North Tower Acceleration

[William Seger]

5. Here's what's wrong with it:

Last edited Wed Dec 28, 2011, 12:44 PM - Edit history (1)

A constant acceleration would produce a straight line on that velocity graph, yes, but imposing a straight line on measurements every 0.2 seconds, with no indication of the error in the measurements, cannot tell you with any accuracy that the acceleration was really constant. You might say it's approximately constant, at some scale, but the difference between that and truly constant gets you into trouble if you try to apply that over-simplification the way Chandler does to say that the resistance of the lower structure was only 36% of the weight of the upper structure. Tracking the roofline falling is to track the aggregate result of thousands of individual failure events, and the acceleration that Chandler is measuring is just the AVERAGE result of all of them. In failure events where a column buckled, there is no reason to think that, locally, the acceleration was anything resembling constant: The column only provided it's maximum resistance for a few inches of downward deflection, followed by rapidly decreasing resistance (and increasing acceleration) as the column went into plastic deformation and buckling, possibly followed by zero resistance (and local free-fall) if the column broke. If all the column failures were due to buckling, then all you could say from Chandler's measurements would be that the columns allowed an AVERAGE acceleration of 64% g through that entire fall to the next floor, not that the column only resisted 36% of the weight. In fact, we know that most columns did not fail from buckling, and that's the second problem with Chandler's argument: Most columns were simply pushed aside after the floor structure was ripped away from them. Again, the maximum resistance was only for a few inches of floor and column deflection, at most, followed by zero resistance (and local free-fall) once the floor broke free, so that's certainly not a constant acceleration, either. Chandler's 64% g, then, is the net AVERAGE of everything from the acceleration through maximum column resistance to free-fall, but by inaccurately claiming constant acceleration, Chandler uses it to claim that the maximum column resistance was only 34% of the weight. It's an idiotic argument.