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Old 21st November 2015, 04:05 PM   #201
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Originally Posted by jaydeehess View Post
Ok
Mice not rats. I should have known something was amiss when that mattress rambled across the landscape.

You Explained that and I understand.

Now try it with your description of KE, mass and momentum wrt your previous unintelligible statements.
We still await consise explanations for "KE... minus p", and upward mass vector.
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Old 21st November 2015, 06:34 PM   #202
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Originally Posted by jaydeehess View Post
Depends how well the web of concrete, rebar, and trusses resist the initial crash.
Yes - of course - that was the scenario I based my thoughts on. And I'm not just "hairy guessing". Here's why - the two extremes are:
1) A clean cut "Wile E Coyote" hole the exact size and shape as the tank; AND
2) A clean shear of of floor from columns with little or no damage to the floor slab and joists.

And it is near dead certain reality would fall between those two extremes. So a patch of floor structure - larger than the tank - not all the floor - and it is broken - folded, bent but the bits still hanging together by reo and other steel bits. So a saggy "sheet anchor".

PLUS I have not explained how the failure would be limited/bounded in the other direction - going "around" the building parallel with outer perimeter/core. And in that direction there is no obvious limit. BUT clearly it would be far less that 100% of the floor.
Originally Posted by jaydeehess View Post
Beach uses a total floor span max load of 29E6 tons. JSO had the numbers for per square foot or meter.
Yes. I'm aware of the limits in both directions. BUT the event would not be at either of those extremes. The tank would not fail the full floor area of the "OOS" - only the bit near where the tank was dropped. And I allowed for a partially quantified range of options. "Radially" it would be between the two extremes - and "peripherally" it would go some distance from "Wile E Coyote" and the actual distance does not change my postulated results - because it is accommodated in the open ended guess at 2-3-4 or maybe a couple more floors.
Originally Posted by jaydeehess View Post
I don't picture the part of the floor span that fails , remains intact. It's going to deform into a somewhat parabolic shape. Concrete will shatter, its not high strength concrete..
Which is the exact scenario I predicted - excuse the unusual brevity of my writing on this rare occasion. And "shatter" probably is too optimistic. Low strength or not it would break into clumps which remain tied by reo - re-bar if you prefer.
Originally Posted by jaydeehess View Post
The combo of bent trusses with a tank in the center with concrete rubble mostly lagging behind slightly, will hit next floor span << Agreed - that is the scenario I'm proposing BUT >> at greater velocity than first impact.,,,, << You are assuming the "greater" - remember it is the second and later floor impacts we are discussing. I'll back my "engineer gut feeling judging (AKA "guessing" )" and so on. << Yes - but the "How many so ons is what we are discussing.
Originally Posted by jaydeehess View Post

But I readily admit I know more physics than applied structures physics.( colloquially referred to as engineering)
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Old 21st November 2015, 07:27 PM   #203
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Originally Posted by ozeco41 View Post
Which is the exact scenario I predicted - excuse the unusual brevity of my writing on this rare occasion. And "shatter" probably is too optimistic. Low strength or not it would break into clumps which remain tied by reo - re-bar if you prefer.
Wasn't the OOS slab just reinforced with wire mesh? That would still probably hold clumps together that cracked without much shear, but I wouldn't expect it to withstand the shear where the tank hit.
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Old 21st November 2015, 09:20 PM   #204
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Originally Posted by WilliamSeger View Post
Wasn't the OOS slab just reinforced with wire mesh? That would still probably hold clumps together that cracked without much shear, but I wouldn't expect it to withstand the shear where the tank hit.

http://i286.photobucket.com/albums/l...thwiremesh.jpg

Had some rebar and the mesh. When all the rebar was in a stack for the entire floor, it looked like a lot, but ...
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Old 21st November 2015, 10:07 PM   #205
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Originally Posted by WilliamSeger View Post
Wasn't the OOS slab just reinforced with wire mesh? That would still probably hold clumps together that cracked without much shear,...
Yes. Or near enough - little more than nominal slab reo. But it wouldn't ALL fail at the tank outline.

