You do understand that I'm imagining a stack of six cubes with the same dimensions, i.e., square towers six times as tall as they are wide?
Claim: Jim Hoffman's "9/11 progressive collapse challenge" can't be met
deirdre
Senior Member.
yup. i understand that.
econ41
Senior Member
That is one of the two main problems I've been trying to guide Thomas around.
1) How much does he want to mimic the real features of WTC Twin Towers collapses; AND
2) How much he wants to rigorously specify his own version of the challenge given that the Hoffman original is so wide open.
I'll state it bluntly and risk accusations of false generalisation >> It is impossible to mimic the actual WTC initiation and transition stages. And the bare minimum criteria to sufficiently resemble WTC collapse is that whatever falls and however it falls MUST cause debris to fall landing on the floors and missing the columns. When I first hypothesised such a mechanism about 2008 I proposed dropping a doughnut shaped weight onto the office space floor area. That method would not accurately model the collapse of the core area. Or guarantee "scattering" of debris at distance outside the footprint.
Agreed. That is the core issue "what it the point?" Stated alternatively "What is the objective?" >> Two of them actually (a) What are we trying to model? AND (b) For what purpose - who are we trying to educate/teach?
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Well, I walked right into that one didn't I! Cheers.
econ41
Senior Member
I don't know about "walked right into" but the issue throughout these discussions has been the need to be clear which challenge we are discussing given that the Hoffman original was so ill-defined or wide open to interpretation/innuendo. Defeating the Hoffman Challenge is trivially easy if we stay with what he actually said. If we read implications into it then the challenge is in two parts - "how far do we go in setting a firm definition of the challenge" AND "how much do we want to replicate WTC 9/11 reality".
With the also undefined at present but overriding criteria "who is the target audience"? Because "building a model that will help laypersons understand WTC Twin Towers progrssion stage" is at least a couple of grades simpler that "building a generic model which will need professionmal expertise to comprehend". And I doubt that there is much flexibility if we try aiming for somewhere between those two extremes. I'm reasonably sure it will have to be one or the other.
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econ41
Senior Member
I understood that was what you had in mind.
I'll just raise one issue for you to keep in mind if you pursue the "stack of multiple hollow cubes" basis for the model. It is the issue of instability.
In the collapses of all three WTC Towers the noticeable feature was how the collapse was both "straight down" and limited in spread of debris. For the Twin Towers the spread of debris was constrained by the material falling inside the guiding tube of the perimeter columns. Then as those columns were disconnected they mostly toppled outwards BUT there was no "toppling" of the structure as a whole. Both "Twins" went "straight down". Similarly - for WTC 7 the perimeter shell includes a very strong "moment frame" and the perimeter shell remained mostly intact after the core had collapsed. Again effectively constraining debris scatter . AND there was no toppling of the building as a whole.
As it stands so far the "6 Cubes Stacked" model does not have the same level of inbuilt stability against toppling. Yes it is symmetrical and yes ideally symmetry should restrain against toppling. BUT that is ideal. In reality there will be slight assymetry in each cube. And if one cube starts to skew its collapse to oneside there is no inbult "correcting" mechanism. So there will be a tendency for the assymetry to increase - positive feedback effect.
I'll leave that as an issue for consideration as discussion progresses. It may be that simple hollow cubes won't meet the goal. But we are still working to clarify the goal so we cannot resolve the issue at this time.
Oystein
Senior Member
In my previous post I tried to get the idea across that Hoffman picked quite arbitrarily three or four alleged properties of the collapses as the targets for his challenge.
But why those properties, and not any of the hundreds, thousands, millions that you could identify if you only looked at the videos long enough? What makes THOSE targets relevant or significant?
And what if meeting the challenge results in a model that is in grossly obvious ways totally different from the actual towers? Like a silly Rube Goldberg machine? Nothing is learned if a Rube Goldberg machine meets the challenge.
Responding to Rube Goldberg machines that meet the challenge by redefining the challenge to rule out that Rube Goldberg machine only ups the ante by favoring a next-generation Rube Goldberg machine that is even sillier in how unlike the real structure it is.
But why those properties, and not any of the hundreds, thousands, millions that you could identify if you only looked at the videos long enough? What makes THOSE targets relevant or significant?
And what if meeting the challenge results in a model that is in grossly obvious ways totally different from the actual towers? Like a silly Rube Goldberg machine? Nothing is learned if a Rube Goldberg machine meets the challenge.
Responding to Rube Goldberg machines that meet the challenge by redefining the challenge to rule out that Rube Goldberg machine only ups the ante by favoring a next-generation Rube Goldberg machine that is even sillier in how unlike the real structure it is.
econ41
Senior Member
Agreed. Hence my focus on the three key issues:
1) Defining which challenge;
2) Deciding how far it needs to replicate WTC Towers; AND
3) Being clear as to who is the target audience.
