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Concrete Pier min. reinforcement for PEMB columns

Concrete Pier min. reinforcement for PEMB columns

Concrete Pier min. reinforcement for PEMB columns

(OP)
I am working on designing 2'-0" x 2'-0" x 2'-0" concrete piers which will transfer load from a PEMB to mat foundations. I am using ACI 318-11. Do I need to follow 10.9.1 "Limits for reinforcement of compression members" which requires As= 0.01Ag-0.08Ag? When I calculate 1% of my area, I find that I need 5.76 sq.in (8 #8's have As=6.32 sq.in) of longitudinal reinforcement. To me, (8)#8 bar seems excessive.

What are your thoughts?

Thanks

RE: Concrete Pier min. reinforcement for PEMB columns

You can defer to section 10.8.4 and use half the section and half the reinforcing.
It's really not that much bar, but it will look funny. And don't forget, that the bars need to be developed, so that might be tough with #8's.
I'd be much more worried about anchoring the PEMB to the pier. Whatever you assume, they'll increase the loads and decrease the anchor spacing.

RE: Concrete Pier min. reinforcement for PEMB columns

I'd ignore it, doesn't seem applicable to a 2 ft cube. Not sure of a reference that would allow you to get around it though.

Professional and Structural Engineer (ME, NH)
American Concrete Industries
www.americanconcrete.com

RE: Concrete Pier min. reinforcement for PEMB columns

(OP)
Thanks guys! In my haste, I missed 10.8.4 allowing half Ag, which does apply to me. I was looking for it, I just couldn't find it. Thanks again!

RE: Concrete Pier min. reinforcement for PEMB columns

See the following link:

http://files.engineering.com/download.aspx?folder=...

Be sure you address the transfer of anchor rod tension into the vertical reinforcing in the pedestal. Since your pedestal is so short, you may want to use a smaller vertical bar size (and more of them), in order to develop the proper strength for load transfer.

RE: Concrete Pier min. reinforcement for PEMB columns

Minimum reinforcement should not be the focus. Those minimums are for compression members. The design of the base for the PEMB needs to be adequate for the uplift, shear, and bending imposed by the frame.

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