Originally Posted by WilliamSeger View Post
...but I wouldn't expect it to withstand the shear where the tank hit.
sure - if the floor was supported close to the line of impact it would most likely shear both concrete and embedded reo.

BUT the support of the floor is needed to provide the necessary equal and opposite reaction to the tank drop impact to create the shearing action. And at that "Wile E Coyote" line immediately next to the tank the support for the reaction is the flexible floor spanning whatever distance from the support columns - perimeter or core. So it would be a competition between the applied downwards shear at that line versus the resistance from the slab which results from bending moment between the point of application of download and the more remote support of columns. (PLUS the support in the "other direction - along the OOSpace - is even less defined.) And all that is complicated by the 3D realities but for this guesstimate the main point is that we recognise that there is not a lot to create the resistance for the undoubted large down force to cause the shear. I'm betting "bendiness, bounce and breakup into lumps of floor held by reo" wins over pure shear.

AND - so far I'm that is only a static viewpoint for first attempt at defining the mechanism. Whilst the event would be very much dynamic. The dynamic effects would obviously move the end result closer to your "shear at the Wile E Coyote" line. Closer IMO - not all the way.

As I said it is still gut feel guessing (AKA "alleged sound experienced professional judgement" but "guessing" will do ) But the odds are IMO against a clear tank outline cut by shear right at the tank outline AKA a "Wile E Coyote" silhouette.

And through out this sequence of posts I've covered my arse as to how far out from the tank the effective break would come. I don't see ALL the reo bars breaking - either immediately in shear OR slightly later in tension. I see a "sheet" of bits of broken concrete under the tank and extending some distance beyond it - all linked by a lot or a few surviving reo bars in tension - the lot pulled up around the tank similar to the end of a sock. And more "sock ends" accumulating floor by floor. Each one would broaden and defocus the impact load - ultimately causing the penetration to stop.

Certainly not at the first impacted floor. But one or two or several floors beyond that.

(There is one "maybe" I've not even looked at - I'm taking it for grated that the tank would penetrate the first floor. )

But it is fun thinking it through - and a change from the Chandler/Szamboti level of alleged engineering idiocies
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Old 21st November 2015, 10:09 PM   #206
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Originally Posted by beachnut View Post
http://i286.photobucket.com/albums/l...thwiremesh.jpg
http://i286.photobucket.com/albums/l...thwiremesh.jpg

Had some rebar and the mesh. When all the rebar was in a stack for the entire floor, it looked like a lot, but ...
Thanks beachnut.
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Old 22nd November 2015, 08:12 AM   #207
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Originally Posted by GlennB View Post
You're covering up for Mothra, aren't you.
Mothra did the Pentagon.
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Old 22nd November 2015, 10:50 AM   #208
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Originally Posted by tsig View Post
Mothra did the Pentagon.

When you say "did" the Pentagon, do you mean... Never mind, I don't want to know.
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Old 22nd November 2015, 11:36 AM   #209
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Originally Posted by Myriad View Post
When you say "did" the Pentagon, do you mean... Never mind, I don't want to know.
But we all know the Pentagon was smoking afterwards...

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Me: So what you're saying is that, if the load carrying ability of the lower structure is reduced to the point where it can no longer support the load above it, it will collapse without a jolt, right?

Tony Szamboti: That is right
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Old 22nd November 2015, 12:30 PM   #210
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Originally Posted by Notconvinced View Post
Again, nobody is contesting that. When you say "floor" you mean literally just the flat span of poured concrete and truss that people walk upon. When I say "floor" I mean the entirety of the space that the elevator moves through from level to level, thus including the exterior and interior support columns which your side like to pretend didn't exist. The "floor" that resists and diminishes the momentum of the falling floor above it includes all of those features, the stairwells, the machinery, the articles, etc.

