WTC 1 & 2. What happened after collapse initiation?

[stateofgrace]

How about trying to answer the other example? In WTC1 the upper block -- the area above the impact zone -- fell 3.7 meters downward onto the lower block -- according to Bazant. However, if this upper block was first pulverized into dust and then dropped onto the lower block, would the results be the same?

If ?

What would have pulverized the upper block into dust before it dropped onto the lower block?

 

[Grizzly Bear]

How about trying to answer the other example? In WTC1 the upper block -- the area above the impact zone -- fell 3.7 meters downward onto the lower block -- according to Bazant. However, if this upper block was first pulverized into dust and then dropped onto the lower block, would the results be the same?

The upper section of tower was not 'pulverized into dust' when it began it's descent. It is falling as an entire 15 to 20-story section of building. The model you are proposing has little to no relevance the the real thing.

 

[pomeroo]

Hey, I just saw Heiwa's photo on a milk carton.

 

[tanabear]

I saw this and stared at it for over an hour trying to comprehend what the hell this was... You're not only making the box a completely solid object by adding the mass of 'sand' into it, but you're also trying to make a comparison with dropping it onto a aluminum can. I'm not sure an experiment can get much weirder than that... this even tops Gage's analogy... and then pouring only the 'sand' onto the can... Explain to me how this in any way compares to the towers...

It was in a response to a statement by "X" in a previous post. He wrote:

Ultimately, it does not matter much.
Whether the upper section is destroyed during or after the collapse should not appreciably change the amount of mass moving downwards. The important thing to note is that the moving mass put more strain on the lower section than the lower section could withstand.

He made the point that it didn't matter if the upper block was intact or not, because it did not change the amount of mass moving downwards. So I asked if the upper block was already pulverized down to a size between 1 and 100 microns then dropped, would the effect on the lower block be the same. According to his previous statement, he implied it should be the same. So I gave another example. Take a cardboard box and fill it full of sand. Then drop it on an aluminum can. Then take the cardboard box and have the sand fall as individual grains on to the aluminum can from the same height. The amount of mass moving downwards might be the same but the force at which it impacts the lower block will not be.

The dust clouds make up an estimated 1% of the total mass. They are insignificant.

Are you talking about the dust clouds within a couple of seconds of the towers collapse or after the towers are completely destroyed? Is there a difference between the "cushion of debris" and the dust clouds?

One correction before I answer: At no point does the debris layer, between the upper block and what remains of the lower block, stop crushing the lower block. I have no idea where you got that from. It is massive, it is moving downward, therefore it crushes.

You had stated in a previous post that you agreed with Ron Wieck's statement, "Once the global collapse ensued, the floors necessarily pancaked. What else could they be expected to do?"

During the collapse, floor by floor an enormous impulse is applied to each set of columns and floors. At some point, energetically the failure mode will favor the floors tearing free of their connections before the core columns buckle. The collapse has enough energy to induce both of these failure modes -- the question is merely which one happens first.

Whether or not the columns buckle first or the trusses fail first, this can't be described as pancaking. Pancaking is when one floor impacts the floor beneath it, and on and on till the building collapses.

Which one happens first is a function of how fast the descending mass is falling. Since the falling mass is largely composed of debris, and the upper block is at an angle in any event, the impact will not be a sudden column-on-column impact. Instead, columns will experience a complex load, and the floors will see a sudden increase in load as well.

Then this cushion of debris must be crushing the lower block at a faster rate than the upper block can fall through this cushion of debris. The cushion of debris is destroying intact steel and concrete at a faster rate than the upper block can move through this cushion. So this cushion can crush and move faster than the upper block can merely fall? That is pretty impressive.

I don't know precisely when this will happen, but it is after a few to a few tens of floors. We can also partially see this effect because, once it sets in, the core can now resist the collapse wave intact. Once the floors shear, the core structure is almost purely vertically loaded, with random side forces approximately cancelling out by virtue of being in the center of the collapse. So they can actually spear through the collapse in reasonably good shape. This does in fact happen for both Towers, leaving remnants several tens of floors high, for a few seconds.

Of course, according to Bazant the upper block stays intact during the crush-down phase only to be destroyed when it hits the rubble pile. Someone defending the pile-driver explanation could simply state that it partially broke up on its way down and thereby "missed" some of the core columns.

I've been thinking about how to reply to this all day.
I'm still not sure. It's almost as though you think the entire mass of the upper section was converted to dust, and expanded out into the surrounding air.
That is the only explanation I can think of that accounts for your statement.

I really shouldn't have to sat this, but it is wrong.

There was dust, this is true. But as has been pointed out already, the dust clouds consist of a very small amount of matter. And most of that was easily crushed stuff like sheetrock and office equipment.

The non-metallic portions of the towers were largely pulverized. Even Bazant mentions this in his paper where he states, "It is shown that the observed size range (0.01 mm—0.1 mm) of the dust particles of pulverized concrete is consistent with the theory of comminution caused by impact..."

The rest of the upper section (a amount so large as to render the mass of dust meaningless) came down. Hard. And as it built up a layer of collapsed structure, it increased in mass and density.

So during the videos, it shows building material being ejected on all sides. But while the video shows the building contents being ejected laterally somewhere in that huge dust cloud mass and density are increasing?

