Minimum Reinforcing for Large Concrete Pier in the Ground

[marinaman]

I have a situation where I will need a concrete pier to support a primary building column, (4) small tube columns (to brace architectural cladding), and to support veneer that wraps the columns, all at the same time.

The loads are small. Column load is around 100 kips (dead and live). No lateral

I'm not concerned about capacity of the concrete pier.

My question is about minimum reinforcing.

The pier has to reach 12' into the ground because of some footing issues dealing with site issues and grades. The pier has to be 80" x 80" square, in plan size, in order to be large enough to support the (5) columns bearing upon it. 4,000 psi concrete.

That said, what is the minimum reinforcing needed?

When I look at ACI 318, 10.9.1 Compression Members, I'd need (81) #8 bars vertical!!! Wow.
When I look at ACI 318, 14.3.2 for walls, I'd need 9.6 square inches, or (6) #6 bars per face...but this really isn't a wall
When I loo at ACI 343R, 13.5 for bridges, I'd need (1) #6 at 12" o.c.....but this really isn't a bridge

The 10.9.1 sounds crazy....because I do not need that kind of r/f for strength. What are your opinions?

Also, whatever vert bars are there......does every other one need to be laterally tied? Per ACI 318 Chapter 10, vertical bars could be no further apart than 6" o.c. and every other one would require a lateral tie.

I'm leading toward #7 bars vertical at 6" o.c. and provide lateral ties at every other bar spaced at 12" o.c. I'd also provide a continuous #4 bar, horizontal, 6" o.c. I'm thinking this because my element really doesn't meet any ACI 318 criteria.....but at the same time, I do not want temp and shrinkage to crack me up.

What are your thoughts?
I'd attached a sketch.

 

[Tomfh]

Its so lightly loaded that its not a compression member in my opinion, it’s more of a mass concrete bearing pad. Reinforce the outside of it with a decent mat and it will be fine.

 

[JAE]

In ACI 318-14 look at section 10.3.1.2.

This has in the past been referred to as the "architectural column provision".

Basically it says that if your column is larger than it really needs to be, you can design it as though it is 1/2 the size (based on gross area) and all the design requirements (including minimum reinforcement) can be based on the smaller theoretical column.

For ACI 318-11 and earlier (the older chapter format) look in 10.8.4.

 

[Smoulder]

Does it tick the boxes for plain concrete? That would let you choose your own skin reo while still complying with code. I would use #6 @ 12" each way because that's about 0.35% when the cibcrete area is based on the outermost 10". That's from the Australian code for thick walls.