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Why the towers collapsed: hit at vulnerable point
Salon ^ | 9/11/01 | Bill Wyman

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.
 


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To: Common Tator
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.

So the innocent among the Palestinians should be denied a state because of actions taken totally outside of their control?

What we really need to do is not to crack down on the terrorists responsible for this, but on ALL of them. We need to make the world a dangerous place for them. We need to FORCE all of the Islamic nations to hunt down and KILL every terrorist inside their borders. They know where the terrorists are.

Why "KILL" and not "imprison?" Because usually when the Muslims imprison terrorists, they let them out a few years later. We need to lodge death blows to terror. International terror is a crime against all of civilized society, we need to fight it ferociously. The harder we strike, the more on the defensive they'll be.

61 posted on 09/11/2001 5:37:25 PM PDT by xm177e2
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To: Looking for Diogenes
When the heat of jet fuel changes the crystalline structure of the steel, this is exactly what happens.
62 posted on 09/11/2001 5:38:07 PM PDT by Maelstrom
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To: katykelly
Insurance companies generally don't have to pay life insurance claims involving combatants, but I'm not sure how non-combatants would fit in. Maybe it's time to pull out the file and check my policy!
63 posted on 09/11/2001 5:39:29 PM PDT by Alberta's Child
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To: AntiTyrant
Well said.

This was not a huge mission logistically. The most important asset they used was prepared for them by the airleines. How much do plastic knives cost anyway? I was thinking maybe as few as eight people were involved, and thosey are already facing justice.
64 posted on 09/11/2001 5:40:35 PM PDT by UnChained
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To: Looking for Diogenes
Twin Towers' steel and concrete construction couldn't have  sustained the hit
By Sharon L. Crenson, Associated Press, 9/11/2001 19:52
NEW YORK (AP)

The image of the World Trade Center's 110-story twin towers crumbling seemed a scene of impossible destruction.

But the miraculous steel and concrete architecture that made them could not withstand the power of Tuesday's attack and ensuing fire. No building designed today could, said Masoud Sanayei, a
civil engineering professor at Tufts University.

Experts in skyscraper construction said video of the collapse led them to believe the towers were perhaps weakened by the initial impact of the airplanes that hit them Tuesday, but that heat from
the resulting fire was likely the most punishing blow.

Hyman Brown, a University of Colorado civil engineering professor and the Trade Center's construction manager, speculated that flames fueled by thousands of gallons of aviation fuel melted
steel supports.

''This building would have stood had a plane or a force caused by a plane smashed into it,'' he said. ''But steel melts, and 24,000 gallons of aviation fluid melted the steel. Nothing is designed or will be designed to withstand that fire.''

Sanayei said the heat may have disconnected one of the towers' concrete floors from the tubular steel columns that ringed the buildings. If one or two floors collapsed, it would have created a
pancake effect of one massive floor caving into the next.

''In my opinion, the fire weakened the connection between the floor system and the columns on the higher floors and caused a couple of the floors to collapse,'' Sanayei said. ''The floors are very heavy, made of reinforced concrete, so when one hits the next, they cause a domino effect ... and it can go all the way down to the first floor.''

Architect Minoru Yamasaki, who died in 1986, worked with engineers John Skilling and Leslie E. Robertson to design the fabled twin towers, once the world's tallest buildings.

In his 2000 book ''Building Big,'' architect David MaCaulay described the towers' engineering as ''a series of load bearing exterior columns spaced 3 feet apart and tied together at every floor by a deep horizontal beam, creating a strong lattice of square tubing around each tower.''

The core surrounding the elevators inside was much the same, with a giant lattice work of steel covered by poured concrete connecting the interior columns to the exterior ones. The design was free enough for each of the towers to hold 4 million square feet of space unencumbered by columns or load bearing walls.

Sections of exterior wall were wrapped around the outside in 24- and 36-foot high sections, creating a sort of patchwork so that not all the floor joints would meet walls at the same height, according
to MaCaulay.

Both Brown and Saw-teen See, a managing partner in Robertson's engineering firm, said the twin towers were originally designed to sustain a direct hit by a large jetliner, but that such construction couldn't make them fire- or bombproof.

Brown said it appeared the attack was meticulously planned.

''If they did it lower in the building the fire department could have gotten to it sooner. In its simplicity, it was brilliant.''

