WTC: Rate of Fall (rate of crush)

Mick West

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That is interesting . . . so the block rotation was arrested by the resistance of the intact building below, but the same resistance isn't sufficient to slow the collapse beyond 10% of a free fall rate in a vaccuum . . .

That's correct (assuming 10% is notional, there's a few estimate of the actual ratio), because the rotation is not being driven by gravity at that point, as the upwards resistance is evenly distributed.

So the resistance needed to stop the rotation is similar in scale to the resistance need to stop the building moving slowing in the absence of gravity.

It's like the difference between pushing a car on a flat road and lifting the car off the ground.
 

George B

Extinct but not forgotten Staff Member
Before you arrived here.


28% or 36% of free fall.

The temporarily-intact core would tend to "thread" the falling floor conglomerate back to the vertical. The external fragments would continue their trajectory and maintain their angular velocity.

WTC I . . . I don't think this research supports your inflated numbers . . .
 
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Mick West

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Yes. Slide off. No mistake. It's got momentum, it's a big mass moving in a direction. It's just physics! Please, think about it. It all says: Dude the whole top of the building just...etc. But 'something else' or 'other' happened.

It's rotating, and pretty slowly too. The upwards force on the left stops the rotation.

What "else" could be happening? Can you suggest a single possible explanation? Magic? Space rays? Invisible explosions off to the left? Magnets?

More important - the towers weren't ultra long layers of horizontals with four fat bits in the middle. I'm sure you could render them more accurately.



You want the middle bits a bit fatter?
 
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Mick West

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There's a good mathematical treatment of the tilt here:

http://www.911myths.com/WTC2TIP.pdf

Details in the the pdf.
 

George B

Extinct but not forgotten Staff Member
Mick said:
So the resistance needed to stop the rotation is similar in scale to the resistance need to stop the building moving slowing in the absence of gravity.

It's like the difference between pushing a car on a flat road and lifting the car off the ground.

I don't discount your analogy but even pushing your car requires expenditure of TIME and effort . . . the point is there was resistance even if small . . . the question is was the resistance the amount expected? . . . more or less than expected? . . . thanks for indicating the resistance required was minimal . . . then what happened to it (resistance) if more was expected?
 

George B

Extinct but not forgotten Staff Member
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Mick West

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I don't discount your analogy but even pushing your car requires expenditure of TIME and effort . . . the point is there was resistance even if small . . . the question is was the resistance the amount expected? . . . more or less than expected? . . . thanks for indicating the resistance required was minimal . . . then what happened to it (resistance) if more was expected?

Yes, pushing a car require time, but the block slowed its rotation over time.

Let's re-phrase the analogy a little, as it's something people can usually imagine, we've all pushed a car at one time or another.

Consider there's a car (an small one, VW Golf or so)



It's rolling toward you on a flat road at 2mph. You try to stop it. You can probably do it within a few seconds.

Now imagine the same car, but this time it's on a 45 degree slope. It's rolling down towards you at 2mph. How long does it take you to stop it?

You can't stop it. It would run you over, barely slowing at all, and within a few seconds would be doing 30mph, and still going.

Extend that to the vertical. You're on a cliff. The car is suspended an inch above your head. Someone cuts the rope.

In all cases the car has the same mass. But on the flat ground, you are just fighting inertia and friction. When gravity gets involved, then you lose.

So arresting rotation require minimal effort. A car that is slowly spinning on a turntable is no harder to stop than a car slowly moving on flat ground (in fact it's quite a bit easier, if you measure speed along the outer radius). But arresting downward motion under gravity is vastly harder. It requires that you exert a force greater than that of gravity.

Let's put some figures on that. A car weighs 3,000 pounds. Let's say you are an average person, strong enough to deadlift 100 pounds, and can apply the same strength to pushing the car. So that means that you are exerting a force on the car 1/30th that of gravity's pull on the car.

So force required to push or turn something slowly is vastly less than the force required to stop something falling. We are using very rough figures here, but 1/30th for pushing, or maybe 1/50 for turning.

So given that the block stopped turning over a second or so does not mean that very much force was needed. Indeed it indicates that the resistance of the floors below was only a small fraction of the force of the block under gravity. Hence the resulting very little difference in acceleration due to gravity as the block fell. The building could no more slow the block than you could slow the Volkswagon rolling down a steep hill.
 