If I actually believed you could somehow consolidate all of the upper tower's momentum onto weak floor joints while miraculously bypassing the outer box columns, stairwells, inner columns, etc we wouldn't be having this discussion.
As you've been already told, the stairwells, the machinery, the articles, all these things are not structural elements. Columns, beams, girders, trusses are. From the point of view of the collapses, it only matters how much load each floor was carrying. It doesn't matter if there were stairwells, elevators, machinery, wallboard or wallpaper. Out of the structural elements and the per-floor load, it makes no difference what was on each floor with respect to the collapses.

Now, vertical elements (columns) need the support of horizontal elements (trusses, beams, girders) in order to perform their function. A long, high column without intermediate horizontal supports can resist much less weight without buckling than one which has these supports. This comes from Euler's formula, which for both ends fixed it can be expressed as:

F=4π≤EI/L≤

The relevant bits for this discussion are L, which is the length of the span between the ends of each section of the column, and F, which is the maximum (critical) vertical load on the column. The shorter the length, the more force (load) the column can resist without becoming unstable, and the proportion is inversely quadratic: double the length means a quarter of the force.

By "section" I mean the span between laterally supported ends; in buildings that's typically one floor, because that's where the horizontal elements are usually placed.

The building's stability depends on these lateral supports. More so on tall buildings. For the towers, the floors collapsed first, in pancake. That deprived both the core and the perimeter of lateral support. The perimeter peeled away like a banana; most of it toppled laterally. The core lost stability and also gave way, presumably also having a good amount of internal horizontal supports affected the same way as the outer floors. Part of both cores remained standing for a bit before they finally collapsed too, and we can see many horizontal elements missing in one of them.

For WTC7 the situation is a bit more complicated because horizontal progressive collapse comes into play. But the very same mechanism is what's believed to have caused column 79 to fail (lack of horizontal support for several floors, after they collapsed). Horizontal spread roughly works like this: when a column buckles, the horizontal elements it's attached to no longer support the columns next to it. That causes them to lose their lateral support and buckle in turn, and so the collapse spreads horizontally.
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Old 22nd November 2015, 12:36 PM   #211
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Originally Posted by Notconvinced View Post
I'm not ignoring gravity, I'm noting that it has been in play all along, and the strength of the construction already overcame the force of g on those members. You folks want to instantly liberate PE for an entire floor (my definition here, not yours) without accounting for the KE required to do so and the consequential loss in v, which reduces p for the falling mass.
That's true. And you keep ignoring two facts:

1) Once released, the new floor contributes to the total crushing energy, because its PE starts to convert into crushing KE.
2) The decelerated floor still has PE, and since it keeps falling, that energy keeps being converted into KE which keeps building up. At that point, it has liberated only one floor worth of its PE, not the whole height. It still has a lot of reserve PE available to convert into crushing KE.

Both PE to KE conversions contribute and make the total energy build up. You can see it as a build-up of mass (if you add the masses and calculate the total energy) or as a build-up of KE (if you consider the impacting and impacted floor as separate and calculate their energies then add them up)


Originally Posted by Notconvinced View Post
There is no build up in m from new floor compaction because the floor is crushed on an axis which already carried it, so what you get is a net depleting KE.
This is plain wrong. The axis didn't carry it. The columns did. Once detached from the columns, it's available to keep crushing. The columns then lose their horizontal support and buckle.
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Old 22nd November 2015, 02:17 PM   #212
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Originally Posted by jaydeehess View Post
Would it be D-baggy to use exponential notation.
Actually, the D-baggy thing is not to use exponential notation and rub all those zeros into the opponent's face

Originally Posted by jaydeehess View Post
Pretty straight forward. I look forward to you continuing
I am not betting on notconvinced addressing this. Truthers know well how not to be led to understanding.
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Old 24th November 2015, 12:08 AM   #213
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Originally Posted by pgimeno View Post
That's true. And you keep ignoring two facts:

1) Once released, the new floor contributes to the total crushing energy, because its PE starts to convert into crushing KE.
2) The decelerated floor still has PE, and since it keeps falling, that energy keeps being converted into KE which keeps building up. At that point, it has liberated only one floor worth of its PE, not the whole height. It still has a lot of reserve PE available to convert into crushing KE.
You get to attribute p (high kinetic load) to the first floor(s) of falling building, but the moment you have impact, the v of that lower floor is roughly zero, as it is simply crushed against itself. The added PE is nowhere near the PE you got when x number of floors got to descend through y vertical space. So you get less KE after impact, less to no PE released, and a system which comes to a halt well above the ground.


