How could the planes wings penetrate the WTC?

[investigating911]

"Rendering software" has the purpose of producing graphics that look good.

Both the paper I cited (plane vs. power plant) and the paper Keith Beachy cited use finite element analysis software that has the purpose of allowing professional engineers to reliably evaluate the strength of real structures.

Blender is a toy when it comes to physics.

Okay, from the discussion about video game simulators and rendering software, it appears that only finite element analysis software is fully suitable for simulating physics as they would occur in the real world, while any other physics simulator games (Teardown, Destructive Physics, Detonate) aren't at all suitable and Blender isn't fully suitable.

If Blender is a toy when it comes to physics and not fully reliable, why then do modelers like Kostack Studio use Blender for simulating the WTC collapses?

Spoiler

WTC 7 Collapse initiation modeled with Blender

Source: https://www.youtube.com/watch?v=VAkTbyENZ5s&list=UUozprHAh-CPdkla4E4MtOIA


WTC north tower collapse initiation scenarios under various length stiffness, bending stiffness, breaking limit, and damping settings (low, medium, high; see test settings for all seven tests at 2:35)

Source: https://www.youtube.com/watch?v=4_J7ak_IZXk

 

[Mendel]

If Blender is a toy when it comes to physics and not fully reliable, why then do modelers like Kostack Studio use Blender for simulating the WTC collapses?

You'd have to ask them.

I'd guess it's because Blender is free, fun to play with, and makes nice youtube videos.
And because their results don't have to be "reliable", they just have to look good to get views.
(Which is, incidentally, the general problem with misinformation on social media.)

 

[Mendel]

Kai Kostack is not using plain Blender, he created an unreleased extension he calls "Bullet Constraints Builder for Blender".

Article:

Project description: The Finnish Laurea University of Applied Sciences is taking part in an EU funded project, named Inachus. The project in general examines measures to improve the first response in case of catastrophic events like earthquakes or explosions etc. A particular part of this project is the simulation of the effects that catastrophic events have on built structures. Within the three year lasting project Laurea researches the application of the discrete element method DEM to virtually simulate collapsing building structures. The DEM approach will be compared with the finite element method FEM and the applied element method AEM.

Add-on for Blender: We are developing an add-on that complements the bullet physics engine in Blender. The add-on will allow to attribute realistic structural dependencies between building elements such as pillars, walls, beams, slabs etc. The tool set in conjunction with the bullet physics engine should deliver satisfactory simulation results. Kai Kostack and Martin Felke have for many years laid a solid ground work for the current development. Kai Kostack has now finished a first script version that automatically sets multiple constraints to enable several force evaluations on precise junction points between rigid objects. The script also automatically calculates the breaking threshold values for each of the constraints based on material properties.

Expectations: We expect, that we will be able to simulate failing building structures under hazardous impact to a degree that allows predictions, what building parts will resist the impact and where falling debris will accumulate. In a best case scenario the simulation will indicate where spatial pockets will be likely to be formed, that allow victims to survive.

Source: https://github.com/KaiKostack/bullet-constraints-builder

tl;dr they're using a method that they hope is as good as established engineering methods (but don't know that yet), and they hope their software will eventually be realistic enough (but don't know that yet either), and they've been working on it for 6 years and are not yet ready to release it.

It's likely that when they release it, there'll be papers validating their methods, but the project description looks like it isn't there yet.

The point is that Kostack is not relying on Blender for the physics; he simply uses Blender to make the output of his own simulation software look good.


P.S. The physics engine they're interfacing with describes itself as "Bullet Physics SDK: real-time collision detection and multi-physics simulation for VR, games, visual effects, robotics, machine learning etc." ( https://github.com/bulletphysics/bullet3 ). Note that "engineering" is not listed.

 

[econ41]

The point is that Kostack is not relying on Blender for the physics; he simply uses Blender to make the output of his own simulation software look good.

That is the fundamental issue. Methods of simulation can have two different goals viz (a) producing a graphic result that looks like the event OR (b) mimicking the actual physics using or producing quantified values of forces and other physical properties. The former "looks like" the real event, the latter produces engineering data and may not "look correct".

