Foundation Wall Minimum Reinforcement

[Apache1]

Hi all, I've got a question about minimum reinforcement in concrete walls. Per ACI 318-14 Chapter 11 the minimum ratio for vertical reinforcement = .0012 and horizontal reinforcement = .002. I was running a calculation for a restrained concrete wall (10' tall basement wall) in RetainPro and the default vertical reinforcement ratio is .0018. I can manually change that to .0012 easy enough, but the program also runs the "at least one-third greater than that required by analysis" check for rebar in flexural members that is mentioned in ACI 318-14 Chapter 9.6.1.3, which is the chapter on Beams. It also checks the 200*bw*d/fy per ACI 318-14 Chapter 9.6.1.1. It got me wondering if RetainPro is being overly conservative or if I need to adjust my own calculations which use .0012 and don't run those extra checks.

- Do you all use .0012 for vertical rebar or .0018?
- Do you use different ratios depending whether the wall is cantilever or restrained?
- Do you believe that the "one-third greater" and 200*bw*d/fy checks apply to walls? That provision is in the Beams chapter in ACI, but RetainPro seems to think that it also applies to walls. I understand that walls do act as "beams" as they have a lateral load on them from the soil.

In my opinion ACI 318-14 Chapter 11 makes it pretty clear that the minimum ratio for walls is .0012 without any exceptions or further checks needed.

 

[hokie66]

A retaining wall is a slab, just one which is vertically oriented.

 

[Apache1]

The same could be said of a basement wall with restraint from a joist floor system at the top too, right? If so, then all concrete walls that have soil behind them should have .0018 as the minimum vertical rebar, and the 4/3 check and 200*bw*d/fy checks should be made?

And that being case...what is the point of the .0012 minimum ratio in Chapter 11 (Walls) of ACI? Does that only apply to walls that do not retain any soil?

 

[hokie66]

I fail to see the point of using that small amount of reinforcement in any structural element.

 

[BAretired]

Perhaps walls require less shrinkage and temperature reinforcement than slabs because gravity is helping to reduce crack width.

BA

 

[Apache1]

Perhaps walls require less shrinkage and temperature reinforcement than slabs because gravity is helping to reduce crack width.

But the rebar I'm talking about here is the vertical/flexural reinforcement

 

[BAretired]

But the rebar I'm talking about here is the vertical/flexural reinforcement

The thread title says you are talking about minimum wall reinforcement. If no flexure exists, that is what the code requires. Some codes permit the use of less than minimum reinforcement, but not less than 1.33 times the amount required by flexure.

BA

 

[Apache1]

Ok, but in the case of any basement wall that is backfilled there will be flexure. So I'd say that it's confusing that a basement foundation wall should be designed using minimum reinforcement from the ACI BEAM chapter rather than the ACI WALL chapter. ACI Chapter 11 (WALLS) does mention that retaining wall should be designed using other parts of the code, but it makes no mention of basement walls.