ACI 318 App. D - Pryout Failure & Supp. Reinf.

[TK406]

I'm in the process of designing some pilasters with fairly large loads and am planning to design supplemental reinforcing to prevent concrete breakout. The problem that is arising for me is that pryout is controlling shear failure.

My interpretation of the code is that supplemental reinf. is for concrete breakout only, exclusive of pryout, but am i being to restrictive on my design?

In appears to me, that Pryout is a similar failure to Tension Breakout, so if i properly design supplemental tension reinf. can i assume pryout will not control the design?

Any thoughts or interpretations on this matter would be great.

 

[strucguy]

check out this paper. It might provide you with some guidance.

http://www.bechtel.com/assets/files/TechPapers/design-of-anchor-reinforcement.pdf

 

[bones206]

As you increase the embedment depth of your anchors, pryout capacity increases. Another reason to have longer anchors is to provide sufficient lap length for supplemental tension reinforcement. I think the Bechtel paper talks about that also.

 

[TK406]

Ultimately, my question is:

Can I prevent concrete Pryout with properly designed (fully developed and sized) supplemental reinforcing in the vertical (Tensile) direction?

In the article you provided (Page 4, Item 4): "When reinf. is used to restrain concrete breakout, the overall anchor should ensure that there is sufficient strength corresponding to the three other modes... (pullout, side-face blowout failure, and PRYOUT).

So, the article indicates that Pryout can't be prevented with supplemental reinforcement, BUT I disagree with this.

If you look at the failure mechanism of PRYOUT in ACI D Figure RD4.1(b)(ii) it is much like Tensile Concrete Breakout. Additionally, the calc. for pryout has a direct correlation to concrete breakout, and is essentially a scaled version tensile concrete breakout capacity.

So if Tensile Concrete Breakout is prevented, then shouldn't Pryout also be subsequently prevented?

 

[bones206]

I don't think that you can make that assumption based on theory alone. Even though pryout capacity is directly correlated to tension breakout capacity in the code, they are two distinct failure mechanisms in reality.

It's possible that supplemental reinforcement can increase your pryout capacity, but I would want to see testing that proves it.