Density is defined as mass per unit volume. If you take the mass of, say, five floors, and collapse that into the volume of one floor (an arbitrary choice), then it has become denser. This is grade-school physics.

Yes, during an actual pancake collapse the building might become denser, as there is no longer any separation between the floors.

Poor analogy. Extremely poor.
The reduced surface area of impact and the pouring of the sand as individual grains make the two scenarios not even remotely similar.

The point was to show that it does matter if the upper block was intact or not.

Remember, the upper section had, for all intents and purposes, no support after it began collapsing. The "dust" you cling so desperately to would not obligingly pour down, one grain at a time. It would all come down at once.

I didn't say that it would fall one grain at a time. I was showing that the impact on the lower block would not be the same if the upper block was already pulverized.

By the way: What does this have to do with the difference in appearance between the Twin Towers and a real controlled demolition involving explosives?

Well, the twin towers weren't real controlled demolitions. They were blown up from top to bottom. My original question was if the towers were blown up top down, how would the destruction of each tower look different from what was actually observed?

 

[X]

I've been thinking about how to reply to this all day.
I'm still not sure. It's almost as though you think the entire mass of the upper section was converted to dust, and expanded out into the surrounding air.
That is the only explanation I can think of that accounts for your statement.

I really shouldn't have to sat this, but it is wrong.

There was dust, this is true. But as has been pointed out already, the dust clouds consist of a very small amount of matter. And most of that was easily crushed stuff like sheetrock and office equipment.

The non-metallic portions of the towers were largely pulverized. Even Bazant mentions this in his paper where he states, "It is shown that the observed size range (0.01 mm—0.1 mm) of the dust particles of pulverized concrete is consistent with the theory of comminution caused by impact..."

Re-read that quote from Bazant. Re-read it again. And once more, for good measure, paying special attention to the part you conveniently bolded.
Where in that does he say that the non-metallic portions of the upper block were "largely pulverized"?
It merely says that the component of the dust that came from the concrete was of an observed size range.

The rest of the upper section (a amount so large as to render the mass of dust meaningless) came down. Hard. And as it built up a layer of collapsed structure, it increased in mass and density.

So during the videos, it shows building material being ejected on all sides. But while the video shows the building contents being ejected laterally somewhere in that huge dust cloud mass and density are increasing?

Yes. The amount of material ejected is tiny in comparison to the amount of material present.

Density is defined as mass per unit volume. If you take the mass of, say, five floors, and collapse that into the volume of one floor (an arbitrary choice), then it has become denser. This is grade-school physics.

Yes, during an actual pancake collapse the building might become denser, as there is no longer any separation between the floors.

Correct.

Poor analogy. Extremely poor.
The reduced surface area of impact and the pouring of the sand as individual grains make the two scenarios not even remotely similar.

The point was to show that it does matter if the upper block was intact or not.

Your analogy fails. The two scenarios are not even remotely similar.
Your assertion that pouring the sand slowly on the can can be equated to a falling mass of dust shows a serious lack of understanding of collision mechanics.
Time period, remember?
Time is extremely important.

Remember, the upper section had, for all intents and purposes, no support after it began collapsing. The "dust" you cling so desperately to would not obligingly pour down, one grain at a time. It would all come down at once.

I didn't say that it would fall one grain at a time. [...]

Yes, you did:

Another example. Take a cardboard box and fill it full of sand. Then drop it on an aluminum can. Then perform the same experiment but instead of dropping the box as one unit, open the bottom and have the sand pour out as individual grains. Which experiment will have the best chance of crushing the aluminum can if dropped from the same height? The moving mass may be the same but not the force at which it impacts the lower block.

Is your memory that short?

[...] I was showing that the impact on the lower block would not be the same if the upper block was already pulverized.

I can't help but notice that you left out the following part of my post:

Tell you what: re-do the second experiment, with a sheet of particle board the same size as the box (bottom area) sitting atop the can.
Then, dump all the sand at once (don't pour it) onto the particle board.

Remember, the upper section had, for all intents and purposes, no support after it began collapsing. The "dust" you cling so desperately to would not obligingly pour down, one grain at a time. It would all come down at once.

BOOM!

Either way, a lot of mass impacting over a very short period of time.

Are familiar with the concept of "Impulse", Tanabear?

[latex]J = \int F dt

F = ma

J = \int ma dt = m\triangle v [/latex]

Note the "dt" term. With respect to time.
This is the area your analogy fails.
The same mass (sand in box, sand poured grain-by-grain) but over vastly different times.
And that is assuming the same amount of mass hits the can.

It demonstrates why the constitution of the impacting mass does not matter, in this scenario.

By the way: What does this have to do with the difference in appearance between the Twin Towers and a real controlled demolition involving explosives?

Well, the twin towers weren't real controlled demolitions. They were blown up from top to bottom. My original question was if the towers were blown up top down, how would the destruction of each tower look different from what was actually observed?

What the ?

I direct you back to my posts on how the observed situation does not support the use of explosives.

Post 1
Post 2
Post 3

Honestly, you are beginning to look like an idiot with assertions of this sort.


ETA: dibs on the Stundie.

