Challenge: Demonstrate Sagging floor Trusses Pulling in Perimeter Columns

[beachnut]

... Let’s use the 35 foot truss from NIST NCSTAR 1-6B. This first scenario is a 1000 lb force on the top side of the truss at a modulus of elasticity of 30 x 10⁶ psi.
... Here is the question, what is happening to the reaction forces?

You use NIST 1-6B, a full up model of the floor with fire protection. Makes your work useless for the task at hand. Any layperson can see your mistake. You use insulated data, for insulated reality. Is this special engineering for spreading the inside job? What is next, you failed this time, using the wrong data.

 

[Newtons Bit]

I apologize, my initial analysis did use a nylon rope, which was flexible. Let me change it to a steel rope that is already taut.
View attachment 28750

Now if we pull on the already taut steel rope, we get...

View attachment 28751

pull in of the columns because, we are pulling them in (I had to apply a magnification for clarity in the FEA results). Care to guess what happens if we double the load on the already taut steel rope?

So we agree that by pulling on steel columns with a steel (or taut) rope, we get pull in. Let’s move back to your “centenary sag is a very effective force multiplier”.

Let’s use the 35 foot truss from NIST NCSTAR 1-6B. This first scenario is a 1000 lb force on the top side of the truss at a modulus of elasticity of 30 x 10⁶ psi.

View attachment 28753

The second scenario is the same force but with a modulus of elasticity of 8.7 x 10⁶ psi.

View attachment 28754

And let’s take that modulus down to 1.7 x 10⁶ psi.

View attachment 28755

It may be a little difficult to see, but the displacement in the middle of the truss is increasing (I had to apply a magnification factor again for clarity)?

Here is the question, what is happening to the reaction forces?

Catenary behavior occurs when a member can no longer carry vertical forces purely through bending. To do this with a truss, you will need to remove a truss web member or two or push said members into a buckled state to generate catenary behavior.

 

[ozeco41]

Catenary behavior occurs when a member can no longer carry vertical forces purely through bending. To do this with a truss, you will need to remove a truss web member or two or push said members into a buckled state to generate catenary behavior.

...or heat the truss.

You are quite correct about "catenary behavior" (my emphasis above). However the discussion between me and enik is not about catenary behaviour. It is a dispute one of the underlying factors.

My comment was correct. My "layman's explanations" prove that. So does your simple example.

enik's denials are false.

Sorry to appear pedantic BUT there is a false claim by Tony Sz still unresolved. In essence he claimed that catenary sag and bending resistance effects in the beam cannot co-exist. That is hogwash so I'm covering my arse in case Tony ever deigns to support his false claim. Rebutting the claim would be straightforward but I would need to go back to engineering basics given that the situation was outside the scope of normal engineering design parameters and the associated assumptions.

There is another point of engineering pedantry which may arise if ever I need to rebut that false claim by Tony. But I'll not confuse the current discussion by diverging.

 

[enik]

...or heat the truss.

You are quite correct about "catenary behavior" (my emphasis above). However the discussion between me and enik is not about catenary behaviour. It is a dispute one of the underlying factors.

My comment was correct. My "layman's explanations" prove that. So does your simple example.

enik's denials are false.

In that case, you should have no problem with my question in Post 400.

 

[enik]

Catenary behavior occurs when a member can no longer carry vertical forces purely through bending. To do this with a truss, you will need to remove a truss web member or two or push said members into a buckled state to generate catenary behavior.

My question about the reaction forces should be a no-brainier for you. Right?

 

[Newtons Bit]

My question about the reaction forces should be a no-brainier for you. Right?

Yes, of course. Assuming that the truss has not yielded, there will be very little (or none, depending on the type of analysis) difference in reaction forces and that they are purely vertical.

The reaction forces for your steel cable example will be parallel to the cable direction (cables are tension only!) and the sum of the vertical reactions of both ends will be equal and opposite to the vertical load applied to the middle of the cable. (self-weight calculated otherwise)

 

[ozeco41]

In that case, you should have no problem with my question in Post 400.

True but I'm not going to follow your derail.

