That's roughly what happened on 9/11. I just want to make sure that the model can't be rejected as easily as it would be if I dropped, say, a single car battery on top of an otherwise unloaded paper tube.1. What does 80% of the mass of the towers being below the level of weakening have to do with anything?
No, I expect my model to collapse to the ground. That's the point of building it -- to reproduce a top-down progressive collapse roughly within the terms of Hoffman's challenge, using simple materials like paper, cardboard, and tape.2. You think the top floor of the remaining 80% of the structure was designed to withstand the impact of the upper 20%
They're not the concrete but the trusses. (Corrugated cardboard is essentially a truss structure.) They will bend slightly when impacted, and the force of the impact will detach them from the walls, to which they have been taped.3. Do cardboard floors effectively replicate how concrete floors would behave when impacted?
The concrete in the system is mainly represented by the batteries, though any recognizably massive household object will do as a unit load. (I want to be able to say, e.g., that its normal state is 2 AA batteries per floor, but that it has been tested with 4 batteries per floor and survived.) This is a clear limitation of the model, but one that I'm willing to accept: the energy to pulverize the concrete will not be demonstrated. Obviously the batteries are much stronger than concrete at this scale.