Originally Posted by pgimeno View Post
This is plain wrong. The axis didn't carry it. The columns did. Once detached from the columns, it's available to keep crushing. The columns then lose their horizontal support and buckle.
You've misunderstood. I think of the columns as the axis, as that is the longest dimension. I see the floor (my definition) as being crushed upon the columns, so net KE decreases.

Trying to see things your way here.... Crushed columns along the axial path would likely release their floor (YOUR definition) upon the next one. What is the KE of JUST the floorspan falling one story? Taking into account the KE it would lose crushing desks, people, cabinets, etc....
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Old 24th November 2015, 12:21 AM   #214
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Originally Posted by pgimeno View Post
That's true. And you keep ignoring two facts:

1) Once released, the new floor contributes to the total crushing energy, because its PE starts to convert into crushing KE.
2) The decelerated floor still has PE, and since it keeps falling, that energy keeps being converted into KE which keeps building up. At that point, it has liberated only one floor worth of its PE, not the whole height. It still has a lot of reserve PE available to convert into crushing KE.
I think you need to draw a distinction between the mass and the velocity of the falling building here. It's as if you are attributing equal importance to both, whereas in fact the velocity is squared, and mass isn't in the kinematic equations.
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Old 24th November 2015, 01:13 AM   #215
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Originally Posted by gerrycan View Post
I think you need to draw a distinction between the mass and the velocity of the falling building here. It's as if you are attributing equal importance to both, whereas in fact the velocity is squared, and mass isn't in the kinematic equations.
This has to be one of the most idiotic posts I've ever seen, in response to a post which only refers to potential and kinetic energy. Are you actually trying to look stupid?

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Me: So what you're saying is that, if the load carrying ability of the lower structure is reduced to the point where it can no longer support the load above it, it will collapse without a jolt, right?

Tony Szamboti: That is right
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Old 24th November 2015, 02:27 AM   #216
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Originally Posted by Notconvinced View Post
... The added PE is nowhere near the PE you got when x number of floors got to descend through y vertical space. So you get less KE after impact, less to no PE released...
Disregarding the egregiously non-physics language that gives away your total cluelessness...
How do you know this? Have you done any calculation.

Formally, you claim

A > B

Where
A = The kinetic energy dissipated by structural resistance, crushing, etc
B = The kinetic energy won from PE by descend through some vertical space "y"

Do verify that A > B, you need to estimate A and B and at least provide a lower numerical bound for A and an upper numerical bound for B.
Have you done this? If yes, please show the numbers!
If not, explain how else you know that some A is greater than some B!
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Old 24th November 2015, 03:57 AM   #217
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Originally Posted by Oystein View Post
Disregarding the egregiously non-physics language that gives away your total cluelessness...
How do you know this? Have you done any calculation.

Formally, you claim

A > B

Where
A = The kinetic energy dissipated by structural resistance, crushing, etc
B = The kinetic energy won from PE by descend through some vertical space "y"

Do verify that A > B, you need to estimate A and B and at least provide a lower numerical bound for A and an upper numerical bound for B.
Have you done this? If yes, please show the numbers!
If not, explain how else you know that some A is greater than some B!
Ah yes, it's our old friend, the Unevaluated Inequality Fallacy. Thanks for highlighting it; I always enjoy seeing a new one in the wild.

