Super Genius
Posts: 1,323 
September 27th, 2006, 08:01 AM
Popular mechanics states
Very nice, but how long does it need to burn at 1100°F for the steel to loose 50% of its strentght?
How come they don't explain this very important fact?
Any idea?
Popular mechanics states
Quote:
"Steel loses about 50 percent of its strength at 1100°F," notes senior engineer Farid Alfawak-hiri of the American Institute of Steel Construction. "And at 1800° it is probably at less than 10 percent." NIST also believes that a great deal of the spray-on fireproofing insulation was likely knocked off the steel beams that were in the path of the crashing jets, leaving the metal more vulnerable to the heat
Very nice, but how long does it need to burn at 1100°F for the steel to loose 50% of its strentght?
How come they don't explain this very important fact?
Any idea?
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September 27th, 2006, 08:29 AM
steel is highly conductive of both heat and electricity. If the flames were at this temperature around the steel, the steel would reach that same temperature in seconds, a minute at the outside. A large explosion like that could certainly generate temperatures high enough to weaken that steel.
Basically skyscrapers were never designed with aeroplane collisions in mind. There is no way you could expect the WTC to withstand such treatment
steel is highly conductive of both heat and electricity. If the flames were at this temperature around the steel, the steel would reach that same temperature in seconds, a minute at the outside. A large explosion like that could certainly generate temperatures high enough to weaken that steel.
Basically skyscrapers were never designed with aeroplane collisions in mind. There is no way you could expect the WTC to withstand such treatment
Executive Member
Posts: 9,531
September 27th, 2006, 09:51 AM
Just a couple of thoughts
We are not talking about small pieces of steel here. These girders are huge. The steel is six inches thick. Steel is a good conductor of heat, but that does not neccesarily make it weaker. The heat would also be conducted along the length of the girder. The point I am trying to make here is that there would have to be a concentration of heat for considerable time to raise the temperature of the steel to the point of failure. It seemed to me that a lot of the jet fuel hurled right through the building and burned in the air.
There is a photo of a woman standing in the hole made by the airliner on the 94th floor and trying to look down to the streert. Heat does not seem to be a major problem where she is.
Just a couple of thoughts
We are not talking about small pieces of steel here. These girders are huge. The steel is six inches thick. Steel is a good conductor of heat, but that does not neccesarily make it weaker. The heat would also be conducted along the length of the girder. The point I am trying to make here is that there would have to be a concentration of heat for considerable time to raise the temperature of the steel to the point of failure. It seemed to me that a lot of the jet fuel hurled right through the building and burned in the air.
There is a photo of a woman standing in the hole made by the airliner on the 94th floor and trying to look down to the streert. Heat does not seem to be a major problem where she is.
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September 27th, 2006, 12:07 PM
the specific heating capacity for iron (the major constituent of steel) is about 0.4Jg-1K-1. now if we assume we have a 1tonne (ie bigger than your average gurder)piece of steel (tonnes are metric, sorry to scare all the americans), then to raise the temperature from 20 to 500 (about 1100F), we need an increase of about 500K (guestimation only). Thus we multiply 1000000g by 500K to get 500,000,000... multiply that by 0.4 and that's how many Joules u need. This works out at 200MJ.
According to the wikipedia, 10MJ is the amount of energy released by the combustion of one kilogram of gasoline. Now we can see the scale of the factors involved. It only takes the energy from 20Kg of gasoline (less energetic than airplane fuel i believe) to weaken one TONNE of iron.
Now i understand that there are assumptions involved in this guesstimate BUT i deliberately made the assumptions in favour of the building not collapsing, and yet it seems quite likely that the already-weakened steel structures within the WTC could be weakened to the point of the catastrophic failure we will never forget.
Add to that the pretty strong evidence that the towers actually did collapse, shortly after the planes crashed, and it seems almost undeniable that the plane crashes and the collapses were linked.
<takes a small bow>
the specific heating capacity for iron (the major constituent of steel) is about 0.4Jg-1K-1. now if we assume we have a 1tonne (ie bigger than your average gurder)piece of steel (tonnes are metric, sorry to scare all the americans), then to raise the temperature from 20 to 500 (about 1100F), we need an increase of about 500K (guestimation only). Thus we multiply 1000000g by 500K to get 500,000,000... multiply that by 0.4 and that's how many Joules u need. This works out at 200MJ.
