Challenge: Demonstrate Sagging floor Trusses Pulling in Perimeter Columns

[JSanderO]

By saying the building in that condition "could take a 100 mph wind", with no other qualifiers, he meant continuously.

Can you cite this statement and discussion. Heck why bother to have all them columns on the facade if they were not needed. Please explain.

 

[femr2]

Whether or not there was inward bowing of the south wall

There was, and your repeated attempts to cast doubt on that are laughable.

it can be safely said not to have had much of an affect on stability

It can be safely said to have had an effect on load distribution, lateral stress on other members, etc..

A three sided vertical section (or a channel type structural section) is nearly as stable as a vertical box section. Most of the stability comes from having at least two corners and normal sides.

You appear, accidentally of course, to be avoiding any suggestion of...

What caused the inwward bowing Tony ?

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.

That wall wasn't removed Tony. Inward bowing, and lots of stress.

Aaand...did you forget about the large hole in the North face... ?

 

[enik]

A waste of time. Enik is playing games pretending that he doesn't understand catenary sag.

I think I finally understand what you are trying to convey. In this first analysis, I attached a nylon rope to two steel columns and pulled horizontally. Note the columns are pulled toward the force applied to the rope, not together as you claim. This has been established that pulling on a vertical column will bend it inwards.

Now we move the force on the rope from the horizontal to the vertical

The force has not changed in either instance, notice the amount of deflection on the rope has increased in the second example. Do you now understand why your statement “catenary sag is a very effective force multiplier” is incorrect?

 

[Newtons Bit]

I think I finally understand what you are trying to convey. In this first analysis, I attached a nylon rope to two steel columns and pulled horizontally. Note the columns are pulled toward the force applied to the rope, not together as you claim. This has been established that pulling on a vertical column will bend it inwards.

View attachment 28744

Now we move the force on the rope from the horizontal to the vertical

View attachment 28745

The force has not changed in either instance, notice the amount of deflection on the rope has increased in the second example. Do you now understand why your statement “catenary sag is a very effective force multiplier” is incorrect?

This is a perfect example of why we require engineering training and licenses (or supervision) to do work that involves the public safety.

 

[ozeco41]

As I said:

Enik is playing games pretending that he doesn't understand...

....and he uses pretty coloured diagrams.

Why? He might be trying to fool the lay people because he certainly won't fool me.

Stop the silly pretending enik.

 

[jaydeehess]

Whether or not there was inward bowing of the south wall it can be safely said not to have had much of an affect on stability. A three sided vertical section (or a channel type structural section) is nearly as stable as a vertical box section. Most of the stability comes from having at least two corners and normal sides.

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.

,,,,and despite the significant damage to the perimeter it did continue to stand. Of course there was also some not insignificant core column damage.
THEN, the structure suffered further insult to loss bearing components over large numbers of columns and over multiple levels. Fire weakened columns directly and also caused floor failures which resulted in loss of lateral bracing.( illustrated in several pictures from the police helicopter that show collapsed floor sections.

I rather doubt that Skilling would day that taking out one perimeter wall and then slowly removing the load bearing capacity of the remaining structure would see the building standing.

Your quote of Skilling is irrelevant and specious since no one I know of has stated that the perimeter impact damage caused the collapse. That is probably because the building did notcollapse upon impact.

 

[jaydeehess]

I think I finally understand what you are trying to convey. In this first analysis, I attached a nylon rope to two steel columns and pulled horizontally. Note the columns are pulled toward the force applied to the rope, not together as you claim. This has been established that pulling on a vertical column will bend it inwards.

View attachment 28744

Now we move the force on the rope from the horizontal to the vertical

View attachment 28745

The force has not changed in either instance, notice the amount of deflection on the rope has increased in the second example. Do you now understand why your statement “catenary sag is a very effective force multiplier” is incorrect?

Assuming your rope did not stretch, when you deflected it sideways you had less length of rope along the line between the two columns. Therefore despite the columns being pulled sideways in the direction of your deflection, there was also a force pulling them towards each other. The force vectors are along the rope which could be represented as the sum of force towards the other column, and a force to the side at 90 degrees.


But note... in the case of the sideways deflection, that force is in the horizontal and perpendicular to both the column and the line between the columns, while the columns are vertical. Moving on we have sagging floors, vertical deflection, attached to,,,,,,, vertical columns. The force vector would be in the direction of the sagged truss. Represent this as the sum of two vectors, one in line with the vertical column and the other in he horizontal in the direction of the original truss line..

