Has anyone seen a realistic explanation for "Progressive Collapse"

Oh, come on Huntsman, isn't it intuitively obvious that if you dropped a 20 story office building onto another building, it would just bounce off and not damage the other building at all????

;)
 
Gravy said:
The Bazant paper is good, although the math is beyond me. I also recommend NIST's paper "Best Practices for Resisting Progressive Collapse in Buildings (draft)" A good layman's treatment is in the book Why Buildings Fall Down, by Mattys Levy and Mario Salvadori. I also highly recommend Salvadori's Why Buildings Stand Up.
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Despite the mathematics the Bazant paper is speculation which even the author is honest enough to admit to.

The NIST paper is at best a compendium of what should be done versus risk perception/hazard versus cost. At worst it could be percieved as a veiled accusation that the Architects and Engineers on the WTC were incompetent. I know for sure that when my Boss asks me to write a "Best Practice" paper somebody is percieved to have screwed up.

It's like progressive failure didn't exist before the WTC collapsed.

The two books I may investigate but reading the prefaces I didn't see anything relevant to WTC.
 
William Rea said:
The two books I may investigate but reading the prefaces I didn't see anything relevant to WTC.
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The topic is progressive collapse. You seem to think the subject wasn't seriously considered before 9/11. You are wrong. The books, which are nontechnical, talk about that at length.
 
William Rea said:
Your analogy is not analogous.

I suggest you should make a 100 story structure out of popsicle sticks, make a cut through the top 20 or so floors while holding onto them and then release them.

I am being generous in the experiment by allowing you to cut through ALL the popsicle sticks.

What do you think would happen then?
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Are we allowed to set light to the popsicle sticks?
 
William Rea said:
Your analogy is not analogous.

I suggest you should make a 100 story structure out of popsicle sticks, make a cut through the top 20 or so floors while holding onto them and then release them.

I am being generous in the experiment by allowing you to cut through ALL the popsicle sticks.

What do you think would happen then?
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Given that the dimensions don't scale with the materials, and the falling mass is a critical variable -- thanks to the differences in density between wood and concrete, and steel -- not a whole lot. You'd have to first scale down the width of the popsicle sticks to aproximate the force/mass/Young's modulus relationships, then rig a series of connecting popsicle sticks, sanded to small radii, to model the floor, and quite frankly, I don't have the time to waste on that. Modeling the entire structure is not a trivial exercise.

Your rejoinder is empty, for the above mentioned reasons, but thanks for playing.

DR
 
roger said:
Oh, come on Huntsman, isn't it intuitively obvious that if you dropped a 20 story office building onto another building, it would just bounce off and not damage the other building at all????

;)
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Of course!

This must be the reason for those "Astropop" popsicles! It's all so clear.

NASA is going to use them to make the cable for their space elevator!
 
Darth Rotor said:
Given that the dimensions don't scale with the materials, and the falling mass is a critical variable -- thanks to the differences in density between wood and concrete, and steel -- not a whole lot. You'd have to first scale down the width of the popsicle sticks to aproximate the force/mass/Young's modulus relationships, then rig a series of connecting popsicle sticks, sanded to small radii, to model the floor, and quite frankly, I don't have the time to waste on that. Modeling the entire structure is not a trivial exercise.

Your rejoinder is empty, for the above mentioned reasons, but thanks for playing.

DR
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So we just proved that your analogy and mine were both worthless and entertained huntsman enough for him to make another hopeless attempt at undermining my argument using that used razor blunt wit of his.
 
William Rea said:
So we just proved that your analogy and mine were both worthless and entertained huntsman enough for him to make another hopeless attempt at undermining my argument using that used razor blunt wit of his.
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Ha ha!

I have been pierced to the quick!

Touche!

Although I'm suprised you didn't go with the classic "I know you are but what am I?"

Well played!
 
What about the "analogy" of 20 or so floors of a very, very wide office building falling onto a steel core office building?
 
Gravy said:
The topic is progressive collapse. You seem to think the subject wasn't seriously considered before 9/11. You are wrong. The books, which are nontechnical, talk about that at length.
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I didn't say that at all!

The subject of progressive failure (or as we have it specifically for buildings progressive collapse) is fundamental for designers. I studied progressive failure from crack propogation and growth 20 years ago.

My point was that it appears to now be a cause of so much concern when engineers have known about this type of failure for years. I drew back from saying it in my post but I will say it now, the NIST "Best Practice" also looks like a publicity exercise to make it look like something is being done when it always has been!
 
Huntsman said:
LOLOLOLOLOLOLOLOLOLO

lik thats reel!!1!

ther wuz no bulding 2 fall!!! an arplan hit it!!!111!!!!one!!!

LOLOLOLOL

u didnt even us chikin wire!!!1!eleven!!

[/CTer]

:D
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You keep doing that and it will freeze that way someday.
 
Gravy said:
The topic is progressive collapse. You seem to think the subject wasn't seriously considered before 9/11. You are wrong. The books, which are nontechnical, talk about that at length.
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OK, I kind of assumed that everyone would get the gist of the topic and make the direct link to 9/11 from my first post. Shall I change the title for the benefit of people who don't read the whole thread before posting in it?
 
William Rea said:
OK, I kind of assumed that everyone would get the gist of the topic and make the direct link to 9/11 from my first post. Shall I change the title for the benefit of people who don't read the whole thread before posting in it?
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Was it a 'gotcha' question that....didn't?
 
The lastest edition of Why Buildings Fall Down does include a chapter on WTC.

Progressive collapse really came into engineering consciousness with the Ronan Point disaster in 1968. However, building codes are VERY ambiguous...with a general statement on "building integrity" being the rule of the day until after the Alfred P. Murrah federal building bombing, and then the progressive collapse "discussion" in ANSI/ASCE 7 got a bit larger. Still progressive collapse provisions are largely left up to the designer in terms of analysis and interpretation, which is why we are seeing discussion and best practices recommendations come out. Worth noting that engineers generally speak of "resisting" progressive collapse as opposed to "preventing" progressive collapse - as WTC very decidedly demonstrated, there is a point at which progressive collapse is inevitable.
 
William Rea said:
I didn't say that at all!

The subject of progressive failure (or as we have it specifically for buildings progressive collapse) is fundamental for designers. I studied progressive failure from crack propogation and growth 20 years ago.

My point was that it appears to now be a cause of so much concern when engineers have known about this type of failure for years. I drew back from saying it in my post but I will say it now, the NIST "Best Practice" also looks like a publicity exercise to make it look like something is being done when it always has been!
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Based on the words in the NIST papers I have read on the WTC, it seemed to me that NIST was doing the standard "how can we do this stuff better" bit that engineers have been doing for a very long time. Your last line on "re- inventing the wheel" made me grin. :D


DR
 
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