Guidance on shelves......

[Argus]

.



Some years ago there was an article in one of the comics - Woodworker, I believe - about making modular shelves. Maybe they are called something else, but basically it consists of two sheets of ply reinforced with glued battens in the void forming a rigid structure. Because of the monocoque cell structure this type of board is stronger than the equivalent size in a plank and don't tend to sag. At least, that's the theory.

Nowadays, having a wide span to cover, I’m in need of such shelves and I seem to recall that they can be tricky to make properly in order to maximise the strength.

I seem to recall that the original article was quite involved, I could probably work it out from scratch, but does anyone know of any guidance on the subject?



.

 

[bodgermatic]

Google for 'torsion box'

 

[Argus]

.


Torsion Box....I knew it was all in the name........

Thank you.


.

 

[mr grimsdale]

"Box Beam".
Often miscalled a "torsion box" in woodwork circles.

 

[RogerS]

"Box Beam".
Often miscalled a "torsion box" in woodwork circles.

Here we go again.

 

[Karl]

My thoughts precisely

 

[bodgermatic]

"Box Beam".
Often miscalled a "torsion box" in woodwork circles.

I'll bite (and regret it, I'm sure). What do you call it when the construction being discussed is not a beam, Grim?

 

[RogerS]

In the interests' of everyones' sanity, a fully worked discussion/argument can be found here.

http://www.woodworkuk.co.uk/forum/viewt ... 37&p=38458

 

[wizer]

and we had it over here a while back too.

 

[Argus]

In the interests' of everyones' sanity, a fully worked discussion/argument can be found here.

http://www.woodworkuk.co.uk/forum/viewt ... 37&p=38458

Thanks.....

As usual, more heat than light 'over there', but some good pictures that shows what I need to do.

The dim and distant memory banks suggests that the original article showed the internal struts at a 45 degree to the edge instead of at right angles as in Modernist's pictures ....... which would explain my suspicion that it was a 'bit complicated....'




well, here goes.



.



.

 

[mr grimsdale]

"Box Beam".
Often miscalled a "torsion box" in woodwork circles.

I'll bite (and regret it, I'm sure). What do you call it when the construction being discussed is not a beam, Grim?

Er, I try to call it whatever it is. What did you have in mind?
A shelf is a form of beam. If a beam has a box construction it's often called a box beam.
Torsion isn't (particularly) an issue with shelves as a rule although of course no structures in the real world are "pure".

 

[TheTiddles]

"Box Beam".
Often miscalled a "torsion box" in woodwork circles.

I'll bite (and regret it, I'm sure). What do you call it when the construction being discussed is not a beam, Grim?

Er, I try to call it whatever it is. What did you have in mind?
A shelf is a form of beam. If a beam has a box construction it's often called a box beam.
Torsion isn't (particularly) an issue with shelves as a rule although of course no structures in the real world are "pure".

Shelves are often a beam simply supported at two points.

If a load is placed in between the two point the shelf will experience compression on the top surface reducing to zero in the centre and increasing to tension on the bottom.

An element with tension and compression on either side is in torsion.

Thank you and goodnight.

Aidan

 

[mr grimsdale]

....
An element with tension and compression on either side is in torsion.

.....

No it isn't. Torsion implies twisting; think corkscrew or propeller blade. The torsion box wing (bi or monoplane) is designed to stop twisting, not merely the bending of a simply distributed load such as a line of books.

 

[Jake]

This is a very important argument.

I think multiple-web-big flanges-beam-construction would be accurate, if not quite so elegant?

 

[TrimTheKing]

....
An element with tension and compression on either side is in torsion.

.....

No it isn't. Torsion implies twisting; think corkscrew or propeller blade. The torsion box wing (bi or monoplane) is designed to stop twisting, not merely the bending of a simply distributed load such as a line of books.

This is a serious question, surely a table top made in this fashion is a torsion box (not beam) due to the fact that it is aimed to be a perfectly flat surface that neither sags nor twists? A table top is supported most often on 4 corners so not a beam?

I haven't read into the details on the other post but this would make sense to me.

 

[TheTiddles]

....
An element with tension and compression on either side is in torsion.

.....

No it isn't. Torsion implies twisting; think corkscrew or propeller blade. The torsion box wing (bi or monoplane) is designed to stop twisting, not merely the bending of a simply distributed load such as a line of books.

This is a serious question, surely a table top made in this fashion is a torsion box (not beam) due to the fact that it is aimed to be a perfectly flat surface that neither sags nor twists? A table top is supported most often on 4 corners so not a beam?

I haven't read into the details on the other post but this would make sense to me.

A "beam" whilst being an actual thing is also a technical term, just not very technical. Though it seems to confuse at least one person.

It's all relative, if you consider the shelf example it doesn't look like torsion as what's twisting? However, imagine you are stood on the thin edge of the shelf at one of the supports looking down the shelf and you are magically able to see forces. What you will see is another support at the end of the beam pushing one way and gravity acting evenly along the shelf pushing the other, therefore twisting the beam, ergo, it's in torsion.

Mr Grimsdale can't get his head round that, I'm sure the rest of you can

Aidan

 

[mr grimsdale]

If you are in the habit of tip toeing along the edge of your shelves well yes you will need stronger shelves than normal. You could go in to 'torsion box' design - a bit over the top as this is engineering for aircraft, car bodies etc. Or just make it thicker in the ordinary way. Or if it's a box beam then make it a stronger box
But most shelves are just in simple bending. There is no special 'torsion' issue.

What would you use a non 'torsion' box beam for?

 

[dannykaye]

I like to support long shelves along the back, this means that I have books pressing down across the shelf and the support pushing up at the back, so definitely in torsion, but hey I know I'm strange

 

[mr grimsdale]

I like to support long shelves along the back, this means that I have books pressing down across the shelf and the support pushing up at the back, so definitely in torsion, but hey I know I'm strange

Strewth that's a bit wierd!
Do you mean that they are cantilevered out from the back edge? If so the issue is simple bending, not torque.
Even if it was torque the engineering problem is not as complicated as a biplanes wing, or the solution to early german dive bombers twisting wings ("torque tube") unless you are really pushing things to a limit.
You just need a firm fixing or stiffer shelves, whether solid or box construction.

 

[TheTiddles]

If you are in the habit of tip toeing along the edge of your shelves well yes you will need stronger shelves than normal. You could go in to 'torsion box' design - a bit over the top as this is engineering for aircraft, car bodies etc. Or just make it thicker in the ordinary way. Or if it's a box beam then make it a stronger box
But most shelves are just in simple bending. There is no special 'torsion' issue.

What would you use a non 'torsion' box beam for?

Your village called, their silly person is missing.