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Oxymoron

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Banned
George, I don't think it is unreasonable to ask for math that might support your assertion that the building should not have fallen the way it did.

But no one seems able to provide mathematical support for the assertion of progressive collapse, despite Mick's heroic attempt, so I think yes it is unreasonable to ask George
 

George B

Extinct but not forgotten Staff Member
Yes, pushing a car require time, but the block slowed its rotation over time.

Let's re-phrase the analogy a little, as it's something people can usually imagine, we've all pushed a car at one time or another.

Consider there's a car (an small one, VW Golf or so)



It's rolling toward you on a flat road at 2mph. You try to stop it. You can probably do it within a few seconds.

Now imagine the same car, but this time it's on a 45 degree slope. It's rolling down towards you at 2mph. How long does it take you to stop it?

You can't stop it. It would run you over, barely slowing at all, and within a few seconds would be doing 30mph, and still going.

Extend that to the vertical. You're on a cliff. The car is suspended an inch above your head. Someone cuts the rope.

In all cases the car has the same mass. But on the flat ground, you are just fighting inertia and friction. When gravity gets involved, then you lose.

So arresting rotation require minimal effort. A car that is slowly spinning on a turntable is no harder to stop than a car slowly moving on flat ground (in fact it's quite a bit easier, if you measure speed along the outer radius). But arresting downward motion under gravity is vastly harder. It requires that you exert a force greater than that of gravity.

Let's put some figures on that. A car weighs 3,000 pounds. Let's say you are an average person, strong enough to deadlift 100 pounds, and can apply the same strength to pushing the car. So that means that you are exerting a force on the car 1/30th that of gravity's pull on the car.

So force required to push or turn something slowly is vastly less than the force required to stop something falling. We are using very rough figures here, but 1/30th for pushing, or maybe 1/50 for turning.

So given that the block stopped turning over a second or so does not mean that very much force was needed. Indeed it indicates that the resistance of the floors below was only a small fraction of the force of the block under gravity. Hence the resulting very little difference in acceleration due to gravity as the block fell. The building could no more slow the block than you could slow the Volkswagon rolling down a steep hill.
There are several differences here in the larger picture . . .

1) So the VW is really a few inches from you when someone cut the rope and you are capable of holding up the VW . . . since you have been there for the last 20 years . . . you are really one strong dude . . .
2) Do you fall like a weakling or do you at least slow the fall significantly . . . also people below you are stronger than you . . . of course, as you fail and fall the people below you have to stop you and the VW . . . that is understood . . .
3) but this is not what the doubters are saying . . . they think someone shot a few of the people below you and so you the VW and the whole mess falls without much resistance at all . . .
 
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lee h oswald

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Banned
Before you arrived here.


28% or 36% of free fall.

The temporarily-intact core would tend to "thread" the falling floor conglomerate back to the vertical. The external fragments would continue their trajectory and maintain their angular velocity.

Bizarre.
 

Mick West

Administrator
Staff member
There are several differences here in the larger picture . . .

1) So the VW is really a few inches from you when someone cut the rope and you are capable of holding up the VW . . . since you have been for the last 20 years . . . you are really one strong dude . . .
2) Do you fall like a weakling or do you at least slow the fall significantly . . . also people below you are stronger than you . . . of course, as you fail and fall the people below you have to stop you and the VW . . . that is understood . . .
3) but this is not what the doubters are saying . . . they think someone shot a few of the people below you and so you the VW and the whole mess falls without much resistance at all . . .

Well yes, that's were the analogy fails. But buildings are not like a human pyramid with a VW on top. That's not what is being illustrated. Just the relative magnitude of inertial and gravitational forces on large objects.

Back to Verinage. Floors holding up the above floors for 20 years does not mean they will hold that weight when dropped on them from ten feet up.

Take a 10lb weight and hold it in your hand. Now, keeping your hand in the same position have someone drop that 10lb weight on your hand from ten feet up. How much does your hand move?

(actually, don't try that, you'll probably break something. Just imagine it).
 

Oxymoron

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I agree, and so does NIST, which is why that was a primary point in their recommendations resulting from the investigations.

But despite their recommendations... there are no, (that I can find), retrofits and given that we are talking about hundreds of buildings this is, IMO, very strange.


