RFC: NIST's Magic Bullet: Removal of Fireproofing in WTC1 Impact

[GregoryUrich]

OK, I've now read the paper in question. I'm sorry, Gregory, you are completely wrong.

The main reason is that we have no idea how much energy fireproofing dislodgment actually dissipates. On Page 10 you state the following:


The problem is that you make the assumption, incorrectly, that the KE was distributed over this entire area all at once. It doesn't work like that. Think of the KE as being contained in a wavefront, but this KE is not necessarily consumed. The wave will disspiate due to three factors -- (a) dispersion into larger space, (b) damage to the structure, i.e. inelastic collisions, and (c) turbulence becoming heating. But since the fireproofing is so fragile, it dissipates virtually nothing. The wave can pass over the fireproofing, dislodging it, and continue with negligible dissipation.

This is the same mistake that Kevin Ryan and so many others have made. The fireproofing doesnt expend 10^5 J/m^2. That's the strength of the wave required to shake it loose. It's like saying I can stand in the ocean and stay on my feet if a wave no higher than 1m washes over me -- if I get knocked down, that doesn't mean I absorbed an entire 1m wave. The wave barely notices me whether I fall down or not.

The other problem, again, is in your assumptions regarding ricochets and lift. The flow inside the structure will be completely turbulent. Gravity will have virtually no effect, and "lift" -- actually drag -- can occur up or down with virtually no bias. Again, if you want to see this effect, estimate the Reynolds and Froude numbers of the flow and see what you get.

NIST's approach, again, was to use LS-DYNA. This predicts, to reasonable granularity, what the flow and momentum of individual particles of debris were throughout the structure. NIST also keeps track of dissipation due to heavy furnishings and transfer to the structure. NIST does not add additional dissipation caused by the fireproofing, but to first order, this is correct. Instead, NIST estimated a lower bound for energy per area (should really be impulse, shame on NIST) required to dislodge the fireproofing, and made a hard cutoff -- after the wave falls below this value, no more dislodgment.

It's coarse, but it is valid. NIST can be criticized for not really finding the lower bound, not attempting other types of dislodgment (e.g. hot jet without any debris, sand-blasting, shock, etc.), and so on, but their method is appropriate.

A rather categorical assessment considering that your "blast wave" only blew out a few windows. What energy level is required for that? A tiny over-pressure and a fast moving bolt, so I don't buy your "blast wave".

I think you are missing an important point. NIST didn't show that a certain impulse or pressure would remove SFRM. They showed that impact by hard objects at 60 degrees or less from perpendicular can remove fireproofing. Once the object hits, its energy is spent or the energy will go into continued motion or rebounding. However, the probability is extremely low that the motion will be in a direction which could cause more SFRM damage.

So if the flow was "completely turbulent" as you say, wouldn't the debris vectors be normally distributed in terms divergence from the original trajectory (ignoring collisions for the moment)? Unless completely turbulent means that gravity is somehow turned off, every single debris vector is subject to gravitation giving a general and significant tendency of displacement towards the floor over time. In case you missed it, I have ignored gravity.

I have taken account for that it is equally likely for drag or turbulence to cause divergence both upward and downward. Given the system as a whole, all of the mechanisms I decribe will affect some proportion of the debris in one direction or another.

 

[Loss Leader]

This would be fantastic if the fireproofing had been applied at all competently.

I've never seen a scholarly paper before that defended the building and construction techniques of the mafia.

 

[R.Mackey]

A rather categorical assessment considering that your "blast wave" only blew out a few windows. What energy level is required for that? A tiny over-pressure and a fast moving bolt, so I don't buy your "blast wave".

Ah, no.

The "blast wave" is the dynamic pressure from the impact itself. It not only blew out windows, it even dislodged (a few) steel columns on the other side of the structure.

If that terminology bothers you, think of the leading edge of the debris field. It's a wave. Its dissipation is actually quite low. You cannot sum the energy over the entire area it passes over and add it all together, because it wasn't in all those places at the same time. It's like trying to compute the fuel efficiency of a car by computing its kinetic energy at every single point along a racetrack and adding them all together. That's a wild overestimate.

