Why Indeed Did the WTC Buildings Collapse?

[Hurricane Angel]

Well my first year of university was in mechanical engineering, and that was just last year. I switched over into biology because I find it more interesting.

Having told you that, it means I know alot about what structural components do what and how they behave.

 

[Ophiolite]

Then you know that steel is weakened by elevated temperatures. Would you accept that the steel was sufficiently weakened by the fire resulting from the impacts that the upper floors collapsed?

 

[Hurricane Angel]

Well yes of course, I can agree to the fact that the plane had severely weakened the building.

Mathematically, I can prove three things to everybody;

1) The flame was not hot enough to significantly heat the steel, and weaken them. However, let's assume it did...

2) The weight of the entire building above the fire was not enough to send it falling in on itself the way it did. But assuming the fire weakened the support sufficiently, this leads us to...

3) The "cascade" as I call it, would have been slowed down in about 20 floors below the fire. This one is a bit more tricky mathematically, but if you think about it; the falling debris could not have achieved high kinetic energy due to gravitation. Acceleration to gravitation is an exponential curve, right? But that's not what would have happened because it would have been slowed down after one floor, then the next, then the next.. etc, essentially not reaching the critical exponential curve and eventually stopping completely. Because the lower floors had complete structural integrity, and steel reinforced concrete has massive compression strength it should be obvious that even the lower floors were weakened by something.

Personally, I called bullshit the second I saw that concrete pulverized into dust, because assuming it was compressed beyond it's UCS (ultimate compressive strength), it would have turned into rock sized chips, not dust.

 

[James R]

You've never smashed concrete with a hammer, have you?

 

[Hurricane Angel]

Don't make this juvenile, either state your complete point (as to what exactly happens with this concrete) or don't post anything at all.

 

[James R]

Ok, Hurricane.

Mathematically, I can prove three things to everybody;

1) The flame was not hot enough to significantly heat the steel, and weaken them. However, let's assume it did...

You can prove mathematically that the flame was not hot enough to significantly heat the steel? I don't believe you.

2) The weight of the entire building above the fire was not enough to send it falling in on itself the way it did.

If you remove supports then ANY weight is enough to cause collapse. The report on the cause of the collapse is quite clear that floor supports were weakened and failed.

3) The "cascade" as I call it, would have been slowed down in about 20 floors below the fire. This one is a bit more tricky mathematically, but if you think about it; the falling debris could not have achieved high kinetic energy due to gravitation.

Show me your maths.

Acceleration to gravitation is an exponential curve, right?

No. Acceleration due to gravity is constant (at least on the scale of the WTC).

But that's not what would have happened because it would have been slowed down after one floor, then the next, then the next.. etc, essentially not reaching the critical exponential curve and eventually stopping completely. Because the lower floors had complete structural integrity, and steel reinforced concrete has massive compression strength it should be obvious that even the lower floors were weakened by something.

The compression strength of the concrete is irrelevant. The floor supports failed, and the whole building concertinaed. There was AIR between the floors, not concrete.

How much weight were the floor supports designed to take? Certainly not the weight of 10 other floors sitting on top of them, for example.

Personally, I called bullshit the second I saw that concrete pulverized into dust, because assuming it was compressed beyond it's UCS (ultimate compressive strength), it would have turned into rock sized chips, not dust.

I seem to remember bulldozers cleaning away rubble for months after the collapse. Don't you?

 

[mars13]

the WTC was designed specificly to withstand that exact attack,and to NOT pancake like it did.

freefall speeds are IMPOSSIBLE without a controlled demolition.

 

[geistkiesel]

the WTC was designed specificly to withstand that exact attack,and to NOT pancake like it did.

freefall speeds are IMPOSSIBLE without a controlled demolition.

I have commented on this previously and after reviewing the second impact of the airplane into the second tower I must revise my conclusion.

The second airplane is seen entering one face of the building and exiting an adjacent face, not the opposite side directly across the first. Is this what occurred?

Even if passing through the entire floor, much of the jet fuel must have been carried outside the building and would not have been available for heating the steel structures to the extent that the structures failed friom heat effects. It seems likely tyhat the entirecenter support member was not materially affected by the aircraft impact such that the heat insulation was destr0oyed to the extent that what ever heat was absorbed was inconsequential to the failure of the supporting members.

The free fall is an extrordiunary event withiout scintifically supported history of having occured in other high rise fires.

It seems that the major disagreement here is as much pitting conspiracy theory vs no conspiracy as is there scientific arguement. To be sure there are both and perhaps each is due its moment in the sun for consideration. Using a worst case scenario approach it would be extremely dangerouus for the people of this country, in fact dangerous for the peoples of the world, to not assume the worst case. We must let the evidence, the suspicious, the intuition, direct the investigation, and we must think creatively allowing no rational conclusion be too far fetched a possibility.

