Has Anyone Seen A Realistice Explanation For Free Fall Of The Towers?

[mortimer]

Another reason the towers fell roughly into their own footprint is the steel outer shells of the towers. They would tend to push falling debris back towards the centers of the buildings before collapsing themselves.

 

[Metullus]

This discussion brings to mind my mis-spent youth. At one point in my tenure as a Boy Scout several of us had the bright idea that we could become overnight acrobats and entertain our fellow scouts at the evening campfire. Our goal: make a tower of boys four kids high (well 3 1/2 high really, the top kid was really small) with seven scouts (four on the bottom, and the others stacked above.)

Needless to say, we never succeded. We did get three high but the last guy kept collapsing us. The point is that when we fell we fell in a heap, even when the collapse was caused by the top guy over-balancing - in other words a top down collapse. We never toppled over like a tree, instead we collapsed in our own footprint, so to speak.

Kinda like the towers.

 

[Alareth]

This discussion brings to mind my mis-spent youth. At one point in my tenure as a Boy Scout several of us had the bright idea that we could become overnight acrobats and entertain our fellow scouts at the evening campfire. Our goal: make a tower of boys four kids high (well 3 1/2 high really, the top kid was really small) with seven scouts (four on the bottom, and the others stacked above.)

Needless to say, we never succeded. We did get three high but the last guy kept collapsing us. The point is that when we fell we fell in a heap, even when the collapse was caused by the top guy over-balancing - in other words a top down collapse. We never toppled over like a tree, instead we collapsed in our own footprint, so to speak.

Kinda like the towers.

Were your skeletons secretly wrapped in C4?

 

[Christophera]

Chris, you actually sit there -- a proven liar -- and question someone else's integrity? Sorry, liars such as yourself simply don't possess the moral authority.

Since you are a documented liar -- proven so by your own words -- nothing you say means anything to anyone.

The is no raw evidence for the steel core columns, A fact proven dozens of times right here in this very thread. I've not lied, you folks paint me as a liar when in fact you support lies.
The only core that can be evidenced with images of the demo is the concrete core.

And the only explanaton for near free fall and total pulverization that exists on the web is based on the concrete core. Which is why it's so important to you folks that there was no concrete core.

http://algoxy.com/psych/9-11scenario.html

 

[Christophera]

I promised myself not to do this, but Chris are you saying that steel core collumns shouldn't have floor beams connected to them?

I'm no structural engineer, but isn't that what a steel core does? Isn't it supposed to support all the floors?
Or is it a single 1300 ft piece of steel that only supports the roof?

that is actually your problem to solve because there are no plans. The concrete core took 20% of the towers weight but primarily acted to resist lateral and torsional forces with its steel reinforced, rectangular cast concrete tubular shape.

To the left of the spire is the concrete shear wall. Notice no core columns left of it where they should be.

http://www.internationalskeptics.com/forums/attachment.php?attachmentid=3003&stc=1&d=1157781276

 

[gumboot]

that is actually your problem to solve because there are no plans. The concrete core took 20% of the towers weight

So what held up the other 80% of the tower's weight? I would expect a concrete core to account for a great deal of the tower's weight. Maybe even more than 20%. Which would mean the core didn't even support it's own weight.

So what did? Pixie dust? Or was the rebar coating in magical nano-C4 that acts like an anti-gravity field?

-Andrew

 

[mortimer]

that is actually your problem to solve because there are no plans. The concrete core took 20% of the towers weight but primarily acted to resist lateral and torsional forces with its steel reinforced, rectangular cast concrete tubular shape.

To the left of the spire is the concrete shear wall. Notice no core columns left of it where they should be.

http://www.internationalskeptics.com/forums/attachment.php?attachmentid=3003&stc=1&d=1157781276

Please make an arrow that points to the concrete shear wall in this photo. Sorry, Christopher, there's nothing in that photo but the "spire", dust, and other buildings.

 

[Dog Town]

near free fall

Your def please!

 

[Alareth]

SO perhaps a better term, one we should introduce to them, would be:

Free Fall Time

or

Time of Free Fall

TAM

Another term I have seen a few places (Including Abby's film) that shows utter ignorance is "speed of gravity"

Gravity is a constant that affects all objects. The amount of effect varys in relation to mass.

It does not have a speed.

 

[Brainache]

that is actually your problem to solve because there are no plans. The concrete core took 20% of the towers weight but primarily acted to resist lateral and torsional forces with its steel reinforced, rectangular cast concrete tubular shape.

