Analysis of Bazant & Zhou (2002)

Mr. Skinny said:

I'm not familiar with the terms "buckle failure" "bend failure" and "break failure" anymore than I am with "collapse failure". Wouldn't one more correctly use compression, tension, torsion, or shear?
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Columns will buckle at or lower than their yield stress. At this point they aren't purely compressive members anymore, kinks develop and rotate (bend). There's about ten times more energy absorbed post-buckling than pre-buckling. This is a concept that is typically used in seismic bracing where we want the braces to compressively buckle.
 
Bofors, since you are a man of science, I cannot understand how you can characterize what you've presented here so far as an «analysis»?

Am I missing something here?
 
Page 1, Paragraph 4:


For a short time after the vertical impact of the upper part, but
after the elastic wave generated by the vertical impact has propa-
gated to the ground, the lower part of the structure can be ap-
proximately considered to act as an elastic spring [Fig. 2(a)].
What is its stiffness C? It can vary greatly with the distribution of
the impact forces among the framed tube columns, between these
columns and those in the core, and between the columns and the
trusses supporting concrete floor slabs.


Point 27 Bazant & Zhou claim that the building-bottom can be considered a one-dimensional elastic spring for a "short time", however they do not say how long this time is.

Point 28 Bazant & Zhou claim the one-dimensional elastic spring approximation is valid "after the elastic wave generated by the vertical impact has propagated to the ground." It is not clear if this a typo or not, it seems that they mean "before" not "after".

Point 29 Bazant & Zhou fail to a use a more optimistic two-dimensional model here where the building-bottom could bend and the building-top fail off.

Point 30 Bazant & Zhou fail to a use a more optimistic (and realistic) model where plastic deformation also occurs instead of merely elastic.

Point 31 Bazant & Zhou fail to a use a more optimistic (and realistic) model where the building top is also spring-like.

Point 32 Bazant & Zhou again note that the distribution of forces and materials properties "vary greatly", yet pessimistically (and unrealistically) assume they are uniform, which would act to stop the building-top from tipping over and falling off the bottom.
 
Good grief, we are only on paragraph 4, and bofors has already started to repeat himself. I predict this will take the rest of the year, and bofors will still fail to understand why Hoffman is wrong.

So who wants dibs on point 32?
 
Everyone, please stop reporting this thread.

bofors - please check PMs
 
bofors, do you realize that Bazant's model assumes that columns fall on top of one another, and loads are distributed evenly around the structure, thus allowing for maximum resistance? You seem to suggest in Point 29 that the rotation of the upper block should be accounted for in the analysis, if it was, neither of these assumptions would be acceptable and resistance would decrease

Furthermore, Bazant justifies not taking into account a scenario where the top falls off with his calculations in appendix 2.
 
chillzero said:
Everyone, please stop reporting this thread.

bofors - please check PMs
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Ok... I will stop posting my analysis of the Bazant & Zhou incrementally.

I now plan to completely finish a rough draft of my analysis off-line.

Then, I will present it here (or perhaps in a new thread) in one long post.

Afterwards, I will respond to any reasonably intelligent comments on my analysis here.
 
bofors said:
Ok... I will stop posting my analysis of the Bazant & Zhou incrementally.

I now plan to completely finish a rough draft of my analysis off-line.

Then, I will present it here (or perhaps in a new thread) in one long post.

Afterwards, I will respond to any reasonably intelligent comments on my analysis here.
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Don't start a new thread, it will only get merged with this one anyway.
 
Uhhh....what the hell is wrong with some people.

Bofors, I hope your not going to cover your eyes when people address your points and as everyone starts to put you on ignore you dont run away to some other forum claiming some strange mental victory...
 
bofors said:
Afterwards, I will respond to any reasonably intelligent comments on my analysis here.
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And by "reasonably intelligent", of course, you mean only those that agree with you. All others will be ignored, as has been your MO to date.
 
bofors said:
Ok... I will stop posting my analysis of the Bazant & Zhou incrementally.

I now plan to completely finish a rough draft of my analysis off-line.