 

[beachnut]

... 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.

Do you make this up, or fail to get the quote right? Failed to source it too? 911 truth is like the kids in grade k passing around a phrase in class, student to student, as the phrase becomes something new, extra special woo. Real good engineering, can't get a quote right, or source it properly.

When you find the quote, please remember, like your big talk of CD and inside job woo, the quote is bragging on the WTC, a promotion, marketing, not engineering reality.

Did Skilling tell you this? How is your inside job going? Why don't your fellow workers support your fantasy?

You got this wrong, and is indicative of your real CD deal; wrong.

 

[enik]

My foray into the discussion referred to the idea that while unsagging caternary forces would increase load on remaining perimeter columns, that introducing sag would further shift the CoG to further increase that load.

Ozeco41, does this support your rope discussion?

… Moving on we have sagging floors, vertical deflection, attached to,,,,,,, vertical columns. The force vector would be in the direction of the sagged truss. Represent this as the sum of two vectors, one in line with the vertical column and the other in he horizontal in the direction of the original truss line..

Maybe you can present a diagram and some calculations?

 

[ozeco41]

...The force vectors are along the rope which could be represented as the sum of force towards the other column, and a force to the side at 90 degrees...

That is the key point. Hence start with the rope taut for maximum "pull in vector".

 

[ozeco41]

The force vectors are along the rope which could be represented as the sum of force towards the other column, and a force to the side at 90 degrees...

That is the key point. Hence start with the rope taut for maximum "pull in vector".

As an alternative to starting with the rope taut try starting with the rope at 45^o. That could lead to a more intuitive grasp for a lay person. Try this rough sketch:

Now quantify the vectors. The logical "easy way" way through is:
Applied weight 2U (I even made it 2U AND set the rope at 45^o to make the outcomes simpler. )
Therefore Av and Bv are each equal to U.
For 45^o the horizontal and vertical vectors are equal.
Therefore the inwards pull vectors Ah and Bh are equal and also equal to U and that is for 45^o rope inclination.

We don't need to calculate rope tension BUT clearly it is √2 times U. Now try it for 30^o and the pull in vectors become ~1.7 times U. "Flatten out" further and at 10^o "pull in" is ~8 times U

Two points for the more pedantic members:
Point 1: The four rope tension vectors are "internal" to the system AND
The four attachment point vectors Av, Bv, Ah and Bh PLUS the weight vector 2U are "external" to the system. So:

Point 2: Those five external vectors must vector add to net zero - otherwise the whole system would be subject to an "external impressed force" and would go merrily accelerating in the direction of the resultant non zero vector.

Some bloke named Newton said that. Sadly he often gets misrepresented on these forums.

Progress with "real people testing".
I tried the issue out on a mature age ex builder now a "building certifier" this AM over coffee:
A) He had no doubt that there was "pull in";
B) Needed to think before accepting that the pull in could be far more than the applied load.

I still have difficulty accepting that an engineer would legitimately question the concept.

AND Newly made family arrangements will see my 6 yo grandson visiting this weekend. I may try the concept on him as suggested in my earlier post.

 

[ozeco41]

My foray into the discussion referred to the idea that while unsagging caternary forces would increase load on remaining perimeter columns, that introducing sag would further shift the CoG to further increase that load.

Ozeco41, does this support your rope discussion?

I have difficulty accepting that this is a serious question...BUT...let me treat it as serious.

The underlying issue is that you are confused as to the taxonomic relationship of two issues. They are distinctly separate issues.

Issue #1: My "rope discussion" arose out of my reference to a simple physical concept - that, stated generically, being the scale of pull in tension forces on two spaced mount points which results from applying a "sideways" force onto a member spanning the gap between the two mount points. Put that back into specifics if you need to but take care to do the transformation accurately.

What JDH refers to in the section he quotes is a different topic. And it as an independent topic. It is neither causal to, consequential from, superior to or subordinate to the first topic of "pull in".

Issue #2: JDH's comment is primarily focussed on the topic of column "weakening" when subject to eccentric axial loading in compression.

As such it is neutral to the simple point of physics fact which I made.

BTW I am unclear what JDH means by "unsagging caternary forces would increase load" but the point is within the scope of his comments about eccentric loading of columns. It is not within the scope of my issue therefore it has no effect on my claim separating the issues.

