Hardfire: Physics of 9/11

It didn't take long for Pee Wee Herman of CIT to chime in....

Craig Ranke said:
He badly failed in a desperate attempt to refute the information in this thread and went running away with his tail between in his legs.
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What a dolt.
 
Hi Ryan,

Thanks for your video. I am looking forward to parts II - ?

If I understood correctly you stated that the pressures involved in the simple fuel impact model were approaching what is needed to fail the columns. I'm concerned that this will be misunderstood. The pressures you calculated were around 4000-9000 psi but the yield stress of the weakest columns was around 32,000 psi. A column may indeed fail due to the force caused by pressure over a large enough area but the pressure itself is not nearly sufficient.

There was a legitimate (by all appearances) article a while back that concluded that if the planes were going even faster they would have caused less damage. I think I posted a link over a year ago. Have you seen that article and do you have any comments on this phenomena?

/Greg
 
GregoryUrich said:
There was a legitimate (by all appearances) article a while back that concluded that if the planes were going even faster they would have caused less damage. I think I posted a link over a year ago. Have you seen that article and do you have any comments on this phenomena?

/Greg
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Hey Greg, do you still have the link to this? Due to the trajectory of the planes I find this hard to believe.
 
3bodyproblem said:
Hey Greg, do you still have the link to this? Due to the trajectory of the planes I find this hard to believe.
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It seems I remembered that incorrectly. The damage at higher speed was apparently in relation to a boundary value for column thickness. Here's the abstract: http://cedb.asce.org/cgi/WWWdisplay.cgi?0527767

By the way, there is an interesting article (available from ASCE) on the impacts:

Structural Responses of World Trade Center under Aircraft
Attacks

Yukihiro Omika; Eiji Fukuzawa; Norihide Koshika; Hiroshi Morikawa; and Ryusuke Fukuda

Most interesting is that they show stresses > yield (= damage) in the perimeter columns.
 
There are at least a couple more:

How the airplane wing cut through the exterior columns of the World Trade Center; Wierzbicki, T.; Teng, X. International Journal of Impact Engineering; 2003 Vol. 28, p601-625. Abstract:
The problem of the airplane wing cutting through the exterior columns of the World Trade Center is treated analytically. The exterior columns are thin-walled box beam made of high strength steel. The complex structure of the airplane is lumped into another box, but it has been found that the equivalent thickness of the box is an order of magnitude larger than the column thickness. The problem can be then modeled as an impact of a rigid mass traveling with the velocity of 240 m/s into a hollow box-like vertical member. The deformation and failure process is very local and is broken into three phases: shearing of the impacting flange; tearing of side webs; and tensile fracture of the rear flange. Using the exact dynamic solution in the membrane deformation mode, the critical impact velocity to fracture the impacted flange was calculated to be 155 m/s for both flat and round impacting mass. Therefore, the wing would easily cut through the outer column. It was also found that the energy absorbed by plastic deformation and fracture of the ill-fated column is only 6.7% of the initial kinetic energy of the wing.
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IIRC the paper above corrected some errors in Wierzbicki's 2002 MIT paper.


Impact of the Boeing 767 Aircraft into the World Trade Center. By: Karim, Mohammed R.; Fatt, Michelle S. Hoo. Journal of Engineering Mechanics, Oct2005, Vol. 131 Issue 10, p1066-1072. From the abstract:
It was found that about 46% of the initial kinetic energy of the aircraft was used to damage columns. The minimum impact velocity of the aircraft to just penetrate the exterior columns would be 130 m/s. It was also found that a Boeing 767 traveling at top speed would not penetrate exterior columns of the WTC if the columns were thicker than 20 mm.
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That last finding is surprising to me. I haven't read the whole article. (Much of the plane would still enter the building through the windows, of course.)
 
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767.jpg

I'll reproduce the entire articles if no one reports me for rule 4:boxedin:
 
GregoryUrich said:
Hi Ryan,
...

There was a legitimate (by all appearances) article a while back that concluded that if the planes were going even faster they would have caused less damage. I think I posted a link over a year ago. Have you seen that article and do you have any comments on this phenomena?

/Greg
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No higher speeds cause greater damage, but yep, if it was really fast it would cut a hole out and keep going, maybe not less damage, just not all the KE used in one place. The article said if the walls are 20mm, then at top speed the 767 would not enter the building. The columns are not 20 mm thick.

The cool part is Robertson design for a 707 impact is confirmed it would take 108m/s to penetrate the wall, and Robertson’s design at 80 m/s would only partially penetrate the WTC exterior and survive since fire systems over multiple floors would not be destroyed.


Flight 11 was going 210m/s – some core damage
Flight 175 was going 263m/s – more core damage

A faster plane causes greater damage. Got physics?

darn, see above posts for more -
 
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A link won't work because you have to pay to have access. I have access through my university's database.
 
Ah, gotcha. Reprinting the whole thing is verboten, as you know.
 