According to the wikipedia, 10MJ is the amount of energy released by the combustion of one kilogram of gasoline. Now we can see the scale of the factors involved. It only takes the energy from 20Kg of gasoline (less energetic than airplane fuel i believe) to weaken one TONNE of iron.
Now i understand that there are assumptions involved in this guesstimate BUT i deliberately made the assumptions in favour of the building not collapsing, and yet it seems quite likely that the already-weakened steel structures within the WTC could be weakened to the point of the catastrophic failure we will never forget.
Add to that the pretty strong evidence that the towers actually did collapse, shortly after the planes crashed, and it seems almost undeniable that the plane crashes and the collapses were linked.
<takes a small bow>
Member
Posts: 242
Location: Vancouver
Location: Vancouver
September 27th, 2006, 12:17 PM
Just a thought... why do the beams need to fail in order for the tower to collapse? What happens if just the bolts holding the beams together were heated and then failed... Did they use bolts or were the beams just welded together?
Just a thought... why do the beams need to fail in order for the tower to collapse? What happens if just the bolts holding the beams together were heated and then failed... Did they use bolts or were the beams just welded together?
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September 27th, 2006, 12:19 PM
i think they use rivets. I don't know about their strength. probably the steel is weaker around them
i think they use rivets. I don't know about their strength. probably the steel is weaker around them
Member
Posts: 96
Location: US
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September 27th, 2006, 01:30 PM
I believe that they used bolts. WTC was designed in a new way and the outside beams were held together by the floor crossbeam things (I think). The floor beams weakened and bent inward, so the attachment to the outside beams couldn't hold up, in my understanding, and broke.
I believe that they used bolts. WTC was designed in a new way and the outside beams were held together by the floor crossbeam things (I think). The floor beams weakened and bent inward, so the attachment to the outside beams couldn't hold up, in my understanding, and broke.
Executive Member
Posts: 9,531
September 27th, 2006, 01:39 PM
The most reasonable thing I've read on this, is that the steel in question, was heated sufficiently to allow it to deflect enough to change the characteristics of the beam end loading from shear to tensile. If one floor let go, it would take the rest like a row of dominoes. Obviously, the planes hitting the building and the building collapsing are related. My only problem was that there didn't appear to be an intense enough fire for a long enough period to affect the steel. The proof, of course, is that the buildings fell down. Conspiracy theories give me a headache............like when LBJ shot Kennedy..
The most reasonable thing I've read on this, is that the steel in question, was heated sufficiently to allow it to deflect enough to change the characteristics of the beam end loading from shear to tensile. If one floor let go, it would take the rest like a row of dominoes. Obviously, the planes hitting the building and the building collapsing are related. My only problem was that there didn't appear to be an intense enough fire for a long enough period to affect the steel. The proof, of course, is that the buildings fell down. Conspiracy theories give me a headache............like when LBJ shot Kennedy..
Bright Spark
Posts: 330 
September 27th, 2006, 05:16 PM
I am sure there will be all kinds of theories to try to cover up where the fault actually occurred.
All the puffs of smoke around floor two seconds before the collapse need to be explained: they are not a coincidence. And what about the collapse of the third building??
I am sure there will be all kinds of theories to try to cover up where the fault actually occurred.
All the puffs of smoke around floor two seconds before the collapse need to be explained: they are not a coincidence. And what about the collapse of the third building??
Steven Hawking's Tutor
Posts: 4,995
Location: Florida, Hurricane Central
Location: Florida, Hurricane Central
September 27th, 2006, 05:27 PM
A very important fact is that steel doesn't burn.
Quoting Logic 7
Very nice, but how long does it need to burn at 1100°F for the steel to loose 50% of its strentght?
How come they don't explain this very important fact?
How come they don't explain this very important fact?
A very important fact is that steel doesn't burn.
September 27th, 2006, 05:51 PM
I've never been great with math and all, but as a professional welder/fabricator, as well as being related to several of the Mohawk High Steel workers that originally erected the towers and subsiquently helped clean up after 9/11. It doesn't take much to degrade the integredy of a steel girder under load. With a torch at 2000 deg. I can cut one of those puppies in half in a heart beat.
