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RE: Reinforcing for Anchor Bolt Breakout

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Another option is to add a plate at the bottom of the anchor bolt.  This increases the area of concrete in the shear cone.  I am not familiar with ACI 318 requirements yet, but am familiar with ACI 349, Appendix B which I was told is similar.  The shear cone starts at the edge of the plate.

 

Also, Figure B.4 of ACI 349 Appendix B shows an example of additional reinforcement for direct tension.  It is similar to a hairpin, but the rebar is vertical and must extend above the shear cone for development.  See Design of Headed Anchor Bolts by Shipp and Hanninger, AISC Engineering Journal 2nd Quarter 1983 and Guide to the Design of Anchor Bolts and Other Steel Embedments by Cannon, Godfrey, and Moreadith.  Design of anchor bolts have been studied to death in the nuclear industy.

 

Gary Loomis, PE

Master Engineers and Designers, Inc.

 

-----Original Message-----
From: Rich Lewis [mailto:seaint03(--nospam--at)lewisengineering.com]
Sent: Thursday, April 20, 2006 11:15 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Reinforcing for Anchor Bolt Breakout

 

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.

 

Rich

 

 

 

 

 

 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)poa02.usace.army.mil]
Sent: Wednesday, April 19, 2006 6:15 PM
To: seaint(--nospam--at)seaint.org
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)lewisengineering.com]
Sent: Wednesday, April 19, 2006 12:46 PM
To: seaint(--nospam--at)seaint.org
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.

 

Rich