I have responded to your false claim that my comment to Tony Sz was wrong. It isn't. And I have rebutted in detail many of your false assertions. You have neither responded to those rebuttals nor posted your own claim about the subject of my original statement of a bit of simple physics. Your example is not about that "bit of simple physics". No matter how many times you shift the goalposts you will not fool me. Take that reality on board.

Sure I could follow your goalpost shift. Newton has in his post. His post is correct for the shifted scenario. It is simple basic engineering.

(Side Note: Any other members who may be unsure as to what is the goalpost shift either post the question or PM me. My previous posts give layman level explanations of the issue that enik has disagreed with. Those explanations of mine have not been addressed and certainly not rebutted by enik. Newton's posts, insofar as they overlap that issue, are fully supportive of my original claim. I have spent a lot of time clearly showing enik's bits of evasive dishonest trickery. I don't want to assit enik with the derailing tactics he is playing.)

My question about the reaction forces should be a no-brainier for you any reasonably competent engineer. Right?

FTFY I can analyse your different scenario as readily as I analyse the one you falsely criticised. I won't at least before you respond reasonable to what I have said.

This post by Newton explains in words some of the same points of principle that I have explained in my previous posts BUT it applies to a different scenario:

Yes, of course. Assuming that the truss has not yielded, there will be very little (or none, depending on the type of analysis) difference in reaction forces and that they are purely vertical.

The reaction forces for your steel cable example will be parallel to the cable direction (cables are tension only!) and the sum of the vertical reactions of both ends will be equal and opposite to the vertical load applied to the middle of the cable. (self-weight calculated otherwise)

...every point agreed....within that scenario.

 

[Tony Szamboti]

it seems Tony although I am no structural engineer by an stretch, that your points have been answered and shown to be incorrect by people who are structural engineers.

I have learnt a fair bit from them but what I have learnt from you is you do not seem to know when to accept defeat.

It would seem to me that you still have a lot to learn. Who would be the structural engineers you mention?

 

[NoahFence]

 

[Newtons Bit]

...or heat the truss.

You are quite correct about "catenary behavior" (my emphasis above). However the discussion between me and enik is not about catenary behaviour. It is a dispute one of the underlying factors.

My comment was correct. My "layman's explanations" prove that. So does your simple example.

enik's denials are false.

Sorry to appear pedantic BUT there is a false claim by Tony Sz still unresolved. In essence he claimed that catenary sag and bending resistance effects in the beam cannot co-exist. That is hogwash so I'm covering my arse in case Tony ever deigns to support his false claim. Rebutting the claim would be straightforward but I would need to go back to engineering basics given that the situation was outside the scope of normal engineering design parameters and the associated assumptions.

There is another point of engineering pedantry which may arise if ever I need to rebut that false claim by Tony. But I'll not confuse the current discussion by diverging.

I'm quite confused as to what your and enik's dispute is about now.

 

[Gamolon]

Two questions Tony.

1. How do you derive the bolded/red statement you make below...

This is why John Skilling was able to say the Twin Towers could have one exterior face and its corners completely removed and be missing half the columns from the two normal side walls and the building could still take a 100 mph wind.

...from the bolded/red statement below?

For those who need a citation to John Skilling's comment about the strength of the perimeter walls, Glanz and Lipton mention it in their book City in the Sky.

The Vierendeel trusses would be so effective, according to the engineers' calculations, that all the columns on one side of a tower could be cut, as well as the two corners and several columns on the adjacent sides, and the tower would still be strong enough to withstand a 100-mile-per-hour wind. --City in the Sky, p 133

How do you get "half the columns for the two sides (meaning 28 from one side and 28 from the other) from "several columns from the adjacent sides"?

2. Is the quote from the book that you reference being made by Skilling himself or the authors? I don't see quote marks or a reference to Skilling saying that.

 

[ozeco41]

I'm quite confused as to what your and enik's dispute is about now.

It is a denial by enik of a simple fact of physics which I stated as an explanatory comment to Tony Szamboti.

It arose whilst Tony was in debate with femr2 and Tony claimed that enik had "proved" something.

