911: THE TERRORISTS SUSPEND LAWS OF PHYSICS!!

DID THE BUILDINGS FALL...
OR WERE THEY PUSHED?

I TRIED TO BE PATRIOTIC

By J. McMichael

Carol A. Valentine, President Public Action, Inc.

Curator, Waco Holocaust Electronic Museum http://www.Public-Action.com Copyright, October, 2001 May be reproduced for non-commercial purposes

[The following was received in the form of an e-mail newsletter published by Carol Valentine]


The following was written by J. McMichael ( jmcmichael@care2.com ) and sent to me under the title "I Tried To Be Patriotic." I have taken the liberty of cleaning up some typos, and pass it on to you with permission.


I TRIED TO BE PATRIOTIC

By J. McMichael

I tried to believe. I watched those quarter mile high buildings fall through their jaw-dropping catastrophes over and over again. I listened to the announcer and the experts explain what had happened. And I worked at my pitiful lack of faith, pounding my skull with the remote control and staring on the flickering images on the TV screen.

But poor mental peasant that I am, I could not escape the teachings of my forefathers. I fear I am trapped in my time, walled off from further scientific understanding by my inability to abandon the Second Millennium mindset.

But enough of myself. Let us move on to the Science and Technology of the 21st Century. Those of you who cannot believe should learn the official truth by rote and perhaps you will be able to hide your ignorance.

Here are the bare bones of the WTC incident: North tower struck 8:45, collapsed 10:29; South tower struck 9:03, collapsed 9:50;

Time Line of Terror

8:45 a.m.

American Airlines Flight 11, Boston to Los Angeles with 92 people onboard, crashes into the north tower of the World Trade Center in New York City.

9:03 a.m.

United Airlines Flight 175, Boston to Los Angeles with 65 people onboard, flies into the south tower of the World Trade Center.

9:31 a.m.

Speaking from Florida, President George Bush pledges the United States will hunt down the guilty parties.

9:40 a.m.

American Flight 77, en route from Dulles Airport, Washington DC, to Los Angeles with 64 people onboard, crashes into the Pentagon.

9:48 a.m.

The U.S. Capitol and the West Wing of the White House are evacuated.

9:49 a.m.

The Federal Aviation Administration bans all aircraft takeoffs in the United States.

9:50 a.m.

South tower of the World Trade Center collapses.

9:58 a.m.

Emergency operator in Pennsylvania receives a call from a passenger on United Flight 93, Newark to San Francisco with 45 people onboard, stating the plane was being hijacked.

10:00 a.m.

United Flight 93 crashes about 80 miles southeast of Pittsburgh.

10:29 a.m.

North tower of the World Trade Center collapses.

11:00 a.m.

New York City Mayor Rudolph Giuliani orders lower Manhattan evacuated.

11:40 a.m.

With U.S. military on nuclear alert, Bush taken to Barksdale Air Force Base in Louisiana.

1:20 p.m.

Bush boards Air Force One for Offutt Air Force Base in Nebraska, headquarters of the U.S. Strategic Air Command.

2:51 p.m.

U.S. military deploys missile destroyers and other equipment in New York and Washington.

5:20 p.m.

Another World Trade Center building collapses.

7:00 p.m.

Bush arrives in Washington.

8:31 p.m.

Bush addresses the nation, vowing to punish "evil acts."

source
http://www.infoplease.com/spot/sept112001.html

Return

Using jet fuel to melt steel is an amazing discovery, really. It is also amazing that until now, no one had been able to get it to work, and that proves the terrorists were not stupid people. Ironworkers fool with acetylene torches, bottled oxygen, electric arcs from generators, electric furnaces, and other elaborate tricks, but what did these brilliant terrorists use? Jet fuel, costing maybe 80 cents a gallon on the open market.

Let us consider: One plane full of jet fuel hit the north tower at 8:45 AM, and the fuel fire burned for a while with bright flames and black smoke. We can see pictures of the smoke and flames shooting from the windows.

Then by 9:03 (which time was marked by the second plane's collision with the south tower), the flame was mostly gone and only black smoke continued to pour from the building. To my simple mind, that would indicate that the first fire had died down, but something was still burning inefficiently, leaving soot (carbon) in the smoke. A fire with sooty smoke is either low temperature or starved for oxygen -- or both.

But by 10:29 AM, the fire in north tower had accomplished the feat that I find so amazing: It melted the steel supports in the building, causing a chain reaction within the structure that brought the building to the ground.

And with less fuel to feed the fire, the south tower collapsed only 47 minutes after the plane collision, again with complete destruction. This is only half the time it took to destroy the north tower.

I try not to think about that. I try not to think about a petroleum fire burning for 104 minutes, just getting hotter and hotter until it reached 1538 degrees Celsius (2800 Fahrenheit) and melted the steel (steel is about 99% iron; for melting point of iron, see below

Iron 26 Fe 55.845(2)

Thermal Properties and temperatures

Melting point [/K]: 1811 [or 1538 °C (2800 °F)]
Boiling point  [/K]: 3134 [or 2861 °C (5182 °F)]
(liquid range: 1323 K)
source:
http://www.webelements.com/webelements/elements/text/Fe/heat.html

I try not to wonder how the fire reached temperatures that only bottled oxygen or forced air can produce.

And I try not to think about all the steel that was in that building -- 200,000 tons of it (see World Trade Center information for stats). .

I try to forget that heating steel is like pouring syrup onto a plate: you can't get it to stack up. The heat just flows out to the colder parts of the steel, cooling off the part you are trying to warm up. If you pour it on hard enough and fast enough, you can get the syrup to stack up a little bit. And with very high heat brought on very fast, you can heat up the one part of the object, but the heat will quickly spread out and the part will cool off the moment you stop.

When the heat source warms the last cold part of the object, the heat stops escaping and the point of attention can be warmed. If the north tower collapse was due to heated steel, why did it take 104 minutes to reach the critical temperature? (See Time Line of Terror).

Am I to believe that the fire burned all that time, getting constantly hotter until it reached melting temperature? Or did it burn hot and steady throughout until 200,000 tons of steel were heated molten - on one plane load of jet fuel? (Quantity of steel in WTC)

Thankfully, I found this note on the BBC web page

( How the World Trade Center fell ):

"Fire reaches 800 [degrees] C - hot enough to melt steel floor supports." That is one of the things I warned you about: In the 20th Century, steel melted at 1538 degrees Celsius (2800 F)

Basic Information

Name: Iron
Symbol: Fe
Atomic Number: 26
Atomic Mass: 55.845 amu
Melting Point: 1535.0 °C (1808.15 °K, 2795.0 °F)
Boiling Point: 2750.0 °C (3023.15 °K, 4982.0 °F)
Number of Protons/Electrons: 26
Number of Neutrons: 30
Classification: Transition Metal
Crystal Structure: Cubic
Density @ 293 K: 7.86 g/cm3
Color: Silvery

table source:
http://www.chemicalelements.com/elements/fe.html),


but in the 21st Century, it melts at 800 degrees C (1472 F).

This might be explained as a reporter's mistake -- 800 to 900 C is the temperature for forging wrought iron. As soft as wrought iron is, of course, it would never be used for structural steel in a landmark skyscraper. (Descriptions of cast iron, wrought iron, and steel and relevant temperatures discussed at Metrum.

But then lower down, the BBC page repeats the 800 C number in bold, and the article emphasizes that the information comes from Chris Wise, "Structural Engineer." Would this professional individual permit himself to be misquoted in a global publication?

I feel it coming on again -- that horrible cynicism that causes me to doubt the word of the major anchor-persons. Please just think of this essay as a plea for help, and do NOT let it interfere with your own righteous faith. The collapse of America's faith in its leaders must not become another casualty on America's skyline.

In my diseased mind, I think of the floors of each tower like a stack of LP (33 1/3 RPM) records, only they were square instead of circular. They were stacked around a central spindle that consisted of multiple steel columns stationed in a square around the 103 elevator shafts.(See Skyscraper Report and University of Sydney Report)

With this core bearing the weight of the building, the platters were tied together and stabilized by another set of steel columns at the outside rim, closely spaced and completely surrounding the structure. This resulting structure was so stable that the top of the towers swayed only three feet in a high wind. The architects called it a "tube-within-a-tube design."

The TV experts told us that the joints between the floors and central columns melted (or the floor trusses, or the central columns, or the exterior columns, depending on the expert) and this caused the floor to collapse and fall onto the one below. This overloaded the joints for the lower floor, and the two of them fell onto the floor below, and so on. Like dominos (see Washington University Professor Harmon).

Back in the early 1970s when the World Trade Towers were built, the WTC was the tallest building that had ever been built in the history of the world. If we consider the architectural engineers, suppliers, builders, and city inspectors in the job, we can imagine they would be very careful to over-build every aspect of the building. If one bolt was calculated to serve, you can bet that three or four were used. If there was any doubt about the quality of a girder or steel beam, you can be sure it was rejected. After all, any failures would attract the attention of half the civilized world, and no corporation wants a reputation for that kind of stupidity -- particularly if there are casualties.

I do not know the exact specifications for the WTC, but I know in many trades (and some I've worked), a structural member must be physically capable of three times the maximum load that will ever be required of it (BreakingStrength = 3 x WorkingStrength). Given that none of those floors was holding a grand piano sale or an elephant convention that day, it is unlikely that any of them were loaded to the maximum. Thus, any of the floors should have been capable of supporting more than its own weight plus the two floors above it. I suspect the WTC was engineered for safer margins than the average railroad bridge, and the actual load on each floor was less than 1/6 the BreakingStrength. The platters were constructed of webs of steel trusses. Radial trusses ran from the perimeter of the floor to the central columns, and concentric rings of trusses connected the radial trusses, forming a pattern like a spider web.