Long span flooring is not inevitably dangerous, it just raises additional issues. The recommendations on NIST are aimed at preventing progressive collapse, not eliminating long span floors.

But long span floors are inevitably dangerous if a fire can take out one structural 'joint' and the whole building collapse in a manner easily confused with a professional demolition.

I would have at least thought they would have been at some pains to reassure people that the new 7 has been engineered without the design fault responsible for the old 7's collapse.
 

Mick West

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But despite their recommendations... there are no, (that I can find), retrofits and given that we are talking about hundreds of buildings this is, IMO, very strange.

But long span floors are inevitably dangerous if a fire can take out one structural 'joint' and the whole building collapse in a manner easily confused with a professional demolition.

I would have at least thought they would have been at some pains to reassure people that the new 7 has been engineered without the design fault responsible for the old 7's collapse.

Do you know of any particular buildings that would benefit? I don't think that's exactly the type of thing you can look up on the internet.

Long spans are not automatically now a design flaw. The just need additional consideration to ensure a progressive collapse will not result from a partial collapse.

http://www.wtc.com/about/office-tower-7
But I really think it's not the kind of thing they like to dwell on. Isn't the fact that it exceeds code good enough?
 

Oxymoron

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Do you know of any particular buildings that would benefit? I don't think that's exactly the type of thing you can look up on the internet.

Not personally no but it was envisaged by NIST that professional assessments of buildings should be done and remedial refits carried out as required. If there have been none, that leaves 7 as unique in yet another area.

Long spans are not automatically now a design flaw. The just need additional consideration to ensure a progressive collapse will not result from a partial collapse.

http://www.wtc.com/about/office-tower-7
But I really think it's not the kind of thing they like to dwell on. Isn't the fact that it exceeds code good enough?

Not really as we have already established all the wtc's exceeded the codes and look what happened to them... so frankly that does not cut it.

Re the math... there is an argument going on over that.

http://www.journalof911studies.com/volume/2009/FGvsNewton.pdf
 

Jazzy

Closed Account
I'm sure you could render them more accurately.
These people did.



If the floors are falling downwards, they are hardly likely to slide sideways, especially as each floor is threaded by the internal column assembly. As you can see here.
 
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Mick West

Administrator
Staff member
Not personally no but it was envisaged by NIST that professional assessments of buildings should be done and remedial refits carried out as required. If there have been none, that leaves 7 as unique in yet another area.



Not really as we have already established all the wtc's exceeded the codes and look what happened to them... so frankly that does not cut it.

Re the math... there is an argument going on over that.

http://www.journalof911studies.com/volume/2009/FGvsNewton.pdf

I agree with the bolded statement there, as would Newton. I've had this discussion with lee.

http://en.wikipedia.org/wiki/Newton's_laws_of_motion
Greening is entirely correct.
 

Oxymoron

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Banned
From the same pdf, it is noted that Greening co authored with Bazant and they are both suspected of deliberate mis representation.

 

George B

Extinct but not forgotten Staff Member
From the same pdf, it is noted that Greening co authored with Bazant and they are both suspected of deliberate mis representation.

Oxy . . . What is the source for the above quote . . . rather interesting if accurate !!!!
 

Mick West

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Staff member
Bazant did publish a paper on 9/14/2001, which was expanded by 9/22 to this:

http://www-math.mit.edu/~bazant/WTC/WTC-asce.pdf

It's a shame that speed of response is often taken as evidence of conspiracy. I'm often accused myself of replying too fast, or having all the answers. Bazant took 11 days to create the above paper. That seems like plenty of time for an expert in the field to create a reasonable hypothesis with rough estimates.

Remember plenty of people understood roughly why the towers fell immediately after they fell. Some people even predicted the collapse ahead of time.

It's also worth noting that people are often accused to taking too long to produce an explanation. Perhaps there's a sweet spot, a time at which explanation will not be suspicious.
 

George B

Extinct but not forgotten Staff Member
Bazant did publish a paper on 9/14/2001, which was expanded by 9/22 to this:

http://www-math.mit.edu/~bazant/WTC/WTC-asce.pdf

It's a shame that speed of response is often taken as evidence of conspiracy. I'm often accused myself of replying too fast, or having all the answers. Bazant took 11 days to create the above paper. That seems like plenty of time for an expert in the field to create a reasonable hypothesis with rough estimates.