Because those last two will interact. If the "audience" is relatively unable to visualise lay persons who "need" a real model before that "see it" or "get it" they will need the familiarity of WTC. And - for that group - comprehending a generic model will be too complex.
econ41
Senior Member
Just a brief comment or two - we are drifting "off-topic":
The "office fires" is a typical misleading truther comment. The 3 WTC collapses were not caused by the "office fires" the buildings were designed to withstand. The base fuel of office contents and fit out material was the only part of the 9/11 fires that matched the designed office fires. For a steel framed building the design criteria is a fire rating - a time in hours - three hours for most of the WTC Towers. That time allows for commencement of active fire fighting and the escape of occupants. It presumes commencement of a fire by some initiation accident and its spreading in the context of "normal" office content. It assumes starting of active fire fighting - personnel attacking fires AND reinforcement of back up water supplies. None of that happened for WTC7 which fires also started at multiple points. And the Twin Towers scenario was an order or two greater in magnitude. Fuel concentrated by "Boeing Dozing" and accelerated start up because of aviation fuel probably the two most significant. Plus simultaneous start up on several storeys. So none of the WTC 9/11 Towers fires were the designed for "office fires" - all three scenarios were an order or two more severe/intense.
The mechanism of top crushing bottom has been well understood and in varying levels of detail in multiple explanations over the years. With a lot of confusion and misunderstanding up til about 2010 - there is still a fair bit of confusion. I can point to examples of valid explanations if you need them. The situation is certainly a lot better explained now than it was pre about 2009 and has been explained in lay person language since about that time 2009-10-11-12.
I think many truthers "learn" something from the fact that not even a Rube Goldberg machine has been proposed to meet Hoffman's challenge. I suspect Hoffman deliberately worded the challenge to imply that you can't build a structure to collapse like WTC even if you tried. A Rube Goldberg machine shaped like the Twin Towers that can stand up in a (reasonably scaled) strong wind and undergoes global collapse when disturbed locally near the top would prove Hoffman wrong.
The main reason to meet the challenge is to definitively debunk the claim that it can't be met.
My alternative challenge was made in response to Econ41's suggestion to do so. This was occasioned by what I thought was an obvious departure from the spirit of Hoffman's challenge: To meet challenge #1, Econ had (it seemed to me) suggested smashing the structure with a brick that wasn't already supported by it.
It's no doubt possible to improve my challenge, but I do like it. It lets you build something that stands and falls by virtue of an easily surveyable combination of columns, beams, joints, dead loads, and floor connections. You can test its strength (increasing the load or exposing it to shear or removing non-critical elements) and then demonstrate that it is nonetheless vulnerable to top-down progressive collapse.
If my rules make it impossible to meet the challenge, I'm interested to hear why. To me, it's a Rube Golberg solution only in the sense that Galileo's inclined planes and Newton's Cradle are "arbitrary" demonstrations of physical laws.
econ41
Senior Member
@Thomas B I'll respond ONLY to the points that refer to me - leaving the topic clear for Oystein's response
Again please stop vacillating between which challenge you refer to. The Hoffman challenge has already been falsified in reference to Item #1 AND I've asserted that the Hoffman Challenge is trivially easy to falsify for #2, #3, and #4 i.e. other than #5 which I decline to do, also because it is so trivial.
Your OP challenge was to falsify the Hoffman claims. I did so for Item #1. The Hoffman Challenge does NOT reject my use of a brisk. You imposed that as your criterion. It is NOT in Hoffman. Rigorously in accordance with the Hoffman specification. Please STOP re-interpreting Hoffman to include criteria which you "mind read" as Hoffman's intention BUT which are specifically NOT in the challenge made by Hoffman.
And as soon as you stop oscillating between your own challenge, the Hoffman Challenge and the challenge you mind read as Hoffman's intent >>> we can seriously discuss WHICHEVER challenge you want to discuss. Pick one. IF you want to discuss all three it would probably be a damn sight easier to use seperate threads. One for each challenge. Because they are very different. And the "stick to the topic" rules of this forum would tie you down to staying on-topic.
Like I say, I walked into it freely, but it seems like it was a mistake to articulate my own challenge. I thought it would make it easier to have the discussion, but it has just made it about me. So let's go back to Hoffman's challenge. There's seems to be general agreement that meeting his challenge is possible. So the OP claim should be easy enough to debunk. That is my main purpose with this thread.
I don't think you met his #1 in your attempt because the brick you introduced was not part of the structure's initial state.
Thinking about this a little more. I suppose there's one sense in which @Oystein 's point should be emphasized. We could imagine a device that has a "release" (like in a folding table or ironing board) near the top -- that is, a machine that is built to be quite strong in a locked position, but which can be "destroyed" at the press of a button. As long as the button is "near the top" it would formally meet Hoffman's challenge.
But this doesn't show that Hoffman's challenge is silly, just that the challenger is not playing along. I'm pretty sure there are sincere observers who would take the whole episode as evidence for the strength of Hoffman's position.
In a sense, my "more rigorous" challenge is just an attempt to steel-man Hoffman's argument before demolishing it. It's certainly possible to straw-man it, but that rarely accomplishes anything.
econ41
Senior Member
Please don't misconstrue robust rigorous argument as making it "about you" The fundamental difficulty throughout this thread has been determning what challenge YOU want to discuss. And you are once again "changing horses in mid-stream" when you make this suggestion:--
By all means but remember it was YOUR choice.
The Hoffman Challenge does NOT include any requirement that the cause of collapse be limited to "...part of the structure's initial state."
The Hoffman challenge is explicit:
"...i.e.: when disturbed near the top, it will collapse from the top down to the bottom, leaving no part standing. The disturbance can include mechanical force, such as projectile impacts,"
If you are seriously suggesting the a "brick" cannot be a "projectile" then say so and I will change it to something you cannot deny. Like an unexploded RPG PROJECTILE.
