Challenge: Demonstrate Sagging floor Trusses Pulling in Perimeter Columns

Newtons Bit said:
Just ran a quick analysis with RISA. It estimates P-delta behavior (but is still a linear analysis) and only does P-BigDelta.

Deflection without compression force is 4.6in.
Deflection with compression force is 15.0in.
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Newtons Bit said:
Based on his latest questions, I'd say he plugged some values into his FEA suite…
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It was Autodesk Inventor, but I guess you felt obligated to poison that water. So I will revert back to ABAQUS and do the analysis as non-linear.

Newtons Bit said:
I would wager that one of the following is wrong:

1) He pinned the bottom and top, which resulted in all of the compression force going into the top reaction.
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If true, you should be able to verify it with your FEA suite.

Newtons Bit said:
2) He didn't turn p-delta on (it's not on by default in all software)
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The software will issue a warning for high deformations. It did not in the case for Autodesk.

Newtons Bit said:
3) His suite only looks at P-BigDelta, and he needs to add structural joints along the length of his column to get the software to estimate P-Delta.
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ABAQUS and non-linearity will resolve this issue (if in fact it was an issue).

A little bird tells me you already know the answer. But here are the results:

First step, applying 6 kips to two locations. Note the agreement with the hand calculations.
Second step, applying 139 kips to the top. Yes, the deflection decreased, but I would have thought the reason would have been obvious.
Here is the corresponding stress for the first case.
And for the second case.

shinchan said:
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I am sure everyone would love to take the focus off of the topic in this thread and answer your question. But there is another thread with a challenge better suited for your questions.
 
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enik said:
It was Autodesk Inventor, but I guess you felt obligated to poison that water. So I will revert back to ABAQUS and do the analysis as non-linear.

If true, you should be able to verify it with your FEA suite.
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I already did it and posted the results. I'll print out a pdf report for you. Given how wrong you are about your results, I didn't poison the well. I was correct. I should apply for Randi's million dollars.

The software will issue a warning for high deformations. It did not in the case for Autodesk.

ABAQUS and non-linearity will resolve this issue (if in fact it was an issue).

A little bird tells me you already know the answer. But here are the results:

First step, applying 6 kips to two locations. Note the agreement with the hand calculations.
Second step, applying 139 kips to the top. Yes, the deflection decreased, but I would have thought the reason would have been obvious.
Here is the corresponding stress for the first case.
And for the second case.
Click to expand...

Are you seriously claiming that the deflection decreased by adding a compression force? Are you sure you didn't add a tensile force?
 
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enik said:
That was fast. I guess, unless you can prove otherwise.
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I already ran the analysis in RISA.

Newtons Bit said:
Just ran a quick analysis with RISA. It estimates P-delta behavior (but is still a linear analysis) and only does P-BigDelta.

Deflection without compression force is 4.6in.
Deflection with compression force is 15.0in.

With the compression force, the column is has exceeded yield capacity and would continue bending inwards until rupture.
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Like I edited in above, I'll post a pdf report for you after I get in to work today.
 
enik said:
Never heard of it. But I will look forward to your pdf with anticipation.
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Not surprising, given that it is only commonly used by structural engineers for building design...

I've attached the report to this post. Why don't you print out your data echo. I'd wager that you're axial load is a tensile force and not a compression force.
 

Attachments

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enik said:
Never heard of it. But I will look forward to your pdf with anticipation.
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Due to a fantasy filled conclusion clouding research/"engineer" skills? Did you peeked at loose change forum, where failure is rewarded with at-a-boys flowing freely, and rational posters are banned?

http://s1.zetaboards.com/LooseChangeForums/topic/4573597/10/
, they would not set up elaborate wiring systems that can be easily detected, and they would clean up any leftover evidence of their presence afterwards. In essence, covert military operations.
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Is this an FEA? You love the chain of command theory, where the NWO order murder and they did what the were ordered...

You can't state a goal for your Challenge thread? You think 911 was an inside job, CD. Why not explain how your thread will teach "skeptics" your inside job is true?

Challenged finished. When will you join reality.

After 11 years of failure by 911 truth, do you have the right stuff to make CD true?
http://s1.zetaboards.com/LooseChangeForums/topic/4724858/1/
Inside Job Evidence is in the Physics of WTC #1
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No.
 
Newtons Bit said:
Not surprising, given that it is only commonly used by structural engineers for building design...

I've attached the report to this post. Why don't you print out your data echo. I'd wager that you're axial load is a tensile force and not a compression force.
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I was wondering how he could possibly get decreased deflection with increased column compression but that would make sense if its tensile rather than compressive.

To my mind, the simplest example is a piece of dry spagetti, standing alone and constrained only at the bottom it remains vertical. Push down on it and it bends. Pull some part of it laterally and it bends. Pull some part of it laterally AND push down on it and it will bend more than either action alone.
 
jaydeehess said:
Core and perimeter columns now have lost lateral support and even if they have not suffered enough from buffeting by falling debris to fail them , they now succumb to long column instability, buckle and fail.
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Its come to my attention that this is not a particularily good description of this part of the collapse (and as pointed out by enik, not even within the pervue of this particular thread. This will be my last post in this thread concerning it). The perimeter columns did not display long column buckling, rather they peeled off in sheets. It is quite obvious even to persons devoid of engineering savvy that an enormous thin wall cannot stand on its own though and no matter the technical description of the detail of perimeter wall collapse, as the perimeter lost lateral support perpendicular to the perimeter plane, it (the perimeter wall) was extremely unstable.