He said that the two towers have staircases in all four corners of the buildings and were designed to be evacuated in an hour, but it appeared that since the planes crashed into the corners, escape
was cut off for those on the floors above. ''I could never conceive of anybody being able to bring down
those two buildings,'' Brown added.

Minoru Yamasaki Associates issued a statement Tuesday saying the firm was in contact with authorities and had offered assistance.

''We believe that any speculation regarding the specifics of these tragic events would be irresponsible,'' the statement said. ''For obvious reasons, MYA has no further comment at this time.''
 

65 posted on 09/11/2001 5:45:40 PM PDT by Looking for Diogenes
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To: Looking for Diogenes
Which vulnerable point? You'll notice from the repeated clips that the collisions were at different points on each building. And Bldg 7 collapsed on its own.
66 posted on 09/11/2001 5:45:45 PM PDT by dr_who
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To: Edmund Burke
No insurance company that wants to stay in business in the U.S. will refuse to pay a claim like this. In an odd, perverted way, insurance companies are almost happy to deal with things like this every few decades because it PROVES just how financially stable they are and how much they care for their clients.

In the case of the business executives who were flying with Ron Brown when his plane crashed (or was shot down), the insurance companies were on solid ground to refuse the claims because the U.S. State Department had made an official declaration warning people about traveling in the Balkans. My understanding is that many large life insurance claims were NOT paid in that case.

67 posted on 09/11/2001 5:47:56 PM PDT by Alberta's Child
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To: PoisedWoman
Chinese... I don't count them out as tactical advisors... they were after all one of the staunch supporters of the terrorist regimes in the mideast... and we took out such an intel office by "accident" under clintong.

They have been supplying saddam's regime with fiber optic technology for their military... They are part of this picture. I feel it.

68 posted on 09/11/2001 5:49:42 PM PDT by Robert_Paulson2
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To: Looking for Diogenes
From the Albuquerque Journal.

September 11, 2001

Explosives Planted In Towers, N.M. Tech Expert Says
By Olivier Uyttebrouck
Journal Staff Writer

   Televised images of the attacks on the World Trade Center suggest that explosives devices caused the collapse of both towers, a New Mexico Tech explosion expert said Tuesday.    

The collapse of the buildings appears "too methodical" to be a chance result of airplanes colliding with the structures, said Van Romero, vice president for research at New Mexico Institute of Mining and Technology.    

"My opinion is, based on the videotapes, that after the airplanes hit the World Trade Center there were some explosive devices inside the buildings that caused the towers to collapse," Romero said.    

Romero is a former director of the Energetic Materials Research and Testing Center at Tech, which studies explosive materials and the effects of explosions on buildings, aircraft and other structures.    

Romero said he based his opinion on video aired on national television broadcasts.    Romero said the collapse of the structures resembled those of controlled implosions used to demolish old structures.    

"It would be difficult for something from the plane to trigger an event like that," Romero said in a phone interview from Washington, D.C.    

Romero said he and another Tech administrator were on a Washington-area subway when an airplane struck the Pentagon.    

He said he and Denny Peterson, vice president for administration and finance, were en route to an office building near the Pentagon to discuss defense-funded research programs at Tech.    

If explosions did cause the towers to collapse, the detonations could have been caused by a small amount of explosive, he said.    

"It could have been a relatively small amount of explosives placed in strategic points," Romero said. The explosives likely would have been put in more than two points in each of the towers, he said.    

The detonation of bombs within the towers is consistent with a common terrorist strategy, Romero said.    

"One of the things terrorist events are noted for is a diversionary attack and secondary device," Romero said.    

Attackers detonate an initial, diversionary explosion that attracts emergency personnel to the scene, then detonate a second explosion, he said.    

Romero said that if his scenario is correct, the diversionary attack would have been the collision of the planes into the towers.

Tech President Dan Lopez said Tuesday that Tech had not been asked to take part in the investigation into the attacks. Tech often assists in forensic investigations into terrorist attacks, often by setting off similar explosions and studying the effects.

69 posted on 09/11/2001 5:50:19 PM PDT by arcane
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To: UnChained
Keep in mind too that only the pilots had to know the final target.
The others could have thought it was a straight hijacking,ie;dangerous but they might survive.
70 posted on 09/11/2001 5:50:27 PM PDT by tet68
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To: tet68
Horrific.

