9/11 silly question

[valis]

Okay I will admit this is probably a really simple obvious question but I will ask anyway.

While listening to Coast to Coast am a week or two ago I heard some guy from the 9/11 scholars for truth. He repeatedly said that the towers could not have been brought down by an aircraft because the melting point of steel is X and the tempature jet fuel burns at is Y: X > Y, therefore the burning fuel could not have brought down the building.

This seemed to be a big thing with the guest as he yelled it repetadly to callers, saying the 'laws of physics' proved his point.

Okay here is the dumb question part, keep in mind I haven't taken physics yet...

Oh yeah...Put aside the issue of whether the steel even had to melt for the building to collapse, lets assume it did.

If the fuel is burning at X temp and is in an enclosed space; for instance the ceiling and floor and what are left of the walls are enclosing the fire somewhat, couldn't the temp in the building be higher than the burning temp of the jet fuel?

For instance if I have a light bulb whose surface reaches 100 degrees when operating and I put it in a box what will the tempeture in box reach; more than 100 degrees? If the heat has no where to go will it increase beyond a hundered degrees? So is the burning temp. of the fuel really a limit to the temps that could be reached in the fire?

edited to make question clearer

[ChaoticLimbs]

A simple flaw in these attempts to somehow turn a national tragedy into a conspiracy is that you don't need to melt steel to weaken it. All you need to do is heat it up. Burning jet fuel is more than sufficient to do that. Add an enclosed space and the mechanical damage of the plane severing supports and the weight bearing skin of the towers and it becomes very likely that the building would fall under its own weight.
The steel columns supporting the building were insulated (lower floors with Asbestos, upper floors with a non-asbestos substitute). There was a good reason to do this. Explosives are completely unnecessary to cause a collapse.
I've also heard people claim that the buildings fell in too controlled a manner, and that buildings shouldn't fall straight down. This also is rather silly when you consider that if an individual floor fails to support the upper floors, they'll fall straight down and the resulting energy release from the upper floors striking the next floor down is huge and primarily downward.
I'm not a physicist but I've not seen a credible trained physicist who actually believes that fuel can't take down a building like the WTC.

[valis]

A simple flaw in these attempts to somehow turn a national tragedy into a conspiracy is that you don't need to melt steel to weaken it...

I appriceate your answer and agree with it. The people doing this are fools and the gentleman I used the word scholar a little too often for my taste. I think he was a scholar like I am a porn star.

That said this isn't really what I am asking. What I am asking is if the heat source is contained somehow can the tempeture inside a container be higher than the tempeture of the heat source? Will the heat 'build up' or will it reach a maximum tempeture at that of the heat source?

[MetalPig]

If the fuel is burning at X temp and is in an enclosed space; for instance the ceiling and floor and what are left of the walls are enclosing the fire somewhat, couldn't the temp in the building be higher than the burning temp of the jet fuel?
No. You can't make stuff hotter than the heat source.

According to the conspiracy-debunkers, the jet fuel was spent within a very short time. After that, it was the building and the stuff in it that was burning. And apparently, that burned at a temperature high enough to weaken the steel in the central columns of the towers.

[Azrael 5]

All buildings collapse in on themselves-certainly at every demolition Ive seen(ok so they are controlled)dont they?

[Ririon]

All buildings collapse in on themselves-certainly at every demolition Ive seen(ok so they are controlled)dont they?
Newton says so. :) If a skyscraper was weakened at the base AND there was a very strong wind, then it might fall to one side while collapsing.

[Dcdrac]

They got hit by an aircraft full of jet fuel travelling at very high speed that is going to do it if nothing else.

[Ririon]

They got hit by an aircraft full of jet fuel travelling at very high speed that is going to do it if nothing else.
Assuming this was a reply to my post: Nope! The towers were still standing for minutes after being hit. So when they started collapsing, gravity did the work. And gravity prefers to work downwards.

[kookbreaker]

I would like to point out now that the 9/11 scholars for truth does not have a Structural Engineer, a Civil Engineer, a Demolition Expert, or any other relevant expert for that matter. The best they have is a fairly incompetant Physics Professor who has spent most of his life researching Cold Fusion. The remaining scholars are software engineers, reiligious studies professors, etc.

Is there a fallacy for appealing to ones own irrelevant authority?

[LTC8K6]

You only need about 800-1,000F to weaken the steel appreciably. The jet fuel was quite enough, anything else such as carpets and furniture just sped things along.

