torsion box shelf strength

[paulchapman]

Hi Jeremy and welcome.

Cheers

Paul

[paulchapman]

mrgrimsdale said:

[ Torsion box is a new one and is redundant; it has nothing to do with torsion in the way it is used.

Whether it's right or wrong, it's a term that has been used for a long time for the type of construction we are talking about and those of us who use the term know what we mean. Like a lot of words and terms in the English language, they get adopted through common useage.

Cheers

Paul

[mrgrimsdale]

Not such a long time. It was new to me altogether when I first read it _{in another place} only a year ago. Perhaps I should get out more!
Also it seems that it was intended to use it with reference to the cardboard egg-box cheap door type construction - not to just any structural box.
So it's meaning is changing already through common usage. Will it become normal to specify doors as torsion box construction? Don't think anubody has as yet.

cheers
Jacob

[paulchapman]

mrgrimsdale said:

Also it seems that it was intended to use it with reference to the cardboard egg-box cheap door type construction - not to just any structural box.
So it's meaning is changing already through common usage. Will it become normal to specify doors as torsion box construction?

I think things have moved on already, at least in the construction of cheapo doors. When I drilled into some doors in my daughter's fairly new house to fit some additional locks, I found that they were filled with polystyrene

Cheers

Paul

[engineerone]

paul, even more worrying, they seem to be made of almost a blow moulded wood too.

certainly the ones which appear to be painted white wood,
from my most recent experience.

deeds, still thinking what we can call them, however jacob for sure you are incorrect in the timing, in one of the earlier issues of GWW, around 10-15 year ago, a then mate called john jacques had a couple of articles about a then quite wide bookshelf unit, and in that he made torsion box shelves. and he had borrowed the idea from america.

my idea is i think lightweight stressed shelves, but not very punchy. ;D


paul

[paulchapman]

engineerone said:

even more worrying, they seem to be made of almost a blow moulded wood too.

certainly the ones which appear to be painted white wood,
from my most recent experience.

The front and back surfaces of my daughter's front door look like painted wood, with imitation fielded panels but, in fact, are covered with a sheet of thin metal I found this out after trying to drill through it and knackering a good drill bit

I dare say the authorities would say that modern houses have good thermal efficiency but they are really nasty to do any work on - I don't like them at all. It seems to me that, like the tower block flats they built many years ago and then pulled down because they were a disaster, the modern houses that they are building today are really rubbish



Cheers

Paul

[nickw]

mrgrimsdale said:

Non of the examples in these threads involve torsion in any way.

This is only true if the load is applied along the central axis^* of the beam/box/shelf/whetever-you-want-to-call-it, or symmetrically placed around it.

^*If you want to be really picky the line of interest is along the shear centre of the beam/...., but for the structures we are discussing here they will be one and the same. The exception will be when a shelf is fixed along its back edge to e.g. a wall, and its sides. Then there will be lots of torsion wherever the books are placed.

See e.g. here

[jfc]

give me something short snappy and "engineeringly" correct (without it sounding too big OR too complicated)

A Shelf .

[nickw]

I'm being a bit slow today.

Anything that is held in a bent state is, by definition, in torsion - i.e. it has a torque (often called Bending Moment in engineering) applied to it. It matters not one jot if that torque is applied about the long axis of a circular bar or across the width of a shelf.

[JasonB]

Was just looking on the Egger site for a colour matched board for some Parapan doors and came across this, just what you need for thick construction and leight weight.

www.egger.com/pdf/210x297_Eurolight_UK_Inter.pdf

Jason

[Telos]

nickw said:

I'm being a bit slow today.

Anything that is held in a bent state is, by definition, in torsion - i.e. it has a torque (often called Bending Moment in engineering) applied to it. It matters not one jot if that torque is applied about the long axis of a circular bar or across the width of a shelf.

Ehh, what? I think everyone is getting a little confused here. Or at least I am. If something is bent along a longitudinal axis it will experience compression on one face and tension on the opposite face. It will only experience torsion if the element is twisted axially whilst being restrained at one end.... I think....

[mrgrimsdale]

nickw said:

I'm being a bit slow today.

Anything that is held in a bent state is, by definition, in torsion - i.e. it has a torque (often called Bending Moment in engineering) applied to it. It matters not one jot if that torque is applied about the long axis of a circular bar or across the width of a shelf.

Torsion in engineering means a twisting stress, not just simple bending. The link you gave explained it and says the structural engineer typically designs steel members to be loaded such that torsion is not a concern.
Same applies to shelf builders unless you want to get into some very complicated details. Yer ordinary stresses including torsion due to uneven loads, are catered for as not a concern. They would be a concern when serious eccentric torsion loads are being catered for - say you had a T shaped shelf with the stem of the T cantilevered out.
But an ordinary shelf or beam, whether box construction or not, doesn't need any special torsion consideration and calling it a torsion box/beam is meaningless.
I can see us poised at the top of a pedantic slippery slope here so I might just sign off on this one

cheers
Jacob

[dom]

Right lads, pitch forks and flaming brands let's lynch him

[engineerone]

interesting, that stuff looks remarkably like the mallite i mentioned earlier. that was used in the very first mclaren formula one car built in 1966. the M2a.

on that theme etc, and thinking about the word for dirty,

how about "MONOCOQUE"

to quote my copy of websters dictionary, a nacelle in which the skin carries the main stresses which typically is what we are talking about.

paul

[mrgrimsdale]

"Monocoque" is shell construction i.e. thin shell having strength through shape usually curved in two directions like an egg.
Pure egg coincidence - that egger stuff looks good - cheapo door technology gone up market. Good idea. Funny thing is though - I have adapted egg box doors by cutting them up and adding edgings etc but never thought of developing it Cudda made a loada dosh. Story of my life. Oy oy

cheers
Jacob

[Scrit]

Mallite loooks like a skinned variation of a packaging material introduced 8 to 10 years (?) back called BeBox. I seem to recall the guys marketing it had chairs made from it on their stand at one trade show and that one application was recycleable pallets

Scrit

[engineerone]

scrit, you didn't read me mallite is over 40 years old ;D

and actually monocoque is wrongly used by almost any one.
we as racers first understood it when colin chapman introduced the lotus 33 for jim clark, in 1963, only a couple of months after he had introduced the 25 and sold replicas to others suggesting that the works cars would be the same but it was not a true monocoque, since it had holes. the essence of what we are discussing is the efficacy of using thin top and bottoms around spars or ribs, just like almost all monocoque aircraft.

seem to remember that it is called monocoque is due to the fact that the first such airplane was a french one, for some odd reason i think voison who also made cars did the first one.

paul

[Scrit]

Correction, not Mallite, but Eurolite - similar to BeBox. Bebox is made from timber pulp - mallite is/was a core of end grain balsa with aluminium skins and is more akin to the modern aluminium sign making materials such as Alucolor. As such it is not the same sort of thing we use for wood/fibre torsion boxes which are much more akin to a box girder bridge in composition

Scrit

[pewe]

I can't seem to find any online, so does anyone know what the price is for the Egger Zoom panelling?

I guess it's not cheap.

If no one knows off hand I may give them a call on Friday when I'm back in the office.

[Scrit]

pewe said:

I can't seem to find any online, so does anyone know what the price is for the Egger Zoom panelling?

Very few trade products are sold on line. One of Egger's distributors is Montague L Meyer who are nationwide. look them up and ask, but I doubt very much that this will be a stock product for many distributors

Scrit