In addition, although its not immediately obvious that the core of the structure could ever have stood 110 storeys high all on its own (my feeling is that it could not have but if someone has math on that saying otherwise I'd defer) the fact of collapse is that the upper part of the core was coming down on the lower portion and the core floor beams were not designed to withstand such dynamic loading and many of them would also fail leaving core columns standing alone or with much less lateral support between each other making them individually susceptible to long column type instabilities. A fact borne out by the remaining core 'spire' and how it could not remain on its own.

One poster here seems to expect a basement core CD charge but in fact the 'spire' negates any such charge immediately
 
jaydeehess said:
I was wondering how he could possibly get decreased deflection with increased column compression but that would make sense if its tensile rather than compressive.

To my mind, the simplest example is a piece of dry spagetti, standing alone and constrained only at the bottom it remains vertical. Push down on it and it bends. Pull some part of it laterally and it bends. Pull some part of it laterally AND push down on it and it will bend more than either action alone.
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I've also had trouble imagining such a scenario. The only one I could come up with where a compressive force would reduce the deflection is a pile of boxes.

If you have a pile of boxes horizontally fixed at both ends, and apply a mild horizontal pulling force in the middle (assuming perfect friction, i.e. no sliding of the middle box or any other out of its place), you will get more deflection than when applying a force from the top to the middle of the boxes. Intuitively it seems that that will keep happening until the deflection makes the vertical axis of the force fall outside one of the boxes, at which point the compressive force will do the same effect as in the spaghetti.

I don't think that scenario applies to a column though.
 
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jaydeehess said:
I was wondering how he could possibly get decreased deflection with increased column compression but that would make sense if its tensile rather than compressive.

To my mind, the simplest example is a piece of dry spagetti, standing alone and constrained only at the bottom it remains vertical. Push down on it and it bends. Pull some part of it laterally and it bends. Pull some part of it laterally AND push down on it and it will bend more than either action alone.
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And that's a good way to look at it. I don't understand how someone could say that it should be obvious the opposite would happen.
 
jaydeehess said:
I was wondering how he could possibly get decreased deflection with increased column compression but that would make sense if its tensile rather than compressive....
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Sure - but I am confident that NB and enik will sort that aspect out. Remember also that the model under discussion is simplified - it is a stand alone single column with some nominated loads applied. Should be of great help in understanding the actual collapse but still has built in approximations.

jaydeehess said:
...To my mind, the simplest example is a piece of dry spagetti, standing alone and constrained only at the bottom it remains vertical. Push down on it and it bends. Pull some part of it laterally and it bends. Pull some part of it laterally AND push down on it and it will bend more than either action alone.
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Well said - That is sort of "Column Instability 101 For Dummies"

The classic analyses go back to Euler circa 1750s It was for slender columns and axial loads. For typical structural columns the Euler simplification has long been superseded.

If we progress a bit towards 201:

The factors of interest in the WTC scenario move us away from Euler simplifications. The columns were not slender and were under the influence of "off axis loading" and imposed bending of the column.

Consider a progression away from purely "axial" loads moving to "eccentric loading" - load still within the column profile but off centre...then load outside the profile - the references to "P-delta" in previous posts refer (good enough for this lay person version) to this aspect. Meanwhile as the column starts to bend it becomes a bent strut. And the column rules no longer apply. The significant aspect for WTC collapse a la 9/11 is that a bent strut has far less strength than a column. It has already failed as a column and residual load carrying is order(s) of magnitude less than for an undamaged column. (Whether it is "order" or "orders" of magnitude needs the maths.)


EDIT PS - I still type too slow. I see Newton beat me to it whilst I was typing this post. :o :blush:
 
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Newtons Bit said:
And that's a good way to look at it. I don't understand how someone could say that it should be obvious the opposite would happen.
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The only possible thing I can think of is using compression to combat sway in a structure. IIRC Toronto's CN Tower has cables running down its core which are in tension thus putting greater compression on the tower itself and offering a counter to tension caused by building sway.(my description here being woefully inadequate, I hope that what I am trying to say is clear)
This would not, however , have any effect towards lessening buckling forces
 
jaydeehess said:
The only possible thing I can think of is using compression to combat sway in a structure. IIRC Toronto's CN Tower has cables running down its core which are in tension thus putting greater compression on the tower itself and offering a counter to tension caused by building sway.(my description here being woefully inadequate, I hope that what I am trying to say is clear)
This would not, however , have any effect towards lessening buckling forces
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That effect is a bit different than what we're discussing here. Lemmie 'splain. No, that would take too long, lemmie sum up.

When a member bends, it develops compression forces on one side and tension forces on the other. Concrete, the material the CN Tower is built out of, has fantastic compressive strength but almost no tensile strength. Through the magic of superimposed* loads, one can add the tension forces due to bending and the compression force due to "pre-compressing" together. This reduces the total net tension in the section and can lower the amount of steel rebar required in the structure and can save a fair amount of money.

*Last time I saw Dr. Klingner, he said I'd owe him a quarter every time I used that word. What a jerk.
 
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