[LTC8K6]

If steel could withstand jet fuel burn temps, turbine blades would be a lot cheaper.

[gruk]

If steel could withstand jet fuel burn temps, turbine blades would be a lot cheaper.

To be fair, there's bound to be differences in the airflow inside a turbine and in a building with punctured outer walls. More air tends to generate a hotter flame (more oxygen per time unit, if nothing else).

Still, steel gets more malleable (and, I guess, less structurally sound) at a few hundred degrees celcius and I can quite imagine that an "office products and jet fuel" mix can burn that hot.

[rwguinn]

You only need about 800-1,000F to weaken the steel appreciably. The jet fuel was quite enough, anything else such as carpets and furniture just sped things along.
This is true.
At 600 degrees F, steel (generally) retains 95% of its room temperature ultimate strength. At 800 degrees, its at 88%, 1000 degrees, 58%, and at 1200 degrees, you're down to 37% of Ultimate (breaking) strength after 1/2 hour exposure.
Yield strengths are even lower--and once you start bending (or buckling, which in this case is the more likely scenario), things progress rapidly, since the geometry of the collumns is a large portion of their strength. Distort the geometry, and destroy the strength.

[LTC8K6]

gruk, I meant to put a :D at the end of that line. :D

[Buckaroo]

No. You can't make stuff hotter than the heat source.

It's not quite as simple as that. To use Valis's example, let's assume that you have a light bulb. When in radiative equilibrium with the open environment, the bulb has a surface temperature measuring 100 degrees C. Now place the the bulb in a box with reflecting sides that isolates it from the environment (but allows current to flow to the bulb). Now, the photons pouring from the bulb cannot escape the cavity, causing the temperature within to rise well above 100 C. The temperature will continue to rise until the bulb is switched off (blackbody physics come into play here, but I'm not going to get into that). In the real world, the box would isolate the bulb imperfectly, and the box itself would begin to radiate heat, so that the system would attain radiative equilibrium. The temperature in the cavity would still be much hotter than it would be otherwise. It all has to do with the distribution of the total heat flux, and the strength of the sink. Similar analyses can apply e.g. to the atmosphere, which is why the surface of the Earth is warm enough to live on, and indeed to the 9/11 case, where burning fuel (including the materials of the building itself) causes a more-or-less-constant flux of heat that is not necessarily able to escape the area efficiently.

This is not to take anything away from those who stated that steel can soften at relatively low temperatures -- which is undoubtedly true -- but it bolsters the case against the conspiracy types.

[rwguinn]

It's not quite as simple as that. To use Valis's example, let's assume that you have a light bulb. When in radiative equilibrium with the open environment, the bulb has a surface temperature measuring 100 degrees C. Now place the the bulb in a box with reflecting sides that isolates it from the environment (but allows current to flow to the bulb). Now, the photons pouring from the bulb cannot escape the cavity, causing the temperature within to rise well above 100 C. The temperature will continue to rise until the bulb is switched off (blackbody physics come into play here, but I'm not going to get into that). In the real world, the box would isolate the bulb imperfectly, and the box itself would begin to radiate heat, so that the system would attain radiative equilibrium. The temperature in the cavity would still be much hotter than it would be otherwise. It all has to do with the distribution of the total heat flux, and the strength of the sink. Similar analyses can apply e.g. to the atmosphere, which is why the surface of the Earth is warm enough to live on, and indeed to the 9/11 case, where burning fuel (including the materials of the building itself) causes a more-or-less-constant flux of heat that is not necessarily able to escape the area efficiently.

This is not to take anything away from those who stated that steel can soften at relatively low temperatures -- which is undoubtedly true -- but it bolsters the case against the conspiracy types.
Yes, it is as simple as that.
The temperature inside the box, or the surface of the box, will NOT be higher than the temperature of the source, which is the fillament of the bulb.
Period. Never. Ever. Not for any given value of time and space.
The bulb may not shed the heat as effectively as when in the open, which means the fillament gets hotter (which is why enclosed bulbs burn out faster than bare bulbs), but the maximum temperature attainable is that of the bulb. And that is limited by available current and voltage.
TANSTAAFL!

[Buckaroo]

Yes, it is as simple as that.
The temperature inside the box, or the surface of the box, will NOT be higher than the temperature of the source, which is the fillament of the bulb.
Period. Never. Ever. Not for any given value of time and space.
The bulb may not shed the heat as effectively as when in the open, which means the fillament gets hotter (which is why enclosed bulbs burn out faster than bare bulbs), but the maximum temperature attainable is that of the bulb. And that is limited by available current and voltage.
TANSTAAFL!

