(This is my first "real" post, so please go easy on me )

The AE911 folks are promoting another kind of numerical calculation of the collapse that centers around what they call the "crush-down" equation, which is a one-dimensional ordinary differential equation (ODE) that models a progressive floor collapse. They come in different varieties, of which the one by Ansgar Schneider [1a, 1b] is the one I have been looking more closely at (because a 9/11-truther at another forum was touting it, claiming it was proof of...something).

The model is, as far as I can see, not validated against any real empirical evidence, but is more like a numerical fitting of the ODE solution to the first few seconds of collapse of the North Tower, after which some extrapolation is done. Then, when the model predictions fail to replicate the empirical data (roofline measurements collected from videos of the collapsing building) after approx 4 seconds, an extra force term is inserted into the equation to adapt the model to the data. Schneider calls this "re-computation of the structural resistance of the building once the downward movement of the building has been quantified". In any case, the model is one-dimensional, it assumes a progressive collapse of one floor at a time. With the one-dimensional approach, he attempts to calculate the energy dissipation of the collapse, and argues that the extra inserted "resistance" force should be sufficient to arrest the collapse. In a recorded video presentation of the paper [2], Schneider presents his conclusion that "The building's structural resistance was reduced by some «unknown phenomenon»!" This conclusion is not in the paper, only in the presentation.

There are several things one can criticize about this approach, for example that it assumes a homogeneous "crush down"-front that completely destroys previously undamaged storeys one by one. After seeing posts #119 and #120 in another thread [3], it occured to me that the basic assumptions Schneider - and also Bažant et al. (see references 2,3,4 in ref. [1]) - have made with the crushing front are false, as the collapse obviously did not happen as assumed in these naïve models. Thus, their approach is invalid.

My truther "opponent" over at the other forum initially acknowledged my criticism of Schneider's approach, but after a few more posts being thrown back and forth, he was back at insisting Schneider "proved" foul play. Now he's ghosting me. *Sob*

[1a] Ansgar Schneider: The Structural Dynamics of the World Trace Center Catastrophe, arXiv:1910.10801v2 [physics.class-ph].

[1b] Presentation of Schneider's paper at ae911truth.org

[2] Presentation of the paper at International Association for Bridge and Structural Engineering (IABSE) on September 5, 2019, available on YouTube.

[3] Debunked: The WTC 9/11 Angle Cut Column. [Not Thermite, Cut Later]

Edit: inserted ref 1b.

The AE911 folks are promoting another kind of numerical calculation of the collapse that centers around what they call the "crush-down" equation, which is a one-dimensional ordinary differential equation (ODE) that models a progressive floor collapse. They come in different varieties, of which the one by Ansgar Schneider [1a, 1b] is the one I have been looking more closely at (because a 9/11-truther at another forum was touting it, claiming it was proof of...something).

The model is, as far as I can see, not validated against any real empirical evidence, but is more like a numerical fitting of the ODE solution to the first few seconds of collapse of the North Tower, after which some extrapolation is done. Then, when the model predictions fail to replicate the empirical data (roofline measurements collected from videos of the collapsing building) after approx 4 seconds, an extra force term is inserted into the equation to adapt the model to the data. Schneider calls this "re-computation of the structural resistance of the building once the downward movement of the building has been quantified". In any case, the model is one-dimensional, it assumes a progressive collapse of one floor at a time. With the one-dimensional approach, he attempts to calculate the energy dissipation of the collapse, and argues that the extra inserted "resistance" force should be sufficient to arrest the collapse. In a recorded video presentation of the paper [2], Schneider presents his conclusion that "The building's structural resistance was reduced by some «unknown phenomenon»!" This conclusion is not in the paper, only in the presentation.

There are several things one can criticize about this approach, for example that it assumes a homogeneous "crush down"-front that completely destroys previously undamaged storeys one by one. After seeing posts #119 and #120 in another thread [3], it occured to me that the basic assumptions Schneider - and also Bažant et al. (see references 2,3,4 in ref. [1]) - have made with the crushing front are false, as the collapse obviously did not happen as assumed in these naïve models. Thus, their approach is invalid.

My truther "opponent" over at the other forum initially acknowledged my criticism of Schneider's approach, but after a few more posts being thrown back and forth, he was back at insisting Schneider "proved" foul play. Now he's ghosting me. *Sob*

[1a] Ansgar Schneider: The Structural Dynamics of the World Trace Center Catastrophe, arXiv:1910.10801v2 [physics.class-ph].

[1b] Presentation of Schneider's paper at ae911truth.org

[2] Presentation of the paper at International Association for Bridge and Structural Engineering (IABSE) on September 5, 2019, available on YouTube.

[3] Debunked: The WTC 9/11 Angle Cut Column. [Not Thermite, Cut Later]

Edit: inserted ref 1b.

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