I'll take that as a yes.
Can anyone here see incompatibility issues between BV, BL, and BLGB and the OOS model?
YES - I can!
Several of us - you and I included - clarified the relevant aspects on this forum back in 2010. The confusions we see being regurgitated here are the same ones which prevailed back then....so "déjà vu". And moving forward to 2008-9.
We had it right then and nothing has changed. Simply stated BV is not compatible with what actually happened. So BV is not compatible with OOS - your label OR "ROOSD" your descriptive acronym. Or the same process as I have described it as the "Three Mechanisms Model". Or any others which may be around. I don't give a damn who was first. Or who put a name on it. "ROOSD" and OOS" are both descriptive of the
specific progression as distinct from
generic progressions.
Earlier today, from memory, I recalled that none of the later Bazant papers are valid when referring to the actual 9/11 collapses at WTC.
So I re-read B&V to check my memory. I will limit my comments to BV at this stage - until I have time to re-read the others. But I cannot see how conclusions validly reached in 2008-9-10 could become wrong through the passing of time.
Synopsis of Key Issues
B&Z was at the time - from 2001/2 through to last year - thought to be a valid limit case.
(Only recently the maths assessing available energy have been challenged and the challenge so far AFAIK unresolved - doesn't matter for this post.).
B&Z assumed columns in line and, as per B&Z maths, there was enough energy available to "crush" storeys by the range of buckling options available.
(I will continue to use the term "crush" to refer to one dimensional mechanism models where the columns are taken into account as the major vertical force resisting element and are failed by buckling as part of the storey being "crushed".)
The actual mechanism of collapse - I repeat "what actually happened" and NOT the abstract model - did not "crush" perimeter columns and the evidence is very strong that it did not "crush" core columns.
So there was a fundamental difference between the B&Z assumption of collapse by columns "crushing"and the actual progression which was
led by material falling down the tube of the OOS space and shearing off the floor joists.
HOWEVER B&Z was a valid limit case because the energy to shear off the floors was orders of magnitude less than the energy which would have been needed to "crush" the columns if that crushing had occurred. It did not occur.
The modelling of B&V is the same one dimensional setting from B&Z - it assumes that columns were in line and "crushed" and B&V relies on B&Z maths as proof that sufficient energy was available to crush the columns.
Except that is not what happened in the real event.
So the BV model is a "columns in line" model which was explicitly defined as an attempt to produce a generic collapse analysis method for progression which have the columns in line.
And that is not what happened at the WTC "Twins".
So BV is NOT COMPATIBLE with what really happened. Which is the model you and I have published - maybe others - and which you label OOS.
Some bits of B&V:
BV said:
A simplified one-dimensional analytical solution of the collapse front propagation will be presented...
Note "simplified" AND "one-dimensional".
BV said:
...progressive collapse was not simulated at NIST because its inevitability, once triggered by impact after column buckling,...
"impact"
- shades of Missing Jolt...actually "The Jolt that Never Could Be"
- but let's not diverge
BV said:
However, a theory describing the progressive collapse dynamics beyond the initial trigger, with the WTC as a paradigm, could nevertheless be very useful for other purposes, especially for learning from demolitions.
So WTC collapse is to be a paradigm? When everyone here except tfk and beachnut agrees that (whatever we call it) the OOS model is what actually happened? So a real
columns not in line collapse is a paradigm for generic progressions which have
columns in line.???
Penultimate for those who can decode engineering gobbledegook:
BV said:
To analyze progressive collapse, the complete load-displacement diagram F(u) must be known (Figs. 3 and 4 top left). It begins by elastic shortening and, after the peak load F(0), curve F(u) steeply declines with u due to plastic buckling, combined with fracturing for columns heated above approximately 450°C, the buckling is viscoplastic. For single column buckling, the inelastic deformation localizes into three plastic or softening hinges (Sec. 8.6 in Bažant and Cedolin 2003; see Figs. 2b,c and 5b in Bažant and Zhou 2002a). For multistory buckling, the load-deflection diagram has a similar shape but the ordinates can be reduced by an order of magnitude; in that case, the framed tube wall is likely to buckle as a plate, which requires four hinges to form on some columns lines and three on others (see Fig. 2c of Bažant and Zhou).
Do they have columns in line or not? Did the real event have "columns in line"? How can two different models be "compatible"?
BV said:
Such a buckling mode is suggested by photographs of flying large fragments of the framed-tube wall, which show rows of what looks like broken-off plastic hinges.
Given the extent of video research that Major_Tom and associates have performed I'll leave the irony of that claim for members to work out for themselves.
BV is not compatible with what actually happened.
I'll read the other papers again and may post more.