Nobody's talking about any free lunches here!

Maybe I was a little sloppy in making my point. As energy accumulates inside the box, the bulb/filament of course heats as well, so you are certainly correct that the temperature in the cavity immediately adjacent to the source will be the same as the source, and I did not mean to imply otherwise. But by your own statement, the temperature of an enclosed bulb does indeed increase over one that is in the open. Looking again at Valis's original question:

For instance if I have a light bulb whose surface reaches 100 degrees when operating and I put it in a box what will the tempeture in box reach; more than 100 degrees? If the heat has no where to go will it increase beyond a hundered degrees?

I think you'll agree that the answer to this question is yes.

I must disagree with you, though, about the temperature of the surface of an imperfectly reflecting box. Let's say we've left the system alone long enough to reach radiative equilibrium. Now, those filaments get darn hot. I sure as shootin' wouldn't want to put my finger on one. Yet I wouldn't hesitate to touch the box, which is waaayyy cooler. Why? The flux per unit area is waaaayyyy lower at the surface of the box. No worries about TANSTAAFL. Integrate around the box, and the flux balances perfectly with that from the filament. It's the distribution of energy, not the total amount of it, that's important in the context of the original question.

[rwguinn]

Nobody's talking about any free lunches here!

Maybe I was a little sloppy in making my point. As energy accumulates inside the box, the bulb/filament of course heats as well, so you are certainly correct that the temperature in the cavity immediately adjacent to the source will be the same as the source, and I did not mean to imply otherwise. But by your own statement, the temperature of an enclosed bulb does indeed increase over one that is in the open. Looking again at Valis's original question:



I think you'll agree that the answer to this question is yes.

I must disagree with you, though, about the temperature of the surface of an imperfectly reflecting box. Let's say we've left the system alone long enough to reach radiative equilibrium. Now, those filaments get darn hot. I sure as shootin' wouldn't want to put my finger on one. Yet I wouldn't hesitate to touch the box, which is waaayyy cooler. Why? The flux per unit area is waaaayyyy lower at the surface of the box. No worries about TANSTAAFL. Integrate around the box, and the flux balances perfectly with that from the filament. It's the distribution of energy, not the total amount of it, that's important in the context of the original question.
yes.

[Rob Lister]

If I remember correctly, the steel beams were only weakened slightly from the heat; just enough to allow them to sag a bit. This sagging caused the bolts that held the beams to shear. Had the bolts holding the beams been stronger, neither building would have collasped. They might have been total losses, but they'd have stood until intentionally brought down.

[rwguinn]

If I remember correctly, the steel beams were only weakened slightly from the heat; just enough to allow them to sag a bit. This sagging caused the bolts that held the beams to shear. Had the bolts holding the beams been stronger, neither building would have collasped. They might have been total losses, but they'd have stood until intentionally brought down.
You have a reference for that?
I'd be interested in reading it. My knowledge of buildings isn't that great--I usualy deal with stuff that moves--but I believe that they use rivets to hold these things together, and they are generally have as high, if not higher, shear strength than the beams they tie together.
Generally, we run a SF that is 2X or so that of the structural members themselves

[Rob Lister]

https://hpds1.mit.edu/bitstream/1721.1/31114/1/61145960.pdf

Just the first I found. You decide

[rwguinn]

https://hpds1.mit.edu/bitstream/1721.1/31114/1/61145960.pdf

Just the first I found. You decide
Thanks--I will take a look.
Quick perusal indicates that there is not a simple failure mode, as I suspected---But I will take the time to read it in depth and get back to you!

[Rob Lister]

Thanks--I will take a look.
Quick perusal indicates that there is not a simple failure mode, as I suspected---But I will take the time to read it in depth and get back to you!

You could probably find a briefer summary. I'm not interested enough to search further.

