okay.
tell us how much energy does it take to "break the supports".
be sure to include whether you are talking about lap joints or butt joints.
this is the central point you keep omitting psiky.
9/11 was an inside job
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tell us how much energy does it take to "break the supports".
be sure to include whether you are talking about lap joints or butt joints.
this is the central point you keep omitting psiky.
The problem is that the strength came from the unit as a whole, not any one part of said unit. It was... an interesting design choice to be sure, but think of it like a tripod - three legs make it quite sturdy and hard to topple... but you take away just one leg, and while you still have 60% of the support, it simply falls to the missing side.
None of that shows your model that results that you stated here - "My model flattened or damaged 6 LEVELS below the point of impact. But there were 20 more that were even stronger."
Neddy Bate
You have been confused by disinformation. On purpose. For example, there was no molten STEEL in the rubble pile, none. Glowing hot steel, with rivulets of dirty firefighting water reflecting that glow looking like molten steel. Second, eyewitness testimony is the LEAST reliable, as any information gained that way is at best second hand, having been processed by the perceptions, interpreted by the knowledge base and infected by the prejudices of the brains of your witnesses. Just ask any trial lawyer. Loud noises are expected when buildings are falling apart and explosions are loud noises but not all loud noises are explosions, air is ejected by floors collapsing on lower floors, throwing clouds of dust out of windows all around, some misinterpret that as "squibs". Your incredulity is not warranted. Those buildings both fell because of physics, they needed no help from mysterious ninja demolition engineers. Damage and heat weakened steel. Just that simple. What is not right here is the whole "troother" movement, it's been a real spectacle of stupidity and disinformation.
As to the frames not standing on their own, why do you think they were assembled floor by floor? Like a house of cards they must be constructed from the ground up, stabilizing the entire structure before proceeding to the next level. And like a house of cards, they must remain whole to continue standing. The three mechanical floors and the dampers kept the core and perimeter frame braced in perfect vertical alignment while allowing the building to flex in the wind. In that configuration the buildings were in no danger of failure, but some asshole flew 250,000 lb aircraft into them. Well they survived that damage, proving their strength and safety margin. It was the multi-floor fires that then caused enough steel to soften and creep, overloading the remaining safety margin and the house of cards fell.
Older skyscrapers were built like cars with a separate frame of steel encased in concrete, the Twin Towers were a monocoque, the frame was the whole thing, there was no structural concrete above ground level, all the concrete used was in the floor pans. All the fireproofing was made of easily damaged foam(blocks on the outer frame and core columns, spray foam on the floor trusses)much of which was blown into dust at impact, leaving steel exposed to fire. Steel loses half it's strength at 500 degrees(ask a blacksmith what color that is)and will start deforming under load, transferring their load to other columns. Once the point is reached where there are not enough columns to hold the load, they will all fail simultaneously.
Experiment: Tie a bowling ball to the ceiling with many small threads. Start cutting one thread at a time. You will reach a point that when you cut one critical thread every other thread will instantly fail simultaneously. That is the same point the Twin Towers reached when they collapsed for exactly the same reason, the remaining structure could no longer support the load. And their method of construction meant that once failure started the remaining structure could barely slow it down.
ALL buildings are a house of cards, except the Pyramids, which are piles of rocks. They are all susceptible to cascading failure when damaged or on fire. Ask any fire chief about the dangers of truss floors, more firemen have been killed by truss floor(or ceiling)collapses than any other cause. There was nothing different about the Twin Towers except the scale.
Grumpy
You have been confused by disinformation. On purpose. For example, there was no molten STEEL in the rubble pile, none. Glowing hot steel, with rivulets of dirty firefighting water reflecting that glow looking like molten steel. Second, eyewitness testimony is the LEAST reliable, as any information gained that way is at best second hand, having been processed by the perceptions, interpreted by the knowledge base and infected by the prejudices of the brains of your witnesses. Just ask any trial lawyer. Loud noises are expected when buildings are falling apart and explosions are loud noises but not all loud noises are explosions, air is ejected by floors collapsing on lower floors, throwing clouds of dust out of windows all around, some misinterpret that as "squibs". Your incredulity is not warranted. Those buildings both fell because of physics, they needed no help from mysterious ninja demolition engineers. Damage and heat weakened steel. Just that simple. What is not right here is the whole "troother" movement, it's been a real spectacle of stupidity and disinformation.