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Me: So what you're saying is that, if the load carrying ability of the lower structure is reduced to the point where it can no longer support the load above it, it will collapse without a jolt, right?

Tony Szamboti: That is right
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Old 24th November 2015, 12:06 PM   #218
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Originally Posted by Dave Rogers View Post
This has to be one of the most idiotic posts I've ever seen, in response to a post which only refers to potential and kinetic energy. Are you actually trying to look stupid?

Dave
No Dave. The top block gets to 19mph in falling one floor height. Maybe you can explain the energy balance. It should arrest within 6 floors.
As for looking stupid, aren't you the guy who backed down from debating me live? Do it. I'll ram your own arrogance right through you and we'll see who is stupid.
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Old 24th November 2015, 12:26 PM   #219
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Originally Posted by gerrycan View Post
No Dave. The top block gets to 19mph in falling one floor height. Maybe you can explain the energy balance. It should arrest within 6 floors.
Because the next one-floor drop gets it right back to 19mph, with added mass. Somewhat faster, in fact, as its fall wasn't fully arrested at first impact.

This is 'duh!' stuff, gerrycan.
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Old 24th November 2015, 01:02 PM   #220
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Originally Posted by GlennB View Post
Because the next one-floor drop gets it right back to 19mph, with added mass. Somewhat faster, in fact, as its fall wasn't fully arrested at first impact.

This is 'duh!' stuff, gerrycan.
okay, so ignoring your "duh stuff" bs, how would this achieve a constant acceleration? You said it would get back up to 19mph. that would presume a fall of about 13.5 ft at freefall from rest every time the upper block impacts the floor directly below it. There's "duh" for ya.
There's no way that the tower can fall in anything like 14s given your "gets it right back to 19mph" presumption.

ETA - I think I see where you went wrong now - you got constant speed confused with constant acceleration.
DUH

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Old 24th November 2015, 01:40 PM   #221
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Originally Posted by gerrycan View Post
okay, so ignoring your "duh stuff" bs, how would this achieve a constant acceleration? You said it would get back up to 19mph. that would presume a fall of about 13.5 ft at freefall from rest every time the upper block impacts the floor directly below it. There's "duh" for ya.
There's no way that the tower can fall in anything like 14s given your "gets it right back to 19mph" presumption.

ETA - I think I see where you went wrong now - you got constant speed confused with constant acceleration.
DUH
95% of each story is air, and 98% of the horizontal area is air, except for the 4 inches of light-weight concrete

What's going to stop most of the falling rubble and steel from accelerating at practically g during the 13 ft drop between slabs?

g is constant acceleration. It doesn't take much energy to hammer the floor joists loose. Most of the kinetic energy goes into inelastic deformation of the floor slabs and core beams. If you do the math (conservation of energy & conservation of momentum) you'll find that, with the collapse starting with 15 top floors, acceleration will average about 2/3 of g.
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Old 24th November 2015, 01:42 PM   #222
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Originally Posted by gerrycan View Post
okay, so ignoring your "duh stuff" bs, how would this achieve a constant acceleration?
Because it's a chaotic collapse, not a synchronised one.

But either way, your concept of "It should arrest within 6 floors" is nonsense, for the simple reason I gave.

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Old 24th November 2015, 01:50 PM   #223
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Originally Posted by gerrycan View Post
okay, so ignoring your "duh stuff" bs, how would this achieve a constant acceleration? You said it would get back up to 19mph. that would presume a fall of about 13.5 ft at freefall from rest every time the upper block impacts the floor directly below it. There's "duh" for ya.
There's no way that the tower can fall in anything like 14s given your "gets it right back to 19mph" presumption
If the calcs done upthread are being used as the metric, for this part of the discussion then the loss is only 1 or meters per second maximum at the instant the impact took place, and then the fall goes for Nother floor level allowing for a net gain in velocity and KE so the dynamics at the moment of subsequent impacts is actually greater unless you want to argue that theres a reason for the opposite to happen.

