# The Uniqueness of the WTC7 Collapse

Jomper, no attacks please. We have been polite to you, you can do the same.

It does not take an application of kinetic energy to make something fall. If you are cutting a 2x4 and you cut through it, the unsupported piece FALLS because of gravity.

When the supports that tied the building together gave, it collapsed, in the easiest direction, straight down.

and thats the part your not comprehending, straight down through the debris isn't the easiest direction, its the hardest actually. It would have to move through itself in order to fall. Far easier to fall off to the outside where there is significantly less resistance

and thats the part your not comprehending, straight down through the debris isn't the easiest direction, its the hardest actually. It would have to move through itself in order to fall. Far easier to fall off to the outside where there is significantly less resistance

If the straight down resistance is only slightly less than the force due to gravity, then straight down IS the path of least resistance.

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I don't understand the can experiment. How can you use your foot to represent gravity, when gravity is already at play? Aren't you essentially saying there's much more gravity than would be natural in that experiment?

Did you not understand the point that I made about scale or are you simply looking for an excuse to insult me again? The force at scale would be many, many times greater than the force of gravity on the Earth's surface. That was my point at the outset.

It's a good point, but misapplied.

Gravity does not have the same effect at every scale, because of the the square-cube law.

The force of gravity is mass multiplied by the constant g (32 feet/sec2 or 9.8 m/sec2).

The strength of a structure (say a beam, or a leg) is proportional to the cross sectional area (the square of a dimension)

The mass of a structure is proportional to the the volume (the cube of a dimension).

So force due to gravity (the effect of gravity) is proportional to the cube, but strength is proportional to the square.

So the smaller something gets, the weaker the effect of gravity, the larger something gets, then the stronger the effect of gravity.

The can is a good example, you asked if Pete was from Jupiter (where g is about 2.5 times that of Earth), which is actually not a bad question, because if we want to scale up the can to the size of the WTC7, then we have to consider the square cube law. The can is about 0.12m high (12 cm)), and weighs about 15grams. WTC7 was 226m high. So to scale the can up to the size of WTC7 it would have to be 1883x as tall (and I assume I'm evenly scaling all dimensions here).

So, the relative strength is proportional to the square of the dimensions, so 1883x1883 = about 3,500,000 times the strength of the small can

But mass is proportional to the cube, so 1883*1883*1883 = about 6,700,000,000.

The large number are not too important, the key is that the force from gravity has increase 1883x as much as the strength has increased.

So essentially it's the exact equivalent of taking the can and putting it on a planet where gravity is 1888x that of earth. Now you were on the right track with Jupiter, but that's only 2.5x, what we are looking at is more like the surface of a compacted brown dwarf star.

With no brown dwarfs handy I have to increase the force in another way, I do this by standing on it. An empty can can support a static load of about 100 pounds (45,000 grams), but will fail for sure at 200 pounds (90,000 grams). The can itself weighs 15 grams, so 15x1883 is 28,000 grams. So a can scaled up to the size of WTC7 would still support its own weight (ignoring wind loading, and simplifying a bit).

So if you run the numbers, it turns out that a can with someone stood on it is not at all a bad analogy for WTC7. And the three can experiment is actually fairly close in terms of the numbers.

(Note for the quibblers, a super tall soda can would probably collapse under its own weight at a much lower height, as the strength of the small can relies on the tension from curvature. But you get the general idea.)

If the straight down resistance is only slightly less than the force due to gravity, then straight down IS the path of least resistance.

dead wrong, your forgetting that there are a number of paths to the ground and that the one with the most resistance is the one with the rest of the building in the way.

I'm pretty sure that statement pretty much concludes our conversation concerning this subject. What I see within it is either a total disregard for basic physics, a complete lack of knowledge of physics, or the denial of the basic physics involved.

I don't think any productive conversation can be had given any of the three possibilities.

The only thing unique about the WTC 7 collapse is that in a world where most people realize just how hideous political science really is, there are still some so horrified, that they prefer to ignore the obvious, for the impossible.

