Gordon Ross: Bazant and NIST, Simultaneous Failures
The paper can be linked below
Criticism of the Paper
Gordon Ross correctly identifies some exaggerated over-simplifications in the Bazant, Zhao (BZ) paper.
Gordon criticizes BZ in two key ways. The first is quoted below:
"Dr. Bazant argues that all of the potential energy associated with the fall of the upper
section of the tower through two storey heights [the storey where the failure occurred and
the uppermost storey in the lower section] would be concentrated into the destruction of
the uppermost storey of the lower section. This energy would overwhelm the ability of
the columns of the uppermost storey to absorb energy and collapse would progress
through this storey. The available energy would then be concentrated into the next storey
down and the tower would collapse one storey at a time to ground level."
Gordon asks how this can be because
"It must be noted that the columns in the upper section could not deliver
a greater force than they themselves were able to transmit. In a situation where the
columns in the upper section were asked to deliver loads at magnitudes sufficient to cause plastic deformation of columns in the lower section, then they themselves would
simultaneously suffer plastic deformation at levels proportionate to their ability and
Gordon's second complaint is quoted below:
"The second error made by Dr. Bazant is his failure to take account of the factor of safety
designed into the towers' construction. He makes no mention whatsoever of this crucial
design parameter. This failure leads to a major underestimation of the ability of the
columns to resist the downward acting forces.
The effect of this error by Dr. Bazant is an error in his ratio of energies. If this is adjusted
to take account of a factor of safety of 4 the ratio is reduced from his value of 8.4 to 2.1.
It must also be noted that the ratio mentioned by Dr. Bazant is relevant only to the first
collision after a freefall of one storey. He is specifically dealing with a situation where
the energy of the fall through two storeys is resisted by the columns of one storey. The
continuation of the collapse would not have these conditions but rather have the fall of
one storey resisted by the columns of one storey. Without the period of uncontested
freefall the ratio of energies would be reduced for the remaining duration of the collapse
from Dr. Bazant's figure of 8.4 to 1.05."
Created on 02/18/2009 10:33 PM by admin
Updated on 02/18/2009 10:54 PM by admin