It was probably slightly more "loss" at each impact if you account for the real collapse dynamics but clearly as observed the simplified conservation of momentum model makes a sufficient enough point; you appear along side notconvinced to grossly overestimate the localized capacity of the system to disperse the amount of force and all involved
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Old 24th November 2015, 01:55 PM   #224
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Originally Posted by Oystein View Post
95% of each story is air, and 98% of the horizontal area is air, except for the 4 inches of light-weight concrete

What's going to stop most of the falling rubble and steel from accelerating at practically g during the 13 ft drop between slabs?

g is constant acceleration. It doesn't take much energy to hammer the floor joists loose. Most of the kinetic energy goes into inelastic deformation of the floor slabs and core beams. If you do the math (conservation of energy & conservation of momentum) you'll find that, with the collapse starting with 15 top floors, acceleration will average about 2/3 of g.
Yeah 2/3g means just under 14s as I said for the collapse.
And "floor joists"?
Not sure what you mean by this though "Most of the kinetic energy goes into inelastic deformation of the floor slabs and core beams."
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Old 24th November 2015, 02:00 PM   #225
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Originally Posted by GlennB View Post
Because it's a chaotic collapse, not a synchronised one.

But either way, your concept of "It should arrest within 6 floors" is nonsense, for the simple reason I gave.
NO glenn, You said that the arrested block would "the next one-floor drop gets it right back to 19mph" It's simple for sure, but bereft of reason.

And you have the audacity to say "this is duh stuff". ??
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Old 24th November 2015, 02:06 PM   #226
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Originally Posted by gerrycan View Post
No Dave. The top block gets to 19mph in falling one floor height. Maybe you can explain the energy balance. It should arrest within 6 floors.
As for looking stupid, aren't you the guy who backed down from debating me live? Do it. I'll ram your own arrogance right through you and we'll see who is stupid.
Does it come to a full stop at each floor? If not, why would it not be accelerating?
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Old 24th November 2015, 02:30 PM   #227
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Originally Posted by gerrycan View Post
No Dave. The top block gets to 19mph in falling one floor height. Maybe you can explain the energy balance. It should arrest within 6 floors.
So you too don't believe in gravity. Falling objects convert potential energy into kinetic energy, and the amount of kinetic energy absorbed by the collapsing of a floor is less than that gained by falling the distance to the next one; as a result, collapse doesn't arrest at all.

Originally Posted by gerrycan View Post
As for looking stupid, aren't you the guy who backed down from debating me live? Do it. I'll ram your own arrogance right through you and we'll see who is stupid.
"Backed down" would imply that I suggested an interest in doing so and then withdrew. If you believe that I did, then you're as deluded about that as about 9/11.

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Old 24th November 2015, 02:33 PM   #228
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Originally Posted by gerrycan View Post
NO glenn, You said that the arrested block would "the next one-floor drop gets it right back to 19mph" It's simple for sure, but bereft of reason.
I was looking at it from your pov :

The initial drop breaks the floor below, leading to collapse progression to some extent at least. The next one-storey fall has exactly the same effect as the first, but with added mass and extra velocity (the first impact didn't halt collapse, as you happily concede).

There is no reason for the collapse to halt for reasons of what you call 'energy balance'. Each storey-worth of collapse liberates 1 storey-height of PE to be turned into KE. In this theoretical floor-hits-next-floor-squarely view of things, the only impact that could be arrested is the first. After that things only get worse.
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Old 24th November 2015, 03:41 PM   #229
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Originally Posted by Dave Rogers View Post
So you too don't believe in gravity.
Eh ??
Originally Posted by Dave Rogers View Post
Falling objects convert potential energy into kinetic energy, and the amount of kinetic energy absorbed by the collapsing of a floor is less than that gained by falling the distance to the next one; as a result, collapse doesn't arrest at all.
Not at all. There's an energy deficit problem in your assertion. Maybe you could just throw the figures in there and I can look at them?

