This is fine, but it is not sufficient to respond to my challenge. I am looking for an individual who does understand, and can explain it to the lay-audience.
Changing the rules again? I thought you wanted someone to explain it to
you. That might be a debate. The terms you just listed above are not well-defined, and thus a lousy requirement.
I have already started an outline that the challenger can follow.
Here is another interesting point that should be covered in the positive case.
Please explain how heat applied to a floor truss lead to an inward pulling force on the perimeter and core columns.
Heck, that's easy, I'll answer that for free.
Suppose you have two columns, and between them is a horizontal truss, acting as a beam. Heat is applied under the truss.
Two things happen. (1) The truss
expands, and yes, I know this is counter-intuitive for inward stress, but bear with me; and (2) the truss yield strength decreases. If enough heat is applied, the yield strength will decrease to zero, but other things will happen before this takes place.
The initial reaction is an outward deformation of the columns, along with a deflection in the truss. The truss will bow downward, initially assuming a more-or-less circular, shallow arc. How much of the expansion is taken up by the columns deflecting outward and how much is taken up by the truss bowing downward depend on the relative strength of the columns and trusses. In the WTC cases, the columns are relatively strong compared to the truss.
Heat is still applied. The truss continues to expand and continues to lose yield strength, tilting the balance of deformation increasingly towards the truss. While the columns will continue to be pushed outward, the bow in the truss will increase more and more.
More heat is applied. Now the weight of the truss becomes an important factor. Now that the truss is no longer horizontal, the truss weight induces an inward pull on the two columns, that will eventually overtake the outward push caused by the truss expansion.
More heat is applied. The truss yield strength drops to a point that the outward push it can sustain is equal to the inward pull from its weight. From this point on, there is no more outward push. The force on the column tops is inward from now until failure.
More heat is applied. At some point, either (a) the truss will simply break, or (b) the columns will reach their plastic limits and fail. This depends on lots of things, like how much else the columns are supporting and how it's distributed. In the WTC case, the columns are also being heated and losing their strength as well.
Regardless of which scenario you follow, at the moment of failure, you have an inward pull on the columns.
Basic strength of materials.