Did NIST even consider this?

OK. We all know that NIST has stated that the floor trusses pulled the outer columns in to cause collapse initiation.

I'm wondering if they even considered this scenario and if not, why not?

My scenario (which I believe has more validity than NIST's theory):

The plane debris gathered at the core structure. This coincides with NIST.

The added weight of the plane caused the horizontal bracing of the core columns to fail.

Once enough support failed, the core columns buckled due to Euler's buckling.

en.wikipedia.org...

This caused the floors to fall along with the core columns and pulled the outer columns in.

I believe my theory has more weight (pun intended) than the NIST theory of floor trusses alone pulling the outer columns in.

We recently had to do an analysis of a building where they wanted to add a small brick wall to an existing wall. We weren't sure if the beams would be able to hold this weight (BTW, we figured out that they would but it was close). The weight of that brick wall would be significantly less than the weight of an airplane IMO.

Any comments?

I thought this is the reason NIST did the whole'heat up the truss ' thingy.

They heated them up, and when they sagged, they measured the 'pull' on the ext columns, and determined that this would be sufficent to do just as we observed.

Or do I remember it wrong?

I like your explanation too btw. Perhaps an aid to the collapse? Floors fail, removing some of the stabilization to the core columns, and when you add in what you talk about, adios? Or would the floors not really add all that much stabilization to the core, and pretty much be a moot point?

I'd say the floors just being attached to the core columns would give them support. But, that's just my guess, as I haven't been able to evaluate the original construction documentation of the towers.

Edit: I threw this out there as a "what if" and trying to stay within the boundaries of observed events without going into the need for explosives.

[edit on 3/11/2008 by Griff]

Originally posted by Griff
The added weight of the plane caused the horizontal bracing of the core columns to fail.

Once enough support failed, the core columns buckled due to Euler's buckling.

So when you say this, would you be implying that the bracing would just shear off and then the core columns would buckle from that alone? Or are we also talking about some kind of overloading of the core columns themselves, or sufficient temperatures?

It definitely sounds a lot more plausible than what NIST offered, but I'd like to see how the numbers would come out on what kind of buckling we're talking about, and from exactly what.

I'm just throwing it out there for discussion. I'd love to do some calcs. Too bad I can't until they disclose the structural documents. I'm not sure if the column bracing has been discussed and I haven't seen it (yet) in the NIST report.

When I get more time, I'm going to teach myself SAP200. That way, I can do some computer sims myself. As much as I can do that is.

BTW, I'm still not quite sure if the explosive global collapse could be attributed to my theory here. Just possibly the collapse initiation (accidently & premature) of the South tower.

Edit: Yes, I mean sheared off. Depending on what kind of shear connections they had. Off the top of my head, I would think not much because there really wouldn't be weight on the supports other than their own weight, so they wouldn't have been designed for shear in the vertical direction, but for axial load (buckling about their strong axis under compression) in the horizontal direction.

[edit on 3/11/2008 by Griff]