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Failure mode in WTC towers

Did floors induce moment in columns?

Newtons Bit,

Would it not make more sense to post a diagram with multiple floors?
 
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Heiwa said:
I would reword 13. as follows.

Once the upper block gets moving due to buckled columns (local failures) in the initiation zone below, the upper block moves down a little and comes to rest on the buckled structure still connected to the structure below (and equilibrium is reinstated). Evidently the load carrying capacity of the intact structure below is sufficient to carry the upper block (as it did it before some columns buckled). No total collapse ensues.
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Did you do that potential energy calculation?

Forgive me if I missed it. This is a busy forum.
 
westprog said:
Did you do that potential energy calculation?

Forgive me if I missed it. This is a busy forum.
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Come on, I know you have seen the videos where they show a floor of a building be wiped out and the top comes to rest on the bottom.

We used to watch them all the time on Saturday morning.
 
Dave Rogers said:
Are you sure it's a standard fallacy? I googled "unevaluated inequality" and only got a couple of hits, one to the post above and the other (indirectly - I had to dig a bit) to a post of mine in January. To be honest I thought it was a term I'd created myself to describe the standard truther "I don't know what it ought to look like but it shouldn't look like that" argument.
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Hmm, maybe I'm wrong. I've seen this in papers on machine reasoning and truth maintenance systems (TMS; has nothing to do with the "truth movement"), but not phrased with respect to rhetoric. Your January post was the first I'd seen it used in this context.

In any event, I didn't invent it. It looks like you did. You should probably start a Wikipedia page on it, because it's very clever.
 
Norseman said:
The compressed air canon is used to launch an explosive charge on to a suspect slope:
http://avalanchemitigationservices.com/photos.htm
http://avalanchemitigationservices.com/images/evolution.pdf

Also for snow avalanches there are many indicators that can be used to determine the likelihood of an avalanche or not, including tests like digging a snowpit or doing a Rutschblock test. But there is no method that gives us an 100% reliable answer unfortunately. It is a bit like earthquake prediction.

Norseman.:)
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Yes, I 've seen this type of air canon as well. All of these however fire a concussive charge. The type of canon I've seen used is a pneumatic bird banger. They never used it to cause an avalanche per se, but they were able to dislodge fresh snow from an overhang at about about 100m. Whether this was as a direct result of the concussion, or simply a chance occurrence due the wind acting at the same moment is certainly debatable. I'm inclined to agree with you that is was most likely as a result of the latter.

As with many of the myths I've seen busted, this rides the fine line between what is theoretically possible under the exact right cicumstances and what is realistically possible. For your inspection, I give to you "Controlled Demolition" :D
 
Gravy said:
Why?
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He wants to see something like this:





The moment in the bottom left column varies linearly from -3.7k*ft at the bottom(N1) to +7.9k*ft at the top(N2). It has an axial load of 19.57k. This is a 100% moment frame all joints are fixed. And yet there is still bending in the column. Huh. Imagine that.


How about another quick example, let's look at the same frame with all pinned joints. I've added diaphragm connections in and out of plane for stability. These connections have to be added otherwise the whole thing would just fall right over.





The moment in the bottom left column varies from 2.3k*ft at the top(N2) to zero at the bottom. This isnt' exactly rocket science, but both Heiwa and Mr. Szamboti have been shown to be morons on this. The bending is less noticeable visually in my second example, however it's still actually there. The deflection amplification is also the same. Notice how the same beam under the same loads bends more in a pinned connection than a fixed.
 
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Is it ever physically possible to connect a load to one side of a vertical column without creating moment?
 
phunk said:
Is it ever physically possible to connect a load to one side of a vertical column without creating moment?
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Kind of. If you have two beams framing into each side of a column with identical loads there will be almost zero induced moment. The beam on one end and its' eccentric connection will be equal and opposite to the other beam reaction. However in the real world, this doesn't happen. One side or the other is going to have more load.

There are also code requirement stipulating that the design engineer MUST do skip live-loading in bays if the beams are designed as continuous (i.e. moment connected) to the columns. This is because there are conditions where a fully loaded bay on one end of the column and a fully unloaded bay on the other will result in differing moments and shears in the beams and columns to the point where it could cause failure. This is very important in concrete construction, however.
 
phunk said:
Is it ever physically possible to connect a load to one side of a vertical column without creating moment?
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Newtons Bit said:
Kind of. If you have two beams framing into each side of a column with identical loads there will be almost zero induced moment. The beam on one end and its' eccentric connection will be equal and opposite to the other beam reaction. However in the real world, this doesn't happen. One side or the other is going to have more load.

