WTC: Rate of Fall (rate of crush)

[Mick]

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.

Yes, that factor is the key here. There's a downwards acceleration of g (gravity), for the buildings to fall as observed, then the net upwards force would have to be around g/10. (Then giving you a downward acceleration of 0.9*g)

There is actually a lot of evidence for the resistance the floors offered. It's been quite well studied. The problem is that the Truthers tend to use either faulty reasoning, or wildly inaccurate estimates (like assuming the fall has to "dustify" everything on the way down, rather than just break the connections). Since the math is beyond most people, you tend to get entrenched positions. There's the basic math here, but even this is still a simplified model (although vastly more accurate than the YouTube whiteboard explanation).

http://metabunk.org/files/Why%20Did%...20Analysis.pdf
http://metabunk.org/files/Mechanics%...20Collapse.pdf
http://metabunk.org/files/00%20WTC%2...Cause%20It.pdf

It think it would be productive to try to get a simpler explanation though.

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

Content from external source:

Citing its one new recommendation (the other 12 are reiterated from the previously completed investigation of the World Trade Center towers, WTC 1 and 2), the NIST investigation team said that "while the partial or total collapse of a tall building due to fires is a rare event, we strongly urge building owners, operators and designers to evaluate buildings to ensure the adequate fire performance of the structural system. Of particular concern are the effects of thermal expansion in buildings with one or more of the following features: long-span floor systems, connections not designed for thermal effects, asymmetric floor framing and/or composite floor systems." Engineers, the team said, should be able to design cost-effective fixes to address any areas of concern identified by such evaluations.

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

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.

[Mick]

Oh, and the building beams getting thicker and stringer as you get further down is somewhat negated by two facts:

1) The falling mass gets heavier and heavier as it falls, accumulating new floors
2) The vertical girder were not crushed, they were stripped of their floors, and then fell from lack of support (see the buckling video above). This is most clearly demonstrated by the "spire" that remained to half the height of the building before it fell.

[Mick]

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 . . . ???

The math is in here:
http://metabunk.org/files/Why%20Did%...20Analysis.pdf

Note from there:

Content from external source:

The details of the failure process after the decisive initial triggerthat sets the upper part in motion are of course very complicated
and their clarification would require large computer simulations.
For example, the upper part of one tower is tilting as it begins to
fall ~Appendix II!; the distribution of impact forces among the
underlying columns of the framed tube and the core, and between
the columns and the floor-supporting trusses, is highly nonuniform;
etc. However, a computer is not necessary to conclude that
the collapse of the majority of columns of one floor must have
caused the whole tower to collapse. This may be demonstrated by
the following elementary calculations, in which simplifying assumptions
most optimistic in regard to survival are made.
For a short time after the vertical impact of the upper part, but
after the elastic wave generated by the vertical impact has propagated
to the ground, the lower part of the structure can be approximately
considered to act as an elastic spring @Fig. 2~a!#.
What is its stiffness C? It can vary greatly with the distribution of
the impact forces among the framed tube columns, between these
columns and those in the core, and between the columns and the
trusses supporting concrete floor slabs.

For our purpose, we may assume that all the impact forces go
into the columns and are distributed among them equally. Unlikely
though such a distribution may be, it is nevertheless the
most optimistic hypothesis to make because the resistance of the
building to the impact is, for such a distribution, the highest. If the
building is found to fail under a uniform distribution of the impact
forces, it would fail under any other distribution.

That's an important point, they are actually calculating things assuming that all the columns buckle at the collapse front. This scenario gives by far the greatest resistance, and yet it's almost certainly not what happened, it's almost certain that the resistance was a lot lower. And yet even with this overly conservative estimate, the upwards resistance is far less than g.

Like I said though, unfortunately most people don't really understand the math involved, so they can't tell the difference between explanation except by if the result meets their expectations.