 

[Tony Szamboti]

Whether or not there was inward bowing of the south wall it can be safely said not to have had much of an affect on stability. A three sided vertical section (or a channel type structural section) is nearly as stable as a vertical box section. Most of the stability comes from having at least two corners and normal sides.

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.

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

 

[Dcdrac]

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.

 

[Newtons Bit]

Is this what you're looking for?

tl;dr: The simply supported beam has an end reaction of 0.5k, the beam with a plastic hinge has an end reaction of 45.5k.

 

[jaydeehess]

BTW I am unclear what JDH means by "unsagging caternary forces would increase load" but the point is within the scope of his comments about eccentric loading of columns. It is not within the scope of my issue therefore it has no effect on my claim separating the issues.

unsagging catenray would be a cantilever with infinite stiffness. Nevermind though as i see now I was conflating two issues, the floor sag and the tilt of the upper structure (and the bending on the lowest of these floors over the area of missing perimeter columns)

 

[jaydeehess]

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

,,,,and despite the significant damage to the perimeter it did continue to stand. Of course there was also some not insignificant core column damage.
THEN, the structure suffered further insult to load bearing components over large numbers of columns and over multiple levels. Fire weakened columns directly and also caused floor failures which resulted in loss of lateral bracing.( illustrated in several pictures from the police helicopter that show collapsed floor sections.

I rather doubt that Skilling would day that taking out one perimeter wall and then slowly removing the load bearing capacity of the remaining structure would see the building standing.

Your quote of Skilling is irrelevant and specious since no one I know of has stated that the perimeter impact damage caused the collapse. That is probably because the building did not collapse upon impact .

The point is sir, that the building continued to suffer damage to structural components other than the perimeter columns on one side, and to components other than the perimeter.

Skilling was correct in describing the effect of the impact damage to the structure, but we are not talking strictly about impact, we are talking about cumulative damage to many components of the building.

 

[ozeco41]

Is this what you're looking for?

tl;dr: The simply supported beam has an end reaction of 0.5k, the beam with a plastic hinge has an end reaction of 45.5k.

A good specific example of what I originally took for granted.

...and have restated in increasingly simple language several times.

unsagging catenray would be a cantilever with infinite stiffness. Nevermind though as i see now I was conflating two issues, the floor sag and the tilt of the upper structure (and the bending on the lowest of these floors over the area of missing perimeter columns)

No problem. As I said it didn't change the point I made but good to see where you were coming from.

If we recall the start of this "mini discussion" it was this claim by enik:

...Oz has stated that truss sag is a very effective force multiplier. I say "hogwash".

It should now be clear for everyone:
A) Who was right. (Me ); AND
B) Whose statement truly was "hogwash". You look I'll point.

Thank you line persons. Thank you ball persons.

Now the OP of this thread was a challenge - I suggest we return to the advertised program.

 

[beachnut]

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

From the chapter, Steel Balloons. Wow, this is not Skilling, who said it? A hearsay quote, is what you have sourced. Good job, this matches your work on the "real CD deal".

Which engineers? Notice it is not a quote sourced?

LOL, you have hearsay. Did James Glanz or Eric Lipton supply this bragging point. Do you have calculation to go with your favorite WTC is too strong to gravity collapse fantasy quote?

You miss quoted your favorite quote.

Originally Posted by Tony Szamboti
... 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.

One exterior face and its corners completely removed?
Now you say cut, not removed? Make up your mind.
Can you ever get a story straight.
You use bragging, marketing talk, and make up your own removed the entire exterior of the WTC.
What was the real quote, who said it, and what does it really mean?

You gave a source which paraphrased another source and failed to source it specifically. It gets worse, this quote is used a lot by the 911 truth makers of fantasy to support the super can't fail building delusions.

What is the real source, and what does it really mean? What about a building on fire? Steel fails in fire - why does 911 truth fail to learn? Did you make up the real CD deal like you did removing the entire face and corner stuff?

There is a quote, and you don't have it yet, but it does not mean anything for you and your CD fantasy, and it will not save enik's inside job sagging floors.

 

[enik]

[qimg]http://conleys.com.au/smilies/clap.gif[/qimg] [qimg]http://conleys.com.au/smilies/clap.gif[/qimg]
That is the key point. Hence start with the rope taut for maximum "pull in vector".

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.


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

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.

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

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

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?