Then, I will present it here (or perhaps in a new thread) in one long post.

Afterwards, I will respond to any reasonably intelligent comments on my analysis here.
Click to expand...

What you're doing isn't an analysis.
 
Newtons Bit said:
Columns will buckle at or lower than their yield stress. At this point they aren't purely compressive members anymore, kinks develop and rotate (bend).
Click to expand...
Isn't this a combination of compression and torsion failure?
There's about ten times more energy absorbed post-buckling than pre-buckling. This is a concept that is typically used in seismic bracing where we want the braces to compressively buckle.
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Not sure I understand your first statement. Your second statement seems to indicate that seismic bracing is designed to selectively fail at certain places in order to prevent total failure.

And please don't spend too much time answering, Newtons Bit. My understanding of this isn't really critical to the discussion, I sense. :)
 
So basically, members of this forum have taken the time to read bofors spam posts and intelligently respond to them and he doesn't have the courtesy to read a single one of them? Or to respond for that matter? Sorry but that really rubs me the wrong way. What a piece of work. And twoofers wonder why no one likes them and will give them any media time.
 
Mr. Skinny said:
Isn't this a combination of compression and torsion failure?

Not sure I understand your first statement. Your second statement seems to indicate that seismic bracing is designed to selectively fail at certain places in order to prevent total failure.

And please don't spend too much time answering, Newtons Bit. My understanding of this isn't really critical to the discussion, I sense. :)
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Seismic bracing: take an x-brace for example, when the lateral forces on the building push one way, one brace is in tension the other is in compression. The compression one buckles and absorbs alot of energy. Then the load reverses, that brace goes into pure tension and the other one buckles. The load reverses again, etc etc. This is how Special Concentric Braced Frames work. Buckling Restrained Braces (which is a patented product) do something similar. If the earthquake is small, there won't be any buckling in the system and it will stay elastic the whole time. There won't be any permanent damage to the building. If the earthquake is small, there will be permanent damage to the building (mostly in the form of architecture, plumbing, etc) but it won't fall down. Thus allowing the people inside to safely gtfo.
 
Newtons Bit said:
Seismic bracing: take an x-brace for example, when the lateral forces on the building push one way, one brace is in tension the other is in compression. The compression one buckles and absorbs alot of energy. Then the load reverses, that brace goes into pure tension and the other one buckles. The load reverses again, etc etc. This is how Special Concentric Braced Frames work. Buckling Restrained Braces (which is a patented product) do something similar. If the earthquake is small, there won't be any buckling in the system and it will stay elastic the whole time. There won't be any permanent damage to the building. If the earthquake is small, there will be permanent damage to the building (mostly in the form of architecture, plumbing, etc) but it won't fall down. Thus allowing the people inside to safely gtfo.
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Beautifully explained, NB. I get it. Also learned a new acronym (gtfo) which will be useful in the future. :)
 
Newtons Bit said:
Seismic bracing: take an x-brace for example, when the lateral forces on the building push one way, one brace is in tension the other is in compression. The compression one buckles and absorbs alot of energy. Then the load reverses, that brace goes into pure tension and the other one buckles. The load reverses again, etc etc. This is how Special Concentric Braced Frames work. Buckling Restrained Braces (which is a patented product) do something similar. If the earthquake is small, there won't be any buckling in the system and it will stay elastic the whole time. There won't be any permanent damage to the building. If the earthquake is small, there will be permanent damage to the building (mostly in the form of architecture, plumbing, etc) but it won't fall down. Thus allowing the people inside to safely gtfo.
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Conversly, buckling failure is what happens to the front fender of your car when you hit a brick wall. The key word there is "Failure", which means, in engineer-speak means permanent damage. Bending failure (we usually say "It will fail in bending" implies that M*C/I is greater than the yield stress of the member.
Both are predictable failures, in that you can predict the load at which it will occur with pretty good precision and accuracy.
What happens after failure in buckling is NOT particularly predictable, except generally. Everything gets very, very non-linear, and you end up with "N" equations in "N+x" unknowns, where x=>1
 
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