Hairpin Anchorage for Pre-Eng Metal Building

[Baffled Engineer]

Hello,

I have encountered this atypical hairpin detail for anchoring pre-engineered metal building frames...

I just wanted to get your thoughts on this, if this would be effective at all?

The hairpin will be cast in the slab, but it's wrapped around another U-bar that is anchored into the pilaster.

I always detail the hairpins to wrap around the anchor rods and it's my first time seeing this detail in the picture.
Would the U-bar open up? and is there a direct bearing steel-to-steel check for the rebar?



Thanks!

 

[KootK]

In some ways I like this better than wrapping around the anchor bolts as that's always felt a little sketchy to me.

You're right though in that the connection between the hairpins and the U-bar lack a commonly available design method. I doubt bearing is a problem so long as the bits are kept in contact. You could check the U-bar for bending as a curved beam but I'd not be hopeful that would work out.

And that still leaves the anchorage connection between the U-bar and the pier.

This is the first time that I've seen this as well.

 

[johnwow]

I can see this being beneficial when you are leaving out the slab for a shell building and can temporarily use cable between opposite columns to tame thrust.

 

[dik]

That U bolt looks awfully short for a tension member.

 

[canwesteng]

I think the cable would just unwind the hook though. You certainly won't come anywhere near the capacity of the 25M bar in tension that way. Better to use a bar coupler

 

[Aesur]

Is this even allowed, doesn't ACI require mechanical splices for anything in constant tension?

 

[ntattose]

The hairpin has two purposes; one is to get the thrust into the slab. The other purpose of the hairpin is so the thrust is not taken out in shear at the anchor bolts, The detail shown relies on shear at the anchor bolts. Sometimes the back pair of anchor bolts is too near the edge of the concrete to count on this.