How are different pieces of furniture rated or built for weight tolerance? Aquarium stands are made out of seemingly flimsy board and can hold hundreds of pounds, but a solid wood coffee table is only rated to hold 50.

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I’ve been looking at different pieces of furniture for a future terrarium and I’m confused as to why some pieces that are seemingly solid are rated to hold little weight. Most furniture labeled as aquarium stands are made out of lightweight material but can potentially hold hundreds of pounds, but an industrial coffee table of solid wood and metal is only recommended to hold 50. Why is their such a huge disparity for weight limits on different pieces of furniture (that are roughly the same dimensions)?

In: 10

Partial answer: It’s in the shape of it. When you have a solid board of wood, you’re distributing the weight over the whole length. When you only have legs, the weight is shared only across legs. You’ll probably notice that the aquarium-holding furniture tend to use more boards, often all the way to the ground.

A simple possiblity is that the lower rated furniture can hold much more weight but the manufacturer didn’t bother to test and verify since most people won’t be loading it to those higher ratings. Furniture advertised as TV stand, book cases or aquarium stands are expected to take heavy loads and customers want to see that the furniture is rated for what they plan to do with it.

The other option is that the internal construction could be less robust than high strength furniture. Using simple glued butt or lap joints vs dowels and other hardware inserts. Even the direction of the wood grain will effect strength.

Wood is very unpredictable regarding to structural properties. Two pieces from the same trunk will vary significantly if one piece is from the bottom, close to roots and the other is from the top.

Therefore when designing with wood you need to use a large factor of safety to be in the safe side. (Meaning if your calculations call for a 3 mm board, you use 6 mm. Or if you are extra cautious you use 8 mm. Then maybe your manager cannot be bothered with future lawsuits and she rounds it up to 10 mm) This can lead to the confusion you are having.

And then there are boards. If that board is plywood, it can take insane amounts of punishment. Skateboards are made of plywood and you can jump and bounce on them all day and they will just take it.

Then there is particle board, and mdf, and hdf…

So if you see a metric about wood strength, take it with a grain of salt.

In construction they use a figure called “working load“ it is 1/3 of the breaking strength to account for bounces and variations in tension