As to the frames not standing on their own, why do you think they were assembled floor by floor? Like a house of cards they must be constructed from the ground up, stabilizing the entire structure before proceeding to the next level. And like a house of cards, they must remain whole to continue standing. The three mechanical floors and the dampers kept the core and perimeter frame braced in perfect vertical alignment while allowing the building to flex in the wind. In that configuration the buildings were in no danger of failure, but some asshole flew 250,000 lb aircraft into them. Well they survived that damage, proving their strength and safety margin. It was the multi-floor fires that then caused enough steel to soften and creep, overloading the remaining safety margin and the house of cards fell.
Older skyscrapers were built like cars with a separate frame of steel encased in concrete, the Twin Towers were a monocoque, the frame was the whole thing, there was no structural concrete above ground level, all the concrete used was in the floor pans. All the fireproofing was made of easily damaged foam(blocks on the outer frame and core columns, spray foam on the floor trusses)much of which was blown into dust at impact, leaving steel exposed to fire. Steel loses half it's strength at 500 degrees(ask a blacksmith what color that is)and will start deforming under load, transferring their load to other columns. Once the point is reached where there are not enough columns to hold the load, they will all fail simultaneously.
Experiment: Tie a bowling ball to the ceiling with many small threads. Start cutting one thread at a time. You will reach a point that when you cut one critical thread every other thread will instantly fail simultaneously. That is the same point the Twin Towers reached when they collapsed for exactly the same reason, the remaining structure could no longer support the load. And their method of construction meant that once failure started the remaining structure could barely slow it down.
ALL buildings are a house of cards, except the Pyramids, which are piles of rocks. They are all susceptible to cascading failure when damaged or on fire. Ask any fire chief about the dangers of truss floors, more firemen have been killed by truss floor(or ceiling)collapses than any other cause. There was nothing different about the Twin Towers except the scale.
Grumpy
Are you blind or just unable to count?
The result of the impact are at 4:49 in the video.
The paper loops are numbered and the rest of the stack is shown to 5:35.
psik
I got bored and only watched the first minute or so of the video. Thanks for clueing me in. That video was hilarious. Your 'model' actually consists of washers and paper rings on a wooden dowel? Oh my God, absolutely perfect!
Take care and thanks again for the laugh.
Neddy Bate
Valued Senior Member
Just to explain my thinking on this...
It seems to me that most of the damage and fires should have been in the vicinity of the impact hole. In this case, that location just happens to be near the top of the building, so the middle and bottom of the building should be mostly undamaged. Presumably the columns had to be thickest and strongest near the bottom, because they had to support the weight of the entire building. This also matches psikeyhakr's experimental results in his video link.
Accordingly, the collapse appears to begin at the top, which makes sense. The top part of the building collapses downward (and outward), and one would expect it to meet resistance from the largely un-damaged, stronger parts of the building. That is also what psikeyhakr's video suggests should happen. Surprisingly, that does not happen, and instead the top part of the building progresses down without decelerating, and the entire building collapses. The explanation (as far as I can understand it) is that the columns relied on the floors to keep them aligned, and so when the floors failed, the columns failed as well. A basic model for this would be something like a "house of cards" which I agree would act something like this. However, I personally find that model somewhat less compelling than psikeyhakr's model which suggests that some unknown mechanism must have weakened the middle and lower parts of the structure. (Not that my opinion makes any difference to what really happened that day).
Neddy - the problem is, you are working on the premise that each floor is designed to hold the weight of the floors above it - they aren't. They transfer their entire weight to the supporting columns using a series of braces that are designed to hold the "live weight" of the floor (which is to say the weight of the floor itself, a reasonable expectation of load weight, and a margin of error for safety). Thus, when an entire extra floor (or, in this case, several floors) of weight were added, the braces failed and the pieces collapsed.
correct.
the floors also relied on the perimeter columns to keep them (core columns) aligned.
in essence, all 3 relied on each other.
unknown weakness?
yes and psiky refuses to address it for some reason.
