torsion boxes, why no triangles?

[Jacob]

I don't know if you've noticed, but a torsion box is an enclosed structure with lateral and longitudinal bracing.

That is the new terminology yes. It seems now to include sandwich constructions too, with egg-box cardboard, foam and other infills, stressed skin, geodesic etc etc.

With the flat, door and bench version most here are familiar with, you can think of it as a series of I-beams fixed together to give a rigid structure that will resist longitudinal, lateral and importantly here, torsional forces.

But there are no particular torsional forces with flat panels, doors and benches, as compared to aircraft wings, unless you are trying to fly with them.

 

[mudman]

That is the new terminology yes. It seems now to include sandwich constructions too, with egg-box cardboard, foam and other infills, stressed skin, geodesic etc etc.

But there are no particular torsional forces with flat panels, doors and benches, as compared to aircraft wings, unless you are trying to fly with them.

If by new you mean within the last 100 years, then yes, it's new. There are many references to be found, it's a thing that's been around since the first world war as a concept and that's within the last 100 years, do okay, let's call it new.

A flat panel can be subjected to torsional forces. If you apply a force to one edge, that will produce torque and so torsion. They are also much lighter than something built with solid materials but with similar strength. Very useful of you want to make it easy to handle it reduce the costs of shipping.

 

[Jacob]

If by new you mean within the last 100 years,

Not new but uncommon. Not a conspicuous part of the history of structural science .
"Torsion" is of course, but "torsion box" isn't. Hardly mentioned.
Suddenly emerged as the magic solution for woodworkers making hollow slabs etc. I reckon due to misunderstanding JE Gordon's one use of the expression to explain something, in a very well known popular science book about Structures. Recommended reading!

A flat panel can be subjected to torsional forces. If you apply a force to one edge, that will produce torque and so torsion.

Yes of course but it's not a structural issue unless torsion is a big component of the stresses involved, as distinct from bending, sheer, compression, etc. Who goes around twisting shelves or worktops?

They are also much lighter than something built with solid materials but with similar strength. Very useful of you want to make it easy to handle it reduce the costs of shipping.

Yes - if you mean any of the countless ways materials are used to reduce weight without losing strength.

 

[Sachakins]

Must be a quiet time over on the "secret" controversial forum thread, looks like most of it's protagonists have come out for the day.
I don't know who you are, but you do, some others do and whom ever they are that don't know what they don't know are probably having a headache or nose bleed over this post too.

 

[sometimewoodworker]

Because you quote it as though it contains a definition of "torsion box" but it does not.

No I don’t, it is you who is fixated on the words.

because you quote it apropos the topic of "torsion boxes": but it makes no mention of them

It is you who is fixated on the words. It talks about the principles involved

If it was it would say so.

it seems as if you have a significantly smaller understanding than I of the way applied and theoretical mathematics works and the fun that can be had trying to explain the concepts in other languages, like English.

But there are no particular torsional forces with flat panels, doors and benches, as compared to aircraft wings

at rest they mostly have small or zero torsional forces to resist. In motion the torsional forces vary. Take away the internal bracing of a hollow core door and you will immediately see the difference and be able to understand the torsional forces it resists. That one is designed to withstand greater force does not invalidate the other.

Who goes around twisting shelves or worktops?

Have you ever actually used a shelf or worktop? from your statement it seems that you haven’t, despite examples of your work, both are designed to resist twisting forces, (unless designed by an incompetent or sadist of course )

However you keep saying that they are just boxes, but what exactly is a box?
Flat bottom? No there are examples without flat bottoms that everyone agrees are boxes, though usually there is at least a flat area.
4 flat sides? No, the number of sides are irrelevant and none of them (or it) needs to be flat (hat box).
Flat top? Again no there are examples of domed to boxes that everyone agrees are boxes.
is the Matryoshka a box? Specially shaped and painted, never called a box, but in essence, yes it is
Is a sarcophagus a box? Unquestionably though some may have few, if any, flat surfaces and used for a specific purpose



A box in general has a single volume that is enclosed within it a torsion box does not, it has many
If your box has (for example) 2 volumes is it still a box or is it 2 joined boxes? I know the general answer, though the thickness of the sides will influence the answer, as will the number of tops.

You are trying to gate-keep a term that few people, if any, agree is incorrectly used

 

[Jacob]

more of theoretical question than for anything specific I'm planning to build.

I've seen a few torsion boxes made up (youtube) and I notice that the internal web always seems to be boxes and rectangles, no triangles, it seemed odd because triangles seem to be so common place everywhere else that you want to maximise strength and minimise weight (I know that is massive over simplification).

Have I missed something obvious?

Anyway - to get back to our OPs question, part of the reason why triangles don't feature in the these "torsion box" designs, is that "torsion" isn't really an issue with shelves, doors and worktops.
It's a misnomer.
The bigger reason is that they would be difficult to implement in wood, as compared to a right angled lattice, but would not serve any obvious purpose anyway.
Different if you were hoping to fly with your shelves, in which case avoid steep high-speed dives, or you could be Fokkered!
And read JEGordon.
PS Gordon enthuses about the efficiency of typical bi-plane construction where torsion is defeated by triangulation; struts in compression and strings in tension, forming triangles between the wings. So triangles aren't irrelevant. This is his "torsion box".
Fokker's improved wing is not - it's more about "stressed skin" construction and designing for the centre of pressure.
PS just passing on a comical remark overheard; "talking about shelves and worktops as "torsion boxes" is a bit like being serious about go-faster stripes on your car."