# WTC: Rate of Fall (rate of crush)

Discussion in '9/11' started by George B, Feb 2, 2013.

1. ### George BExtinct but not forgotten Staff Member

What are the errors in this presentation . . . seems logical and well thought out . . . the failure of the original floors would not logically be all at once but could be gradual or very uneven based on uneven heat transference . . . and then the average resistance force of the remaining building . . . ??? With 8.62 meters per second downward force of the mass of the 15 floors in the North Tower and assuming zero resistance of the missing floor that was removed by fire and crash damage . . . it should have taken at least 44 seconds to crush the building to the ground . . . is he wrong? If so WHY?

Conclusion video #3 below:

2. ### George BExtinct but not forgotten Staff Member

Lee, what is your take on the post above . . . ??

3. ### lee h oswaldBannedBanned

I was just going through your vids, actually - I'll get back to you later on that, have to dash out for a bit x

I've not gone over it in detail, and not seen how he calculated the upwards force, but gravity (the downwards force) is a constant acceleration, so it's speeding up the block the whole time. The upwards retarding force is a mostly instantaneous force during the impact with a floor. So it is is only slowing the upper block down for the period of impact. Hence the effect of gravity is vastly greater than the effect of the upwards resistance.

This calculation is much easier understood in terms of energy. There's the energy in the falling block, which rapidly increases as it falls - both from gravity and from increase in mass, as more of the building is falling.. Then there's the energy required to break the floor-column connections so the fall can continue.

I'm off to superbowl in in a bit, but I'd like to revisit this at some point, as dealing with actual numbers should be a very level playing field.

How familiar are you with the the basic Newtonian equations of motion George? s=u*t+0.5*a*t*t etc?
http://en.wikipedia.org/wiki/Newtonian_mechanics

5. ### George BExtinct but not forgotten Staff Member

Are you saying he did not account for the instantaneous nature of the collisions and the acceleration of the combined mass of the successive crumpling building plus the first 15 floors . . . I thought he addressed that . . . I could be mistaken . . .

6. ### George BExtinct but not forgotten Staff Member

Not since high school . . . didn't take physics in college . . .

7. ### lee h oswaldBannedBanned

1) Miscalculation of the tonnage of the building. Subject quotes, 68,000 tonnes for top 15 floors. 110/15=7.33

So the total weight of the building, according to subject is, 7.33x68,000=496,400 tonnes. That's too much. The concrete (per tower) is close to 100,000 tonnes (plus/minus 10k - more likely +), steel the same figure. So we're really looking at 220,000 tonnes plus furniture. That's not too easy to estimate - but it's going to be in the thousands of tonnes - you try to work it out - how much does a work station, desk, screen, curtain, carpet, weigh exactly? And how many were on each floor of the tower in question? I'd be inclined to add 60,000 tonnes, which represents just over 500 tonnes per floor. Total weight of building at 280,000 tonnes is more accurate. So subject needs to adapt numbers in his sums.

2) The second error stems from the first - and it's the mass calculation which is wrong. The result of that would be to slow down the rate of acceleration a little.

3) No consideration is made for the fact that the structural aspect of the tower becomes more robust as the 'collapse' progresses. ie. more resistance the further down you go, as the lower parts of the tower are made from thicker steel, etc. eg. The vertical steels at the base of the towers were 5inches thick, 4.5foot longx2foot wide box welded columns with 3.5inch welded bracing internally. That's a beast of a thing - specially when it's tied to 46 just the same via diagonal and horizontal bracing. A beast.

The calculations suffer from the same inaccuracies as my own on the reduction of steel rc to 60 micron dust. But you have to start somewhere. And the subject did. And it's important to say that the subject's calculations are exactly right, there's no problem with the maths at all. That may well be my most important point - on behalf of the subject. I feel like a bit of a bitch for pointing out the errors, but at the end of the day, they don't make a big difference to the point, even though I admit it mysef after all these words of mine. And the point is - the given explanation doesn't add up - if it did, we wouldn't be here.

So you would consider this to be conclusive proof of controlled demolition then?