Gravy said:
A link will suffice.

I note that they assume "top speed" to be 240 m/s, or 536 mph, but most estimates put flight 175's speed at impact at somewhere between 540 and 590 mph.
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I wonder how they came up with their top speed. Did they just pick a speed, or talk to Boeing about a one time top speed that would not do significant damage or have major control problems?

The impact of Flight 93 was over 600 mph. It would be easy for 175 to be at 590 mph in a dive and throttles up, the plane is not being used again so damage done by speeding, and/or lost of control are moot as 175 was lined up to impact the WTC even if control was being compromised by exceeding the book top speed of 350 knots (~397mph).

I would not recommend flying a 767 at 590 mph, you are in unknown territory, doubt the 767 was flight checked at low attitude at 590 mph. Maybe .8 MACH, 470 knots, 534 mph. Bingo – top speed could be a flight test point.
 
R.Mackey said:
Can we stop talking about Heiwa's delusions, please? Thanks!
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Good idea. Topic is Ryan's paper and PPP/slides how to model the WTC 1 crush down.

Maybe scale modelling in 1-D is not the right way. Full scale, 3-D, computer simulations are probably better to avoid any scale effects, the latter correctly described by Ryan.

I still have my doubts about slide Model Process, Step 2, where upper part C is a yellow (rigid?) box, lower part A is another narrow box, and the 280+ columns of WTC 1 are two blue/white/blue short lines below part A.

It should be made clear that the cross area of the boxes is >4000 m² and that the lower box A is just a thin concrete floor, that will deform under pressure. The 'inelastic collision' represented by a red, straight line between the boxes and red/orange 'flames' are a little misleading.

I suggest that some photos of upper part C before, at and after inelastic collision with part A are added to the Ryan presentation.
 
Pardalis said:
I thought it was the Hardfire video? :confused:
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You are of course right and the Hardfire video is mostly about part 1 of Ryan's PPP show, e.g. the plane slicing the south wall of WTC 2 and some references to a plane crushing a composite deck on an aircraft carrier. I have no problems with that; I can deform the steel plate (part A) of a deck on a ship by running a heavily loaded rubber tyre (part C) over it, but as the steel deforms due to high pressure of a rubber tyre (!!), the interface changes and there is no crush down, etc. Ryan tells us how much he values truth and physics and hints that there will be a part 2 Hardfire video, where modelling will be presented, and then we are given a pre-view of the model PPP show in post #1 and there I have some objections as outlined above, which I hope Ryan appreciates? :)
 
If i way, i would also like to pose a question about part 2. Modeling, from
Ryans supplement to the Hirdfire presentation: "some basic physics of 9/11"

I am looking at "Model process", part 2 and 3, and i wonder, how come the impact is only transfered to the columns of the first floor, and not the second? ( and the third and the forth and the fifth, and so on, had there been more floors)

You say: "colums absorb impact until they fail and buckle", how come the first columns are the only ones to absorb the impact?


Or are they not?


Niclas
 
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Ryan,

I'm interested in the way in which NIST generates those Pressure-Impulse curves. Could you elaborate.

Second, it seems to me that a "bringing the slug of fuel to a stop" is a good first approximation, but is still physically not realistic. (You wouldn't find the slug sitting there when a column survived.)

In reality, you form a stagnation bow wave in front of the column, and a majority of the fuel gets diverted around the column.

How about a standard hydrodynamic model of a flat front object plowing thru a liquid. Your pressure term is identical to a flat plate, with a drag coefficient of 1, instead of the standard drag coefficient of 2.

I'm just looking for the next more realistic model.

Great presentation, btw.

tom
 
Niclas said:
If i way, i would also like to pose a question about part 2. Modeling, from
Ryans supplement to the Hirdfire presentation: "some basic physics of 9/11"

I am looking at "Model process", part 2 and 3, and i wonder, how come the impact is only transfered to the columns of the first floor, and not the second? ( and the third and the forth and the fifth, and so on, had there been more floors)

You say: "colums absorb impact until they fail and buckle", how come the first columns are the only ones to absorb the impact?


Or are they not?
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I think that depending on shape,such waves won't transfer so well on significant lenght of steel.Second,impulse(I = F[N] X t).Of it is very short but intesive impuls,it won't transfertoo much,but instead will absorb and eventuallly break.

I think that time-negth of impulse in WTC was on scale of 1/100 second.
 
Klimax said:
I think that depending on shape,such waves won't transfer so well on significant lenght of steel.Second,impulse(I = F[N] X t).Of it is very short but intesive impuls,it won't transfertoo much,but instead will absorb and eventuallly break.

I think that time-negth of impulse in WTC was on scale of 1/100 second.
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Perhaps i am misunderstanding you, but i see no mention of scale in
Ryans experiment, it seems to be independent of the lenght of the steel,
"h" in the model, is it not the relationship between "M" and "h" that
matters?
 
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