As I have both hinted and stated explicitly several times you are reading your own limitations into what Hoffman actually said.
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I think it's probably best for us both to make the choice not to discuss this further. Your brick introduces an arbitrarily large force relative to the weight the structure supports in its initial state. Though it's arguably (and I would say pedantically) a "mechanical force" and a "projectile impact", it destroys the structure as trivially as a sufficiently large bomb.If you think that's an instructive and/or clever way to "meet" Hoffman's challenge, that's fine for you. I'm sure your solutions to #2-#5 will be just as clever. But I understand why a truther or fencer would be unimpressed.
econ41
Senior Member
I'm aware of your growing antagonism. However I have steadfastly offered to discuss ANY of the challenges. That offer still stands. I'm prepared to discuss and meet ANY challenge you care to define ONCE you stop changing horses in midstream.
Yes. The Hoffman Challenge is a trivial challenge. That is why several of us including me have been asking you to decide which challenge you want to discuss. Your latest choice was to ignore all the warnings about its triviality and YOU chose the Hoffman Challenge. AND I showed how I had already falsified Item #1. Now you again try to rewrite Hoffman #1 to once again substitute your own interpretation of what it should be in your opinion.
I've never made such a claim. I have repeatedly stated that the Hoffman Challenge is trivial. It doesn't take any cleverness to meet the challange AKA falsify the claims. AND you are the one who persists in changing the challenge to what you want it to say.
OK. I will leave you to it. Your refusal to define and discuss what you choose as "The Challenge" is not likely to be productive. Let me know if you change your mind.
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Oystein
Senior Member
A Rube Goldberg machine is by definition a much too elaborate, costly contraption, massively wasteful of resources, to solve a trivial problem of no discernible significance.
Hoffman's challenge is a trivial problem of no discernible significance, except to a tiny fringe of people who are already resolved to not accepting any model that meets the challenge - or do you foster any hope that, if the challenge is met, the Truther will say "oh, ok, now I understand how the towers could fall, and accept the gist of the NIST reports"? Or would you not rather suspect that they'll respond with some huge "But what about...?"? Like "what about the near-g acceleration?", "what about the lateral ejection of multi-ton steel segments?", "what about the mid-air pulverization of much of the concrete?" - all additions to the challenge as arbitrary, vague and unproven as Hoffman's original targets?
So who in their right mind would waste such resources on a problem of no real importance, when it's going to get rejected anyway?
---
Your post made me think of another challenge that's unimportant and would waste huge resources for nothing:
There is a wide-spread belief among Truthers (and it lies at the heart of the Hoffman "Challenge") that tall office buildings / highrises cannot collapse totally at all from fires. That there is something almost magical about building tall that absolutely protects highrises from such failures.
This belief implies that it would not even be possible to design a highrise with the explicit objective that it can and does collapse from an uncontrolled fire.
And you could post that as a challenge on the internet: Build a steel frame structure that is at least 25 floors / 300 ft / 100 m tall, supports its own weight, withstands high winds, but collapses completely when you set fire to normal office contents on several consecutive floors.
I think it is trivially true that an engineer could meet that challenge, but no one ever will, for building a 300 ft highrise for the sole purpose of destroying it to meet an insignificant dude's challenge on the internet would eclipse all levels of madness.
Truthers no doubt would "learn" from the fact that no one meets that challenge the same illogical nonsense they "learn" from the fact that no one cares enough for the Hoffman challenge.
The Hoffman challenge poses no problem in principle. It's just not important, clever, enlightening enough to warrant the expenditure of time and resources building such a physical model would entail.
Oystein
Senior Member
It would be trivially easy to make the brick a part of the structure's initial state: Just put it on a bit of combustible scaffolding on top of the rest of the structure, and declare brick and scaffolding part of the structure, then burn the scaffolding.
Shape the brick, and make it with some pre-fabricated cracks, such that it breaks in the course of the collapse into four or eight parts which tilt or roll away from the footprint eventually - that might take care already of the silly and unfounded "80% outside foorprint" part of the challenge.
Am I getting close to meeting the challenge?
If so: What can we learn from the model with regard to the real-world collapses of the WTC towers? Anything more than "nothing at all"?
Jeffrey Orling
Senior Member
Too much to read in this thread.. and much of the salient points of the collapse and been very well described on 911FF and other sites include this one.
There is no need to make a physical model in the case of building performance studies as the performance specifications and limits of the materials and connections is essentially settle science.
What has been called "ROOSD" is hardly a mystery... a given floor spec when over loaded fails and collapses. The beam may "part"... the connections may "part" or either/both depending on the force of the superimposed (destructive load)). In the case of the twin towers... the superimposed destructive load was the floor structure and the superimposed live loads on those floors including contents and people. Contents included furniture and office "materials" as well as partitions and MEP equipment.
Engineering "understands" the fact that a moving mass (descending) exerts a great force than it does as a static load. So we can think of dynamic loading as a sort of force multiplier.
So the "progression phase".... is really "trivial" and well understood engineering. Engineers can compute the threshold load / force which would "overwhelm" the typical twin tower floor system. The safe loads are all set forth in load tables for steel, concrete, wood and so on.