Engineering models often don't "look like" the real event because scaling factors needed to produce the correct numerical values result in distortions of the appearance. The NIST simulation of WTC7 is a classic example. It grossly distorts the movements of the frame way beyond the actual ductility limits of the material. Leading to the truther belief that the NIST model is wrong because it doesn't "look like" the real event. It does if you understand that it is grossly exaggerating the movements. BUT that "doesn't look like" feature is why Hulsey's project for AE911 cheated its alleged "simulation". It produced a "looks like" graphic to meet the false expectations of truther supporters. By direct manipulation of the input parameters. The Hulsey "simulation" is actually a bastardised neither one nor the other. The base method is engineering simulation BUT with various bits of graphic manipulation "cheating" to make it "look like" what the customers wanted.

 

[Mauro]

On 18 April 2002 a Rockwell Commander 112 airplane crashed into the 'Pirellone' high rise in Milan. That was no terrorism: the pilot, alone on board, got confused/panicked after experiencing problems with the carriage and in the end he struck the skyscraper (suicide is also an hypothesis, the exact causes of the crash were never confirmed). This is the the same model of airplane:

And this is a picture of the 'Pirellone' after the impact (which caused three deads including the pilot and ~60 wounded):

Yeah, the facade of Pirellone has no structural role and it's not as sturdy as WTC was, but also an RC112 is much, much smaller than a Boeing airliner.

 

[Nada Truther]

an RC112 is much, much smaller than a Boeing airliner.

...and was going much slower than the 9/11 planes....

 

[SR1419]

A plane moving at high velocity penetrating a lot of windows might be easier to understand.

I always wondered why people thought the plane wouldn't penetrate the WTC- especially at the speeds those planes were flying.

 

[Ravi]

I always wondered why people thought the plane wouldn't penetrate the WTC- especially at the speeds those planes were flying.

Many people have no idea about impulse.

 

[Keith Beachy]

I always wondered why people thought the plane wouldn't penetrate the WTC- especially at the speeds those planes were flying.View attachment 47309

Is that the restaurant on top, I don't think those are WTC load bearing columns, save the needed strength to survive hurricanes, high winds, hail, and big birds. It appears those windows are double wide compared to the windows in the tower where the shell holds up nearly half the gravity weight of the WTC.

An aircraft obeying FAA rules would be stopped at the WTC shell. Not saying there would be no death from debris and fire shredding the normal windows, what was it 18 inch windows, killing some, and starting local fires. Nothing like 9/11.

Yes, At speeds on 9/11, the aircraft would have 7 to 11 times more energy than needed to break the WTC tower shell. The velocity squared term in energy, is a killer.

 

[Mendel]

I always wondered why people thought the plane wouldn't penetrate the WTC

Hollywood.

Source: https://m.youtube.com/watch?v=dfDUSAO8D9Q

 

[investigating911]

Is that the restaurant on top, I don't think those are WTC load bearing columns, save the needed strength to survive hurricanes, high winds, hail, and big birds. It appears those windows are double wide compared to the windows in the tower where the shell holds up nearly half the gravity weight of the WTC.

An aircraft obeying FAA rules would be stopped at the WTC shell. Not saying there would be no death from debris and fire shredding the normal windows, what was it 18 inch windows, killing some, and starting local fires. Nothing like 9/11.

Yes, At speeds on 9/11, the aircraft would have 7 to 11 times more energy than needed to break the WTC tower shell. The velocity squared term in energy, is a killer.

I thought it was already established by others like @Jeffrey Orling and @econ41 that a commercial jet airplane obeying FAA rules would have still mostly penetrated the WTC shell (including most of the wings)?

 

[Marc Powell]

Is that the restaurant on top, I don't think those are WTC load bearing columns, save the needed strength to survive hurricanes, high winds, hail, and big birds. It appears those windows are double wide compared to the windows in the tower where the shell holds up nearly half the gravity weight of the WTC.

An aircraft obeying FAA rules would be stopped at the WTC shell. Not saying there would be no death from debris and fire shredding the normal windows, what was it 18 inch windows, killing some, and starting local fires. Nothing like 9/11.

Yes, At speeds on 9/11, the aircraft would have 7 to 11 times more energy than needed to break the WTC tower shell. The velocity squared term in energy, is a killer.

As can be seen in the attached picture, the columns transitioned to a smaller size in the spandrel directly below the Windows on the World Restaurant. This allowed for the wider windows seen in the picture supplied by SR1419. At any rate, it is likely that the planes would have had sufficient energy to dislodge, sever and bend columns exactly as seen on 9/11 even if flying at close to stall speed.