 

[HawksFan]

WTC 1 & 2. What happened after collapse initiation?

Let me put this in terms that even the twoofers can understand:

Buildings fall down go boom.

 

[tanabear]

Re-read that quote from Bazant. Re-read it again. And once more, for good measure, paying special attention to the part you conveniently bolded. Where in that does he say that the non-metallic portions of the upper block were "largely pulverized"?It merely says that the component of the dust that came from the concrete was of an observed size range.

Bazant writes in his paper,

"Let us now check whether the gravitational energy delivered by impact sufficed to produce the large amount of concrete dust on the ground. The dust particles generally ranged from Dmin = 0.01 mm to Dmax = 0.1 mm. Substituting D = Dmax into Eq. (13), and considering, as an upper bound, that all of the concrete of both towers (about Md = 14.6×107 kg) was pulverized, lying on the ground, we can calculate an upper bound on the total impact energy Kt required to produce all these particles, for both towers..."

Yes. The amount of material ejected is tiny in comparison to the amount of material present.

Not according to Brent Blanchard. He wrote,

"With the weight and mass of the upper sections forcing the floor trusses below rapidly downward, there was no way for outer perimeter walls to fall in, so they had to fall out. A review of all photographic images clearly show about 95% of falling debris being forced away from the footprint of the structure, creating a giant “mushroom” effect around its perimeter."

If 95% of the debris is falling away from the footprint of the towers, then that is a substantial amount of the material present.

Your analogy fails. The two scenarios are not even remotely similar.
Your assertion that pouring the sand slowly on the can can be equated to a falling mass of dust shows a serious lack of understanding of collision mechanics.
Time period, remember?
Time is extremely important.

I didn't say that the sand would pour slowly. It would fall under the influence of gravity, the same as the upper block. If you have a cardboard box full of sand, and open the bottom and have all the sand fall out at once, would it impact with the same force as if it was dropped intact onto the aluminum can? Yes, the time period is extremely important.

Yes, you did: Is your memory that short?

I wrote, "Then perform the same experiment but instead of dropping the box as one unit, open the bottom and have the sand pour out as individual grains."

Falling as individual grains does not mean one grain at a time.

I can't help but notice that you left out the following part of my post:

It demonstrates why the constitution of the impacting mass does not matter, in this scenario.

You wrote, "Either way, a lot of mass impacting over a very short period of time."

Both examples would be a lot of impacting mass over a short period of time. But the question was if the upper block fell intact vs. already pulverized, would the effect on the lower block be the same.

I direct you back to my posts on how the observed situation does not support the use of explosives.

Honestly, you are beginning to look like an idiot with assertions of this sort.

ETA: dibs on the Stundie.

You wrote in a previous post, "Beyond that, if all went well, once collapse intiated, it would progress much like what you saw on 9/11 (things falling downwards)."

So a building collapsing under the influence of gravity would look the same as if the building was exploding from the top down.

Let me put this in terms that even the twoofers can understand:

Buildings fall down go boom.

But so do buildings that are exploding.

 

[pomeroo]

Bazant writes in his paper,

"Let us now check whether the gravitational energy delivered by impact sufficed to produce the large amount of concrete dust on the ground. The dust particles generally ranged from Dmin = 0.01 mm to Dmax = 0.1 mm. Substituting D = Dmax into Eq. (13), and considering, as an upper bound, that all of the concrete of both towers (about Md = 14.6×107 kg) was pulverized, lying on the ground, we can calculate an upper bound on the total impact energy Kt required to produce all these particles, for both towers..."



Not according to Brent Blanchard. He wrote,

"With the weight and mass of the upper sections forcing the floor trusses below rapidly downward, there was no way for outer perimeter walls to fall in, so they had to fall out. A review of all photographic images clearly show about 95% of falling debris being forced away from the footprint of the structure, creating a giant “mushroom” effect around its perimeter."

If 95% of the debris is falling away from the footprint of the towers, then that is a substantial amount of the material present.



I didn't say that the sand would pour slowly. It would fall under the influence of gravity, the same as the upper block. If you have a cardboard box full of sand, and open the bottom and have all the sand fall out at once, would it impact with the same force as if it was dropped intact onto the aluminum can? Yes, the time period is extremely important.




I wrote, "Then perform the same experiment but instead of dropping the box as one unit, open the bottom and have the sand pour out as individual grains."

Falling as individual grains does not mean one grain at a time.



You wrote, "Either way, a lot of mass impacting over a very short period of time."

Both examples would be a lot of impacting mass over a short period of time. But the question was if the upper block fell intact vs. already pulverized, would the effect on the lower block be the same.



You wrote in a previous post, "Beyond that, if all went well, once collapse intiated, it would progress much like what you saw on 9/11 (things falling downwards)."

So a building collapsing under the influence of gravity would look the same as if the building was exploding from the top down.



But so do buildings that are exploding.

It's fascinating that the silly fraud Heiwa managed to weather the devastating, super-sophisticated refutations of his incompetent lunacy posted by real engineers. Yet I, someone who knows very little about engineering, caused him to flee the forum, tail between his legs.