I think you are missing an important point. NIST didn't show that a certain impulse or pressure would remove SFRM. They showed that impact by hard objects at 60 degrees or less from perpendicular can remove fireproofing. Once the object hits, its energy is spent or the energy will go into continued motion or rebounding. However, the probability is extremely low that the motion will be in a direction which could cause more SFRM damage.

Kevin Ryan also made this mistake. After impact, each random piece of debris will ricochet elastically, unless it damages the surface underneath -- and you've accounted for structural damage elsewhere. In practice, since these are small pieces at subsonic speed hitting steel substrate, the rebounds will be largely elastic. Furniture impacts are probably less so, but this all part of the LS-DYNA model.

As for "in a direction which could cause more SFRM damage," nonsense. It's contained in the structure. It has nowhere else to go.

So if the flow was "completely turbulent" as you say, wouldn't the debris vectors be normally distributed in terms divergence from the original trajectory (ignoring collisions for the moment)? Unless completely turbulent means that gravity is somehow turned off, every single debris vector is subject to gravitation giving a general and significant tendency of displacement towards the floor over time. In case you missed it, I have ignored gravity.

"Over Time" is the key. Time here is half a second -- giving you at most 5 m/s of velocity, compared to over 200 m/s from kinetics. Gravity is irrelevant at this time scale.

Again, Froude number. Calculate it. This tells you the relative contribution of gravity to the flow in the Navier-Stokes equations. It is trivial. Dynamic forces will dominate, and those forces are turbulent. The only exception is for extremely large fragments, i.e. engine cores, that would travel more or less ballistically. NIST's results capture both of these effects.

I have taken account for that it is equally likely for drag or turbulence to cause divergence both upward and downward. Given the system as a whole, all of the mechanisms I decribe will affect some proportion of the debris in one direction or another.

You're also arguing from energy. As I've already shown, the energy isn't being accounted for properly, so this is really irrelevant, but think of it this way. For a 1 kg chunk of debris, the maximum energy you're going to gain from gravity is about 30 N m, since at most you'll get a piece that "falls" the height of one floor. Otherwise, it'll bounce and recover some of that gravitational energy as gravitational potential.

By comparison, the KE of that 1 kg chunk is 20,000 N m. Almost three orders of magnitude higher.

Gravity is irrelevant here. Its bias on the trajectories of individual fragments will be almost undetectable.

 

[GregoryUrich]

He is saying that, and it isn't correct, as I've pointed out to him before. The dynamics of impact will be extremely turbulent. This is why, for instance, the basically horizontal impacts created enormous vertical loads on the floors near the impact. A similar thing will happen with the fireproofing.

Dislodgement of SFRM on the south side is not the same as an aircraft being wedged between the floors. Are you serious?

Regarding NIST's "energy" estimate, we need to be very carefuly about what NIST is saying. Their energy estimate is not an estimate of total energy. Instead, it is an estimate of the random kinetic energy per surface area, at the blast front, and the value decays as a function of time and distance from impact. It's a strange convention and cannot be treated with the usual dimensional analysis, particularly because this energy would be conservative if all debris impacts were elastic.

Yes, we need to very careful about what NIST is saying. Here is what they said:

Need I say any more?

Doesn't mean I won't...

Note that they use the speed of aircraft fragments as they approached the core as opposed to leaving the core. They do use the lower bound, I'll give them that much credit. Since the core was full of stuff (roughly 1,000 tons of stuff over the four floors), we can expect significant energy dissipation through the core. If we look at the normalized aircraft momentum at 0.3 sec when the first material actually starts leaving the core, we can see that the energy has been reduced by a factor of 4. Another 0.1 seconds and the energy is reduced by a factor of 4 again.

 

[Myriad]

If I'm interpreting it correctly, Gregory's paper is also ignoring the kinetics of secondary debris. If a piece of the plane "plows" downward or horizontally through office contents and floors, it makes it highly likely that pieces of whatever it plows through will be sprayed outward in all directions, with an angular distribution generally resembling a cardioid relative to the initial trajectory of the primary debris.

Any more detailed analysis such as the paper proposes would surely have to focus on the fireproofing of the bottom chords of the trusses. Those bottom chords are simultaneously the most vulnerable to airborne debris impacts (especially from secondary debris) because of their spatial positions, the most likely to vibrate due to heavy lateral impacts in such a way as to possibly dislodge fireproofing at a distance from the impact point, and the most consequential in terms of compromising the whole truss if even isolated portions of their spans are heated by the fire.