 

[Keith Beachy]

You are referring to this paper, which is openly available at ResearchGate:

Article:

Impact of the Boeing 767 Aircraft into the World Trade Center

• October 2005
• Journal of Engineering Mechanics

Source: https://www.researchgate.net/publication/275188710_Impact_of_the_Boeing_767_Aircraft_into_the_World_Trade_Center

"Rendering software" has the purpose of producing graphics that look good.

Both the paper I cited (plane vs. power plant) and the paper Keith Beachy cited use finite element analysis software that has the purpose of allowing professional engineers to reliably evaluate the strength of real structures.

Blender is a toy when it comes to physics.

Every other time I try to find that study, I can't find if free...
"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. "
https://www.researchgate.net/public...eing_767_Aircraft_into_the_World_Trade_Center

 

[econ41]

I thought it was already established by others like @Jeffrey Orling and @econ41 that a commercial jet airplane obeying FAA rules would have still mostly penetrated the WTC shell (including most of the wings)?

Hardly "established". My engineer's gut feeling opinion - with so far zero attempts at quantification - is that even at significantly reduced speeds the aircraft would still "penetrate". And I have described the mechanism of "penetration" qualitatively as a continuum. It was not a binary status. "Penetrate" or "Not Penetrate".

The critical step which remains an undefined elephant in the room is the threshold between "start penetrating and continue so that most of the aircraft ended up inside the building" AND "only penetrate a little bit so that most of the plane would fall outside the building"

Every other time I try to find that study, I can't find if free...

Thanks, @Mendel and @Keith Beachy - I couldn't find a "freebie".

"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. "
https://www.researchgate.net/public...eing_767_Aircraft_into_the_World_Trade_Center

Just a couple of preliminary comments:
1) The paper is dated 2005 and reflects several of the errors of understanding which prevailed in that early era - essentially prior to 2007-9.
....EXAMPLES

The remainder of the buildings fell by dynamic buckling.

Not so. And this is the commonest misunderstanding that plagued the debate of WTC collapse physics for many years. The remainder fell by a mechanism often contentiously labelled "ROOSD"*** (Runaway Open Office Space Destruction.) The contention was because the acronym was coined by persons from the "truther" side of the debate and cut across debunker prevailing wisdom.

Newland and Cebon (2002)
suggested the use of foam or honeycomb materials to absorb impact energy created by the portion of the building above the damaged floors. They concluded that an arrangement of this type would arrest the downward-traveling stress wave that caused ultimate structural collapse of the buildings.

Not so. Same reason as above. The Towers both withstood the initial impact and the resulting shock waves. The ultimate collapse was by "ROOSD".

Quintiere et al. (2002) pointed out that the insulation thickness on the truss rods in these buildings was deficient. With better insulation, collapse could have been delayed and more lives would have been spared.

Not so. Another early misunderstanding. The impact blocked escape paths and started the fires. The combination of blocked escape paths plus fires resulted in deaths. And those deaths would still have occurred if the collapse was delayed. The occupants could not escape.

Turning to the main theme of the paper - penetration:
I've not, so far, studied the paper in depth BUT as per my earlier speculation, the author seems to be treating "penetration" as an issue of binary fact. I don't think it is. At least until someone defines "penetration". As per my earlier comment, the lack of definition is the "elephant in the room".

The three conclusions:
(a) "It was found that about 46% of the initial kinetic energy of the aircraft was used to damage columns." >> Could be - if we accept their scenario. Otherwise "so what?"

(b) "The minimum impact velocity of the aircraft to just penetrate the exterior columns would be 130 m/s." >> What does "just penetrate" mean in real terms?

(c "It was also found that a Boeing 767 travelling at top speed would not penetrate exterior columns of the WTC if the columns were thicker than 20 mm" >> So what? Even if true the towers did not need and could not have been constructed with "prevent penetration" as a criterion. And certainly not with 20mm column wall thickness.
.
.
.
*** To be ultra-pedantic it was a bit more than "ROOSD" as originally defined by the truther side researchers who explained the mechanism and coined the acronym. But the pedantic detail is not relevant here.

