Concrete Break out w/ stirrups? 1

[TonyES]

I have some large steel columns sitting on short (3' tall) piers that are roughly 2" larger than the base plate (in all directions). They have lateral/vertical/uplift forces. I'm trying to determine wether or not the anchor bolts will break out or fail per Appendix D in the ACI. What impact do my stirrups have? I have #3 bars that wrap around the vertical bars as well as the anchor bolts, I would think that they help but haven't seen anywhere that talks about it. Any guidance would be greatly appreciated.

 

[JedClampett]

I would consider it supplementary reinforcing and use the applicable increase.

 

[frv]

Unfortunately, ACI 318, Appendix D does not address the contribution of steel.

Steel helps out tremendously, but Appendix D ONLY considers concrete strength (with one minor exception).

You'll have to use a different approach (such as shear friction) to account for the additional steel.

 

[msquared48]

Laterally, the stirrups do maintain confinement, particularly for any lateral load to the top of the concrete plinth. The ACI requires either two or three stirrups (I think only two now although I commonly use three - old school) at 2" on center at the top of the plinth to resist the lateral force you suggest, maintaining the integrity of the anchor bolts.

Mike McCann
MMC Engineering

 

[Lion06]

Here is a good article on using supplementary reinforcement whencalculating the breakout strengths.

 

[jheidt2543]

StructuralEIT:

You get a star for a very interesting article! In addition, there were some interesting questions/comments at the end, but no resolution of them. Is there a follow up article?

Appendix D is a real pain, I found it notable the the authors try to avoid using it too.