The explanation is simple. He claims to write for children--a claim that nobody has read his "work" could ever doubt--and I asked a child's question: What would happen if you dropped the top third of a building onto the bottom two-thirds from a great height? Although he bluffs and babbles his way past complex math, he was destroyed by my rather simplistic question BECAUSE HE UNDERSTOOD IT! His mindless garble of Newton was revealed for all to see.

The evidence for explosives at the WTC complex on the day of the jihadist attacks is nonexistent.

 

[Grizzly Bear]

Bazant writes in his paper,
"Let us now check whether the gravitational energy delivered by impact sufficed to produce the large amount of concrete dust on the ground. The dust particles generally ranged from Dmin = 0.01 mm to Dmax = 0.1 mm. Substituting D = Dmax into Eq. (13), and considering, as an upper bound, that all of the concrete of both towers (about Md = 14.6×107 kg) was pulverized, lying on the ground, we can calculate an upper bound on the total impact energy Kt required to produce all these particles, for both towers..."

The red bolding was added by me. Tana, use some common grammar sense. In experiments people simplify parameters. He considers all as an upper bound, to "calculate an upper bound on the total impact energy Kt required to produce all these particles, for both towers..."

Regardless of the circumstances, concrete used in the towers was non-structural.

Not according to Brent Blanchard. He wrote,

"With the weight and mass of the upper sections forcing the floor trusses below rapidly downward, there was no way for outer perimeter walls to fall in, so they had to fall out. A review of all photographic images clearly show about 95% of falling debris being forced away from the footprint of the structure, creating a giant “mushroom” effect around its perimeter."

If 95% of the debris is falling away from the footprint of the towers, then that is a substantial amount of the material present.

95% of the exterior structural columns is not 95% of the towers' mass. A little bit of critical thinking skills would tell you this. The floor slabs still bear considerable weight inside the footprint. NONE OF THE STEEL, THE STRUCTURAL STEEL, WAS PULVERIZED

I didn't say that the sand would pour slowly. It would fall under the influence of gravity, the same as the upper block. If you have a cardboard box full of sand, and open the bottom and have all the sand fall out at once, would it impact with the same force as if it was dropped intact onto the aluminum can? Yes, the time period is extremely important.

This is irrelevant because you're automatically assuming that everything is pulverized the moment the tower began to collapse. This is continuing to compare apples and oranges, but then again, anything to make you theory fit huh?

I wrote, "Then perform the same experiment but instead of dropping the box as one unit, open the bottom and have the sand pour out as individual grains."

The towers were not completely pulverized the moment the collapse initiated as you continue to assume. Nice try, but it doesn't work.

Falling as individual grains does not mean one grain at a time.

Same as above

You wrote, "Either way, a lot of mass impacting over a very short period of time."

Same as above

Both examples would be a lot of impacting mass over a short period of time.

Same as above

But the question was if the upper block fell intact vs. already pulverized, would the effect on the lower block be the same.

No, but the collapsing building started collapsing as an intact structure. This renders your experiment moot.

So a building collapsing under the influence of gravity would look the same as if the building was exploding from the top down.

Yes, what do you think happens when a structure fails? Explosives don't throw 50-ton chunks of debris 200-300 ft out without destroying lower Manhattan.

 

[R.Mackey]

What is your source for this statistic and how is it calculated? By dust cloud do you mean the percent of the mass that was ejected outside the perimeter of the tower during the collapse?

Dr. Greening presented such a calculation here a year or two ago. I'm looking for it. It's based on the depth of dust actually observed after collapse. It includes all the dust.

Are you speaking of the core columns, the perimeter columns or both? And by buckle, do you mean snap?

No. "Buckle" has a very specific and unambiguous meaning in structural engineering.

But is the debris that is doing the crushing moving faster than the floors are pancaking? And if the debris is still moving faster and doing most of the crushing, in what way does it make sense to refer to this "collapse" as a pancake?

Uhh... what?

The debris is necessarily in contact with the floors as they "pancake." They produce the load that causes the "pancake." If the debris travelled slower than the floors, then why would the floors come loose to begin with? If it went faster, as you ask, that would mean the debris was going right through the floors.

I would have thought that was obvious, but some of you folks never fail to surprise me...

Why is the core now able to resist the collapse if the downward mass is getting larger and faster?

Because with the floors sheared away, the core -- basically stripped columns and beams -- has a much smaller cross-section. The debris field may (if it's lucky) pass beside the core structure without immediately introducing a supercritical load.

While the floors are still attached, however, this is impossible.

Any question can be "answered," but this does not mean your answers are reasonable, accurate or scientifically demonstrable. Your "answer" is just a string of unprovable and random assertions.

Or so you assert, anyway...

Try this. Create a visual simulation of the collapse of one of the towers minus the dust cloud. That way we can actually "see" what you think is going on, and if it is scientifically plausible.

I'm under no obligation to make a cartoon simply because you can't visualize it. The physics in play here is really quite elementary.

---

So I gave another example. Take a cardboard box and fill it full of sand. Then drop it on an aluminum can. Then take the cardboard box and have the sand fall as individual grains on to the aluminum can from the same height. The amount of mass moving downwards might be the same but the force at which it impacts the lower block will not be.

