Minimum Reinforcement in Foundation Stem Walls that work as Plain Concrete for Design

[MJC6125]

What do people follow for minimum reinforcement in concrete foundation stem walls where the soil is the same height on each side or there is a shallow crawl space to the inside of the foundation wall? See example detail images below that I pulled from the internet. For the vertical reinforcement/dowels in these stem walls, do you space them at 18" oc max and design it for temperature and shrinkage minimum area? If yes, do you automatically go to (2) mats of rebar for walls thicker than 10" per section 11.7.2.3 of ACI? For horizontal reinforcement, do you space them at 18" oc max and design for temperature and shrinkage minimum area?

I have always done plain concrete and included only a minimal amount of reinforcement in these types of foundation stem walls (i.e. vertical dowels at 32" oc and (2) continuous horizontal bars top and bottom). I haven't seen any issues with this approach in practice, but I'm wondering if others are against this plain concrete/unreinforced approach for any reason. I also saw section 14.1.4 of ACI 318-19 says plain concrete is only allowed for foundation walls in residential projects for Seismic Design Category D-F. So if your project is in Seismic Design Category D or higher, do you automatically have to go to a wall reinforced per ACI reinforced concrete requirements?

 

[HTURKAK]

English is NOT my first language but section 14.1.4 is more than clear for me.. ..

- Clause 14.1.4 states ; Plain concrete is permitted for a structure assigned to Seismic Design Category (SDC) D, E, or F, only for the cases (a) and (b) . ..

(b) Foundation elements (i) through (iii) for detached one and two-family dwellings not exceeding three stories and
constructed with stud bearing walls:
...

(iii) Foundation and basement walls not less than 7-1/2 in. thick and retaining mo more than 4 ft of unbalanced fill.

- In case of (SDC) A, B, or C; Clause 14.1.3 plus 14.1.4 is applicable.








Don't underestimate a nail. A nail saves a horseshoe, a horseshoe saves a horse, a horse saves a commander, a commander saves an army, an army saves a whole country.. GENGHIS KHAN

 

[MJC6125]

That makes sense. So, do you design stem walls and shallow crawl space walls as un-reinforced concrete and not worry about having a mat of reinforcement in the wall in SDC A-C?

 

[KootK]

For a "do nothing" stem wall, I don't design it at all. I go temperature and shrinkage longitudinally and #5 dowels @ 24" oc.

I'm not sure that designing the walls as un-reinforced makes sense in this situation. Unreinforced implies uncracked. And you've got a definite crack, at the location of maximum bending, at the cold joint between the footing and stem wall.