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Reinforcing Against Pryout Failure

Posted by Curtis Scottalmost 7 years ago
Reinforcing Against Pryout Failure

Is anyone aware of any basis for using reinforcing bars to preclude pryout failure? Looking at the failure surface it makes sense to me that properly positioned and developed reinforcing can resist pryout, but ACI 318 is silent on it.

ACI318,Pryout

2 Replies
Posted by Bryan Johnsonalmost 7 years ago
Hilti Verified

Curtis,

When it comes to using reinforcing bars to resist pryout, you are correct in that it is not specifically spelled out in the “Concrete Pryout Strength” section (ACI 318-14 Section 17.5.3.1). However, as part of the commentary, it does reference the previous sections specific to anchor reinforcement for cast-in-place anchors, and how it can be used to help resist concrete breakout for an anchor or anchor system. For post-installed anchors, there is not much information due to the difficulty of installing a post-installed anchor adjacent to reinforcement, rather than having it cast-in with the concrete. For additional information, you can reference Section 3.1 “Anchor Principles and Design” from the 2016 Hilti North America Anchor Fastening Technical Guide (https://submittals.us.hilti.com/PTGVol2/), or feel free to give our Engineering Support Group a call at 877-749-6337.  


2 comments on this reply
Posted by Curtis Scottalmost 7 years ago
Do you think it's reasonable to say that if reinforcing is properly designed and details per section 17.4.2.9, that the pryout failure can be precluded? Again, the physics of this make sense to me, but I just haven't found such a conclusion in any literature.

Posted by Curtis Scottalmost 7 years ago
Bryan, I don't see any references to reinforcing in the commentary on pryout strength, section R17.5.3. Are you referring to the fact that, as discussed in section 17.5.3.1, Ncp (or Ncpg) are to be based on the concrete tensile breakout strength per section section 17.4.2.1, which can be supplemented by reinforcing bars? I've noticed this before, but have yet to find any language/research/testing specifically relating the pryout strength to the reinforcing strength per section 17.4.2.9.

Posted by Bryan Johnsonalmost 7 years ago
Hilti Verified

Curtis,

In the commentary provided in Section 17.5.3.1, it states that pryout resistance will be based on the calculations for concrete breakout and bond failure. With that being said, the presence of anchor reinforcement will be most applicable to the shear calculations for concrete breakout. As seen in Section 17.5.2.9 and Section 17.4.2.9, ACI 318-14 Chapter 25 will provide the guidelines that are required for anchor reinforcement, in order to modify the shear pryout equation. Unfortunately, since Hilti does not specialize in anchor reinforcement, there would be no test data/documentation from Hilti that would provide any further guidance on the design of the anchor reinforcement. From the understanding of ACI 318-14, it would be a fair assumption to state that if the anchor reinforcement is designed per ACI 318-14 Chapter 25, then the design strength of the anchor reinforcement shall be allowed to be used instead of the concrete breakout design strength. It may be difficult or impossible to ensure that the post-installed anchor engages the rebar to preclude a pryout or breakout failure.