Can 15 floors crush one floor?

[Travis]

I'm tired of this point being avoided in too many other threads. So this one is all about this.

Truthers or those with Truth Movement sympathies do you think a 15 floor block of building can crush one floor underneath it?

Please don't accuse me of a strawman attack in your answers.

 

[Bell]

 

[cjnewson88]

but... but... there were 80 floors below it..

 

[Kid Eager]

Travis,
I've actually just been thinking about the same thing from a slightly different perspective, and have created a spreadsheet to map the increase in kinetic energy and momentum as each floor was added to the dropping mass.

Does anybody know what each floor of the WTC towers weighed as laden on the day?

 

[Travis]

Oh great, now this is even more reality for Truthers to run away from.

 

[thedopefishlives]

Travis,
I've actually just been thinking about the same thing from a slightly different perspective, and have created a spreadsheet to map the increase in kinetic energy and momentum as each floor was added to the dropping mass.

Does anybody know what each floor of the WTC towers weighed as laden on the day?

Dave Thomas (DaveThomasNMSR on this forum) has done this math already. The average weight was derived from the total estimated mass of the towers. I couldn't tell you offhand what those numbers are, though.

 

[ElMondoHummus]

Does anybody know what each floor of the WTC towers weighed as laden on the day?

Maybe this might help?

• http://www.internationalskeptics.com/forums/showthread.php?p=3275453
• http://oystein-issues.blogspot.com/2010/09/potential-energy-of-mass-of-each-twin.html

There are more discussions of this somewhere, but that I'm able to find rather quickly. If you poke around some, you can dig up some other threads on the matter.

 

[ElMondoHummus]

Dave Thomas (DaveThomasNMSR on this forum) has done this math already. The average weight was derived from the total estimated mass of the towers. I couldn't tell you offhand what those numbers are, though.

Oh, yes. He did. I had forgotten. Found it here:

At the risk of appearing ro pull a femr2, allow me to speculate that the gravitational potential energy of one tower was over 225 tons of TNT, assuming a mass of 4.14 million kg per floor:

That's on the order of the same energy as some of the smaller nuclear weapons in the U.S. arsenal, such as the W-54 (250 tons TNT) (Sublette 2006).

And that's a LOT of energy that had to be expended, as the collapsed towers certainly didn't have a lot of gravitational potential energy.

I simply took Bazant's estimate of 58 million kilograms (from Why Did the World Trade Center Collapse?—Simple Analysis) for the upper North Tower, and divided by 14, an approximate number of the upper floors of WTC 1. Good to know about Urich's careful analysis. 100 tons is still a lot of energy!

Thanks, Dave

So the figure is a rather simple calculation. Of course there's room for improvement on that estimate, but as a back-of-the-envelope number to work with, it's definitely reasonable.

Note that Gregory Urich's work - the subject of the first thread I linked above - also gives figures for that. His, I think, were a bit more than just total mass divided by floors, but I'd have to read it again to make sure of that.

Anyway, like I said above: There's been discussion of this before, so there's definitely threads out there to mine for that information.

 

[sheeplesnshills]

A very simple way to look at the issue is to understand that the factor of safety for any given floor is at best 3X the weight of the floor plus the allowable loading.
The external and internal columns are largely irrelevant other if their mass ends up on one of the floors.

All thats needed to cause the building to collapse is for one floor to collect enough mass from the building above to exceed its factor of safety loading. When that floor fails then all that mass falls onto the floor below exceeding its max loading and so on down the building.
The interior and exterior columns might possibly have been rigid enough to have stayed up without the floors (and indeed the interior ones did for a few seconds) but the falling floors and increasing mass of rubble would have placed sideways forces on them which would caused buckling or, as is seen, failure of the joints between panels.

So a simple static loading could bring the towers down...and once you add in the dynamic forces that in reality would be at play then really there is nothing even remotely strange about the way they fell.

 

[thedopefishlives]

A very simple way to look at the issue is to understand that the factor of safety for any given floor is at best 3X the weight of the floor plus the allowable loading.
The external and internal columns are largely irrelevant other if their mass ends up on one of the floors.

All thats needed to cause the building to collapse is for one floor to collect enough mass from the building above to exceed its factor of safety loading. When that floor fails then all that mass falls onto the floor below exceeding its max loading and so on down the building.
The interior and exterior columns might possibly have been rigid enough to have stayed up without the floors (and indeed the interior ones did for a few seconds) but the falling floors and increasing mass of rubble would have placed sideways forces on them which would caused buckling or, as is seen, failure of the joints between panels.