Where the radial trusses connected with the central columns, I imagine the joints looked like the big bolted flanges where girders meet on a bridge -- inches thick bolts tying the beams into the columns.

The experts tell us that the heat of the fire melted the steel, causing the joints to fail. In order to weaken those joints, a fire would have to heat the bolts or the flanges to the point where the bolts fell apart or tore through the steel. But here is another thing that gives me problems -- all the joints between the platter and the central columns would have to be heated at the same rate in order to collapse at the same time -- and at the same rate as the joints with the outer rim columns on all sides -- else one side of the platter would fall, damaging the floor below and making obvious distortions in the skin of the building, or throwing the top of tower off balance and to one side.

But there were no irregularities in the fall of the main structure of those buildings. They fell almost as perfectly as a deck of cards in the hands of a magician doing an aerial shuffle.

This is particularly worrisome since the first plane struck one side of the north tower, causing (you would think) a weakening on that side where the exterior columns were struck, and a more intense fire on that side than on the other side. And the second plane struck near the corner of the south tower at an angle that caused much of the fuel to spew out the windows on the adjacent side.

Yet the south tower also collapsed in perfect symmetry, spewing dust in all directions like a Fourth of July sparkler burning to the ground. Oh, wait. Here is a picture showing the top 25 floors of one tower (probably south) toppling over sideways.

Why are there no reports of this cube of concrete and steel (measuring 200 ft. wide, 200 ft. deep, and 200 ft high), falling from a 1000 feet into the street below?

But implosion expert Mark Loizeaux, president of Controlled Demolition Inc. in Phoenix, MD is of the opinion that it happened:

Observing the collapses on television news, Loizeaux says the 1,362-ft-tall south tower, which was hit at about the 60th floor, failed much as one would like (sic) fell a tree. (University of Sydney Report 2

I have seen a videotaped rerun of the south tower falling. In that take, the upper floors descend as a complete unit. All the way, the upper-floor unit was canted over as shown on the BBC page, sliding down behind the intervening buildings like a piece of stage scenery.

That scene is the most puzzling of all. Since the upper floors were not collapsed (the connection between the center columns and the platters were intact), this assembly would present itself to the lower floors as a platter WITHOUT a central hole. How then would a platter without a hole slide down the spindle with the other platters? Where would the central columns go if they could not penetrate the upper floors as they fell?

The only model I can find for the situation would be this: If the fire melted the floor joints so that the collapse began from the 60th floor downward, the upper floors would be left hanging in the air, supported only by the central columns. This situation would soon become unstable and the top 40 floors would topple over (to use Loizeaux's image) much like felling the top 600 ft. from a 1300 ft. tree.

This model would also hold for the north tower. According to Chris Wise's "domino" doctrine, the collapse began only at the floor with the fire, not at the penthouse. How was it that the upper floor simply disappeared instead of crashing to the earth as a block of thousands of tons of concrete and steel?

The amazing thing is that no one (but Loizeaux) even mentions this phenomenon, much less describing the seismic event it must have caused.

Where is the ruin where the 200ft x 200ft x 50 story- object struck? Forty floors should have caused a ray of devastation 500 ft. into the surrounding cityscape.

In trying to reconstruct and understand this event, we have to know whether the scenes we are watching are edited or simply shown raw as they were recorded.

But let us return to the fire. Liquid fuel does not burn hot for long. Liquid fuel evaporates (or boils) as it burns, and the vapor burns as it boils off. If the ambient temperature passes the flash point of the fuel and oxygen is plentiful, the process builds to an explosion that consumes the fuel.

Jet fuel boils at temperatures above 176 degrees Celsius (350 F) and the vapor flashes into flame at 250 degrees Celsius (482 F). In an environment of 1500 degrees, jet fuel spread thinly on walls, floor, and ceiling would boil off very quickly. And then it would either burn, or run out of oxygen and smother itself. Or it would simply disperse out the open windows (some New Yorkers claimed they could smelled the spilled fuel).

In no case would an office building full of spilled jet fuel sustain a fire at 815 degrees C (1500 F) for 104 minutes -- unless it was fed bottled oxygen, forced air, or something else atypical of a fire in a high-rise office building. Certainly, the carpets, wallpaper, occasional desks -- nothing else in that office would produce that temperature. What was burning?

OK, since it was mentioned, I am also upset with the quantity of concrete dust (see University of Sydney Report 1).

No concrete that I have ever known pulverizes like that. It is unnerving. My experience with concrete has shown that it will crumble under stress, but rarely does it just give up the ghost and turn to powder. But look at the pictures -- it is truly a fine dust in great billowing clouds spewing a hundred feet from the collapsing tower. And the people on the ground see little more than an opaque wall of dust -- with inches of dust filling the streets and the lungs afterward.

What has happened here?

I need a faith booster shot here. I would like to find a pictures of all those platters piled up on each other on the ground, just as they fell -- has anyone seen a picture like that? I am told it was cumulative weight of those platters falling on each other that caused the collapse, but I don't see the platters pilled up liked flapjacks on the ground floor.

Instead, the satellite pictures show the WTC ruins like an ash pit:



I am told by a friend that a Dr. Robert Schuller was on television telling about his trip to the ruins. He announced in the interview that there was not a single block of concrete in that rubble. From the original 425,000 cubic yards of concrete that went into the building, all was dust. How did that happen?

I have just one other point I need help with -- the steel columns in the center. When the platters fell, those quarter-mile high central steel columns (at least from the ground to the fire) should have been left standing naked and unsupported in the air, and then they should have fallen intact or in sections to the ground below, clobbering buildings hundreds of feet from the WTC site like giant trees falling in the forest. But I haven't seen any pictures showing those columns standing, falling, or lying on the ground. Nor have I heard of damage caused by them.

Now I know those terrorist must have been much better at these things than I am. I would take one look at their kamikaze plans with commercial jets and I would reject it as -- spectacular maybe, but not significantly damaging. The WTC was not even a strategic military target.

But if I were a kamikaze terrorist, I would try to hit the towers low in the supports to knock the towers down, maybe trapping the workers with the fire and burning the towers from the ground up, just as the people in last 20 stories were trapped. Even the Japanese kamikaze pilots aimed for the water line.

But you see, those terrorists were so sure the building would magically collapse that way, the pilot who hit the north tower chose a spot just 20 floors from the top.

(ABC News Report)

And the kamikaze for south tower was only slightly lower -- despite a relatively open skyline down to 25 or 30 stories.

The terrorists apparently predicted the whole scenario -- the fuel fire, the slow weakening of the structure, and the horrific collapse of the building - phenomena that the architects and the NY civil engineering approval committees never dreamed of.

Even as you righteously hate those men, you have to admire them for their genius.

Few officials or engineers have been surprised by this turn of events -- apparently everyone certified it for airplane collisions, but almost no one was surprised when both collisions caused utter catastrophes in both towers. In fact, their stutters and mumbles and circumlocutions would make a politician blush:

"Eventually, the loss of strength and stiffness of the materials resulting from the fire, combined with the initial impact damage, would have caused a failure of the truss system supporting a floor, or the remaining perimeter columns, or even the internal core, or some combination."

( University of Sydney Report 1)

In a hundred years of tall city buildings, this kind of collapse has never happened before. Never. It was not predicted by any of the experts involved when the WTC towers were built. But now that it has happened, everybody understands it perfectly and nobody is surprised.

Is this civil engineering in the Third Millennium -- a galloping case of perfect hindsight?

Only one I have found candidly admitted his surprise:

Observing the collapses on television news, Loizeaux says the 1,362-ft-tall south tower, which was hit at about the 60th floor, failed much as one would like (sic) fell a tree. That is what was expected, says Loizeaux. But the 1,368-ft-tall north tower, similarly hit but at about the 90th floor, "telescoped," says Loizeaux. It failed vertically, he adds, rather than falling over. "I don't have a clue," says Loizeaux, regarding the cause of the telescoping.

(University of Sydney Report 2)

There was one highly qualified engineer in New Mexico who thought the collapse could only happen with the help of demolition explosives, and he was foolish enough to make the statement publicly. But then he recanted ten days later and admitted the whole thing was perfectly natural and unsurprising. I wonder what happened in those ten days to make him so smart on the subject so quickly.

From the Albuquerque Journal:

Van Romero, vice president for research at New Mexico Institute of Mining and Technology says the collapse of the twin towers resembled those of controlled implosions used in planned demolition.

"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.

A demolition expert, 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.

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. Romero told the Albequerque Journal that he based his opinion on video aired on national television broadcasts.

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

And then, as though demonstrating how normal this "building collapsing" phenomenon is, WTC buildings Six and Seven "collapsed," too:

"Other buildings - including the 47-story Salomon Brothers building [WTC 7] - caved in later, weakened by the earlier collapses, and more nearby buildings may still fall, say engineers."

( BBC Report )

and

It seems no building in the area, regardless of design, is immune to galloping WTC collapse-itis. It never happened in the 20th Century, but welcome to the physical universe laws of the Third Millennium.

Pardon me, but this recitation has not given me the relief I hoped for. I must get back to work.

I believe in the president, the flag, and the Statue of Liberty. I believe in the honesty of the FBI and the humility of military men. I believe in the network news anchor-persons, who strive to learn the truth, to know the truth, and to tell the truth to the audience.

And I believe all of America is so well educated in the basic physics discussed above, they would rise up in fury if anyone tried to pull a cheap Hollywood trick on them.

Hand me that remote, will you? I believe [clonk]. I believe [clonk]. I believe ...

J. McMichael




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World Trade Center History
Magnificent buildings graced skyline
by David Johnson

The twin towers of the World Trade Center were more than just buildings. They were proof of New York's belief in itself. Built at a time when New York's future was cloudy, the towers restored confidence and stopped the decline of lower Manhattan. Brash, glitzy, and grand, they quickly became symbols of New York.

