ACI 318 Walls - Minimum Reinforcement

[RFreund]

A few (semi-basic) questions regarding the minimum reinforcement in walls:

What is the reason behind the placement of the minimum reinforcement? Why a certain amount on a certain side?

When they say that basement walls are exempt, why is this?

Cantilever retaining walls are based on chapter 10 (flexural) therefor vertical reinforcement is not needed on both faces, correct?

EIT

http://www.HowToEngineer.com

 

[TXStructural]

Minimum flexural is to control strains in the concrete at the moment of cracking. Ignoring the minimums could result in rupture of the reinforcement when the concrete cracks.
Minimum temperature and shrinkage reinforcement is to control crack width along flexural reinforcement.
Basement walls are subject to minimums for flexural reinforcement, and in many cases, this could apply in both directions.
Cantilever retaining walls may need reinforcement on the front face to control cracking (as T&S in both directions in thick walls), but flexure generally only applies to the tension face.

 

[RFreund]

TX - Thanks for the response.
I'm not trying to suggest ignoring minimums I'm just trying to make sure I understand the code. It's one thing to know it, it's another to understand it. Anyway, let's see if I have this correct:

Walls - minimum reinforcement is on both faces to control crack width on both faces. Is this due to the fact of load reversal?

Basement walls - if in a retaining condition, either cantilevered or propped, should follow minimums presented in Chapter 10 (for flexural members) and because this is not a slab or footing, T&S is not required by code. If they are foundation walls with equal earth pressure both sides, by ACI 318, it appears they do not require any reinforcement although (2) #4 or #5 Top and Bottom (in this area) are commonly provided.

Cantilevered retaining walls - For the stem design this should follow chapter 10 (flexural members) but would not require, by code, T&S steel because it is not a slab or footing.

TX -
You make a point that in basement walls, that are subject to minimums for flexural reinforcement, may require reinforcement in both directions. What are you alluding to here?
Also T&S may be required in some retaining walls to control cracking on the face, is there a particular case that you are referring to?

I think essentially what I'm trying to understand is that if the wall is acting more as a flexural member (usually in the case of some sort of earth retention with loading in one direction) do the minimums of Chapter 14 (Walls) apply or should Chapter 10 apply along with 14.3.3 (minimum horizontal steel). I think this will be somewhat more clear if I can understand why they are applying the minimum steel to both faces - just to control cracking on both faces, or is it more due to load reversal.

Thanks again!

EIT

http://www.HowToEngineer.com