So a simple static loading could bring the towers down...and once you add in the dynamic forces that in reality would be at play then really there is nothing even remotely strange about the way they fell.

The Twoofers' big mistake when looking at WTC1 and 2 is that they think of them as a monolithic block. (Think "Box Boy" Gage's infamous example.) As a result, they see the upper block falling onto the lower block and can't comprehend how a much lighter solid mass could plow through a much heavier solid mass. But neither the upper block nor the lower block were truly "solid masses"; they were a web of interconnected steel framings with a lot of air in between. Once the upper framing was un-aligned from the bottom, it was just a matter of the upper mass breaking that steel web, accumulating more and more mass and velocity as it continued breaking the connections.

 

[DaveThomasNMSR]

Oh, yes. He did. I had forgotten. Found it here:

​

So the figure is a rather simple calculation. Of course there's room for improvement on that estimate, but as a back-of-the-envelope number to work with, it's definitely reasonable.

Note that Gregory Urich's work - the subject of the first thread I linked above - also gives figures for that. His, I think, were a bit more than just total mass divided by floors, but I'd have to read it again to make sure of that.

Anyway, like I said above: There's been discussion of this before, so there's definitely threads out there to mine for that information.

Thanks for digging that up. I hunted down my most recent calculations, and ended up using (based on Urich) the more conservative estimate of 2.1 million kilograms per floor.

This is equivalent to the potential energy of each twin tower being on the order of 114 tons of TNT.

Cheers, Dave

 

[Oystein]

Travis,
I've actually just been thinking about the same thing from a slightly different perspective, and have created a spreadsheet to map the increase in kinetic energy and momentum as each floor was added to the dropping mass.

Does anybody know what each floor of the WTC towers weighed as laden on the day?

Much of that calculation can be done without any actual values in lb or kg, as the mass will cancel out in almost all equations. Just take "1 MassUnit (1 MU)" instead of "x kg".

As for the forces (if forces appear at all in your calculations) that structural members can exert without plastic deformation, you can use terms that include a multiple of 1.5-3 of the static load, as that would be a convenient Demand-to-Capacity ratio.
The most interesting numbers, in my opionin, are those that describe the distance that a member kann flex in elastic response before it buckles and loses its load-carrying capacity. This could perhaps sometimes be expressed as a ratio of static load compression : max load compression, and is certainly a number closer to 1.0 than to 0.9

Anyway, my first 1D-model that I did a while ago went with assumptions like "all the dynamic load goes 100% vertically into the columns", "columns can compress to 90% original lenght, carrying 300% of static load, then they break and go down to 0%", etc.
Note that absolutely no engineering went into this - I modeled columns as entities with dicrete physical properties geared on the one hand towards simplicity of computation, and on the other hand calibrated such that all assumptions fell on the side of overestimated survivability. One such extreme assumption is of course that it's the breaking of columns which propagates collapse. Obviously, this assumption is false; but replacing it with assumptions closer to reality (that mostly see floor-to-column connectors failing) makes survivability less like and acceleration / speed higher.


Crude model, didn't take into consideration transfer of momentum, but still I came suprisingly close to the "real" net acceleration off collapse speed.



Later I modeled the same, this time ONLY considering transfer of momentum (is much easier to calculate) - and came to results that were almost the same - a little slower, IIRC.



Which led me to suspect that the mechanism behind the slowing down of collapse through mere momentum transfer is the same as the mechanism that destroys the structural supports, and of course it is: Momentum transfer happens largely through inelastic collisions, in which kinetic energy is converted to heat (a little bit) plastic deformation and fracture (those two dominate). Since mere momentum transfer predicts a smaller acceleration than mere consideration of structural force, I think that buckling of supports is mostly already included in the energy transfer by inelastic collision, and doesn't add to the resisting forces already included in the momentum transfer.


It follows that modelling the pancking collapse as a series of (110-15) inelastic collisions of top block / rubble with intact floors gives you estimates of energy dissipation and collapse time than mere consideration of structural forces.