9. ### George BExtinct but not forgotten Staff Member

So Lee . . . you agree the (unless you have a better name) Crush Rate would exceed 44 seconds??

10. ### George BExtinct but not forgotten Staff Member

If I may . . . it is potential evidence that what we thought we witnessed in approximately 10 seconds is not explainable by rudimentary physics as was presented by the presenter in the YouTube and a quick analysis by Lee . . .

11. ### George BExtinct but not forgotten Staff Member

It is the position of the presenter that the fall rate could only be justified if the foundation of the buildings were somehow compromised . . . otherwise the upward resistance of the intact 95 floors would prevent such increased acceleration . . . at least at the rate observed. . .

That does not make any sense. If the foundation were compromised, then the entire building would fall as one. The bottom of the building never moved until the collapse wave reached it.

13. ### George BExtinct but not forgotten Staff Member

Compromised does not mean complete failure . . . just providing less resistance to the downward force of the building above . . . I am just reporting what the presenter suggests . . .

As I calculate it, accounting for the terminal velocity of around 90/m/s/s or an average velocity of 45/m/s/s, the building could have fallen 450 meters or 1,476 feet in 10 seconds but fell instead 361 meters or 1,184 meters or 36/m/s/s which is about 80% of a free fall rate at sea level . . . without air resistance the distance would have been 490 meters or 1,568 feet in 10 seconds . . . based on d=(0.5 x 9.8 m/s/s) x (Time Sq or 100) . . .

Conclusion: The bottom 95 floors offered a measurable amount of resistance to the fall of the North Tower . . . it slowed the descent of the top part of the building about 20%.

Question: Is this less resistance or more than would have been expected?

Actually, that's not what he suggests. He says that the top-down collapse of the building is an indication that the foundation was not damaged (in the first video)

Well, according to your video, it's vastly less. However he's making the fundamental error that the upwards force is equal to the downward force. Basically saying that upon impacting a floor, the upper block will stop entirely. That is total nonsense.

You have to look at the basic mechanisms of failure. There's basically horizontal structures (the floors) and vertical structures (the columns). Now the columns can carry a lot of weight, so long as they are both vertical, and braced at regular intervals. The floors cannot carry much weight. So if you drop a large mass on the floor, it will fail. This both removes the bracing, and pushes and pull the vertical columns so they will fail. The outside columns will fall away from the building as their lose floors, the interior columns will fail similarly inside the building, but more needs to be stripped away before they fail.

But these things don't happen at the same time for the same floor. Vertical structures would likely collapse only after several floors worth of horizontal structures have been stripped away. And they would require relatively small amounts of energy to collapse - in fact the exterior columns would have buckled and collapsed simply under their own weight, with no additional force needed.

So it's a bit more complex than his simple equations. You don't have a solid block falling onto another solid block. The initial floor-floor impact would compact the bottom floor of the top block as much as the top floor of the bottom block. But after that you've essentially got a falling mass of compacted floors that grows rapidly, getting bigger and bigger, doing more damage to the lower floor than the upper floors. Each floor detached adds to the falling block. The retarding energy acting on the top of the top block is approximately the energy required to break the horizontal members away from the vertical members, plus a small amount required to push the vertical members.

This is an old argument. The truther versions of it range from simple incredulity to calculations to rely on incorrect assumptions (like in your linked video), to calculations that simply plug in excessively large amounts of energy required to "destroy" each floor, rather than simply separate it, loading to collapse with buckling.