[George B]

I reviewed the info . . . it is still counterintuitive that any building could fall that fast without assistance by removing resistance of the remaining structure . . . as I said find me a building being demolished that falls faster . . .

http://www.youtube.com/watch?v=9E7Ep3U06Nc&sns=em

[George B]

You probably can't find a faster collapse . . . they admit as much in your attached cited reference . . . seems just like the simulations of WTC #7 . . . they took what they saw and modeled their assumptions to fit what they thought they saw . . . including their math . . . sorry this does not fly for me Mick!!!!! At least this time they shared their math and data . . . LOL!!!!!!

Content from external source:


http://metabunk.org/files/Why%20Did%...20Analysis.pdf

So the collapse of the tower must be an almost free fall. This conclusion is supported by the observation that the duration of the collapse of each tower, reported as roughly 10 s, was about the same as the duration of a free fall in a vacuum from the tower top H��416 m to the top of the heap of debris (H0��25 m), which is t����2(H��H0)/g��8.93s. It further follows that the brunt of vertical impact must have gone directly into the columns of the framed tube and the core, and that the front of collapse of the floors could not have advanced substantially ahead of the front of collapse of the framed tube, since otherwise the collapse of the framed tube would have had to take significantly longer than 9 s.

[Mick]

You probably can't find a faster collapse . . . they admit as much in your attached cited reference . . . seems just like the simulations of WTC #7 . . . they took what they saw and modeled their assumptions to fit what they thought they saw . . . including their math . . . sorry this does not fly for me Mick!!!!!

Content from external source:


http://metabunk.org/files/Why%20Did%...20Analysis.pdf

So the collapse of the tower must be an almost free fall. This conclusion is supported by the observation that the duration of the collapse of each tower, reported as roughly 10 s, was about the same as the duration of a free fall in a vacuum from the tower top H��416 m to the top of the heap of debris (H0��25 m), which is t����2(H��H0)/g��8.93s. It further follows that the brunt of vertical impact must have gone directly into the columns of the framed tube and the core, and that the front of collapse of the floors could not have advanced substantially ahead of the front of collapse of the framed tube, since otherwise the collapse of the framed tube would have had to take significantly longer than 9 s.

Most building implosions happen at about the same speed, although they are a considerably different type of collapse, and nothing like as tall



Verinage demolitions also seem very similar in terms of initial speed, but the examples are much shorter, and the building different in construction, so the fall is arrested quicker:

[George B]

Yes, Mick and each and every building has been pre-prepared for demolition . . . so we are back to square one if you ask me . . . you try an explanation and I don't think it fits what I witnessed and intuitively understand . . .

[Mick]

And as an example of the difficult of providing the "evidence" for which you seek (a similar speed, similar type of collapse). Here's one of the closest, overlaid for scale:

[Mick]

Yes, Mick and each and every building has been pre-prepared for demolition . . . so we are back to square one if you ask me . . . you try an explanation and I don't think it fits what I witnessed and intuitively understand . . .

So you are basically saying that unless I can find a 100 story building that accidentally collapsed in the same manner as the WTC, they you are always going to believe it was controlled demolition, because that's your intuition, and you can't follow the math?

[RolandD]

Yes, Mick and each and every building has been pre-prepared for demolition . . . so we are back to square one if you ask me . . . you try an explanation and I don't think it fits what I witnessed and intuitively understand . . .

So, what it comes down to is that since it doesn't make sense to you, it can't be true?

[George B]

So you are basically saying that unless I can find a 100 story building that accidentally collapsed in the same manner as the WTC, they you are always going to believe it was controlled demolition, because that's your intuition, and you can't follow the math?

That is not what I indicated . . . I am saying the math might be correct (however, self fulfilling, insular, finite N) . . . but is based on potential error because they are not using math to prove an outcome of a new event but using math to back engineer (model) what they thought they witnessed . . . forcing the square peg in the round hole as it were . . . I cannot believe you think the building could collapse at nearly the same rate of a bowling ball in a vacuum . . .

Using your own cite as evidence . . .

Content from external source:


http://metabunk.org/files/Why%20Did%...20Analysis.pdf
This conclusion is supported by the observation that the duration
of the collapse of each tower, reported as roughly 10 s, was about
the same as the duration of a free fall in a vacuum from the tower
top5416m to the top of the heap of debris

[George B]

So, what it comes down to is that since it doesn't make sense to you, it can't be true?