 

[Mendel]

It looks to me that a slower aircraft would still have penetrated the windows, so there'd have been some mayhem, and fire (and probably two jet engine compressors) inside, but more of the shell and the core would not have been damaged, and then there'd be more escape paths and much more time to use them. However, that's idle speculation.

 

[investigating911]

Hardly "established". My engineer's gut feeling opinion - with so far zero attempts at quantification - is that even at significantly reduced speeds the aircraft would still "penetrate". And I have described the mechanism of "penetration" qualitatively as a continuum. It was not a binary status. "Penetrate" or "Not Penetrate".

The critical step which remains an undefined elephant in the room is the threshold between "start penetrating and continue so that most of the aircraft ended up inside the building" AND "only penetrate a little bit so that most of the plane would fall outside the building"

Right, but given how the wings aren't the weakest part of the airplane and are as a matter of a fact quite strong and not the first parts of an airplane to come loose, along with how a plane is considered by many people to have at least partially penetrated the building if the wings are able to knock through the exterior facade, I would guess that "penetrate" could be defined as "most of the wings (excluding the wingtips) entering the building during impact".

As you had said earlier, with a slower airplane speed upon impact, less of the airplane will enter the building, while some parts still likely will because of their mass and momentum (such as the heavier engines and portion of the wings housing the heavy fuel tanks).

Turning to the main theme of the paper - penetration:
I've not, so far, studied the paper in depth BUT as per my earlier speculation, the author seems to be treating "penetration" as an issue of binary fact. I don't think it is. At least until someone defines "penetration". As per my earlier comment, the lack of definition is the "elephant in the room".

I think "penetration" could be defined as above, meaning that at least a significant portion of the wings (excluding the wingtips) are able to enter the building during impact.

The three conclusions:
(a) "It was found that about 46% of the initial kinetic energy of the aircraft was used to damage columns." >> Could be - if we accept their scenario. Otherwise "so what?"

I think that the reason they state that is because you need at least a certain speed to damage the columns enough to knock them out of the way. All of the plane's initial kinetic energy doesn't solely go to damaging the columns but can be lost through other means like friction, heat, and sound. If the airplane isn't flying fast enough to have the base amount of kinetic energy, then there will not be enough energy to damage the columns enough to knock them loose and inwards.

(b) "The minimum impact velocity of the aircraft to just penetrate the exterior columns would be 130 m/s." >> What does "just penetrate" mean in real terms?

I assume that by "penetrate" they mean that each part of the plane making impact with the facade (be it the wings or the front fuselage) can sever or knock out the exterior columns upon impact of these plane parts with the facade.

(c "It was also found that a Boeing 767 travelling at top speed would not penetrate exterior columns of the WTC if the columns were thicker than 20 mm" >> So what? Even if true the towers did not need and could not have been constructed with "prevent penetration" as a criterion. And certainly not with 20mm column wall thickness.
.
.
.

This is a good point imo, as if the towers could not be constructed with steel columns thicker than 20 mm, the question of whether the WTC columns would be penetrated by a Boeing 767 traveling at top speed if the columns were that thickness would probably be irrelevant for any real world planning.

 

[Jeffrey Orling]

This is a settled engineering/physics. The speed and mass (and its distribution) of the plane was known. The mass moving at the established speeds were sufficient to destroy the steel facade on impact. Momentum "carried" the mass into the building. It doesn't matter what would happen if the planes were traveling slower... or how much slower.

 

[DavidB66]

I am relatively new to this subject, so I was surprised to see repeated references to the exterior columns of WTC 1 and WTC2 being 20 mm thick. That's about the width of my fingers, and my fingers are not fat! Presumably the cognoscenti of the subject already know what these references really mean, but for my own benefit I looked up some sources, of which the best-known seems to be this overview paper by some experts at NIST:

https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=910105

The key overview description of the columns seems to be here:

The first major structural subsystem was the exterior framing, which was a vertical square tube that consisted of 236 narrow columns, 59 on each face from the 10th floor to the 107th floor (Figure 3). There were fewer, wider-spaced columns below the 7th floor to accommodate doorways. There were also columns on alternate stories at each of the beveled corners, but these did not carry gravity loads. Each column on floor 10 to 107 was fabricated by welding four steel plates to form a tall box, nominally 0.36 m (14 in) on a side. The space between the steel columns was 0.66 m (26 in), with a framed plate glass window in each gap. Adjacent columns were connected at each floor by steel spandrel plates, 1.3 m (52 in) high. The upper parts of the buildings had less wind load and building mass to support. Thus, on higher floors, the thickness of the steel plates making up the columns decreased, becoming as thin as 6 mm (¼ in) near the top down from as thick as 76 mm (3 in) at the lower floors. There were 10 grades of steel used for the columns and spandrels, with yield strengths ranging from 248 MPa (36 ksi) to 690 MPa (100 ksi). The grade of steel used in each location was dictated by the calculated stresses due to the gravity and wind loads... [Emphasis added]

