Torsion Box Shelves

[busbus]

I have the need to for some very long shelves in the garage to hold a bunch of stuff that has been gathering all over the place but I also would like to have a fairly wide space between the shelf supports to make it easier to store some things on it. Many of the items are sort of heavy. Would a torsion box do the trick?

I was thinking about ripping some 2x4's to 1 =BD" to make the torsion box and skinning it on both sides with some =BC" plywood. Do you think I can get, hopefully, six feet between the supports? Maybe a little more? Or won't this work at all?

Thanks. bus

[Charlie Self]

A couple issues ago, Woodworker's Journal had a piece by Ian Kirby on torsion boxes. That might be of some help if you can find a copy locally.

[dgadams]

A torsion box can work in this situation, but I'd guess the cut down 2x4 won't work for that span. I've done shelves that span 3 feet with 3/4 grid and 1/4 skins and the shelves are very stiff. for 6 feet I'd guess a

2 or 3 inch thick grid or fill material would work better. A few rules of thumb:

1. Grid or fill spacing no more than 12 times the skin thickness.

2. Load handling depends a lot on filling thickness.

1. The more glue surface between the skin and the filler the better.

2. Density of the fill is not as important. I've used foamboard.

If I was doing it, I'd build a box with 1x material between 2 and 2.5 inches thick, and use rigid foam panel material for the inner fill. 1/4 inch ply or hardboard for the skins. It's important that the skins be well glued to the fill. Even with this design I'd still treat it as an experiment and see if it could handle a 6 foot span.

Good luck, and let us know how it comes out.

D. G. Adams

[Chris Friesen]

Sure...you just have to size it properly. Generally, for a given strength, torsion boxes are lighter but thicker than solid material.

The strength of a beam (and a shelf is nothing but a thin wide beam) is directly proportional to its width, but is proportional to the cube of the vertical thickness.

Thus, if you make your shelf twice as thick, it's eight times as strong.

Of course, if shelf thickness isn't an issue, just put some 2x4s on edge under the shelf at the front and back.

Chris

[busbus]

Maybe it is because I use Google to view this group but I see there were three responses to my quesiton and I only see one. Do others have this rpoblem? Thsi is happening to some other posts as well.

[busbus]

Charlie, I actually recall seeing that issue, maybe it was June? I just came up with the thought oftorsion boxes recently and now I am kicking mysell in the arse for not at least looking at that srticle. Maybe my local libray has a copy. Thanks.

[busbus]

After hearing what you guys have been saying, I think your sugesstion of just putting a couple 2x4's under the shelf in the front and back would be the easiest way to go.

On the other hand, I may want to shift the shelvs around at some point in time and making the torsion boxes would give me the flexibility and they will be lighter--all the better as things seem to be getting heavier as I grow older for some reason.