Residential Concrete Stem Walls
Residential Concrete Stem Walls
(OP)
Okay, I readily admit my understanding and use of the ACI 318 is still quite limited. I'm much more comfortable with the NDS and everything having to do with wood engineering.
I've recently been doing some work on some detached garages. One story structures with a 24" stemwall resting on a separately poured concrete footer. As far as sizing the footer width, I've usually just looked at the total load at the highest loaded section of wall and if does not exceed 1500 psf (default allowable soil bearing pressure) then I'm good to go.
However, the designer on two very similar projects called out a 6" stemwall on one and a 8" stemwall on the other. Is there a quick, rational check/calculation that I can do to verify that the stemwall size is adequate without getting to muddled up with the details.
My first thought was to simply take the load on the stemwall at is base (so that it includes the selfweight of the stemwall) and check the pressure and compare that to the strength of the concrete (2500 - 3000 psi). However, with the reinforcing (horizontal and vertical) this is probably to simplistic of an approach. I guess it time to really crack open the ACI 318.
I've recently been doing some work on some detached garages. One story structures with a 24" stemwall resting on a separately poured concrete footer. As far as sizing the footer width, I've usually just looked at the total load at the highest loaded section of wall and if does not exceed 1500 psf (default allowable soil bearing pressure) then I'm good to go.
However, the designer on two very similar projects called out a 6" stemwall on one and a 8" stemwall on the other. Is there a quick, rational check/calculation that I can do to verify that the stemwall size is adequate without getting to muddled up with the details.
My first thought was to simply take the load on the stemwall at is base (so that it includes the selfweight of the stemwall) and check the pressure and compare that to the strength of the concrete (2500 - 3000 psi). However, with the reinforcing (horizontal and vertical) this is probably to simplistic of an approach. I guess it time to really crack open the ACI 318.






RE: Residential Concrete Stem Walls
1) Temperature and shrinkage.
2) Nominal flexural capacity to allow the stem wall to span over soft spots in the soil.
This usually adds up to t&s wall reinforcing with an extra 2-#5 continuous top and bottom.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Residential Concrete Stem Walls
RE: Residential Concrete Stem Walls
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Residential Concrete Stem Walls
RE: Residential Concrete Stem Walls
RE: Residential Concrete Stem Walls
You're not going to find a clause that tells you the wall width for some specific stem wall height, because I could design a stem wall that takes only compression, or one that's got shear and moment on top of that along with an uplift case. My stemwall could be holding up a one floor garage or a ten story apartment building.
The IRC is a prescriptive code, so it limits its scope significantly and then it can tell you what details to use for buildings within that scope. If you fall within the scope of the IRC, go ahead and use it.
RE: Residential Concrete Stem Walls
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Residential Concrete Stem Walls
One note from your original post "take the load on the stemwall at is base (so that it includes the selfweight of the stemwall) and check the pressure and compare that to the strength of the concrete (2500 - 3000 psi)" - if you did want to run the calcs you should using factored loads (ACI is based on LRFD) and you can't compare it to the concrete strength directly. You'd need the appropriate code section for whatever you are checking, you were referring to bearing so you'd want that section of ACI which includes phi and reduction factors (you'll end up closer to 50% of f'c).