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Strength of different sizes of steel electrical conduit?

Posted by knoxvillegardener 7a (My Page) on
Wed, Feb 24, 10 at 12:48

Hello,

I would like to build trellises from steel electrical conduit for vine-type garden vegetables (e.g. squashes, melons).

Can someone give me some guidelines on the load-bearing capacity of different sizes of steel electrical conduit?

For example, if I have a six foot span of conduit, how much weight could I expect it to comfortably support and how does this weight change with the diameter of the conduit?

Are there some tables online where I can look up these values? (I tried a Google search but wasn't able to find anything.)

Although some of the plants I'd like to grow are fairly lightweight (e.g. green beans) so load-bearing capacity won't likely be an issue, some others (e.g. watermelons) can produce fruits that weigh 30 pounds apiece. With the possibility of having a number of fruits at once being supported by a single trellis, this could be an issue.

My goal is to figure out the right size of conduit to use - something that's definitely strong enough (e.g. including a margin of error) - but not unnecessarily large as the cost to buy conduit and fittings rises with diameter.

Any useful guidance you could give me on this would be much appreciated.


Follow-Up Postings:

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RE: Strength of different sizes of steel electrical conduit?

1/2" conduit and 3/4" conduit will sag some under weight, and if you're talking excess of 30 lbs I don't think will work.

I would go to hardware store and put some 3/4" rigid conduit(not the cheap EMT) or 3/4" galvanized pipe across 2 stands, then push down in the middle and see if it's strong enough.

You also might check out the 1-3/8" galvenized fence posts as they come 8' long and aren't too high priced... but pretty strong.


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RE: Strength of different sizes of steel electrical conduit?

I use 3/4 EMT for the cantaloupe and butternut squash, zero problem, tiny sag that is immaterial to anything I do. The 1/2 gets the toms (6-7 mostly indeterminate) and cukes with a little sag that rebounds in fall. No problem whatsoever, and for the price I'm very happy. My spans are all either 6 or 7 feet. I secure with either rebar or some extra 1" SCH40 PVC with shims. I couldn't find stress and deformation numbers either, so I went in to the store and made a 7 foot span and put my weight on it until it deformed and was satisfied. Here's first year with them, before paint, closeup after paint.

Dan


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RE: Strength of different sizes of steel electrical conduit?

Thanks for your feedback, everyone!

From what I've been able to find out with further research, galvanized posts and spans used in chain link fencing are very strong and not that expensive (although more so than steel electrical conduit).

Evidently a six or seven foot span of 1 3/8 inch diameter can hold a hundred pounds without difficulty.


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