Hi Illuminist, and welcome to the forum!
The problem with using scale models for such demonstrations is that the effects of scaling are complex, and create enormous differences in behavior. A scale model, constructed along the lines you've suggested (or along most any reasonable-seeming lines) would
not exhibit the kind of progressive collapse the towers did.
And in fact, 9/11 conspiracy theorists have constructed scale models in various ways, from materials such as wire mesh, stacks of plastic trays, and even stacks of pizza boxes, and observed that they do not collapse the way the towers did.
The basic problem is that the structural strength of an object -- say, a steel rod -- scales differently than the mass and weight of the object. So, all other things being equal, smaller scale versions of a structure are much stronger,
relative to forces derived from their own mass such as weight and momentum, than the full scale versions. This is called the "square-cube law," because the strength of similarly proportioned objects such as steel rods increases as the square of the linear scale factor, while their mass and weight increases as the cube of that factor. So larger-scale structures made of identical materials will get weaker relative to their own mass, until at some scale, they would collapse under their own weight.
There are lots of standard examples. A mouse falling one story will likely survive with no injury, while a horse falling one story would suffer at least broken legs, and an elephant would be completely crushed (skull and rib cage collapsed) by the same fall.
Lift up one corner of a wooden doghouse, and the whole doghouse will tilt up with no noticeable distortion and no damage. Lift up a small wooden house by one corner, and the house will split apart somewhere in the middle just as it begins to tilt. Lift up a six story wooden apartment building by one corner, and the corner will crumble away from the rest of the structure before most of it even begins to tilt.
You can easily pick up a cupcake between two fingers, and toss it around. To pick up a birthday cake made of exactly the same materials, you'd better use both hands and treat it gently; if you start tossing it around it will soon crumble apart. But a large wedding cake (still made of the same materials) can't be picked up by two hands at all, not even if you had proportionately larger hands.
These scaling effects are the basic reason that large structures do not behave in intuitive ways, that is, the way familiar smaller objects do. Here's an old post of mine that dramatizes this difference by comparing the "strength" of a large building with that of a delicate glass wine goblet, and showing how in proportion to its own mass, the wine goblet is far stronger.
http://www.internationalskeptics.com/forums/showthread.php?postid=5544363#post5544363.
It is possible to demonstrate progressive collapse with a physical model, but the design of the model has to take into account the effects of the scaling. So if you were using plywood sheets for the floors and metal rods for the columns, the rods would have to be thin enough to have a similar reserve strength to the columns in the towers -- something like, enough strength to hold three times the load they're actually holding. They would therefore be much skinnier, in scale, than the towers' columns.
That would cause other scaling problems, though. Such skinny steel columns, if overloaded, would bend like pieces of wire (since they'd basically
be pieces of wire) rather than fracture like the real columns did; the structural steel of the real columns could not bend that way without breaking apart as they did. So you'd have to compensate for that, perhaps by making the scale columns out of shorter pieces soldered or glued together, or by using a different material with comparable resiliency at the smaller scale, such as glass rods.
And even then, you still have some scaling problems. Gravity doesn't scale, so the fact that each scale model floor only falls a short distance before impacting the next floor down (or the ground) will mean the falling upper section will have significantly less momentum relative to its weight in the scale model. You'd have to compensate for that again, either by conducting the experiment in a centrifuge (increasing the effective "gravity"), or by further increasing the mass of the floors relative to the strength of the supports to compensate, or by making the scale model much taller.
Then there's the effect of scaling on angular momentum to consider, likely making the scale model more prone to tipping over than the actual towers were.
All this means that once you do correct all the necessary scaling effects and demonstrate progressive collapse in such a model, the conspiracy theorists will insist that you "rigged the model to fail" and that your demonstration has no relation to the real towers.
A case where this has already happened is progressive collapse of card towers. The various scaling factors happen to interrelate in such a way as to make large "house of cards" structures behave rather similarly to full-scale buildings, including showing progressive top-down collapse. But of course, "real buildings aren't made of cards!" provides an easy excuse for conspiracists to disregard such phenomena.
Respectfully,
Myriad
. You're thinking of Dave Thomas, who has indeed fought the good fight to great effect.
