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Help me understand the collapse a bit more

Apollo20 said:
I think the biggest problem with explaining the collapse of WTC 1 & 2 is that many people cannot get beyond how they THINK it would look.
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This is especially odd given that a top-down collapse like the WTC towers has never happened before.

So what exactly do twoofers base their expectations on?
 
CHF:

I agree, but I guess folks rely on memories of controlled demolitions they HAVE seen... even if they run the wrong way... they are FAST.

The Twin Tower collapses were FAST, ergo they MUST be CDs!

Isn't that obvious?
 
Citizen Pawn:
For about a year I thought nothing of the way they collapsed, I think I was in shock. Then when I started 911 research in late 2002, I said "Holy ****, this doesn't look natural". I didn't really have a problem with the collapse initiation, I still think it's within the confines of reality, if taken on a purely VISUAL basis to the average person. It's just what happens AFTER that (about 3 seconds into collapse sequence to it's final end) that never sat well with me.

Then digging deeper into the science, it looks even worse than just face value.
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emphasis added
http://z10.invisionfree.com/Loose_Change_Forum/index.php?showtopic=11881&st=0&#last

A classic example of someone who can accept that the buildings could start to collapse but cannot accept that they did collapse.

Also interesting that he mentions 'average person'.

'truthers' don't see themselves as average. 'truthers' are special.
 
Undesired Walrus said:
And does that foot then essentially add onto the weight of the mass going down? Like 14 floors becomes 15, then 16 then so and so forth?
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Bingo! The mass of the collapsing portion was continually increasing throughout the collapse. And since momentum equals mass times velocity, the momentum of the collapsing portion was constantly increasing.

Another thing to consider is that once the collapse got going, the beams in the upper portion weren't necessarily aligned with the beams in the lower section. Someone showed a nice photo a while back which showed that the upper perimeter curtain inside of the lower perimeter curtain. It was just shearing away the floor connections. The beams of the lower portion weren't even supporting anything.

Steve S.
 
I reckon they used explosives, steam would have taken too long, and possibly not worked. Waiting for Popular Mechanics on that one. Not sure what the latest science is.
 
I think people also have trouble because they automatically associate size with strength. When big things clash with little things, the big thing usually wins. We see and live examples of this all the time so it forms part of this "intuition" we have. It becomes a hard fallacy to shake when we try to explain the technical aspects of the collapse. For those who are less versed in the science they need to rely on this "intuition" to fill in the gaps. This eventually leads to the plethora of analogies (or chicken wire models) we have all seen. Most of these analogies attempt to isolate and define specific physical principles. Even then, without a solid understanding of science, much is left to "intuition". If I try to explain that an ant can walk on a drop of water twice its mass, but a man can't do the same, have I taught you all there is to know about surface tension? Do you now see how scale changes everything? For me I see this as a key aspect in understanding the collapse, for others ants and water have nothing to do with buildings and planes. Intuition tells them otherwise. If I tell someone the wood in their house is "stronger" than the steel in the WTC does this register with them at all? Has the concept of safety factor and limitations of building materials been properly conveyed? Some people will focus on "wood stronger than steel?" while others will nod and say "ahhh, yes, a wood framed house has a safety factor of 3, but this steel building only has a safety factor of 1.7". To further compound the confusion, explaining these concepts and principles is hard enough to explain to those who are truly willing to learn, let alone to those with preconcieved notions.
 
3bodyproblem said:
I think people also have trouble because they automatically associate size with strength. When big things clash with little things, the big thing usually wins. We see and live examples of this all the time so it forms part of this "intuition" we have. It becomes a hard fallacy to shake when we try to explain the technical aspects of the collapse. For those who are less versed in the science they need to rely on this "intuition" to fill in the gaps. This eventually leads to the plethora of analogies (or chicken wire models) we have all seen. Most of these analogies attempt to isolate and define specific physical principles. Even then, without a solid understanding of science, much is left to "intuition". If I try to explain that an ant can walk on a drop of water twice its mass, but a man can't do the same, have I taught you all there is to know about surface tension? Do you now see how scale changes everything? For me I see this as a key aspect in understanding the collapse, for others ants and water have nothing to do with buildings and planes. Intuition tells them otherwise. If I tell someone the wood in their house is "stronger" than the steel in the WTC does this register with them at all? Has the concept of safety factor and limitations of building materials been properly conveyed? Some people will focus on "wood stronger than steel?" while others will nod and say "ahhh, yes, a wood framed house has a safety factor of 3, but this steel building only has a safety factor of 1.7". To further compound the confusion, explaining these concepts and principles is hard enough to explain to those who are truly willing to learn, let alone to those with preconcieved notions.
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"Scale changes everything" - never was a truer word said.

