Guardrail Post Concrete Breakout Strength

[spats]

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.

 

[Shotzie]

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.

 

[KootK]

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.

 

[spats]

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.