WTC: Rate of Fall (rate of crush)

Mick West

Administrator
Staff member
Folks, it is impossible for a building to collapse due to an small upper segment falling on the much larger lower portion. It would simply "bounce" off the lower portion. There is simply not enough energy to crush the rest of the building - maybe a much denser thing like solid concrete (or a black hole lol) could do it. Possibly if the building was sheared at a much lower level, say on the 20th floor, the upper part could conceivably crush the lower part but no way up on the 90th floor.
Can you explain how you know this? And given that, how does Verinage demolition work?

 

George B

Extinct but not forgotten Staff Member
Can you explain how you know this? And given that, how does Verinage demolition work?

While Verinage demolition will work on specific buildings. . .after weakening the lower floors mechanically which are not steel reinforced. . . In the case of the WTC Towers this was not the case. . . so the question remains . . . how many of the top floors (minimal number) were necessary to be included in the mass and acceleration in order to smash the remaining building to the ground?
 

Mick West

Administrator
Staff member
While Verinage demolition will work on specific buildings. . .after weakening the lower floors mechanically which are not steel reinforced. . . In the case of the WTC Towers this was not the case. . . so the question remains . . . how many of the top floors (minimal number) were necessary to be included in the mass and acceleration in order to smash the remaining building to the ground?
"smash to the ground" is a rather misleading way of putting it. It more like "cause to fall". And remember for each floor that is made to fall, that's more weight impacting the lower floors.

I don't think the minimal number would be very high, possibly five or less. It depends on the nature of the initial floor collapse.
 

George B

Extinct but not forgotten Staff Member
"smash to the ground" is a rather misleading way of putting it. It more like "cause to fall". And remember for each floor that is made to fall, that's more weight impacting the lower floors.

I don't think the minimal number would be very high, possibly five or less. It depends on the nature of the initial floor collapse.
You really think five or less . . . Wow!! . . . that is scary !!!
 
U

Unregistered

Guest
While Verinage demolition will work on specific buildings. . .after weakening the lower floors mechanically which are not steel reinforced. . . In the case of the WTC Towers this was not the case. . . so the question remains . . . how many of the top floors (minimal number) were necessary to be included in the mass and acceleration in order to smash the remaining building to the ground?
Right, and those buildings were NOT highly engineered structural steel 110 stories high!
 

Mick West

Administrator
Staff member
Right, and those buildings were NOT highly engineered structural steel 110 stories high!
But what exactly is it that makes the top of the building "bounce off" the bottom part? Have you actually done some calculations to quantify this "highly engineered structural steel" property?
 

George B

Extinct but not forgotten Staff Member
What do you mean? Scary that I think it, or scary that it's possible?
That it could be possible . . . still seems counterintuitive . . . would love to see it demonstrated on a condemned, high-rise, steel reinforced building . . .
 

slenderbeam

Member
That it could be possible . . . still seems counterintuitive . . . would love to see it demonstrated on a condemned, high-rise, steel reinforced building . . .
That it could be possible . . . still seems counterintuitive . . . would love to see it demonstrated on a condemned, high-rise, steel reinforced building . . .
I wager 1-2 floors falling from height would have been enough. We're talking about a slab weighing about 300kg/m2 and additional furnishings. The trusses would be OK but the seat connections would be smashed.

Don't forget it wasn't just the floors which fell and smashed the floors below, but the perimeter wall panels fell inward as well. These would have been at LEAST as heavy as the floors, probably heavier on a per-square-metre basis. The dynamic impact load is HUGE when these elements fall from height.

As I said, the seat connections had no chance.

If it could be experimentally proven, in a lab, would you be satisfied?

Note that it's unlikely you'll ever come across a structure like the WTC floors. They were unique. Steel framed buildings are generally much more robust than the WTC towers were. Those open web joist connections - i haven't seen them anywhere since in highrise with such a simple connection detail. It does not happen anymore. Look at the new WTC - massive girders and bolted fin connections everywhere. Guess why.
 

slenderbeam

Member
Right, and those buildings were NOT highly engineered structural steel 110 stories high!
They were highly engineered - in order to save on steel tonnages and costs. They skimmed down the truss joist design. It was marvellous because it meant super quick construction.

