Structural Tube Cross Section

Good question. They seem to be getting rarer and rarer these days (good questions that is).

I don't have an answer for you, but I have a hunch.

I would wager that the Mercedes Benz hood ornament (the one on the far right) Would provide the greatest strength/weight ratio of the 5 you have listed. That is simply my unsubstantiated opinion, with no data/facts to support it.

I also have a hunch that the guys over at the tinker toy plant asked themselves the exact same question, and came up with an answer, began mass producing, and here we are.

I'll hazard a guess that the middle one, although more difficult to extrude, would be the strongest.

I expect that some of our PhD friends can do the math, I can't.

I like the one in the middle too... All-in-all it totally depends on the application as stated, One shape will work best for internal pressure, one will work best for bending, one will work best for compression and so on and so forth.

But I still "Like" the one on the far right, for reasons unknown.

"But I still "Like" the one on the far right, for reasons unknown."

Yah, I can't figger it out, but I like it too!

They are all equal in overall diameter, and in cross sectional area of material (the area of black in each )

It would seem that for the Tinkertoy application - the primary strength requirements are flex/bending, shear at the joints, and compression.

I didn't specify, hoping to hear something I wasn't expecting.

I agree that the ratio of wall to rib thickness would be important and would vary depending on the material properties.

I thought that for sure in bending, having something internal would help, but I could be wrong. Doesn't a composite tube with a core material gain strength from the core?

What do you mean by strength in "axial configurations" ?

Thanks

The strength of carbon fiber is in a singlar direction. In application its the multi-laminate in multi-directions that give it the over all strength.

It would be difficult to extrude carbon fiber without adding different processes to get the multi-directional grain to gain the multi-direction strength of this material.

It is something to thing about though.

I don't know what you mean by a "colossal carbon tube" unless it is "regular round tube." In tension, equal cross section areas will give equal strength. The difference would come in twisting, bending and column buckling, and we really need to know the proportions of wall thickness vs diameter and length to give a definitive answer. However, for anything but pure torque, the middle example has the best potential for maximum resistance to buckling.

The engineers at Tinkertoy may have been looking for improved beam strength with the beam section fully collapsed, or for material providing compression strength during assembly that was not subject to distortion and damage from the assembly process. A similar section is used in oxygen tubing for medical situations, so that you can't kill someone by standing on it or getting a kink in the line.

A colossal carbon tube:

http://www.mse.ncsu.edu/research/zhu/papers/CNT/PRL-CCTs.pdf

It would seem that for the Tinkertoy application - the primary strength requirements are flex/bending, shear at the joints, and compression.

Yes, I agree that the wall-to-rib thickness ratio would be critical, and vary depending on material.

Is this what you were referring to about the oxygen tubing:?

That's pretty clever.

Thanks :)

I assume you refer to nano tubes...

The optimum effectiveness of any of the internal the stiffeners would be at 180° to the applied force. Since there is no definitive orientation ( ie vertical/ horizontal) of the tube when erected into service, the optimum configuration will be the second-last (next to the peace sign).

ie The applied force is always tangential to the tube diameter, so orientation is no longer a factor.

Essentially, the larger number of stiffeners will ensure that whatever the orientation, one of them will be closer to 180° relative to the applied force than any of the other configurations, offering greater resistance to said force.

<quote>

...the optimum configuration will be the second-last (next to the peace sign)...

</quote>

It HAS been a long time, hasn't it? This is a peace sign:

Which is unlikely to get anyone's vote for optimum structural integrity.

You just passed the Age of Aquarius test...

You've asked two questions hoping for one answer. The strongest (in resistance to failure from side loads, for instance) is not the same as the highest strength to weight. You could imagine that the folks at tinkertoy had a minimum strength requirement, so a superior strength to weight ratio was only relevant after they had met that requirement. Furthermore, the folks at tinkertoy had a maximum and minimum rod volume requirement, so that any design was only considered after it satisfied this requirement. Lastly, the folks at tinkertoy had to actually build this rod, so after it met the previous requirements, it had to be manufactured economically.

Of course, knowing the specific weight of the material would allow a specific answer, which would for most of us here would be more informative than selecting from a multiple choice list.

My uninformed guess is that the strongest is number 3, the highest strength to weight is number two.

At some point you have to consider cost and application.

Ron

It all depends on the loading application as others have pointed out....bending vs. compression loading, or a combination of both.

Since each has the identical cross sectional area and presumably identical weight, you also need to calculate the Section Modulus (Sx = Sy), Moment of Inertia, and the Radius of Gyration (rx = ry) of each and see which one would be the best for the intended load scenario.