Anyway: The answer to Travis is: There is a maximum momentum and kinetic energy of the impacting (top) part that the impacted (bottom) part of intact structure can absorb until it gives way completely. My simple model, which overestimated elastic forces, showed that, IF the top 15 floors were allowed to drop through the height of 1 floor, then the next floor would be overwhelmed by an order of magnititude (factor 10) - which in turn means that at > about 10% of the kinetic energy would already be sufficient to kill the next floor. After that, we will see the equivalent of nearly full floors of unresisted fall, and the overwhelm factor will quickly grow.

Total collapse becomes inevitable.

I am happy to find that Professor Bazanz agrees with me



The problem to solve is just: How did collapse initiate in the first place such that the top 15 floors picked up a velocity > sqr(10) larger than what is attained in free fall through one story, while the intact structure would NOT YET be overwhelmed. (The key to the answer lies in the fact that the respective structure wasn't intact after plane crashes and fires )

 

[MG1962]

Travis,
I've actually just been thinking about the same thing from a slightly different perspective, and have created a spreadsheet to map the increase in kinetic energy and momentum as each floor was added to the dropping mass.

Does anybody know what each floor of the WTC towers weighed as laden on the day?

I don't know the exact weight those floors where loading on the day. But as designed they were rated at 3000 tons including their own weight.

The concrete used was a light weigh mix because it was not designed to be load bearing but to cut noise transmission through the steel plates underneath

I dont have the calculations anymore or access to data to make the calculations, but I believe it only needed three floors to fall on a floor to overload its load bearing limits. I never bothered with the kinetic side of the calculations because the exta energy wasn't even needed

 

[uke2se]

Going to bump this so that our regular twoofers can't avoid it.

 

[Animal]

I don't know the exact weight those floors where loading on the day. But as designed they were rated at 3000 tons including their own weight.

The concrete used was a light weigh mix because it was not designed to be load bearing but to cut noise transmission through the steel plates underneath

Not even close.

The concrete floors were load bearing. Simple evidence is the fact that the floor slabs were composite with the supporting beams. Second simple evidence is the reinforcing used in the concrete (show in many photographs during construction. The metal decking for the most part is used simply to form the concrete during the construction process. The concrete slabs......being composite also were load bearing in the horizontal plane, providing lateral support to both the interior and exterior columns.

The only loads the concrete floors did not carry were the gravity loads from floors above.

I dont have the calculations anymore or access to data to make the calculations, but I believe it only needed three floors to fall on a floor to overload its load bearing limits. I never bothered with the kinetic side of the calculations because the exta energy wasn't even needed

 

[Travis]

Going to bump this so that our regular twoofers can't avoid it.

Good thinking.

 

[RedIbis]

I'm tired of this point being avoided in too many other threads. So this one is all about this.

Truthers or those with Truth Movement sympathies do you think a 15 floor block of building can crush one floor underneath it?

Please don't accuse me of a strawman attack in your answers.

I won't accuse you of using a straw man, but I will accuse you of asking the wrong question.

If you ask, "do you think a 15 floor block of building can crush one floor underneath it"? The obvious response is that that floor did just fine with 15 floors above it until 9/11. In fact, all the lower floors did just fine with many more floors above it.

I think what you're really trying to ask is if one floor can resist the 15 floors rapidly descending upon it as a single unit.

 

[Myriad]

How about whether one floor can resist 15 floors descending upon it (whether rapidly or not, whether as a single unit or not).

 

[thedopefishlives]

I won't accuse you of using a straw man, but I will accuse you of asking the wrong question.

If you ask, "do you think a 15 floor block of building can crush one floor underneath it"? The obvious response is that that floor did just fine with 15 floors above it until 9/11. In fact, all the lower floors did just fine with many more floors above it.

I think what you're really trying to ask is if one floor can resist the 15 floors rapidly descending upon it as a single unit.

No. The floors, themselves, never held any of the weight of the floors above them. The supporting columns did just fine, obviously, but once that weight was transferred to the floor assemblies during the collapse, the floors were unable to take the load previously held up by the columns.

 

[R.Mackey]

Thanks for digging that up. I hunted down my most recent calculations, and ended up using (based on Urich) the more conservative estimate of 2.1 million kilograms per floor.

This is equivalent to the potential energy of each twin tower being on the order of 114 tons of TNT.

Cheers, Dave

FWIW, we spent a great deal of time criticising Gregory Urich's estimate back in the day, and while he used a somewhat optimistic ("light") estimate of occupant contents -- consistent with NIST's -- I believe it is the most accurate estimate out there. If we were playing "The Price Is Right" I'd up it by about 5% to reflect a slightly greater live load, but that's just a gut feeling.

