Has anyone seen a realistic explanation for "Progressive Collapse"

[William Rea]

FEMA - "The buildings structural system, composed of the exterior loadbearing frame, the gravity loadbearing frame at the central core, and the system of of deep outrigger trusses in the upper stories, was highly redundant."

FEMA - "The exact extent of this damage (to the structures after impact of the aircraft) will likely never be known with certainty."

I am not putting forward nor am I proscribing to any alternative to the observed collapse as seen in video recordings from countless sources.

I want a realistic explanation as to why "Progressive Collapse" occurred considering the construction of the building and the amount of damage it bore on 9/11.

 

[uk_dave]

Highly redundant means the structure can survive with a certain number of structural members removed.

It follows that a structure cannot survive with a certain number of structural members removed. The redundancy is designed for a given worst case scenario. If the damage exceeds the design, the building will fail.

If you manufacture a table with 4 legs, it will fall over if 1 leg is removed. This would be classed as disproportionate collapse if the likelihood of one leg being removed is great enough. So you design the table to have 6 legs. That way, if 1 is removed the other 5 will maintain a degree of stability long enough for you to either repair it or clear off the good china.

But if the damage to the table exceeds the designed redundancy and 3 legs are removed, it still falls over and the china gets smashed.

If you're lucky the table might only get 2 legs removed and again you might have time to repair it. But if some bugger comes and sets light to 1 of the remaining legs..... well you know what happens then.

Once the table starts to fail (I can see this analogy starting to fail right now) the stress on the remaining legs will also exceed the design. So over it goes and there goes your dinner.

I hope that helps.

Kinda

 

[Spins]

FEMA - "The exact extent of this damage (to the structures after impact of the aircraft) will likely never be known with certainty."

Computer simulations by Purdue University give us a good idea of the extent of the damage caused by the plane impact...

The researchers are analyzing how many columns were destroyed initially in the building's core, a spine of 47 heavy steel I-beams extending through the center of the structure, Sozen said.
"Current findings from the simulation have identified the destruction of 11 columns on the 94th floor, 10 columns on the 95th floor and nine columns on the 96th floor," he said. "This is a major insight. When you lose close to 25 percent of your columns at a given level, the building is significantly weakened and vulnerable to collapse."

...taken from the following article...

http://www.sciencedaily.com/releases/2006/09/060911153219.htm

...here is the link to the simulation...

http://www.cs.purdue.edu/homes/cmh/simulation/phase3/index.html

...hope this answers some of your questions about the damage.

 

[Cuddles]

I am not putting forward nor am I proscribing to any alternative to the observed collapse as seen in video recordings from countless sources.

I believe the term you're looking for is "just asking questions".

 

[Arkan_Wolfshade]

FEMA - "The buildings structural system, composed of the exterior loadbearing frame, the gravity loadbearing frame at the central core, and the system of of deep outrigger trusses in the upper stories, was highly redundant."

FEMA - "The exact extent of this damage (to the structures after impact of the aircraft) will likely never be known with certainty."

I am not putting forward nor am I proscribing to any alternative to the observed collapse as seen in video recordings from countless sources.

I want a realistic explanation as to why "Progressive Collapse" occurred considering the construction of the building and the amount of damage it bore on 9/11.

What specific questions do you have unanwered by the available information from FEMA, NIST, and other engineers analysis?

 

[realitybites]

I've never understood why the progressive collapse proves to be so difficult for people to get their brain around it.

Redundant does not equal invincible.

Half the time it seems the conspiracy crowd is 2 seconds away from thinking that not only should the buildings have withstood their respective kinetic loads to the point of halting the collapse, but they should've been able to push the top 20-30 floors back up and magically repaired themselves.

 

[Z]

I've never understood why the progressive collapse proves to be so difficult for people to get their brain around it.

Redundant does not equal invincible.

Half the time it seems the conspiracy crowd is 2 seconds away from thinking that not only should the buildings have withstood their respective kinetic loads to the point of halting the collapse, but they should've been able to push the top 20-30 floors back up and magically repaired themselves.

You kid, but I've actually had someone try to convince me that skyscrapers have innovative automatic repair systems in them, just in case... and that the Twin Towers would NEVER have fallen, since the ARS would have shorn up any major structural damage.

Of course, this fellow also thought those big power lines out in the country side were designed to walk (hence, their general bipedal appearance) in case of earthquake or other disasters...

Some people will believe anything.

 

[Dog Town]

Half the time it seems the conspiracy crowd is 2 seconds away from thinking that not only should the buildings have withstood their respective kinetic loads to the point of halting the collapse, but they should've been able to push the top 20-30 floors back up and magically repaired themselves.

Like a tree full of elves?

 

[Bell]

It's a realistice explanation

 

[Darth Rotor]

FEMA - "The buildings structural system, composed of the exterior loadbearing frame, the gravity loadbearing frame at the central core, and the system of of deep outrigger trusses in the upper stories, was highly redundant."

FEMA - "The exact extent of this damage (to the structures after impact of the aircraft) will likely never be known with certainty."

I am not putting forward nor am I proscribing to any alternative to the observed collapse as seen in video recordings from countless sources.

I want a realistic explanation as to why "Progressive Collapse" occurred considering the construction of the building and the amount of damage it bore on 9/11.

Get a bunch of popsicle sticks. Build a four story tower with them. Drop a bowling ball on it. Or, drop a brick on it from a 6 inch height. The tower will collapse.

That is what dropping a 20 story building on top of a single floor's supports does. The progressive collapse is the serial failure of each floor's support structure, with the mass of the 20 story building being added to with each blow, and with energy strain weakening the iron members with each successive blow as it is transmitted through the structure vertically, and through the metal connecting points.