To the left of the spire is the concrete shear wall. Notice no core columns left of it where they should be.

http://www.internationalskeptics.com/forums/attachment.php?attachmentid=3003&stc=1&d=1157781276

So once again we have the problem of deciding if this image shows 3' rebar or a concete core, or as has been shown in high resolution close up the steel core collumns. I wish I could have avoided the urge to re-engage you on this Chris. The steel core has been shown many times. Not once has any evidence whatsoever for a concrete core been produced.
What kind of person are you who insist that things which are non existent must be there?
Is this just some kind of sick joke?
It isn't very funny.
I really do think you should be taking some kind of treatment for your condition.

 

[William Rea]

Another term I have seen a few places (Including Abby's film) that shows utter ignorance is "speed of gravity"

Gravity is a constant that affects all objects. The amount of effect varys in relation to mass.

It does not have a speed.

The mathematics is amazingly simple. There are two interesting ways of looking at the problem either in terms of forces and/or in terms of energy.

F (Force or what we consider weight) = m (mass) X a (acceleration)

For gravity we usually substitute g (gravitational force 9.81m/s^2)

Although g is constant, the velocity isn't. Initially the velocity of the upper floors would be zero and the forces acting upon the floors would be in equilibrium so that it is stationary. When that equilibrium of forces is upset say by catastrophic weakening of the structure the falling floors will accelerate by g and fall at increasing velocity until they reach either terminal velocity or another counter force acts upon them.

Terminal velocity is when forces opposing the fall (call them R) are in equilibrium with g and no further acceleration is possible although the falling floors are still moving they are not accelerating...

ma - R = 0 (velocity is constant)

A lot of people struggle here because as Newton observed, a body can be in equilibrium of forces but still be moving.

We must consider then what are the forces opposing g, my list of factors would be the following although I am sure anyone could add to the list...

1. Wind resistance.
2. falling into floors below (energy dissipation)
3. Distortion of steel framework (energy dissipation)

In energy terms the model is...

Total Energy = Potential Energy + Kinetic Energy + Losses

MgH = mgh + 0.5mv^2 + Losses

Interestingly, this explosive force accompanying the initial falling of the floors does not exist as such since the release of kinetic energy is not explosive.

In the above it is the losses that are key. What resistance existed? Bear in mind that energy lost to the Losses during the fall will reduce the kinetic energy and so the velocity of the falling floors.

I don't know how the towers fell anymore than the investigators seemed to in their report but I am suspicious of their claims.

 

[Oliver]

Just find any photo of the collapse in progress and ask them why the debris is falling faster than the building itself...and if the debris is falling faster than freefall. They dont like that argument, but they havent been able to counter it yet.

Delicious.

 

[William Rea]

Having read about the construction it is my understanding that the core is designed to hold the building up against direct gravity (in compression) and that the envelope of supports that double as the outer wall give the building a moment to resist toppling (compression and tension). the outer walls act as classical buttresses to support the core but the core bears the gravitational forces exerted by itself and the trussed floors.

Regardless of the construction of the core (remember concrete is very good in compression and steel reinforcement is only there to resist tension) I am surprised at the mode of failure for the towers. My expectation would be that the floors would certainly pancake on each other leaving the core remarkably intact and that the top would topple over the core and fall to the side of the building.

 

[GlennB]

Actually, they do.

...

Just for the sake of completeness, a steel girder would take 9.03 seconds to fall 400m, reaching a top speed of 88.5m/s (about 198 mph).

Criticism of shoddy argument accepted. Will try harder

So the girders and other dense, substantial debris do reach terminal velocity during a 400m fall? The equations in Wikipedia are way beyond my maths. Any volunteers?

 

[R.Mackey]

The block itself also collapsed, because otherwise it should stay intact until it reaches the ground somewhere. It is impossible to collapse in the air because there is no initial 'helping hand' to let that block (that follows its own "free fall" part in the air) collapse, because it's assumed that the whole magical collapse process starts if the block collapses on the floor below. Why would the block also atomize into dust ? the magical process is a progressive collapse from top to down, under the damaged zone. Does the magical process flow back into the falling block ? That must be a smart process. The same argument for the other building.

Sorry, this is just plain wrong, obviously wrong. As the block hits lower floors, Newton's Third Law applies, and both block and lower floors deform. The block hits over 60 floors on the way down, each one damaging the block almost as much as the floors below. There's nothing but rubble by the time the collapse stops.

 

[R.Mackey]

Criticism of shoddy argument accepted. Will try harder

So the girders and other dense, substantial debris do reach terminal velocity during a 400m fall? The equations in Wikipedia are way beyond my maths. Any volunteers?