It's difficult to debunk this subject, because it's complicated, but one authoritative anaysis of the subject is:

Mechanics of Progressive Collapse: Learning from World

https://www.metabunk.org/files/Mechanics of Progressive Collapse.pdf

and

What Did and Did not Cause Collapse
of WTC Twin Towers in New York by
Zdenek P. Bažant, Jia-Liang Le, Frank R. Greening and David B. Benson
https://www.metabunk.org/files/00 WTC Collapse - What Did & Did Not Cause It.pdf

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16. ### lee h oswaldBannedBanned

Fantasy. These contortions are equal to the 'building within a building' stuff. The guy made an effort to actually do the maths - and the maths is right, no matter your protestations, if not a perfect representation. He doesn't claim perfection. But basically it's correct - and you know it. Don't you? How long should the building have taken to reach the ground? - let's see your maths in his terms and based on my calculation of the total weight of one tower which is 280,000 tonnes including furniture. If what we're told is true, then how long for 'The Crusher' (ie. the top 15 floors - which actually weighed about 38,000 tonnes) to hit the ground after crushing the building and then itself, leaving nothing recognizable as a building, and likewise its contents (yes, that's the story, I feel sullied just repeating it). Can we see that from you in the terms I propose?

17. ### lee h oswaldBannedBanned

And he is right to say that. And to corroborate, there are scores, if not hundreds, of eyewitness accounts of explosions and destruction in the lower levels (lobbies and below) of the buildings. That's a direct connection in evidence.

The mass of the building makes no difference to his calculations. He says that when the falling block is in contact with the building, then the building exerts an upwards force equal to the downwards force. This is correct. It's like if you place one brick on top of a pile of nine bricks, it's in equilibrium, the forces are balanced.

He then says that the upped block exerts a downwards force of ma (mass times acceleration, really should be mg, but it's the same thing). He then says the lower block exerts (or rather is capable of exerting, otherwise he's saying the top of the building should float away) an upwards force of (ma + the mass of the people + some safety factor). This is also true. The lower block is normally capable of supporting the weight building above it plus quite a bit extra. The bottom floors are capable of supporting the entire weight of the building, plus more. In fact, if his logic was correct, the upper block would slow down and stop after just a few floors.

Where he is wrong is in describing this upwards force as a constant force. It's not. gravity is a constant force, accelerating downwards. The upwards force only happens DURING CONTACT. When the upper block fall onto the lower block, there's a collision, the floor fails, and the block continues to accelerate.

So the upwards force will only affect the acceleration WHILE THE FLOOR IS BEING DETACHED. i.e., only while the joints are failing. That failure only takes a fraction of a second. But to calculate the amount of upwards force under his assumptions, you'd need to know how long it takes the floor to fail when 38,000 tonnes are dropped on it.

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Explain how weakening the foundation would make the block fall faster. Are you suggesting that the core columns were disintegrating inside the building from the bottom up?

20. ### George BExtinct but not forgotten Staff Member

Mick, please watch mark 1.27 - 2.00 minutes . . . I feel he discusses the need for the lower floors to be compromised for the entire building to collapse at the rate we observed . . .

21. ### George BExtinct but not forgotten Staff Member

So Mick how much of a fraction of a second does it take . . . how much time are you talking about . . . 95 of them? That would add up rather quickly don't you think?

No, he says if the foundation is broken then the lower part of the building will fall. See 2:25 "however, what we saw was the opposite, we saw a collapse beginning from the top and going down"

The point is that most of the time the building is not slowing down. The MOST it could take, as a proportion of the total time would be the ratio between the thickness of the floor, the the height between the floor and the ceiling. Or about the 20% you mentioned.

Of course that's all a gross simplification - his reasoning is fundamentally flawed.

24. ### SR1419Senior Member

Indeed.

However, a large number of those eyewitness accounts can be attributed to the fireballs down elevator shafts and severed elevators crashing to the lower levels.

25. ### JazzyClosed Account

NONE of the vertical columns, whether internal or external, were capable of stably supporting their own weight. The whole structure relied on the cross-bracing of the floors, and particularly the top hat truss and the engineering floors, for stability. Without that those columns were spaghetti. Even if the column sections were 5" thick at the foundations.

26. ### George BExtinct but not forgotten Staff Member

I know Mick . . . that is the point . . . to explain such a swift failure of the entire building . . . it would normally require the bottom to fail to allow the building above the foundation to fall apart supplying minimal resistance to the upper floors to fail and fall in the time we observed. And yes this did not appear to occur which means there may be another explanation . . . one we don't have . . . that was his point!!