Your example is irrelevant. There is no "trickling" of debris in the WTC Towers collapses as your "individual grains of sand" model implies. If the sand impacts all at once, the pressure-impulse is the same, regardless of container.

Are you talking about the dust clouds within a couple of seconds of the towers collapse or after the towers are completely destroyed? Is there a difference between the "cushion of debris" and the dust clouds?

As above, I was talking about all of the dust. Naturally the dust and debris are different -- the vast majority of debris is not turned to dust at all. That's why the cleanup required cutting torches and jackhammers, and not just skiploaders scooping up dust for months.

You had stated in a previous post that you agreed with Ron Wieck's statement, "Once the global collapse ensued, the floors necessarily pancaked. What else could they be expected to do?"

There is no conflict.

Whether or not the columns buckle first or the trusses fail first, this can't be described as pancaking. Pancaking is when one floor impacts the floor beneath it, and on and on till the building collapses.

Wrong. Just a few posts back, you asked me what "pancaking" meant. I told you. Now you're telling me I'm wrong?

"Pancaking" means the failure mode is floors detaching at the connections. I already explained this, and already explained why the collapse transitions to this mode in the middle of the event.

Then this cushion of debris must be crushing the lower block at a faster rate than the upper block can fall through this cushion of debris. The cushion of debris is destroying intact steel and concrete at a faster rate than the upper block can move through this cushion. So this cushion can crush and move faster than the upper block can merely fall? That is pretty impressive.

You're even more confused than the other guy. The "upper block" does not fall through the "cushion of debris."

There are three regions of structure in mid-collapse:

1. The upper block, a relatively intact chunk of structure roughly ten stories in height or so;
2. The interface, referred to as a "cushion of debris," which is a growing layer of fractured structure; and
3. The lower block, which is the nearly intact remainder of structure from ground level to the interface.

These three remain in contact, by definition, the whole time. There is no "Falling Through" going on here. The objects on either side of the interface are moving at the same speeds and same accelerations.

Of course, according to Bazant the upper block stays intact during the crush-down phase only to be destroyed when it hits the rubble pile. Someone defending the pile-driver explanation could simply state that it partially broke up on its way down and thereby "missed" some of the core columns.

Dr. Bazant presented a model. To first order and for over ten stories, his model is correct. Only much lower down does the upper block actually come apart to the point that the lower core survives.

The non-metallic portions of the towers were largely pulverized. Even Bazant mentions this in his paper where he states, "It is shown that the observed size range (0.01 mm—0.1 mm) of the dust particles of pulverized concrete is consistent with the theory of comminution caused by impact..."

As has been noted, this quote does not imply that he believes all or even most of those materials were pulverized. He's talking about the 1% that actually was turned to dust.

So during the videos, it shows building material being ejected on all sides. But while the video shows the building contents being ejected laterally somewhere in that huge dust cloud mass and density are increasing?

I can't even guess at what this is supposed to mean...

Yes, during an actual pancake collapse the building might become denser, as there is no longer any separation between the floors.

You need to be careful with your definition of "density." The outer perimeter is not well defined during an event like this.

The point was to show that it does matter if the upper block was intact or not.

It really doesn't. That's the cruel irony of your confusion.

I didn't say that it would fall one grain at a time. I was showing that the impact on the lower block would not be the same if the upper block was already pulverized.

Yes, it is. Take a physics class.

Well, the twin towers weren't real controlled demolitions. They were blown up from top to bottom. My original question was if the towers were blown up top down, how would the destruction of each tower look different from what was actually observed?

Yes. No. And radically different. For starters, shrapnel from the blasts would have killed just about everyone within ten blocks who wasn't on the other side of another structure.

 

[rwguinn]

Buckling is a legitimate engineering term. Go look it up, and learn. Before criticizing, one should have at least a tiny bit of knowledge on the subject.

No. "Buckle" has a very specific and unambiguous meaning in structural engineering

If you's study a little, you'd know the debris gets there FIRST because that is its original position-lower down on the chunk

The debris is necessarily in contact with the floors as they "pancake." They produce the load that causes the "pancake." If the debris travelled slower than the floors, then why would the floors come loose to begin with? If it went faster, as you ask, that would mean the debris was going right through the floors.

I would have thought that was obvious, but some of you folks never fail to surprise me

Show us your simulation. You are making the claims.
We are not here to do your work for you.
What if frogs had wings? What if 1+1=29831?
Hell, if we all had Randy Johnson's build and talent, the average MLB game would be a zero-zero no-hit tie...

I'm under no obligation to make a cartoon simply because you can't visualize it. The physics in play here is really quite elementary.





---



Your example is irrelevant. There is no "trickling" of debris in the WTC .

Ok, that's two engineers saying the same thing...
Do we have a consensus yet?

 

[X]

Bazant writes in his paper,

"Let us now check whether the gravitational energy delivered by impact sufficed to produce the large amount of concrete dust on the ground. The dust particles generally ranged from Dmin = 0.01 mm to Dmax = 0.1 mm. Substituting D = Dmax into Eq. (13), and considering, as an upper bound, that all of the concrete of both towers (about Md = 14.6×107 kg) was pulverized, lying on the ground, we can calculate an upper bound on the total impact energy Kt required to produce all these particles, for both towers..."