 

[Travis]

Did it really need to be said that the upper 15 floors are now in motion?

*Sigh* Fine, if the upper 15 floors start descending will they be able to crush one floor beneath them?

Truthers?

 

[uke2se]

Did it really need to be said that the upper 15 floors are now in motion?

*Sigh* Fine, if the upper 15 floors start descending will they be able to crush one floor beneath them?

Truthers?

So the only twoofer reply yet was complaining about the question? Color me surprised.

 

[MG1962]

Not even close. The concrete floors were load bearing. Simple evidence is the fact that the floor slabs were composite with the supporting beams. Second simple evidence is the reinforcing used in the concrete (show in many photographs during construction. The metal decking for the most part is used simply to form the concrete during the construction process. The concrete slabs......being composite also were load bearing in the horizontal plane, providing lateral support to both the interior and exterior columns.

The only loads the concrete floors did not carry were the gravity loads from floors above.

The NIST seem to disagree with you

The floors consisted of 4 inches (10 cm) thick lightweight concrete slabs laid on a fluted steel deck. A grid of lightweight bridging trusses and main trusses supported the floors

 

[NoahFence]

I won't accuse you of using a straw man, but I will accuse you of asking the wrong question.

If you ask, "do you think a 15 floor block of building can crush one floor underneath it"? The obvious response is that that floor did just fine with 15 floors above it until 9/11. In fact, all the lower floors did just fine with many more floors above it.

I think what you're really trying to ask is if one floor can resist the 15 floors rapidly descending upon it as a single unit.

And YOUR answer is?

 

[ElMondoHummus]

Did it really need to be said that the upper 15 floors are now in motion?

*Sigh* Fine, if the upper 15 floors start descending will they be able to crush one floor beneath them?

Truthers?

Not to be nitpicky (sorry, man ), but I think the mistake he made is more fundamental. The floor below was not supporting the load that the upper 15 stories were imposing on the lower structure. The columns were; the floors kept the columns upright.

But when the upper floors came down, the bulk of that rubble fell onto the floors themselves. Which is a lot of what we've been arguing with truthers about: What did the descending rubble hit? Mostly the floors themselves.

That statement is just a misrepresentation all around.

 

[jaydeehess]

No. The floors, themselves, never held any of the weight of the floors above them. The supporting columns did just fine, obviously, but once that weight was transferred to the floor assemblies during the collapse, the floors were unable to take the load previously held up by the columns.

For some unknown and unfathomable reason this simple engineering concept completely escapes those in the 911 'truth' movement.

Including our only non-debunker so far to have responded here.

 

[Bell]

So the only twoofer reply yet was complaining about the question? Color me surprised.

When you know you are beat, revert to semantics.

 

[thedopefishlives]

For some unknown and unfathomable reason this simple engineering concept completely escapes those in the 911 'truth' movement.

Including our only non-debunker so far to have responded here.

I've mentioned before, the Twoofers seem to think of the Towers as a single monolithic block, rather than an intricate web of connected steel assemblies. If you think of it as a solid block, or as a series of layers of solid floors, then it does seem illogical that the collapse would proceed to break through each floor in turn. However, the floors were not vertically supporting, only horizontally bracing, and this simple misunderstanding has led to countless appeals to personal incredulity and even flat-out inventing BS physics.

 

[jaydeehess]

Did it really need to be said that the upper 15 floors are now in motion?

*Sigh* Fine, if the upper 15 floors start descending will they be able to crush one floor beneath them?

Truthers?

Another physics concept that escapes those other people, is that of dynamic forces as opposed to simple statics.

Its fairly obvious that a single floor span is not designed to support, and transfer to the columns, all of the mass, in static load, of both itself and 15 other floors AND the columns on which those other 15 floors are attched, LET ALONE take the dynamic load of those 15 floors.

UNLESS as the collapse progressed, the amount of mass that fell to the outside of the structure could represent enough load loss that a subsequent FLOOR span could survive, the collapse had to continue.

Once stripped of floors the columns could not stand on their own(Euler), yet another unfathomable concept for those people.

 

[Travis]

I'm wondering now how long it will be before there is an answer.

 

[thedopefishlives]

I'm wondering now how long it will be before there is an answer.

We could probably get a betting pool going.

My money's on "never", at least, not a straight answer. There will doubtless be a number of dodges and consummately constructed strawmen.

