Supplemental Reinforcing

[Bammer25]

I have done many, many anchorage calcs, but they have all been fairly simple on a flat slab, only dealing with edge distances and such.

I am designing a pedestal to support large industrial equipment. 70 kip uplift and 8 kip shear. 2 foot tall pedestal to be designed by me (plan dimensions and reinforcing).

I am just going through ACI Chapter 17 per usual and it doesn't seem like concrete breakout strength is influenced much by supplemental reinforcing in the steps in the code (which I know can't be true).

I keep just making my pedestal bigger and having a deeper anchor trying to chase the load down with my capacity, but I know there are ways to take advantage of the reinforcing. Can somebody point me in the right direction? Only thing I see in chapter 17 is just different factors if you have SR.

 

[Bammer25]

Also, for shear calculations, what do you consider for h sub a (slab thickness) when you have a pedestal. Although I am sure whatever I end up with to make the tension work, the shear will be a laugher.

 

[ANE91]

If you can, then use anchor reinforcement, which transfers load from the anchors to the structure. Anchor reinforcement precludes concrete breakout completely. Refer to 17.5.2.1 of ACI 318-19(22); you're just developing steel with 70 kips on either side of the breakout plane.

Supplementary reinforcement is not specifically designed to dump load from the anchor directly into the structure. You benefit from less dimensional restrictions, per 17.3.5, and a slight (5-10%) boost on strength reduction factors, per 17.5.3. Here, the Code acknowledges improved deformation capacity but does not full-on grant the benefits of anchor reinforcement until the additional steel is specifically sized/configured to handle all the loads.

h_a is 24 in...shear could still be an issue, if near an edge.

 

[Bammer25]

Thank you. I’ll jump back in this morning and take a look.

 

[Bammer25]

Ok I haven’t looked that closely before. Pretty straightforward. If I have a bar with a u shape (2 90 degree turns) do I count that as one or two bars as far as anchor reinforcement? As long as my anchor reinforcement tensile strength exceeds my demand I am good? Of course there are a lot of detailing requirements to meet.

 

[Celt83]

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Design of Anchor Reinforcement in Concrete Pedestals by Widianto, Chandu Patel, and Jerry Owen​