The floor design was so lightweight they needed viscoelastic dampers on the trusses to reduce vibration. This is very unusual and only is required on super flexible floors/structures.

So yes, 15 storeys of floor and perimeter column paneling landing on flexible, lightweight trusses will smash the floor trusses. That's a fact.
 

George B

Extinct but not forgotten Staff Member
I wager 1-2 floors falling from height would have been enough. We're talking about a slab weighing about 300kg/m2 and additional furnishings. The trusses would be OK but the seat connections would be smashed.

Don't forget it wasn't just the floors which fell and smashed the floors below, but the perimeter wall panels fell inward as well. These would have been at LEAST as heavy as the floors, probably heavier on a per-square-metre basis. The dynamic impact load is HUGE when these elements fall from height.

As I said, the seat connections had no chance.

If it could be experimentally proven, in a lab, would you be satisfied?

Note that it's unlikely you'll ever come across a structure like the WTC floors. They were unique. Steel framed buildings are generally much more robust than the WTC towers were. Those open web joist connections - i haven't seen them anywhere since in highrise with such a simple connection detail. It does not happen anymore. Look at the new WTC - massive girders and bolted fin connections everywhere. Guess why.
Sure a LAB demonstration would be instructive . . . maybe not definitive . . . but a heck of a lot better than a computer simulation in which the data used was withheld from the public . . .
 

tjohnson_nb

New Member
There is an excellent, simple analysis here . Using the conservation of momentum alone, disregarding resistance due to the structure disintegrating, the author figures 15-16 secs. So structural resistance would certainly add a considerable amount to that - even if poorly built.
 

Mick West

Administrator
Staff member
There is an excellent, simple analysis here . Using the conservation of momentum alone, disregarding resistance due to the structure disintegrating, the author figures 15-16 secs. So structural resistance would certainly add a considerable amount to that - even if poorly built.
The analysis is wrong, even if you assume the simply model of conservation of momentum is correct. It's assuming a single floor initiating the collapse, not a block of 15 floors. So instead of the initial decelerations being 1/2, 1/3, 1/4, 1/5 .... they are 1/16, 1/17, 1/18, much lower.

I knocked up a quick spreadsheet, and it shows a pure conservation of momentum at 12.6 seconds for collapse starting at floor 95. And 11.7 seconds starting at floor 80.

Starting at floor 109, it does result in 15 seconds, which is what he was calculating.
 

tjohnson_nb

New Member
The analysis is wrong, even if you assume the simply model of conservation of momentum is correct. It's assuming a single floor initiating the collapse, not a block of 15 floors. So instead of the initial decelerations being 1/2, 1/3, 1/4, 1/5 .... they are 1/16, 1/17, 1/18, much lower.
No it does not. Even if you had half the building falling on the other half it would take more time than a free fall.
 

tjohnson_nb

New Member
Here is a much more detailed analysis which concludes (as I did intuitively) that the collapse wouldn't even go past one floor. There simply is not enough energy available.
 

Mick West

Administrator
Staff member
Here is a much more detailed analysis which concludes (as I did intuitively) that the collapse wouldn't even go past one floor. There simply is not enough energy available.
Well, before we move on to that, can you confirm that the initial analysis you cited was incorrect, for the reasons I gave?
 

Jazzy

Closed Account
The calculations suffer from the same inaccuracies as my own on the reduction of steel rc to 60 micron dust.
Steel cannot be reduced to 60 micron dust, unless you are using a nuclear bomb. Concrete needs no more than a sledgehammer. You need warming up after a week in the cooler.
 

Jazzy

Closed Account
Sure a LAB demonstration would be instructive . . . maybe not definitive . . . but a heck of a lot better than a computer simulation in which the data used was withheld from the public . . .
It would have to be a full scale model to satisfy your own criteria. A fully-worked simulation is obviously the only practical way of dealing with the matter.

I would withhold data from you, George, in the interests of coming not just to a swift decision, but to any decision at all.
 

George B

Extinct but not forgotten Staff Member
It would have to be a full scale model to satisfy your own criteria. A fully-worked simulation is obviously the only practical way of dealing with the matter.