Controversial Beginnings

The towers were not always popular. A world trade center was first proposed in 1960 by the Downtown-Lower Manhattan Development Association to revitalize seedy "radio row," dominated by electronic stores. Chase Manhattan Bank Chairman David Rockefeller, founder of the development association, and his brother, Nelson, New York governor, pushed hard for the project, insisting it would benefit the entire city.

In 1962, the Port Authority of New York and New Jersey began plans to build the center. Minoru Yamasaki and Associates of Michigan, and Emery Roth & Sons, P.C., were hired as architects. Eventually, Yamasaki decided on two huge towers. Critics charged that a modern monolith would rob New York of character, ruin the skyline, disrupt television reception, and strain city services.

Massive Buildings

However, the project was approved and construction began in 1965. Five streets were closed off and 164 buildings demolished to create the 16-acre site. Construction required the excavation of more than 1.2 million cubic yards of earth which created 23.5 acres of land along the Hudson River, now Battery City Park, a complex of four 60-story skyscrapers and four apartment buildings.

Building the World Trade Center took 200,000 tons of steel, 425,000 cubic yards of concrete, 600,000 square feet of glass, and 12,000 miles of electric cables.

During peak construction periods, 3,500 people worked at the site. A total of 10,000 people worked on the towers; 60 died during its construction.

WTC was made up of:
    –200,000 tons of steel
    –425,000 cubic yards of concrete
    –600,000 square feet of glass
    –12,000 miles of electric cables
More WTC stats
    –Had 110 floors
    –Had its own zip code, 10048
    –Weighed 1.5 million tons
    –Contained 198 miles of heating ducts
    –Used 23,000 fluorescent light bulbs
    –Was visible from 20 miles away


Instant Landmarks

The towers were dedicated in 1973. They were the world's tallest buildings for only a short time, since the Sears Tower in Chicago was dedicated a month later. However, the north tower sported a 360-foot television mast that allowed it to technically remain the world's tallest building. A hotel, a shopping plaza, and three smaller buildings nearby completed the complex.

The twin towers became the most popular postcard image in the world. Some three dozen movies were made at the towers, including the 1976 remake of King Kong.

Thousands of Visitors

The buildings weighed more than 1.5 million tons and contained 198 miles of heating ducts and 23,000 fluorescent light bulbs. Each of the towers had 110 floors, and each floor was roughly 50,000 square feet large. Shopping malls with restaurants, stores, and barbershops dotted the concourses. The mall underneath the towers contained another 75 stores. The six basements also included two New York subway stations and the PATH trains to New Jersey used by 150,000 people daily.



Some 50,000 people worked in the buildings, while another 200,000 visited or passed through each day. The top floor observation deck had 26,000 visitors daily, who could see for 45 miles on a clear day. From the ground, the towers were visible for at least 20 miles. The 43,600 windows were washed automatically, while the air conditioning system was the world's largest, with 60,000 tons of cooling capacity. It took 250,000 cans of paint each year to spruce up the towers.

Each tower had 97 elevators for passengers and six for freight. Express elevators zoomed skyward at 27 feet per second, reaching the top in 4.8 minutes. More than 300 computer main frames in the towers served the towers' occupants.

International Glamour

Most of the nearly 300 tenants were blue-chip firms enjoying the prestige of one of the world's most glamorous business addresses. Eight law firms, six banks, five stock brokerage houses, and three insurance companies had their headquarters in the twin towers. A number of foreign firms, such as the Bank of Yokohama, also had offices there. The complex had its own zip code, 10048.

In 1976, the elegant Windows on the World restaurant opened at the top of the north tower, followed by Cellar in the Sky. The top floor restaurants attracted such performers as Frank Sinatra, John Lennon, Liza Minnelli, and Mick Jagger. Far below, restaurants in the basement concourse served 30,000 cups of coffee each day, while 87 tons of food was delivered to the towers daily.

Publicity Seekers Attracted

Before their collapse, 19 murders were committed and 17 babies born in the towers. They also contained nine chapels representing six different faiths.

As the towers became more famous, they attracted daredevils. Three men parachuted from the top, while one dozen mountain climbers scaled the outside. In 1974 a Frenchman walked a tightrope between the towers.

Previous Bombing

In 1993, terrorists drove a truck packed with 1,100 pounds of explosives into the basement parking garage at the World Trade Center. Despite the size of the blast, only six people were killed and 1,000 injured. After that bombing, the number of parking spaces in the basement garage was reduced from 1,000 to 600.

Security in the buildings was considerable. The lobby in each building had 12 X-ray machines and 16 concierge desks. The towers employed over 300 security personnel, used 300 security cameras, and featured 828 emergency doors.

Buried Treasure

The basements of the World Trade Center also contained vast vaults used by the COMEX metals trading division of the New York Mercantile Exchange. Some 3,800 gold bars, weighing 12 tons and worth more than $100 million, lie buried under the mountains of rubble left after the attack. Authorities say the gold has never been safer.

Rebuilding Plans

In 1999, New York businessman Larry Silverstein purchased the World Trade Center's 99-year lease on the twin towers for $3.2 billion from the Port Authority of New York and New Jersey. Since the attack, Silverstein has vowed to rebuild, suggesting that four smaller towers is a possibility.

source:
http://www.infoplease.com/spot/wtc1.html

Return to Article


How the World Trade Center fell
By BBC News Online's Sheila Barter

The design of the World Trade Center saved thousands of lives by standing for well over an hour after the planes crashed into its twin towers, say structural engineers.

It was the fire that killed the buildings -
nothing on Earth could survive those temperatures
with that amount of fuel burning
Structural engineer Chris Wise

But the towers' ultimate collapse was inevitable, as the steel cores inside them reached temperatures of 800C - raising questions as to why hundreds of rescue workers were sent into the doomed buildings to their deaths.

The steel and concrete structures performed amazingly well, said John Knapton, professor in structural engineering at Newcastle University, UK.

"I believe tens of thousands of lives have been saved by the structural integrity of the buildings," he told BBC News Online.

"They had a lot of their structure taken out, yet they remained intact for more than an hour, allowing thousands to escape."

Temperatures at 800C

But as fires raged in the towers, driven by aviation fuel, the steel cores in each building would have eventually reached 800C - hot enough to start buckling and collapsing.

The protective concrete cladding on the cores would have been no permanent defence in these extraordinary circumstances - keeping the intense heat at bay for only a limited timespan.

Nothing is designed or will be
designed to withstand that fire
World Trade Center construction manager

"It was the fire that killed the buildings. There's nothing on earth that could survive those temperatures with that amount of fuel burning," said structural engineer Chris Wise.

"The columns would have melted, the floors would have melted and eventually they would have collapsed one on top of each other."

The buildings' construction manager, Hyman Brown, agreed that nothing could have saved them from the inferno.

"The buildings would have stood had a plane or a force caused by a plane smashed into it," he said.

I would have given the order to get out -
you would have thought someone with
technical expertise would have been advising them
Professor John Knapton, Newcastle University

"But steel melts, and 24,000 gallons (91,000 litres) of aviation fluid melted the steel. Nothing is designed or will be designed to withstand that fire."

Once the steel frame on one floor had melted, it collapsed downwards, inflicting massive forces on the already-weakened floor below.

Science of collapse

From then on, the collapse became inevitable, as each new falling floor added to the downward forces.

Further down the building, even steel at normal temperatures gave way under the enormous weight - an estimated 100,000 tonnes from the upper floors alone.

"It was as if the top of the building was acting like a huge pile-driver, crashing down on to the floors underneath," said Chris Wise.

Early in the unfolding horror, some office workers were told to stay where they were - dreadful advice, said Professor Knapton.

The towers withstood impact but not inferno

People's only hope was to run and keep running - reaching open ground. The building could have fallen over sideways, he points out, potentially bringing even greater devastation.

Other buildings - including the 47-storey Salomon Brothers building - caved in later, weakened by the earlier collapses, and more nearby buildings may still fall, say engineers.

But the eventual collapse of the twin towers was so predictable that the order should have been given to withdraw emergency services within an hour, said Professor Knapton. He watched in horror, knowing the building would fall within two hours.

The hundreds of dead firemen and police officers should simply not have been there, he said.

"I think they should not have gone in at all," he said. "If they did decide to take the risk, they should have been pulled out after an hour."

But in the panic and horror, the order was never given for rescue workers to abandon the building. "Mistakes were made," said Professor Knapton.

"But I would have given the order to get out. You would have thought someone with technical expertise would have been advising them."

But he acknowledged that the sheer scale of the tragedy probably overwhelmed the operation commanders.

"I think everyone was not thinking. It was like a horror film and I think people's rationale had gone," he said.

Steel-core design

The building's design was standard in the 1960s, when construction began on what was then the world's tallest building. At the heart of the structure was a vertical steel and concrete core, housing lift shafts and stairwells.

Steel beams radiate outwards and connect with steel uprights, forming the building's outer wall.

All the steel was covered in concrete to guarantee firefighters a minimum period of one or two hours in which they could operate - although aviation fuel would have driven the fire to higher-than-normal temperatures. The floors were also concrete.

The building had to be tough enough to withstand not just the impact of a plane - and the previous bomb attack in 1993 - but also of the enormous structural pressures created by strong winds.

Newer skyscrapers are constructed using cheaper methods. But this building was magnificent, say experts, in the face of utterly unpredictable disaster.

source:
http://news.bbc.co.uk/hi/english/world/americas/newsid_1540000/1540044.stm

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Structural engineer can discuss vulnerability of World Trade Center, similar buildings, to terrorist attack

Thomas Harmon, Ph.D.