ROOSD by any name is a destruction of the FLOORS not the steel which supported them. There were other mechanisms which led to the failure of the axial load bearing system(s). There were two of those systems... interior columns and perimeter columns. The long span column free office space was a different system than the floor system within the core was was more traditional column grid with girders and beams,
A key point to understand the failure of the axial systems - both core and perimeter columns is how the stability and strength of a column is related to its slenderness ratio. As a column section is made taller... its slenderness ratio increases... x & y dimensions and z (height). The more slender a column is... the weaker and less stable it is. To make slender columns "perform" they require bracing... which reduces the design length z. In a steel frame high rise the floor beams (steel) perform the function of reducing the slenderness ratio. A tall steel structure cannot stand without the columns braced by the steel floor beams. Same concept would apply to a concrete or even a wood structure.
Once ROOSD was in progress the bracing was being striped from the columns. This was seen in images of the spire after the floor slabs had collapsed.
The videos show how both the perimeter/facade columns and the interior core columns collapse from being too slender. This behavior is describe by a process called Euler Buckling. Euler buckling predicts that then a slenderness ratio of a column exceeds a value... determined by what the material is....the column will "self buckle".... it cannot support itself.
So ROOSD floor collapse is settled engineering and the collapse of the columns is likewise understood by Euler's formulae for slender columns. The column collapse was also aided by lateral forces of the growing collapsing floor mass. (similar to the lateral forces that grain exerts on the walls of a silo, or sand in a cardboard container)
So with the collapse phase completely understood by settled engineering... the question to answer becomes how did the ROOSD mass establish? That mass had been supported by the structure... but somehow lost its support and feel and became the driving ROOSD force which only got larger as it "consumed/destroyed" each successive for on its way to the ground.
The planes did damage swaths of several floor and this did free up some material will in fact did fall. However this was not sufficient mass even locally to go "runaway". To form the entire foot print descending ROOSD mass was likely a more "organic" process of expanding structural failures. But we can't see this happening and so we have to speculate what might have been in play.
What we DO know is that post plane strike fire raged without mitigation. Sprinklers failed or were inadequate. It's possible that the plane strikes severed the water risers. We don't know. But we do know that the fire spread.
Heat from fire will change the properties of steel. It will make it weaker as temperature increases and it will cause it to expand. Engineers allow for heat expansion of bridges to maintain the integrity of the structure. Of course bridges are designed to the range of temperatures of the local climate. Excessive heat can cause roads to buckle.
A reasonable assumption is that the massive fires... fueled by jet fuel and combustible materials inside the structure cause the steel beams in the core to both expand and grow weaker. It's likely that it was the expansion which lead to the collapse of floor slabs.
Beams which are retrained cannot expand, but they could buckle. However beams which are not restrained can exert lateral forces. It's possible that with some columns severed by the plane parts tearing through the building... allowed remaining beams to expand pushing columns which lost some of their lateral support. This possibly could cause those columns to displace laterally and destroy the bearing/alignment with the column below. The effect with be too little bearing area and that would lead to crippling and buckling of webs and flanges.
If this process of expanding columns progresses unabated... the net effect is that there axial load paths are destroyed and the aggregate capacity at the level of the massive fire drops below the minimum required to support what's above. At that instant the above part without adequate support drops... and in one instant a foot print size area of ROOSD mass has been created.
As noted the process was organic and not symmetrical. But the failures likely rapidly spread throughout the footprint and some areas led the collapse and other slightly lagged by small fractions of a second. But in short order the entire structure self destructed. You cannot store ALL the building materials for 10 floors, for example, on the floor slab of one floor. This would collapse the floor and fail the connections of the beams to the columns. ROOSD mass was all the floors above the plane impact zone.
Why model the collapse? Does anyone doubt that placing 12 floor masses on a single floor will cause that that floor to collapse?
Does anyone doubt that a given steel column without any applied loads is height limited and when to tall it self buckles? Isn't that why radio towers / antennas use guy wires?
Physical models of this collapse are for people who are not familiar with structural engineering principals.... or are denying their validity.
++++
There are "unknowables" about the collapse... how it progressed... and where the "structural hollowing out" began and where it moved to. That it happened is a fact.
In the end it turns out that the collapse was completely described by established civil engineering and materials science principals.
There is no need to make a physical model in the case of building performance studies as the performance specifications and limits of the materials and connections is essentially settle science.
What has been called "ROOSD" is hardly a mystery... a given floor spec when over loaded fails and collapses. The beam may "part"... the connections may "part" or either/both depending on the force of the superimposed (destructive load)). In the case of the twin towers... the superimposed destructive load was the floor structure and the superimposed live loads on those floors including contents and people. Contents included furniture and office "materials" as well as partitions and MEP equipment.
Engineering "understands" the fact that a moving mass (descending) exerts a great force than it does as a static load. So we can think of dynamic loading as a sort of force multiplier.
So the "progression phase".... is really "trivial" and well understood engineering. Engineers can compute the threshold load / force which would "overwhelm" the typical twin tower floor system. The safe loads are all set forth in load tables for steel, concrete, wood and so on.
