Babyhighspeed - I completely agree that this building could have been dropped just as shown with controlled demolition. But I am not convinced that a complete collapse was impossible due to fire.
I do agree that it is unusual and unlikely.
The firefighters absolutely did not do a structural analysis of the building before its collapse, they would not have a clue what to look for.
When I look at Disputeone's videos, there is a strong relationship between the video you see and the computer simulation. Pause the first video at 1:35 and play back with the simulation. I think the simulation is a good indication of what could have happened. The penthouse(?) disappears following with clear buckling of the facade right under it before the collapse started. clearly, as Babyhighspeed also mentions, the core was stripped out first.
What surprises me is that the other section of the building also collapsed. I would have expected the collapse to stop at the 0:29 seconds mark in the simulation, and then the rest of the building should keep standing from that point forward.
What was mentioned in the report was lateral movement of an entire floor structure. If one whole floor area had significant horizontal movement, moving the connection points between beam and columns in any horizontal direction far enough, all the columns above that point would lose their base. It would be similar to removing one (2 actually, 1 row above and 1 row below) whole floor of columns. This is mentioned in the report, and recommends that future designs allow for more slip joints on primary beams.
Babyhighspeed what would happen to any multistory building if you pushed the bases of all the columns on one floor horizontally in any one direction? You will need some serious cross bracing to keep the building together.
Disclaimer* I have not read the entire report, so it is possible you know whats in it a lot better than I do.
I just find this interesting.
You can add 20 slip joints and that won't compensate for a foot of horizontal movement lol...You are still going to have a serious Structural issue, and even a possibility of a localized collapse failure.
Ok..I see we can agree my very brief explanation, (I actually have more detailed descriptions in this thread if I can dig them up) is an accurate representation of how the building would be demoed, as well as what we saw would be an accurate representation of a building that did get CDed.
We can also agree it would be unlikely if not impossible for a localized fire to emulate a controlled demolition.
So we can step from there for a moment....Let's move the discussion, could a localized fire, in the manor according to NIST have emulated a controlled demolition.
Let's look at the beam moving horizontally they say moved (almost 6 inches) at the floor proposed. We can determine it was not multiple, as multiples would have shown an Exoskeleton reaction.
Actually, let's move to this first. On the NIST model they showed the floors collapsing having a detrimental effect upon the overall Vertical and compression stability of the building. This alone is Incorrect, let's say we had floors collapse, the core would become vertically stronger with each missing floor.
Now...If we kept dumping floors (say 85 percent or more) then yes, the core could collapse in a multitude of directs (not into its own foot print) as it would have lost too much of it's sheer protection of the Exoskeleton. However, this would have obviously looked entirely different than what we saw. Nor do I predict an entire building collapse... Also, remember, the lower 20 of the core, since it was boxed supported could have stood without the Exoskeleton (it would obviously had to have ditched the floors)
I am trying to stay with only one or two subjects per post, since the subject matter is so big.
As for your question at the end...If you pushed ALL core columns one floor horizontally past the 20th floor, collapse, no argument. Even at the base, 95 percent collapse. Though this would not be possible with the NIST model.
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