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Has Anyone Seen A Realistice Explanation For Free Fall Of The Towers?

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RenaissanceBiker said:
I'm a licensed professional engineer in 4 states. I have a Master's degree in Civil Engineering. I knew about the basic structure of the WTC towers from school and other technical seminars on structural engineering. On 9/11 I was in my office when a co-worker told me to come and see what was on television. After hearing the announcers mention that the planes were fully loaded for long flights the term "jet fuel" would not leave my mind. I watched the smoke for about a minute and said, "Those towers are going to fall." Jet fuel burns much hotter than the fire protection on the structural steel was designed for. Additionally, I figured the impact may have knocked some of it off. Those around me were surprised and asked if I should call someone. I said, "Surely they know that." It was horrible to think that maybe they didn't. They fell exactly how I pictured it. There is no coverup. The burning jet fuel caused the towers to collapse. There is no evidence to suggest otherwise.
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I am going to nit pick your last comment, as there is no evidence to suggest a sustained supply of jet fuel lasting 56 and 102 minutes respectively.

The Jet fuel in each crash was most likely consumed within the first 5-10 minutes of the fire. The containers holding the fuel were destroyed, so the fuel was either part of the initial fire ball, or was dispersed in the direction of travel and in response to the compression wave of the initial explosion.

The rapid spread of the initial phases of the fire was doubtless linked to the dispersion of the fuel, which (along with other flammable things) distributed itself throughout the impact zone.

Your statement is technically incorrect. Everything that the jet fuel set fire to, and the fire that kept burining Everything Else, is what weakened over time the various damaged and whole load bearing structures, which caused the towers various members to lose the ability hold the loads in floors above the impact and fire damaged zone, and thus collapse. :D Cumulative dynamic loading explains the follow on destructive collapse.

For those who prefer a condensed version: The Jet Fuel began the big fire, but was consumed and thus could not sustain the fire for the time it was observed to burn. There was plenty else to burn once the temperatures were raised sufficiently to complete and sustain the fire triangle.

DR
 
Darth Rotor said:
I am going to nit pick your last comment, as there is no evidence to suggest a sustained supply of jet fuel lasting 56 and 102 minutes respectively.

The Jet fuel in each crash was most likely consumed within the first 5-10 minutes of the fire. The containers holding the fuel were destroyed, so the fuel was either part of the initial fire ball, or was dispersed in the direction of travel and in response to the compression wave of the initial explosion.

The rapid spread of the initial phases of the fire was doubtless linked to the dispersion of the fuel, which (along with other flammable things) distributed itself throughout the impact zone.

Your statement is technically incorrect. Everything that the jet fuel set fire to, and the fire that kept burining Everything Else, is what weakened over time the various damaged and whole load bearing structures, which caused the towers various members to lose the ability hold the loads in floors above the impact and fire damaged zone, and thus collapse. :D Cumulative dynamic loading explains the follow on destructive collapse.

For those who prefer a condensed version: The Jet Fuel began the big fire, but was consumed and thus could not sustain the fire for the time it was observed to burn. There was plenty else to burn once the temperatures were raised sufficiently to complete and sustain the fire triangle.

DR
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The jet fuel was likely the cause of the fire protection coating on the steel failing (in addition to the collision stripping some coating off), in the first few minutes. After that, the end was unavoidable. I think that is what he meant, from the context.
 
rwguinn said:
The jet fuel was likely the cause of the fire protection coating on the steel failing (in addition to the collision stripping some coating off), in the first few minutes. After that, the end was unavoidable. I think that is what he meant, from the context.
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Yep, thanks for expanding on it, Darth Rotor. I just made it as simple as possible for Christophera. It really doesn't matter though. He can't imagine someone with real credentials that would disagree with him.
 
RenaissanceBiker said:
Yep, thanks for expanding on it, Darth Rotor. I just made it as simple as possible for Christophera. It really doesn't matter though. He can't imagine someone with real credentials that would disagree with him.
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Hey--That was ME
Now, I'm only registered in 1 state, and a lowly ME (and only a BS at that!) to boot, but, gosh, Mr. Edison, can I get a little credit?:D

edited to fix bold
 
I didn't mean to leave you out. I quoted you and agreed, then I thanked Darth Rotor for expanding the explanation. Thanks to you, rwguinn, for clarifying my post.

My father and brother are both MEs. They joke that MEs design weapons and CEs design targets. I like to reply that civil engineers design civilizations.

edit: Yes, we do put wastewater pipes through recreational areas for a reason.
 
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RenaissanceBiker said:
I didn't mean to leave you out. I quoted you and agreed, then I thanked Darth Rotor for expanding the explanation. Thanks to you, rwguinn, for clarifying my post.

