Embedded guard rail post

[XR250]

I have a residential project where the architect wants to use a steel guardrail system around a concrete front porch. The posts are 3 x 3 tube steel embedded in the concrete. They are stainless steel and I have detailed stainless all-thread welded to them that extends back into the slab to resist the couple from the bending moment. The architect showed ¾" cover at the outboard side of the post. Obviously, this doesn’t work, however what is the minimum edge cover that y'all would be comfortable with to prevent cracking around the post? Should I run a rebar along this edge? I suggested 3” and the Arch. was OK with it but it seems a bit excessive.

Thanks.

 

[r13]

Doesn't that ACI App. D apply in this case - concrete embedment.

 

[JoelTXCive]

Put the geometry into the free Hilti or Simpson software. The software will give you the concrete related limit states.

I don't think 3" edge clearance sounds excessive. We do a lot of industrial/OSHA steel guardrails and our standard detail has 5" edge clearance so that there is at least 1 rebar there to confine the concrete breakout.

 

[XR250]

Hmm, did not know I could use the software for this purpose. I am using the threaded rod to take the the outward load of the post so the cover is really only aesthetic. Probably could use a high and low rod in case someone decides to pull on the rail instead of push.

 

[jayrod12]

I think 3-4" seems reasonable and sneak in a #3 bar top and bottom.

 

[JoelTXCive]

XR250 I might have typed too fast. I was thinking you would have a baseplate of some sort and then stainless anchors embedded.

The software can definitely do that. I don't think the software will let you enter in a 3x3 anchor.

For a ballpark idea, you could enter 1" diameter (or what ever the largest Hilti or Simpson anchors are) and see what the software says on the concrete failure modes. I would think that if you are breaking out with a 1" anchor close to the edge, then you would definitely be breakout with a 3" square object.

 

[Celt83]

embedded rail poles are not the same as anchors you end up trying to develop two compression blocks to form your couple to resist the handrail moment and then need to try and rationalize a breakout cone similar to a shear lug.

Typically recommend against embedding the pole for this as well as maintenance reasons and try to push for a surface mounted plate+anchors.

My Personal Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

Open Source Structural GitHub Group:

https://github.com/open-struct-engineer

 

[XR250]

Typically recommend against embedding the pole for this as well as maintenance reasons and try to push for a surface mounted plate+anchors.

I did push for that but - Because Architect.
I feel the stainless material will mitigate any maintenance needs and the attached horizontal rods tying back into the slab will minimize the compression block requirements.


Thanks for everyone's insight

 

[dik]

If stainless, you want to passivate the welds using nitric acid... or something to prevent rust.


Dik

 

[EdStainless]

I have seen posts set using a round extension that is welded into the bottom of the upper post.
In your case there would be a machined block that fit up into the post (with notches in corners to allow drainage) that is welded in and then a 1.5" or 2" diameter solid rod welded into that.
The round bar is what would be set into the concrete.
I have seen these epoxied into drilled holes or set and poured around.

As mentioned the welds would need to be cleaned (fresh abrasive followed by an acid wash and the lots of water to rinse).

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[GC_Hopi]

I would recommend more cover then less and some rebar. If you get water running down the post or thermal expansion of the post then the concrete will not stand a chance and will spall off.