I call it an I-Beam because it is shaped like a capital I....hubby says it is a floor joist. When we did our remodel last Spring the carpenter mismeasured and had to cut 1 foot off every joist and was going to toss them...so, I snagged them with the thoughts that they would make great free-standing base for all types of mixed media techniques.
Recycle....and another cool thing, it can be reverseable or viewed from both sides if you choose. And if you don't have any lying around, you can get them at the lumber yard cut to size, if you take a whole beam, at about 2 bucks a foot... much cheaper than canvas.
I also wanted to mention that the barbwire is one of Tim Holtz's Masks and I used the throw-away waste and used it like a stencil.