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ACI 318 - App D - pullout & blowout

ACI 318 - App D - pullout & blowout

ACI 318 - App D - pullout & blowout

I have a question regarding concrete pullout & side-face blowout requirements for a highly loaded anchor bolt(s) in tension. This bolt will be supporting a column base plate that sits on a drilled shaft, which will have a (yet to be designed) rebar cage of some sort.

Taken from the "8 Nov 14 22:26" response on this thread:


As far as development goes, it is perfectly acceptable to lap an anchor with a rebar cage. The same rules would apply as for non-contact lap splices. Presumably the anchor rods would be inside the confined core of the foundation, so most of the limit states from App D are restrained by the surrounding reinforcement, i.e., "supplemental reinforcement." Appendix D is typically applied to reduce the embedment depth to less than a typical Ld. Also, many anchors are higher capacity than a similarly-sized rebar, making a strict lap a bit difficult.

And there's a paragraph in ACI-318 (08, in front of me) D.5.2.9 that states:


Where anchor reinforcement is developed in accordance with Chapter 12 on both sides of the breakout surface, the design strength of the anchor reinforcement shall be permitted to be used instead of the concrete breakout strength in determining φNn...

Is there an ACI/CRSI document or paragraph that makes a similar statement with regard to Pullout (D.5.3) and Side-Face Blowout (D.5.4)?

i.e.: Is there definitive statement somewhere that says if you provide a sufficient rebar cage, with a long enough anchor rod, you can ignore the pullout & blowout requirements of Appendix D?

Thanks for the feedback!

RE: ACI 318 - App D - pullout & blowout


RE: ACI 318 - App D - pullout & blowout

Definitive statement - no. Though, I wouldn't worry about requiring a definitive code statement, because this problem is solved relatively easily with some careful thinking. Providing a non-contact lap splice of bars and anchor will preclude anchor pull out if you have a headed or nutted anchor - it is evident when you compare the required anchor pull-out length verses the lap length required of the vertical rebar. 9 times out of 10, your required rebar length is longer that that required for anchor pull-out. Again, there is no specific US code statement, but this practice has been going on for decades with success.

Side blow out restraint is a bit trickier to quantify(unless you meet the minimum edge distance to preclude it). Typically, at a minimum I require 4#3 ties at 2" o/c at the anchor heads, which I believe restrains the side blow out wedge much a like a hairpin for pre-eng building foundations, precast connections, etc. The detailing is important here, because the ties need to be close to the anchor heads but not so close that the blow out wedge develops outside the ties. Also, I am not super convinced that this spall would "take down" the entire connection. If there is amble anchor length above this spall to the top of the pier/pile, the blowout will remain local and a non-issue at the strength limit state, IMO.

Strut and tie method is a very good way to capture the most important parts. It is referenced in other engtips threads.

"It is imperative Cunth doesn't get his hands on those codes."

RE: ACI 318 - App D - pullout & blowout

Thanks for the feedback!

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