Hardfire: Physics of 9/11

[ozeco41]

Oz,

Howdy & welcome. Excuse me for missing it, if you mentioned it before, but what is your background. You sound like an engineer to me. I'm mechanical.

Civil - 1965/67 first degree, practiced in most fields but not building structural. However much experience in Engineering management so correcting "narrow minded technical engineers" who get lost in detail and lose the plot.

Experience includes oversight of emergency response and follow up engineering forensic analyses.

16 years Army reserve engineers - with demolition qualifications.

...A couple of points, but ones that are significant.

all read and broad agreement - some details follow

...
In your rework of Heiwa's sketches, I believe that it is important to NOT include the damaged 6 floors or so in either section A or C. A & C are basically intact & not weakened by damage, distortion or fire. Those weakened floors (93 - 98 in WTC1) are likely the ones that collapsed first. By the time that any collapse got to an intact section of the towers (A or C), it had already gathered 6 stories worth of momentum.

..understood but it is not six stories of fully free fall momentum - doesn't matter anyway IMO the dead load itself was near enough once the impact zone collapsed. The momentum was just the "initial kick" IM(Guess)O

...Second in your last sketch, you show the debris collecting predominantly in the part A, the lower section. This is wrong. Think about any floor that is hit by debris and begins to fall. It is starting from a standing start, as a fast descending hammer comes down from above. For the first 2-5 stories (my SWAG), the faster descending upper block is going to sweep the debris into its open structure and pack in there. After a couple of stories, the bottom surface of the upper block C will be so impacted with debris, that it'll approximate a solid surface...

..See where you are coming from - partly accept - let me think about it BUT I was interested in getting the broad picture on the table -- not the detail.

...Thrid point. Think about the effect that the stagger of the peripheral & core columns had on the destruction of any give floor. By the time that the descending upper block arrives at some given floor (say the 80th), fully 2/3rds of the columns supporting the 80th floor have already been destroyed. This is because 1/3 of all those columns reached up to the 82nd floor and another 1/3 reached up to the 81st floor. These have been ripped away BEFORE the descending block even arrives at the 80th floor.

Ditto my previous comment

There ain't that much more work to do to snap the 1/3rd connections that are left supporting that floor.

Kerrect -- and one the none engineers miss. The "radial" section modulus of the outer columns was very small compared to the "circumferential" one - along the walls a tremendous mutual interconnecting arrangement.

.....And I feel strongly that Bazant goes off course in calculating work required to buckle columns. This is an important calculation in the collapse initiation, but not after that point.

AFTER the collapse had initiated, the failure mode was snapped connections, gross breakup of the concrete floors and deformation of the cross trusses. This it the calculation that should have been used in calculating the work of disassembly....

Yes - but so much of the "approach from energy" explanations is wrong because they presume top block and bottom stub act as solid homogeneous entities. You cannot understand the collapse from that perspective. Some of the engineering ones coming from "energy" on the wrong modeling got the right answer but really their answer is a fraud. It just happened that the energies were so massive as to come out on the side of "no demolition" no matter what wrong reasoning was used. (Gawd - there goes my Membership of the Engineers' Club AGAIN! Forget how many times I've been evicted. )

...Your correction to Heiwa's sketch, that the unsupported columns become immediately unstable & snap off, is right on the money. I would tend to think, tho, that the impacting of debris at the bottom of the upper block will give those bottom columns of the upper block some lateral support.

.. a good point but detail below the broad brush explanation I was giving.

The top "stubs" of broken off columns in the lower section have approximately zero ability to resist side loads, however.

.. or less if that is possible

...This is one (of many) of Heiwa's fundamental errors. He distributes the strain energy of the of the lower (larger) section uniformly over its entire structure. And he ignores the stress concentrations and side loads that are applied to the non-braced column in the top floor that is being crushed.

... Yes - all subsumed within my explanation of "treat as solid block"

Thanks Tom

Eric

 

[ozeco41]

You are using facts and evidence and these are lost to the delusion believers who use fantasy, lies and hearsay. They will not recognize logic and evidence.

...yup. It is like "debating" creationist creotards in another life I have. I give everyone benefit of the doubt for first post or so. Then if dealing with "Goddidit Believers" the discussion is for the benefit of the sideline observers - not the person I am apparently engaged with.

....To explain the unique design of the WTC is lost on those not looking for truth but saying they are. They are interested in the anti-intellectual poppycock to feed their delusions, not reality based explanations involving research, math and physics. They are political trolls who have religious based faith in some elusive 911Truth delusion.

