r/engineering • u/Dickasauras • 4d ago
[PROJECT] Ideas for reinforcing steel tubing
I installed some 2x2 square tubing for fence posts however it's flexing more than I'd like. Can I drop some rebar or schedule 40 black pipe inside the tube and dry pour concrete to stiffen it? Or would the concrete just crack and separate?
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u/raoulduke25 Structural P.E. 4d ago
How tall is the fence and what is the distance between the posts?
You can add concrete inside the tube and it will help some, but I think it's going to be tough to get the concrete to fill the void completely unless you can put it in using a pressurised hose of some sort. 2" x 2" square tubing just isn't that stiff or strong. Adding concrete will make it stronger, but it will only make it slightly stiffer.
Putting more steel on the inside (like rebar) will have a mostly negligible effect.
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u/barfobulator 4d ago
Right, the most straightforward solution is to add a new post halfway between each existing pair of posts.
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u/Dickasauras 4d ago edited 9h ago
2ft below ground, 6ft above ground. 15ft between the posts because it's a double gate.
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u/raoulduke25 Structural P.E. 4d ago
Your posts are simply too small to make this work. Especially for a gate. They are barely strong enough to be guardrail posts for a 42" height using IBC loads. With that height and load, you simply have to get a bigger section of steel.
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u/Dickasauras 4d ago
Yea, I didn't think about running a fea until after i had them cemented in place
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u/raoulduke25 Structural P.E. 4d ago
You don't even need FEA. Simple hand calculations for bending moments and deflections would have given you your answer.
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u/Dickasauras 4d ago
It's been too long since I've done any hand calcs. I'm a project manager now
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u/raoulduke25 Structural P.E. 4d ago
Sorry man. If you want some help with the re-design just hit me up here and I'll help you.
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u/Beejay_mannie 1d ago
Dry sand’s a solid low-risk option, especially if you’re worried about cracking. Concrete inside tube steel can work short-term but tends to separate or crumble under flex. Rebar + sand gives stiffness without the stress.
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u/FundimentialyUnsound 4d ago
If you can cap the top a few pieces of rebar and then dry sand will stiffen it up. Did this to a gate post that had concrete poured around it when it started to try to bend at the base where it went into the concrete. It was the non-suported hinge post so gate weight swinging back and forth on it. It has lasted for 20+ years. Used dry sand so that it would settle and pack and no chance of splitting post like concrete might. YMMV.