Drop a mouse 3x its body length onto solid ground and it will jog off healthy (though maybe a tad miffed about all this "drop" business)

Drop an elephant 3x its body length onto solid ground and you shatter every major bone in its body and rupture many of its internal organs. It dies.

Which is why elephants have much sturdier legs (relatively speaking) than mice, and why they can't do somersaults.
 
Apollo20 said:
I think the biggest problem with explaining the collapse of WTC 1 & 2 is that many people cannot get beyond how they THINK it would look. And their IMAGINATION tells them that if the upper section collapsed onto the lower section it would take a finite amount of time to destroy the floor below. And they IMAGINE that this finite time must be similar to the time it would take to bend a metal bar in the way a circus "strong man" bends a metal bar. That's why you hear people claim that is should take a second, for example, to destroy each floor or 100 seconds for the entire building to come down.
Now calculations show that a floor can be destroyed in more like 10 to 20 milliseconds. That's the fact that needs to be conveyed to people who claim that the towers fell "too fast".
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Neu-Fonze, if there is a collapse it will be a fast one, that's the whole idea of progression and the release of energy stored. But even if there is a collapse you can question whether it should collapse in the observed way. The stepwise behaviour is suspicious and inconsistent with general mechanical principles.
 
Again its a matter of scale. If you ever stood below the towers and looked up in amazement at their sheer size you would instantly realize if there was a faiure at one floor level the whole building would collapse.

(toof mode) Its just common sense!! and Physics!! (/troof mode)
 
Einsteen:

According to you "if there is a collapse it will be a fast one".

But according to G. Ross, the collapse could start and then stop!
 
Most of the people here are showing a pancake theory. This is not how the building collapsed. Most of the debris from the early stages of the collapse punched through the floor slab, damaging that floor slab and the floor slabs below it. This damages the floor slab and truss system for a great deal of floors. This vastly lowers the capacity of the columns to resist axial load (buckling) and makes it easier for the columns to be peeled away. The floor slabs in the upper block would detach due to the upper block accelerating and deaccelerating as each floor of columns fails. The columns were also peeled away due to lateral forces. Nothing in this collapse is coming just straight down, the debris that is punching through floor slabs will eventually hit the exterior columns. Being that they were spaced at 3'4" o.c. they will act as a virtual net to "catch" things.

This is *A* collapse mechanic that I personally believe had alot to do with the actual structure. It's almost impossible to verify this with math, hence all of the pancake collapse theories. The math there is relatively easy, it is conservative in favor of collapse prevention, and shows that collapse occurs. Unless one thinks 2/3rds of the energy of collapse should go into heat of all things.

I also think vibrations played a large role in the destruction of the lower floors. The continual impacts from debris in the upper block would create vibrations that would loewr the capacity of the building to resist compression loads.
 
Apollo20 said:
I think the biggest problem with explaining the collapse of WTC 1 & 2 is that many people cannot get beyond how they THINK it would look. And their IMAGINATION tells them that if the upper section collapsed onto the lower section it would take a finite amount of time to destroy the floor below. And they IMAGINE that this finite time must be similar to the time it would take to bend a metal bar in the way a circus "strong man" bends a metal bar. That's why you hear people claim that is should take a second, for example, to destroy each floor or 100 seconds for the entire building to come down.
Now calculations show that a floor can be destroyed in more like 10 to 20 milliseconds. That's the fact that needs to be conveyed to people who claim that the towers fell "too fast".
Click to expand...

Also I am pretty certain if we were able to see what a collapse of the towers would look like if it took 1/2 second per floor (ala Dr Griffin) it would appear unnatural and slow motion.

Of course if it had taken 45 seconds "truthers" would say that was proof that it was caused by controlled demolition because everyone knows that it should have taken 12-14 seconds. "Truthers" would be arguing how by slowing down the collapse it would have allowed for total "dustification " of the towers thereby ensuring all the evidence was atomized.
 
