WTC: Rate of Fall (rate of crush)

[Jazzy]

There is not 1 example you could point to of a building collapsing and not decelerating as it crushes through it's structure. There is no justification for what you have written and it is not supported by any experimental evidence.

But that is what the towers (and for that matter WTC7) did, and that is what I've been saying. You appear to be agreeing with me. I have not ever claimed otherwise. It is you that needs to read what other people have written, and make sense of it. Best not involve others in your own confusion, eh?

Apostrophe? Tut-tut.

 

[Mick West]

"The key is what force is required to STOP it" The key isn't what force is required to stop it. The key is what effect should upward force that is capable of holding the objects weight have on it's rate of acceleration. I never stated that the bottom structure should stop the top structur so you are completely misrepresenting my argument.

In fact no there is no fixed force that is required to stop it. There is a fixed force to cause the object to decelerate at a fixed rate but the force required to stop it depends on how fast it is going and how long the force is being applied for.

If you measure the rate of acceleration of the 30lb weight in video you posted you will see that the force required to break through the bottom object slows the weight down as it breaks it, the weight does not continue to accelerate into the bottom object.

It did not continue to accelerate into the ground (although it give it a good go), but the cardboard box did not slow it in any noticeable manner.

There's a difference between reducing acceleration, and slowing (reducing speed).

In a very simple way, if the upwards force is less than the downwards force, then the acceleration will simply be reduced. It will continue to get faster though. And that's what happened in the WTC collapses, the dynamic force of the falling parts of the building were far greater than the static resistance of the lower parts, so all that happened (globally) was the downwards acceleration was reduced to about 2/3 gravity.

 

[Pete Tar]

There is not 1 example you could point to of a building collapsing and not decelerating as it crushes through it's structure. There is no justification for what you have written and it is not supported by any experimental evidence.

Well there is not one half kilometre building that has catastrophically failed before either. Maybe this is what happens 8 times out of ten when you have a 500 metre building collapse into itself, maybe it happens 2 times out of ten. What practical field experiments have taken place with 500 m structures other than this one?

 

[Carlito Jax]

The way that corregated cardboard is made it has a lot of strength in 1 dimension only as soon as it bends slightly it loses most of it's strength. However if you consider the tensile strength of steel collumns the amount of stress needed increases during elastic deformation into plastic deformation increasing to a maximum just before they snap. The moment that the weight hit the corregated cardboard it would have decelerated in accordance with newtons laws, if there was a super slow motion clip of this and you measured it you would be able to detect a deceleration at the moment of impact. However as soon as the cardboard bent it would have lost most of it's resistance. This is not the case for steel beams, see: http://en.wikipedia.org/wiki/Ultimate_tensile_strength

 

[Carlito Jax]

If you look at this building collapse https://www.metabunk.org/files/pull-verinage.gif you can roughly see an initial acceleration as the support which was holding it up is removed, then as it impacts the structure below and crushes through it starts to decelerate. It does not continue to accelerate through the structure which is capable of supporting it's weight. Every single example of a building collapse if you measure the rate of acceleration you will see an initial acceleration followed by a deceleration in accordance with Newtons laws. Every experiment you can conduct no matter what the scale a structure which is capable of holding another structures weight when static will cause the crushing structure to decelerate as it crushes through it in accordance with Newtons universal laws of motion.

 

[Mick West]

If you look at this building collapse https://www.metabunk.org/files/pull-verinage.gif you can roughly see an initial acceleration as the support which was holding it up is removed, then as it impacts the structure below and crushes through it starts to decelerate. It does not continue to accelerate through the structure which is capable of supporting it's weight. Every single example of a building collapse if you measure the rate of acceleration you will see an initial acceleration followed by a deceleration in accordance with Newtons laws. Every experiment you can conduct no matter what the scale a structure which is capable of holding another structures weight when static will cause the crushing structure to decelerate as it crushes through it in accordance with Newtons universal laws of motion.

You are still making the incorrect assumptions the energy required to "crush" the supports under a floor is greater than the energy gained by the above floors falling on it.