To parrot grizzly Bear, this is in reference to an "upper bound".
That is, an extreme case.
It is not necessarily the case that actually occured.

Not according to Brent Blanchard. He wrote,

"With the weight and mass of the upper sections forcing the floor trusses below rapidly downward, there was no way for outer perimeter walls to fall in, so they had to fall out. A review of all photographic images clearly show about 95% of falling debris being forced away from the footprint of the structure, creating a giant “mushroom” effect around its perimeter."

If 95% of the debris is falling away from the footprint of the towers, then that is a substantial amount of the material present.

You misread Blanchard, I think.
He says: "A review of all photographic images clearly show about 95% of falling debris being forced away from the footprint of the structure ...".
You read: "95% of the debris is falling away from the footprint of the towers ...".

It is a fine distinction, but one that fundamentally changes the meaning of his words.
In the quote from Blanchard, it reads as though he is saying that 95% of the debris seen falling outside the towers is being ejected away from the footprint.
You seem to interpret that as saying 95% of the debris created is ejected.

Also, read Grizzly's post on this quote.

I didn't say that the sand would pour slowly. It would fall under the influence of gravity, the same as the upper block. If you have a cardboard box full of sand, and open the bottom and have all the sand fall out at once, would it impact with the same force as if it was dropped intact onto the aluminum can? Yes, the time period is extremely important.

"I didn't say that the sand would pour slowly."
See below.

I wasn't talking about the speed at which the grains of sand fell. I was talking about the volume of sand which would hall in a given time.

Oh, and bear in mind it would impact with the same force, but only if all that sand hit the can. Which is why, in the suggestion I gave you, I said to put a plate over the can, to increase it's surface area so that it would be the same as that of the box used previously.

I wrote, "Then perform the same experiment but instead of dropping the box as one unit, open the bottom and have the sand pour out as individual grains."

Falling as individual grains does not mean one grain at a time.

Do you now care to specify that all the sand comes out at once? Then is is not longer indivdual grains. Pouring the sand as individual grains explicitly means individual grains. One grain at a time.
Perhaps English is not your first language. It's possible, so I'm willing to let the issue drop. Just be aware of what you write next time.

You wrote, "Either way, a lot of mass impacting over a very short period of time."

Both examples would be a lot of impacting mass over a short period of time. But the question was if the upper block fell intact vs. already pulverized, would the effect on the lower block be the same.

Yes, the effects would be the same. It is simple physics.
F = (mv₂ - mv₁)/t
where:

F = total net force applied (assumed constant)
m = mass of moving object
v₁ = initial velocity of moving object (at beginning of impact, t = 0)
v₂ = final velocity of moving object (at end of impact, t = t)
t = time interval over which force is applied​

There is no term that considers the type of constitution of the moving object.
Perhaps you are confusing this with collisions, where the elasticity of the moving object comes into play.

You wrote in a previous post, "Beyond that, if all went well, once collapse intiated, it would progress much like what you saw on 9/11 (things falling downwards)."

So a building collapsing under the influence of gravity would look the same as if the building was exploding from the top down.

Liar!
That is not what I said and you know it.
(And I'm not faulting your quoting of me, I'm faulting the straw-man interpretation of it, so don't accuse me of denying what I said)

 

[Myriad]

I just want to point out that likening the debris falling inside the tower's footprint as loose particles falling through open air (like sand released from a box, or like the debris observed falling outside the footprint during the collapse) is misleading to the point of absurdity. The debris falling within the tower's footprint is being pressed down on from above by the upper structure (for as long as any intact upper structure remains, which is for at least most of the collapse) and at the same time its fall is being resisted by the intact lower structure. In other words it's being compressed between acre-sized structures. Even if it made a difference whether sand is in a box or not when it lands on something, the debris during the tower collapses is much more like the sand in a box.

Respectfully,
Myriad

 

[tanabear]

The red bolding was added by me. Tana, use some common grammar sense. In experiments people simplify parameters. He considers all as an upper bound, to "calculate an upper bound on the total impact energy Kt required to produce all these particles, for both towers..."

Bazant is arguing that the gravitational potential energy of the towers is sufficient to pulverize all the concrete in each tower. He argues against explosives(TNT) because it is inefficient at pulverizing concrete. Bazant writes, "The particle sizes observed on the ground range essentially from Dmin = 0.01 mm to Dmax = 0.1 mm "

Energy Required to Produce All of Pulverized Concrete

The total gravitational potential energy g released by one tower is calculated as the tower weight multiplied by the distance between the mass centroid of the tower and the mass centroid of the rubble heap on the ground...So there is far more impact energy than necessary....

1) The comminution energy of particles< 0.1 mm produced by impacts on the floor slabs prior to the end of crush-down; 2) the comminution energy of particles  0.1 mm produced during crush-down which are comminuted to sizes < 0.1 mm during the impact on the foundation; and 3) the comminution energy of particles < 0.1 mm produced during the crush-up...

...Only gravity driven impact could have produced the concrete dust as found on the ground.