I never once said that . . . I am saying it is not adequate evidence to convince me . . . I recognize I am not the judge of the "Truth" . . . far from it . . .

[George B]

My corrections to your quote below . . . No I am saying you cannot find any building to dissuade me . . . because the building fell at the same rate or faster than a controlled demolition . . . that is not possible in my simple little mind . . . sorry . . .

So you are basically saying that unless I can find a 100 story building that accidentally collapsed in the same manner as the WTC, then you are always going to believe it was controlled demolition . . .

[Mick]

That is not what I indicated . . . I am saying the math might be correct (however, self fulfilling, insular, finite N) . . . but is based on error because they are not using math to prove an out come of a new event but using math to back engineer (model) what they though they witnessed . . . forcing the square peg in the round hole as it were . . . I cannot believe you think the building could collapse at nearly the same rate of a bowling ball in a vacuum . . .

Using your own cite as evidence . . .

Content from external source:


http://metabunk.org/files/Why%20Did%...20Analysis.pdf
This conclusion is supported by the observation that the duration
of the collapse of each tower, reported as roughly 10 s, was about
the same as the duration of a free fall in a vacuum from the tower
top5416m to the top of the heap of debris

I don't think that. It think it fell at about 90% the acceleration of free fall. Which is what the cite shows if you had continued that quote:

Content from external source:

This conclusion is supported by the observation that the durationof the collapse of each tower, reported as roughly 10 s, was about
the same as the duration of a free fall in a vacuum from the tower
top H5416m to the top of the heap of debris (H0525 m),
which is t=sqrt(2*(H-H0)/g) = 8.93 s.

8.93s vs. "roughly 10", so quite a bit slower than free fall.

[Mick]

My corrections below . . . No I am saying you cannot find any building to dissuade me . . . because the building fell at the same rate or faster than a controlled demolition . . . that is not possible in my simple little mind . . . sorry . . .

So you are saying that NOTHING will persuade you short of a full scale replicate being built of the WTC?

Would that even persuade you? Say someone decided to send $200M on such a replica, then destroy it, and it kind of looked like the original WTC, then would you change your mind?

Wouldn't it be a bit simpler for you to just study the math for a while?

[George B]

So you are saying that NOTHING will persuade you short of a full scale replicate being built of the WTC?

Would that even persuade you? Say someone decided to send $200M on such a replica, then destroy it, and it kind of looked like the original WTC, then would you change your mind?

Wouldn't it be a bit simpler for you to just study the math for a while?

No, as I said (paraphrased) earlier . . . If you can show me a high-rise, steel reinforced, building in a controlled demolition collapsing at a reasonably faster rate than the fastest WTC failure . . . I would then consider the evidence as significant and useful . . . the math is basically only supportive otherwise . . .

[George B]

Geeeez . . . you are fast Mick . . . new home for the discussion . . . LoL!!

[Mick]

No, as I said (paraphrased) earlier . . . If you can show me a high-rise, steel reinforced, building in a controlled demolition collapsing at a reasonably faster rate than the fastest WTC failure . . . I would then consider the evidence as significant and useful . . . the math is basically only supportive otherwise . . .

Do you realize that the fastest possible collapse of a building is free fall, which (using the figures above) is only 1 second quicker than the observed free fall rate for a 110 story building? Do you realize then that for the height of the tallest building that have been demolished (40 stories), then this difference in speed is going to be approximate 0.25 seconds? Would you consider that "reasonably faster"?

The key point here is how much upwards force the building exerts by individual floors (and even columns) resisting collapse. Your intuition says "a lot". But can you put a number on it?

Compare to the verinage demolitions? What does your intuition tell you about them? Don't they also look "too fast"?

[Mick]

Have a look at this George, what the first thing in it you either disagree with or don't understand:

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

[Mick]

Another illustration. Here's one estimate of the rate of fall of WTC 1 and WTC2 compared to free falls



I've also added a grey line indicating the height (realtive to the top of the wtc) of the J.L. Hudson department store, one of the highest buildings ever imploded. The yellow line indicates the height of the debris pile, which would be where it stopped falling (although it would have reduced acceleration before that point).

