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RE: Reinforcing for Anchor Bolt Breakout

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Title: RE: Reinforcing for Anchor Bolt Breakout

This is a good question that has generated a significant amount of debate in the anchoring industry.  Specific guidance for your question is provided in ACI 318-05 Appendix D, Section D.4.2.1 and commentary (should be the same in ACI 318-02).  In tension, the CCD design method predicts a concrete failure prism starting at the head of the bolts and projecting on to the surface.  If this concrete breakout is your limiting state and you need to increase the capacity of the connection, without changing the concrete configuration, you can provide reinforcing that is developed on both sides of the failure plane.  In other words, the reinforcing should be developed in the breakout prism and back in the main concrete member.  This is easier to achieve with hairpins since it reduces the developmental length, but can be done with straight bars as well.

ACI Committee 355 is publishing some design examples and I am sure one of them addresses your situation.  I believe we will make these available during Appendix D training courses (currently being offered by ACI). 

Hope this helps,

Jake Olsen, PE
Director of Product Development
Powers Fasteners

From: "Rich Lewis" <seaint03(--nospam--at)>
To: <seaint(--nospam--at)>
Subject: RE: Reinforcing for Anchor Bolt Breakout

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Thanks for the info.   I don't believe a hairpin in applicable here.
Concrete breakout is the tension shear cone pullout.  The ACI specifically
states hairpins are good for shear reinforcing but they don't give any
suggestions for tension breakout.  I don't see how a hairpin would help the
breakout failure.  I was considering thickening the footing at the anchor
bolts, extending the anchor bolts down below the bottom mat of footing
reinforcing and using the concept of shear friction reinforcing from the
bottom mat reinforcing to intercept the failure cone.  I would like to see
some printed literature stating this works first though.  I have heavily
loaded anchor bolts in tension.
 The "PIP STE05121 Anchor Bolt Design Guide" uses hairpins or additional
straight rebar next to the anchor bolts to do this.  PIP stands for Process
Industry Practices.  The guide is based on App D 318-02.


From: Haan, Scott M POA [mailto:Scott.M.Haan(--nospam--at)]
Sent: Wednesday, April 19, 2006 6:15 PM
To: seaint(--nospam--at)
Subject: RE: Reinforcing for Anchor Bolt Breakout

I thought ACI appendix D is meant for unreinforced concrete.  It seems
logical that if the concrete has to pop out past horizontal reinforcement
that the shear friction the horizontal reinforcement produces could be used
to resist the pop out and that if the pop-out happens adjacent to vertical
reinforcement that you could count on the strength of the steel developed
above and below the pop-out to resist the pop-out.
I have not seen this is a design guide but I have seen engineers do it.


From: Rich Lewis [mailto:seaint03(--nospam--at)]
Sent: Wednesday, April 19, 2006 12:46 PM
To: seaint(--nospam--at)
Subject: Reinforcing for Anchor Bolt Breakout

Are there any practical ways to reinforce a footing for concrete breakout of
anchor bolts as defined in ACI appendix D, section 5.2?  If Break Out is the
controlling factor in the design of the anchor, and I don't want to design
the footing thickness based on anchor bolts, what would be a reinforcing
configuration to strengthen the breakout capacity?


Thanks for any insight.