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Uh, what? I'm unaware that a structure that is ~95% air has any trouble imploding in any situation. That's what happens when it collapses. It's all air, it just falls through itself.applepowerpc said:You just demonstrated precisely why it is impossible for the building to implode at near free-fall velocity due to weakening steel rods.
Once the supports on the outside start snapping it is an all or nothing deal. They don't just deform constantly until they hit the ground (it's steel, not silly putty, you'll never get very large deformations from it). The outer supports start snapping, it transfers load to supports that were never designed to support that load, they start snapping, eventually they're all gone. Once a support snaps the rest is dominos (the support that snaps is the one that can bear the load the best - the rest can't bear it as well, and once that stress is on them, they'll inevitably snap too).applepowerpc said:You just said steel weakens in a continuous fashion. It's not an all-or-nothing deal. Yet the WTC imploded at near free-fall velocity. How can that be? Could it be a chain reaction from the momentum? How? If steel weakens gradually, then how can there be any significant momentum?
Years ago I did professional accounting. The fire department of a small town near me started a "controlled" burn on a small shed to "practice" putting out a fire. Unfortuantely a wind came up that they hand't expected. The fire went out of control, leapt the highway and burned the field across the road.Prophetable said:Good point - Especially considering the fact that the molecules within the steel aren't necessarily going to reach the temperature of the fire.
The fires original fires were limited to certain floors. There weren't leapers or survivers from those floors.applepowerpc said:Not 800 degrees, 2000 degrees. And I might point out that there were people jumping out of the WTC. If the 2000 degree fires were weakening the outer structure, how were the people able to make it to the windows? They'd be already dead.
I have the word of some pretty damn competent structural engineers and scientists that the jet fuel burned up the oxygen in there pretty quickly, leaving it to be fed by the oxygen blown in. It got hot, but not that hot. That's what every single structural analysis says.TexasSky said:It did not run out of oxygen.
It might have, in a controlled lab setting, but this was not a controlled lab setting.
First, the jet was CARRYING oxygen of its own.
Second, and there is and was wind on those towers. In fact, the towers were specifically designed to give a little in the wind because at that height the wind is so severe.
Given that there was a gaping hole in the building, there was more wind there to fuel the fire than there was on the plains of Texas.
No, it's one of the few things that's not a major flaw in the paper posted earlier. Think about a floor. It was 43,000 square feet (208x208), The side of the building was 110 feet long, 10 feet high, or slightly over 1,100 feet. Assuming 100% destruction on all 4 sides, the open area for the fire was 4,400 square feet, while the floor covered 43,000 square feet which were open to the air in your texas fire. That means that about 10% of the oxygen volume was available assuming the wall destruction was 100% on all 4 sides. Now clearly this doesn't factor in air density, wind, et al, but is it clear that the fire was oxygen starved?Once the plane broke through the structure there was no 'containment'.
Once the windows broke due to heat - there was no 'containment'.
This is one of the major flaws in the paper that was posted earlier.
I'm not a conspiracy theorist here. I'm stating facts.Not to mention a certain level of "contradiction of itself." First "the fire wasn't hot enough to melt steel," then "the fire was too hot to allow for any oxygen."
Don't lecture me on the laws of physics. First, that isn't a law of physics. It's a chemical reaction. And the laws of chemical reactions say that reactions have a limiting factor. In any reaction there is one reactant that is available in greater proportions then the other. React baking soda and viniger, and unless you are very, very, very careful you will have baking soda on the bottom or excess vinager. In the fire's case, the limiting reactant was oxygen. It was only available at a constant rate that was smaller than the amount of jet fuel readily available.One of the absolute basics of fire is that it must have air to breath.
If there was no oxygen, there would have been no fire.
The fact that there was fire, is evidence there was obviously oxygen.
You just cannot have one without the other. Ever. Period. Without re-writing the laws of physics.
