Correct. But the fires never got hot enough to weaken the steel.
I assume you mean the steel of the core columns (reading your previous posts). Suffice it to say, both statements are incorrect.
Heat changes some basic material properties of metal. Most importantly, it changes the modulus of elasticity, defined as the slope on the linear region of a stress-strain curve. Specifically, the modulus of elasticity lowers with ANY increase in heat. As the modulus of elasticity decreases the capacity for accelerated creep, as well as heat induced strain increases.
NCSTAR 1-6, appendix D (starting at page 320) provides a detailed explanation of the load cycling occurring in the towers. The pull in forces created by the sagging of the floor trusses (whose steel did exceed 250 C) caused positive moment buckling for both the perimeter and core columns. Due to the heat present in the system, NIST modeled inelastic buckling as modified by increased creep strain.
My point is that "weakening" is an overly simplified term. As the steel heats to temperatures that far exceed the office environment, plastic creep strain, induced thermal stress and inward buckling will remove the load capacity of the column without necessarily altering the compressive strength of the steel.
If you read NCSTAR 1-6, page 243, you will find that NIST reports values of 500 to 700 degrees centigrade in the core of the towers.
So now we have analysis which states the towers could withstand significant column damage, even greater than experienced on 9/11, even against massive shear force.
But without the buckling of the columns. Your report says that the columns were severed, not plastically deformed, subjected to differential thermal stresses, and then underwent plastic buckling.
That leaves the fires. It is a huge assumption that fireproofing was dislodged from the entirety of the floor or floors.
Actually, it is the inevitable conclusion of a series of complex, iterative calculations. The fireproofing dislodged in the NIST model was actually conservative as it only included the areas that were in the direct path of the debris. For the summary, you would want to read page 332 of 1-6. For the detailed analysis of the fireproofing calculations, you want pages 33 to 35, and chapter 5. I would suggest starting at page 129, though the entire chapter contains necessary information.
To summarize, NIST had several criteria for inferring the dislodgement of the fire protection.
There's also no evidence that the plane was responsible for this dislodging. But it's all moot.
No, it's not moot simply because your misconceptions have led you to illogical conclusions. There is ample evidence for dislodgement, not the least of which involves the analysis of damage caused by hundreds of thousands of pounds of material slamming into the WTC towers. With the adhesive strength of the SFRM below 12 psi, you would expect that red-hot shrapnel, traveling at 500 mph would cause some damage, right?
With or without fireproofing, there is no evidence that the fires heated the steel sufficiently.
That would only be true if one was incapable of solving a series of mathematical equations. It turns out, however, that as the fires burned, the steel changed shape and underwent plastic deformations and buckling. This would not have happened without heat induced changes.
The S tower is down in 52 mins. That's not a lot of time to weaken the steel.
I do not care about your opinion.
