Anchor Reinforcement for Shear Parallel to Edge 2

[ChiEngr]

Hello,

I have a condition where I am trying to transfer in-plane shear to the top of a concrete shear wall. The slab-on-steel floor deck construction runs over the top of this interior wall, so I am planning on connecting the deck down to an embed plate at the top of the wall. I am providing welded headed studs centered in the embed plate every 12" on center. The wall is 14" thick. Due to the large in-plane shear force, I am limited by concrete shear breakout. I was planning on providing hairpins along the length of the wall and parallel to the wall. However, I am now wondering about a potential failure cone along the edge parallel to the wall. To preclude breakout from governing, would I need anchor reinforcement in both directions? Given that I only have a 14" thick wall, I am not sure how I could develop any reinforcement across the wall thickness.

 

[bones206]

I don’t think there is an effective way to reinforce anchors in the top of a wall for shear perpendicular to the wall. Just have to take the capacity assuming plain concrete.

I also have doubts about the hairpin effectiveness parallel to the wall. Having one or two continuous longitudinal bars close the the anchors would probably be easier to build and more effective.

 

[Eng16080]

Assuming you're using ACI 318, Ch. 17:
[ol 1]
[li]I don't see how you'll be able to develop reinforcement to control concrete breakout, as mentioned in Section 17.5.2.9[/li]
[li]But, per Section 17.5.2.7, you may be able to get a slight increase with the psi_c,V factor. For example, you can use a factor of 1.2 "for anchors in cracked concrete with reinforcement of a No. 4 bar or greater between the anchor and the edge." I think this would be applicable in your case.[/li]
[li]Be sure that you're designing the anchors as a group considering that your anchor spacing is less than 3*ca1. Also, along those lines, I could be wrong, but I want to say you won't get any additional strength by spacing the anchors closer than that distance (21"), at least in terms of concrete breakout.[/li]
[/ol]

 

[ChiEngr]

Eng16080:

I agree with item #1 for shear parallel to the edge. Any reinforcing I place won't be able to be developed. However, I believe per the Code that the shear capacity for breakout parallel to the edge would be twice that of the capacity perpendicular to the edge, correct? Using this, coupled with item #2 you list should work for my loads.

 

[Eng16080]

ChiEngr: Yes, that's exactly correct, per Section 17.5.2.1(c).

 

[bones206]

However, I am now wondering about a potential failure cone along the edge parallel to the wall.

Just to be super clear for the benefit of anyone reading this thread, you are referring to this failure mode correct?

 

[ChiEngr]

That is correct, bones206.

 

[KootK]

I feel that you could reinforce this adequately if you could manage to locate the hairpins properly, as shown below. This leans on the provision that we use for beam stirrups that imagines near instantaneous development for bars sizes #5 or smaller that are hooked around longitudinal reinforcing.

You are contemplating a long plate that would have to be wet set, correct?

 

[KootK]

I feel that this would be a pretty conventional way to hand this situation. Field bend the wall bars into the slab and call it shear friction. This, too, will have some anchorage issues. It's also a bit annoying to have to start and stop the decking. Better if the wall is actually a support for the deck.

 

[ChiEngr]

Thanks, Koot!

I really like your second detail. Didn't even think to implement something like that.

 

[KootK]

You're welcome ChiEngr.

I'd also contemplated something like this. ACI has provisions now for shear transfer between the flanges and webs of concrete girders. You can move gobs of shear that way. Some testing has indicated that you don't even need reinforcing to get that done. In many ways, this kind of feels like that.

I'm sure that my first detail would be preferred by you contractor over my second.