# Steel Tube Bend/yield strength

• posted
followups intellignetly, thanks...
Anyhoo, the boss just asked me to look up OSHA regs on guardrails.
It's fairly straightforward - minimum OD 1 1/4", and able to stand
a minimul load of 200 lbs, from the top or the side. The maximum
spacing for vertical supports is 19".
So, I've got a thing like this to spec:
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• posted
In order to come up with a real answer you have to analyze the railing structure as a whole, and it's almost certainly statically indeterminate. Which means you need to account for the elastic properties of the verticals as well as the rail, and the type of joints between the members and the foundation. With some simplifying assumptions (for example, if the rail is straight and short, ignore the verticals and treat it as a simple beam) you could produce a conservative design and just go with it if it's not outlandish.
My daughter, the architect, was ranting on just this subject last week. The engineering firm her office uses assigned the new guy to verify a railing design for her, and he was analyzing it to death. I can't say I blame him if he lacked the experience to apply lessons learned in earlier to designs to the one in front of him.
• posted
Ned is right. The structure is more complicated that you might think. But I did the calculations based on similar assumptions to those Ned suggested, and got the following results.
For 1.25" OD mild steel tube with a 0.065" wall, the minimum load that will result in permanent deformation (not necessarily collapse) of a 19" span is 491 lbs. With a 0.120" wall that figure rises to 765 lbs.
You can see what I did here:
In reality, the handrail could be several times stronger than this due to the stiffness of the joints. Or the vertical sections, which I haven't considered, could be weaker and prove to be the limiting factor.
It's just an estimate. Don't consider it to be an answer in itself. Just add it to your knowledge and intuition when making a decision. Incidentally, those figures are provided without warranty. I might have made a mistake, although I've checked them and the answers seem sensible.
It's also worth noting that handrails are not often damaged by humans. More often they're damaged by things like prowling forklifts. You're going to need stronger tubing than this to stand up to a forklift. But it all depends where your handrail is going to be situated.
Indeed. If I was designing a handrail I wouldn't do any calculations. I'd go with my intuition.
Best wishes,
Chris
• posted
No problem. I can do the verticals too if you want, but whether it'll tell you anything useful I doubt. Handrails are not especially complex. Make it strong so that it doesn't break, and it's unlikely that anyone will ever care how you arrived at your design!
Best wishes,
Chris
• posted
Rich, I think your info about OSHA is a little off. My book shows 1-1/2" Sch-40 pipe minimum. Posts can be spaced up to 8'-0" on center. You can use a single midrail instead of the balusters every 19". OSHA Standards - 29 CFR Part 1926 Subpart M Appendix B
Tim

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