If there was no domestic conspiracy, this is what we are discussing aftr all, domestic conspiracy -treason, then, no harm, no foul'.

But we must be as conservative and thorough as possible in leaving no stone unturned, to investigate the suspicious, the contradictory, all that which "smells", enquire deeply into those entities that refuse to provide evidence in their possession and allow no exceptions, whatever the reasons, even "national security" claims, for withholding of evidence.

This is what it is all about isn't it, national security, and the waging of war on the United States of America?)
Geistkiesel​

 

[James R]

Using a worst case scenario approach it would be extremely dangerouus for the people of this country, in fact dangerous for the peoples of the world, to not assume the worst case.

We'd better assume that aliens are visiting Earth, too - just in case.

 

[Anomalous]

I know why you think it was not uniform, because it mushroomed as it went towards the bottom. While it might appear that way, most of that mushroom shit was just dust. Remember ground zero? It didn't span as many blocks as the video might make you believe.

There was another building inbetween WTC7 and WTC 1 2

I think real evidence could be concluded that scientifically fire does not weaken steel because it cannot reach such temperature. I think real evidence can also be considered that other buildings have been on fire for a much longer time (20 hours) and didn't collapse. And entire floors were gone, as in you could see straight through the building and only the steel columns were there.. but I don't think they collapsed.

Was this the first time ? The buildings were infact fire proof, so who disabled the sprinklers ?

Also, this is my thought experiment, if you can humour me. If the steel did start to weaken, it would not implode like it did. So what I mean by the steel, is that it would sway and wobble, the building would tilt off into one direction because of the forces caused by the wind (I'm sure you know buildings sway), what you see with the WTC is that it fell on itself, and should have fallen to the side.

It did go on one side but it failed to slide down.

Another thing, this "cascade" is also bullshit material. Imagine this, the section of the building above the fire was airlifted aobve the building, and then dropped. Would it fall straight through the building, or have the building cascade in on itself? No, it would hit the top, crash through a couple floors before being stopped, and then fall to the side. Because none of that lower steel was weakened, and the compression strength of steel is ridiculously high. What happened to all the beams (snapping in half) is a shear force, which only happens when something is applying pressure to its side.

The building could pulvarise the full speed HUGE HEAVY Planes, but could also collapse.

 

[Anomalous]

You've never smashed concrete with a hammer, have you?

Hi James R, How r u

I did smash them manytimes, it requires lot of power and it quickly desepetates energy on breaking just like Racing cars.

 

[Anomalous]

... essentially not reaching the critical exponential curve and eventually stopping completely. Because the lower floors had complete structural integrity, and steel reinforced concrete has massive compression strength it should be obvious that even the lower floors were weakened by something. ....

Dont forget that lower the floor the stronger the structures.

 

[Ophiolite]

JamesR has asked most of the follow on questions and made most of the comments I was planning on. While we bot await your maths proofs with interest could you address the following off topic points.

Personally, I called bullshit the second I saw that concrete pulverized into dust, because assuming it was compressed beyond it's UCS (ultimate compressive strength), it would have turned into rock sized chips, not dust.

Am I to understand that the abbreviation UCS has a completely different meaning in civil engineering than it does in geomechanics, where it represents unconfined compressive strength?

Would I be correct in thinking that the ultimate compressive strength, in this context, is the compressive yield strength?

Finally, would you agree that, bar minor exceptions of which I am totally unaware, that all material failure is actually a tensile failure, even when this tension is induced by compression or shearing?

 

[Hurricane Angel]

Alright onto the hydrocarbon problem. I hope you'll thank me for all my hard work, James.

Jet fuel, aka kerosene and derivatives, has a chemical formula of C12H26 or C13H28, depending on which fuel you're using. Now there is a term called "enthalpy" which measures how much energy there is within the bonds of any given molecule. This is textbook chemistry stuff;

C-O = 358 kJ/mol
H-O = 463 kJ/mol
C-C = 348 kJ/mol
C-H = 413 kJ/mol

C13H28 + 30 O2 => 13 CO2 + 14 H2O

Bond energies = [(12 x [C-C]) + (28 x [C-H])] - [(26 x [C-O]) + (28 x [H-O])] = (4,176 kJ/mol + 11,564 kJ/mol) - (9,308kJ/mol + 12,964kJ/mol) = 6,532 kJ/mol

molecular weight of C13H28 = (13 C x 12g/mol) (28 H x 1g/mol) = 184 AMUs or 184g/mol (we'll need this for later)

Basically what do all these derivations mean? It means that for every 184g of this fuel perfectly combusted, 6,532 kilojoules of energy are released into the environment. Now there is something called specific heat capacity, which is a term that describes how much energy (joules) is required to raise a kilogram of a given substance by one degree celsius. We'll see how that converts into heat now;

Specific heat capacity of austenic (construction) steel = 500 J/ kg-K. This means that 1kg of steel needs 500 joules to raise its temperature by 1 degree Celsius.

