Gamolon
Active Member
Nope.
We're now testing your understanding of scaling and models.
Both models should act the same.
Buckled Structural Steel in Building Fires
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We're now testing your understanding of scaling and models.
Both models should act the same.
Mendel
Senior Member.
the load didn't provide the bracing, the bracing provided the bracing
That's an interesting possibilty. I'll have to think a little more about that. We agree that their connection to the ground was stronger than those joints, right?
So it's fine if I build the smaller one first?
I just meant that the floors provided the load and the bracing.
Gamolon
Active Member
Why?
I hadn't thought of that. Thanks. Will get back to you when I make some progress.
Gamolon
Active Member
We can save you the trouble of building anything.
Do you think the 1:1000 scale model will act the same as the 1:100 model both using paper and tape?
I would use different grades of paper and different amounts of tape. That is, I would scale those factors too. But, yes, my goal is to make a desktop model in paper of the collapse of a 1700' steel-framed building.
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Jeffrey Orling
Senior Member
I believe that you can't use physical scaled models to study the collapse. Strength of materials cannot be scaled. Or... what materials would you use to have the model behave exactly as the full size structure... in some or all aspects/conditions?
What is constant is gravity.... that is not scaled. Some aspects can be studied with a model... but it would be impossible to make a small scale model collapse exactly as the towers did.
What is constant is gravity.... that is not scaled. Some aspects can be studied with a model... but it would be impossible to make a small scale model collapse exactly as the towers did.
Gamolon
Active Member
How did you determine that the paper for your 1:1000 model is scaled down correctly and models the inherent characteristics of the actual steel façade?
Gamolon
Active Member
That is exactly what I (and others) have been trying to explain to Thomas B.
Gamolon
Active Member
What type of paper are you using for your 1:1000 scale model?
I think I keep explaining this. I do it experimentally. The structures I build have to be able to support a significant load under significant lateral forces.
But they also have to collapse under their own weight when damaged only near the top. Until I suceed, I haven't proven anything. When I do, I have understood how the WTC collapses were, in principle, possible.
Gamolon
Active Member
And you think paper and cardboard replicate the scaled down forces/loads of the actual towers? Without doing any math whatsoever?
Your model is based on words like "significant", "experimentally", "intuitively", "imagine", and "tastes". That's not scientific in any way and just makes your model nothing but a farce.
I asked asked you this before. Take your paper and tape model ideas to a couple licensed engineers and see if they agree that your model will help you understand the collapses of the towers.
Let us know what they say.
You're making assumptions about what I have tried and who I've talked to.
You also seem unware of how engineers actually teach these principles to their students. The structural behavior of paper is very instructive.
Gamolon
Active Member
So your paper is about 112 microns thick (.112mm) for the 1:1000 scale model. What paper thickness would you use for the 1:100 model?
Gamolon
Active Member
So you have talked to engineers and explained your paper and tape model and what you are trying to accomplish?
What did they say?
Jeffrey Orling
Senior Member
You can't scale structural performance... ie strength of materials.
Gamolon
Active Member
And you are making assumptions also. I worked in an engineering firm for years with all kinds of engineers.
Please provide evidence to support your claims.
Young's modulus for steel is about 200; for paper, as far as I can tell, it's about 5. But the steel used in WTC can be measured in inches whereas for paper we're talking about thousandths of inches. So there's some scaling on the order of 1:1000 there somehow.
Withdrawn.
They said, for example, that if you want to understand the strength of a box column, just fold a piece of paper four ways.
Gamolon
Active Member
That's not what I asked you.
I asked you to present your 1:1000, scale paper and tape model, and it's characteristics to some engineers and ask them if it would help you replicate and then understand the collapse of the towers. What about replicating the entire tube/façade standing on it's own?
Gamolon
Active Member
Please address post #258
He wi
He withdrew his claims in Post #264.
FatPhil
Senior Member.
Were they comparing the strength of a flat piece of paper with the strength of a piece of paper folded up into a box column?
That would indeed be informative, but it doesn't tell you anything about structures made from other materials or at other scales.
