Supporting bookshelves

Hi all. I picked up 5 lengths of 20mm x 200mm oak. The plan is to build a bookcase of 2 verticals and 3 shelves with some 4mm thick veneered ply at the back. It will be screwed to the wall affair, in the metre wide gap at the side of the chimney breast. I want to use moulded battens to carry the weight of the shelf unit.

So what section do you recommend for these weight bearing moulded battens and what screw size? The shelves will be well stacked with books.

Thanks.

Arthur

Reply to
Arthur2
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If you are adept enough to create a strong box structure from the timber, then suitable hidden brackets could be fixed to the rear of the uprights and so secured to the wall. Remembering that the weight of the assembly will be creating a straight down the wall force direction, as Isaac Newton says in his papers.

Securing the shelving to the wall is all dependant on the construction of said wall. If it is plasterboard, either single or double skin, it will not support even a straight down force from the mass of a heavy object. On the other hand, if the wall is built from solid stone or brickwork, with a plaster coating adhered to the inner surface, then a mature fixing system which passes sufficiently into the solid mass of the wall, and not just the plaster coating, should suffice in supporting a rather large weight which produces a straight down force.

A good shelving system should only produce straight down forces, so fixings don't need to be huge to obtain a large holding force. If the shelving is made to hold any weight that you may want to place on them, then that is the most important part of the project. It is pointless hanging the shelves on the wall with huge fixing, if the shelves themselves can't support the weight of the objects they are meant to hold.

My advice is to build your shelves as you want them. Then have a look at the fixing technique. You may find that the whole unit only needs a couple of small brackets will be enough to support it. If you are hanging individual shelves, then good practice is to allow for support as close to both ends as is needed, with a small central support to alleviate any bending properties that may be apparent in the shelving material.

But it really depends on how you want the shelves to look on the wall.

Reply to
BigWallop

This might be interesting

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Reply to
The Medway Handyman

You are obviously unaware of the Principle of Moments, or Varignon?s Theorem. Please don't confuse this with the album "Principle of Moments" by Robert Plant!

It is true that a set of shelves fixed to the wall exerts a net downwards vertical force on the wall due to gravity. But it is also true that, because the force is not in the line of the wall, but some distance external to it, there are also horizontal forces where the shelving unit touches, or is fixed to the wall.

These horizontal forces will be outward (away from the wall) at the top and inward (towards the wall) at the bottom. They will balance each other out, resulting in no net horizontal force, but they do have to be allowed for in design, especially the design of the fixings.

The top fixing will have to contend with not only a downward force, but an outward horizontal force that is trying to pull the fixing out of the wall. It is no good trying to deny this; the horizontal force definitely does exist. Overall, it might be arithmetically balanced out by the inward horizontal forces lower down, but the top fixing still needs to withstand it.

The reason for this is the Principle of Moments. The downward forces caused by the shelving system and the items it supports result in a net downward force that acts through the centre of gravity of the system. Since the centre of gravity is some distance away from the wall surface, it exerts a turning force, couple*, or torque that is equal to the weight of the shelves and contents times the distance of the centre of gravity from the wall.

That torque has to be resisted by horizontal forces in the fixings. If there are fixings top and bottom, the force in the upper fixing is outwards and that in the lower fixing is inwards. They will balance each other. The forces can be calculated from the calculated torque from the shelves and the vertical distance between the fixings.

I emphasise, for the absolute avoidance of any doubt, that these forces are definitely NOT zero as you appeared to imply above. The upper fixing MUST be designed for the outward force, as it can be very significant indeed. Anyone who puts up shelves believing that there is no outward force on the upper fixings is in grave danger of being buried under the shelves and what they were carrying before they fell.

  • giving rise to the well worn phrase "every couple has its moments".

;-)

Reply to
Bruce

Don't talk bollocks and get real

He's fixing the shelves in between a chimney breast and the end wall

The obvious solution is end brackets, in which case the force will be downwards only

Reply to
geoff

It's OK, I'll get it. What type of coat were you wearing? :-)

Of course, you are correct in your hypothesis. But, in reflection, if the actual construction of the shelving were in such a way as to allow the whole to be secured to the wall surface with just high level fixings. With the actual content weight being supported by the materials of the shelf manufacture. Then the horizontal forces would be cancelled by the opposing holding force against the top most section of the structure. Which would then give the whole a solely suitably useable downward force to negotiate.

Or, in other words, why use four when two is enough.

Reply to
BigWallop

ROTFLOLPMP!

Peter Crosland

Reply to
Peter Crosland

My apologies. ;-)

Reply to
Bruce

Full body armour. Polished. ;-)

True, although a degree of redundancy (more fixings than the absolute minimum needed) is always a good idea in case one of them should fail.

There is still an outward force on the top fixings, balanced by an inward force of the bottom of the shelving against the wall. As I said: "The upper fixing MUST be designed for the outward force, as it can be very significant indeed." That does not depend on whether there are bottom fixings, or not. The outward force is still there.

Reply to
Bruce

NT

Reply to
meow2222

If your sides are constrained from moving sideways, and you're only stacking books on, moulding doesnt need a lot of strength. If you screw through the sides into the oak shelves as well, the moulding can be even lighter. I'd not expect any problem from 1" moulding, as long as the screws holding it go most of the way through it. If you used good glue all along you could go much smaller.

NT

Reply to
meow2222

However, for a 200mm depth, and say - fixings at the top of a 1.5meter bookcase, teh monent is about in te ratio 0f 0.1/1.5 or a ratio of pull out fore to shear force of some 16 times

So not hugely relevant

Reply to
The Natural Philosopher

There bloody will if it has old vinyl records on it.

Or large books.

Should be OK for paperbacks of the 'lighter' variety though..Archer, Cartland etc.

No weight in any of those.

Reply to
The Natural Philosopher

Almost all wall fixings have far greater resistance to shear forces than to pull out forces.

So hugely relevant. ;-)

Reply to
Bruce

But not 16 times.

Reply to
The Natural Philosopher

To suggest 1m of 20mm oak wont be upto hardbacks is cobblers.

NT

Reply to
meow2222

It depends what you think is acceptable deformation.

It certainly wont break, but I would say it would bow over time.

I wouldn't use more than 4-500mm spans on that grade of wood for a really fine finish.

Supporting the back edge will help a lot.

But I would still prefer central support at the front on that span

Reply to
The Natural Philosopher

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