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.
Yep. You said more in one sentence than Salon said in their whole article of manutia.
Someone with a fairly sophisticated military. I DO NOT believe that Bin Laden could have pulled this off by himself.
This article kills that conspiracy theory, hopefully.
In today's world any act that requires a large number of people can not be kept secret. This had to be fairly small number of people willing to die for a cause.
They had to consider the cause more valuable than their own lives. We must prove to the world that when you give your life to attack us for a cause, that results in the cause being totally destroyed.
Only then will we be safe from the terrorists.
No to mention the tons of water released to put out the fires.
http://www.freerepublic.com/forum/a3b9e390647f1.htm
17 Posted on 09/11/2001 09:32:42 PDT by Plummz:
A word on the structure of the WTC towers: The WTC towers had a distinctive structural system which utilized the exterior wall framing for lateral bracing -- a so-called lattice framework. This allowed minimization of internal lateral bracing and opened up the floor plans. You can see the effect of that when the buildings collapsed, with the lattice framework crumbling and the interior imploding. The lattice works so long as it remains intact as a system: if a part of it goes, then the whole systemgoes. The planes punched holes in the lattice, one tower punched on two sides, maybe the other too. Portions of the lattice of the second tower briefly remained standing after the collapse,then fell. The system was considered daring at the time of construction, for it distributed loads more efficiently than legacy column-and-beam-supported systems. Probably the legacy systems would not have totally collapsed due to damage at upper floors, although floors above the damage would have come down if columns wereweakened.**********
All you need are about 16 fairly intelligent people, some knives, and Microsoft Flight Simulator.
I cannot fathom why people think this required state support at all. The planning was somewhat intricate but the mechanics and level of knowledge and research needed were not particularly sophisticated.
Of course, people don't WANT to believe that small autonomous groups are capable of this much destruction but when you look at the items and training necessary, you'll see that, at root, this was a fairly simple operation.
I'm no engineer, but the source for the article is Gregory Fenves, a professor of Civil Engineering at the University of California at Berkeley.
The collapse mechanism you suggest does not account for the hour or so that passed between collision and collapse.
I am inclined to believe that they aimed the jet at a place where they thought it would do the most damage. Any passenger jet with fuel would do the job, I think, considering the mass times velocity. They wouldn't want to bounce off the top and it would be hard to get down low, I think.
A fireman talked about bombs planted in the building possibly or in the jet. One bystander said a bomb had gone off after the collision. I think they missed no opportunities to make this a major terrorist victory.
I have spent the better part of today listening to interviews of people who specialized in security, all of whom say the same thing. Unless you think there is a massive press conspiracy, what reason would they all have to lie?
People go back to live on earthquakes in California. My father in law worked on the 90+floor of the WTC 10 years ago. If you like living in New YOrk it has its attractions.
The WTC towers performed admirably today and they managed to stand even after the massive impacts that destroyed much of the integrity of the perimeter columns. I suspect that as the airliners passed through the buildings they also heavily damaged the interior core (and likely severed exist stairs to those trapped above the impact points).
The final reason the towers all fell today was fire. Fire is incredibly destructive, even to a hi-rise sturcture that seems to be fire proof. the reality is at high enough temperature, steel and concrete burns and vaporizes. It was only a matter of time before the nominal 2-3 hour of fireproofing protection applied to all structural members disintegrated under the intense heat of thousands of gallons of aviation kerosene burning unchecked.
This is what happened to the WTC towers 1, 2 and 3.
All buildings in the Unites States are subject to similar rigorous safety and fire codes but obviously none can save a building subject to intentional suicide bombings by large airliners. Unless you want to work in underground bunkers, NO BUILDINGS ARE 100% SAFE FROM TERRORIST ATTACKS!
I also watched from my roof as the WTC towers collapsed after I saw occupants jump 80 floors to their deaths.
I tend to agree somewhat. First attempt in '93 failed. Somebody went back and did their homework, and this time were successful.
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. Second plane appears to have gone in one side and sheared its way through to the point of almost (or perhaps succeeding in) coming out the other. Conflagration ensues, weakening the structure over time to the point of collapse of that floor. All floors above come down, floors below cannot accomodate this sudden weight crashing down from above, and they all pancake down to the ground.
One tower collapsing, perhaps luck plays a role in bringing the whole thing down. Two towers collapsing, damn good luck, or, as I am more inclined to believe, somebody had to have a darn good idea how to make it happen.
And when I refer to luck above, I am strictly referring to the luck running with the maniacal cowards, to accomplish their objective, not to be construed that I was hoping this would happen.
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