Neddy Bate
The damage was, but the fires spread both up and down. Down from flaming fuel washing down and up due to convection, fires spread upward when they can. By the time One fell most of the top section was involved and four floors below the impact zones had extensive fires. Two had concentrated fire zones on one side and the corner, was hit lower down and off center.
That strength is irrelevant once the columns were no longer connected, as the kinetic energy falling on them was the equivalent of a small atomic bomb. It simply snapped them to pieces at the bolted joints.
Explain the exact mechanism where that falling rubble was connected(and transferred their energy)to those strong beams. When you find out why you cannot, you will start to realize how wrong you are. A standing beam offers zero resistance to the beams falling past them in the spaces where the floors used to be, without the bracing of those floors the rubble pressure pushed the outer wall outward and the core beams bent and disconnected as the hat truss hammered them down.
Surprising only if you didn't know or understand the physics involved. Once the tops fell just one floor the kinetic energy of that falling mass overwhelmed the ability to resist of the lower floors and the rubble pushed most of them into the basement, leaving the unsupported outer frame and core to disintegrate as it's butt joints and 5/8 inch bolts failed..
That is what we saw happen that day, twice. The collapses were not started by the floors failing, it was started by a failure in the perimeter frames and core, THEN the floors raced into the basement(you can see the puffs in Tower One several floors below the outwardly visible collapse of the outer frame).
"As generally accepted by structural engineering and structural mechanics experts (though not by some laymen and fanatics seeking to detect a conspiracy), the failure scenario, broadly proposed by Bazant (2001), and Bazant and Zhou (2002), on the basis of simplified analysis, and supported by very realistic, meticulous and illuminating computer simulations and exhaustive investigations by S. Shyam Sunder's team at the National Institute of Standards and Technology (NIST, 2005), may be summarized as follows:
1. About 60% of the 60 columns of the impacted face of framed-tube (and about 13% of the total of 287 columns) were severed, and many more were significantly deflected. This caused stress redistribution, which significantly increased the load of some columns, near the load capacity for some of them.
2. Fire insulation was stripped during aircraft impact by flying debris (without that, the towers would likely have survived). In consequence, many structural steel members heated up to 600±C (NIST 2005) (the structural steel used loses about 20% of its yield strength already at 300±C, NIST 2005, and exhibits significant visco-plasticity, or creep, above 450±, especially at high stresses that developed; see e.g. Cottrell 1964, p. 299; the press reports right after 9/11, indicating temperature in excess of 800±C, turned out to be groundless, but Bazant and Zhou's analysis did not depend on that).
3. Differential thermal expansion, combined with heat-induced viscoplastic deformation, caused the floor trusses to sag. The sagging trusses pulled the perimeter columns inward (by about 1 m, NIST 2005). The bowing of columns served as a huge imperfection inducing multi-story buckling. The lateral deflections of some columns due to aircraft impact and differential thermal expansion also decreased buckling strength.
4. The combination of six effects
a) overload of some columns due to initial stress redistribution,
b ) lowering of yield limit and creep,
c) lateral deflections of many columns due to sagging floor trusses,
d) weakened lateral support due to reduced in-plane stiffess of sagging floors,
e) multi-story buckling of some columns (for which the critical load is an order of magnitude less than it is for one-story buckling), and
f) local plastic buckling of heated column webs finally led to buckling of columns (Fig. 1b). As a result, the upper part of tower fell, with little resistance, through at least one floor height, impacting the lower part of tower. This triggered progressive collapse because the kinetic energy of the falling upper part far exceeded the energy that could be absorbed by limited plastic deformations and fracturing in the lower part of tower. (Bazant, Verdure, 2006)"
http://www.civil.northwestern.edu/people/bazant/PDFs/Papers
http://www.debunking911.com/collapse.htm
Grumpy
/ProgressiveCollapseWTC-6-23-2006.pdf
The damage was, but the fires spread both up and down. Down from flaming fuel washing down and up due to convection, fires spread upward when they can. By the time One fell most of the top section was involved and four floors below the impact zones had extensive fires. Two had concentrated fire zones on one side and the corner, was hit lower down and off center.