Here's a simplification:

Consider the upper part of the building starts at rest, with a velocity 0.
It then falls a floor, hits the floor below it, and must then either be:

A) Stopped, because it could not destroy the floor below it, or
B) Moving downwards at V, less the energy needed to crush the supports, say V-C

If it were, A, then we'd just see the top of the building drop a floor and then stop. Clearly it is B.

So, it's now starting out falling both heavier than it was before, and moving faster than it was before. When it hits the next floor, it will hence be faster again. And again and again. Hence it's accelerating, just at less than g.

This is, or course, a simplification. Just less of a simplification than your analogy.

 

[Mick West]

And here's a thought experiment, taking your argument to extremes. Consider you have three very rigid blocks that each weight 1 million tons. You have some 1000 foot long columns each of which can support 0.500005 million tons before shattering into dust. So two columns can support one block, and four columns can support two blocks, etc. We build a tower from out three blocks like the one on the left below.



Now lets say there's a fire or something and the top columns fail. The Million ton block hits the block below it with a force of 1000g for a fraction of a second, shattering the columns below it. We now have two blocks falling together at a speed above zero. They fall down to the next block.

Now consider you'd made this up of 1000 levels in the same manner. Would it not accelerate, collapsing all the way to the bottom?

Or according to your argument, it should stop. At what level will it stop?

 

[Carlito Jax]

Steel columns don't shatter, they are ductile not brittle. Steel columns bend and snap.

 

[Mick West]

Steel columns don't shatter, they are ductile not brittle. Steel columns bend and snap.

But I'm starting with an extreme example of your statement that "Every experiment you can conduct no matter what the scale a structure which is capable of holding another structures weight when static will cause the crushing structure to decelerate as it crushes through it in accordance with Newtons universal laws of motion." To show that is false.

Replace the columns with 100 foot long rebar if you like. Or 10,000 foot long rebar.

The point is at some scale your statement can be shown to be obviously false. So then the question is at what point, if any, does it become true?

 

[Carlito Jax]

If you think that it can be shown to be false then create an experiment showing that it is false.

 

[Mick West]

If you think that it can be shown to be false then create an experiment showing that it is false.

I was thinking of doing that. I'd use straws for the columns, 2x4 sections for the floors. But it's a bit of pointless experiment as that's not how the WTC collapsed. It was a complex combination of floors failure, exterior peeling, and column buckling and failing in various ways across a quite tall chaotic collapse front. Rather hard to model.

 

[Pete Tar]

The steel that can be seen being ejected in the collapse - was that structural? That would have an effect on the calculation wouldn't it?

 

[Jazzy]

Every single example of a building collapse if you measure the rate of acceleration you will see an initial acceleration followed by a deceleration in accordance with Newtons laws. Every experiment you can conduct no matter what the scale a structure which is capable of holding another structures weight when static will cause the crushing structure to decelerate as it crushes through it in accordance with Newtons universal laws of motion.

This plainly isn't true just as soon as any beam attempts to take the "loading" of any column. You aren't being logical. You are referring to a "classical" approach: "the column beneath the column will be able to take load of the descending column above", when clearly this never happened ever again.

Static structural analysis requires that floors be horizontal and columns vertical and doesn't concern itself with energy at all.

Dynamic structural analysis has more to do with the Theory of Machines, and has everything to do with energy, and it's not so well understood by anyone. It is a GAP you can dance in, (you clearly are), but not without being denuded.

 

[Ron J]

Ah ok, well you can rig a building with explosives in a certain way so as to define where the collapse will occur. In most cases buildings are rigged to fail at the bottom but they can be rigged to fail at any specific point. Considering the counter argument that no explosives were needed at all to make the building fail at the precise point where the plane impacted it doesn't seem like a very good rebuttal. Also in the video of the collapse of wtc 1 you can see the spire of the building start to fall a fraction of a second before the outer structure starts to fall showing that it was the core collumns that failed first and not the precise point where the plane hit or the trusses holding the floors in place.