Originally Posted by Dave Rogers View Post
"Backed down" would imply that I suggested an interest in doing so and then withdrew. If you believe that I did, then you're as deluded about that as about 9/11.
On reflection you may be correct. The character I was remembering was wrong, but his assertions were not quite as dumb.
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Old 24th November 2015, 03:43 PM   #230
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gerrycan, you avoided my question - please answer it:

95% of each story is air, and 98% of the horizontal area is air, except for the 4 inches of light-weight concrete
What's going to stop most of the falling rubble and steel from accelerating at practically g during the 13 ft drop between slabs?

Originally Posted by gerrycan View Post
Yeah 2/3g means just under 14s as I said for the collapse.
Yes. Cool.

Originally Posted by gerrycan View Post
And "floor joists"?
I see a question mark, but I can't discern what your question is. Full sentence, perhaps?

Originally Posted by gerrycan View Post
Not sure what you mean by this though "Most of the kinetic energy goes into inelastic deformation of the floor slabs and core beams."
Exactly that.
Do you not understand what "inelastic deformation of the floor slabs and core beams" means?
Floor slabs: Mostly fracture (think "pulverisation")
Core beams: All sorts of failure modes of bolts and welds, and, well, permanent deformation.
Or perhaps I should have been more pedantic, saying "most of the kinetic energy dissipated during vertical collapse progression (~1/3 of potential energy) is turned into concrete fracture and steel deformation (and most the remaining 2/3 are dissipated at the end of the collapse, on the ground, as deformation, heat and seismic waves)".
Better?

And don't forget:
What's going to stop most of the falling rubble and steel from accelerating at practically g during the 13 ft drop between slabs?
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Old 24th November 2015, 04:03 PM   #231
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Originally Posted by gerrycan View Post

Not at all. There's an energy deficit problem in your assertion. Maybe you could just throw the figures in there and I can look at them?

Maybe you can "throw some figures". It looks to me like you keep dipping into the first impact to help the next (the reason I asked about a "full stop"). After the first impact there's a complete reset with new mass and added velocity (what's left over from the first).
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Old 24th November 2015, 04:06 PM   #232
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Can we agree on these first to make this easier -----
The buildings structural mass per floor increases from top to bottom. ie half the mass in the first 35 or so floors. (i'll try to get this more precise if you dispute it - it's my estimate)
The floors trusses were not load bearing.
The corner floor truss arrangements were transverse, so much stronger there than at the middle of each face.
The upper block impacts will not just have an effect on the topmost impacted floor below.
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Old 24th November 2015, 04:25 PM   #233
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Originally Posted by gerrycan View Post
Can we agree on these first to make this easier -----
The buildings structural mass per floor increases from top to bottom. ie half the mass in the first 35 or so floors. (i'll try to get this more precise if you dispute it - it's my estimate)
Probably a bit too extreme.
Gregory Urich wrote a paper years ago, tallying all building elements and adding up their mass. He determined the total mass of the north tower to be 288,100 tons, and he also gave a total for potential energy of 480,600 MJ. Since PE = m*g*h, it is straightforward to compute the height of the center of mass from that as h = PE/m/g, and that works out to 170 m (rounded to full meters), or 41% of the height of WTC1, or ~45 floors.
The columns are heavier in the lower floors, but the floors are more or less uniform from bottom to top.

ETA: Details in my other blog: http://oystein-issues.blogspot.de/20...each-twin.html /ETA

Originally Posted by gerrycan View Post
The floors trusses were not load bearing.
Exactly - and that's why they failed so easily, without dissipating much energy at all!

Originally Posted by gerrycan View Post
The corner floor truss arrangements were transverse, so much stronger there than at the middle of each face.
What failed was the floor truss seats. I don't think the seats were stronger in the corners than in the middle.