 

[Animal]

The NIST seem to disagree with you

The floors consisted of 4 inches (10 cm) thick lightweight concrete slabs laid on a fluted steel deck. A grid of lightweight bridging trusses and main trusses supported the floors

No. It doesn't disagree with me. You just don't know what you are talking about.

Lets recall your original claim.

The concrete used was a light weigh mix because it was not designed to be load bearing but to cut noise transmission through the steel plates underneath

For starters, try researching what a composite floor does, had how it reacts.
Then you may want to look up the purpose of steel reinforcing bar in concrete.
Then you may want to find out the load bearing capacity of metal decking.


Then you might want to just quit while you are so far behind.

 

[Sabrina]

Meh.

I never bet on a sure thing.

 

[MG1962]

No. It doesn't disagree with me. You just don't know what you are talking about.

I will pass your concerns onto the James Hardie Australia R&D team, they were the people who helped me with the problem back in 2006 - Only had 16 degrees between them....obviously idiot all

 

[Animal]

I will pass your concerns onto the James Hardie Australia R&D team, they were the people who helped me with the problem back in 2006 - Only had 16 degrees between them....obviously idiot all

They are if they think that the concrete slabs were not load bearing at all and were only used for sound deadening.


And your appeal to authority is noted.

 

[RedIbis]

Not to be nitpicky (sorry, man ), but I think the mistake he made is more fundamental. The floor below was not supporting the load that the upper 15 stories were imposing on the lower structure. The columns were; the floors kept the columns upright.

But when the upper floors came down, the bulk of that rubble fell onto the floors themselves. Which is a lot of what we've been arguing with truthers about: What did the descending rubble hit? Mostly the floors themselves.

That statement is just a misrepresentation all around.

And yet Travis said, "do you think a 15 floor block of building can crush one floor underneath it?"

Do you think Travis meant the actual floor or the entirety of that bldg floor's mass?

I was just pointing out how imprecise that question is. It's one thing for so-called debunkers to ask leading questions, it's another to ask leading, imprecise questions.

 

[DGM]

And yet Travis said, "do you think a 15 floor block of building can crush one floor underneath it?"

Do you think Travis meant the actual floor or the entirety of that bldg floor's mass?

I was just pointing out how imprecise that question is. It's one thing for so-called debunkers to ask leading questions, it's another to ask leading, imprecise questions.

So now that you understand what he meant. Care to address the question?

 

[The Big Dog]

And yet Travis said, "do you think a 15 floor block of building can crush one floor underneath it?"

Do you think Travis meant the actual floor or the entirety of that bldg floor's mass?

I was just pointing out how imprecise that question is. It's one thing for so-called debunkers to ask leading questions, it's another to ask leading, imprecise questions.

That is the awesome part of it, Red, we are not in Court. So you can say something like this:

"travis, I'm not sure I follow your question, but if you are asking whether a 15 story descending segment of a building striking one floor in a steel framed building can cause the catastrophic failure of that floor, the answer is HELL’s YEAH BABY, and anyone saying differently is a maroon, HIGH FIVE!”

Or you can do what it is you are doing, because we all know that you are going to quibble about the question, and bitch and moan, and when you finally are backed into a corner, run off. Kinda like this, huh bro?

|
|
|
|
|
|
|
V​

 

[Bell]

So now that you understand what he meant. Care to address the question?

You are kidding, right?

 

[ozeco41]

And yet Travis said, "do you think a 15 floor block of building can crush one floor underneath it?"

Do you think Travis meant the actual floor or the entirety of that bldg floor's mass?

I was just pointing out how imprecise that question is. It's one thing for so-called debunkers to ask leading questions, it's another to ask leading, imprecise questions.

I have to agree with RedIbis.

The imprecision focuses on the word "crush". In this context what does "crush" mean??? Does it mean just the floor OR does it mean the floor LEVEL complete with columns and beams? Using the word "crush" by implication reopens all the confusion which has existed for years. Does he want truthers to support the understanding that the columns were involved in the crushing? That would amount to asking truthers to prove what didn't happen -- he would be leading them into false argument. Surely not his intention?

I don't want to verbal Travis but a more accurate question could be:

"...do you think a 15 floor block of building could land on one floor underneath it and cause that floor to shear off from the columns?"

Provided that is what he meant. Otherwise I don't have a clue what he is referring to other than repeating a phrase which has caused confusion for years and one which most of us have learned to avoid.