I don't understand the can experiment. How can you use your foot to represent gravity, when gravity is already at play? Aren't you essentially saying there's much more gravity than would be natural in that experiment?

The can experiment is a distraction IMHO, it has zero bearing on real life events and fails in just about every way to accurately model the collapse of 7.

If you go back to post 103 and look, you will see the can distraction came up right about the time a physics based rebuttal was offered which pretty much humiliates the NIST generated view of the fall. There was no reasonable rebuttal, ergo, the change of subject, and a long drawn out ruse to ignore the obvious and argue the physics of a can instead of the relevant subject. NIST failed to model the fall even remotely accurately, but claims its good enough. NIST failed to describe the fall accurately, and admits its description has a "low probability" NIST ignored film evidence of both controlled demolition and of superheated components of the rubble pile, making no attempt whatsoever to describe the events of that day accurately. Those simple facts are irrefutable, although I'm sure a couple of our believers are just chomping at the keyboards to start typing.

A lot of people subconsciously introduce these types of distractions into a debate they don't feel they are doing well in. There's a physiological term for it, but I can't remember it at the moment.

the can has zero significance,

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actually if I were leading an investigation the first thing I'd do is demand criminal charges be brought on whoever is responsible for the failed mapping of field marks on the structural components, which makes it impossible to answer any further questions as to the exact nature of the collapse. We can dredge up a plain from thousands of feet below the ocean and reassemble it in a hanger, spending millions of dollars to determine exactly the point of origin of the failure and understand how that failure propagated throughout the structure, but these guys couldn't record a few marks on a pile of steel beams right smack in front of them ? Seems like about the most grossly negligent investigation of a structural failure I've every even remotely heard of.

Assuming its was a manufactured event, we don't know who "they" are. We can safely assume if it was a manufactured event that "they" intended the result. We don't know how "they" coordinated the event, nor do we know why these events occurred or why so many people died.

Actually I'm not the one speculating here. I'm willing to consider any and all video evidence that we can agree isn't manipulated or otherwise altered. I would like to consider evidence based argument only and avoid what has traditionally been found to be highly unreliable, eye witness accounts, many of which conflict with other eye witness accounts or film evidence.

I'd still like to see some film evidence that supports either the Captains or the Deputy Chiefs testimony. Without such evidence and without a map of the fall characteristics of the structural components of the building, the only reasonable way to determine the nature of the fall, is to observe it within the video evidence.

Speaking of which. This buildings failure is entirely different than the towers, this one is a classic removal of the base structure in a systematic manor, virtually exactly synonymous with a manufactured event. The base of every structural component was removed in perfect sequence in order to first "kink" the structure, and then drop that energy inward in a free fall pattern. Which is why those outward facades eventually fell inward onto the rubble pile. Exactly what happens in a manufactured event. My bet is you guys haven't reviewed enough controlled demolitions or you'd have noticed that.

The visual evidence does show the asymmetrical failure of the pent house. It then shows an incredibly symmetrical failure of the rest of the building. What occurred within the structure is unknown, we have no record of the fall pattern and there is zero video evidence from within the building. What happened to the penthouse after it disappeared behind the roofs parapet wall must be admittedly unknown if we are to remain honest in our review.

But to clarify my use of the term symmetrical. And not to be rude or anything, but a woman can be beautifully symmetrical, which doesn't mean all straight lines and no bounce. The term can and IMHO does refer to a condition in which a pattern emerges, one dependent on the performance of the surrounding elements. Kinda like what happens in a controlled demolition. The series of explosions must remain symmetrical in order to develop the inward pull against the outside facade required to produce a rubble pile not much larger than the footprint of the original building. The interior structure is used to generate this pull, ( thus the term "pull" in the industry ) typically secondary floor connections.

What I observe in the video evidence is the exactly required simultaneous failure of the strongest portions of this structure, its base, in exactly the symmetrical pattern required to bring the building down into its own footprint. Is any drop a perfect drop, no, but this one is as near perfect as you could want. Assuming someone wanted it, and I think its a safe assumption.

