Use of U-Shaped anchor bolts at base plates
Use of U-Shaped anchor bolts at base plates
(OP)
I am designing sound wall foundations. The sound wall manufacturer is showing anchor bolt sizes and configurations, but I am checking for anchorage to the foundations (drilled caissons). One wall particular has very high overturning forces and thus very high tensile forces. They are showing U-Shaped anchor bolts here. My question is does anyone know how to design for U-Shaped anchor bolts? Appendix D does not cover this. Side face blowout is for headed anchors and I'm not sure if this applies to the U-Shaped bolts. Picture attached.






RE: Use of U-Shaped anchor bolts at base plates
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Use of U-Shaped anchor bolts at base plates
My thoughts were similar in that the crushing at the radius may control. A colleague of mine gave me the idea of placing 180 degree bent rebar looped over the straight portion of the U-Shaped anchor bolt. The idea is to develop it below the anchor bolts to resist the tensile forces.
RE: Use of U-Shaped anchor bolts at base plates
1) It's tough to quantify that help and;
2) I don't know that you've eliminated the issue of crushing in the radius.
Do you have to use these U-bolts? I'd much prefer long, conventional anchor bolts with double nuts effectively lapped with rebar.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Use of U-Shaped anchor bolts at base plates
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Use of U-Shaped anchor bolts at base plates
RE: Use of U-Shaped anchor bolts at base plates
If an alternate anchor bolt is permitted, I'd recommend going with threaded rebar. That increases the effective lap length required but eliminates the blowout issue.
Another option could be to use a stiff, rectangular bearing plate spanning between the anchor bolts. This is the same concept as the U-bolt but more convincing. The bearing plate could be a small channel if you need the extra stiffness. I guess this suggests another way to check the U-bolt. If the U-bolt could work as a bearing plate spanning between the vertical bolt legs, and concrete bearing stresses are okay, maybe you're good to go as is. You'd also need to do this check if you were using the hairpins that your colleague suggested.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Use of U-Shaped anchor bolts at base plates
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Use of U-Shaped anchor bolts at base plates
Thank you for your input. The other option was a plate as you mentioned, but it is more costly. The actual forces from the wall panels to the post base plates are moment and shear. The moment resolves into the T-C couple and the tension is placed on two of the anchor bolts or one U-Shaped anchor bolt.
RE: Use of U-Shaped anchor bolts at base plates
RE: Use of U-Shaped anchor bolts at base plates
Do you mean that the blowout concrete cone is held in place by shear friction through the vertical pier reinforcement?
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Use of U-Shaped anchor bolts at base plates
RE: Use of U-Shaped anchor bolts at base plates
I don't see how this force is transferred via shear friction. The force will be transferred to the vertical caisson reinforcement once the concrete has cracked and the crack develops through the vertical steel. This places the vertical reinforcement into tension, not shear. Are you talking about a typical footing where the top horizontal bars would experience shear friction?
RE: Use of U-Shaped anchor bolts at base plates
RE: Use of U-Shaped anchor bolts at base plates
RE: Use of U-Shaped anchor bolts at base plates
RE: Use of U-Shaped anchor bolts at base plates