Concrete Breakout Strength

[Alves21]

Hello, everyone!

I am designing an endplate to be anchored on a concrete reinforced column with chemichal anchors. I am evaluating shear on the direction shown in attached picture (column height direction).

I have two analysis situation
(Situation 1)
According to ACI 318 for shear parallel to an edge I have this:
(c) For shear force parallel to an edge, Vcb or Vcbg shall be permitted to be twice the value of the shear force determined from Eq. (17.5.2.1a) or (17.5.2.1b), respectively, with the shear force assumed to act perpendicular to the edge and with ψed,V taken equal to 1.0.

I made this consideration in Profis software and the result is fine for the Concrete Breakout Strength of Anchor in Shear.

(Situation 2)
If I consider the column as having an edge even if far away I will end up in

17.5.2.4

Where anchors are located in narrow sections of limited thickness such that both edge distances ca2 and thickness ha are less than 1.5ca1, the value of ca1 used for the calculation of AVc in accordance with 17.5.2.1 as well as for the equations in 17.5.2.1 through 17.5.2.8 shall not exceed the largest of:
(a) ca2 /1.5, where ca2 is the largest edge distance

(b) ha /1.5

(c) s/3, where s is the maximum spacing perpendicular to direction of shear, between anchors within a group

And considering this aproach, my verification will Fail.

My doubt is if in this situation I can ignore the edge and proceed as in (situation 1)

 

[JStructsteel]

But looking at your picture, you dont have a edge distance issue. Model as the situation you have and then go from there.

 

[Alves21]

I agree, but I was wondering if I should or not consider an edge where column ends on footing

 

[Agent666]

This is really what the parallel-to-edge requirement is asking, you evaluate as if your proportion of the load in 2 anchors acting towards the edge and then double it. It's something I see people misinterpreting all the time trying to evaluate or say the edge is the bottom of the column here. The same occurs on both sides of the column.

So take V/2 shear acts towards the edge, and double the resulting concrete breakout capacity. The appropriate edge distance is denoted as c, you of course are also influenced by the distance to the second edge at the top of the column. But not influenced by the 300-column depth as the indicated breakout surface does not go through the entire depth based on your implied geometry as it looks like 1.5c<=300. So influenced by 2 edges, not 3. Verify you get the same answer in this configuration for the concrete breakout and you're good to go.

I'd be fairly certain Hilti is picking up the parallel-to-edge scenario, but you know, doesn't hurt to independently verify it as programmers are involved here.....

It would of course be potentially easy to add some stirrups at the top of the column if they were coordinated with the drilled-in anchor positions, this could be designed as anchor reinforcement to ACI quite easily and replace the breakout mechanism parallel to edge with the anchor reinforcement capacity as per ACI.

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