...yup again!
The "room for assisting" is to the non engineers who need a simple understanding of the structures - especially the unique aspects of WTC designs.

 

[Furcifer]

Second in your last sketch, you show the debris collecting predominantly in the part A, the lower section. This is wrong. Think about any floor that is hit by debris and begins to fall. It is starting from a standing start, as a fast descending hammer comes down from above. For the first 2-5 stories (my SWAG), the faster descending upper block is going to sweep the debris into its open structure and pack in there. After a couple of stories, the bottom surface of the upper block C will be so impacted with debris, that it'll approximate a solid surface.

I think this is correct. To further it, after another 20-30 floors the core was strong enough to pierce through the impacted bottom of section C, and it (C) was destroyed. This is evidenced by the free standing core section which can be observed in many videos. "Crush up" and "crush down" were simultaneous and happened around the 44th service floor. IMHO.

 

[ozeco41]

I think this is correct. To further it, after another 20-30 floors the core was strong enough to pierce through the impacted bottom of section C, and it (C) was destroyed. This is evidenced by the free standing core section which can be observed in many videos. "Crush up" and "crush down" were simultaneous and happened around the 44th service floor. IMHO.

Probably a good guess. My focus has been on answering yes or no to the demolition question - been doing it for ~2 years in a couple of avenues.

I have never concerned myself with the "exactly where" question.

The top block started off at the upper level as an integral whole.

It ended up mostly in component parts at near ground level.

It came to pieces in between.

Those were/have been good enough bounds for me.

Key point I think is that the mass falling in the outer tube and shearing the floor joists is the same (more or less) whether it is one interconnected set of bits OR all those bits separated.

 

[bardamu]

I asked the question because your model/theory seems to depend on the assumption that the joins between the horizontal beams and the vertical core columns would have held up.

So for this point whether I hold that assumption or not is not critical. That is not evasion it is because either option would not change the outcome. Take the beam on beam "collision". If the connections held up the beam would bend - the primary point I made AND the columns attached would be bent inwards - the secondary point I made. Both those would be moves towards collapse. HOWEVER if the end connections of the beam failed the beam would immediately cease to be a part of the structure and would join the falling mass of debris - still heading towards collapse.

But if the end connections of all the beams failed, the core columns would still be standing, even though they might be unsteady.

...Assuming for now that the joins would not fail, have you roughly estimated the energy that would be needed to bend all the horizontal beams and pull in the core columns?

... no .. because I cannot, I doubt anyone could add up all the bits. But I can legitimately move to an acceptance that each one and the sum of them would be "overwhelming".

The key word is "overwhelming" - many parts were hit by descending forces that were "overwhelming" to THAT PART.

I suspect that may be not satisfying for you YET - can you see where I am heading?

I suppose you're heading towards the conclusion that the falling bits would have enough energy to cause the failure of the core columns via the horizontal beams. You've probably guessed already that I'm very sceptical any such failures could continue for more than a few floors. When I try to imagine the force it would take to bend so many steel beams, it's hard for me to accept that the small upper block could overwhelm the structure below.

Does it help?

It's very informative. Thanks for another detailed reply. I look forward to reading further installments of your theory.

This completely and utterly misses the point Mackey explicitly stated. He's not trying to do anything other than model a single issue regarding the collapse. Overall, he's trying to demonstrate to others how to think about the collapse. His model is not consistent because it's simplified in order to teach people how to consider the individual element being discussed.

I can't believe that Ryan came out and very clearly and explicitly stated this, and people still complain about the model anyway. I just can't believe it. People: Understand his point! It was to teach an approach, not fully describe the event!

The third Hardfire show was about how to build a model, but I was talking about the 'crush-down' collapse model supported by NIST, Bazant, Greening and Mackey. That's what most people in this thread appear to be discussing.

Please point out where Mackey has said his model is suppose to replicate the scenario, and then within those areas, how his model differentiates from the photographic and video evidence, with reference to the areas in his model and the corresponding incongruities in the videos/photos.
Thanks
TAM

According to the crush-down model, the upper block falls 12ft onto the lower block, which turns the top floor of the lower block into rubble. In the videos and photographs of the North Tower collapse, after the upper block is severed from the lower block, the roof and mast drop a distance of well over 12ft before the collapse front begins to move downwards.

I disagree. I'm not the only one. To those who actually understand Mackey's model the building is doing exactly what one would expect it to do.

People can't agree on what the building would be expected to do. The model would be better if it did exactly what it does in the videos.

Do you have a better model, then?

How about merging ozeco41's and Heiwa's models?