Oh and thats another thing to consider. This building clearly failed at its base, not in the middle where I see minor fires and not at the edge where I see minor damage. Not only did it fail at its base ( or at least at a point below the camera view ) but in a manor so precise as to preserve the angle of the roof line once the "kink" was established. IE every supporting columns resistance to collapse systematically disappeared in perfect symmetry. In response to what NIST suggests is the interiors asymmetrical natural collapse caused by asymmetrical influences.

The only thing the NIST story has accurate in regards to bldg 7 is that a progressive collapse is obvious in the penthouse structures failure. Which makes a symmetrical response to that failure even less likely. Oh and speaking of which again, that progressive failure ( IE takes time to propagate throughout a structure ) is "always" evident in a natural collapse. At no point that I've ever seen at least does one end of a structure simultaneously "let go" in sympathy to the other end suffering failure.

Think tree falling in the forest, does it fall over, or does it fall straight down through itself ? In this case it would have to fall with all branches moving in toward the center in order to mimic what happened to building 7.

Why do you think a building with voids and open spaces should act like a tree? And by the way, to get a tree to fall, one does not cut straight through the trunk. If you try to cut straight through, the weight of the tree will bind your saw up.

dead wrong, your forgetting that there are a number of paths to the ground and that the one with the most resistance is the one with the rest of the building in the way.

I'm pretty sure that statement pretty much concludes our conversation concerning this subject. What I see within it is either a total disregard for basic physics, a complete lack of knowledge of physics, or the denial of the basic physics involved.

I don't think any productive conversation can be had given any of the three possibilities.

The only thing unique about the WTC 7 collapse is that in a world where most people realize just how hideous political science really is, there are still some so horrified, that they prefer to ignore the obvious, for the impossible.

I see my communication skills are failing again. I do actually know a lot about physics, but sometimes it's hard to put into English.

Yes, straight down has the "most resistance", but only if that's all you are considering. What you really need to consider when seeing in what direction something will move is the sum of the forces acting on that object. It's the net resistance.

A building basically has two forces acting on it, both of which are vertical. There's the weight of the building due to gravity, which acts straight down, and then there's the resistance of the structure (and ultimately the ground) which acts straight up. When these forces are in equilibrium, then the building is at rest, and does not move.

Now if the strength of the building is degraded a bit, by some columns buckling, say, then eventually the strength of the building is less than gravity, and the building collapses.

All other things being equal, then you've just got the force of gravity pulling straight down, and a weaker force pushing straight up, so the building will move straight down.

It's only going to move sideways if there is a sideways force acting on it. And the only way that's going to happen is if the collapse is uneven, and the upper part of the building pivots. Buildings do not start spontaneously moving sideways just because there is no resistance.

It's about pivoting. And pivoting requires a fulcrum. So if you are going to suggest that the building take a different path, then you've got to explain what it's pivoting on. Then you want to look into if the pivot could actually support that weight. What happens when a pivot point collapses?

Sorry this is not well explained. It really needs some animated diagrams.

I see my communication skills are failing again. I do actually know a lot about physics, but sometimes it's hard to put into English.

Yes, straight down has the "most resistance", but only if that's all you are considering. What you really need to consider when seeing in what direction something will move is the sum of the forces acting on that object. It's the net resistance.

A building basically has two forces acting on it, both of which are vertical. There's the weight of the building due to gravity, with acts straight down, and then there's the resistance of the structure (and ultimately the ground) which acts straight up. When these forces are in equilibrium, then the building is at rest, and does not move.

Now if the strength of the building is degraded a bit, by some columns buckling, say, then eventually the strength of the building is less than gravity, and the building collapses.

All other things being equal, then you've just got the force of gravity pulling straight down, and a weaker force pushing straight up, so the building will move straight down.

It's only going to move sideways if there is a sideways force acting on it. And the only way that's going to happen is if the collapse is uneven, and the upper part of the building pivots. Buildings do not start spontaneously moving sideways just because there is no resistance.