I never want to hear a single Palistinian defender on this forum ever again. I never want to hear another Islamic defender on this forum again.

I just saw Osama Bin Ladin on television. An unusual form of murderous rage descended upon me. I want him, I want him very very much.

71 posted on 09/11/2001 5:53:34 PM PDT by Lazamataz
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To: Alberta's Child
No insurance company that wants to stay in business in the U.S. will refuse to pay a claim like this.

I'm not so sure about that. The total casualty claims could exceed the $20 Billion of hurricane Andrew, and that almost broke several large companies. These companies may have to refuse to pay in order to stay in business.

Both my home owners policy and life insurance policies state they do not pay for acts of terrorism or war. If the insurance companies don't pay, I'm sure Uncle Sam will just inflate the currency and pay all the bills.

72 posted on 09/11/2001 5:55:42 PM PDT by LJ
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To: DallasDeb
DallasDeb, you have a terminal case of the dumb ass. The planes hit at about the 70th floor. There is not a fire department in the world that has the equipment to put water 700 feet in the air. Go get a brain transplant...
73 posted on 09/11/2001 5:58:00 PM PDT by LaMudBug
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To: vooch
"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."

These planes can't be that hard to aim. Pilots manage to aim them successfully at narrow runways hundreds of times daily.

74 posted on 09/11/2001 5:59:30 PM PDT by Godebert
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To: cdwright
Exactly, what are the chances of a plane hitting huge building like the WTC unless it was with a purpose. Any who claims that the building would not have collapsed if the structural design was "stronger" are full of it and taking the typical liberal response of blaming anything. What next? Ambulance-chasers suing the structural engineers?
75 posted on 09/11/2001 6:02:23 PM PDT by TransOxus
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To: BushMeister
Back when passenger jets were being hijacked on a weekly basis in the early 1980s, a radio talk show host made a very reasonable recommendation: build these airplanes with a ventilation system that will allow the flight crew to seal itself in the cabin and flood the passenger compartment with a non-lethal gas.

Actually, this was his second suggestion. His first (idiotic) idea was to have a trap door mechanism in the aisle of every plane. If a plane is hijacked, a member of the crew could release a hatch while the hijackers are walking up and down the aisles and drop them out of the bottom of the plane at 32,000 feet.

76 posted on 09/11/2001 6:05:25 PM PDT by Alberta's Child
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To: Edmund Burke
You don't just waltz in an steal an aircraft. There is training, intelligence, surveillance, planning and more training. Then there is the support infrastructure: Safehouses, vehicles, cover stories, equipment, communications - A lot of logistics.

And all of this must be done clandestinely. This is not as easy as it sounds, even in a relatively open operating environment like the U.S. - This was not an easy operation to mount.

77 posted on 09/11/2001 6:06:50 PM PDT by LouD
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To: tet68
ABC news has some architectural experts who are in agreement that the fires in this building (1500 degrees F) caused the steel to weaken and it then became unable to support the weight once the tensile strength of the steel was depleted. So, the structure was sound enough to withstand the impact. It was just that the loadbearing steel was weakened by the fire. When the top floors fell, it was too much stress for the lower structure and the whole thing collapsed straight down without tipping. Straight down in a pile.

I think within three days, we're all going to be sick of structural analysis.
78 posted on 09/11/2001 6:06:55 PM PDT by George W. Bush
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To: dr_who
Building 7 sustaned damage from the collapse of one of the towers, there was a huge gash from top to bottom.
79 posted on 09/11/2001 6:07:01 PM PDT by aquawrench
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To: RedBloodedAmerican
"Heat from the jet fuel melted away the internal support, and the top caved in, and collapsed the structure."

Actually, I believe that what happened is called a "Cascade Failure." It's similar to that concrete walkway collapse that occurred in Kansas City about 10 years ago. Once the top floor collapsed onto the one below it, the weight just kept on gaining as it hit each subsequent floor, like dominoes falling over. The effect was the same you see when demolition contractors implode a building. They study the statics of the building to see which members are key and need to be taken out. I'm amazed that the building imploded, as opposed to falling over, which would have resulted in many more casualties.

What many people also don't understand is that steel structural members heat up much like your stove burners and the heat transfer which occurs is devastating. As each member heats up, it ignites flammables such as wood which are in proximity to it....

80 posted on 09/11/2001 6:07:29 PM PDT by yooper
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