 

[Furcifer]

Key point I think is that the mass falling in the outer tube and shearing the floor joists is the same (more or less) whether it is one interconnected set of bits OR all those bits separated.

Yep.

The floor collapse wave preceeded the upper section by approximately 3 stories (due to the lengths of steel used). The upper section exerted lateral forces on the walls of the "tube" severing the floors from the exterior at the same time, the accumulating mass inside the tube sheared the the floors core and exterior connections. It's hard to say which, the falling upper section or the accumulating mass inside the tube were more responsible for the shearing of the floor joists. I'm guessing the accumulating mass.

 

[Newtons Bit]

But if the end connections of all the beams failed, the core columns would still be standing, even though they might be unsteady

No, they would collapse under their own self-weight. Which is what happened. If you look at photos immediately post collapse you will see a "spire" of core columns that remained. It fell almost immediately after the smoke cleared.

 

[ozeco41]

But if the end connections of all the beams failed, the core columns would still be standing, even though they might be unsteady.

Yes ...AND..... Remember some could "fail" that way othersmay fail other ways.... The clue is "they might[most certainly would] be unsteady.

....I suppose you're heading towards the conclusion that the falling bits would have enough energy to cause the failure of the core columns via the horizontal beams.

I am only heading towards helping you understand. So the next point is we need to address what you mean by "failure"

. You've probably guessed already that I'm very sceptical any such failures could continue for more than a few floors.

Your perception difficulty seems to be one of scale. The "small upper block" is in reality the totatal structure of 10 or 20 storeys It is a bloody big block. And potentially all that weight is available to strike any single member that blocks the fall.

. When I try to imagine the force it would take to bend so many steel beams, it's hard for me to accept that the small upper block could overwhelm the structure below.

...same problem of perception

....It's very informative. Thanks for another detailed reply. I look forward to reading further installments of your theory.

Just giving you some clues as to where you can exercise the old Embedded Module (Grey Cell) Mk 1

...The third Hardfire show was about how to build a model, but I was talking about the 'crush-down' collapse model supported by NIST, Bazant, Greening and Mackey. That's what most people in this thread appear to be discussing.

..and that is a trap - remember the discussion is about what actually happened at WTC NOT whether Fred or Susan's model was correct

...How about merging ozeco41's and Heiwa's models?

As long as you only add the bits Heiwa gets right which are...

..errr

mmm....

I'll let you pick them.

 

[bill smith]

I'm interested in your answer:

How much of section A could be crushed by section C?

2 floors? 8 floors? 30 floors? 0 floors?

The downward facing core columns in part C would punch through the floors and elements of part A just as the upstandng core columns of part A would punch through the floors and elements of part C. Equual and opposite forces. I I think myself that the collapse would have stopped through friction after only a few floors but at worst 13 floors above nd 13 floors below would be destroyed and then part C would be shattered and disassembled and fallen off the sides-gone.

 

[beachnut]

The downward facing core columns in part C would punch through the floors and elements of part A just as the upstandng core columns of part A would punch through the floors and elements of part C. Equual and opposite forces. I I think myself that the collapse would have stopped through friction after only a few floors but at worst 13 floors above nd 13 floors below would be destroyed and then part C would be shattered and disassembled and fallen off the sides-gone.

Oh? Funny stuff as Robertson makes your post pure claptrap from some kid.

Robertson the chief structural engineer for the WTC, the top expert for how the WTC would collapse says what happen on 911 was how it would fall.

You are wrong and proven wrong by the top expert on the WTC. Failure comes early and often for the uniformed and unprepared.



Your statements on 911 have all been wrong; try to gain knowledge and you will do much better.

 

[Furcifer]

The downward facing core columns in part C would punch through the floors and elements of part A just as the upstandng core columns of part A would punch through the floors and elements of part C. Equual and opposite forces. I I think myself that the collapse would have stopped through friction after only a few floors but at worst 13 floors above nd 13 floors below would be destroyed and then part C would be shattered and disassembled and fallen off the sides-gone.

Might i suggest considering that gravity was pulling debris down onto the lower section and not up into the upper section? And perhaps that debris was damaging the lower section, detaching floors and twisting core columns. And perhaps that's why the lower section, at least at the point of initiation and a little while afterwards, was less structurally intact?

You might also want to consider how much force it would take to deflect the mass of the upper section plus, what did you say 13 floors? So that's about what 30 stories? So you might want to consider what it would take to move a falling 30 story building 107 feet in any direction.

 

[ozeco41]

....You might also want to consider how much force it would take to deflect the mass of the upper section plus, what did you say 13 floors? So that's about what 30 stories? So you might want to consider what it would take to move a falling 30 story building 107 feet in any direction.