My recollection was that Tony was claiming more than had in fact been "proved". That discussion led to me making this comment to Tony SZ:

I am relying on memory - haven't researched historic posts.....[BUT for your "could not"]...... to be correct it would require catenary sag to not produce enough force to bend the columns. I don't recall that being shown...I could be wrong. But catenary sag is a very effective force multiplier....

So my claim was one of basic physics - "catenary sag is a very effective force multiplier" - the apparent limit to "catenary" arose from the discussion. The principle however is not confined to catenary. Any "taut rope pushed sideways" will exert a pull in force on the end attachments that is much larger than the applied "push sideways force". You proved the generic point with a specific example back a couple of posts with this part of your drawing:

Your example shows ~45 kip "pull in" for 1 kip applied sideways force. (near enough - T is not the actual horizontal vector but the angle is small)

That simple fact of physics is all that I relied on in my original explanation for Tony. And Tony accepted that aspect without question.

Whatever his agenda enik is persisting in trying to prove me wrong by changing the scenario/assumptions/ whatever. I have presented explanations at very simple lay person level. Enik true to his style ignores my explanations and tries to change the subject. I won't fall for it.

Hence my extreme care to agree with what you correctly stated in each of your recent posts BUT noting that your examples were from a different scenario.

 

[Gamolon]

The way I understand the "ozeco41 vs. enik catenary sag" debate...

Quote from Tony...

Enik showed that the trusses and floors by themselves could not generate enough force to pull in and cause buckling of the perimeter columns, although they could transmit the force generated by downward moving outer core columns which were fully capable of generating the required force.

Quote from ozeco41 in response to Tony's quote above...

I am relying on memory - haven't researched historic posts because the issue is minor - I recall several discussions and the problem that sometimes besets FEA work of assumed contexts which do not match reality.

Then, at first examination I do not see how the two options you identify "could not generate" BUT "could transmit" can be correct. The "could transmit" almost certainly correct - masses of force from core column sinking >>> plenty of tensile strength in joists >>>enough to bend perimeter cols. So for "could not generate" to be correct it would require catenary sag to not produce enough force to bend the columns. I don't recall that being shown...I could be wrong. But catenary sag is a very effective force multiplier. If "could not generate" is in fact claimed my interest in the rationale (and the numbers) could be aroused.

EXCEPT that the issue is moot unless it is needed to resolve the discussion you v femr2.

Nevertheless I may do some post archaeology.

As I understand it, ozeco41 is saying that catenary sag is an effective force multiplier and that he did not recall it being shown anywhere the catenary sag cold NOT produce enough force to bend the columns.

enik then quoted this part of ozeco41's quote above...

...But catenary sag is a very effective force multiplier.

...and then stated this...

You will need to provide some calculations to further this argument.

So, based on ozeco41's latest post above, he provided calculations that show that "catenary sag is an effective force multiplier.

The question I have is this. Was enik asking for calculations showing basic catenary sag (as provided by ozeco41 above) or was enik asking for calculations showing how the catenary sag affected the columns? If it is the latter, then enik is asking for the same thing that ozeco41 said he doesn't remember seeing.

Am I getting this right?

 

[ozeco41]

The way I understand the "ozeco41 vs. enik catenary sag" debate...

[Context described correctly by Gamolon] ...
...

Yes

As I understand it, ozeco41 is saying that catenary sag is an effective force multiplier and that he did not recall it being shown anywhere the catenary sag cold NOT produce enough force to bend the columns...

Correct but those are two separate points. Three if the lawyer in me gets legally pedantic.

A) The first one "catenary sag is an effective force multiplier" is a simple fact of applied physics - a "truism". That is where enik is saying I am wrong and moving goalposts all over the planet to try to sucker me into a different argument. I'm not falling for it.

B) The second one - legal pedantry - "that he did not recall it being shown anywhere" was true - at the time I could not remember.

C) The third one "the catenary sag could NOT produce enough force to bend the columns.." is more complicated. Believe it or not it is NOT the topic of the current discussion. It should be because it is the OP for this thread but.... Leave it for now.

