Anchor bolt concrete breakout cone area overlap

[BAGW]

Hi,

I have columns with 2’x2’ base plate. There are 6 bolts, 3 on each side of the flange. I need 7’x7’x24’’ footing to get anchor bolt breakout to work.

At the expansion joints, the columns are spaced 2.5’ apart. The concrete break out area for the anchor bolts over lap at the expansion joint as shown in the image. How to deal with such situations? Can this be ignored as there is 6’ of concrete available on either side of overlapped breakout area as to required 3.5’ per single column design.

 

[canwesteng]

You can't ignore it - the intersection of the breakout cones is the edge of the breakout cones for the purpose of caluculating the failure surface.

 

[WARose]

Generally what I have done is to (either) consider the combined groups (i.e. to get the capacity as a whole), or treated the edge near another group as a free edge (i.e. cutting off the failure zones before they overlap).

 

[BAGW]

(either) consider the combined groups (i.e. to get the capacity as a whole), or treated the edge near another group as a free edge (i.e. cutting off the failure zones before they overlap).

Treating as a group gives entirely different result as compared to other way of analyzing. Which method is more accurate? Any code or document which addresses such situation?

 

[WARose]

Treating as a group gives entirely different result as compared to other way of analyzing. Which method is more accurate?

I would say treating it like a group. The free edge approach is a bit conservative.

Any code or document which addresses such situation?

Overlapping embedments are part of the code (i.e. Appendix D).

 

[BAGW]

I agree with treating it as a group. The spacing between the anchors is less than 1.5heff, so they have to breakout as a big group.

 

[jdarr02]

You might want to consider downloading Hilti's PROFIS anchor design software. It should check this situation.

https://www.hilti.com/content/hilti/W1/US/en/engineering/software/profis.html

 

[KootK]

or treated the edge near another group as a free edge (i.e. cutting off the failure zones before they overlap).

This I like.

consider the combined groups (i.e. to get the capacity as a whole)

This I question. In my opinion, group treatment requires a rigid base plate etc forcing everything to act in concert. Getting anything resembling a rigid distribution member for this going to require some rather extreme hoop jumping.

Another reason that I prefer the free edge solution is good old fashioned tractability. At an expansion joint, in presumably high seismic environment, in presumably moment frames, you're going to have a zillion load cases to consider with those damn columns whipping around in various directions independently. I think it's a much simpler problem, and therefor a more reliable solution, to treat the column connections independently if possible.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[WARose]

This I question. In my opinion, group treatment requires a rigid base plate etc forcing everything to act in concert. Getting anything resembling a rigid distribution member for this going to require some rather extreme hoop jumping.

Good point Kootk.