Because of this, I think it's likely that NIST could be correct (though others disagree) that fireproofing damage was a necessary condition for the collapse, without necessarily being correct about the total amount of fireproofing damage that occurred. Also remember that a primary purpose of the study was to expose vulnerabilities in structural designs, and mechanical damage to sprayed-on fireproofing materials is clearly a potential and previously unrecognized vulnerability under some scenarios (scenarios involving a possible combination of mechanical stress and fire hazard, such as vehicle collisions, earthquakes, or bombs) -- and not only that, it's a vulnerability that could be reduced by various types of measures. I could understand their desire to emphasize this causing them to overstate the certainty with which they judged that the collapse "would not have occurred" without it.

Gregory, regarding the basic presentation of your paper, I suggest adding some introductory text at the start of your "Debris trajectory scenario" section, explaining what it is you are setting out to do, and your methods. Right now it's a bit confusing. I eventually figured out that you were making a determination of the overall spatial distribution of debris based on assigning probabilities for different scenarios for how each individual piece of airplane debris might move through the structure. But since you go directly from presenting NIST data right into your individual scenarios without any discussion of the methodology you're about to use, it took me a while to follow the argument.

Respectfully,
Myriad

 

[R.Mackey]

Dislodgement of SFRM on the south side is not the same as an aircraft being wedged between the floors. Are you serious?

I'm finding it increasingly difficult to follow you. The aircraft isn't strong enough for any "wedging" to occur. Apart from a few solid structures, after initial contact the aircraft is basically a fluid phenomenon -- a density flow.

Yes, we need to very careful about what NIST is saying. Here is what they said:

Need I say any more?

Doesn't mean I won't...

Note that they use the speed of aircraft fragments as they approached the core as opposed to leaving the core. They do use the lower bound, I'll give them that much credit. Since the core was full of stuff (roughly 1,000 tons of stuff over the four floors), we can expect significant energy dissipation through the core. If we look at the normalized aircraft momentum at 0.3 sec when the first material actually starts leaving the core, we can see that the energy has been reduced by a factor of 4. Another 0.1 seconds and the energy is reduced by a factor of 4 again.

Yes, that is exactly right. The difference between what you're doing and what NIST is doing is this: NIST is taking the aircraft KE and dividing it into the area of the wave front. You are taking the KE and dividing it into the area the wave passes over. Dimensionally they are the same, but you cannot replace one with the other. That's why your calculation makes no sense.

Likewise, NIST is describing energy dissipation over time, but you are describing it over distance. You are correct that after 0.3 seconds, NIST predicts the energy has dropped by a factor of 4. But translating that 0.3 seconds into distance depends on where we are relative to the impact point. Along the direction of travel, 0.3 seconds is pretty far -- most of the way across the structure. Perpendicular, it's less. This is why NIST's fireproofing dislodgment estimate is basically a semi-ellipse radiating from the point of impact.

I also remind you that the dissipation predicted by NIST is an output of the LS-DYNA model. That means they've already applied energy transfer to the structure to arrive at that total. You cannot take their normalized momentum curve and layer dissipation mechanisms on top of it again, because to do so is double-dipping into the energy budget.

 

[T.A.M.]

Theoretically (not likely, but possible), no damage to fireproofing had to be done, as enough may have already fallen off...

Adhesion failures were common, likely because of the exposed conditions of the columns
and the inherently low bond strength of the SFRM.
Inspections of the shafts and accessible columns were reported as early as 1971. Problems were noted in
the form of fallen insulation or with the over-spray material used to provide a harder surface. In 1993, the
Port Authority commissioned Leslie E. Robertson Associates (LERA) to carry out a continuing Structural
Integrity Inspection Program to appraise the condition of the accessible columns located in the core of the
towers (see NIST NCSTAR 1-1C). The columns were inspected visually for signs of rusting, cracking,
bowing, and loss of thermal insulation. During the first inspection, carried out in 1993, particular shafts
were chosen based on the quantity and types of accessible columns, and the convenience to the Port
Authority. Subsequent inspections involved sampling of the structural components and assemblies,
which were more important to the structural integrity of the towers, and at locations with a relatively
higher potential for defects and problems. The Structural Integrity Inspection Report21 stated that the
accessible columns in selected elevator shafts in WTC 1 and WTC 2 were “generally in good condition,
no structural deficiencies such as cracking or bowing were found, the most common irregularities
observed were missing fireproofing and light surface rusting of the exposed steel.”