Key point - no way was the top block going "over the side".

Straight down with the added advatage that it had the outer tube of the lower bit to keep it on track after which that tube, left behind with no friends, could quietly fall over and drop to the ground.

Now there were 8 bits which went a bit further and two of those (which hit the Verizon building) still puzzle me as to how they managed that trick. The only one I can eliminate is explosives because that is another "no way" - no way could you fly columns from the Towers under the 9/11 scenario using explosives. It would need rocket motors or similar.

 

[Furcifer]

Key point - no way was the top block going "over the side".


Now there were 8 bits which went a bit further and two of those (which hit the Verizon building) still puzzle me as to how they managed that trick.

The tilt alone is impressive, you can you imagine the amount of energy to move the upper section outside the footprint?

Speaking of tilt, correct me if I am wrong, but the Verizon building was hit by the section that can be seen at 0.28-0.29s in this video :http://www.youtube.com/watch?v=ESaIEVxLnK4

This is the side opposite of the tilt. I think the Verizon building got hit by a very large section of the WTC north wall. I think the direction of tilt meant that the south face was completely destroyed, but the north face may have remained fairly untouched as the collapse wave passed. If a section of the north face remained intact, say from the 50th to 69th floor, and then started to tilt and fall over, it would have been flung fairly far.

Just a thought.

 

[ozeco41]

The tilt alone is impressive, you can you imagine the amount of energy to move the upper section outside the footprint?

Speaking of tilt, correct me if I am wrong, but the Verizon building was hit by the section that can be seen at 0.28-0.29s in this video :http://www.youtube.com/watch?v=ESaIEVxLnK4

This is the side opposite of the tilt. I think the Verizon building got hit by a very large section of the WTC north wall. I think the direction of tilt meant that the south face was completely destroyed, but the north face may have remained fairly untouched as the collapse wave passed. If a section of the north face remained intact, say from the 50th to 69th floor, and then started to tilt and fall over, it would have been flung fairly far.

Just a thought.

Agreed and good thinking - the mechanisms to throw bits could include a sort of a cricket "bowling" action rather than a baseball type pitch. I readily visualise a tall bit of wall falling over and throwing a loose bit off the top as it goes.

Try this for locations:

If you identify the orange coloured "lozenge" bits showing how most material fell straight out from the original wall location the puzzler about the Verizon two is that they are more off the corner than the face.

The ones over the WinterGarden side are not special - could be just the random outfliers of the distribution. But I cannot guess how the Verizon 2 gor there. BUT I don't say "Godddidit" er "it was explosives. Too big a quantum leap AND I don't know how you could put them there with explosives. No focussing structure to direct a blast. Even using a low explosive "lifter" such as ANFO there is no area for a blast to act on . No time for blast induced acceleration etc etc

So on the "interesting puzzles" shelf for me.

 

[tfk]

Hey Oz,


Nice to meet 'cha.

Mine's BSMechE, Cornell '74.

Yeoman Project Engr & R&D Engr. (Product Design & Development).

Agreed and good thinking - the mechanisms to throw bits could include a sort of a cricket "bowling" action rather than a baseball type pitch. I readily visualise a tall bit of wall falling over and throwing a loose bit off the top as it goes.

Try this for locations:
http://conleys.com.au/webjref/FEMA2.jpg

If you identify the orange coloured "lozenge" bits showing how most material fell straight out from the original wall location the puzzler about the Verizon two is that they are more off the corner than the face.

The ones over the WinterGarden side are not special - could be just the random outfliers of the distribution. But I cannot guess how the Verizon 2 gor there. BUT I don't say "Godddidit" er "it was explosives. Too big a quantum leap AND I don't know how you could put them there with explosives. No focussing structure to direct a blast. Even using a low explosive "lifter" such as ANFO there is no area for a blast to act on . No time for blast induced acceleration etc etc

So on the "interesting puzzles" shelf for me.

One of Chandler's objections is that he feels that there is no way for the beams to get thrown to the side faster than the upper block is descending. This would be true for pure collisions, but there are a couple of ways that this speed could be mechanically amplified.

It strikes me that the options are 1) multiple pure collisions, 2) flips or 3) flat springs. While 1) seems low probability to give you that distance, I think that 2) & 3) will.

Flips: This would involve turning a descending peripheral column assembly (3 3-story beams & 3 spandrels) into a pinball flipper, throwing itself or another assembly outward faster than the building was descending. If the bottom of one of these assemblies started down on the outside of a horizontal bar and the top of the assembly then moves to the inside of the building, it'll turn the the lower section into a flipper. Depending on the location of the fulcrum, the horizontal speed of the bottom end can be much greater than the descending speed.