27. ### RolandDActive Member

First of all, he doesn't use any physics, he only speculates.

He seems to be an individual whose only knowledge of physics was learned through other WTC CT websites and decided to put together a video showing his solution using that meager knowledge.

28. ### George BExtinct but not forgotten Staff Member

Ok, please use your knowledge of physics and the appropriate equations to show how the building failed and fell in 10 seconds . . .

29. ### RolandDActive Member

Sorry, my knowledge is only extensive enough to recognize bullshit when I see it.

I thought you mean he was suggesting there was a bomb in the foundations, like lee is suggesting.

I know that. It's pretty obvious you can't have a free-standing 1000 foot tall girder. My point was more that the column would become spaghetti after just a few floors had been stripped from them, especially with a large eccentric dynamic load on them.

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32. ### George BExtinct but not forgotten Staff Member

I don't think he implicitly suggested any specific cause other than the speed of collapse wasn't supported by the official story . . . I personally don't have a specific theory . . . however, I don't think the official story fits what I witnessed . . .

33. ### JazzyClosed Account

Ah. Well done with that vid! I had seen it once but was unable to rediscover it.

Bearing in mind that inverse L squared in the diagram below, then one can see the outside tower columns would be close to being compromised with TWO consecutive detached floors, even if undamaged by fire. THREE, and it would be gone with the wind.

34. ### George BExtinct but not forgotten Staff Member

It is counterintuitive to me that a 110 story building could fall to the ground in ten seconds even if it were made of paper clips and tin foil. Sorry, you will have to build me a scale model to prove to me it is possible . . .

Find me a successful controlled demolition of a high-rise building of known height and known collapse time and prove to me it can be accomplished faster or in the same rate as WTC 1 . . . If WTC fell faster or the same as the demolition . . . how would you explain that??

A scale model? That's not going to help. You'd need to build a 1:1 replica.

The square cube law is one of the reasons that the "it looks weird" argument still gets traction. It does look weird. It look weird because it's so big, and our simple brains are just scaling up our experience with smaller things. But that scaling doesn't work. You can't demonstrate it with a scale model.

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37. ### George BExtinct but not forgotten Staff Member

OK . . . High Rise steel reinforced buildings are fragile . . . until 911 no one had seen such a demonstration of fragility in the collapse of three monsters by two different mechanisms . . . in almost free fall speeds . . . so show me some similar occurrences and I might start to change my mind . . .

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They are not fragile. They are very strong. The planes flew into them, and they were fine. It takes an incredible amount of force to collapse them. But once it got started, the force was unstoppable.

A rope is strong, but you can cut it with a razor blade.

I can't show you a similar occurrence, because there are no similar buildings. You are going to have to do the math.

39. ### George BExtinct but not forgotten Staff Member

If the math supports it . . . show me . . . the doubters think the collapse(s) are so reminiscent of a controlled demolition you cannot tell one from the other . . . show me demolitions that collapses in less time . . . ???

40. ### OxymoronBannedBanned

This is a point I have often raised in other debates... thanks for bringing it up here Lee, as I think it very important.

I also think it very important to note that acceleration due to gravity is only relevant when there is only the normal impedance due to air resistance and cannot be applied where further resistance is encountered.

People keep using this to demonstrate 'how it is mathematically possible for the towers to fall in such a time frame', when this really does not apply at all as the resistance of the supporting structure would significantly impede acceleration from taking place. By what factor seems impossible to conclude as there is no mathematical or evidential data on the resistance.

Long Span flooring sections are in common use and I think it important that people should be assured that the same design faults as allegedly caused wtc1, 2, & 7 to fall, are not inherent in all these other buildings.

I cannot seem to find if the new wtc 7 has long span flooring?

http://www.scribd.com/doc/19184820/Economic-Long-Span-Concrete-Floor-Slabs

As for asbestos and other toxins... I think it typical of the cover up and disinformation that is put out and is appalling.

World Trade Center Rescue Workers Believed EPA, Ended Up Sick http://www.ucsusa.org/scientific_int...pollution.html
Politics over science... would they really do that?