Shear Stud Design

[cancmm]

Question regarding the design process for shear stud connectors...

I'm designing an H-Pile to concrete cap connection using shear studs due to high tensile loads in the pile. My immediate thought process is to design the connection using a shear friction approach, with appropriate checks against concrete breakout, etc. In other words, I would design the shear studs in tension.

Initial calculations suggest a 3/4" stud (smallest available from Nelson) needs to be embedded at least 12" to be fully developed. This seems excessive because I've seen much shorter studs in composite bridge decks before.

I feel like I'm missing something so I wanted to see if anyone could point me in the right direction. Is shear friction not the correct approach for some reason?

Thanks!

 

[mike20793]

Are you trying to attach headed studs to the H-pile and cast part of the pile cap around it? If so, you may want to check out AISC 360-10 Section I2.1 for encased composite members for axial force. The calculations are pretty straight forward.

 

[KootK]

I've spent some time contemplating this in the past. Here's what I've come up with:

Section I8.2 applies to a composite flexural member where steel anchors are embedded in a solid concrete slab or in a slab cast on formed steel deck. Section I8.3 applies to all other cases.

In my opinion, this kicks you into I8.3.

The steel headed stud anchor strength provisions in this section are applicable to anchors located primarily in the load transfer (connection) region of composite columns and beam-columns, concrete-encased and filled composite beams, composite coupling beams, and composite walls, where the steel and concrete are working compositely within a member. They are not intended for hybrid construction where the steel and concrete are not working compositely, such as with embed plates.

Again, in my opinion, this kicks you our of I8 altogether. I feel that neither the pile nor the cap is a true composite member. I think that the connection really has much more in common with an embed plate.

So what method should be used? I agree with cancmm's supposition that shear friction is the way to go.

Initial calculations suggest a 3/4" stud (smallest available from Nelson) needs to be embedded at least 12" to be fully developed. This seems excessive

What's governing the requirement for 12" studs? I'm going to hazard a guess here that it's ACI 318 APP.D breakout failure modes. If that's the case, then I'd like to suggest ignoring some of those failure modes. Tension breakout won't apply because when the concrete failure cone tries to break out, it will be restrained by the steel section that it's shearing against. I'd also argue that pryout would be moot in a confined concrete scenario. Shear breakout would apply but most of your studs will likely be far enough from edges that this won't matter much. The only concrete checks that matter, in my opinion, are bearing at the head of the studs and group action factors. And those should be easy to satisfy with proper spacing and head/shank proportioning.



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.

 

[KootK]

And, of course, shear breakout of the whole damn thing needs to be checked as well. I'd consider tying this back into the main member with rebar for good measure.

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.

 

[wannabeSE]

What are the results if the headed studs are assumed to be anchors loaded in shear using ACI 318 Appendix D?

 

[Agent666]

Eurocode 4 has a procedure exactly for this purpose for the transfer of load.

If I remember correctly the capacity basically equates to a similar capacity you might calculate for a composite beam with some modifications. There is some enhancement due to the confinement of the concrete from the flanges when studs are on the Web of the H pile if I remember correctly.

 

[KootK]

I did a little research on this last night. Example A2 of this document contradicts my assumption that tension breakout would not apply: Link. The situation is not identical and the method has been revised in later versions of this document. I thought that I'd table the information anyhow in the interest of full disclosure.

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.

 

[Yao1989]

Are you trying to transfer tension load from column into pile cap, then into H-Pile? Do you have a sketch?

12" does not sound excessive at all if you are using it for direct tension. Composite bridge deck is using shear stud to resist shear, not direct tension so it make sense that they are usually very short (usually 4"~10"?). Maybe I am understanding the problem incorrectly, but for direct tension perhaps a different solution (i.e. not shear stud) may be merited? I have seen details before where there is a hole in the H-pile web/flange, and you use a 180 hook rebar to hook to H-pile, and the rebar would pretty much be the full depth of the pile cap.