Remember plenty of people understood roughly why the towers fell immediately after they fell. Some people even predicted the collapse ahead of time.

It's also worth noting that people are often accused to taking too long to produce an explanation. Perhaps there's a sweet spot, a time at which explanation will not be suspicious.
Thanks for the info . . . at least it verifies the time window . . . I am not as suspect of the collapse as much as the speed of failure and the speed of collapse . . . as well as, of course, we have two methods of failure on the same day . . . unprecedented simply unprecedented . . .
 

lee h oswald

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Banned


You want the middle bits a bit fatter?


No. I want you to be honest with yourself and everyone else. You've based your graphic on the most unrepresentative image of a tower you could possibly hope to find. Why would you want to do that? And who said the camera never lies?



One of the biggest criticisms from detractors of the towers' design was the small proportion of glass to steel/al cladding.

See that ^^^^? It's all steel - as you well know. Why do you use an image and a graphic which does not represent the reality of the object it depicts? You want to present it as a hollow glass tube, all the better to support what you believe - but again, the Emperor is in the altogether, in his birthday suit, stark bollock naked. You've made attempts before to characterize the towers' facades as 'mostly glass'. They weren't, they were about 60% steel.

Why did you choose that picture and that graphic?

Have you asked your engineer mates about using Verinage on that? Thought you might want to clear that up. The answer will be, No.




Hardly a hollow glass tube, is it? - but if you catch the light just right, you can find an image that makes it look just like how you want it to look.

So, yeah, I reckon you should make a more accurate rendering - and desist from using misleading images because they present better accompaniment to your 'theory'. Why would you do that?
 
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lee h oswald

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Banned
Not personally no but it was envisaged by NIST that professional assessments of buildings should be done and remedial refits carried out as required. If there have been none, that leaves 7 as unique in yet another area.



Not really as we have already established all the wtc's exceeded the codes and look what happened to them... so frankly that does not cut it.

Re the math... there is an argument going on over that.

http://www.journalof911studies.com/volume/2009/FGvsNewton.pdf

All good points.


Greening: "Newton's 3rd Law applies to bouncing billiard balls, not the interiors of
collapsing buildings ........"

That sounds familiar.
 

lee h oswald

Banned
Banned
And still waiting for the example of global 'progressive collapse' of a steel and concrete high rise without the help of explosives.
 

Mick West

Administrator
Staff member
No. I want you to be honest with yourself and everyone else. You've based your graphic on the most unrepresentative image of a tower you could possibly hope to find. Why would you want to do that? And who said the camera never lies?

It's a 2D representation for illustrating the mechanics. would you have me illustrate it as a solid black block?

The building did have long span floors. It has a steel core, and a steel exterior. There is a lot of space between the two, linked by the floor spans. That's a 2D representation.

The image with the sun shining through it has all the structural steel in place. So why is it unrepresentative?

And you know I retracted my "mostly glass" statement about a year ago ( was a bit of a WTC noob back then), so why bring it up again?
 

Mick West

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Staff member
And still waiting for the example of global 'progressive collapse' of a steel and concrete high rise without the help of explosives.

There are none, as has been said many times. So why keep bring it up? The WTC collapses were obviously unique events. That does not automatically mean they were the result of a conspiracy involving controlled demolition.

Can you give me an example of a building of similar construction hit by a plane with a similar fuel load, which burned on several floor for an hour, and did NOT collapse?

Uniqueness does not equal planned.
 

Jazzy

Closed Account
Lee Harvey Oswald said:


No. I want you to be honest with yourself and everyone else. You've based your graphic on the most unrepresentative image of a tower you could possibly hope to find. Why would you want to do that? And who said the camera never lies?
^^^^^^^^^^^^^
That truly IS bizarre. And very revealing. So a side elevation is "the most unrepresentative image", is it? Would you prefer a plan?
 
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lee h oswald

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Banned
I agree with the bolded statement there, as would Newton. I've had this discussion with lee.

http://en.wikipedia.org/wiki/Newton's_laws_of_motion
Greening is entirely correct.


No he is not. The key word to look for in description of Newton's laws is idealized.
 

lee h oswald

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There are none

Can you give me an example of a building of similar construction hit by a plane with a similar fuel load, which burned on several floor for an hour, and did NOT collapse?