There has to be credible evidence of rigging of explosives, which is certainly lacking. Controlled demolitions don't just happen. Power outages and "sounds of construction on empty floors" is not proof of anything, except an active imagination.

The out of control fire was the act of destruction which was occurring in all three building which collapsed.

The building failed at the level at which the jetliner struck WTC1, not the point at which the plane struck the building. Out of control fire was occurring at that level. Once catastrophic failure occurred, the momentum of the collapse could not be contained by the standing floors below, due to the amount of debris that was rapidly crashing down upon each floor, in it's turn below.

 

[Ron J]

Here's an accompanying explanation:

The twin towers and Newton's Universal laws of motion:
W=weight
F=supporting force
a=acceleration

In figure 1 we can see the situation just before the collapse of either of the towers, although there is damage to the area that the plane hit the bottom section of the tower is still holding the entire weight of the top of the tower. The tower is stationary therefore according to Newtons 3rd law the forces are balanced

In figure 2 we can see the moment of collapse. For the sake of argument let's assume that all of the supporting force in the area that the plane hit has been reduced to 0. In this case the top section of the tower will fall at freefall acceleration until it smashes into the bottom section of the tower which has not been damaged by fire and should still be able to support the entire weight of the top section

In figure 3 the top section of the tower smashes into the bottom section which has been designed to support at least 1.6 times the weight of the top section. In this case The supporting force should be 1.6 times the weight before it fails. The upward force should be greater than the downward force and therefore according to Newtons 2nd law the acceleration should be upwards meaning the top section of the tower should decelerate (slow down)

Conclusion: Both towers 1 and 2 fell at roughly 60% of freefall acceleration meaning that during the collapse the supporting force of the bottom section must have been compromised by an outside force as the weight of the top section was not enough to produce the acceleration observed.

That is simply not true. The 94th floor could not support 15 floors falling down upon it.

If you took out one floor and gently placed 15 floors properly aligned, down onto the columns below, the columns might well hold the weight being gently placed down upon them, but that is not what happened as a result of catastrophic failure. The outside force compromising the bottom section was the downward MOMENTUM of the upper section, which could not be seriously contained by the floors standing below it.

 

[Carlito Jax]

the problem with your assertion that ""the column beneath the column will be able to take load of the descending column above" when clearly this never happened ever again." is that the core collumns clearly failed. If the core columns had not taken their maximum load then they would not have failed and the tower would have collapsed around it and the core columns would still be standing. You're trying to have your cake and eat it - The columns didn't fail but they did fail.

 

[Carlito Jax]

"There has to be credible evidence of rigging of explosives, which is certainly lacking." credible evidence like over 500 eye witness testimonies of explosions throughout the building before the collapse, multiple squibs during the collapse, melted steel which couldn't be formed by office fires, traces of nano thermite in 4 separate samples of wtc dust, molten steel sparks from a thermitic reaction seen coming out of the towers. This is all evidence that explosives were rigged in the building. In order to know that controlled demolition is the only possible way it could have been done it is not necessary to catch them in the act of rigging explosives. In the same way that you know dinosaurs existed in the past without ever seeing a living dinosaur.

 

[Mick West]

Please keep on topic. Rate of fall/crush. No discussion of explosives needed.

 

[Ron J]

"There has to be credible evidence of rigging of explosives, which is certainly lacking." credible evidence like over 500 eye witness testimonies of explosions throughout the building before the collapse, multiple squibs during the collapse, melted steel which couldn't be formed by office fires, traces of nano thermite in 4 separate samples of wtc dust, molten steel sparks from a thermitic reaction seen coming out of the towers. This is all evidence that explosives were rigged in the building. In order to know that controlled demolition is the only possible way it could have been done it is not necessary to catch them in the act of rigging explosives. In the same way that you know dinosaurs existed in the past without ever seeing a living dinosaur.

What did any witnesses see exploding?

