Posted on 09/11/2001 4:27:20 PM PDT by Looking for Diogenes
Sept. 11, 2001 |
The World Trade Center's twin towers were the tallest buildings in the world at the time of their opening in 1970. They each stood 110 stories and more than 1,300 feet tall. They are the dominant features in an enormous office complex totaling more than 9 million square feet of office space and together make up one of the most recognizable architectural landmarks in the world.
Today they were reduced to heaps of rubble after one of the worst catastrophes in U.S. history. A pair of jetliners crashed into them Tuesday morning -- at precisely the points at which they would do the most damage, according to architectural experts. The impacts created fires and, ultimately, brought about the collapse of both buildings.
Why did the buildings collapse?
According to Gregory Fenves, a professor of Civil Engineering at the University of California at Berkeley, the planes weakened the buildings' structures at key points. Fenves, working on information gleaned from preliminary TV reports, stressed that he was speculating. He said that if the planes had hit the structures higher, they could have merely damaged their tops; if they had hit lower, they would have been up against the enormous weight and resistance of the base of the buildings.
The buildings were architecturally interesting in many ways. Each structure is based on a central steel core, which is surrounded by the outside wall, a 209-foot by 209-foot cube of 18-inch tubular steel columns, set 22 inches apart. The cores and "tube walls" share the enormous physical weight of the structures and protect them against the extraordinary wind forces of buildings that tall. There are trusses that support each floor, but no other columns between the cores and outside walls. Some floors contain nearly 40,000 square feet of open office space.
News reports said the planes were jetliners, a 757 and a 767. The 757 has a 124-foot wingspan, is 155 feet long and can weigh 100 tons. A 767 is bigger, with a 156-foot wingspan and 159-foot length and can weigh a maximum of 200 tons. (A 747 is more than 200 feet long and can weigh 400 tons.)
The planes hit the buildings near the 70th or 80th floors. Their impact severely damaged the tube walls, which carried a large proportion of the buildings' weight. CNN footage of the second plane hitting a tower appeared to show that a large part of the jetliner went all the way through the building, suggesting that the interior core was also damaged.
Once a building like a World Trade Center tower loses some of its support, the building in effect goes to work, Fenves said. "The loads are trying to redistribute," he said. "The loads are figuring out how to get back down to the ground." At the same time, he noted, the fires are deforming the physical properties of the support steel.
"It's a very rugged system," he said. "It takes a long time for the collapse mechanism to develop. It's not like kicking the leg out from underneath a chair. The building is 200-foot square and there's a lot of structural system there."
But once the upper floors began to give way, terrible force was set in motion. Each floor of a building that big might weigh 6 million pounds, he said. Once impact is factored in as well, he said, the force becomes irresistible.
The disaster is a terrible echo of another disaster involving a New York landmark.
On July 25, 1945, a B-25 bomber slammed into the north side of the Empire State Building, then the tallest building in the world. A reckless pilot was flying over Manhattan in poor visibility; it was apparently an accident. Thirteen people died, mostly in fires started by burning gasoline.
The Empire State Building, Fenves noted, was built during the Depression, and made with a much heavier structural system. The bomber in that accident was also a much smaller plane, said Fenves.
The WTC buildings' official names are One and Two World Trade Center; their respective heights are 1,368 and 1,362 feet tall. They are part of a massive seven-building complex near the southeastern end of Manhattan. The center's architect was Minoru Yamasaki. The engineers were John Skilling and Leslie Robertson of Worthington, Skilling, Helle and Jackson.
The complex cost $350 million in 1966, or nearly $2 billion in today's dollars. Ground was broken in 1966, and the buildings opened in 1970, but the complete center was not finished until 1974; there are now seven total buildings, a large shopping mall, and an enormous garage. An observation deck is a popular tourist destination. Beneath the center two New York subway lines converge; there is also the Manhattan terminus of PATH commuter trains from New Jersey.