Clifford W. Murphy Professor of Civil Engineering;

Director of the Construction Materials and Management Center

Harmon, a structural engineer, has been involved with the design of buildings similar to the World Trade Center. He is available to discuss design and engineering issues that may have contributed to the building's collapse. Harmon says that the World Trade Center building design is known as a tube structure. It consists of lots of small, closely spaced columns that resist two sets of loads, vertical and lateral. Harmon worked on the analysis of the Standard Oil Building in the early 1970s, an 87-story structure that is in some ways similar to the World Trade Center. The Sears Tower in Chicago also is similar in design and was built in the same era. All three buildings are designed as structural tubes.

"The idea behind the World Trade Center design is to make the exterior wall as efficient as possible," Harmon says. "One way to do that is to make the space between the columns on the perimeter wall as short as possible so that the horizontal members, the beams, are very stiff to resist the lateral load."

Harmon speculates that the short distance between exterior columns in the World Trade Center buildings — about four to five feet apart, compared with 15 feet apart in the Sears Tower — might have made the buildings more vulnerable to the impact of the planes and less resistant to fire. The columns of the world trade towers are smaller because they are closer together.

"As the fire went up and destroyed the upper floors, the trusses probably collapsed under their own dead weight because the steel was heated and maybe the fire proofing was removed by the impact," he says. "What then probably happened was the floors collapsed on top of each other and you got a domino effect. All these floors holding the walls up, and they all just cave in."

He said that he believed the structure of the World Trade Center buildings is an interior core with long trusses going from that core to the perimeter walls.

"As the upper building collapses and hits those floors, they collapsed," he said. "When there's nothing to support the exterior walls, the walls probably just crumpled in on the building."

Harmon expressed incredulity that the buildings collapsed, speculating that it was due to the melting of the fire.

"I was utterly shocked that the buildings actually collapsed," he says. "I can't imagine that whoever did this thought the buildings were going to totally collapse."

source:
http://news-info.wustl.edu/News/nrindex00/harmon.html

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The University of Sydney - Department of Civil Engineering
World Trade Centre - New York - Some Engineering Aspects
General | Structural System | Why Did It Collapse | Other Links


General Information:

Height: 1,368 and 1,362 feet (417 and 415 meters)
Owners: Port Authority of New York and New Jersey.
(99 year leased signed in April 2001 to groups including Westfield America and Silverstein Properties)
Architect: Minoru Yamasaki, Emery Roth and Sons consulting
Engineer: John Skilling and Leslie Robertson of Worthington, Skilling, Helle and Jackson
Ground Breaking: August 5, 1966
Opened: 1970-73; April 4, 1973 ribbon cutting
Destroyed:  Terrorist attack, September 11, 2001

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The Structural System:

Yamasaki and engineers John Skilling and Les Robertson worked closely, and the relationship between the towers’ design and structure is clear. Faced with the difficulties of building to unprecedented heights, the engineers employed an innovative structural model: a rigid "hollow tube" of closely spaced steel columns with floor trusses extending across to a central core. The columns, finished with a silver-colored aluminum alloy, were 18 3/4" wide and set only 22" apart, making the towers appear from afar to have no windows at all. 

Also unique to the engineering design were its core and elevator system. The twin towers were the first supertall buildings designed without any masonry. Worried that the intense air pressure created by the buildings’ high speed elevators might buckle conventional shafts, engineers designed a solution using a drywall system fixed to the reinforced steel core. For the elevators, to serve 110 stories with a traditional configuration would have required half the area of the lower stories be used for shaftways. Otis Elevators developed an express and local system, whereby passengers would change at "sky lobbies" on the 44th and 78th floors, halving the number of shaftways.

(skyscraper.org)

The structural system, deriving from the I.B.M. Building in Seattle, is impressively simple. The 208-foot wide facade is, in effect, a prefabricated steel lattice, with columns on 39-inch centers acting as wind bracing to resist all overturning forces; the central core takes only the gravity loads of the building. A very light, economical structure results by keeping the wind bracing in the most efficient place, the outside surface of the building, thus not transferring the forces through the floor membrane to the core, as in most curtain-wall structures. Office spaces will have no interior columns. In the upper floors there is as much as 40,000 square feet of office space per floor. The floor construction is of prefabricated trussed steel, only 33 inches in depth, that spans the full 60 feet to the core, and also acts as a diaphragm to stiffen the outside wall against lateral buckling forces from wind-load pressures."

www.greatbuildings.com

Typical Floor Plan of the World Trade Center:

A perimeter of closely spaced columns, with an internal lift core.  The floors were supported by a series of light trusses on rubber pads, which spanned between the outer columns and the lift core.

 

 

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Why Did It Collapse?

Tim Wilkinson, Lecturer in Civil Engineering

(This is an initial suggestion on one possible reason for failure, and should not be regarded as official advice)

The structural integrity of the World Trade Center depends on the closely spaced columns around the perimeter.  Lightweight steel trusses span between the central elevator core and the perimeter columns on each floor.  These trusses support the concrete slab of each floor and tie the perimeter columns to the core, preventing the columns from buckling outwards.

After the initial plane impacts, it appeared to most observers that the structure had been severely damaged, but not necessarily fatally.

It appears likely that the impact of the plane crash destroyed a significant number of perimeter columns on several floors of the building, severely weakening the entire system.  Initially this was not enough to cause collapse.

  

However, as fire raged in the upper floors, the heat would have been gradually affecting the behaviour of the remaining material.  As the planes had only recently taken off, the fire would have been initially fuelled by large volumes of jet fuel, creating potentially enormously high temperatures. The strength of the steel drops markedly with prolonged exposure to fire, while the elastic modulus of the steel reduces (stiffness drops), increasing deflections.

 

Modern structures are designed to resist fire for a specific length of time.  Safety features such as fire retarding materials and sprinkler systems help to contain fires, help extinguish flames, or prevent steel from being exposed to excessively high temperatures.  This gives occupants time to escape and allow fire fighters to extinguish blazes, before the building is catastrophically damaged.

It is possible that the blaze, started by jet fuel and then engulfing the contents of the offices, in a highly confined area, generated fire conditions significantly more severe than those anticipated in a typical office fire.  These conditions may have overcome the building's fire defences considerably faster than expected.

Eventually, the loss of strength and stiffness of the materials resulting from the fire, combined with the initial impact damage, would have caused a  failure of the truss system supporting a floor, or the remaining perimeter columns, or even the internal core, or some combination.  Failure of the flooring system would have subsequently allowed the perimeter columns to buckle outwards.  Regardless of which of these possibilities actually occurred, it would have resulted in the complete collapse of at least one complete storey at the level of impact.

Once one storey collapsed all floors above would have begun to fall.  The huge mass of falling structure would gain momentum, crushing the structurally intact floors below, resulting in catastrophic failure of the entire structure.

(US readers note:  storey is the Australian/English spelling of story)

Sydney Morning Herald graphic

The only evidence so far are photographs and television footage.  Whether failure was initiated at the perimeter columns or the core is unknown.  The extent to which the internal parts were damaged during the collision may be evident in the rubble if any forensic investigation  is conducted.  Since the mass of the combined towers is close to 1000000 tons, finding evidence will be an enormous task. 

>

Perimeter columns, several storeys high, and still linked together, lie amongst all the debris on the ground.

This photograph shows the south tower just as it is collapsing.  It is evident that the building is falling over to the left.  The North Tower collapsed directly downwards, on top of itself.  The same mechanism of failure, the combination of impact and subsequent fire damage, is the likely cause of failure of both towers.  However, it is possible that a storey on only one side of the South Tower initially collapsed, resulting in the "skewed" failure of the entire tower.

The gigantic impact forces caused by the huge mass of the falling structure landing on the floors below travelled down the columns like a shockwave faster than the entire structure fell.  The clouds of debris coming from the tower, several storeys below the huge falling mass, probably result from the sudden and almost explosive failure of each floor, caused by the "shockwave".

(Pictures taken from various news sources on the Internet)

 

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source:
http://www.civil.usyd.edu.au/wtc.htm

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Cast Iron



. . . growth of human greed. But leaving out of consideration the references to moral explanations that result from the tendency of some Greek philosophers to ascribe profound ethical value to Spartans institutions, ancient sources are correct when they connect the use of iron money with the isolation of Sparta from the general stream of Greek economy. The archeological data suggest that the Spartan economic decline began around 600 B.C. But the problem is that of deciding whether the use of iron money is the cause or the effect of the economic isolation of Sparta.

In my study of Greek chronology I shall show that historians used the date of the imaginary Pheidon of Argos to establish that of Lykourgos: they made Lykourgos, who would have made compulsory the use of a currency of iron oboloi in Sparta, a contemporary of Pheidon, who would have abolished this currency in the rest of the Peloponnese. The date of Lykourgos and of the Spartan constitution was moved from one century to another according to the shifts in the position of Pheidon in the several chronological schemes. This link indicates that the peculiar economic position of Sparta is related to the setting up at the Heraion of standards that were later associated with the name of Pheidon.

I would suggest the following explanation of the events. Up to the time the standards were set up at the Heraion (roughly about 670 BC), the currency of the Peloponnese was utensil-money consisting of oboloi. The objects of the Heraion introduced a new concept of currency, metals measured by weight, whether they be iron or silver, and established a relation of value between the utensil-money of oboloi and the new currency. When an equivalence of value is established between two currencies, Gresham’s law becomes operative; hence, I would suspect that there was some factor by which the iron currency turned out to be the “bad money” in Sparta, so that silver money was driven out. This may have caused, or contributed to, the economic isolation of Sparta.