There were no squibs seen during the collapse. Do you know what a squib is? I have used them in setting up fireworks displays. The top 15 floors of WTC1 simply collapsed onto the 94th floor, starting a chain reaction global collapse of the building. The east wall of WTC2 was bowed in where the collapse began. A major fire had been raging there previously.

What melted steel? I have seen at least one photograph of a column that had a cutting torch used on it, but that was after the collapse.

There was no thermite reaction. Sparks seen falling from WTC2, minutes before it fell, were not due to thermite. There was no nano thermite in any samples of dust. That has been debunked.

There is no credible evidence that explosives were rigged in the buildings.

"In order to know that controlled demolition is the only possible way it could have been done it is not necessary to catch them in the act of rigging explosives. In the same way that you know dinosaurs existed in the past without ever seeing a living dinosaur."

The fires were the destructive force on the buildings that collapsed. Out of control fires. The fires were the only possible way that the buildings collapsed as they did. There were no dinosaur bones found in the wreckage of the WTC.

 

[Carlito Jax]

Some witnesses got their skin blown off from explosions in the basement 30 mins after the plane impact. Instead of getting side tracked just prove that a structure can accelerate through a ductile structure that is capable of supporting it's weight when stationary. Instead of proving anything NIST simply asserted that "Global collapse was inevitable" because they failed to do their job, if you expect the collapse theory to have the slightest credibility you should prove that the collapse at the acceleration observed is possible never mind inevitable.

 

[Cairenn]

Really, got their 'skin blown off'? That doesn't make any sense. You are also ignoring all the explosive items that were scattered through the buildings.

 

[thedude953]

Some witnesses got their skin blown off from explosions in the basement 30 mins after the plane impact. Instead of getting side tracked just prove that a structure can accelerate through a ductile structure that is capable of supporting it's weight when stationary. Instead of proving anything NIST simply asserted that "Global collapse was inevitable" because they failed to do their job, if you expect the collapse theory to have the slightest credibility you should prove that the collapse at the acceleration observed is possible never mind inevitable.

Actually there is no mathematical certainty of a collapse in the way it did as proved throughout this thread just theoretical possibilities with potential of the collapse happening in this way. And saying that it for sure would have fallen with this rate of acceleration is absurd read through the thread ln no way is it ever proved in a realistic way that any of the buildings could have fallen with the speed they did. Mick and jazzy have a clear opinion on the matter weather they try to hide it just read the whole thread nothing they presented proves anything with certainty. Although there is plenty I room forskepticism.

 

[thedude953]

But to say for sure either way is just absurd

 

[Carlito Jax]

"Really, got their 'skin blown off'? That doesn't make any sense." Hot explosions makes peoples skin melt and peel off. Have you ever seen a burn victim?

"You are also ignoring all the explosive items that were scattered through the buildings." So it seems perfectly reasonable to you that things just started to spontaneously combust?

 

[Ron J]

Some witnesses got their skin blown off from explosions in the basement 30 mins after the plane impact. Instead of getting side tracked just prove that a structure can accelerate through a ductile structure that is capable of supporting it's weight when stationary. Instead of proving anything NIST simply asserted that "Global collapse was inevitable" because they failed to do their job, if you expect the collapse theory to have the slightest credibility you should prove that the collapse at the acceleration observed is possible never mind inevitable.

"Some witnesses" does not sound very specific. Seems you are referring to Rodrigues, seeing a burned man exiting an elevator in the basement, just after the Jetliner hit WTC1. Burning fuel went down the elevator shaft. That wasn't 30 minutes after the plane struck the Tower.

The controlled demolition theory is what has no credibility. From looking at the videos of the fire, i can see that much damage was being inflicted on both Towers.

A building that can support its weight when stationary is no match for 15 or 30 floors collapsing down upon the floor below the collapse initiation. Place a large rock on the roof of a car. It sits there. Now lift the large rock 12 feet above the roof of the car and drop it. The roof smashes in.

In the collapse of WTC2, debris can be seen falling down from the floor above the bowed in columns. Very quickly, the floors directly below the bowed in columns had debris collapsing onto them and the momentum of collapse did not decrease, all the way down to the ground.