The center has been the target of an attack before. On Feb. 26, 1993, terrorists linked to Osama bin Laden planned and carried out a truck bombing in the parking garage. Prosecutors said the weapon was a 1,200-pound truck bomb. Six people died and more than 1,000 were injured in the attack. The explosion created a five-story crater beneath the building, but its structure held.
After the center opened in 1970, for several years it was feared the complex would become a real-estate white elephant. But for decades it then reigned as one of New York City's premier office buildings. A recent press release from the New York and New Jersey Port Authorities, which own the building, says that more than 430 companies from 28 countries are tenants. The authorities said that 40,000 employees work in the buildings daily, besides 140,000 daily visitors.
The World Trade Center lost its position as the world's tallest building in 1974, when the Sears Tower in Chicago opened. In 1998 the two Petronas Towers in Kuala Lumpur, Malaysia, opened; they are each more than 100 feet taller than the World Trade Center structures.
According to an eyewitness report I heard on the news, the plane that crashed into the Pentagon actually hit the ground first and skidded into the building. Since I can't think why a kamikaze would do such a thing, my only guess is that the pilot didn't know how to visually judge ground clearance on the large aircraft.
I am still a bit unclear as to exactly where the first plane struck tower #1. Dead center, (side to side, that is, not top to bottom), or approximately centered between the core and one side, as the second plane seemed to.The flaming holes from the first impact looked very similar. Also, late last night and this morning, Fox News showed some footage they got from a crew in the area that did film/video the first impact. It was similar to the second, only higher. It's really hard to tell from the video they shot, but it looked like that plane had to come in higher because of other buildings in the area. I think the second plane had a more open approach, so it could hit lower.
Perhaps it could have been hit by a 707 and survive. But planes got much bigger since then.Actually, they have. The 707 had a 130' wingspan and a gross weight of 80 tons.
The 767-400 (the largest 767 variant) has a wingspan of 170' and a maximum weight of 225 tons. The 767-200 has a wingspan of 156' and a maximum weight just under 200 tons.
Also, the building stood up to the impact of the 767. It was the fire damage that caused the building to collapse. I'm pretty sure that the engineers that claimed it could take an impact from a 707 weren't considering the effects of the resulting fire. If the airlines still flew 707's, one of those would probably have done the job.
I'm pretty sure that destroying the buildings was the goal of these terrorists. However, I'm not convinced that they did that much engineering and analysis. It's entirely possible that they went with "Well, a bomb in the basement didn't do it, let's try a big airplane in the side."
Even if they didn't completely destroy the buildings, this was still would have been a successfull terrorist strike. They would have killed all the passengers on both planes and also most of the people on the floors that they hit directly. They picked planes that were bigger than the public claims of the engineers. They probably figured that they would do enough damage to make the buildings unusable (and possibly unrepairable) for a long time. Actually, if they wanted a monument to their attack, they probably would have preferred the big hulking, uninhabitable wreckage to stay standing.
I agree that they picked their flights carefully, choosing planes that would have been fully loaded with fuel. But this doesn't take any particular engineering skill. It's pretty obvious that a flight from Boston to San Francisco would have more fuel aboard than a flight from Boston to Washington DC.
Also, I saw some radar traces on one of the networks last night. I wasn't impressed with the navigation skills and flying skills of these "pilots." It looked to me like strictly a VFR type approach. You can see New York City and especially the World Trade Center towers from a very long way away. I don't think they used any of the navigation tools available to them. They more likely turned and pointed the plane at the target visually.
Also, the speed variations and altitude wierdness also makes it look like these "pilots" weren't very well trained. Possibly just some PC based flight simulator time plus some time looking at pictures in those flight training manuals they apparently had. I'm not saying they might not have had more skills, but those are the minimal skills required to do what they did.
The only cascading failure in Kansas City was horizontal, as the supporting-rod/box-beam joints failed and caused the load they'd supported to be transfered to other joints on the same level which failed in turn.