That strength is irrelevant once the columns were no longer connected, as the kinetic energy falling on them was the equivalent of a small atomic bomb. It simply snapped them to pieces at the bolted joints.
Explain the exact mechanism where that falling rubble was connected(and transferred their energy)to those strong beams. When you find out why you cannot, you will start to realize how wrong you are. A standing beam offers zero resistance to the beams falling past them in the spaces where the floors used to be, without the bracing of those floors the rubble pressure pushed the outer wall outward and the core beams bent and disconnected as the hat truss hammered them down.
Surprising only if you didn't know or understand the physics involved. Once the tops fell just one floor the kinetic energy of that falling mass overwhelmed the ability to resist of the lower floors and the rubble pushed most of them into the basement, leaving the unsupported outer frame and core to disintegrate as it's butt joints and 5/8 inch bolts failed..
That is what we saw happen that day, twice. The collapses were not started by the floors failing, it was started by a failure in the perimeter frames and core, THEN the floors raced into the basement(you can see the puffs in Tower One several floors below the outwardly visible collapse of the outer frame).
"As generally accepted by structural engineering and structural mechanics experts (though not by some laymen and fanatics seeking to detect a conspiracy), the failure scenario, broadly proposed by Bazant (2001), and Bazant and Zhou (2002), on the basis of simplified analysis, and supported by very realistic, meticulous and illuminating computer simulations and exhaustive investigations by S. Shyam Sunder's team at the National Institute of Standards and Technology (NIST, 2005), may be summarized as follows:
1. About 60% of the 60 columns of the impacted face of framed-tube (and about 13% of the total of 287 columns) were severed, and many more were significantly deflected. This caused stress redistribution, which significantly increased the load of some columns, near the load capacity for some of them.
2. Fire insulation was stripped during aircraft impact by flying debris (without that, the towers would likely have survived). In consequence, many structural steel members heated up to 600±C (NIST 2005) (the structural steel used loses about 20% of its yield strength already at 300±C, NIST 2005, and exhibits significant visco-plasticity, or creep, above 450±, especially at high stresses that developed; see e.g. Cottrell 1964, p. 299; the press reports right after 9/11, indicating temperature in excess of 800±C, turned out to be groundless, but Bazant and Zhou's analysis did not depend on that).
3. Differential thermal expansion, combined with heat-induced viscoplastic deformation, caused the floor trusses to sag. The sagging trusses pulled the perimeter columns inward (by about 1 m, NIST 2005). The bowing of columns served as a huge imperfection inducing multi-story buckling. The lateral deflections of some columns due to aircraft impact and differential thermal expansion also decreased buckling strength.
4. The combination of six effects
a) overload of some columns due to initial stress redistribution,
b ) lowering of yield limit and creep,
c) lateral deflections of many columns due to sagging floor trusses,
d) weakened lateral support due to reduced in-plane stiffess of sagging floors,
e) multi-story buckling of some columns (for which the critical load is an order of magnitude less than it is for one-story buckling), and
f) local plastic buckling of heated column webs finally led to buckling of columns (Fig. 1b). As a result, the upper part of tower fell, with little resistance, through at least one floor height, impacting the lower part of tower. This triggered progressive collapse because the kinetic energy of the falling upper part far exceeded the energy that could be absorbed by limited plastic deformations and fracturing in the lower part of tower. (Bazant, Verdure, 2006)"
http://www.civil.northwestern.edu/people/bazant/PDFs/Papers
http://www.debunking911.com/collapse.htm
Grumpy
/ProgressiveCollapseWTC-6-23-2006.pdf
I do not dispute that a bigger heavier model than mine would be better especially if it had a tube in tube design.