6. In my opinion the history of the Peloponnese, and of Mykenai and Sparta in particular, cannot be properly reconstructed without collecting all possible data about mining and metallurgy in the area. After submitting my doctoral dissertation I tried to obtain institutional support for a metallurgic testing of the iron found at the Heraion and at Sparta. The basis of my request was a statement of Ploutarchos (Lysandros, XVII), drawn from older sources, that the Spartan iron money as it was drawn out of the fire was dipped in vinegar, so that it would become unfit for forging, brittle and incapable of taking good edge.

A metal which is quenched by dipping into vinegar certainly is not wrought iron; it must be cast iron or steel. The quenching in vinegar, instead of water, is mentioned in the Pirotechnia of Vannoccio Biringucci (1480-1539 A.D.); ancient metallurgists ascribed great importance to the nature of the quenching medium, and many of their notions, such as the preference for the water of particular streams, may have been superstitions, but vinegar may actually be a better wetting agent than water, as would be a saline solution. I concluded that the metal described by Ploutarchos was cast iron. A number of ancient sources mention the preservation of cast iron in temples as particularly valuable or marvelous. According to Pausanias (III, 12, 10) the edifice called Skias in Sparta was built by Theodoros of Samos (a sort of Leonardo da Vinci of the Greeks—architect, sculptor, inventor), “who first found the way to pour iron and to mold statues with it.”

In spite of such clear statements of ancient authors, the occurrence of cast iron in antiquity has been denied a priori with the argument that ancients could not obtain the temperature of about 1500° Celsius necessary for liquefying iron. For the smelting of the ore a temperature of 500° may be sufficient; at a temperature between 800° and 900° wrought iron becomes sufficiently soft to be worked with the hammer. I may quote as typical the opinion of the specialist of ancient Egyptian technology, Lucas, to the effect that only in the fourteenth century of our era the construction of furnaces become advanced enough to obtain the temperature necessary for the melting of iron. It is true that the furnaces used in Europe up to this time and those currently used in classical antiquity were not intended to generate a high temperature; but from the metallurgic treatises of Renaissance it can be gathered that metallurgists were on the alert against letting the temperature of a furnace rise too high lest cast iron be produced. Until steel began to be produced by reducing the carbon content of cast iron, was considered a useless from of iron, “sick iron” in English terminology.

Even when iron is smelted in furnaces of low temperature that are intended for the production of wrought iron, parts of the bloom that forms in these furnaces is composed of cast iron and even of steel. Metallurgists used to break up the bloom and separate the pieces that are wrought iron; the pieces of cast iron were considered rejects. It is for this reason that around 1500 AD there was introduced in Europe a method for utilizing more fully the products of the furnace; the pieces of cast iron were melted forming what Biringucci calls latte di ferro, “milk of iron” and into this there were dropped pieces of wrought iron. Since cast iron has a high content of carbon, whereas wrought iron contains less than 0.2 per cent of carbon, by making an average there was obtained steel. Low-carbon steel has a carbon content between 0.2 and 0.8; high-carbon steel with a content between 0.8 and 2.0 is much harder, but it must be cast into forms and cannot be easily welded. The reason for the spread of the use of steel in modern Europe was in part that of utilizing what were originally the wasted parts of the bloom.

A fundamental contribution to the solution of the problem of Spartan metallurgy was made when Lyle B. Borst, Chairman of the Department of Physics at New York University College announced (The New York Times, January 31, 1961) that he had taken some samples from specimens of Spartan iron money and found then to be made of low-carbon steel, with a carbon content of between 0.2 and 0.8 percent. A few days later, in answer to a letter of mine, he kindly informed me that he had not had an opportunity of obtaining a sample of the oboloi of the Heraion.

It could be said that the finding of Borst is not as sensational as the press report made it to be, since the existence of Spartan steel is mentioned in specialized literature. But, for the first time, scholars are provided with a solid objective datum in a field where there is good deal of confused thinking and there are too many unjustified assumptions.

In order to obtain a precise bearing I may quote the opinion expressed in 1956 at the Colloque International: Le Fer à travers les ages a specialist of Celtic metallurgy, Albert France-Lanoud:

It seems that steel become known in Greece at an extremely early date, but this not established as certain. But it is a fact that the Celts of the Noricum around 500 BC discovered the method to avoid a complete decarburization of the bloom and to produce an excellent malleable steel. It should be called natural steel. It is this discovery that gave a reputation to the iron works of Noricum; it must have been the secret of several groups of ancient ironsmiths. But in Gaul steel appears later, in the second century BC Noricum roughly corresponded to the western part of contemporary Austria and the neighboring part of Bavaria.

The objective fact ascertained by Borst acquires transcendental significance for the study of Greek history, because he has brilliantly liked it with a passage of Herodotos (I. 67, 68) that provides information about the relation between Spartan metallurgy and Spartan ascendancy in the Peloponnese. Herodotos reports that at a time that preceded the age of king Kroisos of Lydia (middle of sixth century B. C.) the Spartans had been repeatedly defeated in their efforts to establish their ascendancy over the people of neighboring Arkadia. When they asked the oracle of Delphoi for advice, they would have received the following answer:

In a level part of Arkadia there is a place called Tegea: there two winds blow under forceful compulsion, there is hitting and counterhitting and misery lies upon misery. There the fertile earth holds the son of Agamemnon; by getting him you shall become the master of Tegea.

The riddle was solved when a Spartan emissary by the name of Lichas visited the shop of an blacksmith at Tegea. He recognized that the smithery was the place indicated by the oracle: he saw two bellows opposite to each other blowing toward the fire (such opposite bellows appear in Egyptian portrayals of ironworks), he saw an anvil upon which there was falling a hammer and he saw the beaten metal, which is misery upon misery, “since iron was invented for the evil of man.” The blacksmith told Lichas that the reason why the latter was finding the particular working of the iron an object of wonder was that in digging a well in his shop the smith had found an urn of unusual size, seven cubits long, containing the bones of a man of the same size. The Spartan understood that these were the bones of Orestes mentioned by the oracle. By paying the blacksmith, the bones were brought to Sparta: as a result Sparta became much stronger in war and was able to subject a great part of the Peloponnese.

It is indeed a commentary on the state of Greek studies that a professor of physics who does not know Greek was one who realized the vital importance of this statement of Herodotos for the understanding of Spartan history. According to Herodotos, the supremacy of the Spartans in the Peloponnese resulted from their acquiring a metallurgical secret formerly kept the people of Tegea.

In Borst’s view this passage of Herodotos indicates that Spartan military superiority was based on the knowledge of process for the production of steel. I do not know how Borst explains the technical details of the process involving a box and the bones of Orestes, but I believe that the explanation is provided by a famous memoir of the scientist Réamur on the making of steel, published in 1722 AD He tells how he searched for a method to improve the qualities of cast iron, which “is absolutely incapable of being worked with the hammer and is at the same time so hard.” He found a method of transforming it into steel by heating it up packed together with calcinated and pulverized bones. Since cast iron was considered worthless iron up to rather recent times, a “sick iron,” it is possible to understand why the combination of bones with cast iron was called a piling up of “misery upon misery.” I suspect that Herodotos missed the explanation of this element of the riddle.

The method used by the Spartans must have been similar to that used by the Chinese. It seems that iron began to be produced in China in the fifth century B. C.; the method used by the Chinese was that of producing cast iron and then reducing it to steel. Pliny, in the first century of our era, mentions China and Parthia as the important producers of steel. Some scholars, being wary of accepting that steel was produced at very early times, have tried to choose the to lowest possible date for the production of Chinese steel. But Chinese texts of the first century AD mention the production of steel by melting wrought iron in a bath of cast iron. It has been argued that the other process, that of reducing the carbon content of cast iron, was discovered later, because this has been the consequence of the developments in Europe; but the Spartan evidence suggests that decarburation may have been the earlier process. The process of co-fusion of cast iron with wrought iron requires a temperature, such that the cast iron becomes a liquid in which the pieces of wrought iron melt.

Several scholars have been confused by the fact that steel is a highly desirable metal for us. But the ancients were looking for a metal that was highly malleable and considered anything that was not malleable an inferior product. For instance, it has been noticed that in the Homeric poems iron is mentioned, but the weapons of the heroes are described as of bronze; on the basis of this fact it has been argued that weapons of iron were current in the age of Homer, but the poet deliberately chose to describe the customs of an age that preceded him. In my doctoral dissertation I argued that Homer was not an antiquarian: by the metallurgy of his time armor and swords could not be made of iron, but objects such as a ploughshares, hoes and mattocks could. By further investigating the problem I found that iron armor was seldom produced before the beginning of our era. Up to this time, the best possible use of iron could be that of making small cutting blades, points of spears and short swords. A highly capable blacksmith could succeed in producing a full-sized sword of steel, but this must indeed have been a rare piece that was not cheaper than a sword of bronze.

Henry B. Noss submitted in 1959 a doctoral dissertation on ancient copper metallurgy, in which there are incidental remarks on iron metallurgy that agree with my general view. He observes that “the heat treatment of iron was very difficult and complicated, that of copper comparatively simple”; he properly calls to attention the ancient texts that describe iron as an evil metal. Homer calls iron polykmeitos, “wrought with great toil.”

To Noss there occurred the wise idea of examining the first occurrence in Greek literature of words composed with sidero-; as a result he established the following timetable: in the first century A. D. flesh-hooks and crowbars; in the, second century, anchors and files; in the third plaiting and borers; in the fourth, tunics, fetters and horseshoes; in the fifth, breastplates; in the tenth, wheels. Of course, the first occurrence of the terms is not an absolute evidence when certain objects began to be commonly made of iron, but the timetable taken as a whole indicates that iron metallurgy was still growing from an infant state at the beginning of our era.

The written and material evidence indicates that here and there in the ancient world there were produced steel blades and even steel swords; these steel objects may even have preceded the general use of iron. The Egyptian iron objects that occur in solitary fashion in the two millennia preceding the Saite Dynasty should be examined to determine how often they are made of steel.

