Shear breakout at top of concrete pier.

[MidwestSE]

Hi all,

Here is a question I've been trying to find an answer for. I attached a sketch to clarify.

ACI 318-11 Section 7.10.5.7 requires you to have ties in the top 5" of a column (or pier) to "improve load transfer from the anchor bolts to the column or pier..."

ACI3 318-11 Appendix D.4.2.1 says where anchor reinforcement is provided in accordance with D.6.2.9, breakout can be neglected and the steel is designed to carry the load.

My question is, can the ties required by 7.10.5.7 be designed to carry the load in accordance with D.6.2.9 for the situation in the attached sketch?

Thank you for any advice.

 

[KootK]

My question is, can the ties required by 7.10.5.7 be designed to carry the load in accordance with D.6.2.9 for the situation in the attached sketch?

I vote yes, tepidly. That is essentially the idea with this strut and tie method for anchorage design: Link. For serious loads, I prefer the strut and tie method. While not explicitly stated as such, I feel that appendix D is the domain of smaller scale things. It really gives no direct consideration of the concrete struts involved in the load transfer method and was developed primarily with unreinforced concrete in mind.

Disclaimers aside, one of the first things that I'll do in the design of a laterally loaded pier is to see if I can get enough stirrups at the top of the pier and near to the anchor bolts to deal with 100% of the applied shear (phi = 0.75). It's a good start.

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.

 

[MidwestSE]

Thanks, KootK!

 

[Guastavino]

Based on the sketch, I'd be cautious doing that. The commentary has some verbiage about using stirrups and ties, I'm looking at RD.6.2.9 in the 2008 ACI Code. Not to discourage you, but I'd read through the commentary and get a good feel for it.