September 13th, 2018 7:13 PM
WTC
Please don’t dork on my wall.
Not to be too nerdy, but WTC failed at weakest point: holding the floors to the center and perimeter. so it only had to heat the weakest point on one floor sufficiently to lose half its strength and the weight of the stack did the rest.
Pancaking is a very common method of architectural failure and is the principle reason for collapse after exterior wall failure, and foundation failure. In other words, buildings tilt and fall, or collapse and pancake depending upon whether it is built as a honeycomb (apartments) or a stack (office building).
There are MANY regulations in place during the construction of buildings precisely because pancaking is so dangerous during the process. Particularly with buildings that jack the floors into place. There have been calls in the past for prohibiting the practice. I don’t know how common it is today. But it appears that most floors are poured in place today.
WTC was designed with less masonry, more exterior and core columns, with no midpoint columns, but long spans of floor braces covered with concrete. This meant that floor pressure bearing on the joint between column and floor was not distributed across as many columns by short runs but concentrated in core and edge by long runs.
These points only had to soften enough to lose 50% of their carrying capacity. When that happened, the floor sank, exterior columns bowed, and the pressure of the floors above just used gravity and momentum to overload each set of floors below it.
Thus pancaking.
The MIT report is correct – I cannot find any fault with it. I can however attest to the … dunning kruger effect of everyone who disagrees with it.
======UPDATE===
The building was designed to be light. The columns were box-columns of decreasing thickness with height.
The diagram attached helps understand that the building was constructed out of TUBES, like building something out of straws. This is why there are huge pieces of the exterior still standing, because unlike most buildings, the exterior was structural. The pictures of the wreckages show the columns as sheet steel. The attached photo shows the I-beam that connected the box columns and a box column it’s attached to. Heck, just looking at the floor plan shows the tubular structure of the building.
====== UPDATE ====
You don’t understand. I don’t make mistakes. It’s my job.
From the Journal of Materials and Metallurgy
Thomas W. Eagar, the Thomas Lord Professor of Materials Engineering and Engineering Systems
MIT, 77 Massachusetts Avenue, Room 4-136, Cambridge, Massachusetts 02139-4301;
Eagar was the author of the “steel didn’t melt” findings.
The NIST Report is online, and makes the same argument. Heat, buckle, break, pressure, collapse. Eyewitnesses reported that one or more floors ‘in the nineties’ had collapsed. Eyewitnesses reported the buckling of the exterior (Structural) walls. We were all witness to the pancaking.
Damage > Burn > Break > Buckle > Squish > Pancake.
Buildings tilt from foundations and cause buckling, buckle from exterior damage and pull the structure over, pancake from weight above, and on occasion all three.
But as in all things:
—“the tendency of all solids when heated is increase in plasticity”–
—“The tendency of a rock is to fall straight down”.—
—“The tendency of the dim to overestimate their competency is infinite”—
Please don’t be stupid in my presence. Policing the informational commons is a moral obligation of all men, and stomping on intellectual bunnies is tedious and not an honorable use of time.