed three critical functions: 1) Transmit the total live load of the entire building to the ground. 2) Allow for additional load stressors, including winds, future improvements to the structure, and impacts from flying aircraft, up to and including the 707/720 jet aircraft (the largest jet flying in and around NYC at the time of design). 3) Carry the load around (and over) the basement substructure, which included connecting tunnels between WTC 1, 2, and the other buildings in the WTC complex, and the joint NYCT/PATH lines, which were connected by a shopping mall. Brannigan teaches us (In the first chapter!) that high-rise buildings are our enemy when they are burning. Structural strength of steel load-bearing members decreases proportionally with corresponding increases in temperature; the character of the metal changes. With these changes in the properties of the load-bearing members, comes a new subset of live load figures. Given that gravity is trying to pull the structure down at all times (-G on all live load bearing members=32fps squared), pliable, softened metal with no fireproofing (as was stripped away in boh towers upon impact of each plane), will begin to "give" as it tries to continue distributing the live load of the building to the ground. WTC 1, the north tower, was struck by a Boeing 757-200 flying at around 450 mph. struck by a 767-300ER flying nearly 100 mph faster than that. Both planes have a MGTOW (Maximim Gross Take-Off Weight) at least half again that of a 707. In the case of WTC 1, the plane strick the tower broadside, pulverizing itself and Columns A23 through 29 on the outer core, and virtually all of the columns on the inner core. The live load of the building was instantly redistributed to the remaining intact or partially intact columns. Add to this several thousand gallons of JP-5 jet fuel, which is kerosene, and tons of burning office materials. Brannigan reminds us that in addition to burning buildings being our enemy, we are constrained to a very short timetable in which to fight the fire and make our rescues. I was present at the WTC as a lieutenant from 9:01 AM onwards on 9/11 and I digress a moment here, but you can best believe the damage to both buildings, on visual inspection (FDNY crews actually reached both crash sites before collapse) was far in excess of what the towers would have typically been able to handle. Anyway, in our very limited window in which operations at the scene may be carried out, Brannigan writes,"Every column which is removed from the structure increases the likelihood of its collapse exponentially." Put another way, remove enough cards, and the house WILL come down. Add to this the fact that there were open spaces immediately below the footprints of each tower. Those who have visited the pre-9/11 PATH station at the WTC will recall that track level was three levels below the shopping mall, or five levels below the street. Because the tracks entered the Hudson River tunnels directly from the WTC, the station was driven deep. This contributed to the collapse of both towers because once the collapses began, they were accelerating into a series of voids below. Additionally, the WTC 2 took two other buildings down with it during its collapse, adding to the total tonnage that had to be delivered to the ground. WTC 2, in fact, sustained even more critical structural damage than did WTC 1, as it sustained a corner strike from the plane that hit it. It lost outer columns B1-16 and C20-36, plus 23 of the 47 core columns. The fact that it collapsed in just 30 minutes as opposed to WTC 1's nearly 90 minute delay, speaks to this. Fires from both planes, however, were the accomplices, not the direct causes of each collapse. The buildings fell primarily from severe structural loss and the inablitity of the surviving columns to carry the redistributed load to the ground, exactly as Brannigan predicted in his textbooks. WTC 7 sustained a tremendous amount of damage from being struck by falling debris from the earlier collapse of both towers. I myself saw the south face of WTC 7 after the smoke cleared a bit, and it was evident that large sections of the facade and much of the load bearing beams had been gouged away. Ths fact is often overlookede in reports of WTC 7. THe fires in WTC 7 burned as long as they did because: 1) After the collapses of WTC 1 and 2, water mains in the area were broken in over 20 places, 2) Unprecedented losses in manpower and equipment, plus a massive, ongoing rescue and recovery operation (without the upper echelon of FDNY management, almost all of whom had died by that time), left hardly any resources available to fight a high-rise fire at WTC 7. Brannigan states that when the right conditions are met (as they WERE in WTC 7) gravity will take over and bring the building down. In conclusion, trust me: there was NO "controlled demolition" of ANY building at the WTC on 9/11, Controlled demolition requires weeks or months of planning, and it is necessary to make the structure as light and as weak as possible, to prevent a partial demolition. All three high-rises (WTC 1, 2, and 7, were way too heavy on 9/11 for controlled demolition to work, even if there was an actual conspiracy afoot.) The towers were EXEPTIONALLY well engineered, as evidenced by the fact that they remained standing in failure mode far longer than even Brannigan predicts they should have. THe design and performance of each tower is the reason 25,000 people were saved that day. The death toll would have been far higher had the buildings not been so well-thought-out. I await your reply. |
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