"U" bolt Anchor in Concrete

[BS2]

I am analyzing the anchors for an AASHTO pedestrian fence according to the following detail. This configuration was provided to me and I typically use an alternate anchoring detail. However, for this project, the detail was specified by another engineer and I am tasked with checking it. I have reviewed the ACI 318 but have found little direct information about this configuration.

The fence is mounted to this concrete barrier:

My question is: How should this be analyzed? Do the "U" bolts get checked for development? Or do I use the anchoring to concrete provisions with some sort of modification?

Thanks for any help!

 

[hokie66]

Nothing wrong with either of those approaches, except for transportability of the previously welded assembly.

 

[BridgeSmith]

Corrosion is a massive issue with reinforced concrete. So much so that many DOTs in salt regions are going to 100% galvanized rebar in all parts of their bridges.

Well, the bridge deck is a whole different beast than a fence anchorage on top of a barrier. Plus, the rebar and bottom corners of the U-bolts, where the galvanizing would be removed to tack weld the rebar, are embedded 5"+ into the concrete, while the top layer of deck reinforcing has typically only 2" to 2-1/2" of cover.

I also don't know of any DOTs that are using galvanized rebar in their substructures.

 

[BS2]

That looks like a detail from a highway department standard detail.

If in USA, then what state are you in?

Yes, it is for a Missouri DOT project.

BS2, have you superimposed the fence anchorage on the barrier with the reinforcing, with everything drawn to scale (including bend radii) to see if/how everything fits? If my assumptions about the U-bolt dimensions are correct, the analysis may be very much simplified. Read on.

If the continuous longitudinal bars in the top of the barrier are going to have to go through the U-bolts, then breakout of the U-bolts is pretty much impossible, and the tensile strength of the U-bolt is the limiting capacity. I would say the same would be true if at least a couple of the #5 stirrups/ties encompass the #4 by 18" bars that go through the U-bolts.

Here is the overlayed detail:

It looks like one of the longitudinal bars will go through the U-bolts. And the #5 stirrups are at 12"oc so the #4 by 18" bars should be encompassed by at least one stirrup.

Thanks for the help!

 

[BridgeSmith]

It's going to be hard to get those U-bolts in there with the #4 bars welded to them, unless they're placed before that longitudinal bar in the barrier that goes through the U-bolts.

As far as anchorage, I think you're pretty well set, with a continuous bar through the U-bolts, and a stirrup or 2 around the #4. It might be a little better to move the one #4 so they're both inside the stirrups.