From NIST 1-6

Anyone accusing NIST of anything remotely sinister, should look at how conservative they were in calculating the removal of fireproofing, and its impact.

For instance, they did not include the "Gaps" in fireproofing, from fallen insullation, or gaps in spraying, simply because they could not accurately quantify it. Now certainly alot of circumstantial evidence supports it, but they did not include it.
As well, they did not include any allowance of potential removal of fireproofing from vibration, even though it was most likely that this had an effect.

TAM

 

[GregoryUrich]

Ah, no.

The "blast wave" is the dynamic pressure from the impact itself. It not only blew out windows, it even dislodged (a few) steel columns on the other side of the structure.

Poppy-cock. The nose gear went straight down the hallway and took out one panel. There is a photo of the nose gear wedged in the panel on the ground on the far side of the church (whatever it's name was).

If that terminology bothers you, think of the leading edge of the debris field. It's a wave. Its dissipation is actually quite low. You cannot sum the energy over the entire area it passes over and add it all together, because it wasn't in all those places at the same time. It's like trying to compute the fuel efficiency of a car by computing its kinetic energy at every single point along a racetrack and adding them all together. That's a wild overestimate.

I agree, they wildly over-estimated the energy, but that's as far as I'll go. They took the energy of the entire volume and applied it to a plane area parallel to the z-axis and perpendicular to the general momentum. Then they applied that energy to four surfaces parallel to the general momentum.

Kevin Ryan also made this mistake. After impact, each random piece of debris will ricochet elastically, unless it damages the surface underneath -- and you've accounted for structural damage elsewhere. In practice, since these are small pieces at subsonic speed hitting steel substrate, the rebounds will be largely elastic. Furniture impacts are probably less so, but this all part of the LS-DYNA model.

As for "in a direction which could cause more SFRM damage," nonsense. It's contained in the structure. It has nowhere else to go.

I'd like to see you come up with a reasonable effective ricochet factor considering that most debris that hit the SFRM first had to go through the ceiling tiles and mostly hit the SFRM covered corrugated steel decking. The next most likely rebound is off of office furniture which will not be elastic.

"Over Time" is the key. Time here is half a second -- giving you at most 5 m/s of velocity, compared to over 200 m/s from kinetics. Gravity is irrelevant at this time scale.

Again, Froude number. Calculate it. This tells you the relative contribution of gravity to the flow in the Navier-Stokes equations. It is trivial. Dynamic forces will dominate, and those forces are turbulent. The only exception is for extremely large fragments, i.e. engine cores, that would travel more or less ballistically. NIST's results capture both of these effects.

I think you are making a Froudian slip. Avg. displacement would be 1.25 m downward unless gravity and randomness is somehow cancelled out by turbulent flow. I don't know how to calculate the Froude number. Maybe you could do that for us?

You're also arguing from energy. As I've already shown, the energy isn't being accounted for properly, so this is really irrelevant, but think of it this way. For a 1 kg chunk of debris, the maximum energy you're going to gain from gravity is about 30 N m, since at most you'll get a piece that "falls" the height of one floor. Otherwise, it'll bounce and recover some of that gravitational energy as gravitational potential.

Except that down low is where all the stuff is, which when impacted will reduce the momentum of the impacting debris. Every trip to the floor is most likely a loss of energy.

By comparison, the KE of that 1 kg chunk is 20,000 N m. Almost three orders of magnitude higher.

Gravity is irrelevant here. Its bias on the trajectories of individual fragments will be almost undetectable.

It's bias on the mean horizontal trajectory is 1.25m downward.

 

[GregoryUrich]

I'm finding it increasingly difficult to follow you. The aircraft isn't strong enough for any "wedging" to occur. Apart from a few solid structures, after initial contact the aircraft is basically a fluid phenomenon -- a density flow.



