CONCRETE SIDE FACE BLOWOUT STRENGTH OF HEADED ANCHOR IN TENSION

[LARC]

I AM DESIGNING A FIXE BASE IN A SPECIAL STEEL MOMENT FRAME SYSTEM. I AM USING HEADED ANCHOR IN TENSION.

THE ANCHOR IS DESIGNED TO LAP WITH THE PIER REINFORCING BECAUSE THE PIER BREAKOUT CONCRETE STRENGTH IS NOT GOOD IN MY CASE.

DO I NEED TO CHECK THE CONCRETE SIDE FACE BLOWOUT STRENGTH OF HEADED ANCHOR IN TENSION? I NEED TO CHECK THIS FAILURE MODE IF I AM USING LAPPING WITH CONCRETE REINFORCING?

THANKS

LUIS ROMERO

 

[sdz]

Yes you should check side face blowout to ACI 318 App D. Include effects for proximity of the side of the pedestal and spacing of the anchor rods. The results can be scary.

 

[JedClampett]

You might want to do a search under the "Structural Engineering other topics" forum. This subject (the side blowout) has been discussed quite extensively there.
Unfortunately, ACI defies common sense and will give you no credit for the lap of the anchor with a reinforcing bar. You're pretty much stuck with the low value governed by edge distance. It might be preferable to model the base as pinned.

 

[Lion06]

I'm going to disagree and say that you don't need to worry about it. If you are lapping the studs with rebar, then you needn't worry about tension failure modes in the concrete. You do still have to worry about shear failure modes in the concrete.

Side face blowout rarely controls, so I am guessing you have a pretty deep anchor that is pretty close to the edge. If the edge distance is greater than 0.4*embedment then you don't even have to worry about side face blowout. This shouldn't be a difficult criteria to meet. Even if you have a 12" deep stud, just provide 5" edge distance and you're out of the woods with side face blowout.

 

[kslee1000]

I think EIT is correct in saying "Side face blowout rarely controls".

Before ACI got into the business of anchor bolt checks, we used to onlt take a look at shear on anchors, and tension on the bolt. The concrete was assumed cracked at the bolt head level, then the gap was closed by the reinforcement, which was designed for all loads combined. The concrete is likely to break near the top of the pedestal/pier due to high shear, that's been the reason the stirrups were such closely spaced.

Do not take my words for granted, if you are strickly code person. Good luck.

 

[pehiggins]

Per ACI App. D, side-face blowout is expliclity a tension failure mode and can control the design. ACI 355.1R, Report on Anchorage to Concrete, does not use the term side-face blowout, but discusses the failure mechanism in section 3.4, Behavior of cast-in-place anchor bolts in uncracked piers. In this section the report is looking at long embedment lengths and small edge distances. You can see that the App D forumula is a modified version of the formala presented for what the report calls wedge-splitting mode for bolts in tension.