Of course, you don't need an engineer to tell you why the towers fell down: two Boeing 767s, travelling at hundreds of miles an hour, and carrying more than ten thousand gallons of jet fuel each (if you converted the energy in the Oklahoma City bomb into jet fuel, it would amount to only fifty-one gallons), crashed into the north and south buildings at 8:45 A.M. and 9:06 A.M., respectively, causing them to fall—the south tower at 9:59 A.M. and the north tower at ten-twenty-eight. Nor do we need a government panel to tell us that the best way to protect tall buildings is to keep airplanes out of them. Nevertheless, there is considerable debate among
Leslie E. Robertson is the engineer who, with his then partner, John Skilling, was mainly responsible for the structure of the Twin Towers. Unlike most of his colleagues, who have been widely quoted and interviewed, he has remained largely out of the public eye since September 11th. His only public appearance was at a previously scheduled meeting of the National Council of Structural Engineers Associations, on October 5th, in New Hampshire, where, as the Wall Street Journal reported, on being asked by an engineer in the audience, "Is there anything you wish you had done differently in the design of the building?," Robertson broke down and wept at the lectern.
Guy Nordenson, a structural engineer in New York and a professor at Princeton, who, like many of his colleagues, regards Robertson with great respect, showed me a recent E-mail he had received from him.
"Before the buildings collapsed," I asked, "did any part of your brain, calculating, say, 'There's probably this amount of jet fuel, this amount of fire protection—the building has this long to last'?"
"I can't . . . I think there are times when logic just isn't the right way to think." Robertson's eyes were filling with tears. "This all took place in an hour and a half. The TV was on. I don't know if what I saw was the buildings falling down on rerun or whether it was live. I was just focussed on getting back to New York City.
During the last hundred and twenty years, three major types of structures have been employed in tall buildings in New York City. The first type was used in the cast-iron buildings of the eighteen-eighties and nineties, in which the "gravity load"—the weight of the building—was carried mostly by the exterior walls.
It still gets hot, but not hot enough to melt steel. Weaken it? Yes.
The second generation of tall buildings, which includes the Metropolitan Life Building (1909), the Woolworth Building (1913), and the Empire State Building (1931), are frame structures, in which a skeleton of welded- or riveted- steel columns and beams, often encased in concrete, runs through the entire building. This type of construction makes for an extremely strong structure, but not such attractive floor space.
The interiors are full of heavy, load-bearing columns and walls, and, as you move toward the center of these buildings, the more cryptlike they feel. Charlie Thornton, of the Manhattan-based structural-engineering firm of Thornton-Tomasetti Engineers, a leading designer of the structures of modern high-rises, said to me recently, "A building like the Empire State Building is way overdesigned and overbuilt. The building didn't need all that support. Those engineers didn't understand loads the way we understand them—they used slide rules to work them out, whereas we have computers—and so they erred on the side of caution."
Most high-rises erected since the nineteen-sixties use a third type of structure—a synthesis of the best aspects of the two previous kinds of structure. The perimeter structures of these buildings resemble tubes. Inside, a massive hollow core made of steel and/or concrete contains many of the services: elevators, stairwells, and bathrooms. Because the core and perimeter columns carry so much of the load, the designers could eliminate interior columns, with the result that there is more open floor space for the tenants. And, because frame structures require ironworkers to weld or rivet the beams to the supporting columns on site, which is both expensive and dangerous, reducing the extent of the frame means that more of the structure can be fabricated off site, making the building safer and more cost-effective to erect. Finally, improvements in metallurgy increased the strength of the structural steel in these buildings, allowing engineers to reduce, or eliminate, the use of concrete in supporting the structure. Reinforced concrete, although it is more fire-resistant than steel, is messy and expensive to work with, especially in Manhattan, where traffic and space constraints at sites make it difficult to bring in the daily fleets of cement mixers necessary for a big job.
(continued)But, as the new high-rises sprouted, some New York City firefighters began to point out that the same innovations that make these buildings more economical to erect and more pleasant to inhabit also make them more vulnerable to fire.
In 1976, the New York City Fire Commissioner, John O'Hagan, published a book entitled "High Rise/Fire and Life Safety," in which he called attention to the serious fire-safety issues in most high-rise buildings constructed since 1970, referring to such buildings as "semi-combustible." Unlike the earlier generation of skyscrapers, which used concrete and masonry to protect the structural steel, many of the newer buildings employed sheetrock and spray-on fire protection. The spray-on protection generally consisted of either a cementlike material that resembles plaster or a mineral-fibre spray, such as the one used to protect the floor joists in the World Trade Center. O'Hagan pointed out that, even when these spray-ons are properly mixed and applied to the steel (which must be clean), they are much less dense than concrete and can be easily knocked off. The swaying of the cables in the elevator shafts has been known to dislodge the fire protection from the columns in the cores of these buildings, and the coating used on floor supports is often removed by workers who install the ducts and wiring inside the hollow floor. The questionable performance of the fire protection used in these buildings, combined with the greater expanse of lightweight, unsupported floors, O'Hagan said, created the potential for collapse, of the individual floors and of the entire structure. He also pointed out that the open spaces favored by modern developers allowed fires to spread faster than the compartmentalized spaces of the earlier buildings, and that the synthetic furnishings in modern buildings created more heat and smoke than materials made out of wood and natural fibres.