Since the distinction between Bronze Age and Iron Age is the the most fundamental classification scheme in ancient archeology, it is followed by people who have given little thought to metallurgy, or none at all. As a result there have been formed myths in the history of metallurgy that wen be dispelled only with a most detailed technical study of the evidence. A first effort in the right direction has been made by Noss, who has shown that there is no such thing as a unified copper metallurgy: a number of separate techniques must be distinguished, some more primitive and some highly advanced, that appeared in different areas and at different times, some being lost in the course of time. He has shown that the manufacture and the general use of tools characteristic of the so-called Stone Age continued through the Bronze Age in some areas. On my part, I would stress the point that iron appears to have been known about as early as copper, but was considered an inferior metal. The only specific advantage of iron was that of providing a better cutting edge; for the manufacture of cutting instruments iron was more desirable than copper even if it was more expensive. It would seem that cutting blades of iron were produced during the Bronze Age; hence, the first iron to be produced must have been steel. The Greek name for “steel” is stomoma; since stoma means “mouth, front part, point of a weapon,” the name of steel may refer to the fact that originally it was used just for the cutting edge or the point of instruments, being even mounted on a bronze support. When historians speak of Iron Age they actually refer to the fact that at a point in history it became possible to produce some objects more cheaply with wrought iron than with bronze; the number of the objects that could be so produced kept increasing in the course of the Greek and Roman period. The Greeks continued to use the term chalkeos for “smith,” a term that properly applies only to the “coppersmith,” because only copper or bronze was the metal truly fit for all the operations of smithing.

Noss suggests that there was a resistance to adopt iron, because the metallurgy of copper had achieved such a high level of perfection that it would not be abandoned in favor of a more primitive technique; but he does not explain why the technique used for iron should have remained in a primitive state. I believe that the proper exploitation of iron required a technique even more advanced than the highest copper technique. I am inclined to think that a sociological factor must be taken into account: up to the first century B. C. there had not been established any method for the advanced training of slaves. Since metallurgy was usually entrusted to slaves, the highly developed skills in iron metallurgy that were developed here and there could not be easily transmitted to future generations. Apparently the skill needed for handling copper was at the level of the usual training of slaves. It could be that in Lakonia where there was a social class, the perioikoi, with a status intermediary between that of full citizens and that of slaves, the social conditions were more favorable to the formation of a group that could acquire the secrets of steel metallurgy and transmit them to future generations. Metallurgists have been secretive up to recent times; but the formation of so-called trade secrets was inevitable as long as there had not been developed a language that would allow to explain the operations properly. The difficulty that we meet in interpreting ancient authors, such as Aristotle, when they deal with metallurgy, indicates that such a language did not exist. The history of alchemy indicates that the lack of a proper language caused the efforts to transmit chemical knowledge to founder in a sea of superstitious constructions. The description of iron metallurgy is particularly difficult. In the case of bronze and brass the main problem is that of obtaining the right proportion of metals; but in the case of iron the metal comes out of the smelting furnace with a variable content of carbon that radically affects its characteristics. Furthermore, any process of heating and hammering alters the characteristics of iron, which depend on the size, the distribution and the orientation of the composing crystals.

It would seem that the effort to develop a metallurgy of wrought iron caused the loss of the technique for the production of cast iron and steel in Greece and Rome. When I wrote my doctoral dissertation I suggested that the iron objects mentioned by Homer were of cast iron; now I would conclude that they were of cast iron and of steel, possibly high carbon steel. In describing the blinding of Polyphemos, the poet compares it vividly with the quenching of iron in water. Both cast iron and steel become harder and more brittle by being quenched in water, but only steel can have a sharp edge. Odysseos and his ten companions plunge into the eye of Polyphemos the charred point of a pole, and the effect is compared with the sizzling of water when an iron axe or an adze is plunged into it by a smith to make it hard. A number of editors expunge this passage (IX. 391-394) as a late addition, but the evidence seems to suggest that the making of steel was better known in preclassical than in classical times. It has been argued that the text is late, since it contains the phrase megala iaconta, “with great shout” which ignores the digamma at the beginning of the second term. But the usual epic form is mega Fiaconta, so that the text must have originally taken the digamma into account; when the digamma was no longer pronounced, mega was changed into megala so that the verse may sound correct.

7. Considering again the statement of Ploutarchos about the Spartan iron money, it seems that he telescoped the information. He mentioned the production of cast iron and the process of quenching the metal, but he did not mention the intermediary process of decarburizing the metal. Ploutarchos may have shortened or misunderstood the information provided by his source: the metal that was unfit for forging, brittle, and incapable of taking a good edge when it came out of the smelting process, was subjected to the process mentioned by Herodotos and then heated again to be quenched in vinegar which would make it even more brittle and more unfit for forging, but capable of taking a good edge. Ploutarchos instead states that it was quenched in vinegar so that it would become unfit for forging, brittle, and incapable of taking a good edge.

The evidence gathered by Borst indicates that the Spartans acquired from the people of Tegea the technique of decarburizing cast iron or high carbon steel. It is significant that Tegea is in the southeastern part of Arcadia on the road from Sparta to Argolis. In the period of the fifth century B. C. in which Argos destroyed the neighboring cities and took control of the Heraion and of Nauplia, Tegea revolted against Sparta and became an ally of Argos. Since the process of decarburation is connected with the name of Orestes, son of Agamemnon, king of Mykenai, it maybe that the process originated in the area of the Heraion.

I have listed the sources that state that iron was invented in Euboia, that is, at the Heraion and that mention Euboia as a famous metallurgic center. Here, I must call attention to a line of Aischylos that mention an Euboic sword called autotektonos. It may be a sword of steel. The term autotektonos maybe compared with the term autokhoónos that occurs in Homer. In the funeral games for Patroklos, Achilles offers a great ball of iron as a prize to the hero that will throw it the greatest distance; the narrative indicates that to lift the object at all is already a feat. Achilles states that the object would be of use to the holder of a large estate, who will be able to provide all the iron needed by his farmers and shepherds for five years. The object is called solon autokhoónon literally “self-poured lump.” Some interpreters have understood that it is a matter of meteoric iron which is “self-smelted.” But the Hellenistic scholar Aristarchos never doubted that melted metal is mentioned, since he observed that it must be a matter of copper in spite of the words of Homer, because iron cannot be melted. Paul Mazon translates: un bloc de fer brut; this translation is rather indefinite, but at least does not contain an error. The glosses to the passage explain that autokhoónos means as the metal comes from the smelting. It would seem, therefore, that the prize offered by Achilles is a bloom of iron as it is formed in the furnace. In substance both autokhoónos and autotektonos may have referred to metal in its usual first state of production. The usual practice of ancient times, followed up to modern times, was to produce a bloom in a low-temperature furnace and then break it up, separating the pieces of wrought iron from those of steel and cast iron. The practice of classical times, followed up to the Renaissance, was to discard all the pieces that were not wrought iron. It would seem that in some areas of Greece at some time the pieces of steel were utilized. A bloom found in the ruins of the Roman Corstopitum near Corbridge, on the Tyne was analyzed and found to be composed of parts that are steel. It may be suspected that the ancient metallurgy was always based on the low-temperature furnace producing a bloom; but at first the furnace was operated so as to produce as much as possible cast iron and steel. It may be conjectured that the first parts of the bloom to be utilized were these of steel; then development took two opposite directions, that of utilizing wrought iron and that of converting cast iron into steel.

8. In spite of the fact that the oboloi tested by Borst are of steel and possibly all oboloi were of steel, I still am inclined to believe that Spartan iron money was made of cast iron in classical times. In the Temple of Artemis Orthia the main holiness of Sparta, there have been found iron bars that have roughly the shape of oboloi, but are short and thick, and cannot have been used as roasting spits. In general when a utensil is used as currency its shape and metal tends to degenerate and acquires a merely symbolic character. Therefore, I suggest that the Spartans may have used cast for making the oboloi used as currency.

The indications that the iron money of the Spartans come to be made of cast iron are the following. The pseudo-Platonic dialogue Eryxias (400 B) states that Spartan money is made of useless iron, in order to prove that money may have a purely conventional value. This statement can hardly refer to oboloi of steel. The true oboloi found at Sparta, from which Borst took some samples, may have been pieces preserved in temples like the oboloi found at the Heraion. The Spartan iron money used in classical times was called pelanos. A number of inscriptions indicate that pelanos, like obolos, passed its name to the monetary unit obol, particularly to the obol paid as fee for the consultation of an oracle. The fee continued to be called pelanos even when it became more than an obol. Linguists explain the term by referring to the root of the Latin planus and of the English flat (German platt), and it has been suggested that originally a flat cake was offered to the oracle. But I would rather consider a derivation from the root of plassó, “to mold a soft substance” from which there is derived plasma and our term plastic. Suidas explained that pelanos is a kind of mushy pastry, the froth around the mouth, the gum of a tree and the obol paid for the consultation of an oracle. A gloss to Nikandros (Alexipharm, 488) remarks that pelanos, means “obol” and also pemma, “pastry”; it explains this last word by epsema, “boiled-down substance.” The smelting of ore is called epsesis. The term pelanos, therefore, seems to suggest that Spartan money was made of melted metal.

It is possible that in the case of oboloi used as currency, the Spartans come to skip the process of decarburation with the urn and the bones of Orestes. The oboloi of cast iron had to be made short and thick lest they break. In his Dictionary Pollux refers to the quenching in vinegar of Spartan oboloi, but in terms different from those used by Ploutarchos: “They quench the point of the obolos in vinegar so that it becomes incapable of being cut.” This statement is perfectly sensible from a metallurgical point of view: the point of the obol is quenched so as to make the steel harder; but the shaft is not quenched, because the quenching would make it harder but also brittle.