It's about pivoting. And pivoting requires a fulcrum. So if you are going to suggest that the building take a different path, then you've got to explain what it's pivoting on. Then you want to look into if the pivot could actually support that weight. What happens when a pivot point collapses?

Sorry this is not well explained. It really needs some animated diagrams.
Why wouldn't you expect the building to collapse asymmetrically towards the most fire weakened or structurally damaged area as it begins to move down?

The can experiment is a distraction IMHO, it has zero bearing on real life events and fails in just about every way to accurately model the collapse of 7.

If you go back to post 103 and look, you will see the can distraction came up right about the time a physics based rebuttal was offered which pretty much humiliates the NIST generated view of the fall. There was no reasonable rebuttal, ergo, the change of subject, and a long drawn out ruse to ignore the obvious and argue the physics of a can instead of the relevant subject. NIST failed to model the fall even remotely accurately, but claims its good enough. NIST failed to describe the fall accurately, and admits its description has a "low probability" NIST ignored film evidence of both controlled demolition and of superheated components of the rubble pile, making no attempt whatsoever to describe the events of that day accurately. Those simple facts are irrefutable, although I'm sure a couple of our believers are just chomping at the keyboards to start typing.

A lot of people subconsciously introduce these types of distractions into a debate they don't feel they are doing well in. There's a physiological term for it, but I can't remember it at the moment.

the can has zero significance,

The can was to illustrate the principle of crumpling of a thin walled structure (i.e. WTC7 after the collapse of the interior). I explained how the scale worked, and why I had to stand on it to get the equivalent force. I gave a detailed mathematical explanation of this above:

I understand though that my explanation is not entirely comprehensible, and is certainly unintuitive. Sorry about that.

I'm not sure where your "physic based rebuttal" is. Can you provide a link? Post 103 does not seem to be it.

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Why wouldn't you expect the building to collapse asymmetrically towards the most fire weakened or structurally damaged area as it begins to move down?

It did, internally. The exterior collapse was not due to the fire weakening the exterior. It was a combination of the lack of lateral support, and the original impact damage.

It did, internally. The exterior collapse was not due to the fire weakening the exterior. It was a combination of the lack of lateral support, and the original impact damage.
So you hypothesize. Why would the exterior not show an asymmetric movement for the same reason?

So you hypothesize. Why would the exterior not show an asymmetric movement for the same reason?

Because it's "moment resisting", meaning it's a very strong skin, like the soda can. The interior was not, so it kind of fell to pieces. The exterior held together because it was so strong. If one side of the exterior were to fall faster than the other, then it would essentially pull down the other though the strength of the connections. So it crumples more than it falls to pieces.

Of course, this crumpling you describe occurs below the line that any of the video evidence shows, just as the internal collapse is supposed to occur without any visual evidence except the fall of the penthouse. Can we conclude from this that you deny there was any simultaneous failure of structural columns across the building, despite the visual evidence showing the roofline descending with remarkable horizontal integrity (entirely absent from the NIST model)?

Of course, this crumpling you describe occurs below the line that any of the video evidence shows, just as the internal collapse is supposed to occur without any visual evidence except the fall of the penthouse. Can we conclude from this that you deny there was any simultaneous failure of structural columns across the building, despite the visual evidence showing the roofline descending with remarkable horizontal integrity (entirely absent from the NIST model)?

The lower exterior columns must have failed within a second or two. There's some distortion of the roofline, but once the skin started to fall though, the strength of the exterior meant it would all fall at pretty much the same rate. It split up a bit as it got closer to the ground.

The lower exterior columns must have failed within a second or two. There's some distortion of the roofline, but once the skin started to fall though, the strength of the exterior meant it would all fall at pretty much the same rate. It split up a bit as it got closer to the ground.
Perhaps one of the things that makes the collapse so remarkable in the video evidence is the way the corners of the building we can see, separated by hundreds of feet of roofline representing the whole width of the structure, both begin to descend at exactly the same moment, wouldn't you agree?

