"U" bolt Anchor in Concrete
"U" bolt Anchor in Concrete
(OP)
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!

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!
RE: "U" bolt Anchor in Concrete
RE: "U" bolt Anchor in Concrete
That sounds a bit iffy.
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P.E. Metallurgy, consulting work welcomed
RE: "U" bolt Anchor in Concrete
I agree that the welding of the rebar is a bit weird, but I'd consider that just a fitup helper so they are one unit for placement. They've basically set the dimensions as a template with the rebar being welded like that and the use of the u-bolts.
RE: "U" bolt Anchor in Concrete
Why not just use wire tires. Cut plywood templates of the post holes to hold the tops during casting.
RE: "U" bolt Anchor in Concrete
RE: "U" bolt Anchor in Concrete
RE: "U" bolt Anchor in Concrete
-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates
-Dik
RE: "U" bolt Anchor in Concrete
Because it's a waste of galvanizing. Only the exposed portions of the u-bolts, and maybe an inch or so of the embedded portions, need protection.
RE: "U" bolt Anchor in Concrete
RE: "U" bolt Anchor in Concrete
RE: "U" bolt Anchor in Concrete
If in USA, then what state are you in?
Every now and then we have to do a manual back check of a TxDOT standard detail......and they all fail miserably.
RE: "U" bolt Anchor in Concrete
What type of details are you checking?
RE: "U" bolt Anchor in Concrete
The TxDOT retaining wall standards are pretty scary if you put them into retaining wall software. The new standards are better than the old ones, but in my experience, they all slide or have other issues with the footings in the software.
The TxDOT headwall standard will let you go 16ft tall with an 8" wall. A guy in our office built a Staad model with their geometry and loading assumptions. He couldn't get it to work.
RE: "U" bolt Anchor in Concrete
RE: "U" bolt Anchor in Concrete
RE: "U" bolt Anchor in Concrete
I think they are empirically good walls, and am comfortable using them on most jobs. On TxDOT specific jobs, there really isn't any decision to be made since the state is only going to build one of their standard walls. And there is plenty of money available to change out the back fill if needed.
RE: "U" bolt Anchor in Concrete
RE: "U" bolt Anchor in Concrete
Anyway, back to the subject.
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.
RE: "U" bolt Anchor in Concrete
I'm not sure I follow. 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. Galvanizing anchors is hardly unprecedented or even unusual. I would do exactly what dik said; fabricate the u-bolt/rebar assembly first and then dip the whole thing.
RE: "U" bolt Anchor in Concrete
RE: "U" bolt Anchor in Concrete
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.
RE: "U" bolt Anchor in Concrete
Yes, it is for a Missouri DOT project.
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!
RE: "U" bolt Anchor in Concrete
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.