Tower Collapse Questions for Critical Thinkers

rwguinn said:
Although to be painstakingly fair, bending over backwards, as it were, it is through change in momentum over time that "mass gains force", so from a purely pedantic POV, you are correct...
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It's not pedantic, it is the crucial difference between momentum and acceleration. Mass gains force though acceleration, not momentum. While the momentum changes as mass falls, the acceleration is the constant force of gravity.

As for dynamic load:
Dynamic Load
This type of load varies over time.
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I'm curious to know; where are you all deriving a different definition from?
 
kylebisme said:
It's not pedantic, it is the crucial difference between momentum and acceleration. Mass gains force though acceleration, not momentum. While the momentum changes as mass falls, the acceleration is the constant force of gravity.
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Mass doesn't change with velocity. You got that part right.
Force and velocity are related through changes in velocity. Momentum is a steady-state condition. It converts to a force when velocity changes.
As for dynamic load:

I'm curious to know; where are you all deriving a different definition from?
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Dynamic loading/ conditions are short-term (dT is small) Increases Changes over a time span > 1/wn (wn=Natural frequency) are not dynamic, but are considered static or quasi-static
 
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kylebisme said:
You are correct, but you are missing Bill's point. You could take a giant 2,000 pound weight that covered the area of your porch and collapse it by dropping that weight from high enough. However, if your broke that weight into a bunch of pieces, they wouldn't hit at the same time, and hence would have to be dropped from far higher to collapse your porch.
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kylebisme said:
As for dynamic load:

Dynamic Load
This type of load varies over time.
Click to expand...
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:confused:
 
rwguinn said:
Dynamic loading/ conditions are short-term (dT is small) Increases Changes over a time span > 1/wn (wn=Natural frequency) are not dynamic, but are considered static or quasi-static
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Ah, fair enough, my bad. It's been well over a decade since I used such terms regularly, and it seems I let live load and dynamic load blend together since then.
 
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Hokulele said:
:confused:
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kyle thinks he hasn't dumbed it down enough for us. It simply doesn't occur to him that he has absolutely no idea what he is talking about.

The arrogance of truthers is astounding, isn't it?
 
Hokulele said:
:confused:
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If he wants to be more specific the dynamic load as defined in architectural text is one which is applied suddenly. In the context of the towers this load was applied in such a short time period that the disjointed nature of the debris they claim should have a lesser effect is negligible. Approximately the same mass is loading the floors within the span of a second or less (extremely conservative estimate) as if the mass was still intact. It wasn't exactly powder hitting those floors, many of those individual "pieces" were several to tens of tonnes each.
 
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Grizzly Bear said:
If he wants to be more specific the dynamic load as defined in architectural text is one which is applied suddenly. In the context of the towers this load was applied in such a short time period that the disjointed nature of the debris they claim should have a lesser effect is negligible. Approximately the same mass is loading the floors within the span of a second or less (extremely conservative estimate) as if the mass was still intact. It wasn't exactly powder hitting those floors, many of those individual "pieces" were several to tens of tonnes each.
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Yep. The puzzled face was over why he thought it mattered whether or not the mass was intact or not. Overload is overload (in the static case of triforcharity's porch) and dynamic load is dynamic load (in the case of any of the collapses under discussion), regardless of the number of "pieces" it is in.
 
WildCat said:
And what do you think the design live load of the WTC floors was?
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I've had no reason to really look into it in detail, but while reading Makey's whitepaper I saw he suggested at least 500,000 tons, and and notes it was estimated to be carrying at least 2/3s of that at the time by NIST. Note of course that is the whole building, each floor has it's own limit too.
 
Hokulele said:
Yep. The puzzled face was over why he thought it mattered whether or not the mass was intact or not. Overload is overload (in the static case of triforcharity's porch) and dynamic load is dynamic load (in the case of any of the collapses under discussion), regardless of the number of "pieces" it is in.
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Try dumping a bucket's worth of sand on a a cardboard box, and then sweep up all the sand, put it in a bag, and try again.
 
You cannot compare a cardboard box to anything that is load bearing. The cardboard box gets its strength fromm it's sides, certainly not from the top.

Please, someone correct me if I am wrong.

Oh, and my dad is still laughing at you. He is now about to pee on himself.
 
bill smith said:
Well the broken floor is not really one mass. It is many small masses. These small masses will strike the lower solid intact floor independently as small masses. The small masses will also interaact with each other while falling, losing some energy in the process.
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Do they make baby masses while they are at it?:cool:
 
triforcharity said:
You cannot compare a cardboard box to anything that is load bearing.
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I'm comparing a bunch of loose mass to a solid one, the box is just for simplicity of the example. The same applies to a load bearing structure, but you'd need a lot more sand and and a much bigger bag.
 
Son, I think you just gave my dad a heart attack. I think most people here would agree, that a cardboard box is not the best anology. Either way, its still fail.

Wanna use a bucket and some water instead??
 
kylebisme said:
You are correct, but you are missing Bill's point. You could take a giant 2,000 pound weight that covered the area of your porch and collapse it by dropping that weight from high enough. However, if your broke that weight into a bunch of pieces, they wouldn't hit at the same time, and hence would have to be dropped from far higher to collapse your porch.
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Why wouldn't they hit at the same time if you dropped them at the same time?
 
kylebisme said:
Try dumping a bucket's worth of sand on a a cardboard box, and then sweep up all the sand, put it in a bag, and try again.
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That depends on how you dump it and how strong the box is. If you can dump it all at once, there will be essentially no difference. If the box cannot hold the weight of the sand, it doesn't matter how fast you pour it. Either way, you will have a crushed box.
 
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