# How much shear load can rebar withstand?

I'm thinking of integrating rebar into a short grape trellis as horizontal supports for the vines to climb on. Is there anywhere I can get the deflection/load information for rebar spans? As currently planned the spans will be 10ft and the rebar I have access to is 1/2in. Will that diameter rebar span 10ft under some load without serious/fatal deflection?

(I realize this isn't the intended use of rebar, but It seemed like a potential alternative to horizontal beams, and its a little more vine friendly)

• How much is "some load"? How much deflection is acceptable? Nov 13, 2017 at 19:20
• In the short Googling I did, I saw numbers in the range of million of Pascals as well as millions of Newtons, but that's all expected inside concrete. With 3/4" rebar, I'd expect you to be able to climb that trellis without serious deflection, as long as the vertical supports could handle that. Then again, if that's your vertical supports, too, you'll probably be fine to load it with your whole family. ;-) Then again, I'm not a construction worker or a structural engineer, so I'm just guessing at this. Nov 13, 2017 at 19:24
• Ah, you changes to 1/2" rebar, so maybe only load you and the missus, not the kids. :-P Nov 13, 2017 at 19:24
• Apparently wire is the usual choice for the horizontal supports. Look at how much thicker rebar is than 10-gauge wire, and consider that the wire is suitable for a 28-foot span. I think you may be overengineering it somewhat - or are you intending to avoid having tension in the horizontal supports? Nov 13, 2017 at 19:29
• Sorry about the change! :) The load would hopefully be small. I plan to have at least 3 runs of rebar from post to post (walking up the post). So the load on each run would be the load of the vine between one run and the next - Since each run should only have to support it's own portion. Nov 13, 2017 at 19:30

If you are using re-bar I would go with a #6 (3/4"). Anything less will deflect too much. Buy it from a local concrete supply yard or metal service center. If it were me I would use cable and run it across, like Andrew suggested with wire. This way you can increase the tension in the future without worrying about the vines.

• What's "too much"? That's really the question. #6 is going to be crazy heavy and will sag quite a bit on its own, without any load. Nov 13, 2017 at 21:22
• I checked some re-bar as well some rigid conduit at the hardware store. Even those deflect a noticeable amount at 10ft. So i think im gonna go with good 'ol pine :). The 2x4s and 2x6s dont deflect at all really when spanning 10ft. With 3 levels of 2x4s to support the vines I think it'll be just fine. Also avoids the rust problem. Nov 14, 2017 at 20:38

One of the 1/2” rebar “you have access to” has enough “shear strength” to support my car full of groceries with me in it.

However, you don’t want to use it for a horizontal support of grape vines, because it will rust and deposit so much rust in your vineyard that you’ll be labeled a hazardous waste site.

Also, that rust will contaminate the taste and bouquet of that wine so much that I’d have to hold my nose to drink the wine.

Try something a little more common like wire.

To add a comment, Keep in mind the re-bar will rust like a like crazy. Unless you use PVC covered re-bar; I don't think you are going to like the price. Consider how rusting re-bar would look. And do you want water droplets filled with oxidized steel particles dripping on your fruit. Let me recommend 10-guage galvanized steel wire or 1/8" galvanized or vinyl covered wire cable. If you make your end posts sturdy, you can stretch either of these two items tight and have an attractive trellis.

• You're right--this is a comment. It doesn't belong in an answer. Nov 13, 2017 at 21:21