Steel is a finiky critter, it can hold up mountians, but cause it the slightest stress and she'll turn on ya.
I, my Uncles and cousins have no doubt in our minds that the avionics fuel mixed with all the flammable materials in the towers, coupled with the removal of several supports on impact, was more then enough to cause the inicial collaps of the tops, and the structure not being built to take that downward force or load, caused them to drop like a controlled pull.
I've never been great with math and all, but as a professional welder/fabricator, as well as being related to several of the Mohawk High Steel workers that originally erected the towers and subsiquently helped clean up after 9/11. It doesn't take much to degrade the integredy of a steel girder under load. With a torch at 2000 deg. I can cut one of those puppies in half in a heart beat.
Steel is a finiky critter, it can hold up mountians, but cause it the slightest stress and she'll turn on ya.
I, my Uncles and cousins have no doubt in our minds that the avionics fuel mixed with all the flammable materials in the towers, coupled with the removal of several supports on impact, was more then enough to cause the inicial collaps of the tops, and the structure not being built to take that downward force or load, caused them to drop like a controlled pull.
Council Member
Posts: 2,250
September 27th, 2006, 05:57 PM
Quoting #juan
The beams are not 6" thick. Whoever wrote that doesn't understand structural steel, and hasn't seen the details of the building. Steel is an excellent conductor of heat, and a steel beam loses its strength very, very quickly when it is heated while under a huge load. I watched the damn thing on tv when it happened, and as soon as I saw it, I said to a co worker that those towers wouldn't last an hour with that fire in there.
Just a couple of thoughts
We are not talking about small pieces of steel here. These girders are huge. The steel is six inches thick. Steel is a good conductor of heat, but that does not neccesarily make it weaker. The heat would also be conducted along the length of the girder. The point I am trying to make here is that there would have to be a concentration of heat for considerable time to raise the temperature of the steel to the point of failure. It seemed to me that a lot of the jet fuel hurled right through the building and burned in the air.
There is a photo of a woman standing in the hole made by the airliner on the 94th floor and trying to look down to the streert. Heat does not seem to be a major problem where she is.
We are not talking about small pieces of steel here. These girders are huge. The steel is six inches thick. Steel is a good conductor of heat, but that does not neccesarily make it weaker. The heat would also be conducted along the length of the girder. The point I am trying to make here is that there would have to be a concentration of heat for considerable time to raise the temperature of the steel to the point of failure. It seemed to me that a lot of the jet fuel hurled right through the building and burned in the air.
There is a photo of a woman standing in the hole made by the airliner on the 94th floor and trying to look down to the streert. Heat does not seem to be a major problem where she is.
Executive Member
Posts: 9,531
September 27th, 2006, 06:47 PM
Interesting article
THE WTC WAS DESIGNED TO SURVIVE
THE IMPACT OF A BOEING 767.
Fact. The twin towers were designed to withstand a collision with a Boeing 707.
The maximum takeoff weight for a Boeing 707-320B is 336,000 pounds.
The maximum takeoff weight for a Boeing 767-200ER is 395,000 pounds.
The wingspan of a Boeing 707 is 146 feet.
The wingspan of a Boeing 767 is 156 feet.
The length of a Boeing 707 is 153 feet.
The length of a Boeing 767 is 159 feet.
The Boeing 707 could carry 23,000 gallons of fuel.
The Boeing 767 could carry 23,980 gallons of fuel.
The cruise speed of a Boeing 707 is 607 mph = 890 ft/s,
The cruise speed of a Boeing 767 is 530 mph = 777 ft/s.
So, the Boeing 707 and 767 are very similar aircraft, with the main differences being that the 767 is slightly heavier and the 707 is faster.
In designing the towers to withstand the impact of a Boeing 707, the designers would have assumed that the aircraft was operated normally. So they would have assumed that the aircraft was traveling at its cruise speed and not at the break neck speed of some kamikaze. With this in mind, we can calculate the energy that the plane would impart to the towers in any accidental collision.