Our engineering schools should have been able to make such models years ago. I have not heard of any schools suggesting such a thing.
psik
ROFLMAO
The amount of steel changes on the various levels down the building. The amount of energy required would increase as the amount of steel increases.
But we are not told the amount of steel on each level so calculating the amount of energy is complete nonsense.
The science can't be done because the people who just believe say we don't need the data.
psik
You refuse to go looking at technical sources that contain all the information you're demanding (or heck, go find the info for a similar skyscraper somewhere else and show us why it couldn't collapse the same way once the top 10 floors are falling), so that leaves many people here wondering if you've heard of any schools, period.
Neddy Bate,
It should be considered that before the entire "problem" of collapse, the building had already taken a Horizontal impact at over 3/4ths it's height. (A "Moment of Force")
That impact would of pushed trusses into the central core causing a structure failure at that point, it would of also potentially caused further failures further down the core due to the translation of energy, that would occur at whatever point the force would of been resisted (a pivot) Ideally that would have been at the ground level, the likelihood is though it would of been further up.
It should be considered that before the entire "problem" of collapse, the building had already taken a Horizontal impact at over 3/4ths it's height. (A "Moment of Force")
That impact would of pushed trusses into the central core causing a structure failure at that point, it would of also potentially caused further failures further down the core due to the translation of energy, that would occur at whatever point the force would of been resisted (a pivot) Ideally that would have been at the ground level, the likelihood is though it would of been further up.
correct, assuming that piece of steel was one solid piece.
the situation changes when it is jointed AND with the type of joints used.
how does your model account for that?
the info for the core columns was published in the 911 report by congress.
i assume the floor panels would be constant.
i'm quit sure the info for the perimeter columns is published somewhere.
the main question is how does your model account for the perimeter and core butt joints?
we are talking about one of weakest joints known to engineering here.
leopold
psik has a problem understanding that that building's strength cannot be considered as being "one piece". That building had more in common with a stack of blocks than it did with a pyramid and any strength remaining in the lower section had no mechanism to apply that strength to slow any falling beams or frame sections(most of which fell outward)disconnecting as their bending limits were reached. It is irrelevant how much strength a beam has left to a beam that is falling down BESIDE it, where the floors used to be.
Grumpy
psik has a problem understanding that that building's strength cannot be considered as being "one piece". That building had more in common with a stack of blocks than it did with a pyramid and any strength remaining in the lower section had no mechanism to apply that strength to slow any falling beams or frame sections(most of which fell outward)disconnecting as their bending limits were reached. It is irrelevant how much strength a beam has left to a beam that is falling down BESIDE it, where the floors used to be.
Grumpy
So you are saying that the joints were not stronger down the building as the steel got thicker?
That is a pretty interesting CLAIM.
psik
It's a pretty standard fact that almost any joint, especially a butt joint, is, invariably, going to be the weakest point of a structure...
psikeyhackr
They were not stronger, the bolts were identical, they were also irrelevant to the strength of the column, all those butt joint fasteners did was maintain alignment, they contributed nothing to the vertical strength of the column, the forces being transferred directly plate to plate. Bending any of those butt joints more than a few degrees would destroy those bolts, allow the plates to move out of alignment and then fall past each other on the way down, just as we saw happen twice that same day.
Grumpy
They were not stronger, the bolts were identical, they were also irrelevant to the strength of the column, all those butt joint fasteners did was maintain alignment, they contributed nothing to the vertical strength of the column, the forces being transferred directly plate to plate. Bending any of those butt joints more than a few degrees would destroy those bolts, allow the plates to move out of alignment and then fall past each other on the way down, just as we saw happen twice that same day.
Grumpy
psikeyhackr
They were not stronger, the bolts were identical, they were also irrelevant to the strength of the column, all those butt joint fasteners did was maintain alignment, they contributed nothing to the vertical strength of the column, the forces being transferred directly plate to plate. Bending any of those butt joints more than a few degrees would destroy those bolts, allow the plates to move out of alignment and then fall past each other on the way down, just as we saw happen twice that same day.
Grumpy
Are you talking about the perimeter columns? There were columns in the core also.
psik
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