Originally Posted by gerrycan View Post
The upper block impacts will not just have an effect on the topmost impacted floor below.
Let's say the upper block is 15 floors.
The first floor it impacts is the 15+1st floor from top. That impacted floor has all its floor truss seats fail in a snap.
The descending top block (which has the 15th and 15+1st floors partially rubblized by now) now consists of 16 floors that fall in unison. These 16 floors start their fall not from zero but from some residual velocity.
The second impact happens at a velocity greater than the first impact, and with greater mass. It will bring the falling mass to 17 floors, which start out at a higher velocity still.
The third impact happens at a velocity greater than the second impact, and with greater mass. It will bring the falling mass to 18 floors, which start out at a higher velocity still.
Etc.
Etc.
Etc.
Etc.
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Old 24th November 2015, 04:27 PM   #234
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Originally Posted by gerrycan View Post
Can we agree on these first to make this easier -----
The buildings structural mass per floor increases from top to bottom. ie half the mass in the first 35 or so floors. (i'll try to get this more precise if you dispute it - it's my estimate)
Sure but, it doesn't mater as it is not in motion.
Originally Posted by gerrycan View Post
The floors trusses were not load bearing.
Close enough considering your first point is moot.
Originally Posted by gerrycan View Post
The corner floor truss arrangements were transverse, so much stronger there than at the middle of each face.
As above.......
Originally Posted by gerrycan View Post
The upper block impacts will not just have an effect on the topmost impacted floor below.
No idea what this means. You're not suggesting that the rest of the building will aid in stopping the effected floors (on the local level).
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Old 24th November 2015, 04:32 PM   #235
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Originally Posted by gerrycan View Post
Can we agree on these first to make this easier -----
The buildings structural mass per floor increases from top to bottom. ie half the mass in the first 35 or so floors. (i'll try to get this more precise if you dispute it - it's my estimate)
The floors trusses were not load bearing.
The corner floor truss arrangements were transverse, so much stronger there than at the middle of each face.
The upper block impacts will not just have an effect on the topmost impacted floor below.
Your mass distribution is wrong.
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Old 24th November 2015, 04:53 PM   #236
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Originally Posted by JSanderO View Post
Your mass distribution is wrong.
Ok, I did kind of put a disclaimer in there - what floor do you reckon represents the 50% mass mark?
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Old 24th November 2015, 05:28 PM   #237
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Originally Posted by jaydeehess View Post
We still await consise explanations for "KE... minus p", and upward mass vector.
Looks like this isn't going to happen.
Qu'elle suprise.
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Old 24th November 2015, 06:28 PM   #238
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Originally Posted by gerrycan View Post
Ok, I did kind of put a disclaimer in there - what floor do you reckon represents the 50% mass mark?
Except for the mechanical floors and hat truss area, the floors were all about the same. It was the column mass which changed with height. You can find a story by story mass breakdown at this link http://www.journalof911studies.com/v...ssAndPeWtc.pdf

With the pdf up go to chapter 5.2 and pick the hyperlink for the actual mass analysis spreadsheet which would be the xls file.

I think the midpoint in mass would be around the 50th story of the 110 story building as the steel in the lower stories is heavier.

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Old 24th November 2015, 06:44 PM   #239
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Originally Posted by Tony Szamboti View Post
Except for the mechanical floors and hat truss area, the floors were all about the same. It was the column mass which changed with height. You can find a story by story mass breakdown at this link http://www.journalof911studies.com/v...ssAndPeWtc.pdf

With the pdf up go to chapter 5.2 and pick the hyperlink for the actual mass analysis spreadsheet which would be the xls file.

I think the midpoint in mass would be around the 50th story of the 110 story building as the steel in the lower stories is heavier.
Good job Tony.

Now explain what this has to do with the mass that actually was in motion.

You guys remind me of the dogs in the move "up". Except you expect us to follow the squirrels.
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Old 24th November 2015, 06:52 PM   #240
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Originally Posted by Tony Szamboti View Post
With the pdf up go to chapter 5.2 and pick the hyperlink for the actual mass analysis spreadsheet which would be the xls file.
Hi Tony, and thanks. I make it to be between fl 43 and 44 according to that.
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