So for an existing building to fall "faster" than WTC2, it would have to be in that region above the yellow line, and between the black free-fall line, and the blue WTC2 line. A barely noticeable difference. And since you discard all the implosions, and Verinage is not tall enough, then you've basically set yourself up to be trapped in a belief.



The only way out is for you to to look at the math.

[George B]

Have a look at this George, what the first thing in it you either disagree with or don't understand:

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

Again . . . the investigator matches reality with his math . . . self-fulfilling re-engineering . . .

Content from external source:

We note in concluding this Section that the values for tc given above represent the calculated values for the time of collapse of the WTC towers neglecting the energy required to crush or otherwise destroy the support structure of each floor. This energy, which we will call E1, is considered in detail in Section 4.2. For now it is sufficient to note that the collapse times calculated without allowing for E1 are already in reasonable agreement with the observed collapse times. This suggests that E1 is relatively small compared to the kinetic energy associated with the falling blocks of floors; let us now place this qualitative prediction on a quantitative basis. To do this we must calculate the energies involved in each stage of the WTC collapse and then correct for the resistance offered by each floor.

[Mick]

Again . . . the investigator matches reality with his math . . . self-fulfilling re-engineering . . .

Content from external source:

We note in concluding this Section that the values for tc given above represent the calculated values for the time of collapse of the WTC towers neglecting the energy required to crush or otherwise destroy the support structure of each floor. This energy, which we will call E1, is considered in detail in Section 4.2. For now it is sufficient to note that the collapse times calculated without allowing for E1 are already in reasonable agreement with the observed collapse times. This suggests that E1 is relatively small compared to the kinetic energy associated with the falling blocks of floors; let us now place this qualitative prediction on a quantitative basis. To do this we must calculate the energies involved in each stage of the WTC collapse and then correct for the resistance offered by each floor.

That's not what he's doing. He's nothing an observation, then checking to see if it matches the physics. "place this qualitative prediction on a quantitative basis." means to back up the observation with real figures.

Would you only be satisfied if the person creating the estimate had never heard of the World Trade Center?

Just follow the math. See if he got anything wrong.

[George B]

then you've basically set yourself up to be trapped in a belief.

If you say so . . . LoL!! I could say look in the mirror . . . you have trapped yourself in believing the official story using the logic . . . if it is a reasonable explanation then accept it . . . mick's Razor . . . .

[Mick]

Not incredibly useful as there's no timing, and it's an implosion, but here's a nice photoset of the collapse of a steel framed building:

http://www.flickr.com/photos/5504320...n/photostream/

The description of how it was done is interesting though:

http://www.controlled-demolition.com/biltmore-hotel

Content from external source:

Seconds after the final warning signal blared Sunday afternoon at a downtown redevelopment site in Oklahoma City, precisely placed explosive charges dropped a 28-story building almost in its tracks. When it fell, the 245-ft-high structure became the tallest steel-frame building to be demolished with explosives.

Built in 1932 of heavy beams and beefed-up steel columns, the Biltmore Hotel stood in the way of a $39-million urban renewal plan to construct a cultural and recreational complex. Some structures on the site have been removed while others await demolition.

But none presented the problems that the Biltmore did. "It’ s the heaviest steel we’ve ever worked on," says Mark Loizeaux, of Controlled Demolition, Inc. (CDI), Towson, Md., which dropped the brick-clad structure for contractor Wells Excavating Co., Inc., Oklahoma City.

"Because of the thickness of the steel, a single charge wouldn't penetrate completely through," he says. “We had to attack a single 3-in.-thick stem plate from both sides." Each 16-in. steel column with built-up flanges totals 2.5 to 3 tons per floor.

To blast in this fashion, says Loizeaux, it is imperative that the charges on opposing sides go off simultaneously. If one goes off too soon, it will dislodge the other before it can cut through the steel.