ROOSD by any name is a destruction of the FLOORS not the steel which supported them. There were other mechanisms which led to the failure of the axial load bearing system(s). There were two of those systems... interior columns and perimeter columns. The long span column free office space was a different system than the floor system within the core was was more traditional column grid with girders and beams,
A key point to understand the failure of the axial systems - both core and perimeter columns is how the stability and strength of a column is related to its slenderness ratio. As a column section is made taller... its slenderness ratio increases... x & y dimensions and z (height). The more slender a column is... the weaker and less stable it is. To make slender columns "perform" they require bracing... which reduces the design length z. In a steel frame high rise the floor beams (steel) perform the function of reducing the slenderness ratio. A tall steel structure cannot stand without the columns braced by the steel floor beams. Same concept would apply to a concrete or even a wood structure.
Once ROOSD was in progress the bracing was being striped from the columns. This was seen in images of the spire after the floor slabs had collapsed.
The videos show how both the perimeter/facade columns and the interior core columns collapse from being too slender. This behavior is describe by a process called Euler Buckling. Euler buckling predicts that then a slenderness ratio of a column exceeds a value... determined by what the material is....the column will "self buckle".... it cannot support itself.
So ROOSD floor collapse is settled engineering and the collapse of the columns is likewise understood by Euler's formulae for slender columns. The column collapse was also aided by lateral forces of the growing collapsing floor mass. (similar to the lateral forces that grain exerts on the walls of a silo, or sand in a cardboard container)
So with the collapse phase completely understood by settled engineering... the question to answer becomes how did the ROOSD mass establish? That mass had been supported by the structure... but somehow lost its support and feel and became the driving ROOSD force which only got larger as it "consumed/destroyed" each successive for on its way to the ground.
The planes did damage swaths of several floor and this did free up some material will in fact did fall. However this was not sufficient mass even locally to go "runaway". To form the entire foot print descending ROOSD mass was likely a more "organic" process of expanding structural failures. But we can't see this happening and so we have to speculate what might have been in play.
What we DO know is that post plane strike fire raged without mitigation. Sprinklers failed or were inadequate. It's possible that the plane strikes severed the water risers. We don't know. But we do know that the fire spread.
Heat from fire will change the properties of steel. It will make it weaker as temperature increases and it will cause it to expand. Engineers allow for heat expansion of bridges to maintain the integrity of the structure. Of course bridges are designed to the range of temperatures of the local climate. Excessive heat can cause roads to buckle.
A reasonable assumption is that the massive fires... fueled by jet fuel and combustible materials inside the structure cause the steel beams in the core to both expand and grow weaker. It's likely that it was the expansion which lead to the collapse of floor slabs.
Beams which are retrained cannot expand, but they could buckle. However beams which are not restrained can exert lateral forces. It's possible that with some columns severed by the plane parts tearing through the building... allowed remaining beams to expand pushing columns which lost some of their lateral support. This possibly could cause those columns to displace laterally and destroy the bearing/alignment with the column below. The effect with be too little bearing area and that would lead to crippling and buckling of webs and flanges.
If this process of expanding columns progresses unabated... the net effect is that there axial load paths are destroyed and the aggregate capacity at the level of the massive fire drops below the minimum required to support what's above. At that instant the above part without adequate support drops... and in one instant a foot print size area of ROOSD mass has been created.
As noted the process was organic and not symmetrical. But the failures likely rapidly spread throughout the footprint and some areas led the collapse and other slightly lagged by small fractions of a second. But in short order the entire structure self destructed. You cannot store ALL the building materials for 10 floors, for example, on the floor slab of one floor. This would collapse the floor and fail the connections of the beams to the columns. ROOSD mass was all the floors above the plane impact zone.
Why model the collapse? Does anyone doubt that placing 12 floor masses on a single floor will cause that that floor to collapse?
Does anyone doubt that a given steel column without any applied loads is height limited and when to tall it self buckles? Isn't that why radio towers / antennas use guy wires?
Physical models of this collapse are for people who are not familiar with structural engineering principals.... or are denying their validity.
++++
There are "unknowables" about the collapse... how it progressed... and where the "structural hollowing out" began and where it moved to. That it happened is a fact.
In the end it turns out that the collapse was completely described by established civil engineering and materials science principals.
Once I hit on the idea of using Upwork, I realised this ostensibly rhetorical question actually has measurable, economic answer. The question is how crazy would you have to be to spend how much money hiring an engineer to design a structure to meet Hoffman's challenge?
Implicit in this is that there must be enough disposable income out there to do it even if just for fun, grift, pure entertainment, or to satisfy brute curiosity. Yet, no one does it. This seems to suggest that it can't be done (i.e., seems to support the OP claim). All it would take is a little a pooling of people's disposable income.
Moreover, leave aside the cost of building the structure, we don't even have the drawings. Surely, if it's "in principle easy" then it's a small matter of hiring a reasonably qualified engineer looking to make some easy cash to get a good set of blueprints?
I raise these questions in all seriousness. How crazy (or how rich) would I, personally, have to be to spend a few thousand dollars satisfying my curiosity about this, instead of my itch for any number of other things I don't really need (think travel, fine wine, rare books, etc.)? Would my money be spetter spent getting that same engineer to meet my challenge than Hoffman's? (I'd be happier, of course; but is my challenge much harder and therefore much more expensive? Can my challenge be met with a design that would be easier/cheaper to build?) Like I say, these are not rhetorical questions.
Jeffrey Orling
Senior Member
Your challenges show you don't understand physical properties of materials and forces. Math / computational models are more accurate and sensible. Of course, for most people... seeing is believing largely because they don't understand science, math, and engineering.