 

[Jazzy]

the problem with your assertion that ""the column beneath the column will be able to take load of the descending column above" when clearly this never happened ever again." is that the core collumns clearly failed. If the core columns had not taken their maximum load then they would not have failed and the tower would have collapsed around it and the core columns would still be standing. You're trying to have your cake and eat it - The columns didn't fail but they did fail.

All the columns that failed did so because they were rendered unstable by losing their connections with the floors.

They did not fail because they were "crushed from above", but because they lost a sufficient lateral ties to lose their stability and buckle. Such columns cannot stand upright on their own.

 

[Mick West]

All the columns that failed did so because they were rendered unstable by losing their connections with the floors.

They did not fail because they were "crushed from above", but because they lost a sufficient lateral ties to lose their stability and buckle. Such columns cannot stand upright on their own.

They can to a degree, they fail a lot quicker if they are still supporting a significant load, or if something pushes them.

 

[Jazzy]

They can to a degree, they fail a lot quicker if they are still supporting a significant load, or if something pushes them.

I'll agree with you if you care to define what you mean by "to a degree".

If all the floors in a tower had been made to vanish then those columns would have dropped (under only their own loads) like so much wet spaghetti. The remaining core columns demonstrated this.

 

[Mick West]

I'll agree with you if you care to define what you mean by "to a degree".

If all the floors in a tower had been made to vanish then those columns would have dropped (under only their own loads) like so much wet spaghetti. The remaining core columns demonstrated this.

The degree would be somewhere between losing one floor, and losing all the floors. Obviously the core columns could free-stand with no load with no lateral restraint to a certain height, and with a heavy dynamic load they would free stand to a much lower height.

I think my "to a degree" has similar precision to your "sufficient"

 

[jomper]

All the columns that failed did so because they were rendered unstable by losing their connections with the floors.

They did not fail because they were "crushed from above", but because they lost a sufficient lateral ties to lose their stability and buckle. Such columns cannot stand upright on their own.

You mean like this?



Where everything falls off to the side, rather than down through the line of greatest resistance?

It's one of your favourite videos, isn't it, Jazzy?

 

[Mick West]

You mean like this?



Where everything falls off to the side, rather than down through the line of greatest resistance?

It's one of your favourite videos, isn't it, Jazzy?

It's one of my favorite videos. Of course you need to account for scale in a variety of ways to apply it.

Imagine 100 of those side by side. They still "fall off to the side", but now that's only 1/100th the width of the building.

 

[jomper]

The centre of mass of the [top part of the] South Tower moved considerably more than that.

 

[Mick West]

The centre of mass of the South Tower moved considerably more than that.

Where's the center of mass in that animation? And what does its motion imply to you?

 

[Pete Tar]

That's cool, but isn't a bit misleading to keep those lines stiff? There would be crumpling and folding, which makes that movement more understandable.

 

[jomper]

That's cool, but isn't a bit misleading to keep those lines stiff? There would be crumpling and folding, which makes that movement more understandable.

The lines are simply overlaid the video, Pete. Can you see any crumpling and folding beneath them?

 

[Pete Tar]

I don't have x-ray vision to see the internal structure. Do you really think that top bit holds its shape?
..
Can a side-by-side of doctored vs undoctored be added?
The lines make you see what the lines want you to.

 

[jomper]

Are the lines of the structure really not clear to you in the top right of the animation?

<shrug>

 

[Pete Tar]

Not where it would be folding and collapsing and transferring the center of mass.

 

[jomper]

They still "fall off to the side", but now that's only 1/100th the width of the building.

Here's another illustration of how much the centre of mass shifted in the South Tower at the onset of destruction. Certainly more than 1/100th the width of the building.

 

[jomper]

Can a side-by-side of doctored vs undoctored be added?

This is the best I can do, Pete: slightly more zoomed in and wrongly titled, but the same footage. The animation was never "doctored" with the addition of lines to illustrate the shift in the centre of mass of the upper section: those lines were simply overlaid.