Heat required to weaken steel? It gets red-hot at 1650 Celsius (3000F), so let's assume it weakens at 1000C (1800F).

*Therefore 500,000 J/kg or 500 kJ/kg of steel to raise its temperature to weakening point.

A 757 with a full tank of fuel contains 40,000 litres of jet fuel. This is 40,000,000 grams of fuel, or 40,000,000 / 184g/ mol. Therefore it had 217,391 moles of fuel, and these moles had an energy potential of 1,420,000,000kJ. A huge amount of energy.

Divide that by 500 (the necessary amount of kJ/kg) and that leaves 2,840,000 kg, or 2,840 tonnes of steel that could potentially be "weakened". As for how much steel is on each floor I can only speculate. But here's an estimate;

A construction fact regarding WTC is that 150,000 tonnes of steel were shared between the two towers, and together they have 220 floors. That leaves 681 tonnes of steel per floor, but I'll subtract 6 tonnes per floor to leave 1,000+ tonnes for the basements. So, 675 tonnes of steel per floor?

There you have it, if this much energy were perfectly transferred to the steel, the building would have collapsed because the jet fuel incineration was the highest energy reaction out of all the events. The subsequent fires wouldn't have had nearly enough fuel, oxygen, or time to weaken the beams further.

Now for my favourite part, the points to note;

1 - This is the most important point. Much of that potential chemical energy was not spent on heating steel. The only time you can get such a perfect transfer of energy is in electric arc welding, not burning gasoline. Most of the energy went to heating the environment inside and outside the building, and the steel of the airplane surrounding the fuel, which would have been heated before the WTC steel.
*Taking this into consideration practically eliminates any possibility of the plane's impact weakening the structural steel.

2 - The plane wouldn't have a full load of fuel, so the total energy will be slightly lower.

3 - The plane struck the building on multiple floors, I would estimate at least 5. So now the 685 tonnes becomes 3,425 tonnes... more steel than the total energy (assuming perfect combustion and transfer) would be able to weaken.

4 - The south tower had much of the jet fuel spill on the outside, so what could possibly heat the steel so much as to make it fall 15 minutes before the north tower?

5 - The plane did not damage the internal structural steel. I can't find the source right now, but on the Discovery Channel there was a research firm hired to find out what happened to the plane. Basically it was turned into minced meat, and I seriously wish I could find the picture (yes they had an animated version of what happened to the plane) to show you all. I'll look for it as we're discussing the maths.

5a - Having conclusively proven that is what happened to the plane, it is clear that all it's kinetic energy was lost when it was sliced by the outer steel columns and left the internal core columns relatively sound.

6 - There was not enough oxygen to drive the subsequent fires to high enough temperatures. Proof? Smoke.

6a - Assuming there was a steady flow of oxygen, the fires would have needed at least several hours to sufficiently heat the steel, and enough of the steel.

By the way, I would like to fully discuss these particular derivations until its been made clear, either to myself, or to yourselves, whether these mathematics are correct/incorrect.

 

[Hurricane Angel]

Finally, would you agree that, bar minor exceptions of which I am totally unaware, that all material failure is actually a tensile failure, even when this tension is induced by compression or shearing?

Well in tensile failure there must be an increase in volume of whatever is "failing".

Am I to understand that the abbreviation UCS has a completely different meaning in civil engineering than it does in geomechanics, where it represents unconfined compressive strength?

They are different. Ultimate compressive strength/ UCS is just a short way of talking about the the 'ultimate strength' with regards to a loss in volume. Yield strength is the stress at which a material begins to deform, though not necessarily fail completely, unlike the 'ultimate'.

 

[qwerty mob]

Then you know that steel is weakened by elevated temperatures. Would you accept that the steel was sufficiently weakened by the fire resulting from the impacts that the upper floors collapsed?

Forgive my jumping in here, I'm following your discussion more anxiously now...

I am somewhat familiar with Jim Hoffman's arguments but believe he is missing important points which would both help and hurt his research. My background and training are architecture and electronics engineering; so the physics models I'm most accustomed to working with are statics (equilibrium) and waves (electromagnetism). I studied the WTC TOWERS quite extensively in the 1980's and know for a fact that an out-rigger tower cannot POSSIBLY "pancake" without seismic disturbance; even then, outriggers are designed to retard motion on four axes (lateral, vertical, and rotational).

