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Old 7th January 2008, 12:29 AM   #234
Heiwa
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Join Date: Jul 2007
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Originally Posted by GregoryUrich View Post
As I understand it, the paper is supposed to be a simplification for laymen. I think any simplification should be based on an underlying solution of the mechanics of the collapse. As far as I can tell, this is not the case.

Problems:



The spandrels create a Vierendeel truss which resists forces parallel to the spandrels. The only significant element resisting forces perpendicular to the wall (preventing inward/outward deflection) is the floor trusses.



NIST NCSTAR 1-3 (p. 111) gives the temperature/yield strength curves from high temperature tests for many WTC steel samples with values (for 500 C) ranging from 45-85% with 65% being the approximate average.



The mass calculation is superficial and incorrect. The correct mass for floors 95-roof is 38,400 tonnes. The masses of the individual components are simply guess work. Note: Since the collapse was between floors 97-98 the mass should be 32,800 tonnes.



NIST NCSTAR 1-3 (p. 111) gives the data from yield strength tests which were performed on recovered steel.



NIST NCSTAR 1-3 (p. 111) gives the temperature/yield strength curves from high temperature tests for many WTC steel samples with values ranging from 45-85% with 65% being the approximate average.



Bazant gives the energy for plastic deformation in the buckling columns as 12% of the available potential energy for room temperature steel. Bazant uses an incorrect mass (58 x 10^6 kg), so it should actually be 21%. This is the upper limit for energy consumed in buckling.

I don't think the conclusion is convincingly supported. I have pointed out most of the above problems previously to Heiwa, but he has ignored my criticisms.
Actually it is a paper written for children and for the sake of children.

If one wall column tries to deflect outward, while the adjacent ones remain in position, the spandrels will try to prevent this deflection (in tension or compression). If the whole wall deflects outward (all the floors are disconnected), evidently the spandrels have no real effect, except at the corners of the building.

The mass calculation is, as shown, superficial to enable approximate, static stresses to be computed. But the value is close enough.

I have not seen any results of tests of steel from the initiation zone or, for that matter, any pieces from the initiation zone that show sign of buckling, deformation, being affected by heat, etc. Heat evidently affects steel, and for the sake of simplicity, it is assumed that heat contributed to the failure of some columns. My personal opinion is that in that case the load carried on the failed columns would be transferred to adjacent intact columns with a completely different result.

Bazant apparently assumes that both the structure below the initiation zone (A) and the structure above the initiation zone (B) are extremely stiff (!) and that (B) impacts (A) with an enormous energy and significant speed and that (A) then collapses like a house of cards. What happens to (B) is not clear.

In my article for children it is shown that the enormous energy corresponds to maximum 40 kgs of diesel oil used efficiently and that the significant speed is that of a child on a bike running into a wall (10 km/h) so there isn't a real big impact between (B) and (A). It is just like children (B) jumping on a bed (A). Not a hammer (B) hitting a nail (A). Bazant got it all wrong.

It is thanks to Gregory Urich's (and others) kind comments that article ( http://heiwaco.tripod.com/nist.htm ) is what it is even if I am of course responsible for facts and conclusion.

The conclusion is evidently a recommendation to correct the Nist and Bazant reports ... for the sake of our children.

And nobody has debunked that conclusion, I am glad to see.
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