http://www.journalof911studies.com/resources/2014JanLetterPepper.pdf
I thought this thread would be the most recent and appropriate one to post this in. I'm sure a lot of this is well-worn territory, but the crux of the matter appears to be that NIST did not include the web stiffeners or some lateral support beams in their report. NIST responded that the structural analyses did not show any web crippling failures; therefore, it wasn't necessary to include them in their Report. Peppers contends that the lateral support beams provided critical support to the buckled beam and that the stiffeners provided critical girder support.
So as always, without rancor, please point me to the best debunking of this assertion that has already appeared in past threads that specifically address this omission, (not the whole thread, please, just the posts) or the best arguments for why NIST did not need to include these components in their analyses to arrive at a conclusive theory.
The status AFAIK is that NIST proposed a failure mechanism to explain the collapse of WTC7.
That failure mechanism recognised as key features:
1) The East Penthouse fell early in the collapse;
2) Col 79 was the main element of the structure supporting EPH;
3) Therefore Col 79 must have failed; THEN
4) The rationale for failure of Col 79 was a loss of horizontal bracing over several storeys PLUS "girder walk-off"
Comment: Col 79 must have failed and Euler buckling due to removal of bracing is near certain the cause - sight unseen - because there are really only two options - buckling from loss of bracing OR imposed massive overload which is not possible.
Now the issue of contention is that several truth movement advocates have claimed that the girder walk-off component of the NIST hypothesis in not possible.
Persons arguing from both "sides" have resorted to two types of logic:
A) arguments based on temperature expansion/contraction - all of which worked in fractions of inches dimensions and assumed that the columns supporting the girder remained unmoved at their original precise spacing. That argument opposed by me against T Szamboti on this forum. I did not disprove his claim - merely pointed out that he had not justified the "original spacing" assumption - and that in a heat ravaged building such an assumption was very dubious. Status of the me v Szamboti discussion - I counter claimed that Tony's case was "not proven" because of the unsupported and unlikely assumption.
B) A class of arguments related to the minor structural details such as those identified in the report you cited. The details are typical of those which NIST has omitted or discounted and the truth movement had focussed on - in isolation from context on the premise that if a single error can be proven against NIST is actually proves whatever the truth movement counter claim is. Always false logic.
I doubt that any of the arguments about those details relevant to this situation will ever be definitely resolved.
The girder walk off is only one aspect of the full collapse scenario.
If the objective is prove NIST wrong on a detail - I cannot say about that specific detail.
If the objective is to dismiss NIST's broad scenario - it is not relevant - the key features remain in place - EPH fell>>>Col79 must have failed>>>failure not overload THEREFORE must be removal of bracing.>>>Girder was only one of many elements.
So if the girder walk-off is in error it does not negate the overall scenario - merely one detail. BTW JSanderO has proposed an alternate initiating factor. There could be several more.
I'll leave it there for the quick summary. Beware of the risk of FEA based counter claims - FEA is the most advanced calculator available for engineering structures BUT is is as prone to GIGO as slide rules (my era) OR calculators (the era when I was first managing engineers).
So I acknowledge your request was for help in understanding the specific details. I suggest the place to look is at what use is made of those details - i.e. the bigger picture, The details are almost certainly irrelevant in the high level argument - viz "CD or not" . They are also irrelevant in the "broad explanation of collapse mechanism" and IMO they are only significant if the objective is "Prove NIST wrong on a detail". On that one I cannot help. NIST may have been wrong but it makes no difference.
And I think that is "without rancor"
Cheers.
