So Just Fire Brought Down WTC7 In A Perfect Free Fall Collapse ?

Originally posted by -PLB-
A top section falls on the beams and trusses, making them fail, leaving the core columns unsupported. Its that simple. There is nothing extraordinary here. On top of that the columns are pushed all around be the chaotic falling mass, making them even more unstable, maybe even pushing them over altogether.

I am totally reading what you say, and I'm trying to help you see what makes that phenomenon so extraordinary.

First of all, the core of the tower does not need the support of anything beyond its structure, quite the contrary: the core is the spine of the tower, holding everything in place, it is the vertical cantilever by which all the floors are appended. It is self-supporting. Take everything away, and the core will remain standing like an obelisk, more stable than ever before since it doesn't have to support all the floors.

Secondly, your image of the collapse assumes that the mass of the falling section impacts the floor slabs and rips them down by virtue of its dynamic load - the inertia of something heavy travelling fast in one direction. This is a very long force vector pointing downwards. While this is a very valid explanation, as wmd_2008s examples (Skyline Plaza, Ronan Point etc) for a disproportionate progressive collapse show, the picture also assumes that the falling mass somehow magically takes hard turns left and right on each floor to horizontally slam against the columns of the inner and outer core, displace them, and still resume their vertical descent -- all this with a mean deceleration of only 30%.

You may want to draw the parallelogram of force to better understand. From point (0,0), you draw one vector AB for the free fall acceleration downwards, and then construct a horizontal vector AC with arbitrary length perpendicular to this one, again starting at (0,0). Remember, this sideway vector must be long enough to do displace the columns, so be generous. Now what you want to arrive at is that the vertical portion of the resulting parallelogram is 30% shorter than the first vector for the free fall acceleration to account for the forces that resisted the freefall, so draw vector AD pointing upwards, with 30% the length of vector AB.

Now attach all the vectors to each other. Draw a line between the starting point and the ending point. This vector AE indicates the force that acted on each point during collapse.

Now draw another vector AF, twice as long as AB, for the sum of forces that held up the towers for 30 years with a FoS of 2. Attach it to the AE vector and draw the vector FE. Congratulations! You have found the vector for the built-in pre-stress :-) Easy, wasn't it?

If you attach AF, the sum of forces that kept the tower aloft, to the built-in pre-stress vector FE now, you get what you wanted: a force (AE) acting vertically down on the floor slabs and horizontally on the columns, and the whole tower comes tumbling down.

Of course you can draw this diagram for each and every single element in the structure, however, the sum of all vectors will look like what is on your sheet of paper right now. Don't complain it looks so complicated, it was you who insisted on splitting the equation and go all detailled, but I promised it wouldn't help your theory, because in the end, you still have to explain that enormous FE vector away. Even if you go into the 3rd dimension, FEM and stuff.

Originally posted by AkareyonFirst of all, the core of the tower does not need the support of anything beyond its structure, quite the contrary: the core is the spine of the tower, holding everything in place, it is the vertical cantilever by which all the floors are appended. It is self-supporting. Take everything away, and the core will remain standing like an obelisk, more stable than ever before since it doesn't have to support all the floors.

You seem to ignore that the floor system with its beams in the core fail just like the office floors. What makes you think the core floors remail undamaged when you drop the mass of at least 15 floors plus core columns plus mast on them? Sounds like an extraordinary assumtion that will need extraordinary evidence.

The evidence that the core columns were stripped from almost all horizontal support is abundand by the way. Look at the columns in the debris. Look at the spire.

Secondly, your image of the collapse assumes that the mass of the falling section impacts the floor slabs and rips them down by virtue of its dynamic load - the inertia of something heavy travelling fast in one direction. This is a very long force vector pointing downwards. While this is a very valid explanation, as wmd_2008s examples (Skyline Plaza, Ronan Point etc) for a disproportionate progressive collapse show, the picture also assumes that the falling mass somehow magically takes hard turns left and right on each floor to horizontally slam against the columns of the inner and outer core, displace them, and still resume their vertical descent -- all this with a mean deceleration of only 30%.

You seem to forget that core columns, core beams, truss hat and mast are also rushing down, just behind the collapse front. Its not just floorslabs. So no turns needed. More than enough material coming down to do all kind of damage.