Gathering all the data, I would conclude that the Spartans abandoned the process of producing wrought iron and adopted from the people of Tegea a process which consisted in producing cast iron and then decarburizing it, the process used by the Chinese. This process was excellent and most desirable for the production of oboloi used as utensils, but too expensive for the oboloi used as currency. Svoronos may be right in assuming that the bar of the Heraion was of wrought iron. If the bar was of wrought iron, the relation of value 1:400 established by this bar between silver and iron applied to wrought iron. When the Spartans began to produce oboloi of steel, this relation was too unfavorable to iron in the case of steel objects. They may have exported oboloi of steel to be used as utensils; but as money they used oboloi of cast iron for which the rate of the Heraion was too favorable to the iron. Since Ploutarchos may be interpreted as saying that the proper rate for oboloi of cast iron was 1:1200, the Spartan money was considered worthless outside Sparta. However, the entire history of Sparta, and not only her monetary history, will continue to hover in the realm of legends and be a fit subject for rhetorical exercises of Spartan virtues and on auri sacra fames, as long that the metallurgic data potentially available are not gathered.

source:
http://www.metrum.org/measures/castiron.htm

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The University of Sydney - Department of Civil Engineering
World Trade Centre - New York
Some Engineering Aspects


Taken from Engineering News Record

In the aftermath of the Sept. 11 terrorist attacks in New York City and Washington, D.C., which brought down the twin 110-story towers of the World Trade Center and damaged the Pentagon, designers and contractors say they are skeptical that signature structures can be hardened against extreme acts of barbarism. 

"Only the containment building at a nuclear powerplant" is designed to withstand such an impact and explosion, says Robert S. Vecchio, principal of metallurgical engineer Lucius Pitkin Inc., referring to the hijacked Boeing 767 airplanes, heavy with fuel, that slammed into each WTC tower. 

The attacks appeared to be coordinated and in parallel. In Manhattan, at least two hijacked Boeing 767 airplanes, one with 92 people on board and the other with 65, crashed into the World Trade Center's twin towers, disappearing within and triggering fire and explosions. The north tower, called One WTC, was hit at 8:45 a.m.; the south tower, Two WTC, at 9:03 a.m. Another hijacked airliner, a Boeing 757 with 64 people on board, crashed into a section of the Pentagon at 9:40 a.m. 

Some 50,000 people work at the World Trade Center and some 23,000 at the Pentagon. Specifics on death tolls and damage were not available at press time. WTC rescue efforts were put off until Sept. 12 because the area was still a "hot zone" late in the day on Sept. 11, with falling debris from the stumps that were once among the world's tallest buildings, and a thick blanket of soot for blocks around. In addition, the 47-story Seven WTC collapsed in the evening, causing more chaos. "It'll take about a year to clean up" the remains, says Vecchio. 

Sources close to the carnage indicate that those below the 89th floor in the north tower and the 60th floor in the south tower were most likely to have survived. Reports indicated that at least 200 of the 400 firefighters at the scene are presumed dead and 78 police officers were missing. 

Confirmation of collateral damage to the numerous subway lines that converge under the WTC was not available. The owner, the Port Authority of New York and New Jersey, which just leased the WTC complex to Silverstein Properties, New York City, set up a command center across the Hudson River in Jersey City, N.J., trying to locate its employees, who were on floors 63 to 85 in the north tower. Additionally, in the hours after the attack, the port authority located temporary quarters at sites at John F. Kennedy International Airport in Queens; at the Teleport on Staten Island; and in Newark, N.J. 

The port authority issued the following press release: "Our hearts and our prayers go out to the families of the countless people, including many members of the port authority family, who were killed today in this brutal and cowardly attack. We at the port authority are doing everything in our power to rescue and care for the injured, and to comfort and assist the families of the victims." 

Meanwhile, Jim Rossberg, director of the Structural Engineering Institute of the American Society of Civil Engineers, is organizing two forensic teams, one for the WTC and the other for the Pentagon. 

The twin towers, framed in structural steel, had exterior moment frames with 14-in. steel box columns spaced 39 in. on center. The configuration created a complete tube around the building. The central steel core carried gravity loads only. The exterior tube provided all the lateral resistance. Horizontal steel trusses spanned 60 ft from the exterior wall to the core. Concrete on metal deck completed the floor diaphragm. 

Each tower contained about 100,000 tons of steel and 4 in. of concrete topping on the 40,000-sq-ft floors, according to Henry H. Deutch, assistant to the chief structural engineer for construction manager Tishman Realty & Construction Co. Inc., New York City, during the construction of the WTC and currently head of HHD Consultants Inc., Osceola County, Fla. 

Deutch says that originally, the north tower contained asbestos in its cementitious fireproofing as did the first 30 stories of the south tower. He believes the asbestos, which had been encapsulated, was removed after the 1993 bombing. In a press conference, Mayor Rudolph W. Giuliani said the city's health department had tested the air in the area and found no undue amount of chemical agents. 

The attacks were witnessed by hundreds of people in each of the locales. Vecchio, who was part of the investigation of the 1993 bombing of the WTC, was an eyewitness to the Manhattan debacle from Pitkin's office about 1¼2-mile north of the trade center. "The explosions were so tremendous," he says. "You could smell the jet fuel in the air." 

Millions across the nation also "saw" the towers collapse, through live television news coverage. The south tower fell at 10 a.m. and the north tower at 10:29 a.m. 

Reports indicate that the impact of each plane compromised the structural integrity of each tower, knocking out perimeter columns and the interior structure. The explosions then caused further damage, sweeping through several floors. "These were airliners scheduled for long flights, full of fuel, causing massive explosions," says Richard M. Kielar, a Tishman senior vice president. "No structure could have sustained this kind of assault," says Kielar. 

As the fires burned, the structural steel on the breached floors and above would have softened and warped because of the intense heat, say sources. Fireproofed steel is only rated to resist 1,500 to 1,600° F. As the structure warped and weakened at the top of each tower, the frame, along with concrete slabs, furniture, file cabinets, and other materials, became an enormous, consolidated weight that eventually crushed the lower portions of the frame below. 

Jon D. Magnusson, chairman-CEO of Skilling Ward Magnusson Barkshire Inc., Seattle, one of the successor firms of Skilling Ward Christiansen Robertson, structural engineer for the original World Trade Center, agrees: "From what I observed on TV, it appeared that the floor diaphragm, necessary to brace the exterior columns, had lost connection to the exterior wall." 

When the stability was lost, the exterior columns buckled outward, allowing the floors above to drop down onto floors below, overloading and failing each one as it went down, he says. 

A big question for implosion expert Mark Loizeaux, president of Controlled Demolition Inc., the Phoenix, Md., is why the twin towers appeared to have collapsed in such different ways. 

Observing the collapses on television news, Loizeaux says the 1,362-ft-tall south tower, which was hit at about the 60th floor, failed much as one would like fell a tree. That is what was expected, says Loizeaux. But the 1,368-ft-tall north tower, similarly hit but at about the 90th floor, "telescoped," says Loizeaux. It failed vertically, he adds, rather than falling over. "I don't have a clue," says Loizeaux, regarding the cause of the telescoping. 

The twin towers were part of a seven-building complex designed by architect Minoru Yamasaki that covers eight city blocks. An 800 x 400-ft foundation box, 65-ft-deep and with 3-ft-thick retaining walls, is under more than half the complex, including the twin towers and the adjacent hotel. The complex was completed in phases beginning in 1970 (ENR 7/9/64 p. 36). The 1.8-million-sq-ft Seven World Trade Center, constructed in the mid-80s, also had a steel moment frame from the seventh story up (ENR 11/28/85 p. 30). 

Security measures were tightened at the 12-million-sq-ft WTC complex after a terrorist bomb on Feb. 26, 1993. That bomb blew out one section of a north tower basement X-brace between two of the perimeter columns. The blast ripped out sections of three structural slabs in the basement levels between the north tower and the hotel, threatening the structural integrity of the foundation box. It did little damage to the north tower's structural tube, other than the affected X-brace. Damage was extensive to the other building systems, however, because the bomb compromised major utility lines in the basement, and the brace compromised the central core wall, allowing soot and smoke to shoot up the building core (ENR 3/15/93 p. 12). 

In Washington, Pentagon officials were still assessing the damage and the fire was still burning nearly seven hours after the building was hit. At press time there were no details about injuries and fatalities. 

The impact was between the newly renovated Wedge I and the about-to-be-renovated Wedge II, according to an aide in the Pentagon's Renovation Office. Wedge I "did hold up," the aide says. 

Reports of damage also remain sketchy and Pentagon officials decline to discuss specifics. However, the Pentagon aide reports that the plane slammed into the southwest side of the Pentagon adjacent to the heliport. The airliner reportedly hit at the first and second floors, but later the upper three floors collapsed. 

The U.S. Dept. of Defense's 6.5-million-sq-ft headquarters, built as a temporary structure 58 years ago, was not constructed with fire-resistant or bomb-resistant materials. The overdue, multiyear renovation includes technologically advanced materials designed to ward off severe damage from such attacks (ENR 9/4/00 p. 58). 

Fire was leaping out the windows, primarily on the upper floors of the unrenovated section. The adjacent renovated section appeared to have less damage, likely because of the reinforced glass windows and firewalls used in the renovation that was completed less than a year ago. 