The kinetic energy released by the impact of a Boeing 707 at cruise speed is
= 0.5 x 336,000 x (890)^2/32.174
= 4.136 billion ft lbs force (5,607,720 Kilojoules).
The kinetic energy released by the impact of a Boeing 767 at cruise speed is
= 0.5 x 395,000 x (777)^2/32.174
= 3.706 billion ft lbs force (5,024,650 Kilojoules).
From this, we see that under normal flying conditions, a Boeing 707 would smash into the WTC with about 10 percent more energy than would the slightly heavier Boeing 767. That is, under normal flying conditions, a Boeing 707 would do more damage than a Boeing 767.
In conclusion we can say that if the towers were designed to survive the impact of a Boeing 707, then they were necessarily designed to survive the impact of a Boeing 767.
So what can be said about the actual impacts?
The speed of impact of AA Flight 11 was 470 mph = 689 ft/s.
The speed of impact of UA Flight 175 was 590 mph = 865 ft/s.
The kinetic energy released by the impact of AA Flight 11 was
= 0.5 x 395,000 x (689)^2/32.174
= 2.914 billion ft lbs force (3,950,950 Kilojoules).
This is well within limits that the towers were built to survive. So why did the North tower fall?
The kinetic energy released by the impact of UA Flight 175 was
= 0.5 x 395,000 x (865)^2/32.174
= 4.593 billion ft lbs force (6,227,270 Kilojoules).
This is within 10 percent of the energy released by the impact of a Boeing 707 at cruise speed. So, it is also a surprise that the 767 impact caused the South tower to fall.
Overall, it comes as a great surprise that the impact of a Boeing 767 bought down either tower. Indeed, many experts are on record as saying that the towers would survive the impact of the larger and faster Boeing 747. In this regard, see professor Astaneh-Asl's simulation of the crash of the much, much larger and heavier Boeing 747 with the World Trade Center. Professor Astaneh-Asl teaches at the University of California, Berkeley.
Although the jet fuel fires have been ruled out as the cause of the collapses, it should still be pointed out that the fuel capacities of the Boeing 707 and the Boeing 767 are essentially the same. And in any case, it has been estimated that both UA Flight 175 and AA Flight 11 were carrying about 10,000 gallons of fuel when they impacted. This is well below the 23,000 gallon capacity of a Boeing 707 or 767. Thus the amount of fuel that exploded and burnt on September 11 was envisaged by those who designed the towers. Consequently, the towers were designed to survive such fires. It should also be mentioned that other high-rise buildings have suffered significantly more serious fires than those of the twin towers on September 11, and did not collapse.
Interesting article
THE WTC WAS DESIGNED TO SURVIVE
THE IMPACT OF A BOEING 767.
Fact. The twin towers were designed to withstand a collision with a Boeing 707.
The maximum takeoff weight for a Boeing 707-320B is 336,000 pounds.
The maximum takeoff weight for a Boeing 767-200ER is 395,000 pounds.
The wingspan of a Boeing 707 is 146 feet.
The wingspan of a Boeing 767 is 156 feet.
The length of a Boeing 707 is 153 feet.
The length of a Boeing 767 is 159 feet.
The Boeing 707 could carry 23,000 gallons of fuel.
The Boeing 767 could carry 23,980 gallons of fuel.
The cruise speed of a Boeing 707 is 607 mph = 890 ft/s,
The cruise speed of a Boeing 767 is 530 mph = 777 ft/s.
So, the Boeing 707 and 767 are very similar aircraft, with the main differences being that the 767 is slightly heavier and the 707 is faster.
In designing the towers to withstand the impact of a Boeing 707, the designers would have assumed that the aircraft was operated normally. So they would have assumed that the aircraft was traveling at its cruise speed and not at the break neck speed of some kamikaze. With this in mind, we can calculate the energy that the plane would impart to the towers in any accidental collision.
The kinetic energy released by the impact of a Boeing 707 at cruise speed is
= 0.5 x 336,000 x (890)^2/32.174
= 4.136 billion ft lbs force (5,607,720 Kilojoules).
The kinetic energy released by the impact of a Boeing 767 at cruise speed is
= 0.5 x 395,000 x (777)^2/32.174
= 3.706 billion ft lbs force (5,024,650 Kilojoules).