WASTE OF TIME
CHALLENGE #1:
Build a structure with a vertical aspect ratio of at least 2 (twice as tall as it is wide) and induce it to undergo top-down total progressive collapse.
You can't scale a physical model as it relates to GRAVITY
CHALLENGE #2:
Build a structure with a square footprint and a vertical aspect ratio of at least 6.5 (6.5 times as high as it is wide), and induce it to undergo top-down total progressive collapse.
You can't scale a physical model as it relates to GRAVITY
CHALLENGE #3:
Build a structure as required by CHALLENGE #2 which, in the process of collapsing, will throw pieces outward in all directions such that at least 80% of the mass of the materials ends up lying outside of the footprint, but their center of mass lies inside the footprint.
You can't scale a physical model as it relates to GRAVITY
CHALLENGE #4:
Build a structure as required by CHALLENGE #2 which is capable of remaining intact in 100 MPH cross wind.
Mechanical forces do not scale
CHALLENGE #5:
Build a structure that meets the requirements of both CHALLENGES #3 and #4.
You can't scale a physical model as it relates to GRAVITY and Mechanical forces do not scale
WASTE OF TIME
CHALLENGE #1:
Build a structure with a vertical aspect ratio of at least 2 (twice as tall as it is wide) and induce it to undergo top-down total progressive collapse.
You can't scale a physical model as it relates to GRAVITY
CHALLENGE #2:
Build a structure with a square footprint and a vertical aspect ratio of at least 6.5 (6.5 times as high as it is wide), and induce it to undergo top-down total progressive collapse.
You can't scale a physical model as it relates to GRAVITY
CHALLENGE #3:
Build a structure as required by CHALLENGE #2 which, in the process of collapsing, will throw pieces outward in all directions such that at least 80% of the mass of the materials ends up lying outside of the footprint, but their center of mass lies inside the footprint.
You can't scale a physical model as it relates to GRAVITY
CHALLENGE #4:
Build a structure as required by CHALLENGE #2 which is capable of remaining intact in 100 MPH cross wind.
Mechanical forces do not scale
CHALLENGE #5:
Build a structure that meets the requirements of both CHALLENGES #3 and #4.
You can't scale a physical model as it relates to GRAVITY and Mechanical forces do not scale
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Some here say it's easy, trivial; some say it's impossible (yes, often due to scale). The first suggests to me that the OP claim can be simply debunked; the second suggests it should be dismissed. I state both options in the OP.
I take it we all agree that the problem is rooted in a failure to understand science. The question is just how to bring that understanding about.
Jeffrey Orling
Senior Member
Technical understand is for those who "need to know"... You don't have to know all the technical matters to get on a plane and fly from here to there. You don't need to understand meteorology to decide whether to play golf of go sailing, or understand a computer or how a cellphone works to use one.
People who are intelligent and inquisitive will inform themselves of matters of science and specific technical matters... which interest them. To understand a person needs to educate themselves and technical knowledge is built on a base. No short cuts to the top.
Most people are content to go through life ignorant because most knowledge has no benefit to their lives.
I found it interesting that a biologist of good reputation fell for truther nonsense. It illustrates how intelligent people can act stupid because of limited technical knowledge and training. Civil engineering and physics are of no use to that biologist. Yet many intelligent people want their ignorant ideas accepted because they have a degree from a university or a licence in architecture.
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deirdre
Senior Member.
You dont need to be intelligent. Just inquisitive.
(and ps Thomas, inquisitive means following through to find out/educate yourself...not just repeating "i dont understand how contrails form, how can we make this easier to understand?", when people are telling you how they form but you are too lazy/not-inquisitive to listen and learn)
It's the bane of teachers everywhere. Uninquisitive, uninterested students.
Jeffrey Orling
Senior Member
So to bring this to the confounding building collapses on 911....
Buildings/structures do not fall down without cause
Causes may include:
weakening of connections cause by corrosion/aging/failure to maintain
earth quakes
explosions which damage structure sufficiently
out of spec environmental extreme conditions
mechanical destruction of (impacts with) axial supports (columns)
On 911:planes with enormous kinetic energy impacted the twin towers
fires raged without mitigation in all 3 towers
Few to no high rises have massive fires without mitigationJohn and Jane Q. Public have little to no understanding about how structures "work" and no understanding of how progressive failures work in structures which are complex systems. ALL complex systems are subject to runaway progression of failures leading to total system collapse. This was seen in the recent TX electric system collapse.
Keith Beachy
Senior Member
This Challenge was done in the 70s, two full up model, WTC1, and WTC2... then on 9/11 they collapsed as seen on video. Challenge complete!
I think if Jim Hoffman understood the structure of the WTC, he would not make his absurd challenge.
Hoffman does not understand the structure of the WTC towers, which is not surprising based on the massive amount of misinformation posted at his website. The towers collapsed after initiation because a floor in the WTC can only hold 29,000,000 pounds, and the upper section weighed more than 29,000,000 pounds, plus the upper section mass was moving. Each floor failed in turn as each was overloaded. The failure as the mass hit each floor essentially instant, resulting in a simple momentum mass problem reflected by the collapse timing. Part of the core seen standing failed as it was void of lateral support (aka the shell, which was fastened to the core by floors). NIST figured this out, Leslie Robertson knew this in 1970s. The 29,000,000 pounds a floor can hold could be estimated by examining the floor connections, like NIST did. Even a layperson could spend time to investigation and figure out a rough estimate of the connections, and come up with some figure for floor failure, if they took the time and energy to do learn, study, and do it. The NIST faq on tower collapse talks about this in more detail, not to mention the entire thousands of pages of NIST's work on the WTC. ( https://www.nist.gov/topics/disaste...vel of collapse initiation in both WTC towers.)