None.

Wtc 7 wasn't hit by a plane with any fuel load, but it did collapse - does that count? No. Course not. It's just uniqueness all round, eh?
 

Mick West

Administrator
Staff member
Hollow glass tube under construction, core rising in the middle



That's a very strong looking structure. After all, it has to carry the weight of the entire World Trade Center. Of course the exterior beams you show there are the underground levels and the lobby floor (which actually was "mostly glass" in terms of area, not that that changes anything). Here's a better image you can use showing it more clearly.



Here's a nice photo showing fireproofing being applied to the columns. Where the guy at the top is spraying is the about the top of the exterior in the previous two images. This shows the empty space in the lobby level quite nicely. Of course it's 3-4 times the height of a normal floor, but the open area is the same.


As things get a bit higher though, the skin is a bit less substantial looking. Still incredibly strong, of course. The WTC was a very strong structure, able to withstand the impact and explosion quite well.


Towards the top, thing start to look relatively spindly. Still strong enough for its function of course, but perhaps the photo of the ground levels is not indicative of the strength of the upper floors of the building?
 
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lee h oswald

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As things get a bit higher though, the skin is a bit less substantial looking. Still incredibly strong, of course. The WTC was a very strong structure, able to withstand the impact and explosion quite well.


Towards the top, thing start to look relatively spindly. Still strong enough for its function of course, but perhaps the photo of the ground levels is not indicative of the strength of the upper floors of the building?

Yes, but the question was, Why did you choose this image? You think a long-exposure photograph looking straight at the sun and bleaching out the structure so it is nearly invisible is a good representation of the reality? Why did you choose this image above all the others?

Originally Posted by Mick





As things get a bit higher though, the skin is a bit less substantial looking

You must have excellent eyesight. And it's not a skin - it's the structural steel perimeter - and it's exactly the same dimensions when formed into box welds as the rest of the building's perimeter columns (apart from the lower levels, ofcourse). The only difference is in the thickness of the steel, which gets thinner as it goes up, obviously. But yes, congratulations on that visual acuity. Shame you couldn't apply it to the above photo as well.


You can't have it both ways. If it's so spindly, then how did it crush the rest of the building you're now bigging up? Or maybe it's the dreaded spindly sledgehammer - they're the worst kind. Look at those titchy little cranes sitting on top - they look a bit spindly to me.
 
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George B

Extinct but not forgotten Staff Member
Yes, but the question was, Why did you choose this image? You think a long-exposure photograph looking straight at the sun and bleaching out the structure so it is nearly invisible is a good representation of the reality? Why did you choose this image above all the others?





You must have excellent eyesight. And it's not a skin - it's the structural steel perimeter - and it's exactly the same dimensions when formed into box welds as the rest of the building's perimeter columns (apart from the lower levels, ofcourse). The only difference is in the thickness of the steel, which gets thinner as it goes up, obviously. But yes, congratulations on that visual acuity. Shame you couldn't apply it to the above photo as well.



You can't have it both ways. If it's so spindly, then how did it crush the rest of the building you're now bigging up? Or maybe it's the dreaded spindly sledgehammer - they're the worst kind. Look at those titchy little cranes sitting on top - they look a bit spindly to me.
"the dreaded spindly sledgehammer " . . . that is a great catch phrase Lee . . . !!!
 

Mick West

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Staff member
I didn't actually choose that image as the basis of my sketch, I was just drawing a rough 2D representation of the internal structure from memory to illustrate a point. That iconic photo happened to match.

The thing is though, physics is not based on adjectives. Regardless of whether it is "spindly" or "solid", the question is if it would fall when a floor failed. That's not really a question we can simply put to our intuition, nor is it a question we can answer based on marveling at photos of incredibly strong girders and rivet plates.

Instead, one has to ask actually how much energy would it take to break the support of all the girders on one floor. Then one has to ask how much energy there is in the falling block over one floor, then one subtracts on from the other, and we see if the falling block could actually break one floor under the most conservative estimates - despite what our intuition tells us, and despite what our experience with smaller structures is.

lee, would you agree that the collapse of a structure can be described in terms of energy expenditure? Potential, kinetic, destructive? That we can describe the energy required to buckle a girder? Multiple girders? We can get a rough estimate of the energy expended to destroy each floor?
 
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