I would withhold data from you, George, in the interests of coming not just to a swift decision, but to any decision at all.
Lol!! How about a demonstration, any demonstration . . . humor us doubters . . . what would it hurt . . . unless you know it would always fail ???
 

Cairenn

Senior Member.
I have found it interesting that the U of Penn vet school has been doing follow up studies on all the dogs that worked at Ground Zero. They did not see any increase in lung or other problems with ANY of the dogs. Many of them worked for several years afterward, I think the last one retired last year. I know and may two of them were shot in their other duties as police dogs.

Just interesting
 

tjohnson_nb

New Member
Well, before we move on to that, can you confirm that the initial analysis you cited was incorrect, for the reasons I gave?
I believe your spreadsheet is accurate. I found another interesting take on it. The only way the upper section could crush the lower section is with an impact, with a corresponding rapid deceleration. This is obvious since the lower part of the building has no trouble holding up the upper part normally. This detailed analysis of the video of the collapse shows no impact or reduction in velocity when the two sections meet. It is as if the lower part was not even there.
 

lee h oswald

Banned
Banned
Steel cannot be reduced to 60 micron dust
Originally Posted by lee h oswald

The calculations suffer from the same inaccuracies as my own on the reduction of steel rc to 60 micron dust.

The rc stands for 'reinforced concrete'. So all together it's steel reinforced concrete.

You need warming up after a week in the cooler.
You need waking up, after a lifetime in denial.
 
Last edited by a moderator:

Mick West

Administrator
Staff member
I believe your spreadsheet is accurate. I found another interesting take on it. The only way the upper section could crush the lower section is with an impact, with a corresponding rapid deceleration. This is obvious since the lower part of the building has no trouble holding up the upper part normally. This detailed analysis of the video of the collapse shows no impact or reduction in velocity when the two sections meet. It is as if the lower part was not even there.
So I'm a little curious why, after you discover that one analysis was incorrect, that you continue to assume that the others are also correct? Have you personally been able to verify them?

You've present three analyses. The first you admit was wrong. The other two directly contradict each other. One claims the top would have "bounced off" the bottom part, the second simply claims there would have been a measurable deceleration.

So which do you think is correct? And why?
 

tjohnson_nb

New Member
So I'm a little curious why, after you discover that one analysis was incorrect, that you continue to assume that the others are also correct? Have you personally been able to verify them?

You've present three analyses. The first you admit was wrong. The other two directly contradict each other. One claims the top would have "bounced off" the bottom part, the second simply claims there would have been a measurable deceleration.

So which do you think is correct? And why?
My objective in this exercise was to suggest that the buiding could not have fallen by gravity alone. All 3 of the links I provided agree on that point.
 

slenderbeam

Member
Here is a much more detailed analysis which concludes (as I did intuitively) that the collapse wouldn't even go past one floor. There simply is not enough energy available.
I stopped reading this on the first page where it mentioned the first critical failure mode being the dynamic buckling of the columns.

Accept that it is the weakest link that fails first.

i.e. the seat connection.
 

slenderbeam

Member
Lol!! How about a demonstration, any demonstration . . . humor us doubters . . . what would it hurt . . . unless you know it would always fail ???
it would cost a shedload of money, but maybe that's what's required. A full scale test. I guarantee you - throw a fully loaded floor and some perimeter column panels on the same WTC floor and hey presto. Debunk time.
 

tjohnson_nb

New Member
I stopped reading this on the first page where it mentioned the first critical failure mode being the dynamic buckling of the columns.

Accept that it is the weakest link that fails first.

i.e. the seat connection.
There are infinitely many explanations of how the buildings collapsed but there is one way we know for sure it did not, and that is by the force due to gravity alone. All other arguments simply change the amount of time it took.
 

MikeC

Closed Account
There are infinitely many explanations of how the buildings collapsed but there is one way we know for sure it did not, and that is by the force due to gravity alone. All other arguments simply change the amount of time it took.
I'm completely sure that it the buildings did collapse solely due to gravity.
 

