For WTC1, it will be quite easy to show that the energy was split over at least two floors and that less than 5% was applied to the core. Essentially only 4% of the debris wave had an orientation and trajectory to enable a free shot at the core columns after passing through the external shell. The rest of the debris was hindered by the floor slab, the truss matix, and 67 tons of office contents.
Well, I don't know about "easy." You also have to keep in mind that there was a lot of potential for secondary damage, so the 4% with a "free shot" doesn't tell the whole story. Personally I've eyeballed it at 5%, and further assumed that the spread over two floors nonetheless hits the same columns, so the destruction energy of those columns is (to first order) not affected by the vertical spread. But it's just a WAG (Wild-Ass Guess).
Also, the energy was not applied as a single impulse but rather spread out over time (~0.5 seconds). This further reduces the potential damage. For example: two simultaneous impacts with a combined energy equivalent to the failure energy will fail the column. However, the same two impacts a second apart will not fail the column. The question remains how close together the impacts need to be to fail the column. Nonetheless, a continuous wave of debris over 0.5 seconds is much different than a single impact with equivalent energy.
Yes, quite. NIST discusses this in some depth in NCSTAR1-2, in discussing the different pressure-impulse curves to fail different columns. Also, most columns that are going to fail would not have withstood until the very last of the 0.5-second aircraft duration, but instead failed upon being hit by the shorter and sharper impact of flattened aircraft and the leading edge of entrained debris. In any case, the total energy is still plausible.
If I may indulge in turnabout, Dr. Wierzbicki estimated that about 30% of the impact energy was expended on the columns -- much higher than either you or I have speculated. No, I don't agree with this, but proving otherwise is not so trivial.
A significant portion of the energy available to be applied to the core was the impacting fuel mass. Liquid is much less effective at momentum or energy transfer. In fact NIST concluded that the fuel could not fail core columns.
Fuel alone, no, but only because of dispersal at the perimeter. Had the wing sections impacted core columns directly, some could have failed. In any case, this is why we expect the majority of core damage to lie axially along the aircraft's fuselage, which is what NIST predicted. The fuel evolution is much more important for perimeter column damage, destruction and mobility of furniture, and fireproofing damage than core damage, for both towers.
In any case, remember that my 5% is just a guess. The point is that there was a marked excess of energy available to cause the damage NIST predicted. This is my answer to Dr. Griffin's claim that the aircraft should have inflicted virtually no significant structural damage -- a claim, I remind you, that he offers without any calculation whatsoever.
We can, of course, refine our estimates. If we do so
ad nauseum we will eventually end up with a near copy of NCSTAR1-2B, or perhaps the Purdue results. I'm satisfied with both of those until someone demonstrates where they went wrong. My 5% guess is just a grossly simplified way of explaining those results.
Your hard hitting analysis is comical. You reject a white paper that was a completed analysis yet accept Robertson's analysis without him providing any proof whatsoever?
The only accident threat is because of being lost in the fog? And you work on planes, correct? I'm sure you may have heard of mechanical malfunction as a cause of accident, right? So the building stands if the pilot makes an error, but golly the building comes collapsing down if the plane has a malfunction?
I'm inclined to believe Skilling's assessment considering it was done right after the 1993 attack when the structural integrity would have been examined rather extensively instead of an off the cuff comment after the collapses when nothing could be examined.
Swing, I understand you're responding to
beachnut, but since this thread concerns my whitepaper, I should tell you that you've missed the point. The point is that Dr. Griffin is using the 1964 study and Skilling's off-hand comments to remark that the structures were
designed to specific requirements that they must survive an impact with a jetliner at speed. This is not so. The existence of a worst-case analysis does not imply the existence of any such requirement. Designers routinely perform analyses of scenarios that are far beyond any actual requirement, design envelope, or anticipated event.
And again, while I'm sure such a study was done (albeit probably at an extremely low level of fidelity), and Skilling did make such a comment, they were both grievously in error. Both actual events demonstrated this, and every analysis after the fact confirms this. It is a complete
non sequitur.