There are also code requirement stipulating that the design engineer MUST do skip live-loading in bays if the beams are designed as continuous (i.e. moment connected) to the columns. This is because there are conditions where a fully loaded bay on one end of the column and a fully unloaded bay on the other will result in differing moments and shears in the beams and columns to the point where it could cause failure. This is very important in concrete construction, however.
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I think phunk is considering the fact that real beams/columns have actual physical dimensions, e.g., a 2X4 is 1 5/8 in thick X 3 3/4 Wide, while we (analysts) consider them to be a Centerline...:D
In either case, the reality-based answer is, as NB said... "no, not really"
 
DGM said:
So the exterior of the building would sway independent of the core.:eek:
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No, horizontal wind forces on one wall are transmitted by the floors to the core and then to the opposite wall via the floor pin joints to the columns.

Evidently these intermittent (wind) axial forces in the floors produces shear forces and thus bending moments in the perimeter columns. But they are ... intermittent.

The floors would not drop down due to that. Or anything else for that matter, incl. air plane crashes, fire, etc.

No total, global collapse of structure below is ever possible due to some local collapses up at the top.

More questions? Hopefully, intelligent ones.
 
funk de fino said:
Threads like this are normally the ones I like the most because I learn a lot of stuff from the postings by NB, Dave R, rwguinn, R Mackey, GU, Gravy etc etc

Unfortunately they are generally always have to be spoiled by trolling posters like Heiwa and realdcdeal et al who display an inability to display any level of understanding of what they post about (which is obvious even to the layman)

Is there any way these could be structured so that only the relevant players could be involved that keeps the chaff and flare from the trolls out?
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Hopefully not.
 
Heiwa said:
No, horizontal wind forces on one wall are transmitted by the floors to the core and then to the opposite wall via the floor pin joints to the columns.

Evidently these intermittent (wind) axial forces in the floors produces shear forces and thus bending moments in the perimeter columns. But they are ... intermittent.

The floors would not drop down due to that. Or anything else for that matter, incl. air plane crashes, fire, etc.

No total, global collapse of structure below is ever possible due to some local collapses up at the top.

More questions? Hopefully, intelligent ones.
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So your statement earlier is false.
As the floors are in principle hanging on the columns via a pin joint, no moment is transferred to the column! Just the weight of the floor adjacent to the column is transferred as shear via the pin joint to the column, where it adds to the compressive load in the column.
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Thanks for clearing that up.
 
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Newtons Bit said:
Wow, Heiwa and Mr. Szamboti are crazy. Heiwa says that moment can't be induced in a core column because the reaction is pinned, and Mr. Szamboti says that moment can't be induced because they're fixed connections. I guess you can't ever have moment induced in columns.

[qimg]http://www.internationalskeptics.com/forums/imagehosting/thum_16329479baa90cc44e.jpg[/qimg]

Especially not in connections that look like the above, nope never (/sarcasm).
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Evidently any excentricty "e" in the floor pin connection to the column produces a bending moment in the column due to a load P on the floors. But "e" is very small. Can be ignored in serious analysis. More intelligent questions?
 
westprog said:
Did you do that potential energy calculation?

Forgive me if I missed it. This is a busy forum.
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Full story at http://heiwaco.tripod.com/nist.htm and http://heiwaco.tripod.com/nist1.htm . Takes 10 minutes to study. The PE of the upper block is very small! Cannot produce any total, gravity driven collapse of avalanche type of the structure below. The structure below is much too strong for that and the strength below is located where any PE from above will never be applied.
 
Newtons Bit said:
He wants to see something like this:

[qimg]http://www.internationalskeptics.com/forums/imagehosting/thum_1632947b0a464a6144.jpg[/qimg]

[qimg]http://www.internationalskeptics.com/forums/imagehosting/thum_1632947b0a47ce560f.jpg[/qimg]

The moment in the bottom left column varies linearly from -3.7k*ft at the bottom(N1) to +7.9k*ft at the top(N2). It has an axial load of 19.57k. This is a 100% moment frame all joints are fixed. And yet there is still bending in the column. Huh. Imagine that.


How about another quick example, let's look at the same frame with all pinned joints. I've added diaphragm connections in and out of plane for stability. These connections have to be added otherwise the whole thing would just fall right over.

[qimg]http://www.internationalskeptics.com/forums/imagehosting/thum_1632947b0a48d4e8e4.jpg[/qimg]

[qimg]http://www.internationalskeptics.com/forums/imagehosting/thum_1632947b0a497966ed.jpg[/qimg]

The moment in the bottom left column varies from 2.3k*ft at the top(N2) to zero at the bottom. This isnt' exactly rocket science, but both Heiwa and Mr. Szamboti have been shown to be morons on this. The bending is less noticeable visually in my second example, however it's still actually there. The deflection amplification is also the same. Notice how the same beam under the same loads bends more in a pinned connection than a fixed.
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Sorry, as joints N1, N2, etc are pin joint there is no bending moment in left column N, anywhere! Just compression. OK, if top joint N4 moves transversly there is some moment ... but negligible. And your model cannot calculate that! But your are 100% right - horizontal floor beams bends more when the connection to the column is a pin. Reason? The bending moment is zero at the pin. More intelligent questions?
 
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