[rwguinn]

You could probably find a briefer summary. I'm not interested enough to search further. I have read most of the detail description, and I pretty much agree. I am going to paraphraase a lot of their stuff here:
A large number of supporting columns were destroyed by impact. There were sufficient supports left to hold up the building under normal circumstances, but these weren't normal. There was a fire.
What I found most interesting was the assertion that a "diffuse flame will usually not exceed 1000 C" (Which is 1830F), and that the temperature probably didn't exceed 750-800C (1380-1470F)---which is hot.
Steel expands when it gets hot. They point out that the heating was most likely uneven, and that beam buckling probably occurred in the floors, which would start failing the floor beams.
Now, column strength is a function of length. In the Towers, the length of the support columns was reduced by having the floors in there. As a beam doubles in length, the column's ability to resist buckling is 1/4 what it was. Lose 1 floor, and you now have 1/4 the weight bearing capability you had. 2 floors, 1/9th--and you are in over your head very quickly- and the collumns start buckling and the building comes down.
The way I read it, softening of the fasteners may have been a contributer, but it was thermal loading (Elongation of the trusses due to thermal expansion) which overloaded the fasteners holding the floor/ceiling trusses to the columns. And by failing enough floor trusses, you get a high load on the floor where this debris all accumulates, as well as a buckling failure in the vertical supports. When this collapses, you get an impulse loading on the lower part of the system, which it wasn't designed for (who could forsee this! Or if he/she could, that engineer would be eligible for a $1000000 reward--and would need a new job) and the whole thing collapses just like you had cut the supports with explosives.
Now, that is over-simplification to many, I'm sure, and probably clear as the Rio Grande to others. But anyway--Thank you for the interesting link. I do appreciate it.

Edited for speling...a'hm a injuneer, not anglish majer...

[Hamradioguy]

Steel trusses similar to what was used in the WTC are rather common in building construction these days. Next time you're in a Wall Mart, Sam's Club or similar Big Box store take a look up at the roof. This type of construction has killed more firefighters over the years than you could imagine: Fire in the building and firefighters working on the roof to ventilate. When the steel gets heated it softens and sags. Down comes the roof...and often the firefighters. Hard to believe, but laminated wood generally holds up longer and better in fire conditions.
Check out some of Francis Brannigan's books on building construction for more on this.

[articulett]

Steel trusses similar to what was used in the WTC are rather common in building construction these days. Next time you're in a Wall Mart, Sam's Club or similar Big Box store take a look up at the roof. This type of construction has killed more firefighters over the years than you could imagine: Fire in the building and firefighters working on the roof to ventilate. When the steel gets heated it softens and sags. Down comes the roof...and often the firefighters. Hard to believe, but laminated wood generally holds up longer and better in fire conditions.
Check out some of Francis Brannigan's books on building construction for more on this.

And yet another reason why evidence trumps conjecture and faith.

[Dr. Popalot]

Here's a link to a video about the 911 conspiracy: http://video.google.com/videoplay?docid=-8260059923762628848&q=911

There are a few obvious flaws with their "theory", but it is interesting.

[valis]

Well thank you for all the replies.

I must say I would have thought 'common sense' would dictate that you could heat something to a higher temp than the heat source by containing the heat. I guess that is the problem with common sense.

[Freakshow]

No. You can't make stuff hotter than the heat source.

According to the conspiracy-debunkers, the jet fuel was spent within a very short time. After that, it was the building and the stuff in it that was burning. And apparently, that burned at a temperature high enough to weaken the steel in the central columns of the towers.The central columns may or may have not been weaked. But as I understand it, that isn't what cause the collapse. The trusses were weakened and collapsed (due to the fire). That removed the ability of the central columns and the external steel structure to support each other. The external structure gave way.

[kookbreaker]

Here's a link to a video about the 911 conspiracy: http://video.google.com/videoplay?docid=-8260059923762628848&q=911

There are a few obvious flaws with their "theory", but it is interesting.

Not just a few flaws. Its outright full of [rule 8].

[CFLarsen]

valis,

I lived in NYC at the time. I visited the Towers on several occasions. I saw them fall. Not, as most other people, on TV, but for real. If you didn't get a chance to see them, you would simply not believe how huge these constructions were. They were not "towers", but mountains of steel. They dominated the Manhattan Skyline, a view that is filled with the most awesome buildings in the world.

But big passenger planes, fully loaded with jet fuel, hammering mercilessly into these structures?

Instant hell.

Fireballs the size of football fields. Everything burned: Paper, carpets, inventory, people. The temperatures were immense. What could burn, did. What could melt, did.

I am a great admirer of the scientific endeavours of mankind, but I cannot see how any structure could have withstood the attack of such huge planes. It is ludicrous to even consider building megastructures that can withstand a big passenger plane hitting it at full speed, with full tanks.

