Jango
Graduate Poster
Oh God...
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WTC Twin Towers - Ozeco41 accepts a Jango Challenge to explain "Initiation"
- Thread starter ozeco41
- Start date
ozeco41
Philosopher
Mutual.
And my thanks to all those members who left the thread free of noise for the duration of my explaining.
We got it all in one noise free page - must be some sort of a record.
ozeco41
Philosopher
Jango
Graduate Poster
Perhaps we can expand to Building #7?
From what I have read and seen, the formula for collapse was damage from debris and fires. IIRC, column 79 failed and global collapse began. Does your explanation for the Twin Towers apply to Building #7 or are there significant differences?
Jango
Graduate Poster
..our help in ages past.
If I were from the east coast, like New Jersey or New York, the way I meant it would have been spelled out 'Oh Gawd'. But I am not from the east coast. I am from the Midwest.
ozeco41
Philosopher
I cannot explain it with the assured rigour I can for the Twins.
Sure I can critique the arguments both ways. And there is also a lot of the debunker argument which fell for the traps inherent in the truther claims.
It was a steel framed building subject to unfought fires. Odds on it would collapse. It did. Steel framed buildings subject to fire rely on conduct of active fire fighting methods. The designs are premised around 1, 2, whatever hours fire resistance - to give time for occupants to escape and ACTIVE fire fighting started. The occupants escaped. The decision was taken to not start active fire fighting. That left the building to take its chances. It lost. No big deal in logic. The sort of choice firies make every day in bush fire situations - which houses to save and which ones to let go - except a few more decimals on the size and cost.
Broadly that is the NIST explanation - I have a minor pedantic disagreement which changes nothing of consequence.
No. Totally different.
Oystein
Penultimate Amazing
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...
My Objective - to explain the cascade failure process of WTC1 and WTC2 "initiation stage" up to the point where the Top Block was falling AND ROOSD/Three Mechanisms progression was under way.
I will not be addressing CD claims which means that I must allow for CD options in the mix of contributors to collapse. The understanding of cascade failure is not affected whether or not there was CD. (Think about that before (any of) you ask)
...
Detailed explanation finished by Post #37, therefore thread OP plus following posts now ripe for an # oysteinbookmark.
Thanks ozeco41 for the effort, and thanks all who took their comments to the Peanut Gallery and kept the first page clean
Newtons Bit
Penultimate Amazing
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No. The strength of the column is not "inversely proportional to the square of EL". The columns near the plane impact have a small effect length and as a result are inelastic. You're using elastic behavior. This is the actual formula for nominal compressive capacity from the AISC Specification:
The perimeter columns have a r~=5.5in, which makes the slenderness ratios:
KL / r (L= 12'4") = 26.9
KL / r (L= 37'0") = 80.7
Which is less than the limiting slenderness of 4.71 SQRT(E/Fy). Equation E3-2 controls and as a result, the difference in nominal compressive capacity is in the ballpark of 20%.
ozeco41
Philosopher
Yes---of course---BUT...
Remember that my explanation was for Jango - AFAICS a non-engineer and I needed to get some broad concepts across.
I only listed a couple of the "building block mechanisms" and didn’t explain the common error(s) made with perimeter inward bowing. If Jango asks for more explanation I will provide it - No point me confusing the lay person with lots of engineering details which don't change the broad message.
My objective was (and still is) explaining to the relative novice - not making a doctoral dissertation which can withstand detailed professional scrutiny by those who shouldn't need my explanation.
Newtons Bit
Penultimate Amazing
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I don't believe you. Either you're intentionally misstating your case to make it sound better or you didn't remember that elastic buckling was a thing. Personally I think the former is much more likely than the latter.
This statement of yours:
is 100% false in the context of your example. If you just wanted to explain the basics then you could have explained that the compressive capacity is some function of the length and that increasing the length reduces the capacity. That'd be fine. That would actually achieve the objective you're claiming you set out for. But by using the providing the terms that you did, terms for elastic buckling that do not apply in your example, you're misleading him. And, in my opinion, it seems to be intentional.
This statement of yours:
is 100% false in the context of your example. If you just wanted to explain the basics then you could have explained that the compressive capacity is some function of the length and that increasing the length reduces the capacity. That'd be fine. That would actually achieve the objective you're claiming you set out for. But by using the providing the terms that you did, terms for elastic buckling that do not apply in your example, you're misleading him. And, in my opinion, it seems to be intentional.