The challenge is proof Jim does not understand the WTC tower structure. He failed to study the WTC towers to understand why it collapsed after the initial upper floors failed.
Floors in the WTC do not offer support for upper floors, the floors are hanging on (connected to) the core and shell. The core and shell share the gravity load of the floors almost equally. This is simple to understand, rendering the challenge ridiculous. Making up the challenge is easy, a little more than the time to type it up... understanding the structure of the WTC takes more effort.
This is precisely why it seems like it would be easy to build a simple structure that demonstrates these principles with loads in the 1-3 pound range. Why does this need millions of pounds to work? Just make a weaker lower structure with weaker floor connections. Like you say, it's "a simple momentum mass problem". (You don't have to go to the moon to demonstrate the basic principles of rocket science.)
I lean to Keith's understanding of this. The principles that need to be explained to laypeople are pretty simple. The WTC towers did not collapse under the weight of their complexity; they were simply overloaded. What puzzles me is that these simple mechanisms can't be demonstrated with simple machines in a laboratory or workshop setting.
benthamitemetric
Senior Member
Disproportionate/progressive collapse is a widely studied area of structural engineering and there many highly educated and experienced professionals who are literally every day modeling, based on widely accepted engineering principals and a robust professional literature (which is based in part on actual real-world experimentation with scale models), the propensity of structures to undergo disproportionate/progressive collapse. With a few hundred dollars for academic article access and the use google scholar, you could understand these topics very well from a first principals perspective. Before you try to explain something to laypeople, you should consult with at least one of the people who truly understand the topic and study these issues for a living to ensure you actually fundamentally understand it yourself. Those people are listed as authors on the thousands of academic articles you will find if you search the extant literature re disproportionate/progressive collapses. Why not start there instead of trying to recreate with an arbitrary experiment the massive foundation of knowledge that those experts have already built over the decades of their professional lives?
econ41
Senior Member
That inability to visualise has been a persistent problem with debate of WTC 9/11 collapses. You are spot on target with those two observations Deirdre "...some people cant ,or haven't tried to, envision (1) what is happening behind the debris skirt. or (2) what is happening INSIDE the outside walls."
In the early days, pre about 2009, when "both sides" were struggling to understand the rapid collapse of the Twin Towers both sides got it wrong. Because they could not - did not - "envision what is happening behind the debris skirt".
"Truthers" then as now were obsessed with the false presumption that "Free Fall proves CD". (It doesn't.) "Debunkers" were mostly led astray by misunderstanding Bazant (Bazant & Zhou - 2001-2, the "limit case" paper).
The debunker side split into two schools in 2008 and the two pursued different tracks but the same fundamental error. They looked at the gross overall mechanism. And NEVER asked what really happened "...INSIDE the outside walls". Many debunkers still cannot accept that Bazant could be and was wrong on some of his explanations. Many still kow-tow to academia and professional papers which are of no relevance to explanations intended for lay persons. And despite all the shifting of goalposts that @Thomas B engages in he is clear that the target audience is lay persons and the purpose is explaining to those lay persons.
Mick modeled the key feature in his project a few years back. I first explained it in 2007 with this crude graphic:
My graphic and Micks modelling explain the same feature. The same explanation was put into mainstream debate by a couple of agnostic researchers who started from truther side concerns. The labelled it ROOSD (Runaway Open Office Space Destruction) - a descriptive acronym which has been ridiculed by debunkers who cannot acknowledge that some truthers can be correct. So that is what actually happend and whenever @Thomas B finally firms up as to which challenge he wants to discuss >> the model will need to comply with ROOSD OR Micks Model OR my graphic.
I'm not aware of any professional or academic paper that is aimed at or suitable for the lay person audience subject of this thread.
Oystein
Senior Member
The main question I ask is: What would we learn about the events of 9/11 when an money and resources have been spent and the Rube Goldberg machine built that meets the challenge - would we have learned more than nothing at all about the actual WTC collapses of 9/11?
My main claim is that the challenges set arbitrary targets.
Oystein
Senior Member
It is easy, in principle, to meet the challenge via a Rube Goldberg machine - i.e. a model that has as its purpose to meet arbitrarily set target, as opposed to understanding the WTC collapses. Such a model would of necessity by almost comically different from the WTC towers, and would not educational about the events of 9/11.
It is very difficult to build actual scale models of the WTC towers that behave like the originals, in displaying the same failure modes due to the same reasons with the same results. Such a model, while being instructive and educational, might very well not meet the challenge.
What we would learn from such a situation is not that the theories of how the towers collapsed are bad, but that the challenges are bad.
Oystein
Senior Member
I think you don't appreciate just HOW damned weak and brittle such a human scale structure would have to be to mimic the behavior of the full scale originals under the same gravity.
It would be easier if we could build a 1:200 model and test it in a gravity field 200 times stronger than planet earth's (or 40,000 times stronger? I haven't thought that through). It is kind of important that, between consecutive floor slabs, gravity can pull the entire 11 feet 8 inches before falling slab runs into the next static slab.