The way you are looking at it is some perfect and clean pancake collapse. There is a very old video of that idea. That's not what happened. A lot of effects were at play. A lot happened. We may never know what exactly went on, but we do not need to resort to extraordinary explanations. It can all be explaned by rather simple to imagine effects.

I don't have the time right now to go into the rest of your post, maybe later.

Originally posted by -PLB-
You seem to ignore that the floor system with its beams in the core fail just like the office floors. What makes you think the core floors remail undamaged when you drop the mass of at least 15 floors plus core columns plus mast on them? Sounds like an extraordinary assumtion that will need extraordinary evidence.

Look, it is funny you ask such a thing after all the discussion we had, because it is all answered already in great detail. It is for this reason that I describe the compression as a simple, summarized 1D model, because once you start going into detail, you can shift and twist and concentrate on this and leave that out - until you have a perpetuum mobile.

And it goes like this: first you say all the mass goes into ripping down the floor slabs. I ask how all the mass was supposed to concentrate on the slabs, I get no answer, so I just go along with it for the sake of the argument and ask what ripped the core down then, then you say, well, all the mass dropped on the core, how could it possibly not fold down into itself?

Maybe you didn't notice until now, but that's not how it works, which should be clear from the tons of evidence and equations and models I have shown you.

The evidence that the core columns were stripped from almost all horizontal support is abundand by the way. Look at the columns in the debris. Look at the spire.

Extraordinary indeed, especially all the straight columns atop the debris field which look like fresh, as if nothing ever was attached to them. No beam, no bracing, no buckle, nothing. Also the part of the spire that just falls over as if all connections to the rest of the structure have been cut.

You seem to forget that core columns, core beams, truss hat and mast are also rushing down, just behind the collapse front. Its not just floorslabs. So no turns needed. More than enough material coming down to do all kind of damage.

Remember: only about 30% of the potential energy go into doing any kind of damage, the rest is converted to kinetic energy. With just 30% of the potential energy you have to account for all the displacement work that is done. That includes dustifying the concrete, accellerating the floor slabs, throwing the perimeter columns on the roofs of adjacent buildings, shearing, buckling and breaking columns, bolts, weldseams and beams, ripping down the core... and even destroying WTC 7. With 30% of the potential energy, you have to overcome all the forces that were in place to decelerate the structure to 0m/s, counteracting the contant pulling force caused by earth's acceleration, making sure the potential energy is not converted to kinetic energy. Let us put is this way: 0.3*E_potential = E_damage. So for each cubic meter, since E=p*V --> 0.3*p_tensile = p_compression. So for each square meter, since p=F/A, 0.3*F_up = F_down. Or from the E=F*s approach, for each meter in height, 0.3*F_up = F_down.

For every Newton keeping the structure together, there were more than three Newton pulling it apart - by design, but the effects didn't show until the latent forces finally got the chance to do their magic.

[obi-wan kenobi]This is not the steel you're looking for. [/obi-wan kenobi]

The way you are looking at it is some perfect and clean pancake collapse.

Why, yes of course, that is the picture that has been painted here so far.

There is a very old video of that idea.

The FEMA animation? Yeah, I remember that one, we all laughed heartily at that, how could they not notice the core remained upright?

That's not what happened.

Of course not!

A lot of effects were at play. A lot happened.

I totally agree.

We may never know what exactly went on,

I'm with you on this!

but we do not need to resort to extraordinary explanations. It can all be explaned by rather simple to imagine effects.

Like, resonating the whole structure like a huge guitar string in overtones of the n-th octave until the molecular bonds snap, like Tesla did a few decades ago?

reply to post by Akareyon


Watch the video collapse starts at around 0:31 seconds.



It's about 3 seconds into the collapse before anything is ejected from the walls for that 3 seconds were has the falling mass gone IT'S impacting anything in its way within the walls of the tower.

Here is a drawing showing the position of the plane entry relative to the core for the North Tower.



The core steel is also THINNER higher up the structure.

Using the link from the other thread (for the 250,000 ton mass) the steelwork + concrete mass from impact to roof level will be around a minimum of Steel 3190 tons concrete 11700 tons or 14890 tons that's minimum that doesn't include services, office equipment etc.

Also because of the way the column trees are built the truss supports are at different spandrel positions on different trees see this picture.



If you now look at this drawing you will see the trusses (floor slab)line up with the top middle then bottom spandrel of adjacent column trees.