Yes, that is exactly right. The difference between what you're doing and what NIST is doing is this: NIST is taking the aircraft KE and dividing it into the area of the wave front. You are taking the KE and dividing it into the area the wave passes over. Dimensionally they are the same, but you cannot replace one with the other. That's why your calculation makes no sense.

Likewise, NIST is describing energy dissipation over time, but you are describing it over distance. You are correct that after 0.3 seconds, NIST predicts the energy has dropped by a factor of 4. But translating that 0.3 seconds into distance depends on where we are relative to the impact point. Along the direction of travel, 0.3 seconds is pretty far -- most of the way across the structure. Perpendicular, it's less. This is why NIST's fireproofing dislodgment estimate is basically a semi-ellipse radiating from the point of impact.

I also remind you that the dissipation predicted by NIST is an output of the LS-DYNA model. That means they've already applied energy transfer to the structure to arrive at that total. You cannot take their normalized momentum curve and layer dissipation mechanisms on top of it again, because to do so is double-dipping into the energy budget.

I having trouble following you too. I'll try again tomorrow.

 

[T.A.M.]

Can someone point me to the section in NIST 1-6 where they talk about debris taking out the SFRM directly? My reading (right now on page 140) is that they made assumptions the SFRM was dislodged based on structural damage from aircraft impact and debris on an area by area basis.

Is there somewhere else in this section of the NIST report, where they reveal that they actually calculated or modeled SFRM removal, rather than assumed based on structural damage to columns and partitions in given areas.

Insulation was assumed to be dislodged from core columns only if the columns were subject to direct
debris impact that failed wall partitions in the immediate vicinity of the column. For exterior columns, the
debris impact was required to be strong enough to damage or destroy room furnishings (modular office
workstations) adjacent to the columns. For floor trusses, the debris impact was required to be strong
enough to damage or destroy room furnishings (modular office workstations) in the same area of the
affected floor.

From page 150 of NISTNCSTAR 1-6

Thanks

TAM

 

[Kent1]

Poppy-cock. The nose gear went straight down the hallway and took out one panel. There is a photo of the nose gear wedged in the panel on the ground on the far side of the church (whatever it's name was).

Did you mean this?
Fig. 6-16
http://img182.imageshack.us/img182/4088/wheel2bin2bbroken2bsteeei0.jpg

Also see NIST figure 7-70 where they mention the landing gear was embedded in the exterior panel from WTC 1?
http://www.911disinformation.com/noplanes/NoPlanesCounterEvidence.html

 

[pomeroo]

What is 911 but assuming outsiders did it, and working backwards?

Forgive the intrusion of reality, but when Satan al Suqami, Wail al Shehri, and Waleed al Shehri were flagged by the CAPPS system in Logan Airport, and Hani Hanjour, Khalid al Mihdhar, and Majed Moqed were flagged in Dulles, was that an assumption, or was it an event--you know, something that actually happened?

Those damned inconvenient facts!

 

[Alferd_Packer]

This would be fantastic if the fireproofing had been applied at all competently.

I've never seen a scholarly paper before that defended the building and construction techniques of the mafia.

Yo, You got a problem with that?

FUGGETABOUTIT

 

[Major_Tom]

There is both a particulate and wave portion to the destruction caused by the aircraft.

Maybe it is best to view the particle distribution as different from the wave propagation, though happening at the same time.

R. Mackey states: Apart from a few solid structures, after initial contact the aircraft is basically a fluid phenomenon -- a density flow.

This ignores the particulate portion of the damage. NIST is obviously looking at the particle aspect in the bullet experiment. (a particle, very directional and non-diffractive).




R. Mackey, why does NIST use a bullet if they are studying a fluid flow?

If you claim that collisions are basically elastic, aren't you ignoring the probability (very high probability) that the particulates themselves become highly deformed in a collision with a column? If you shoot a malleable bullet at a steel column, do you expect an elastic collision?

Isn't aluminum rather malleable?


Strength and dissipation of the blast wave (the fluid portion of the destruction) can be roughly seen by the distribution of window breakage.

The particle portion of destruction would be highly directional and only by overestimating elastic bouncing can you consider it to not be highly directional.

 

[Max Photon]

Major, back for more dopium?

