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Reply #191: You miss my point. [View All]

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eomer Donating Member (1000+ posts) Send PM | Profile | Ignore Wed Nov-11-09 12:56 PM
Response to Reply #189
191. You miss my point.
Edited on Wed Nov-11-09 01:09 PM by eomer
You continue to miss the point that crush-up did occur. It is impossible, therefore, for Part C to have imparted all the kinetic energy onto Part A in either an instant of time or a short interval up to the time at which the Part A columns would buckle.

If you take the hypothetical case of only crush-up initially then you can see the point more clearly.

In this hypothetical, the Part C leading edge begins applying some of the kinetic energy to Part A but the Part C leading edge buckles before the Part A leading edge does. Clearly Part C applied some of the kinetic energy to Part A during this time interval, but not all of it. Now a new leading edge of Part C continues impact with Part A (and a Part B that is piled on top of Part A). The new leading edge of Part C again buckles first before that of Part A does and a second time interval has occurred during which some but not all of the kinetic energy was applied to Part A. Continue with additional similar time intervals until at least half (and maybe more) of Part C has crushed-up. Now there has been a significant period of time during which the kinetic energy was gradually applied to Part A at a rate that Part A was able to resist.

I admit that the hypothetical is a bit too neat, but it is essentially what is seen in the video referenced elsewhere in this thread. Part A resists whatever energy Part C is able to apply against it for a significant time period during which Part C is crushing-up to half its original size or less. Obviously, therefore, Part C was not able to apply all the kinetic energy at once or even during the time interval it took to crush-up one floor. The application of a limited portion of that kinetic energy was spread over at least the time (and then some) that it took to crush-up at least half of the Part C floors. At the end of that time the remaining kinetic energy that wasn't already applied to Part A had been dissipated in various ways, ejected outboard, or was still oncoming in whatever part of Part C remained intact.

To claim that all the kinetic energy can be counted in determining whether the Part A columns will buckle in the initial impact is clearly false. No way is the leading edge of Part C able to deliver all that energy in that time interval.

Bazant's entire approach depends on the premise that crush-up will not occur. In that case you can count all the kinetic energy because it will keep being poured on by the unbuckled Part C until Part A buckles. But if Part C buckles first then all bets are off and Bazant's entire approach is flawed. Part C does appear to buckle first in the video, so Bazant's entire approach is flawed.

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