The various components are named here just in case you are not sure we don't want another cleat problem!


Now if we look at pictures of the debris after collapse and look at the position of breaks in column trees






The last image is a nice hi-res image and you can click on it to see lots of detail including broken floor slab and column connections.

For anyone to think that all that material falling within the wall space of the towers would not strike ALL parts of the structure within ie core columns/floor area,floor slabs and wall steel makes me wonder what has happened to the education system worlwide over the last 20-30 years and also good old common sense.

Originally posted by Akareyon
And it goes like this: first you say all the mass goes into ripping down the floor slabs. I ask how all the mass was supposed to concentrate on the slabs, I get no answer, so I just go along with it for the sake of the argument and ask what ripped the core down then, then you say, well, all the mass dropped on the core, how could it possibly not fold down into itself?

For some odd reason you are arguing that the floors inside the core will not suffer the same fate as the floors outside the core. As if there is some magic forcefield preventing mass from falling on the floors inside the core. Reality check: Mass falls down, and hits floors outside and inside the core.

So can you explain on what according to you the majority of mass fell instead? The floor area was what, 95% of the total area? What is keeping the upper floors in the core area, the core columns, the truss hat and the mast from falling on the floors inside the core? Why do you think it is extraordinary when it does?

You are making extraordinarily little sense to me.

Extraordinary indeed, especially all the straight columns atop the debris field which look like fresh, as if nothing ever was attached to them. No beam, no bracing, no buckle, nothing. Also the part of the spire that just falls over as if all connections to the rest of the structure have been cut.

Laymen may find a lot of things extraordinary. Does not mean that it is.

Remember: only about 30% of the potential energy go into doing any kind of damage, the rest is converted to kinetic energy. With just 30% of the potential energy you have to account for all the displacement work that is done. That includes dustifying the concrete, accellerating the floor slabs, throwing the perimeter columns on the roofs of adjacent buildings, shearing, buckling and breaking columns, bolts, weldseams and beams, ripping down the core... and even destroying WTC 7. With 30% of the potential energy, you have to overcome all the forces that were in place to decelerate the structure to 0m/s, counteracting the contant pulling force caused by earth's acceleration, making sure the potential energy is not converted to kinetic energy. Let us put is this way: 0.3*E_potential = E_damage. So for each cubic meter, since E=p*V --> 0.3*p_tensile = p_compression. So for each square meter, since p=F/A, 0.3*F_up = F_down. Or from the E=F*s approach, for each meter in height, 0.3*F_up = F_down.

For every Newton keeping the structure together, there were more than three Newton pulling it apart - by design, but the effects didn't show until the latent forces finally got the chance to do their magic.

If you ignore all the rational explanations you have been given, it may indeed seem like magic to you.

Why, yes of course, that is the picture that has been painted here so far.

No, its the picture you created in your mind, due to a lack of imagination.

The FEMA animation? Yeah, I remember that one, we all laughed heartily at that, how could they not notice the core remained upright?

Only fools that do not understand conceptional models to show a specific phenomena laughed. The rest of the world got the point.

Originally posted by -PLB-
You are making extraordinarily little sense to me.

Yes, you mentioned something like that a few times and I'm beginning to suspect that by now, even if I tried to explain - with sources, links to Wikipedia and quotes by Newton - that a rock will fall down if dropped from a high building, you would make a puzzled face and wonder what I'm trying to say. I'll try again.

I am saying that uniaxial collapse in all tall buildings is inevitable once 2% or more of the structure are damaged. The mass of the building's section above the damaged floors will be accelerated towards the center of the planet's mass. All the parts of the structure in the path between the falling body and ground level will be cut, torn, sheared, ripped, pulverized and buckled out of the way, a process which takes up only 30% of the acceleration, therefor, the structure will not have the slightest chance to withstand the tremendous force of the dynamic load. It is because of the high velocity of the impacting mass that the momentum is great enough to accelerate every particle it encounters. When the top section hits the first floor, it does so with many times the force of its static load, way beyond the design strength, destroys all connections and accelerates it. After that, it picks up speed again, together with the mass of the first floor, and crashes into the second floor. Again, the dynamic load is so huge after that one-story freefall that it easily buckles and bends all connections, investing only a small portion of its momentum, accelerates that mass as well and crashes into the third floor and so on.