To cast doubt on how these buildings fell is to piss on the victims and their families.

That makes me mad.

[aggle-rithm]

Newton says so. :) If a skyscraper was weakened at the base AND there was a very strong wind, then it might fall to one side while collapsing.

In a TV special shortly after the collapse, I remember hearing about an engineering principle that explained why the towers went straight down. When a tall building is designed, it is engineered to take vertical stresses from gravity -- NOT diagonal stresses. It is designed to sway a certain amount, but never over a certain limit. Thus, if a tower leans more than a certain number of degrees, it is no longer able to support its weight and drops straight down. If you watch the video, you can see the tower tilting one way and the other as it went down, correcting itself as the angle of the tilt became too great on one side.

I only heard this explanation once, and its never been mentioned since then, as far as I know.

[aggle-rithm]

A few years ago my brother slipped on the floor of a public restroom and broke his leg. It was a brutal tib-fib fracture that required surgery and sent several small emboli into his lungs. To this day I can't imagine how a healthy adult in the prime of his life could injure himself so badly by slipping on a bathroom floor -- yet it did happen. I'm sure if I was there, I would understand in an instant how it could happen.

My point is, there are many things that happen that seem to defy common sense. That is simply because common sense is often wrong. It only applies to predictable, commonplace events. Something that is totally outside our experience does not always conform to our expectations. The conspiracy theorists don't seem to understand this.

Would they also cry "foul" when told that Japanese torpedoes in Pearl Harbor were able to sink ships ACROSS THE HARBOR from the ships that they hit, just from the shock wave of the explosion? It seems impossible to me, but then, I wasn't there, nor am I an explosives expert. So I trust those with more experience when they tell me what happened.

[rwguinn]

In a TV special shortly after the collapse, I remember hearing about an engineering principle that explained why the towers went straight down. When a tall building is designed, it is engineered to take vertical stresses from gravity -- NOT diagonal stresses. It is designed to sway a certain amount, but never over a certain limit. Thus, if a tower leans more than a certain number of degrees, it is no longer able to support its weight and drops straight down. If you watch the video, you can see the tower tilting one way and the other as it went down, correcting itself as the angle of the tilt became too great on one side.

I only heard this explanation once, and its never been mentioned since then, as far as I know.

Actually, that's not the way things happened. It would take a LOT of lean--It's in that report linked elsewhere, so I don't know haw far, but we're talking BIG lean...
To demonstrate what happened, go get a beverage-of-your choice in acan, and drink it.
Set the can on the floor with the opening up. very carefully, place one foot on the can, and gently transfer all your weight to the can, so you are standing on it. If you are less than 225 lb weight, it will hold you up.
Now, get off the can, and do it again, only this time, transfer your weight all at once-or, if you are small, start with your foot 2" above the can and step on to it.
No difference in weight--just that the same weight impacting the can casuse collapse. That's what happened when the collumns bowed, and several floors worth of debris dropped onto a single floor.

[Hellbound]

Actually, that's not the way things happened. It would take a LOT of lean--It's in that report linked elsewhere, so I don't know haw far, but we're talking BIG lean...
To demonstrate what happened, go get a beverage-of-your choice in acan, and drink it.
Set the can on the floor with the opening up. very carefully, place one foot on the can, and gently transfer all your weight to the can, so you are standing on it. If you are less than 225 lb weight, it will hold you up.
Now, get off the can, and do it again, only this time, transfer your weight all at once-or, if you are small, start with your foot 2" above the can and step on to it.
No difference in weight--just that the same weight impacting the can casuse collapse. That's what happened when the collumns bowed, and several floors worth of debris dropped onto a single floor.

Even better, stand on the can as you first indicated, then have a friend tap the side of the can with a pencil while you're standing on it. Only a slight deformation of the aluminum, but it will instantaneously crumple (and straight downward, even though the force that initiated the collapse came from the side).

[CurtC]

If you watch the video, you can see the tower tilting one way and the other as it went down, correcting itself as the angle of the tilt became too great on one side.This is true with the second tower that was struck (the South tower I think), and the first to fall. You can see the section of the building above the impact start to tilt as a single unit, before the area around the impact suddenly stops supporting it. This was the tower that the plane hit more on one side, and that side was the one to give way.

With the North tower, it fell straight down, and you can actually see the TV tower on its top begin falling well before the outer walls. It collapsed from the middle. This tower was struck in the middle, so its center supports were likely more damaged.