There doesn't seem to be a diagram showing the structure of the individual columns, but the photographs at Figure 4 help flesh out the textual description. The columns have a square cross-section, with a side of 0.36 m (14 inches), according to the text. (In the photographs, due to perspective, they may appear rectangular, but where the tops are visible they appear square, as implied by the phrase 'on a side'.) The component steel plates varied in thickness from top to bottom of the building (see the passage I have bolded.) As the columns hit by the planes were closer to the top than the bottom, one might expect the thickness to be closer to 6 mm than 76 mm, so 20 mm may be the most relevant figure for the plates affected. But the thickness of the plates themselves may be less relevant than the behavior of the columns as a structure, including the connections between the columns and each other, and with the floors. From the photographs of the damaged facade earlier in this thread (e.g. at #154), most of the damaged columns appeared to have been ripped out of their positions as whole pieces. Some of them are bent inwards, but I don't see any obvious examples of plates being cut or torn through their middle.

 

[Jeffrey Orling]

I am relatively new to this subject, so I was surprised to see repeated references to the exterior columns of WTC 1 and WTC2 being 20 mm thick. That's about the width of my fingers, and my fingers are not fat! Presumably the cognoscenti of the subject already know what these references really mean, but for my own benefit I looked up some sources, of which the best-known seems to be this overview paper by some experts at NIST:

https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=910105

The key overview description of the columns seems to be here:



There doesn't seem to be a diagram showing the structure of the individual columns, but the photographs at Figure 4 help flesh out the textual description. The columns have a square cross-section, with a side of 0.36 m (14 inches), according to the text. (In the photographs, due to perspective, they may appear rectangular, but where the tops are visible they appear square, as implied by the phrase 'on a side'.) The component steel plates varied in thickness from top to bottom of the building (see the passage I have bolded.) As the columns hit by the planes were closer to the top than the bottom, one might expect the thickness to be closer to 6 mm than 76 mm, so 20 mm may be the most relevant figure for the plates affected. But the thickness of the plates themselves may be less relevant than the behavior of the columns as a structure, including the connections between the columns and each other, and with the floors. From the photographs of the damaged facade earlier in this thread (e.g. at #154), most of the damaged columns appeared to have been ripped out of their positions as whole pieces. Some of them are bent inwards, but I don't see any obvious examples of plates being cut or torn through their middle.

This may help:

 

[econ41]

I am relatively new to this subject, so I was surprised to see repeated references to the exterior columns of WTC 1 and WTC2 being 20 mm thick.

The discussion is about the ability of a plane to penetrate the Twin Towers. The columns were NOT 20mm at the location of impact. See the full details provided by @Jeffrey Orling. The 20mm comes from a 2005 academic paper linked in previous posts. That paper postulates that IF the columns had a wall thickness of 20mm the perimeter of the Twin towers would have prevented penetration by the aircraft.

I disagree for reasons stated in my previous posts. Other members have commented on that hypothetical claim. I think the issue is insufficiently defined as per my several comments. It does NOT define what is meant by "penetration" in any way which meaningfully relates to the range of plausible scenarios whatever the variations of aircraft speed and column wall thickness.

 

[Mendel]

The columns were NOT 20mm at the location of impact.

Are you sure?

(by MesserWoland, CC-BY-SA, https://commons.m.wikimedia.org/wik...lustration_with_Vertical_Impact_Locations.svg)

Details from Jeffrey Orling's post:

0.875" = 22.2 mm, 0.5" = 12.7 mm

Flight 175 crashed the sturdier section.

 

[Jeffrey Orling]

Are you sure?
View attachment 47354
(by MesserWoland, CC-BY-SA, https://commons.m.wikimedia.org/wik...lustration_with_Vertical_Impact_Locations.svg)

Details from Jeffrey Orling's post:

View attachment 47355View attachment 47356
0.875" = 22.2 mm, 0.5" = 12.7 mm

Flight 175 crashed the sturdier section.

