Hooked Anchor Side-Face Blowout 1

[ChadV]

Hi all. For checking existing anchorage, has anybody come across a rational way to approach side-face blowout of hooked anchors in tension? I know they're not advisable for new construction, but this is a check of existing anchorage for new increased loads.

ACI 318-14 provides side-face blowout expressions for headed anchors but is silent on hooked anchors. I was able to find a dusty 9-year-old thread here where great minds seemed to agree it was a valid failure mode, but not one that we have a rational method to assess for a hooked anchor.

I have a case with 2" diameter hooked anchors, ~48" embedment depth, where the centrelines of the anchors are about 13" from the closest side face. The side face has #5 bars at 12" c/c horizontal and vertical. My thinking is that if the blowout "chunk" is akin to the breakout prism, the blowout should be intercepted by two bars in both directions, although again there's not a rational way that I know of to quantify the load they'd have to resist.

Does anybody have any thoughts, helpful or otherwise? Thanks!

EDIT: for context, these anchors pass the applicable tensile strength, pullout, and breakout checks... just trying to rationalize the side-face blowout failure mode.

 

[WARose]

You could probably just use the bearing area of the leg as your bearing area (in the side face blowout formula) and check it that way.

For a L or J bolt.....you are probably going to run into issues with the steel bending before there are any issues with side face blowout. It may not be codified anywhere, but I have always checked L/J bolts for that failure mode. (And it typically controls.)

The steel you are talking about on the side (i.e. the #5's) can be used to stop such a failure (i.e. side face blowout) if they are detailed properly. The load they would have to resist would probably be a portion of the uplift (maybe half; maybe all of it would be conservative).

 

[ChadV]

Thanks WARose!

What's your approach in checking the steel bending? I can see taking the pullout load (required to crush the concrete above the hook), distributing it along the hook and checking it as a cantilever, but this seems quite conservative. Is that the kind of check you're describing?

 

[WARose]

What's your approach in checking the steel bending? I can see taking the pullout load (required to crush the concrete above the hook), distributing it along the hook and checking it as a cantilever, but this seems quite conservative. Is that the kind of check you're describing?

It is. Appendix D of ACI 318-11 had equation D-15 (for hooked bolts), and I've taken that as a limiting force to cantilever (that or breakout strength; whichever is less).....but I've never been too certain if that is for concrete only or if it will cover you for the steel as well. Logically, before it could crush the concrete by bearing there could be a bending (or shear; I forgot to mention that before) issue in the steel at the point where the bend begins.

It's probably overkill....but I'm not sure what else to do to be sure. (There are also multiple takes on the cantilever load distribution: i.e. triangle shaped starting at the bend, linear, etc.)

It's just one of those grey areas in what we do.