DR

 

[Peephole]

I'd suggest you read the bazant and verdure paper:

Abstract:
Progressive collapse is a failure mode of great concern for tall buildings, and is also
typical of building demolitions. The most infamous paradigm is the collapse of World Trade Center
towers. After reviewing the mechanics of their collapse, the motion during the crushing of one floor
(or group of floors) and its energetics are analyzed, and a dynamic one-dimensional continuum model
of progressive collapse is developed. Rather than using classical homogenization, it is found more
effective to characterize the continuum by an energetically equivalent snap-through. The collapse,
in which two phases-crush-down followed by crush-up-must be distinguished, is described in each
phase by a nonlinear second-order differential equation for the propagation of the crushing front of
a compacted block of accreting mass. Expressions for consistent energy potentials are formulated
and an exact analytical solution of a special case is given. It is shown that progressive collapse will
be triggered if the total (internal) energy loss during the crushing of one story (equal to the energy
dissipated by the complete crushing and compaction of one story, minus the loss of gravity potential
during the crushing of that story) exceeds the kinetic energy impacted to that story. Regardless of
the load capacity of the columns, there is no way to deny the inevitability of progressive collapse
driven by gravity alone if this criterion is satisfied (for the World Trade Center it is, with an order-
of-magnitude margin). The parameters are the compaction ratio of a crushed story, the fracture of
mass ejected outside the tower perimeter, and the energy dissipation per unit height. The last is the
most important, yet the hardest to predict theoretically. Using inverse analysis, one could identify
these parameters from a precise record of the motion of floors of a collapsing building. Due to a
shroud of dust and smoke, the videos of WTC are useless here. It is proposed to obtain such records
by monitoring the precise time history of displacements in different modes of building demolitions.
The monitoring could be accomplished by real-time telemetry from sacrifcial accelerometers, or
by high-speed optical camera. The resulting information on energy absorption capability would be
valuable for the rating of various structural systems and for inferring their collapse mode under
extreme fire, internal explosion, external blast, impact or other kinds of terrorist attack,
as well as earthquake and foundation movements.
http://www.civil.northwestern.edu/people/bazant/PDFs/Papers/ProgressiveCollapseWTC-6-23-2006.pdf

 

[einsteen]

I don't think so

http://members.lycos.nl/einsteen/wtc1/

btw when I posted this at the Loosers it wet down, conspiracy ?

 

[Gravy]

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.

 

[Muckar-duva]

I'm going to order the "Why buildings fall down" book. I can't really debate in any satisfying manner as matters are now.

I've spent some time reading http://www.mindfully.org/Reform/2006/911-WTC-NIST-Lies30mar06.htm

...to be able to continue a debate elsewhere- and I think I threw up a little in my mouth. It's the same thing, over and over again, and I really just need to be able to remember some numbers in order to reply, but it's so... tiresome.

Gravy, I don't get how you manage it. Kudos.

 

[Bell]

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.

It's only because one of the writers was involved with both books.
Because it looks like one book is the rebutal of the other

 

[Gravy]

I don't think so

http://members.lycos.nl/einsteen/wtc1/

btw when I posted this at the Loosers it wet down, conspiracy ?

einsteen, you keep pointing out that in papers such as Greening's, the upper "block" of the towers is assumed to be infinitely strong. I think a fundamental mistake made on both "sides" of this argument is to oversimplify by thinking of the upper mass as acting like a "block." The fact that it doesn't behave that way makes it much more – not less – destructive.

I recall someone on Brumsen's forum arguing that even if a floor or two were removed magically from the towers, the upper columns should have come to rest on the lower, which would have borne the weight, as below:

|||||||||||
xxxxxxxx remove floor or floors
|||||||||||

Result, as if the upper columns were guided on rails to meet perfectly with the lower:
|||||||||||
|||||||||||

But of course we know that's not what happens. The upper portion does not act as a solid block on the lower, and vice-versa. The columns are not perfectly aligned. The forces are not perfectly vertical.
||||||||||||
\|||||( {/|\
||||||( ))|/
||||||||||||

Even considering only the vertical component, misaligned columns in a falling section mean the swift destruction of two floors, not one, and the plastic deformation of many intact columns on those floors. The "pancake" analogy is a poor one, especially if we're talking about American or Canadian pancakes! The 4" (10cm) concrete in the WTC floors had a thickness to width ratio that made them more analagous to a very thin crepe.

Then we have enormous lateral and torque loads created by the falling mass, which is also leaning and twisting (both towers). No simplified analysis can account for these forces. We're talking about millions of variables. I don't think the analysis that you linked to above is helpful in understanding what happened in the real world on 9/11.

 

[Arkan_Wolfshade]

Okay, Gravy's breaking out ASCII art. I think it's time we pitched in and sent him on vacation for a week. I'm thinking Cancun.

 

[Bell]

Okay, Gravy's breaking out ASCII art. I think it's time we pitched in and sent him on vacation for a week. I'm thinking Cancun.

I've got 2 cents laying around somewhere. I was saving them for another thread, but what the hell.

 

[William Rea]

Get a bunch of popsicle sticks. Build a four story tower with them. Drop a bowling ball on it. Or, drop a brick on it from a 6 inch height. The tower will collapse.

That is what dropping a 20 story building on top of a single floor's supports does. The progressive collapse is the serial failure of each floor's support structure, with the mass of the 20 story building being added to with each blow, and with energy strain weakening the iron members with each successive blow as it is transmitted through the structure vertically, and through the metal connecting points.

DR

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?

 

[Hellbound]

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?

THAT is supposed to be analogous?

*chuckle*

You have no idea how strutural strength scales in comparison to mass, do you?