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Guardrail Post Concrete Breakout Strength

Guardrail Post Concrete Breakout Strength

Guardrail Post Concrete Breakout Strength

(OP)
I design a lot of steel guardrails, more than a few of which are core-drilled and epoxied into either precast or cast-in-place concrete stairs and landings. In terms of the strength of the concrete embedment, the only procedure I am familiar with to calculate the capacity comes out of the PCI Design Handbook, 5th Edition. Section 6.9 provides a procedure for embedding structural steel shapes in concrete. The problem is that the post is in close proximity to the edge of concrete, and in all likelihood, breakout probably controls.

I normally embed 4" with 4" edge distance to the center of the post. I'm now confronted with a situation where they want to use 3" edge distance to keep a post out of a doorway. I don't think that's enough. Is anybody familiar with a procedure to calculate breakout strength of the concrete?

I'm thinking of telling them "tough luck", it has to be at least 4", but I would like to be able to back it up with calculations, and for future reference.

RE: Guardrail Post Concrete Breakout Strength

Supplier manuals from Hilti typically have reduction factors you can apply to breakout values based on edge distance and anchor spacing. Also, you can download Hilti Profis and/or Simpson StrongTie Anchor Designer which is a little less harsh with compounding reduction factors, if I remember correctly. Alternatively, here in Canada we have the Appendix D in our concrete code which covers anchorage failure modes and how to calculate them.

RE: Guardrail Post Concrete Breakout Strength

I suspect that our rather inconclusive discussion here represents the state of the art on this.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Guardrail Post Concrete Breakout Strength

(OP)
Thanks KootK. I searched the threads, but for some reason this one did not pop up. I'll look it over and see if it helps.

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