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.
it is neigh well impossible to "aim" a 767 within 50 ft of a spot on a building..........unless one has 4,000 hours or so of flight time. IMHO, the guys who running the show were seeking to simply hit the dang thang
I liked your analysis until you got to this point. It was Salon's expert who screwed up the analysis (in a way that made me wonder if he has any knowledge of physics or engineering.) You went after a bogus theory the result of which is that those who read your comment learned something. IMO thats one of the strengths os these forums. THANKS. YOU SAID IT BETTER THAN I WOULD HAVE.
MASSIVE amounts of fuel.
re the resources and expertise required to pull off today's attacks, it's plausible that it could've been done by less than 10 people, with less than $75,000, and no more flight experience than that offered by a couple of months drilling on microsoft flight simulator. all day long people are making the attackers out as possibly much more sophisticated and financed than perhaps they were; they were precise, dedicated, and fanatical, but not necessarily wealthy or well connected. if we don't reach the logical conclusions from that reality and act accordingly, we're going to have a long haul of being the world's new sitting ducks.
For example, it's actually MORE comforting believing a famous leader was assassinated by a massive government/international conspiracy than by a lone kook..strangely, the thought that a lone person or small group of fairly ordinary people can cause horrific death and destruction is worse than the idea that that massive governmental conspiracies could do that.
Also, people HATE randomness. If something bad happens, it's comforting that it was the result of a grand plan involving lots of people..makes it seem to have some sort of larger purpose, no matter how evil.
But the problem is it's quite possible for a few intelligent people to engage in massive destruction without the support of thousands in shadowy agencies or foreign governments.
Two, the towers technically did withstand the collision, the ensueing fire probably did a lot of damage, warping the i-beams and generally weakened the structure.
Three, the guy said "a". The first tower hit was the last to fall, it's entirely feasable without the second collision it wouldn't have fallen; more than likely the shockwave of the first collision rattled through the entire structure (remember all 7 "buildings" used the same basement complex, they were very much attached to each other), probably weakening the entire thing, the second plane looks to have come in a little lower, able to do more damage to an already weakened building. Again the shockwave ran through the entire complex, exaserbating the damage to the first tower. The 2nd tower, apparently haveing taken more damage, collapsed first, again another huge shockwave.
Of course during all of this you have fire and gravity weakening the structure, you also have literally thousands of feet running down the stairs, making more vibration. Every piece of masonry that fell loose, every degree of fire heat applied to the structure, every second gravity was pulling down on the buildings, weakened the structure. Eventually gravity wins, it always does.
Someone with a fairly sophisticated military. I DO NOT believe that Bin Laden could have pulled this off by himself.
As Post #20 by an engineer points out, the collapse of the building did not require great planning once you got an airliner into anywhere near the middle of the structure.
Reports from the passanger that managed to call on her cell phone reported that the highjaker's stabbed the stewardesses with knives and carpet cutting blades. These can be bought at any hardware store.
The planning consisted of finding four guys who could fly (not necessarily land) a plane once the pilots were stabbed, planning to board flights that took off at approximately the same time and smuggling carpet cutters past the X-Ray security agent.
I believe that this was the work of Osman bin Ladin but this was a pretty low-tech operation.
Such an attack can be prevented in the future with similarly low-tech solutions.
From now on, airline cockpit compartments must be armored, cockpit crews must be armed, the cockpits must locked before take-off and must not be opened under ANY circumstances even if every single passanger is threatened with death. In case of a bomb threat, the pilots must fly to the nearest body of water or unpopulated area and circle since, if you are going to die anyway, it is much nobler to die protecting others on the ground. As the Israelis do, plain-clothed, armed security must be aboard every flight to shoot it out with the bad guys in the passanger compartment.
And, as Politically Incorrect as it is (or was until this morning), there is a value in racial profiling. If you look Middle Eastern, you must expect that special attention will be given to you by security.
I saw a building that had an accidental rocket motor burn take place in it. The building bulged out almost in the shape of a foot ball from the expanding gas. The building did not collapse but had to be torn down because warpage in the long steel beams made it structurally unsound.
Same thing happenes in high rise buildings with a different twist (intended pun). The concrete and steel interface adhesion will be destroyed both by steel warping and concrete spalling. The heat can travel through the beams to parts untouched by the fire and experience failures there.
I sympathize with RKBA, but I draw the line on airplanes. Your average permit holder shouldn't be able to carry a gun onto a plane where he/she'd have a captive group of 50-400 people at the potential point of a gun, and the use of a massive, directable bomb at his/her disposal.
If your answer is that some *other* permit holder would draw to counter terrorism, I'd point out that an airplane is not the ideal place for a shootout.
What to do:
1- Keep all weapons out of the cabin, as far as possible
2- Have a trained air marshal service (don't hold your breath, 'cause you'll see one now).
but really, do we expect anything to survive a 150 ton missile full of explosive fuel??? "vulnerable point" my ass
Perhaps it could have been hit by a 707 and survive. But planes got much bigger since then
yes, that is the only sophistication and it is a fairly major one -- indicating some money and major friendlies.
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