It could be shown that there are unusual (possibly unreconcilable) differences between these failures, and a provable commonality of missing energy. Whether or not I could make that case would represent quite a challenge, especially since I'd have to brush up on kinematics and fluid dynamics (which could take several days for this purpose).

...

I'm not a "conspiracy nut" but I know that there are several incoherencies at play which are fatal to the popular "sanctioned" or "official" account, especially the bad science drafted to support the meme of "planes hit buildings, buildings catch fire, buildings fall down"... which is, sadly, our new contemporary "lone gunman" myth.

(Aside: It doesn't seem very well known that the House Select Committee on Assassinations declared JFK's death to have been the result of a conspiracy in 1978 -- but funny how, even as recently as last February (2005) Peter Jennings was STILL peddling such "lone gunman" myths!)

...

I think it is easily agreed that plane crashes alone do not explain either tower collapse, and had there been no planes, that ordinary hydrocarbon fires would not have brought them down; this makes it unreconcilable that building 7 also fell. Only FEMA had the honesty and integrity to say that "the causes [...] remain unknown at this time." To me, it's still a mystery *how* they were caused (as well- by whom), but it is no mystery that they were all deliberate demolitions (not necessarily "controlled"- and that should be a gravitational point of great distinction)... the towers resulting in explosive silo-type collapses, and Building 7 in a core-failure implosion.

...

Sorry, back on topic:

[...] sufficiently weakened by the fire resulting from the impacts that the upper floors collapsed

Accepting this is the whole key to the progressive collapse door; I haven't accepted it (yet) because (1) the tower collapses then happened in reverse order (the least damaged building with the least severe fires collapsed first) and in my estimation much too short a time frame (only 56 minutes for the South Tower? this is where my jury is still out- because fire fighters on the scene said they could "knock them down with two lines"), and (2) the worst physical damage to Building 7 (southwest corner?) is not where the collapses began (top dead center, indicative of core failure).

Ofcourse, my two reservations are a weak defense because "scientific skepticism" only really works if one can provide a "better theory," which I confess, at this point, I do not have...

But wouldn't mind looking for, either way.

Cheers

 

[Ophiolite]

Heat required to weaken steel? It gets red-hot at 1650 Celsius (3000F), so let's assume it weakens at 1000C (1800F).

I am somewhat confused. In an earlier post you had claimed to know alot about what structural components do what and how they behave.

Yet here you are making assumptions - invalid assumptions I might note - about steel properties. Steel, much like your argument, weakens at much lower temperatures, by significant amounts. Did you think that by providing such detailed analysis of the chemical energy released we would overlook this obvious and glaring weakness in your thesis? Think again. You may wish to do so after perusing this document:

http://www.rautaruukki.com/tenw1f.nsf/0/dd66dc4288a24b91c2256a4e00212555/$FILE/TKK1fin.pdf

For those of you unwilling to wade through this detailed report a crude summary is to say that significant reduction in strength is found at 200 degerees C and by 500 degrees C steel's yield strength is reduced by about 50%. [Note that this report examines specifically the response of structural steels to fire and predates the 911 attack.]

 

[Hurricane Angel]

No need to get patronizing, I can explain why I "assumed" this. Steel needs to be at least at 1000C in order to be effectively worked, and forged, according to a coffee discussion I recently had. Me being to lazy to confirm this is mine own fault, and unfortunately regarding my "earlier boastful comment" I probably forgot to specify thermochemistry and metallurgy comes in 2nd year engineering, something which failed to interest me enough.

The only result of this 1000 -> 500 switcheroo is that regarding the steel, the energy potential has doubled, which is still short unfortunately.

Can we get back to the lack of sufficient kilojoules necessary to effectively heat the metal workings?

 

[The Devil Inside]

the steel wouldnt have melted yet. regardless of how it was built,this is the material they were made of (the wtc towers), there should have been no collapse.

 

[funkstar]

Hurricane,

You're also assuming that jet fuel was the only thing burning in those fires. Now, I've personally sat in a container (wearing full firefighter gear, of course) and watched a couple of plywood boards burn. Flash fires in the smoke, temperatures in excess of a thousand degrees celcius at the ceiling, and several other things made that an altogether unpleasent environment, that. The amount of gasoline we used to light the boards was almost negligable, and certainly not a significant factor.

Four or five floors worth of combustible materials such as carpets, chairs, tables, papers, wire insulation, isolation, wall boards, floor planks and padding etc. binds a lot of energy. Any defeciency in energy is more than made up for by this.