The trick to designing tall buildings in windy places (like New York City and Chicago) is to endow them with enough elasticity to move with the wind but enough stiffness so that the people working on the upper floors don't know the building is moving.
The World Trade towers used the perimeter walls, rather than the core, to brace the buildings against the wind, a concept that recalled the first generation of high-rises. As Robertson described the models and experiments he had devised to test how the towers would stand up to external forces that might topple them, he looked almost happy for the first time that morning. He built models of the towers and placed them in a wind tunnel; he put people in motion simulators and observed their behavior; he invented a new kind of damper system to lessen the effect of the wind throughout the buildings.
(continued)listed all the bad things that could happen to a building and tried to design for them. I thought of the B-25 bomber, lost in the fog, that hit the Empire State Building in 1945. The 707 was the state-of-the-art airplane then, and the Port Authority was quite amenable to considering the effect of an airplane as a design criterion. We studied it, and designed for the impact of such an aircraft. The next step would have been to think about the fuel load, and I've been searching my brain, but I don't know what happened there, whether in all our testing we thought about it. Now we know what happens—it explodes. I don't know if we considered the fire damage that would cause. Anyway, the architect, not the engineer, is the one who specifies the fire system."
On September 11th, each building took the impact of a 767 (which is nearly twenty per cent heavier than a 707) and stood long enough to allow most of the people below the crash sites—the ninety-fourth floor to the ninety-ninth floor in the north tower, and the seventy-eighth floor to the eighty-fourth floor in the south tower—to escape. Had the buildings toppled immediately, nearly all those survivors would have died, and there would have been huge losses as well in the buildings and streets around the towers. The fact that the terrorists chose to hit the buildings on opposite faces suggests to some that they intended to knock the buildings over—which would have increased the destruction and loss of life. "Ninety-nine per cent of all buildings would collapse immediately when hit by a 767," Jon Magnusson said.
But did the special structural characteristics of these buildings, qualities that made them so resistant to attack from without, also make them vulnerable to collapse from within, once the fires started?
In any fire, it is logical to assume that the weakest link in the structure will be the first to fail. In the towers, the weak link was the floors. "Floor beams or trusses will heat up faster than columns, because [they're thinner pieces of steel," W. Gene Corley, the leader of the FEMA team, says. The floors were supported with sixty-foot-long right angles of steel (on the long sides), and these were bolted, not welded, to the inner and outer columns. "The whole floor system was a very lightweight construction," Eduardo Kausel, a structural engineer at M.I.T., told me. Another engineer described the floors to me as "flimsy." Jerome Connor, also of M.I.T., said, "The weakest link was definitely the connections of the floor trusses to the vertical members." Those connections were protected with the mineral-fibre spray, but most of it was probably knocked off by the impact of the airplanes. Ron Hamburger told me, "If you knock it, that spray-on protection will come off. When I visited the site, I went through the American Express and the Bankers Trust buildings, and I saw large chunks of the fireproofing in those buildings knocked off—and that was only by falling debris, not by an airplane hit. I think we can assume there was a lot of unprotected steel in the towers after the planes hit."
The columns in the core were massive, and were capable of bearing huge gravity loads, but they depended on the floors to provide lateral support. As the floors around the crash site began to give way in the intense fire, ever greater lengths of the core columns, which were already overloaded because of the destruction of exterior columns, became exposed. If you stand an inch-long drinking straw on end and press on it with your finger, you have to press pretty hard before it bends. But if you do the same thing with a seven-inch-long straw it buckles easily. The same principle was at work in the towers' core columns. Once the core columns buckled, the entire weight of the floors above the crash sites came down like a jackhammer on the remaining floors, starting a chain reaction of pancaking floors and buckling columns which demolished the entire structure within fifteen seconds—the same amount of time it took the people who jumped from the top of the towers to hit the pavement. "Once the collapse started, it was essentially a free fall," Eduardo Kausel said.