This problem is a lot harder than it sounds, especially for steel girders, because their terminal velocity will be a strong function of whether the girder is falling down vertically (like a spear) or sideways. Much like people jumping out of planes reach about 120 MPH in proper position, but more like 180 MPH if head-down and arms tucked back.

The majority of debris hit other parts of the building on the way down, and very little of it started at roof height. The average starting height of material is more like half the building's height, or only 200m. I suspect few of the large chunks reached their drag-limited speed. Not sure it matters, either.

 

[gumboot]

Having read about the construction it is my understanding that the core is designed to hold the building up against direct gravity (in compression) and that the envelope of supports that double as the outer wall give the building a moment to resist toppling (compression and tension). the outer walls act as classical buttresses to support the core but the core bears the gravitational forces exerted by itself and the trussed floors.

I gather the exterior columns of the building actually carried a significant portion of the weight, as did the core. The floor trusses provided rigidity between the two "tubes".

Regardless of the construction of the core (remember concrete is very good in compression and steel reinforcement is only there to resist tension) I am surprised at the mode of failure for the towers. My expectation would be that the floors would certainly pancake on each other leaving the core remarkably intact and that the top would topple over the core and fall to the side of the building.

You mean like a tree?

Do you think the Keebler Elves would survive such an event?

By the way, a 60-storey or so section of the North Tower core remained standing a good 15-25 seconds after the rest of the building had collapsed.

-Andrew

 

[William Rea]

I gather the exterior columns of the building actually carried a significant portion of the weight, as did the core. The floor trusses provided rigidity between the two "tubes".

You mean like a tree?

Do you think the Keebler Elves would survive such an event?

By the way, a 60-storey or so section of the North Tower core remained standing a good 15-25 seconds after the rest of the building had collapsed.

-Andrew

I like your simplification of the structure into two tubes it is a good analogy except that the inner tube is built with immense strength very much like a tree trunk supporting branches. My understanding is that the inner tube carried the majority of the weight, even the weight transferred through the trusses from the concrete floors. The outer tube although significant is really a buttress transferring transverse forces from the inner core into the ground.

It is interesting that the inner core stood 15 to 25 seconds longer, it kind of bears out what I thought.

I tend not to read the conspiracy theory sites so I was not aware of the Keebler Elves story until now, now you have made me go and look I'm going to get dragged into it!

The tree is not a good analogy in terms of structural soundness and response to external forces. Wood is a very different material to steel and concrete so I don't accept the analogy in those terms except to point out that if you look at the remains of forest fires the cores or trunks often remain intact to the point that they are still able to resist considerable transverse forces and they are able to support their own weight.

 

[gumboot]

The tree is not a good analogy in terms of structural soundness and response to external forces. Wood is a very different material to steel and concrete

I'm glad we agree. The 9/11 "scholar" Judy Woods used the analogy of the top of a tree falling to claim the top section of the towers would have "tipped over" rather than compressing the remainder of the building.

Of course, trees are entirely solid, with a fairly high density, thus the amount of force needed to compress a tree trunk would be absolutely enormous.

In contrast, a building is primarily air, and as such has a very low density. The amount of force required to tip it over would be enormous - I have heard it would have to tip over its centre of gravity by several hundred feet in order to topple.

I recall, from the first time I saw the collapses, I described them as "peeling open like a banana" (I have always been mystified by the "looks like a CD" claim). Additional research confirms my interpretation - the forces of collapse pancaked the floors. As they gave way the building lost rigidity (because the floor trusses made the building rigid) thus, as the upper mass crashed down on the building the exterior cladding peeled outwards like a banana skin. This left the naked, stripped core, some of which remained standing for some time before it too collapsed (since I think we can agree the core of the WTC, having suffered the collapse of the rest of the structure, was not going to remain standing).

-Andrew

 

[Belz...]

Mancman I think you've actually found the only image that might be legitimately labeled core columns, ... but they are not.

???

The first one that topples out has floor beams connecting 2 interior box columns. The few that stand momentarily cannot be seen clear enough to see the floor beams connecting them and might qualify, but because the stills which are clearer do not show columns in the core at many other phases, we can safely stay with the fact that no steel core columns are visible and the concrete core is.

Only problem is, if the concrete core WAS there you'd see it in the video. All you see is those columns. Where's the concrete in the video, Chris ?

Congratulations! Seriously, you have some real integrity when it comes to digging up evidence. Good try.

So integrity is finding videos and images that can agree with ?