As you can see, there is no way any part of the structure could have stopped the collapse. Which is quite logical too, if you look at it mathematically. Due to gravity, the sum of forces acting downwards was much greater than the strength keeping the structure in place. The towers consisted of tons and tons of steel, concrete, glass, plumbing, elevators and so on, of course there was a huge force pulling the whole structure down. And since they were never designed to cope with the load of one third of their own weight pushing down on the other two thirds, in technical terms, the towers stood under so much stress with all their own weight and the live load, that a certain amount of additional weight would inevitably result in a disproportionate progressive-compressive collapse.

So when the mass of the top section became dynamic, it was as if the mass on top of the building had been multiplied by a factor of 30, in other words, it was as if ten towers had been stacked on the roof! It would be insane to suggest that any structure in the world could withstand that. You don't expect a wooden cottage to survice a rock being hurled on it, would you? The redundancy required for that would come close to carving caves into a solid block of steel, but that would have little in common with modern, economic, light-weight steel architecture. Suggesting that the towers were brought down by a controlled demolition team ignores the fact that there are only a few firms world wide who specialize on tasks like this one and that it would have required months of preparations, calculations and rigging the whole building without anyone taking notice, and since you suggest the towers were brought down by magic, it is only because of your lack of imagination.

Otherwise, you would easily see before your inner eye how when the top fell, its floor slabs accreted and crashed into the other floor slabs, tearing them from their connections, while the core floor crashed down on the core columns and the other way round (since everything was totally out of plumb now). The core beams were not designed to hold any vertical weight, so they sheared each other off, leaving the columns without support so they buckled under their own weight and crashed down on the next level, repeating the process until only the spire was left. The spire video proves that all horizontal connections were damaged, otherwise, the long shard couldn't have fallen over without buckling, and hidden in the dust cloud is the part of the core that forms three plastic hinges, allowing for a vertical descent of the last erect splinter of the structure.

And of course the same goes for WTC7. Although office fires wouldn't be hot enough to actually melt steel, they would easily compromise the yield strength of the columns and it is not unusual that once one or more columns fail due to stress, the load is distributed to other columns which then are also stressed beyond their design load and fail simultaneously, initiating a progressive collapse very similar to those seen in conventional controlled demolitions.

I hope this makes more sense now.

Originally posted by Akareyon
I am saying that uniaxial collapse in all tall buildings is inevitable once 2% or more of the structure are damaged.

Most of the stuff you write here actually does make sense, with the occasional straw man, like the quoted bit.

Anyway, it looks like you agree its silly to argue that most mass did not fall on the floors, as you haven't come with an alternative.

reply to post by -PLB-
Okay, that's cool. Other than that, I was successful at summarizing your position?

Please point out other strawmen, because I suspect I have found out where our problem is.

You may also consider this an invitation to play along and do what I did - empathize with me and dissect my post. You know my argumentation by now. What would my answer be to that post?

Even if you think this is childish, it's great to break down barriers. And don't be shy, I won't make fun of you, it's not a trap or so. Because now you have a chance to point out where I misunderstand you and the other way round. We'll be getting there, you'll see :-)

reply to post by Akareyon


I am not going to play along, don't really have the time for it at the moment too. But just as an example:

I am saying that uniaxial collapse in all tall buildings is inevitable once 2% or more of the structure are damaged.

Not any tall building (you will have a hard time with pyramids). Not just any damage, but very specific damage, which can either be induced intentionally (controlled demolition) or unintentionally (fires, plane crashes, construction work).

Your whole post is riddled with inaccuracies like this. But the general idea is more or less in the right direction.

Why is so much focus on the mechanics of the collapse? Unless you have a good education on the topic, you cant even debate. Wouldnt you be more curious what players were involved, where the money and training came from and who set everything in motion?

This expert confirms my original OP.


Why some people at ATS put this persons obvious expertise into the "cognitive dissonance" zone is a question only they can answer ?

But ATS motto bears repeating "Deny Ignorance"

Again we don't have all the answers, but the OS on WTC 7 is bogus, that much is factual.

reply to post by Blue_Jay33


Well lets look at what he says as usual with these clowns at Architects for the Truth the events are quoted in ISOLATION.

It wasn't just the fire that caused the collapse the impacts the structural damage and the fires ALL had a part .

He just quoted the usual BS you get from that bunch !!!