The idea, as I understand it, is to show how much stronger a box column is than the steel plates it is made of. For example, a thin steel plate that is long enough (basically a strip of steel) will buckle if you stand it on its end. But if you weld four strips together the resulting column will stand up easily and even be able to support some weight. This can be demonstrated with that folded piece of paper.
Jeffrey Orling
Senior Member
For one you should compare the strengths of columns with the same cross sectional area... and of course the same material. Columns need strength in both the X and Y axes. Box and WF sections accomplish this. I believe WF are more economical to make as they can be rolled. Boxes need to be "assembled". I suppose at some size point (cross section) there is limit to manufactured sections.... then engineer would go to built up sections if more strength were required.
A plate as a column is (much) weaker in one axis... and makes a plate alone poor choice for a column.
I don't know yet. Until I get any model to collapse progressively, figuring out how (or whether) to scale it one way or another is not my main concern.
You asked what kind of paper, and I told you. But, as I see it, the scaling lies in paper vs. steel, not any particular grade of either. Also, the way I'm trying to get the strength of the columns right is by varying the size and shape of the holes I cut into them, not the weight of the paper. (At one point I tried multiple layers of paper, so that at the bottom it was three layers thick, then, in the middle third, two layers, and in the top third a single layer. But this turned out to be way too strong given the loads I could fit onto the floors.)
Jeffrey Orling
Senior Member
So... scaling down from full size... at what point (how "small") will the model not collapse?
Gravity is not scaleable
Strength of materials is not scaleable. You would have to select materials of less strength... no?
So... Aluminum is weaker than steel... cardboard is weaker than aluminum.
Gravity is not scaleable
Strength of materials is not scaleable. You would have to select materials of less strength... no?
So... Aluminum is weaker than steel... cardboard is weaker than aluminum.
Oystein
Senior Member
Volume would be 1:1,000,000,000 then.
If all dimensions are scaled 1:1,000, then mass also is 1:1,000,000,000.
Your model would weigh only 280 grams then, yet have to model the equivalent of 26,400 truss seats.
Is that easy to build?
But column strength scales only by the square, not cube, of scale, so everything would have to be made of a material that is only 1:1,000 of specific "strength" relative to structural steel.
How are you going to ensure that your paper, your gue, your whatever comes even close to the required order of magnitude in all these properties of yield strength, elasticity, capacity in compression and in tension, mass, etc?
Trying to model EVERYTHING, at 1:1000 scale on your desk, is a preposterous fool's errand.
It cannot be done.
You are very much determined to persist in doing your modelling WRONG.
Waste of your time and energy, waste of our time and energy.
You will not ever build anything that will make anyone understand anything that translates to any aspect of the WTC reality. This is absolutely 100% certain the way you approach this. Hopeless!
I thank you for your input. This is the general tenor of the message I'm getting here. Still, some of the pushback is giving me ideas to try. I'm not giving up yet. But you are of course free to ignore me.
I'm not sure how closely you've been following the thread. We're at paper.
Jeffrey Orling
Senior Member
Understood. Different materials have different properties. A wide flange section of paper is weak than one made from alum or steel. I don't think you can find a material which scaled down behave like the scaled up steel does.
Oystein
Senior Member
He could use steel "plates" for box columns, spandrels etc. that are 1:1,000 the thickness of the original steel. In the upper floors, that would e.g. be 0.000,020 m thin (20 micrometers) insteaf 0.020 m (20 millimeters). This is pretty much within the range of common gauges of houshold aluminium foils.
But they would have to be a thousand times heavier somehow, or gravity a thousand times stronger...
Interesting. At one point I bought a bunch 15 gram lead plates at a hobby store. The plan is in fact to distribute about 20 of them throughout the building as dead weight.
This level of complexity if of course not realistic. I'm happy to reduce this by roughly 1:1000. So about 4 seats x 6 or 7 floors with 40 or so grams of lead on each.
Don't we just solve this by adjusting the dead loads *on* the structure. Is there a useful difference between being a 1000 times heavier and gravity being a thousand times stronger?
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