Mick West

Administrator
Staff member
My objective in this exercise was to suggest that the buiding could not have fallen by gravity alone. All 3 of the links I provided agree on that point.
One of those links you agree was wrong, and since they contradict each other you must also agree that AT LEAST one other must be wrong. Hence at least two out of three of your links are factually incorrect - so the fact that they agree with your point hardly helps bolster that point.
 

Mick West

Administrator
Staff member
There are infinitely many explanations of how the buildings collapsed but there is one way we know for sure it did not, and that is by the force due to gravity alone. All other arguments simply change the amount of time it took.
Clearly though it was the impact and the fire that initiated the collapse?
 

slenderbeam

Member
There are infinitely many explanations of how the buildings collapsed but there is one way we know for sure it did not, and that is by the force due to gravity alone. All other arguments simply change the amount of time it took.
Fire and gravity = softening and buckling followed by collapse of upper floors, followed by pulverisation of slabs below.
 

Cairenn

Senior Member.
There is also the weight of the airplane to be figured in. That was another 110 tons of weight on a damaged structure
 

Jazzy

Closed Account
All these buildings sagged and visibly distorted before their collapses. They didn't just collapse out of the blue, they leaned, sagged, stretched in a progressively worsening manner from the onset of the fires.

When their floors began to detach, which happened several minutes before final buckling collapses, their column stability became immediately compromised. If two floors detached in one spot, then the columns' stability would be utterly gone, as the effective length of the column would be tripled, and thus its stability reduced to one ninth of what it was a split second before. Goodbye all safety factors.

As it was, falling floors tended to accumulate together.

saght1.jpg

Once an external line of columns collapsed it began a lightning sequence of load transfer and buckling failure around several hot floors, causing the signal tower to sway (WTC1) on its way down.

The intact part of the structure wasn't capable of bringing tens of thousands of tons of steel to an abrupt stop from 12 mph, even if the top were lined up with it, which it wasn't.

What demolition? Snarf.
 

tjohnson_nb

New Member
Once an external line of columns collapsed it began a lightning sequence of load transfer and buckling failure around several hot floors, causing the signal tower to sway (WTC1) on its way down.

The intact part of the structure wasn't capable of bringing tens of thousands of tons of steel to an abrupt stop from 12 mph, even if the top were lined up with it, which it wasn't.

What demolition? Snarf.
Sorry but massive things are alot slower than lightning :). It doesn't matter if the intact structure stops the upper one or not - it most definitely has to impede its progress somewhat. Can we agree on that much?
 

George B

Extinct but not forgotten Staff Member
No, that is not clear at all. If we know it didn't fall by gravity alone then something had to remove the structure in the floors below the impact.
No you have it wrong. . . .these three buildings were the only structures in the world that were engineered to collapse the way they did. . . you cannot find any other structures of their size and construction that ever have historically or ever will collapse this way again (it was the perfect storm, unprecedented in 4,000 years of human history). . . They can prove it because it was captured on video and tons of other evidence supplied by the authorities who decided how everything would be researched, who would do the research, what data to release when the collapse was simulated, and only reported to the public years and years after the fact to make sure they had it all harmonized and correct of course . . . why should you question such a thing??? If you do you are obviously a nut case and do not understand basic physics . . . Sorry to be so blunt but you know who you are. . . .


See if you don't know how something happened (and are not allowed to consider unusual, alternative explanations) . . . you start with the end result and back engineer it so the assumed process explains the result. . . .as in developing a theory and simulation that fits your preconceived ideas. . . and of course withholding the information you used to construct your simulation . . . You then tell everyone this information and data was withheld for security reasons. . . .
 

Jazzy

Closed Account
Sorry but massive things are alot slower than lightning
Massive things fall at the same speed as light things - were it not for air resistance. That tower dropped as swiftly as a ping-pong ball if you like. Remember Galileo?

The transferred loadings would have moved around the structure at the speed of sound in steel, which is about 5 miles per second. That is similar to the speed of lightning.

It doesn't matter if the intact structure stops the upper one or not - it most definitely has to impede its progress somewhat. Can we agree on that much?
Of course we agree on that. The building fell at about 0.7 G, or 22.5 feet per second per second.
 

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