Among the dozens of people I have spoken to recently who are experts in the construction of tall buildings (and many of whom witnessed the events of September 11th as they unfolded), only one said that he knew immediately, upon learning, from TV, of the planes' hitting the buildings, that the towers were going to fall. This was Mark Loizeaux, the president of Controlled Demolition Incorporated, a Maryland-based family business that specializes in reducing tall buildings to manageable pieces of rubble. "Within a nanosecond," he told me. "I said, 'It's coming down. And the second tower will fall first, because it was hit lower down.' "
Before September 11th, the largest building ever to be imploded by accident or design was the J. L. Hudson department store, in Detroit, with 2.2 million square feet of floor space, which C.D.I. "dropped" on October 24, 1998.
(continued)They are structural undertakers, which may explain why Mark, when confronted with the spectacle of the crippled buildings, lacked the sentiment that builders feel for their creations—that innate sympathy which helped blind the engineers of the World Trade towers to the reality of what was about to occur. "I thought, Somebody's got to tell the Fire Department to get out of there," Loizeaux told me. "I picked up the phone, dialled 411, got the number, and tried it—busy. So I called the Mayor's Office of Emergency Management"—which was in 7 World Trade. "All circuits were busy. I couldn't get through."
Loizeaux said he had an enhanced video of the collapses, and he talked about them in a way that indicated he had watched the video more than once. "First of all, you've got the obvious damage to the exterior frame from the airplane—if you count the number of external columns missing from the sides the planes hit, there are about two-thirds of the total. And the buildings are still standing, which is amazing—even with all those columns missing, the gravity loads have found alternate pathways. O.K., but you've got fires—jet-fuel fires, which the building is not designed for, and you've also got lots of paper in there. Now, paper cooks. A paper fire is like a coal-mine fire: it keeps burning as long as oxygen gets to it. And you're high in the building, up in the wind, plenty of oxygen. So you've got a hot fire. And you've got these floor trusses, made of fairly thin metal, and fire protection has been knocked off most of them by the impact. And you have all this open space—clear span from perimeter to core—with no columns or partition walls, so the airplane is going to skid right through that space to the core, which doesn't have any reinforced concrete in it, just sheetrock covering steel, and the fire is going to spread everywhere immediately, and no fire-protection systems are working—the sprinkler heads shorn off by the airplanes, the water pipes in the core are likely cut. So what's going to happen? Floor A is going to fall onto floor B, which falls onto floor C; the unsupported columns will buckle; and the weight of everything above the crash site falls onto what remains below—bringing loads of two thousand pounds per square foot, plus the force of the impact, onto floors designed to bear one hundred pounds per square foot. It has to fall."
Loizeaux said that when he demolishes buildings he sometimes tries to make the top twist and fall sideways, which can generate enough "reverse thrust" to push the rest of the building the other way. "The top part of the south tower almost did fall off, which is what would happen in most buildings. Did you see how, when that top part started to fall, it began to rotate? If that piece had kept going out, it probably would have pushed the rest of the building the other way as it fell. But those long trusses saved the day—they gave way, guided that top downward just like a bullet through the barrel of a gun, and mitigated the damage." He added, "Let me tell you something. Far more people would have died if those buildings had been built differently. A conventional frame building would have fallen immediately—no question. Only a tube structure could have taken that hit and survived."
The oxygen was extremely limited. The wind that day wasn't very strong at all, the air was nearly still (for proof, look at the smoke clouds rising nearly vertically).TexasSky said:BTW, the oxygen was not limited. Where do you keep getting that the oxygen was limited? It was a high rise building in New York city where wind was so strong that the did extensive tests on wind resistance, and it had gaping holes in the building.
As to baking soda. I've put fires out with it. The "chemical reaction" you see is that the soad absorbs oxygen. I don't recall any baking soda on the planes at the WTC.
Why did you ignore all of these links?applepowerpc said:Is this a cut-and-paste contest? I will take the high road. I will stick with links. Such as the BYU physics professor's paper:
http://www.physics.byu.edu/research/energy/htm7.html
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