From this, we see that under normal flying conditions, a Boeing 707 would smash into the WTC with about 10 percent more energy than would the slightly heavier Boeing 767. That is, under normal flying conditions, a Boeing 707 would do more damage than a Boeing 767.
In conclusion we can say that if the towers were designed to survive the impact of a Boeing 707, then they were necessarily designed to survive the impact of a Boeing 767.
So what can be said about the actual impacts?
The speed of impact of AA Flight 11 was 470 mph = 689 ft/s.
The speed of impact of UA Flight 175 was 590 mph = 865 ft/s.
The kinetic energy released by the impact of AA Flight 11 was
= 0.5 x 395,000 x (689)^2/32.174
= 2.914 billion ft lbs force (3,950,950 Kilojoules).
This is well within limits that the towers were built to survive. So why did the North tower fall?
The kinetic energy released by the impact of UA Flight 175 was
= 0.5 x 395,000 x (865)^2/32.174
= 4.593 billion ft lbs force (6,227,270 Kilojoules).
This is within 10 percent of the energy released by the impact of a Boeing 707 at cruise speed. So, it is also a surprise that the 767 impact caused the South tower to fall.
Overall, it comes as a great surprise that the impact of a Boeing 767 bought down either tower. Indeed, many experts are on record as saying that the towers would survive the impact of the larger and faster Boeing 747. In this regard, see professor Astaneh-Asl's simulation of the crash of the much, much larger and heavier Boeing 747 with the World Trade Center. Professor Astaneh-Asl teaches at the University of California, Berkeley.
Although the jet fuel fires have been ruled out as the cause of the collapses, it should still be pointed out that the fuel capacities of the Boeing 707 and the Boeing 767 are essentially the same. And in any case, it has been estimated that both UA Flight 175 and AA Flight 11 were carrying about 10,000 gallons of fuel when they impacted. This is well below the 23,000 gallon capacity of a Boeing 707 or 767. Thus the amount of fuel that exploded and burnt on September 11 was envisaged by those who designed the towers. Consequently, the towers were designed to survive such fires. It should also be mentioned that other high-rise buildings have suffered significantly more serious fires than those of the twin towers on September 11, and did not collapse.
Steven Hawking's Tutor
Posts: 4,995
Location: Florida, Hurricane Central
Location: Florida, Hurricane Central
September 27th, 2006, 07:14 PM
Again, simply because it was designed to withstand a jet crash does not mean it will.
The Tacoma Narrows Bridge was supposed to withstand wind. It did not.
http://www.enm.bris.ac.uk/research/n...ma/tacoma.html
Again, simply because it was designed to withstand a jet crash does not mean it will.
The Tacoma Narrows Bridge was supposed to withstand wind. It did not.
http://www.enm.bris.ac.uk/research/n...ma/tacoma.html
Knows No Bounds
Posts: 2,976
September 27th, 2006, 07:35 PM
I'm not wading into this mud puddle but I will let my husband who's been a pilot of both Fixed Wing and Helos (for 30 years) answers some question tomorrow. He's read the thread and quite surprised at the assumptions made by the "It was built to withstand" crowd. Stayed tuned.
I'm not wading into this mud puddle but I will let my husband who's been a pilot of both Fixed Wing and Helos (for 30 years) answers some question tomorrow. He's read the thread and quite surprised at the assumptions made by the "It was built to withstand" crowd. Stayed tuned.
Member
Posts: 69
Location: Baltimore,MD
Location: Baltimore,MD
September 27th, 2006, 09:13 PM
PLEASE inform, because I have seen nothing but "guesstimates" so far...and really does it matter? Whether the planes caused it, or whether the perps planted bombs on the inside, is irrelevant....
Quoting Sassylassie
I'm not wading into this mud puddle but I will let my husband who's been a pilot of both Fixed Wing and Helos (for 30 years) answers some question tomorrow. He's read the thread and quite surprised at the assumptions made by the "It was built to withstand" crowd. Stayed tuned.
PLEASE inform, because I have seen nothing but "guesstimates" so far...and really does it matter? Whether the planes caused it, or whether the perps planted bombs on the inside, is irrelevant....
