Man, have you got that all wrong.
There were moment frames on every other floor. I don't remember all the details but the exterior walls were extremely well tied together.
Where did you get your info?
I got it from two lines before the freefall phase quote you like so much. It says that just before the final collapse, and after the core columns had collapsed, all perimeter columns were laterally unsupported on three out of four sides.
NCSTAR 1-9 p.588 said:
As the interior columns buckled across the building, the exterior columns were left laterally unsupported normal to the east, south and north faces.
The problem is, the building went from not falling to free fall acceleration instantaneously. That means all the exterior columns failed simultaneously and instantaneously. That can't happen. The buckling takes a short amount of time but not fast enough to result in simultaneous, instantaneous free fall.
It went from not not falling to freefall in almost
2 seconds. Buckling is an unstable phenomenon. Asymmetric loads cause buckling, which creates more asymmetry etc. Now your hunches as to how long that takes are not really useful. I prefer numbers.
At this point none of the exterior columns were braced by any of the floors but the moment frames braced the exterior walls in the vertical and horizontal planes of the wall.
...leaving them free to buckle in any perpendicular direction. Read the quote from the report above.
Most of the fires had burned out and the walls cooled down when the fires moved on. Only a few small areas were hot.
Do you have a source for this claim? Where were the hot spots?
Very crude and based on bad data. Show your math before making those kind of statements.
Didn't you see the math? The model shows exterior colums buckling between at least floors 7 and 14. (figures 12-62 and 12-63), meaning these columns were unsupported over about that length before buckling. Normally the columns are unsupported over the length of one storey, but at that point a length of 7 storeys or more. Load bearing capacity for columns is proportional to the inverse square of the unsupported length. That is, if I increase the unsupported length by a factor of 7, the load bearing capacity will decrease by a factor 7
2. Asymmetry in the loading can further decrease this dramatically, as you will see as soon as you stand on an empty soda can.
Now assuming that the loadbearing capacity is 1% of its orignal value, the opposing force to the collapse is 1% of the weight of the top part of the building. The top part will then be pulled down by a force of 99% of its own weight, causing it to fall at 99% of g. This gives us a ballpark estimate showing us that a collapse over 8 storeys at g is well within the error margins of extrapolating acceleration from video.
So tell me, where is my error?
But that is not the way NIST said it happened. NIST said the all the core columns collapsed over 7 floors progressing from east to west and they had all collapsed before the onset of 'global collapse'. That did not happen in the video.
What? No they had all
buckled, not collapsed. that is, the insides of the building were not supported anymore, and therefore also not structurally connected to the perimeter anymore.
They say the model collapsed at free fall acceleration but it can't buckle the walls as shown and fall at free fall acceleration.
I'm sure this made sense to you when you wrote it down, but I'm not sure where you get this bizarre disconnect from.
The exterior columns clearly buckle in the model,
and the top part falls at freefall acceleration in the model,
and does so while the columns are buckling.
H, the camera was NOT shaky and the rest of that doesn't make nay sense.
Okay it wasn't shaky. Doesn't change much though. It's not exact data. It's data that's as good as it gets. They fit a curve through the data and see that the acceleration is not distinguishable from freefall, meaning that the load bearing capacity of the supporting columns is not distinguishable from zero in the context of having to support two thirds of a building.