Which shows how much momentum the plane had and was able to destroy steel box columns made with 7/8" thick plate flanges... but thinner webs.. maybe 8mm.

 

[Keith Beachy]

The discussion is about the ability of a plane to penetrate the Twin Towers. The columns were NOT 20mm at the location of impact. See the full details provided by @Jeffrey Orling. The 20mm comes from a 2005 academic paper linked in previous posts. That paper postulates that IF the columns had a wall thickness of 20mm the perimeter of the Twin towers would have prevented penetration by the aircraft.

I disagree for reasons stated in my previous posts. Other members have commented on that hypothetical claim. I think the issue is insufficiently defined as per my several comments. It does NOT define what is meant by "penetration" in any way which meaningfully relates to the range of plausible scenarios whatever the variations of aircraft speed and column wall thickness.

The paper used top speed of 240 m/s. Flight 11 was about 210 m/s, and 175 was ~263 m/s. Flight 175, hitting lower at thicker walls, had more energy than the papers speed point of 240 m/s.

In addition, the shell steel had different strengths. From grades of steel ranging from 36 ksi to 100 ksi minimum yield strength. I think the higher yield strengths were as needed to keep weight down, and yield strength increased with height. (sorry, I think this is true, but I can't find the diagram I had once which showed how they used the various yield strengths based on their engineering models to withstand winds, support the load, and be the lateral support)

It makes it more complicated to compare the paper results to the real event due to speed differences and the strength of steel.

 

[econ41]

Are you sure?

No. I didn't even check. Mea a little bit culpa - excuse some minor blushing. My focus was on the other big problems with both the references paper and the undefined concept of "penetration".

So my apology for causing a bit of derail on that factor because the actual thickness of the real towers is irrelevant to the discussion of the real event. It is only relevant to the hypothetical scenario claimed in the referenced paper.

And the fact that the relevant plane did without the slightest doubt penetrate WTC2 tends to confirm my "engineers gut feeling" doubts about the claim in the paper that 20mm wall thickness would stop penetration. It looks like my guess was closer than I realised - and I should have checked @Jeffrey Orling's data.

 

[econ41]

It makes it more complicated to compare the paper results to the real event due to speed differences and the strength of steel.

We can be very confident that the claim that 20mm would stop penetration is wrong. BUT the same "elephant in the room" viz: "Penetration" is not defined and the presumption appears to be binary. i.e. either "would stop" or "would NOT stop" but nowhere does it explain "stop" in any form which would resemble the actual mechanism of such an event.

 

[Mendel]

Well, the model in the paper is unrealistic in a few ways.
https://www.researchgate.net/public...eing_767_Aircraft_into_the_World_Trade_Center

The aircraft model only has one wing (the left wing is missing), and it's modeled as being perpendicular to the fuselage. Because of this, in the model figure 7 (c) and 9 (c), the wing tips hit the columns before the inner part of the wing does. In reality, the swept wings break the columns one after the other from the inside out. (There's a reason only toy arrows have blunt heads.)

The other problem is that the columns are modeled as aligned 10.9m spans fixed at the top and bottom, with no interconnections. In reality, the columns were longer and not fixed, but had weaker interconnections where shearing could and did occur. The columns were then bent as the aircraft's momentum forced it through the gaps.

The spandrels at the ends of the columns constrained motion in all directions. Therefore, fixed-fixed boundary conditions are given at the top and bottom of the bracing columns.

Photographs of the damaged columns of the WTC indicated that they were severely bent before the aircraft cut through the building. Had they been sheared upon impact, the deformation would have been a lot more localized [..]

To get this model of the aircraft to penetrate that steel lattice model realistically, the author has to reduce the thickness of the columns to 9.5 mm, which does not reflect the conditions at either impact zone.