My father and brother are both MEs. They joke that MEs design weapons and CEs design targets. I like to reply that civil engineers design civilizations.

edit: Yes, we do put wastewater pipes through recreational areas for a reason.
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My youngest brother is a CE. The middle brother is a ChE. We both razz him unmercifully...
One doesn't believe in Force. One believes that Forces sum to zero. Only I know the truth.:D
ChE's design bombs. ME's design delivery systems. CE's design targets.
 
rwguinn said:
The jet fuel was likely the cause of the fire protection coating on the steel failing (in addition to the collision stripping some coating off), in the first few minutes. After that, the end was unavoidable. I think that is what he meant, from the context.
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Does not compute, in my brain.

I didn't read in NIST's report any comment on Jet Fuel dissolving the fire protective coating on the structural members.did I miss some details? Big report.

I am not smart enough on chemistry to know if the fireproofing would be rapidly dissolved by aerosol Jet A fuel, but I have my doubts. My expectation is that most of a thin/splashed layer of jet fuel would ignite as the temperature rapidly increased once the fire started, and burn off before it could dissolve the coating.

Happy to be corrected.

DR

RenaissanceBiker: I was just tweaking your nose. A friend of mine was an Army Combat Engineer (Civil Engineering degree in college) who used this line when chatting with fellow alums. "You guys build bridges? I blow them up. My job's more fun." :)
 
The jet fuel didn't dissolve the protection, it just burned hotter than the insulation was designed to protect against. Once the steel got hot enough (and weak enough) and began to deform, the insulation would fall off and the process would accelerate. The impact probably knocked a good bit of the protection off as well. I think the WTC designers assumed that fire suppression systems would limit the amount of time the structure would be exposed to heat. Sadly this was not the case with a fire of this magnitude. Your term "cumulative dynamic loading" describes the subsequent method of structural failure perfectly.

I had 2 weeks of combat engineer training as part of my Army AIT (62J). Demolitions was fun, landmine removal was scary, and installing concertina wire was a pain. Later, the only one I got to use in an actual operation was the concertina wire.
 
RenaissanceBiker said:
The jet fuel didn't dissolve the protection, it just burned hotter than the insulation was designed to protect against. Once the steel got hot enough (and weak enough) and began to deform, the insulation would fall off and the process would accelerate. The impact probably knocked a good bit of the protection off as well. I think the WTC designers assumed that fire suppression systems would limit the amount of time the structure would be exposed to heat. Sadly this was not the case with a fire of this magnitude. Your term "cumulative dynamic loading" describes the subsequent method of structural failure perfectly.

I had 2 weeks of combat engineer training as part of my Army AIT (62J). Demolitions was fun, landmine removal was scary, and installing concertina wire was a pain. Later, the only one I got to use in an actual operation was the concertina wire.
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Designing for the failure of all 4 major systems simultaneously would have been a real stretch. Under what circumstances do you anticipate 1) Major structural damage, 2) failure of passive protective systems, 3) failure of active protective systems, and 4) loss of evacuation/rescue corridors, all occurring pretty much simultaneously, and 7-800 feet up in the building?

Talk about 5-Sigma events!
 
Just thought I would add the fire ball of jet fuel had a sand blasting effect because it carried pieces of the plane and building plus anything else in the building with it. That is how the fire proofing was destroyed.
The heat of the fuel had nothing to do with the stripping of the insulation it was what the fireball carried with it.
 
I haven't read the NIST report, but that sounds resonable. Then I'm sure the fireball-pancake fairies began jumping up and down all at once. There isn't an LRFD factor that covers that so the building would fail, right Christophera? Hello?
 
rwguinn said:
Designing for the failure of all 4 major systems simultaneously would have been a real stretch. Under what circumstances do you anticipate 1) Major structural damage, 2) failure of passive protective systems, 3) failure of active protective systems, and 4) loss of evacuation/rescue corridors, all occurring pretty much simultaneously, and 7-800 feet up in the building?

Talk about 5-Sigma events!
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From NIST and the dynamics of impact/Kinetic Energy Transfer, the blunt trauma/'sandblasting'/imperfect thickness causal factor of thermal barrier damage reduced structural steel's resistance to heat prematurely. So long as the fire was burning, thermal stress was going to accrue, and creep. The thermal barrier break down was always an issue, based in the NIST comments, and could only prevent thermal stress for "X" hours in any event.

Heat protection itself was, in the NIST tests, withstood the 2 h standard and beyond, as I read the report. The report clearly spelled out that without the initial damage to the structural members, the thermal stress alone would not have done the deed, and without the added thermal stress, as we saw, the impact alone tore a hole in but did not cause structural failure beyond the local areas effected.