95% of the exterior structural columns is not 95% of the towers' mass. A little bit of critical thinking skills would tell you this. The floor slabs still bear considerable weight inside the footprint. NONE OF THE STEEL, THE STRUCTURAL STEEL, WAS PULVERIZED

Brent Blanchard is talking about the falling debris, not just exterior columns. Brent Blanchard writes,

"As we know, significant amounts of heavy structural debris rained down for blocks around the site. Many of the closest WTC buildings were completely destroyed and others heavily damaged...These facts indicate that a relatively small amount of structural support debris actually landed straight down in the towers' footprints, making this event notably dissimilar to a planned demolition event."

Dust from the towers was inches thick up to six blocks away from the towers.

I never said that the structural steel was pulverized. I stated previously that the non-metallic portions of the buildings were largely pulverized.

This is irrelevant because you're automatically assuming that everything is pulverized the moment the tower began to collapse. This is continuing to compare apples and oranges, but then again, anything to make you theory fit huh?

I was not assuming that. It was in a response to a statement by "X" that it didn't matter if the upper block remained intact or was pulverized as it destroyed the tower.

Your example is irrelevant. There is no "trickling" of debris in the WTC Towers collapses as your "individual grains of sand" model implies. If the sand impacts all at once, the pressure-impulse is the same, regardless of container.

Where did I use the word "trickling"? The original hypothetical example I gave was asking if there would be a difference between the upper block falling onto the lower block as an intact unit or falling as a pulverized mass. If the upper block is pulverized then how can it impact the lower block all at once? Is the height of the falling debris exactly the same?

As above, I was talking about all of the dust. Naturally the dust and debris are different -- the vast majority of debris is not turned to dust at all. That's why the cleanup required cutting torches and jackhammers, and not just skiploaders scooping up dust for months.

So what percentage of the building was pulverized?

"Pancaking" means the failure mode is floors detaching at the connections. I already explained this, and already explained why the collapse transitions to this mode in the middle of the event.

Is that pancaking or pancake initiation? So when a floor truss becomes separated from a perimeter column that is called pancaking or pancake initiation? But it doesn't actually mean that a floor is falling and impacting the one beneath it?

You're even more confused than the other guy. The "upper block" does not fall through the "cushion of debris."

There are three regions of structure in mid-collapse:

1. The upper block, a relatively intact chunk of structure roughly ten stories in height or so;
2. The interface, referred to as a "cushion of debris," which is a growing layer of fractured structure; and
3. The lower block, which is the nearly intact remainder of structure from ground level to the interface.

These three remain in contact, by definition, the whole time. There is no "Falling Through" going on here. The objects on either side of the interface are moving at the same speeds and same accelerations.

Yes, according to your example there is no "falling through" going on. I was asking you why. You stated previously, "After a few floors collapse, the upper block is riding on a cushion of debris, and relatively smooth behavior is guaranteed...It will quickly become larger than the upper block, and it is responsible for most of the crushing." So this cushion of debris must be able to crush through the lower block at least as fast as the upper block can fall. But how is this possible? The upper block doesn't have to crush through anything, it is merely falling.

You need to be careful with your definition of "density." The outer perimeter is not well defined during an event like this.

I was referring to a regular pancake collapse, not what happened to the towers on 9/11.

Yes. No. And radically different. For starters, shrapnel from the blasts would have killed just about everyone within ten blocks who wasn't on the other side of another structure.

It depends on the types of explosives. But the question was how would the destruction of WTC 1 and 2 look different if explosive charges destroyed the towers from top to bottom.

 

[R.Mackey]

Where did I use the word "trickling"? The original hypothetical example I gave was asking if there would be a difference between the upper block falling onto the lower block as an intact unit or falling as a pulverized mass. If the upper block is pulverized then how can it impact the lower block all at once? Is the height of the falling debris exactly the same?

Makes. No. Difference.

So what percentage of the building was pulverized?

Depends on your definition of pulverized. Anywhere from 1% to 99% depending on how large a chunk you consider "pulverized." Stop hiding behind semantics.

Is that pancaking or pancake initiation? So when a floor truss becomes separated from a perimeter column that is called pancaking or pancake initiation? But it doesn't actually mean that a floor is falling and impacting the one beneath it?

We are not a dictionary. If you don't know what "initiation" means, look it up.

Yes, according to your example there is no "falling through" going on. I was asking you why. You stated previously, "After a few floors collapse, the upper block is riding on a cushion of debris, and relatively smooth behavior is guaranteed...It will quickly become larger than the upper block, and it is responsible for most of the crushing." So this cushion of debris must be able to crush through the lower block at least as fast as the upper block can fall. But how is this possible? The upper block doesn't have to crush through anything, it is merely falling.

Your confusion is greater than that I would have imagined possible in a literate being. Let me try it again with really, really small words.

The upper block is on top of the debris. They fall together. They fall because there is nothing that can hold them up. They hit floors. They break floors loose. Broken floors add to the pile of debris. The part that is debris gets bigger. This falls on more floors. They break too. By the time all the floors break, there is no building left, just a big pile of debris, maybe with some of the upper block still on top. It falls until it hits the ground. Only the ground is strong enough to stop the pile of debris. The upper block slowly comes apart as it falls. It comes apart because it isn't designed to stand on a shifting pile of debris. If some of the the upper block is still there when the debris hits the ground, the upper block then crumbles too, because the debris stops when it hits the ground. When the debris stops the upper block feels more resistance. It can't handle this. It breaks too. Nothing left but debris.