...enik then quoted this part of ozeco41's quote above...

...and then stated this...

You will need to provide some calculations to further this argument.

Correct. But the point did not need calculations and calling for unnecessary calculations is a standard evasion trick played by enik (and Tony Sz)

...So, based on ozeco41's latest post above, he provided calculations that show that "catenary sag is an effective force multiplier...

Yes - mea culpa. I compromised my tough stand. The problem was that I had to do a trade off. There were lay persons reading and some posting on the topic. enik was trying to fool them. He knows that he won't fool me so I posted the "lay persons explanations" so he has less chance of fooling the lurkers -- with near zero calculations but ...I put some very simple ones in. BTW enik wont count them - they are not FEA.

However Newtons bit also posted some more engineering looking calcs.....

...The question I have is this. Was enik asking for calculations showing basic catenary sag (as provided by ozeco41 above) or was enik asking for calculations showing how the catenary sag affected the columns? If it is the latter, then enik is asking for the same thing that ozeco41 said he doesn't remember seeing....

Yes - and remember that "what I don't remember seeing" is a actually "what I DIDN'T remember seeing" at the time I made the comment. I've since done the extensive post archaeology. Here and across on 911Forum. It doesn't help. It is just as vague and foggy as most of enik's posts. But I'm 90% sure enik didn't prove what he and Tony Sz claim he did prove. BUT that discussion can wait until we get back to the actual original real OP topic of this thread. If that miracle ever eventuates.

...Am I getting this right?

Actually even I'm getting confused. BUT will you accept "I think so?"

 

[Gamolon]

Actually even I'm getting confused. BUT will you accept "I think so?"

Absolutely!

 

[ozeco41]

Absolutely!

Thank you.

The current disagreement with enik is his evasion tactic - the issue of physics is without doubt. Waste of bandwidth discussing further.

The complexity is with the OP of this thread. And I'm not going there unless the original protagonists re-open discussion AND both sides make errors which need correction.

Let's hope it dies a natural death.

Cheers.

 

[enik]

Yes, of course. Assuming that the truss has not yielded, there will be very little (or none, depending on the type of analysis) difference in reaction forces and that they are purely vertical.

Yes. Too bad Ozeco41 didn't answer up similiarly.

 

[beachnut]

Yes. Too bad Ozeco41 didn't answer up similiarly.

similarly, Too bad? How does this tie in to the inside job claims you have made, the CD fantasy? How did you put it it? "Inside Job Evidence is in the Physics of WTC #1". Does this stand in your fantasy inside job? How does the failed FEA you have support your Inside Job Evidence?

Where is your paper published, or letter, refuting Usmani's work? https://www.era.lib.ed.ac.uk/bitstream/1842/1216/1/WTCpaper.pdf What did Usmani say about your effort? Your challenge was beat up before it was posted. Is that moving the goal post to exclude Usmani, wave your hands declare some BS stuff, etc? The paper is published where? Your Pulitzer Prize winning inside job evidence, with the help of Physics, is published where? Why have zero newspapers grabbed your outstanding work and got the Pulitzer? Watergate was big Pulitzer material, why is 911 truth inside job CD stuff not making the grade? Will this work push you into the Pulitzer race with your local Newspaper? If I knew 911 was an Inside Job and I proved NIST was wrong on the Sagging floor, I would have nothing... lol

How does NIST 1-6B fit with your no insulation analysis? Explain in detail. Is this work going to be your thesis?

 

[Newtons Bit]

Yes. Too bad Ozeco41 didn't answer up similiarly.

What was your point behind that question?

 

[Grizzly Bear]

What was your point behind that question?

It has to do with his post on page 8, basically being in disagreement with the NIST report on a single element which he though was relevant to what Ozeco was talking about in the Tony Szamboti new publication thread.

Which doesn't make such sense to me... the section he was referencing mentions several different factors working in tandem and the impression I get is that he's centering all his criticism around that single one point of interest... along with the whole strong holding of using FEA measurements absolutely...

And I've yet to figure out what the implications are supposed to be, if running under the assumption the question he raises is valid...