 

[Jeffrey Orling]

Well, the model in the paper is unrealistic in a few ways.
https://www.researchgate.net/public...eing_767_Aircraft_into_the_World_Trade_Center

The aircraft model only has one wing (the left wing is missing), and it's modeled as being perpendicular to the fuselage. Because of this, in the model figure 7 (c) and 9 (c), the wing tips hit the columns before the inner part of the wing does. In reality, the swept wings break the columns one after the other from the inside out. (There's a reason only toy arrows have blunt heads.)
View attachment 47405
View attachment 47404
View attachment 47406

The other problem is that the columns are modeled as aligned 10.9m spans fixed at the top and bottom, with no interconnections. In reality, the columns were longer and not fixed, but had weaker interconnections where shearing could and did occur. The columns were then bent as the aircraft's momentum forced it through the gaps.

The spandrels at the ends of the columns constrained motion in all directions. Therefore, fixed-fixed boundary conditions are given at the top and bottom of the bracing columns.

Photographs of the damaged columns of the WTC indicated that they were severely bent before the aircraft cut through the building. Had they been sheared upon impact, the deformation would have been a lot more localized [..]

To get this model of the aircraft to penetrate that steel lattice model realistically, the author has to reduce the thickness of the columns to 9.5 mm, which does not reflect the conditions at either impact zone.

A model is useless when it is so far from what the real world is. This model is a fail.

 

[Keith Beachy]

We can be very confident that the claim that 20mm would stop penetration is wrong. BUT the same "elephant in the room" viz: "Penetration" is not defined and the presumption appears to be binary. i.e. either "would stop" or "would NOT stop" but nowhere does it explain "stop" in any form which would resemble the actual mechanism of such an event.

I think based on strength of steel and 20 mm, it might keep the majority of the mass out of the interior. Too busy now, but iirc the higher steel section are stronger, and the lower are not as strong, albeit thinner.

I think Robertson was right, a 707 low on fuel, lost in the fog/clouds, like an emergency, going 180 mph configured for "final approach" would be stopped from entering the WTC. The event would be equal in Kinetic Energy to 184 pounds of TNT, no where near 9/11's ~1300 to 2000 pounds of TNT. I believe Robertson took it serious to keep the aircraft out of the WTC at the shell, unlike the ESB event where a measly kinetic energy of 42 pounds of TNT impact crashed through the ESB with an engine ejected the other side.

There is a speed where the aircraft will be "stopped" at the shell. Yes, the shell will suffer damage, debris will break the windows, and depending on the fuel load, fires will be all over.

I think it is a fact, if the planes had been going 180 to 200 mph, they would not make the cutouts and damaged core columns. I think you need a kinetic energy equal to 500 pounds of TNT to break the shell, any more speed and kinetic energy will then damage the interior. The damage to core columns was 7 to 10 core columns on 9/11. This is where the extra energy went to after breaking the shell.

Source: https://www.youtube.com/watch?v=Wc-zmb3jAgo

 

[Ashley Pomeroy]

I think Robertson was right, a 707 low on fuel, lost in the fog/clouds, like an emergency, going 180 mph configured for "final approach" would be stopped from entering the WTC. The event would be equal in Kinetic Energy to 184 pounds of TNT, no where near 9/11's ~1300 to 2000 pounds of TNT. I believe Robertson took it serious to keep the aircraft out of the WTC at the shell, unlike the ESB event where a measly kinetic energy of 42 pounds of TNT impact crashed through the ESB with an engine ejected the other side.

Off the top of my head I remember reading at the time that the buildings had been designed to withstand impact from a 707, because it was the most widespread large airliner when the towers were under construction. This NYT report from 12 September 2001 implies this:
https://www.nytimes.com/2001/09/12/...-safe-proved-vulnerable-intense-jet-fuel.html

"The towers were built to withstand the stresses of hurricane-force winds and to survive the heat of ordinary fires. After the 1993 trade center bombing, one of the engineers who worked on the towers' structural design in the 1960's even claimed that each one had been built to withstand the impact of a fully loaded, fully fueled Boeing 707, then the heaviest aircraft flying."

Which brought me to this thread from Airliners.net in which the OP wonders if the WTC could survive an impact from a jetliner. What makes it interesting is that it was posted in 2000, when the reference points were a B-25 crash into the Empire State Building an the El Al apartment block crash:
https://www.airliners.net/forum/viewtopic.php?t=60625

"I do believe that the result of a large airliner hitting a large modern building would be much closer to the EL AL incident than the B25 incident in '43. The 757/767 etc. would be much faster and heavier than the B25 so I wouldn't be too optimistic that the Empire State would survive either.

Hopefully, we'll never have to find out."

Alas the OP did find out.