Unlike a "pancake" collapse where the lower level supports the upper level, and the collapse of the other level hits the lower level with an unsurvivable dynamic load, the balconies in Kansas City were all supported from above, with the upper balcony directly supporting the lower balcony [note: this represented a change from the original plan]. The joints connecting the upper balcony to the rods from above could not withstand the combined wait of both balconies so the upper balcony fell. The lower balcony fell not because the upper balcony hit it, but because there was no longer anything supporting it.
This is why amateurs never make any money in the stock market. People are going to be running around in a panic, dumping their insurance company stocks, while professional traders will be buying them at extremely low prices.
Three days later, some moron who just dumped all his insurance stocks is going to do a little research.
"Wait a minute!" he'll say, "I just found out that the Port Authority of New York & New Jersey doesn't carry any insurance!" -- (the agency is so large that it has the financial means and bonding capability to cover its losses in the event of a catastrophe)
Then that same person is going to sit around and whine that "the government isn't doing enough for the economy."
As they say on Wall Street, SOME PEOPLE ARE BORN TO BE CUSTOMERS.
They both survived the crash. They probably did not analyze for the jet fuel fire!
I agree with your statement about the collapse of the building as being gravy but it is obvious that you have never flown a plane.
The reason I posted that speculation yesterday was that I was aware that the design of the structures was considered innovative at the time and hadn't been used before on a structure as large as the WTC.
I've got to re-register opposition to this idea. If they were "stupid and crazy" they couldn't have succeeded in keeping this secret.
I'm not aware of any coordinated terrorist or military attack in history that was designed, financed and implemented by only those immediately involved in its execution.
One sociopath acting alone is always a possibility. In that regard, we'll likely see some kind of copycat hijacking attempts soon. Four, eight or sixteen like minded capable disciplined martyrs must be the product of a culture where there is no doubt as to the virtue of their actions. Otherwise, the reasoned thinking needed to manage the operation would also act to weaken their resolve. And there are no domestic organizations that are both vicious enough to do this as well as being capable of attracting and supporting these individuals.
Like a great athletic accomplishment, it's not as easy as it looks. Athletes require financing, recruiting, socialization, and coaching. There's no president for four skilled people planning and independently executing a simultaneous crime against humanity.
But this looks like a moot point now anyway, apparently suspects are being arrested and insiders are alluding to signals intelligence showing Ben Laden's involvement.
Notice the successes that would have happened IF the fire could have been put out (in 2-4 hours, maybe in 4-6 hours) .... Nobody knowss how the building might stand.
First. The 4,000 - 8,000 people alive in the floors ABOVE the impact area would have been saved by the first firefighters to get through the stairs.
Second. IF the fire could have been out - and it certainly MIGHT have been under different circumstances - the weakened structural steel - WHICH DID withstand the impact of the collision for hours - might have been strong enough to give enough time to evacuate the whole building.
Third. IF the fire had been put out - in one or both buildings - then the damages MIGHT have been limited to the immediate fire and explosion, since the buildign might not have fallen at all. Not 10,000 dead and 3 billion dollars of losses.
Your loss is very real - but the firefighters WERE NEEDED to TRY to reach/protect/evacuate those thousands of the higher-level occupants - who were still alive until the building collapsed.
Also, until the collapse itself began - there is NO WAY to predict how long the building would stand....minutes more, hours, or "forever" -
Nobody at street level could predict how long, if ever, the building may stay up. You cannot tell from the ground, or even in the fire itself, how strong any given steel member is without rigorous lab-condition analysis. And even if you know how strong any single member is, you can't tell without hours of elablorate computer simulation, what's the result of one or more members failing. Since the damage was widespread, over several floors, and was in the midst of flames ..... you can't take the time to analyze - you MUST PROTECT IMMEDIATELY those threatened.
(And of course, removing steel pieces from the building is impossible during the fire. And would weaken the building itself. Even surveying the building would delay other rescuers from going up to try to make a passageway down for those trapped.)
If the building did not immediately fail - which it did not - then the those trapped and burning to death up became priority.
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