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Perhaps one off the things that makes the collapse so remarkable in the video evidence is the way the corners of the building we can see, separated by hundreds of feet of roofline representing the whole width of the structure, both begin to descend at exactly the same moment, wouldn't you agree?

Pretty close together, however, the east side starts to fall first, it actually moves down and away for a second.
In this overlay the green is the original position (after the penthous fell). The red overlay is just before the right side started to drop.

At some point though all the lower structure has failed, so all the upper structure moves down at the same speed, as it is all connected.

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dead wrong, your forgetting that there are a number of paths to the ground and that the one with the most resistance is the one with the rest of the building in the way.

...
But how much energy does it take to divert the unleashed energy and momentum of falling building to the side, rather than succumb to its force, adding to it it in the process, that takes it straight down? Much more than is present in the compromised structure of WTC7.
And the building did go down and not to the side, so why are you saying it shouldn't have?

I see my communication skills are failing again. I do actually know a lot about physics, but sometimes it's hard to put into English.

Yes, straight down has the "most resistance", but only if that's all you are considering. What you really need to consider when seeing in what direction something will move is the sum of the forces acting on that object. It's the net resistance.

A building basically has two forces acting on it, both of which are vertical. There's the weight of the building due to gravity, which acts straight down, and then there's the resistance of the structure (and ultimately the ground) which acts straight up. When these forces are in equilibrium, then the building is at rest, and does not move.

Now if the strength of the building is degraded a bit, by some columns buckling, say, then eventually the strength of the building is less than gravity, and the building collapses.

All other things being equal, then you've just got the force of gravity pulling straight down, and a weaker force pushing straight up, so the building will move straight down.

It's only going to move sideways if there is a sideways force acting on it. And the only way that's going to happen is if the collapse is uneven, and the upper part of the building pivots. Buildings do not start spontaneously moving sideways just because there is no resistance.

It's about pivoting. And pivoting requires a fulcrum. So if you are going to suggest that the building take a different path, then you've got to explain what it's pivoting on. Then you want to look into if the pivot could actually support that weight. What happens when a pivot point collapses?

Sorry this is not well explained. It really needs some animated diagrams.
I've tried to say this same thing many times.

Pretty close together, however, the east side starts to fall first, it actually moves down and away for a second.
In this overlay the green is the original position (after the penthous fell). The red overlay is just before the right side started to drop.

At some point though all the lower structure has failed, so all the upper structure moves down at the same speed, as it is all connected.
I think we can reasonably say this degree of deviation is insignificant to the question of whether or not there was a simultaneous failure of columns. As I said to Cairenn soon after I started contributing to this thread, quibbling about fractional deviations from the perpendicular makes further discussion rather pointless.

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No it doesn't. What makes further discussion pointless is someone that disregards the opinions of experts.

No it doesn't. What makes further discussion pointless is someone that disregards the opinions of experts.
Appeals to authority and bare assertion. That's all I've seen here.

So asking a brain surgeon for input on brain surgery is an 'appeal to authority'? I think not. You seem to not understand what an appeal to authority fallacy is.

Using recommendations from a geologist to say that there is no disease called HIV is one.

Cairenn: you can't even get your Ralph Waldo Emerson quote right.

Well that isn't surprising since I NEVER quoted him. I never said I did. Did I?

It seems that you make up things as it suits you .

You (mis) quote him every time you post, my dear.

I think we can reasonably say this degree of deviation is insignificant to the question of whether or not there was a simultaneous failure of columns. As I said to Cairenn soon after I started contributing to this thread, quibbling about fractional deviations from the perpendicular makes further discussion rather pointless.

I think the fact that one corner moves about ten feet before the other started to move is a little more than "fractional".

You guys sure are quick to call an end to the discussion

Are you referring to 'Knowledge is the antidote for fear.' ? That is not from Emerson, it is original with me.

