Calculating load for furniture?

[Andrew More]

Are there any tools or ways to determine this?

I ask because I'm currently trying to make a loft bed for my kids, and I'm trying to figure out how thick the legs need to be. My father made something similar out of southern yellow pine a few decades ago, and ended up using 3" legs. It held together for several decades, and is still going strong I believe. I've been looking at a plan in Wood magazine issue 144, and they're using maple with 2 1/4" thick legs.

My current plan is to do this out of hard maple, and shoot for the 2 1/4" legs.

However, I'd rather not have a problem.

FWIW, this will be made to take apart, using 6" stretchers between head and tail board, and the Rockler bed rail fasteners.

Are there any good calculators for load over a span and how thick legs need to be to withstand the load? I understand wood being a natural product is going to vary a bit.

[Albert Lee]

Are there any tools or ways to determine this?

I ask because I'm currently trying to make a loft bed for my kids, and I'm trying to figure out how thick the legs need to be. My father made something similar out of southern yellow pine a few decades ago, and ended up using 3" legs. It held together for several decades, and is still going strong I believe. I've been looking at a plan in Wood magazine issue 144, and they're using maple with 2 1/4" thick legs.

My current plan is to do this out of hard maple, and shoot for the 2 1/4" legs.

However, I'd rather not have a problem.

FWIW, this will be made to take apart, using 6" stretchers between head and tail board, and the Rockler bed rail fasteners.

Are there any good calculators for load over a span and how thick legs need to be to withstand the load? I understand wood being a natural product is going to vary a bit.

To do this properly you will need the property of the timber you are using and the limit state you will be using, you want the bed to flex a little

Making a loft bed for static load is easier, but the problem is, the load will not be static. kids move on the bed.

generally speaking check point load or a uniformly distributed load on the bed. the span of the bed will determine a lot of things. the main beam of my loft is ususally 6 inch deep

[Brian Tymchak]

https://workshopcompanion.com/KnowHow/Design/Nature_of_Wood/3_Wood_Strength/3_Wood_Strength.htm

I've used this page as a guide when I had a similar question. Bottom line is the compressive strength of most species is way beyond the load you are going to apply. So, the answer of how thick to make legs will come down to design accomodation for lateral stability and aesthetics.

[Richard Coers]

The best thing you can do to add strength is triangular bracing. Nearly all the bed loading is vertical, but with a motion all the load has to be through the fasteners. Before long they crush wood fiber and now your joinery is loose. Knee bracing is a great place to start.

[Andrew More]

The best thing you can do to add strength is triangular bracing. Nearly all the bed loading is vertical, but with a motion all the load has to be through the fasteners. Before long they crush wood fiber and now your joinery is loose. Knee bracing is a great place to start.

Good point. I've noticed a number of the commercially available pieces have some sort of bracing bar running around the outside at about 3' up. That would probably address the problem of racking.

https://www.ikea.com/us/en/images/products/stora-loft-bed-frame-black__0749152_pe745510_s5.jpg?f=s

[Tom Bender]

It's not going to be used for sandbags, but for people climbing and moving around. Consider the effect of 3 kids in a pillow fight with an adult on the floor. Weight would not be my main concern. My first concern would be for the joinery. Those halfway up stretchers won't help the 4th side. Add an integral desktop.

[David Gutierrez]

A
ssuming one or more sides will be up against a wall, consider attaching it to the wall on one or more sides. This will significantly reduce the wracking.

[Richard Coers]

Those lower boards prevent the legs from spreading a little, but rely totally on the fasteners to prevent racking. You need something like knee braces that angle from the bottom of the bed to the posts to give it strength from kids jumping and playing on it.