CDI placed 991 separate charges, about 800 lbs. of explosives in all, on seven floors from the basement to the 14th floor and detonated them over a five-second interval. CDI’s detonation sequence aimed to drop the building in a southerly direction in what is called a controlled progressive collapse in order to lay out the demolished structure to ease removal of debris

Imagine if you had to extend that to the size of the WTC, and its considerable more substantial steel.

[Mick]

If you say so . . . LoL!! I could say look in the mirror . . . you have trapped yourself in believing the official story using the logic . . . if it is a reasonable explanation then accept it . . . mick's Razor . . . .

I accept it because I see no reason to doubt it. I see no place in which it does not fit the facts. I accept it because it it matches all the math that I can follow.

You doubt it because of your "intuition".

[George B]

That's not what he's doing. He's nothing an observation, then checking to see if it matches the physics. "place this qualitative prediction on a quantitative basis." means to back up the observation with real figures.

Would you only be satisfied if the person creating the estimate had never heard of the World Trade Center?

Just follow the math. See if he got anything wrong.

Yes, absolutely, completely on the mark . . . bulls eye . . . Bingo!!!!!!!!!!!!!

[Mick]

Yes, absolutely, completely on the mark . . . bulls eye . . . Bingo!!!!!!!!!!!!!

It's not like we are testing for PSI ability here George. Nor are we simply taking the work of the person doing the math. You can verify it for yourself.

[George B]

I accept it because I see no reason to doubt it. I see no place in which it does not fit the facts. I accept it because it it matches all the math that I can follow.

You doubt it because of your "intuition".

I would be lying if I did not say that I find the whole 911 event a bit suspect . . . so I probably require a greater degree of proof to accept the official story . . . gray areas will always be problematic to me . . .

[George B]

It's not like we are testing for PSI ability here George. Nor are we simply taking the work of the person doing the math. You can verify it for yourself.

Content from external source:

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

Unfortunately there appears to be no simple way to calculate E
1 from first principles since the collapse of just one floor of a WTC tower is an extremely complex
process involving the bending and fracturing of numerous support structures


J. Unfortunately Bažant et al. do not give a detailed exposition on how this
value for E1 was derived, stating only that it is based on “approximate design

calculations” for one WTC tower /3/

Mick, math formulas are only as accurate as the assumptions, the weights and values used in them . . . I am not faulting the physics formulas or math theory, or computations used in them . . . I am saying the assumption that the floor resistance E1 has to be near zero is based upon what?. . . it needs to be (x) to fit what we observed so we will make (were biased by what they thought reality was) the value fit the situation . . . not the other way around . . .

[Mick]

Mick, math formulas are only as accurate as the assumptions, the weights and values used in them . . . I am not faulting the physics formulas or math theory, or computations used in them . . . I am saying the assumption that the floor resistance E1 has to be near zero is based upon . . . it needs to be (x) to fit what we observed so we will make (were biased by what they thought reality was) the value fit the situation . . . not the other way around . . .

Eh? Who said it was near zero? It's measured in the billions of newtons, billions of pounds of force.

[Dan Wilson]

If you say so . . . LoL!! I could say look in the mirror . . . you have trapped yourself in believing the official story using the logic . . . if it is a reasonable explanation then accept it . . . mick's Razor . . . .

Plenty of things in science end up being counterintuitive, doesn't mean it's unlikely or untrue. George, here is a question to consider, what kind force would it take to stop or even delay 15 floors of the WTC after it falls, say, 10 ft.? What amount of "upward force" would it take to stop/slow it? I feel as though that question should be answered if you are to make a case for the collapse not being consistent with physics.

[George B]

Eh? Who said it was near zero? It's measured in the billions of newtons, billions of pounds of force.

Near zero in its ability to retard the downward crush of the falling block ( I am not totally convinced it was an intact block) based on time to crush . . . not its value in newtons . . .

[George B]

Plenty of things in science end up being counterintuitive, doesn't mean it's unlikely or untrue. George, here is a question to consider, what kind force would it take to stop or even delay 15 floors of the WTC after it falls, say, 10 ft.? What amount of "upward force" would it take to stop/slow it? I feel as though that question should be answered if you are to make a case for the collapse not being consistent with physics.

