Yes, that's right. Do you understand that this is what NIST's simple calculation demonstrates?
I guess I just don't understand this emphasis on the floor trusses, as if they were what was holding up the building. In my mind, the entire weight of the upper block wouldn't be applied to the floor below, because the
core columns would be providing resistance. It reminds me of this 3D animation that I believe was presented in a 2002 documentary purporting to explain the collapses. They animated the floors "pancaking", but just left the core standing there, strangely:
The trusses had no vertical support below, and were just designed to hold a thin layer of concrete, and then furniture and people on top of that. So I don't find it surprising that you can do a bit of math showing that if six or more floors came down on one floor, it would fail. But in order for those floors to come down at all, wouldn't the core have to fail first?
I wanted to check what exactly NIST said about the core in their FAQ, and there's not much... Here for example is question #11, which purports to be a quick explainer on why the building collapsed:
11. What caused the collapses of WTC 1 and WTC 2?
Based on its comprehensive investigation, NIST concluded that the WTC towers collapsed because:
- The impact of the planes severed and damaged support columns, dislodged fireproofing insulation coating the steel floor trusses and steel columns, and widely dispersed jet fuel over multiple floors; and
- The subsequent unusually large number of jet-fuel ignited multi-floor fires (which reached temperatures as high as 1,000 degrees Celsius, or 1,800 degrees Fahrenheit) significantly weakened the floors and columns with dislodged fireproofing to the point where floors sagged and pulled inward on the perimeter columns. This led to the inward bowing of the perimeter columns and failure of the south face of WTC 1 and the east face of WTC 2, initiating the collapse of each of the towers.
Both photographic and video evidence—as well as accounts from the New York City Police Department aviation unit during a half-hour period prior to collapse—support this sequence for each tower.
It does talk about "columns" in general, but does not explicitly talk about the core at all, focusing instead on the trusses pulling on the perimeter columns. But there's also question #21:
21. Since the melting point of steel is about 1,500 degrees Celsius (2,800 degrees Fahrenheit) and the temperature of a jet fuel fire does not exceed 1,000 degrees Celsius (1,800 degrees Fahrenheit), how could fires have impacted the steel enough to bring down the WTC towers?
In no instance did NIST report that steel in the WTC towers melted due to the fires. The melting point of steel is about 1,500 degrees Celsius (2,800 degrees Fahrenheit). Normal building fires and hydrocarbon (e.g., jet fuel) fires generate temperatures up to about 1,100 degrees Celsius (2,000 degrees Fahrenheit). NIST reported maximum upper layer air temperatures of about 1,000 degrees Celsius (1,800 degrees Fahrenheit) in the WTC towers (for example, see NCSTAR 1, Figure 6-36).
However, when bare steel reaches temperatures of 1,000 degrees Celsius, it softens and its strength reduces to roughly 10 percent of its room temperature value. Steel that is unprotected (e.g., if the fireproofing is dislodged) can reach the air temperature within the time period that the fires burned within the towers. Thus, yielding and buckling of the steel members (floor trusses, beams, and both core and exterior columns) with missing fireproofing were expected under the fire intensity and duration determined by NIST for the WTC towers.
Okay, so they seem to be saying the core columns were "yielding and buckling" from the heat. But even if that were happening, it would only be at the impact zone. Immediately below that, the core columns were stone cold and good as new. So if the core columns yielded at the impact zone, I would maybe expect the upper block of the South Tower to start tipping over, not come straight down through the undamaged structure.
I'm also a bit lost on how the core columns get so hot anyway... NIST says there the fires were around 1,000 degrees Celsius, and when steel gets that hot, its strength reduces to about 10 percent of its room temperature value. But just because you have 1,000 degree fires going on in the vicinity of steel columns, that does not mean the columns themselves become 1,000 degrees hot. Google tells me a campfire is about 900 degrees Celsius, but everyone knows you can hold your hand quite close to a campfire without your hand also becoming 900 degrees. The core columns were in the... well, core, and the fires were mostly in the office spaces, ie
outside the core. And all of these processes would be so uneven... Some columns would be closer to the fires than others, some would have more of their fire proofing intact, and so on. So I don't think that all 47 core columns could be evenly heated, and the ones in the middle likely wouldn't heat up much at all.
This became pretty longwinded, but I guess to summarize, you and NIST both seem particularly focused on the floor trusses. Whereas for me, it's the core that seems practically indestructible, and that's what is giving me a hard time understanding how the observed collapse could happen without "assistance".