 

[beachnut]

Poppy-cock. The nose gear went straight down the hallway and took out one panel. There is a photo of the nose gear wedged in the panel on the ground on the far side of the church (whatever it's name was).

I find you lack of knowledge and lack of research on the small points of 9/11 to be one of your weaknesses which leads to your poor performance on this paper. If you want to comment on objects ejected why not express the energy lost; we have done that before and found it to be negligible compared to the energy damage in the WTC. I doubt you have studied 9/11 enough to know how many wheel are on a 767/757 aircraft. I expect you have done 1/10 of the research you need to, and even less time gathering the tools needed to do a good job on this subject. You have the correct term, but it needs to be applied to your paper, not R.Mackey's statement.

The lack of knowledge in this post, is indicative of the failings of your paper. You did a shabby job trying to show cause for NIST to redo their assessment.

As an engineer, I conclude your present paper, fails to meet it's goal.
As an American, I see your lack of knowledge as an insult to those who died on 9/11, and further insulting because you have claimed to have "ample evidence" as stated in your 9/11 truth petition which is a lie as you and 9/11 truth blame Americans for 9/11. I see this paper as a pure 9/11 truth effort until you realize the facts and have to back off to a statement of how you are going to teach the rest of 9/11 truth, this is how it is.

But, this is from one Electrical and Computer Engineer to another. Albeit, I think your IT work does not translate as well as my work on weapons systems. I clearly see your present paper as failing to meet it's goal; as I would expect my peers from college with no experience.

 

[R.Mackey]

This ignores the particulate portion of the damage. NIST is obviously looking at the particle aspect in the bullet experiment. (a particle, very directional and non-diffractive).

R. Mackey, why does NIST use a bullet if they are studying a fluid flow?

NIST didn't only use "bullets" (specifically plated shot), they also used fasteners. However, it would be valid to criticize NIST for not trying it with liquid as well, but given the many uncertainties it may be moot. Purdue made some progress in this department.

If you claim that collisions are basically elastic, aren't you ignoring the probability (very high probability) that the particulates themselves become highly deformed in a collision with a column? If you shoot a malleable bullet at a steel column, do you expect an elastic collision?

Isn't aluminum rather malleable?

Shooting steel at steel deforms the bullet a lot, but only at rifle velocities, say 800 m/s or so. At the aircraft impact speeds, 200 m/s, different story. Even lead fired at steel will survive with little deformation in this case. I believe ricochets will be common and efficient at these speeds.

Aluminum is more brittle than malleable, though it depends on alloy. I've never fired aluminum bullets at anything, though since the strength-to-weight is higher for aluminum than steel, I expect aluminum projectiles to actually survive better than steel projectiles. At 200 m/s, of course -- at rifle speeds, aluminum may crack, flake, or even ignite; all bets are off.

 

[R.Mackey]

I'm actually not trying to be a jerk about this. My apologies if I'm coming on too strong.

Poppy-cock. The nose gear went straight down the hallway and took out one panel. There is a photo of the nose gear wedged in the panel on the ground on the far side of the church (whatever it's name was).

I agree that the massive landing gear was a factor in punching out the far panel of WTC 1, and without that it isn't clear that finer debris would have caused the same effect. For completeness's sake, though, the landing gear did not go "straight down the hallway" -- it passed through the core and through a floor to get there.

I agree, they wildly over-estimated the energy, but that's as far as I'll go. They took the energy of the entire volume and applied it to a plane area parallel to the z-axis and perpendicular to the general momentum. Then they applied that energy to four surfaces parallel to the general momentum.

NIST did not over-estimate the energy, I was referring to your accounting. However, here you raise a valid criticism. Because NIST only tested fireproofing against total impulse, NIST never establishes the pressure-impulse relationship required to dislodge fireproofing. It is not clear what effect smearing out the debris wave over, say, 25 milliseconds does to the fireproofing. Maybe nothing. Maybe it overpredicts dislodgment.

I can't answer this. I suspect, since most of the dislodgment is due to small pieces, there would be local dislodgment and the additive effect would be roughly the same, i.e. assuming the debris wave all hits in one instant is close enough. But this could be wrong. Clearly time-smear will not help dislodgment.

I'd like to see you come up with a reasonable effective ricochet factor considering that most debris that hit the SFRM first had to go through the ceiling tiles and mostly hit the SFRM covered corrugated steel decking. The next most likely rebound is off of office furniture which will not be elastic.