Flat springs: Take a credit card. Hold it between your thumb & first finger near the tips of each. Bring your fingers together. Watch the credit card fly across the room much faster than your fingers approach each other of the top.

While it's tough to get a sense of the flexibility of a 14" square x .2 WT x 37' long steel beam, scale it down to a 1" square x .016 WT x 36" long piece of tubing. It isn't gonna bend elastically as much as a credit card, of course, but you are going to get some flex. And starting from 1000' in the air, you don't need a whole lot of lateral speed to reach out 300' - 600'. I think I figured it at around 50 - 70 mph a while ago.

Just a couple of thought experiments...

tom

 

[tfk]

The downward facing core columns in part C would punch through the floors and elements of part A just as the upstandng core columns of part A would punch through the floors and elements of part C. Equual and opposite forces. I I think myself that the collapse would have stopped through friction after only a few floors but at worst 13 floors above nd 13 floors below would be destroyed and then part C would be shattered and disassembled and fallen off the sides-gone.

"... I think myself ..."

lol.

No you don't.

 

[psikeyhackr]

kips is a unit of measurement for WEIGHT. Again. Why do you have to know the exact weight of the exterior panel? Why can't you be off by a few kips.

I've asked this question FIVE TIMES now.

.
KIPS is not the weight of the perimeter wall panel It is the PRESSURE, thousand pounds per square inch, that they could withstand. The pressure capacity would be somewhat related to the weight.

I already showed in my two videos that the mass/inertia on every level affects the motion of the building. Both horizontally in the impact and vertically in the collapse. So you don't know enough physics to comprehend that?

psik

 

[R.Mackey]

For the record, the ejected material does not have to be moving faster than the descending mass. See pages 95-98 of my whitepaper.


Also, to get my poor, wounded, staggering thread back on topic, I have finally received a useful reply to my Hardfire Modeling Challenge! The submitter has put together a simulation rather than a physical model, which is perfectly fine, and one that I believe is close enough to do some useful experiments. I've replied to its creator with a list of questions, most having to do with the assumptions used, but nonetheless this is good enough for some valid experimentation. The model is found here: http://femr2.ucoz.com/

Enjoy.

ETA: The model also includes a detailed spreadsheet with tower mass, by floor, in terms of steel and concrete. So, as you can see, even people in the Truth Movement are capable of finding these answers.

 

[beachnut]

...

ETA: The model also includes a detailed spreadsheet with tower mass, by floor, in terms of steel and concrete. So, as you can see, even people in the Truth Movement are capable of finding these answers.

His models show how it can happen but he is a 911Truth believer? What?


The poor guy is hung up on making all the concrete into dust. Stupid from the minds of superior 911Truth expert beings who are not challenged, or checked. The dust to remind myself is mostly insulation, ceiling tiles, dust, and wallboard, not cement. But having a super brain and believing 911Truth are ego stupid problems.


First glance this guy is a dustification 911Truth failure.

 

[tfk]

You might also want to consider how much force it would take to deflect the mass of the upper section plus, what did you say 13 floors? So that's about what 30 stories? So you might want to consider what it would take to move a falling 30 story building 107 feet in any direction.

3body,

I think that you'd get a better idea of why the upper block cannot fall to the side if you consider geometry rather than forces.

Let's spread the curvature that gives the upper block its tilt over, say, 5 stories. Let's assume a POV that has the upper block tilting to the left. Imagine all the columns connecting the upper block to the lower block. You've got four sides to consider.

I'll talk about the peripheral columns, but the same applies to the core columns. They aren't as far removed from the "neutral axis" of the bend, of course, so they don't have to elongate or bend nearly as much as the peripheral columns do.

When the towers were straight, then all the columns were in (approx) uniform compression. About 1/3rd their yield strengths.

Once the top of the tower starts to lean, the columns on the right (outside of the bend) have their loads dramatically reduce. If it weren't for the dead weight preload, these would actually go into tension.

Those on the left side have to go into massively increased compression to compensate for the load reductions in the columns on the right.

The columns on the near & far side go into a complex stress that is compression plus bending. Now, in the middle of these enormous bending forces, you've got joints & small bolts holding each column to the one above and beside it... A prescription for failure.

My point is: work your way around the building, imagining how much deformation the individual beams have to go thru in order to get a significant amount of curvature. Especially the one on the front & back sides that have lots of bending in them.

Steel just doesn't like to go thru this much strain.

tom