Can two horizontal pieces of ½" square tubing support twice the weight of just one?

I am building a metal frame for shelves to hold wine bottles. I plan on using ½" tubing to support the wooden shelves but am concerned that it won’t be strong enough support the weight of the bottles. Would putting to ½" tubes side-by-side increase the amount of weight the shelves can support?

Assuming both pieces are attached to something other than each other, sure.

Practically speaking, yes.

Thanks for the replies. My partner was convinced that if one ½" square tube would bend under the weight of the bottles than any number of additional tubes would be just as weak.

That is, assuming both tubes are bearing the weight at the same time. You could have a pathological arrangement where only one tube bears the force and then fails, allowing most of the weight to transfer to the next tube and causing it to fail too.

In general, the force is divided among all the elements simultaneously bearing it.

If this wasn’t true, it would be basically impossible to build anything useful.

Consider a structure at 99% of its weight limit. Now consider another one standing right next to it. They both stay up, right? Now stick a piece of tape between the two structures. The tape won’t make it collapse, will it? But now you have a single structure twice as heavy, supported by two beams. So clearly, it’s possible.

It’s the classic bundle of sticks metaphor. You can easily break one stick. If all that mattered was what the original stick could take, you could just as easily break a whole bunch of sticks at once. But you can’t.

Hence the metaphor says you should work together to make yourself stronger.

Assuming these are uprights, then the problem is securing the shelves to them. Two tubes side by side that can’t maintain the rigid right angle support of the shelves may not be any better than one.

Look at rope. The tiny strands on their own won’t bear much weight, but braided together they can hold a lot.

It all depends on the span and the load. For educated guessing purposes…

Deflection Calculator for Square Tubing

Ninja’d, but this is another calculator that takes more variables. You should note that the load support capability depends on the size and thickness of the tube, and the distance between centres. For example, you can double the tubes at each end, or maybe add another in the centre. You must also consider how the load will be spread.

http://www.engineeringtoolbox.com/beams-support-forces-d_1311.html

Sharing load properly depends on the structural members have a bit of flexibility to them. If you aren’t careful, it’s quite possible to get into a situation where one member takes almost all the load compared to the others.

Consider a set of bolts holding something in place–torque one of them more than the others and it will carry the most load, even though it is only stretched by a fraction of a millimeter extra compared to the others. If they were instead equally torqued, but the element they were holding collapsed or shrunk by the same amount, you would have the same mismatch in load. Lug nuts work well because steel stretches by a predictable amount under load.

For long tubing in an application like this, there’s no problem at all–any misalignment is going to be small compared to the flex under heavy load. But it could be a problem in other situations and it would be a consideration in any structural analysis.