Which cc measurement for best load capacity?

[tlundberg]

anaitis: fifth points, you say... Have I understood correctly that you should place the brackets one-fifth of the length from the edge then? So, for example, 20cm in from the outer edge if the shelf is 100cm. Or 40cm in my example where the shelf is 2m.

How should one think to arrive at that? Feel free to explain a bit more

 

[daugaard]

For even load along the entire shelf, it's best to mount the brackets like Ts option 2, that is, 50 cm in on a 2-meter shelf. For uneven load, do the same but also screw the brackets into the shelf! If the shelf bends, it's overloaded!

 

[tlundberg]

daugaard: So you are saying that anaitis is wrong? I think you need to back it up with some actual calculations

 

[Granngubben]

With evenly distributed load, the optimal positioning will always be at the fifth points. It can be calculated, but I think it would be unnecessarily technical.

Yes, if you know the answer, calculating it is unnecessary Then the distance between the supports should be three-fifths (60%) of the shelf's length if I interpret you correctly. That matches pretty well with my calculation above which gave 56%.

 

[injonil]

Saying that the consoles should be 50cm in is the same as saying that the shelf at that position can be split in half and the shelf will still have the same strength. And that is obviously not the case

 

[anaitis]

With the placement of the supports at fifth points, the support moments become equal to the field moments. Calculating this is an exercise commonly performed in many engineering programs.

 

[kalubah]

Injonil: Theoretically, it works that way. If you have exactly the same load on both sides, it works in practice too, but you have to be careful not to nudge the shelf or remove something from one side, thereby changing the load.

Otherwise, it is true that the moment becomes approximately the same at the fifth-point. Support moment Ms=q*a^2/2, Field moment Mm=q*(L^2-4*a^2)/8 for those who want to try. a is the length between the edge of the board and the support, L is the length between supports, q is the distributed load.

 

[daugaard]

daugaard: So you are saying that anaitis is wrong? I think you need to back that up with some actual calculations

Can at least answer with a question
In your calculation, you place a 10kg weight 50 cm to the left.
Then the same weight in the middle between the brackets.
Shouldn't you calculate with 20 kg weight between the brackets instead?

 

[tlundberg]

Well, it depends on what you want to calculate. The ten-kilo stack of books weighs ten kilos whether it's placed on the far left or right in the middle between the brackets So if you're calculating how to position the brackets so the shelf bends as little as possible regardless of where the stack of books is placed, you shouldn’t calculate with 20kg in the middle.

 

[anaitis]

With the placement of the supports at the fifth points, the support moments become as large as the field moments.
Calculating this is an exercise done in many engineering courses.

Forgot to mention that this applies to evenly distributed loads. I assumed that this load case was of interest.
It corresponds to having roughly similar books on the shelf everywhere.
With point loads, it becomes a completely different load case.

 

[tlundberg]

Both cases are interesting But an evenly distributed load is probably the most general. Often you fill your shelves. Maybe not exactly evenly distributed weight-wise, but evenly enough to suffice for calculating the evenly distributed case

 

[daugaard]

So should one not count on 20kg in the middle for evenly distributed load?

 

[tlundberg]

It's probably unfortunately more difficult than that. Someone mentioned the formulas Moment_stöd=q*a^2/2, Moment_fält=q*(L^2-4*a^2)/8. a is the length between the edge of the board and support, L is the length between supports, q is the distributed load.

 

[anaitis]

It is probably unfortunately harder than that. Someone mentioned the formulas Moment_support=q*a^2/2, Moment_field=q*(L^2-4*a^2)/8. a is the distance between the edge of the board and support, L is the distance between supports, q is the distributed load.

And if you insert the fifth points into these formulas, both moments become equal!

 

[ToRy]

Excuse someone who doesn't quite keep up with all the calculations, but what are you planning to store on the shelf? If it seems like there's a risk of the brackets or the board getting deformed, wouldn't it be wise to simply choose a different, sturdier dimension for the items, or alternatively find a less sensitive place to store your 200-liter aquarium or your motorcycle?

That said, I can certainly understand human curiosity and thirst for knowledge, so by all means, carry on.