I think large centrifuges exist that might accommodate our model to expose it to 200g, but renting such a centrifuge for, say, a day would be costly.
Oystein
Senior Member
These simple mechanisms can be demonstrated with simple machines, like Mick did with his model with magnets for structural connections: Mick actually demonstrated a principle.
Your of Hoffman's challenge do not seek to demonstrate a principle. They instead seek to reach an arbitrary set of data points, no matter how educational or noneducational the winning Rube Goldberg machine may turn out to be.
econ41
Senior Member
A word of caution. The original goal was to build something that could be used to explain collapses to uninformed lay persons. And that specific sub set of lay persons who need explanation in the form of physical models. The goal was for "we" to have a model to help explain what we already understood to persons who did not understand what we already knew.
IF the goal is to become something that "we" - those informed on WTC collapses can benefit from - that is a fundamental change of objective. (and - I'll anticipate an obvious "yes - but" IF the we is inclusive of both "us" the informed and the uninformed lay original target.)
So - if "we" are to be the target the challenge is very different. And fundamentally different to the OP topic.
And:
Yes. And we still have not firmed up the choice or definition of challenge. We need to fix the goalposts.
The two issues for this discussion remain as:
(1) Defining the parameters of the challenge; AND
(2) Defining the target "audience"
econ41
Senior Member
As did my graphic of 2007, as did ROOSD in 2009. All three demonstrate or at least describe the same principle. They use different modes of presentation. Mine visually, ROOSD by word descriptions and Mick's by physical modelling.
But all three illustrate the same principle. Mick's the more appropriate for this OP topic because the audience is implicitly that demographic sector of lay persons who are not good at visualising and need physical modelling.
FatPhil
Senior Member.
Isn't the "progressive" - or is that better described as "unstoppable"? - nature of the collapse most easily demonstrated by one of those trashy karate tile-breaking demonstrations where there are pencils between the tiles? If there's nothing to diminish the stress that reaches the lower layer, the thing that was great enough to cause the higher layer to fail will cause the lower layer to fail too. In order for that to not happen, one would need a believable mechanism for the stress to diminish at subsequent levels, as the failures accumulate on top of it. That seems like the place where the burden of proof would lie.
I could be horribly wrong, it's late, and I've possibly misunderstood some of the arguments by the CTers.
I could be horribly wrong, it's late, and I've possibly misunderstood some of the arguments by the CTers.
econ41
Senior Member
Agreed near enough on "progressive" >> "unstoppable". There are different "school of thought" on the definition of "progressive". For some it includes both stoppable and unstoppable. BUT the distinction maters not for WTC - all three WTC collapses were unstoppable.
I'll suggest a different perspective on "easily demonstrated" And I'll take a bet that some (most??) will disagree with me - either explicitly or by ignoring my comment.
It is NOT a technical problem per se and we are seeing "technical people" suggest solutions to what is an issue of behavioral psychology and cognition.
The need is for something which helps a specific group of persons understand. The persons of that target group NEED physical models because they have limitations of visualising skill which the model overcomes. Which means the model should (probably "must") visually resemble what is being explained. Using a differnt physical layout to present a similar - generic similar - process actually reintroduces a need for visualising. It asks a person whose visualising skills are limited to apply visualising skills. The target audience person needs to visualise what the alternate model would look like when translated into the original setting. i.e. it requires the one area of skill where the target is by definition limited.
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benthamitemetric
Senior Member
To reinforce my point that the actual principles at issue are tested and demonstrated constantly, here is one of the tens of thousands of academic articles written in the past 20 years on the subject of disproportionate/progressive collapses. Here's the abstract:
This is how the incredibly robust understanding of these issues has been developed: through carefully constructed numerical models that are rigorously tested against carefully controlled experiments. Just go to Google Scholar and start searches for "progressive collapse" (the more common term) or "disproportionate collapse" to see that I am not exaggerating the extent of this literature.
So while the argument rages on here about whether some arbitrary model can be made to show some arbitrarily chosen facets of a single known case of progressive collapse (and this isn't knock on those engaging in that argument in good faith), it just seems to me the forest is being completely missed for the trees. It's like standing outside of SpaceX or NASA while arguing about whether a very specific subtype of rocket that you sketched on a napkin could theoretically fly if built. Just go in and ask. Doubtlessly someone inside has already thought about whatever issue with your doodle is troubling you. (Google Scholar is SpaceX/NASA in this metaphor, in case that's not clear.)
This is how the incredibly robust understanding of these issues has been developed: through carefully constructed numerical models that are rigorously tested against carefully controlled experiments. Just go to Google Scholar and start searches for "progressive collapse" (the more common term) or "disproportionate collapse" to see that I am not exaggerating the extent of this literature.
So while the argument rages on here about whether some arbitrary model can be made to show some arbitrarily chosen facets of a single known case of progressive collapse (and this isn't knock on those engaging in that argument in good faith), it just seems to me the forest is being completely missed for the trees. It's like standing outside of SpaceX or NASA while arguing about whether a very specific subtype of rocket that you sketched on a napkin could theoretically fly if built. Just go in and ask. Doubtlessly someone inside has already thought about whatever issue with your doodle is troubling you. (Google Scholar is SpaceX/NASA in this metaphor, in case that's not clear.)
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