He said
Knowledge is the antidote to fear. -- Ralph Waldo Emerson

I didn't misquote I came up with my own statement. Knowledge is what lessens fears. It gives us the ability to understand them, and to deal with them.

I've tried to say this same thing many times.

It's a hard thing to get across in in words.

dead wrong, your forgetting that there are a number of paths to the ground and that the one with the most resistance is the one with the rest of the building in the way.
Which is pretty much the state of things BEFORE the collapse. But not the state of things once the tower tops had separate motions from their bases. So what is your argument?

I'm pretty sure that statement pretty much concludes our conversation concerning this subject. What I see within it is either a total disregard for basic physics, a complete lack of knowledge of physics, or the denial of the basic physics involved.
The thing is, how basic is your physics? Does it extend into dynamics beyond the experience gained throwing stones? Because if it doesn't, any conversation you enter, and then attempt to lead, is bound to lead nowhere.

I don't think any productive conversation can be had given any of the three possibilities.
That's not the correct attitude to further discussion.

The only thing unique about the WTC 7 collapse is that in a world where most people realize just how hideous political science really is, there are still some so horrified, that they prefer to ignore the obvious, for the impossible.
And what is obvious? That you're grinding an axe?

You are attempting to have a technical discussion in the rudest way possible.

The tower collapses began when falling floors compacted together in an agglomerating mass as the supporting external columns spectacularly buckled in floor-deep strips. Initial misalignment of the tower tops ensured that the core column bracing was torn away during the descent, leaving standalone interior columns which toppled finally onto the spread-out wreckage.

In the case of WTC7 the floors expanded over the seven hour fire to destabilize column 79. This led to a general collapse of the floors on one side of the building, and the piled-up floors pushed aside a bridge beam beneath the remaining interior columns, bringing about the central collapse of the whole interior of the building. Its external face buckled (below the camera frame) giving a general impression of free fall, as it would - that being the failure mode for any buckling structure.

A contributory factor, in both cases, is CREEP, the behavior of civil steels of deforming under relatively light loads (namely the building loads) once heated past their crystal phase transition point of 475 deg C. In a loaded and damaged skyscraper the consequences of this creep are catastrophic if left alone, as loads will inevitably be transferred to components least able to withstand them.

I suggest you haven't yet been able to grasp the sequence of events here. It's not surprising. Grasping the scale alone is difficult enough for anyone.

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Why wouldn't you expect the building to collapse asymmetrically towards the most fire weakened or structurally damaged area as it begins to move down?
Because it conserves its motion. If one face fails first, then the tower will rock. This converts some downward motion into a rotational motion of the whole falling tower top. That rotational motion is conserved within every separate structural element, and thus will alter all the positions of, and all the force relationships of, all future impact events.

These impact events would not usually have ever occurred within the structure and would be individually spaced over time, allowing inertia forces to be transmitted from the surrounding structure to accumulate for long enough to damage the weaker of the two impactors sufficiently to allow the downward velocity vector of the descending tower top to increase. The proportion of G overridden being around 30%, this is a measure of the kinetic energy loss during collapse. More precisely it is proportional to the area between the graph of the actual fall and the graph of pure free fall.

The kinetic energy that was not overridden became the heat found at the wreckage base, less the energy lost in deforming that steel. That heat was so tightly insulated that even hydrogen didn't burn down there, but at the surface it did.

So, not thermite. And so not thermite.

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Here's another little animation showing the sagging and the drop away of the left side before the fall:

[imgsize=80]https://www.metabunk.org/files/WTC-7-sagging-loop.gif[/imgsize]

The question for the "demolition" theorists must be: why would the building sag and lean like that if there was no resistance?

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Are you referring to 'Knowledge is the antidote for fear.' ? That is not from Emerson, it is original with me.

He said
Knowledge is the antidote to fear. -- Ralph Waldo Emerson

I didn't misquote I came up with my own statement. Knowledge is what lessens fears. It gives us the ability to understand them, and to deal with them.
Ignorance is bliss.... Jazzy will like that one lol.

