Railing Post Concrete Breakout Strength

[csways_]

Hi,

I am working through @slickdeals calculations posted here. Can anyone clarify the derivation of A1 and A2 on the first sheet?

Thanks!

 

[GC_Hopi]

I didn't look through the calcs in detail but from what I saw on page 1 Ac=A2-A1 where Ac is the failure cone. so the author is essentially subtracting the area due to the post hole.

 

[csways_]

I get that; it's the actual derivation of A1 and A2. The second page shows a sketch, but I am unable to replicate the values.

 

[GC_Hopi]

You have to use the equation for the surface area of a cone. Try imagining what the failure surface would look like. But I would definitely caution against putting the post close to the edge of the concrete. You will have concrete failure.

 

[csways_]

Do I have this right? The results match for A1, but not for A2.

 

[csways_]

This is correct. I noticed a mistake in my spreadhseet and it now works for A1 and A2. Thanks.

 

[NorthCivil]

just an aside - this detail is really only appropriate indoors or for very short design service life.

Engineers dont allow rebar to be permanently exposed protruding from concrete. these steel posts are no different.

paint it all you like, in exterior environments it will eventually corrode, swell, and turn out like the image posted by GC Hopi

 

[nonplussed]

It looks like in the image that GC_Hopi posted, there was another core drilled hole next to the post which is why it cracked. Probably the builder misplaced the first hole and drilled a second one, so I wouldn't really count that photo as normal.

Engineers dont allow rebar to be permanently exposed protruding from concrete. these steel posts are no different.

What about U-bolts and J-bolts for fixing of column baseplates?

 

[NorthCivil]

nonplussed - good point.

for steel that protrudes, for exterior environments, then stainless should probably be specified. otherwise the corrosion will swell and crack the concrete.

similarily, this post should be stainless. or, a more economical solution would be to have stainless anchors, connecting to glav/painted baseplate for the railing.

I thought J and U bolts died with the dinosaurs though? at least in my area, they are never used anymore. the standard detail is straight rods with a nut at the end, sometimes a nut and small plate.