In the aftermath of the 1993 bombing, WTC structural consultant Leslie E. Robertson, Skilling's project engineer for the original job, was convinced that the terrorists had meant to take down the twin towers. After the events of Sept. 11, there's little doubt that Robertson was correct.
source:
http://www.civil.usyd.edu.au/wtc_enr.htm

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The World Trade Center
Height: 1,368 and 1,362 feet (417 and 415 meters)
Owners: Port Authority of New York and New Jersey
Architect: Minoru Yamasaki, Emery Roth and Sons consulting
Engineer: John Skilling and Leslie Robertson of Worthington, Skilling, Helle and Jackson
Ground Breaking: August 5, 1966
Opened: 1970-73; April 4, 1973 ribbon cutting

The World Trade Center is more than its signature twin towers: it is a complex of seven buildings on 16-acres, constructed and operated by the Port Authority of New York and New Jersey (PANYNJ). The towers, One and Two World Trade Center, rise at the heart of the complex, each climbing more than 100 feet higher than the silver mast of the Empire State Building.

Construction of a world trade facility had been under consideration since the end of WWII. In the late 1950s the Port Authority took interest in the project and in 1962 fixed its site on the west side of Lower Manhattan on a superblock bounded by Vesey, Liberty, Church and West Streets. Architect Minoru Yamasaki was selected to design the project; architects Emery Roth & Sons handled production work, and, at the request of Yamasaki, the firm of Worthington, Skilling, Helle and Jackson served as engineers.

The Port Authority envisioned a project with a total of 10 million square feet of office space. To achieve this, Yamasaki considered more than a hundred different building configurations before settling on the concept of twin towers and three lower-rise structures. Designed to be very tall to maximize the area of the plaza, the towers were initially to rise to only 80-90 stories. Only later was it decided to construct them as the world's tallest buildings, following a suggestion said to have originated with the Port Authority's public relations staff.

Yamasaki and engineers John Skilling and Les Robertson worked closely, and the relationship between the towersí design and structure is clear. Faced with the difficulties of building to unprecedented heights, the engineers employed an innovative structural model: a rigid "hollow tube" of closely spaced steel columns with floor trusses extending across to a central core. The columns, finished with a silver-colored aluminum alloy, were 18 3/4" wide and set only 22" apart, making the towers appear from afar to have no windows at all.

Also unique to the engineering design were its core and elevator system. The twin towers were the first supertall buildings designed without any masonry. Worried that the intense air pressure created by the buildingsí high speed elevators might buckle conventional shafts, engineers designed a solution using a drywall system fixed to the reinforced steel core. For the elevators, to serve 110 stories with a traditional configuration would have required half the area of the lower stories be used for shaftways. Otis Elevators developed an express and local system, whereby passengers would change at "sky lobbies" on the 44th and 78th floors, halving the number of shaftways.

Construction began in 1966 and cost an estimated $1.5 billion. One World Trade Center was ready for its first tenants in late 1970, though the upper stories were not completed until 1972; Two World Trade Center was finished in 1973. Excavation to bedrock 70 feet below produced the material for the Battery Park City landfill project in the Hudson River. When complete, the Center met with mixed reviews, but at 1,368 and 1,362 feet and 110 stories each, the twin towers were the world's tallest, and largest, buildings until the Sears Tower surpassed them both in 1974.

source:
http://www.skyscraper.org/tallest/t_wtc.htm

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In Washington, a plane crashed into the Pentagon, causing part of the building to collapse. A passenger plane also went down near Pittsburgh. The Federal Aviation Administration ordered all airports around the country closed in the first such nationwide shutdown.

At Barksdale Air Force Base in northwest Louisiana, President Bush told reporters: "Freedom itself was attacked this morning by a faceless coward, and I assure you freedom will be defended," Bush said. "Make no mistake. The United States will hunt down and pursue those responsible for these cowardly actions." The U.S. military is on its highest state of alert.

The president had started the day at an elementary school in Florida, but landed in Louisiana shortly before noon. He was to leave there on Air Force One and continue traveling to undisclosed locations, said ABCNEWS White House correspondent Ann Compton, who was with the president. The pared-down press corps traveling with the president were not being told where they were going.

In the wake of the attacks, the U.S. Capitol, White House and other federal buildings were evacuated in Washington. In New York, U.N. headquarters was also evacuated, as were skyscrapers in several other cities.

There were no immediate details available on casualties, but thousands of people work in the buildings affected in both New York and Washington.

Chronology of Destruction

The chaos began at about 8:50 a.m. ET when a hijacked American Airlines passenger plane smashed into the One World Trade Center, the northern tower. Then, at 9:04 a.m., another jet crashed into the southern tower, Two World Trade Center.

According to the FBI, the planes involved in the trade center crashes were American Airlines Flight 11, a Boeing 767 en route from Boston to Los Angeles carrying 81 passengers, nine flight attendants and two pilots, and United Airlines Flight 175, a Boeing 767 also headed from Boston to Los Angeles. Officials said the plane was carrying 56 passengers, two pilots and seven flight attendants.

At about 10 a.m., the southern tower collapsed, enveloping lower Manhattan in a cloud of dust, ash and debris. A half-hour later, the northern tower also fell in on itself.

"Lots of smoke and then the next thing I heard was an explosion in the building from the top, the south building just crumbled, just completely went down, I saw it," said witness Joan Fleischer. "It's hard to see all the pieces, but you could see it tipping over and just crashing to the ground."

Part of the Pentagon also collapsed after a plane crashed into it shortly after the disasters in New York. The building was on fire, and military personnel were evacuated.

Shortly after the World Trade Center catastrophe, at about 9:38 a.m., FBI officials say American Airlines Flight 77, a Boeing 757 en route from Washington Dulles Airport to Los Angeles crashed into the Pentagon. The plane was carrying 58 passengers, four flight attendants and two pilots.

Then, at about 10:20 a.m., United Airlines Flight 93, a Boeing 757, en route from Newark, N.J., to San Francisco, crashed in western Pennsylvania in Somerset County about 80 miles southeast of Pittsburgh. The plane was carrying 38 passengers, two pilots and five flight attendants.

Highest Level of Alert

All military bases were put on Threatcon Alpha, the highest level of alert. The FAA shut down all air traffic in the country at 9:25 a.m. ET, ordering any planes in the air to land at the nearest airport. It was the first time the FAA ever ordered a nationwide "groundstop."

All trans-Atlantic flights were re-routed to airports in Canada.

In response to today's attacks, the U.S. Atlantic Fleet based in Norfolk, Va., has sent ships to sea to contribute to the "air defense" of Washington, D.C. and New York City. Other ships have been directed to get underway with embarked personnel and medical assets to provide humanitarian and medical support.

At least one of the planes involved in today's crashes was able to communicate that it had been hijacked, FBI officials said.

Law enforcement officials at the highest levels are stunned at the level and sophistication of the attacks, officials said, and have launched a massive probe. Although it is still too early to know the source of the attacks, the earliest theories are focusing on a connection to the turmoil in the Middle East.

Suspected terrorist Osama bin Laden warned three weeks ago that his followers would carry out an "unprecedented attack" on the United States, an Arab journalist told Reuters news agency.

"It is most likely the work of Islamic fundamentalists. Osama bin Laden warned three weeks ago that he would attack American interests in an unprecedented attack, a very big one," said Abdel-Bari Atwan, editor of the London-based al-Quds al-Arabi.

"Personally we received information that he planned very, very big attacks against American interests," he said. "We received several warnings like this. We did not take it so seriously, preferring to see what would happen before reporting it."

At least one military fighter jet patrolled the skies above Manhattan this morning in the wake of the tragedy.

Protecting the White House

As the morning went on, and the horror of the initial crash grew with each new disaster, officials in Washington and New York moved to try to limit any further loss of life.

Police in Washington closed off a two-block perimeter around the White House and agents with automatic weapons and machine guns moved tourists out of the area, locking down entire buildings around the area.

Cell phones may have been deliberately turned off by servers because of fear the phones could be used to detonate a bomb.

In New York, Mayor Rudolph Giuliani ordered that lower Manhattan be evacuated, asking everyone below Canal Street to walk north out of the area. The city's subway system was also shut down.

"I would like to take this opportunity to tell everyone to remain calm and to the extent that they can, evacuate lower Manhattan," Giuliani said in a broadcast on local cable news channel NY1.

An evacuation was ordered at the Sears Tower in Chicago, Los Angeles mobilized its anti-terrorism division, the Space Needle in Seattle was closed, and security was intensified around the naval facilities in Hampton Roads, Va. The financial markets in New York were closed.

‘Unbelievable, Unbelievable, Unbelievable’

Palestinian leader Yasser Arafat condemned the aircraft attacks, shortly after an anonymous caller told Abu Dhabi television that a radical Palestinian group was responsible for the attacks. The group later denied any involvement.

"I send my condolences, the condolences of the Palestinian people to American President Bush and his government and to the American people for this terrible act," Arafat told reporters in Gaza. "We completely condemn this serious operation … We were completely shocked. It's unbelievable, unbelievable, unbelievable."

In lower Manhattan, as police, fire and emergency personnel tried to cope with the mayhem, witnesses were in shock.

"I'm sitting down and I'm crying and I couldn't believe that something like this could actually happen," said Tony Bristow, who was working on a nearby pier when the planes smashed in the towers. "Then about 10 minutes later the whole building just started to collapse and now two seconds ago both of them collapsed and now there's no more World Trade Center. It's — this is ridiculous. I don't believe this." Before they collapsed, large holes were visible in sides of the 110-story buildings, landmark twin towers, which were struck by terrorist bombers in February 1993.

The tops of the twin towers were obscured by the smoke, and thousands of pieces of what appeared to be office paper came drifting over Brooklyn, about 3 miles from the tower.

The World Trade Center bombing on Feb. 26, 1993, left six people dead and injured more than 1,000 others.

In 1945, an Army Air Corps B-25, a twin-engine bomber, crashed into the 79th floor of the Empire State Building in dense fog.

ABCNEWS' Geraldine Sealey, Dean Schabner, Michael McAuliff and Corey Goldman contributed to this report.

source:
http://abcnews.go.com/sections/us/DailyNews/worldtrade010911.html

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