|
|
 Originally Posted by OngBonga
Sure, but the structural integrity of the building went from 100% to 0% in a very short amount of time. That does not support the idea that there was a gradual weakening, which one would expect under the circumstances. It implies that once the stress reached critical point, that once collapse was inevitable, it was almost instantaneous. We also have the problem of what should be an uncompromised steel structure below the impact level and the range of the fire completely failing to support the collapsing mass, not even to the point of tipping it.
What do you mean by "very short amount of time?"
Note: the collapse of each building took tens of minutes from impact to critical failure.
***
F = ma = dp/dt
dp/dt is change in momentum with respect to time.
When a single floor collapses, it slams down into the floor below. It delivers significant momentum in a short time, causing a spike in the reaction forces which support the floor it slams into. The delivers a wave of stress through the entire structure of the building. The wave moves at the speed of sound through the various materials. If any parts of the structure are pushed beyond their yield stress, either due to prior weakening or simply the magnitude of the stress, then they will permanently deform. This displaces the stress from those supports to other supports, which are now bearing more load. If those supports were previously weakened, by whatever means, then they are notably more likely to yield, themselves. Rinse and repeat.
If that lower floor later falls, then the effect is repeated, but multiplied by the added weight of 2 falling floors worth of debris. This usually leads to complete collapse of the entire building in a process called - I'm not making this up - pancaking. It is extremely likely that the process will destroy the structural core of the building where the floors are collapsing, which drops the whole top of the building, at which point... it's all over.
It is very true that once the collapse is begun, it happens quite rapidly. The collapse of the structure due to overloading travels through the structure at the speed of sound in steel. This will look "instantaneous" on a seconds-based time scale. Slow it down enough, and you'd see a wave of failures pass through the structure, each failure making the next failure more severe.
Originally Posted by OngBonga
I find it intruiging that an educated physician can accept such a uniform and rapid collapse of a reinforced steel stucture due to impact and fire at the top of the structure. It just seems so implausible. Especially given we're supposed to believe a passport managed to emerge from the rubble intact.
I mean come on.
[...] removed 'cause not physics-related
Physicist - not physician. Unless you're talking about someone else besides me.
I only speak for myself, not any club or group or otherwise.
It's not like the entire building went up in flames. Much of the structures never burned, just fell.
It would be implausible if there wasn't a fair amount of debris that was mostly unscathed by the fall due to the randomness of it all and some bits would just have "gotten lucky" in how they came down. It's perfectly reasonable that a bit of paper could have been sandwiched in between 2 things which prevented Oxygen from getting to it, and therefore, it couldn't burn.
What's intriguing to me is that I can offer you a step by step reason for why every step of the process is plausible. I can do so in ways that you can personally test to determine whether or not I'm fooling you. Yet, you do not perform the tests, and you say I'm fooling you, and that it is not plausible.
But then I can talk GR where I'm hard pressed to present you any way you could test it yourself, and you accept what I tell you and do not accuse me of fooling you.
*shrug*
People are strange.
|
Reply With Quote
