Does anyone mind if I look for a different tack on this dispute? (That's a rhetorical question.)
I believe that the real problem here is simple incredulity. No matter what calculations and analysis show, Tony cannot accept that the lower part of a building can be destroyed by the dynamic load of the upper part falling on it. Therefore he concludes that any analysis that does show that must be wrong.
One likely contributing factor to the incredulity is that smaller scale objects, even fragile ones, do not behave that way. A stack of glass tumblers might very well shatter all the way to the bottom if an anvil is dropped onto it, but not if a smaller stack of the same type of tumblers is dropped on it.
And buildings aren't even fragile like glass. They're extremely strong. So it's even less likely -- to the point of being unthinkable -- that a steel office tower could collapse that way. Not unless some enormous additional factor is involved. One possible additional factor is magnification of the effective weight of the falling upper portion, resulting from high decelerations of the entire upper block acting as a monolithic mass to generate massive hammer blows. If that possibility is ruled out by failure to observe any such large decelerations, other possible additional factors such as explosives must be considered.
I offer a different explanation: no additional enormous additional factors are needed, because the premise that implies such a necessity is false. That premise is that buildings are very strong compared with drinking glasses or cardboard boxes or other small-scale objects.
It's just not true. In a very significant way, buildings are actually extremely fragile compared with small-scale objects. Specifically, in comparison with forces derived from their own mass (such as their weight), buildings are almost unimaginably fragile.
To illustrate this, I offer a simple thought experiment (which I've presented before on this forum, but not recently).
First, imagine a building. Actually, imagine four buildings, all the same, with normal contents, fifty or more stories tall, proportioned however you'd prefer.
Now, halfway up one of the buildings, build a big tray around it, strongly attached to the building's frame. Then, disassemble the other three identical buildings, and put all the materials and contents from all three buildings into the big tray. Imagine that the building survives -- perhaps creaking and groaning, maybe it would collapse if just one more brick were put in the tray, but it stands, supporting not only its own weight but an additional three times its own weight.
Would you agree that that must be an exceptionally strong building? Or at least, that such a building cannot be of below average strength? (That is a massive understatement, but if you'll admit that much, the argument will still work.)
Now, imagine another object: a wine glass. But it's a very delicate wine glass, with a bowl thinner than an egg shell and a stem thinner than a strand of thin spaghetti. It weighs only an ounce. And it is so delicate that if it were to be filled with more than four ounces (by weight) of wine, it would shatter.
Note that to fill such a glass, you'd have to use an eye dropper or some similar means, because the force of a normal stream of wine poured from a normal wine bottle landing in the bowl would exceed the force of four ounces of weight, and destroy it. When the glass is filled to its four-ounce capacity, don't even think about picking it up by the stem with your fingers. The stem would snap from the unbalanced sideways forces, or the upward acceleration of the wine when you lifted it would overload the stem. (It might be possible to pick it up by carefully cradling the bowl in your hand, but you'd have to have very steady hands; any tremble would shift the weight of the wine in the bowl, or apply torque to the base, causing the glass to exceed its limits and break.)
Would you agree that I've just described an extremely delicate wine glass? Or at least, a wine glass that's not of greater than average strength for a wine glass?
Here's the problem: if you accept that the building is strong and the wine glass is fragile, how do you explain the fact that as described, the wine glass is stronger than the building? The wine glass can (barely) support an additional four times its own weight, while the building can only (barely) support an additional three times its own weight.
And of course, real skyscrapers are not anywhere near strong enough to support an additional three times their own weight. And real wine glasses are amply strong enough to support at least 25 times their own weight when resting on a level surface, and are also strong enough to be picked up, moved around, and even (during toasts) impacted (albeit at low velocities) against other similar glasses.
The conclusion is that buildings, relative to forces derived from their own mass such as the weight of their upper floors, are really really really fragile. Far more fragile than wine glasses, by orders of magnitude.
Ditto cardboard boxes.
Ultimately, the reason for that is scale.
And that, folks, is the sought-after "additional factor" that explains why tall buildings can collapse the way the towers did on 9/11. Not explosives, and not massive high-deceleration hammer blows by the entire upper section. They're just very fragile, compared with the forces generated by large parts of themselves in motion.
Come to think of it, buildings are so fragile that many of them can actually be damaged by earthquakes! A mere few seconds of shaking! Can you imagine an empty cardboard box being damaged by being shaken by an earthquake (that is, without something else falling on it)? Ridiculous! Cardboard boxes are vastly stronger, that's why many of them able to support hundreds of times their own weight.
Intuition is usually very unreliable when it comes to effects of scale. Incredulity based on such intuition will lead even well-meaning and intelligent people to ridiculous conclusions. Correct quantitative analysis and intellectual honesty in accepting the results of such analysis even if counterintuitive, are the usual ways around that problem. But developing better intuition might also help.
Respectfully,
Myriad
