ACI Appendix D - Applies Only to Anchors 2" Diameter or Less? 1

[JennyNakamura]

Hi Everyone,

I am designing a concrete connection using HRC headed rebars with 2.25" diameter (#18). I am using App D to check concrete breakout so I can determine how deep the HRC heads need to be. According to D.4.2.2 (I am using ACI 318-02) the equations in App D for concrete breakout are only applicable for anchors not exceeding 2" in diameter and 25" embedment. I already used the concrete breakout equations to come up with a 39" embedment for 2.25" diameter anchors before I saw this. Is my analysis still valid? If not, can someone point me to some reference material as to what the proper procedure is that I need to follow?

Thanks in advance!

 

[JedClampett]

I think the problem is that there is no research on anchors beyond 2 inches in diameter or with very deep embedments. So the code takes the prudent approach of not giving guidance based on extrapolations.
I don't know of any codes that define allowables for large anchorages, although I am sure that if there is any, someone will reference it on this thread.
If you can't reduce the diameters of your anchoring element, you'll have to use your judgement. Following the general format of Appendix D backed with a healthy dose of conservatism is probably pretty sound.

 

[WillisV]

IBC limits overrule the limiting provision of ACI Appendix D and allows you to use the equations for larger anchors with higher embedment depths. Just look into the concrete chapter of IBC 2006.

 

[TXStructural]

Once you reach the kinds of forces in a #18 bar, you should probably be depending upon fully developing the headed bar to the other bar(s) in the concrete, rather than relying on the breakout resistance of the concrete itself.

 

[InDepth]

Well I believe the diameter and the fact that a preinstall reinforcing bar will have different behavior than a preinstalled rod makes appendix D inapplicable...because the corragations on the reinforcing bar will cause a different stress field distribution in the concrete. With headed adapters you should be using the ICC Evaluation Services Report which reports embedment depth and other requirements. Ie. Use the tested data for that product. Forget App D. Also agree that if you are using headed adapters you should be developing the full bar...why go less, especially for such a large bar....then again if I remember correctly ACI had no test data for developing bars greater than a #12....go figure.

 

[Teguci]

ACI 318-11 will allow appendix D to be used up to 4" diameters. Apparently the Koreans did some additional testing for very big and long anchor bolts. So if you can wait unitl IBC 2012 (I know, I'm holding my breath too!) then you can use the "simple" approaches highlighted in appendix D for large anchors.

 

[InDepth]

Why wait, use the latest ACI... I always say that in a court of law they will always want you to use the latest and state of the art knowledge..."why did you choose a lesser standard?"...regardless of the building code says to use a previous version...remember codes are just a minimum and if you use the latest you are going above the minimum!