It would take an equal or greater resistance than the mass and velocity of the falling mass that hits it (to stop it and less than that to slow it) . . .

[Dan Wilson]

It would take an equal or greater resistance than the mass and velocity of the falling mass that hits it (to stop it and less than that to slow it) . . .

And what, in numbers, would that be? If you're going to push your case of something being fishy here then that is a crucial piece.

[George B]

And what, in numbers, would that be? If you're going to push your case of something being fishy here then that is a crucial piece.

Please cut to the chase . . . I can dig out the formulas and put in the estimated values, etc. but I am not a physicists or engineer . . . I have already done it for free fall of objects, terminal velocity accounting for atmospheric resistance at sea level, etc . . . the issue here is can a building, any high-rise steel reinforced building fall at near free fall rates unless it is one that is undergoing a controlled demolition . . .?? All the formulas require weights, estimates, data . . . I am questioning the data, weights and assumptions . . . not the formulae . . .

[Oxymoron]

Content from external source:

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

Unfortunately there appears to be no simple way to calculate E
1 from first principles since the collapse of just one floor of a WTC tower is an extremely complex
process involving the bending and fracturing of numerous support structures


J. Unfortunately Bažant et al. do not give a detailed exposition on how this
value for E1 was derived, stating only that it is based on “approximate design

calculations” for one WTC tower /3/

Mick, math formulas are only as accurate as the assumptions, the weights and values used in them . . .

http://en.wikipedia.org/wiki/Black_swan_theory

Content from external source:

"What we call here a Black Swan (and capitalize it) is an event with the following three attributes. First, it is an outlier, as it lies outside the realm of regular expectations, because nothing in the past can convincingly point to its possibility. Second, it carries an extreme 'impact'. Third, in spite of its outlier status, human nature makes us concoct explanations for its occurrence after the fact, making it explainable and predictable."

[Mick]

http://en.wikipedia.org/wiki/Black_swan_theory

Content from external source:

"What we call here a Black Swan (and capitalize it) is an event with the following three attributes. First, it is an outlier, as it lies outside the realm of regular expectations, because nothing in the past can convincingly point to its possibility. Second, it carries an extreme 'impact'. Third, in spite of its outlier status, human nature makes us concoct explanations for its occurrence after the fact, making it explainable and predictable."

You mean like how people concoct explanation involving nano-thermite, mini-nukes, or space based energy beams?

Do the math.

[George B]

You mean like how people concoct explanation involving nano-thermite, mini-nukes, or space based energy beams?

Do the math.

Hmmm . . . you admitted, I believe, yourself the events were unprecedented . . . the explanations; therefore, require a higher standard of scrutiny . . . I see no problem with that . . . I don't have a reasonable explanation, but that does not mean there isn't one . . .

[Dan Wilson]

Please cut to the chase . . . I can dig out the formulas and put in the estimated values, etc. but I am not a physicists or engineer . . . I have already done it for free fall of objects, terminal velocity accounting for atmospheric resistance at sea level, etc . . . the issue here is can a building, any high-rise steel reinforced building fall at near free fall rates unless it is one that is undergoing a controlled demolition . . .?? All the formulas require weights, estimates, data . . . I am questioning the data, weights and assumptions . . . not the formulae . . .

And is my question not essential to the issue? It would be nice if you did dig out the formulae, you can't go off intuition and what you think is the right answer. Mick has put together a strong case here, you don't need to be an engineer or physicist to get a grasp of this stuff. If you're going to make the case you might as well do the math.

[Mick]

Hmmm . . . you admitted, I believe, yourself the events were unprecedented . . . the explanations; therefore, require a higher standard of scrutiny . . . I see no problem with that . . . I don't have a reasonable explanation, but that does not mean there isn't one . . .

Well, so why are you not scrutinizing the explanations? Why just rely on your intuition, which is known to be fallible, and has been thrown by the scale of the buildings.