I was referring to a regular pancake collapse, not what happened to the towers on 9/11.

Semantics again. "Pancake collapse" is a model. There are no perfect pancake collapses. The collapses on 9/11 were totally as expected given their design and the initial failure mode.

It depends on the types of explosives. But the question was how would the destruction of WTC 1 and 2 look different if explosive charges destroyed the towers from top to bottom.

Once again, attempting to gauge your level of comprehension:

There would have been lots of bombs. Bombs would shatter steel and make small pieces. They would shatter windows. They would break concrete and break furniture. Small pieces would fly very fast. Just like shrapnel. They would fly all over the place. They would be like bullets in all directions. Thousands of tons of bullets -- billions of bullets! Anyone close by would be killed. This didn't happen.

 

[Myriad]

Brent Blanchard is talking about the falling debris, not just exterior columns. Brent Blanchard writes,

"As we know, significant amounts of heavy structural debris rained down for blocks around the site. Many of the closest WTC buildings were completely destroyed and others heavily damaged...These facts indicate that a relatively small amount of structural support debris actually landed straight down in the towers' footprints, making this event notably dissimilar to a planned demolition event."

This could very well be true. However, the structural support columns are only about 18% of the total mass of the towers.

The LIDAR maps of Ground Zero show that the debris was fairly concentrated in the towers' footprints. By my rough calculations a meter-thick layer of debris would have to extend to a diameter of 1250 feet (about 4/5 of the width and height of the image below) to equal the volume of just the pile in the North Tower's footprint.

Dust was concentrated in the streets and formed drifts due to air currents; hence the maximum dust thickness at a given distance doesn't equate to an even layer of that thickness.

Also there's this:

Yes, according to your example there is no "falling through" going on. I was asking you why. You stated previously, "After a few floors collapse, the upper block is riding on a cushion of debris, and relatively smooth behavior is guaranteed...It will quickly become larger than the upper block, and it is responsible for most of the crushing." So this cushion of debris must be able to crush through the lower block at least as fast as the upper block can fall. But how is this possible? The upper block doesn't have to crush through anything, it is merely falling.

Because the debris mass is not only falling but accelerating, the upper block does not press with its full weight on the debris mass. Instead of mg the force it exerts on the debris (and that the debris exerts on it, to damage it) is m(g - a) where a is the debris mass downward acceleration. That's one reason why the upper block stays intact longer, and there's no reason to expect it to penetrate the debris mass (which again, is not "loose" but rather is compressed and far denser than the intact structure). The upper structure remains on top of the debris mass for roughly the same reason you cannot shove your foot down through several feet of gravel -- especially when you and the gravel are on an elevator descending at 1/2 to 2/3 g.

Respectfully,
Myriad

 

[TsuDhoNimh]

How about trying to answer the other example? In WTC1 the upper block -- the area above the impact zone -- fell 3.7 meters downward onto the lower block -- according to Bazant. However, if this upper block was first pulverized into dust and then dropped onto the lower block, would the results be the same?

It was not "pulverised to dust". When the steel supports heated enough to lose the structural strength necessary to hold up the upper block, it dropped onto the top floor of the lower block, suddenly applying a large force to beams that were not designed to resist that sort of force. They buckled, the concrete shattered, and the upper part and all the debris under it dropped down another few meters ... landing on another floor that in turn buckled and shattered and fell. Each floor became part of a debris cloud of falling chunks of concrete, steel girders, and the interior objects, smashing the floor it lands on.

Think of a landslide ... except it's all going straight down, with the top block like a big slab of rock "riding" on top of boulders and smaller rocks and flying dust. Every floor that gets shattered makes the debris cloud a bit bigger ... until it piles up when it hits the ground and then it gets further broken by the impact of the later debris.

It's possible that the first few floors that were shattered also damaged the lower floors of the top block, but you can see it gracefully descending - apparently intact- until the rising dust cloud hides it.

 

[rwguinn]

It was not "pulverised to dust". When the steel supports heated enough to lose the structural strength necessary to hold up the upper block, it dropped onto the top floor of the lower block, suddenly applying a large force to beams that were not designed to resist that sort of force. They buckled, the concrete shattered, and the upper part and all the debris under it dropped down another few meters ... landing on another floor that in turn buckled and shattered and fell. Each floor became part of a debris cloud of falling chunks of concrete, steel girders, and the interior objects, smashing the floor it lands on.

Think of a landslide ... except it's all going straight down, with the top block like a big slab of rock "riding" on top of boulders and smaller rocks and flying dust. Every floor that gets shattered makes the debris cloud a bit bigger ... until it piles up when it hits the ground and then it gets further broken by the impact of the later debris.

It's possible that the first few floors that were shattered also damaged the lower floors of the top block, but you can see it gracefully descending - apparently intact- until the rising dust cloud hides it.

And that makes 3 people saying the same thing--at least 2 of whom are engineers...

Comments?

 

[pomeroo]

Heiwa has left the building, no doubt to establish a new equilibrium.

 

[TsuDhoNimh]

I'm not an engineer ... but I sleep with one.