Merged Applicability of Bazant's model to the real world

[1stClassAlan]

Well, as folks say - twelve years on and the debate continues - may be, even takes a few backward steps!

I Emailed and, I point out - received a vast reply from Mr Bazant within days of him producing his first "crush up/ down" tome - because I took great issue with the whole idea of "pancake" collapse - if it happened at all - I didn't see it and nor did anyone else, shrouded as it was in a dust cloud.

What could be seen was the outside tube walls disintegrating into their original single components or sections of components - all peeling away from the core, similar to a doughnut sliding down a broomhandle! This sliding doughnut progresses to the ground or at least - out of sight behind other buildings - to leave quite tall core columns standing fully connected waving about - these eventually fall still mostly connected and those that can be seen to fall out of the dust cloud do not break up till almost horizontal.

This is not a global crush up/ down in action - it's just individual joints being overwhelmed one by one ( despite this happening very quickly).

In my experience ( nearly fifty years ) in all building types - construction materials arrive on site in various sizes bits to be fixed together - the structure that slowly rises is mainly an illusion of stability and strength - when usually there is very little stopping them separating and tumbling to the ground.

The Conspiracists can't take that in because they are mainly idiots with political agenda but then the Engineers are seemingly mystified as to why the damn things fell down which regardless of why - must be the most embarassing happening the profession has ever had to endure - I'd say on a par with the British surrender of Singapore, the Russians backing down and taking their missiles off Cuba and the American pull out from Siagon in 1975 - all rolled into one.

 

[beachnut]

... the Engineers are seemingly mystified as to why the damn things fell down which regardless of why - must be the most embarassing happening the profession has ever had to endure - I'd say on a par with the British surrender of Singapore, the Russians backing down and taking their missiles off Cuba and the American pull out from Siagon in 1975 - all rolled into one.

BS, the engineers are not mystified. You might be, but not engineers.

 

[Grizzly Bear]

Well, as folks say - twelve years on and the debate continues - may be, even takes a few backward steps!

I Emailed and, I point out - received a vast reply from Mr Bazant within days of him producing his first "crush up/ down" tome - because I took great issue with the whole idea of "pancake" collapse - if it happened at all - I didn't see it and nor did anyone else, shrouded as it was in a dust cloud.

You've conflated the "collapse initiation" theory with the the "collapse progression"

The "pancake collapse theory" was a theory about the collapse initiation premised on the floor systems giving way successively during the time the building's burned, leaving the supporting columns unrestrained against lateral forces and eccentric loading and thereby initiating the collapse.

During collapse progression it happened and there's little to discuss at that point because it wasn't stopping anyway.

This is not a global crush up/ down in action - it's just individual joints being overwhelmed one by one ( despite this happening very quickly).

Sounds to me like you're over-analyzing the scope of Bazants' work. He laid out specific conditions for a limiting case model and the applicability only extends as far as determining if the building's collapse could have been arrested after it initiated under the most ideal circumstances.

What you describe from your own interpretation is essential describing that the collapse involved a progressive propagation of structural failure... I fail to see the problem there...

The Conspiracists can't take that in because they are mainly idiots with political agenda but then the Engineers are seemingly mystified as to why the damn things fell down which regardless of why - must be the most embarassing happening the profession has ever had to endure - I'd say on a par with the British surrender of Singapore, the Russians backing down and taking their missiles off Cuba and the American pull out from Siagon in 1975 - all rolled into one.

I think the buildings represented in many ways the successes of engineering. They were hit by projectiles, severely damaged with tens of stories above the impact points, flash ignited on several floors, with a physically crippled fire suppression system. Yet 99% of the people (below the points of impact) were able to evacuate and survive because the buildings maintained enough of their integrity long enough for everyone to escape. As far as I'm concerned property can be replaced, human life can't... and occupant safety is the core of what building codes get enforced for.

Having the egress paths concentrated within the core wasn't such a good idea and neither was the lack of compartmentalization for fire containment, but I still give credit to the fact that in a situation where the buildings were in serious trouble their designs performed essentially as intended from life safety standpoint anyway...