DR
 
Crazy Chainsaw said:
Just thought I would add the fire ball of jet fuel had a sand blasting effect because it carried pieces of the plane and building plus anything else in the building with it. That is how the fire proofing was destroyed.
The heat of the fuel had nothing to do with the stripping of the insulation it was what the fireball carried with it.
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And don't forget, the Jet Fuel was passing through the building at 500 MPH. In the Pentagon simulations they determined that the Jet Fuel itself had severed a lot of the steel columns, simply because of the enormous speed of the liquid.

So the Jet Fuel in the WTC that didn't ignite acted like a super-mega sand blaster and the fire proofing didn't stand a chance.

-Andrew
 
RenaissanceBiker said:
The jet fuel didn't dissolve the protection, it just burned hotter than the insulation was designed to protect against. Once the steel got hot enough (and weak enough) and began to deform, the insulation would fall off and the process would accelerate. The impact probably knocked a good bit of the protection off as well. I think the WTC designers assumed that fire suppression systems would limit the amount of time the structure would be exposed to heat.
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The protection was knocked off by impact. Additionally some columns were not protected on all faces and quite a bit of the spray on protection was unevenly applied (also some of the protection failed to adhere properly, the NIST report has several pictures from inspections that show bare joists).

NIST tested all these scenarios and on properly applied, fully applied non-blown off protection probably would've been sufficient to last long enough for fire fighters to get the fires under control.

If you refer to sprinklers for fire suppression, then I don't believe the designers would consider them as limiting the structure exposure to heat. Sprinklers are generally hung below the joists and under the drop ceiling. There is no way for the water to spray back up and cool the joists and columns are usually hidden behind drywall. I don't think the cooling effect on the floor would be significant either (mostly due to the limitation that sprinklers only go off in the area where there is heat, not across a whole room or floor). The primary effect that would limit heat is sprinklers putting the fire out, but I'm not sure you should design around the fire being short duration due to sprinklers.

I'm also not sure the WTC had sprinklers. In the 60's those weren't as pushed by fire codes as they are today.

BTW, one of the towers had a significant fire in it in the 70's. I believe it lasted several hours. It should've been as hot as the main fires in 9/11. The protection did not burn off at that time, nor was the structure affected.
 
christophera - you claim the concrete core of the WTC was being build 7 floors beneath the top floor being worked on. Please explain what the floors were attached too while they waited for the core to catch up to them.
 
The Concrete Core Created A Ridgid Stable Tower.

A tiny bit of flex is always going to exist. Steel deforming from designed dimensions caused failures of steel shear walls. Concrete shear walls hold the shape, steel then carrys the loads.


kevin said:
christophera - you claim the concrete core of the WTC was being build 7 floors beneath the top floor being worked on. Please explain what the floors were attached too while they waited for the core to catch up to them.
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The floors were attached to the interior box columns and perimeter box columns by the floor beams fastened to the columns. The Concrete Core brought rigidity and stability to the steel structure as it advanced.




The significance of the concrete core is seen here.

Demolition
 
Christophera said:
A tiny bit of flex is always going to exist. Steel deforming from designed dimensions caused failures of steel shear walls. Concrete shear walls hold the shape, steel then carrys the loads.




The floors were attached to the interior box columns and perimeter box columns by the floor beams fastened to the columns. The Concrete Core brought rigidity and stability to the steel structure as it advanced.




The significance of the concrete core is seen here.

Demolition
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Christopera,

I believe this fully addresses your "concrete core".
 
Christophera said:
A tiny bit of flex is always going to exist. Steel deforming from designed dimensions caused failures of steel shear walls. Concrete shear walls hold the shape, steel then carrys the loads.




The floors were attached to the interior box columns and perimeter box columns by the floor beams fastened to the columns. The Concrete Core brought rigidity and stability to the steel structure as it advanced.




The significance of the concrete core is seen here.

Demolition
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The core was a feature in all tube frame buildings that is true, I have seen the original designs the core allowed the building to sway only eight inches in a 100 mile per hour wind, the only problem the core was designed only to resist side loading, not compression load.
Plus you main problem is not what would destroy the core, the weight of the building will do that, but what would make an explosive survive the intense sonic shock of the plane striking the inner columns.
Concrete is fragile it was not enforced to hold the building, but so it could hold up its own weight. Add to much weight on top, and it is gone.
PS. people are confusing the design of the high speed elevator shaft which had a drywall board construction with the main Central core, which was designed as a movement arrester with out it the building would have made people sea sick from oscillation in the wind.
 
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