Because it conserves its motion. If one face fails first, then the tower will rock. This converts some downward motion into rotational motion. That rotational motion is conserved, and thus alters all the positions and all the force relationships of all future impact events.

These impact events would not usually have occurred within the structure and would be individually spaced over time, allowing inertia forces to be transmitted from the surrounding structure to accumulate for long enough to damage the weaker of the two impactors sufficiently to allow the downward velocity vector to increase. The proportion of G overridden being around 30%, this is a measure of the kinetic energy loss during collapse. More precisely it is the area between the graph of the actual fall and the graph of pure free fall.

The kinetic energy that was not overridden became the heat found at the wreckage base, less the energy lost in deforming that steel. That heat was so tightly insulated that even hydrogen didn't burn down there, but at the surface it did. So, not thermite. So not thermite.

And all this happens in milliseconds does it?

So why do they need demolition crews to bring buildings straight down?

Why are most collapses 'asymmetric' or partial?

Why don't all demolitions of big buildings have fires that burn for months at extreme temperatures?

Here's another little animation showing the sagging and the drop away of the left side before the fall:

The question for the "demolition" theorists must be: why would the building sag and lean like that if there was no resistance?

But it is nothing Mick. What you show there is a 'perfectly symmetrical collapse initiation'... you cannot go around saying 'oh it moved fractionally different in the middle so therefore it is not perfect'. It is as near perfect as anyone could expect it to be if it was planned to the minutest detail and as for random fires causing it... it is about as believable as a fully formed adult woolly mammoth suddenly coagulating from primordial soup and saying 'where am I'.

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But it is nothing Mick. What you show there is a 'perfectly symmetrical collapse initiation'... you cannot go around saying 'oh it moved fractionally different in the middle so therefore it is not perfect'. It is as near perfect as anyone could expect it to be if it was planned to the minutest detail and as for random fires causing it... it is about as believable as a fully formed adult woolly mammoth suddenly coagulating from primordial soup and saying 'where am I'.

So, if the interior of the building had collapsed, then how would you expect the exterior to collapse?

So, if the interior of the building had collapsed, then how would you expect the exterior to collapse?
Moment resisting frames are primarily to protect from lateral distortion such as high wind gusts, bomb blasts, partial collapse and earthquakes.

It makes no sense to construct a building where, if, the interior collapses it is immediately followed by the exterior. That would defeat the whole concept of designing to resist earthquakes.

https://www.cement.org/buildings/Capacity-of-Joints-SEI-07.pdf

Moment-resisting frame (MRF) systems have been widely used in building applications
throughout the U.S. and the world. Such systems provide resistance to forces primarily
by flexural action of frame members.

When designing structures for
blast loads, inelastic deformations are allowed to take place in some critically stressed
elements. Similar to seismic design, structural members and joints of moment resisting
frames must be properly designed and detailed to satisfy sufficient levels of deformability
in order to survive blast load effects without collapse. W. G. Corley[4] reported that with
seismic detailing for special moment frames, damage due to blast can be significantly
reduced. Corley also reported that if the current detailing for special moment frames had
been used in the Alfred P. Murrah Federal Building, the failed columns would have had
enough shear resistance to develop a mechanism without failure

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Moment resisting frames are primarily to protect from lateral distortion such as high wind gusts, bomb blasts, partial collapse and earthquakes.

It makes no sense to construct a building where, if, the interior collapses it is immediately followed by the exterior. That would defeat the whole concept of designing to resist earthquakes.

There's no building design at all where (for a tall building) if the interior collapsed, then the exterior would be stable.

WTC7 was not designed to withstand earthquakes. Only the exterior was moment resisting, for wind resistance.
http://www.earth.columbia.edu/articles/view/2235
External Quote:
Earthquake-resistant building codes were not introduced to New York City until 1995, and are not in effect at all in many other communities.
The non-moment-resisting internal frame is another way that WTC7 differs from some of the other similar looking building fires, like the One Meridian Plaza fire in Los Angeles (which has had very Earthquake specific building codes for a long time).

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