Apollo20 said:
I agree, but I guess folks rely on memories of controlled demolitions they HAVE seen... even if they run the wrong way... they are FAST.
Click to expand...

I think that's a big part of it, no matter how fast the collapse was.

Before 9/11 controlled demolitions were the only circumstance in which most of us have seen a building collapse. So when the towers came down people automatically thought back to demolitions even though it looked nothing like any demolition ever done.

This leads to one of the funnier twoofer talking points:

"The towers were obviously demolitions...but they were a new kind of demolition that's never been done before."

Huh? :eye-poppi
 
I agree, mostly, with Newtons Bit, though that's not actually the specific way that I visualize the collapse. It's certainly plausible, and it's true that it's darn near impossible to account for everything mathematically once things start moving. I hope he wasn't thinking that I was endorsing pancaking as a collapse mechanism.

As far as CHF and Apollo go, I agree also - as far as "common sense" goes, people have to relate to what they are familiar with and can understand - or think that they understand. There's not really anything comparable in the average person's experience. That's why the CD theories are so prevalent. Our minds tend to equate an event to something we can relate to. And, specifically, since WTC7 "looks" the most like a typical building demolition, (minus the sounds and the lights that should be present) people latch onto that as the "smoking gun" so to speak.
 
Newtons Bit said:
Most of the people here are showing a pancake theory. This is not how the building collapsed. Most of the debris from the early stages of the collapse punched through the floor slab, damaging that floor slab and the floor slabs below it. This damages the floor slab and truss system for a great deal of floors. This vastly lowers the capacity of the columns to resist axial load (buckling) and makes it easier for the columns to be peeled away. The floor slabs in the upper block would detach due to the upper block accelerating and deaccelerating as each floor of columns fails. The columns were also peeled away due to lateral forces. Nothing in this collapse is coming just straight down, the debris that is punching through floor slabs will eventually hit the exterior columns. Being that they were spaced at 3'4" o.c. they will act as a virtual net to "catch" things.

This is *A* collapse mechanic that I personally believe had alot to do with the actual structure. It's almost impossible to verify this with math, hence all of the pancake collapse theories. The math there is relatively easy, it is conservative in favor of collapse prevention, and shows that collapse occurs. Unless one thinks 2/3rds of the energy of collapse should go into heat of all things.

I also think vibrations played a large role in the destruction of the lower floors. The continual impacts from debris in the upper block would create vibrations that would loewr the capacity of the building to resist compression loads.
Click to expand...

Well I proposed there were 2 collapse waves. The first wave strips the floors from the exterior and interior columns, approximately 3-4 stories before the second wave, which is the bottom of the falling upper section. This first collapse wave can best be visualized by the "pancaking" or "bagelling" of the floors. Due to the construction of the WTC floor and truss system this is somewhat of a misnomer, as the floors would not have remained intact during the collision. Instead it would have been more of a churned up mess of cement and steel. The second wave would have been responsible for destruction of the core, and peeling away the now detached exterior columns. I personally think this theory is supported by the video evidence and can account for the freestanding core. I proposed this over at PhysOrg but was immediately shot down due to the following: the inertia of the floors would have slowed that collapse wave down and allowed the upper section to catch up. I contended that this would manifest as an oscillation, in the sense that if the second wave caught up to the floor collapse wave, the pressure the upper section exerted would accelerate the floor collapse wave ahead of it. The period of oscillation would of course be very short due to the speed of the collapse. Again I didn't get much of a response from that so I kinda dropped it. Not much of a point developing a model if you're not going to get any support :) It's still the way I visualize the collapse until I get any new information on the matter.
 
Newtons Bit said:
snip>>>
I also think vibrations played a large role in the destruction of the lower floors. The continual impacts from debris in the upper block would create vibrations that would loewr the capacity of the building to resist compression loads.
Click to expand...

NB:
I think you are on to the whole thing.
As the lateral support system disappears due to debris impact, the column length increases, as does the mass loading. The natural frequency of the individual columns decreases. When Wn=0, of course the beam has buckled--but as the frequency decreases, the amount of energy available from all the ongoing shake, rattle and roll to drive them in fundamental is going up. It all relates to 90% of the energy in a vibrating system will be in the fundamental mode.
that was Badly worded, but Newtons Bit and other engineers should get the idea. Maybe one of you guys can word it for the layiety?
 
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