Side-face blow out question?

[COstructural]

Can side face blowout cause anchors with a greater embedment to fail? I'm trying to design some anchor bolts into concrete with a pre-determined layout and anchor size. However when I make the bolts longer to satisfy my requirements, the bolts fail using the interaction equation with the side-face blowout. My side face blowout becomes relevant because ca1 becomes less than 0.4hef. What am I doing wrong? Any suggestions?

 

[CELinOttawa]

You're not doing anything wrong, you just need to move further away from the edge. Absolutely lengthening the anchor can cause a concrete cone failure - You've changed the failure mechanism by making the bolt too long to be that close to the edge.

If this doesn't make sense, I've likely misinterpreted your question. A sketch would help a lot.

 

[dcarr82775]

Yep. Maybe look at providing rebar to control the concrete breakout and move back to shorter bolts

 

[COstructural]

Unfortunately my concrete pedestal size is restricted. I think my best bet is as you suggested, to decrease the length of bolts and provide rebar. For my information though, is there anything you can do besides increasing your edge distance to make side face blowout work? Add rebar or something?

 

[CELinOttawa]

Yes, you can develop hairpin bars around your anchors.... They are effectively a long rebar bend to standard (6 dia typically) radius and thus doubled back on themselves.... Normally done at the edge of slabs where a pedestal is composite with the full slab.

If you are on a raised pedestal, you can do something similar by borrowing seismic stirruping detailing to confine the full top of the pedestal, ensuring you have lapping steel to the two sides of your anchor bolt.

I had to do this on a number of pre-engineered structures overseas on which I was the "local" or site engineer adapting the system to be installed.

 

[Lion06]

When I've come across situations where the Appendix D calculations won't check out and there is no reasonable way to make it check out then I've abandoned headed studs in favor of rebar welded to the embed plate.