And those hits on the office furniture are already reflected in the momentum vs. time graph. Hits on steel that do not damage steel will be highly elastic.

I think you are making a Froudian slip. Avg. displacement would be 1.25 m downward unless gravity and randomness is somehow cancelled out by turbulent flow. I don't know how to calculate the Froude number. Maybe you could do that for us?

No. Gravity does not lead to an "average displacement." Gravity is another source of potential energy. If you integrate the gravitational force, this gets summed with the other forces in the problem, and those forces are much higher and rapidly changing. Displacement is the double-integral of those forces. Over a long period of time, you would be able to see the bias, but not in a fraction of a second. Outside the containment of the structure, where debris isn't pinballing between hard and soft surfaces or entrained in the aircraft wake, forces are less random and a ballistic tendency would be more readily discernible.

The Froude Number, Fr = v / (g' h)^1/2, I eyeball at about 20, using v = 200 m/s and h = 10 m as characteristic velocity and length. Not very high. By comparison, the Reynolds number is on the order of 10⁸. This says that for a given fluid parcel, the relative strength of dynamic and gravitational forces is more than a million times different. For solid aluminum, much more dense, only about a thousand times. Gravity is not even a roundoff error in this calculation.

 

[Major_Tom]

Shooting steel at steel deforms the bullet a lot, but only at rifle velocities, say 800 m/s or so. At the aircraft impact speeds, 200 m/s, different story. Even lead fired at steel will survive with little deformation in this case. I believe ricochets will be common and efficient at these speeds.

So you are saying that the airplane components, much of which are in the form of sheet metal, struck against steel columns, perimeter and core, can be considered elastic collisions? You mentioned that if a steel column is damaged in the collision, the degree of elasticity is reduced, which is correct. Wouldn't that apply equally to the striking object? (Yes).

Wouldn't we anticipate that the object more damaged and deformed would be the striking object (the aircraft component) as opposed to the steel beam?

In view of this, should we still consider these collisions to be elastic, airplane parts bouncing around inside the building as if in a pinball machine?


Why do you think NIST used the bullet experiment (particle by nature, not liquid) as opposed to some other more liquid collision process? Could it be that they implicitely assumed that solid object or particle deflection was the thing to study and not the fuel blast wave or some other fluid mechanics phenomena?

Clearly time-smear will not help dislodgment.

Exactly. It would dissipate the damaging effect, not strengthen it.

Thanks for the reply.

Major, back for more dopium?

If the focus was on collapse initiation and certain high temperature "heating helpers", as you have written about, my interest would be rekindled. I think you were right about many things.

 

[R.Mackey]

So you are saying that the airplane components, much of which are in the form of sheet metal, struck against steel columns, perimeter and core, can be considered elastic collisions? You mentioned that if a steel column is damaged in the collision, the degree of elasticity is reduced, which is correct. Wouldn't that apply equally to the striking object? (Yes).

Yes to the first, no to the second. There's no reason damage has to be applied equally. Small pieces, which is what we are talking about, have a high strength-to-weight, and impart low impulse that will not destroy structure. The result is a nearly elastic collision.

Collisions with the furnishings or soft objects, ones that can deform when hit by small pieces, are different.

Wouldn't we anticipate that the object more damaged and deformed would be the striking object (the aircraft component) as opposed to the steel beam?

No. Depends on the speed. Back to the firing range, a small bullet can make a huge hole in a much stouter piece of steel plate, if it has enough velocity. Newton's Third Law does not say anything about deformation, it only talks about forces.

In view of this, should we still consider these collisions to be elastic, airplane parts bouncing around inside the building as if in a pinball machine?

Yes.

Why do you think NIST used the bullet experiment (particle by nature, not liquid) as opposed to some other more liquid collision process? Could it be that they implicitely assumed that solid object or particle deflection was the thing to study and not the fuel blast wave or some other fluid mechanics phenomena?

Testing limits. The fireproofing dislodgment tests are almost without precedent. With fluids, you have a whole new list of variables to consider, and it probably wasn't deemed worth the accuracy to try to sort through them all. Firing small pieces, however, is easy from an apparatus and analysis standpoint.