I always use pinned. You can lap splice your vertical reinforcement with dowels into the foundation to develop a "fixed" condition if you absolutely need it, but the lap lengths can be very long if you have bars at the face (not centered in each cell) or large bars (#7 and larger) in a shear wall. I will only fully lap splice my vertical reinforcement when I have uplift in the wall or it is cantilevered.
In the past, I've considered a single line of dowels placed in the center of the wall to be fixed.
As long as you have a tensile force and a compression force with some distance between them - there's your couple.
With a single line of dowels down the middle, you have a very small arm between the two, but it's helpful in some cases.
In this case, I assume we're talking about out of plane loading.
In order to use any fixity, your need to develop the couple, and the foundation/soil below the soil need to resist the moment couple.
For the sake of simplicity, I'd treat it as pinned.
It is neither fixed nor pinned. You could consider the footing to be providing a rotational restraint which would be dependent on the properties of the soil.
I remember my masonry instructor telling us about a job where he walked out for inspection and grabbed a tall masonry wall from the scaffold. He and the wall nearly fell over. The wall was apparently quite easy to move because of the large cantilever arm and leverage effect provided by the easy access of the scaffold. He said he never designed tall masonry walls with a fixed base again.
I've lost track of it now but used to have an excellent paper on concrete walls that showed that, from a buckling perspective, it takes very little rotational flexibility before a fixed-ish wall becomes effectively pinned.
Here, I thought that any fixity would come from 4+ feet of embedment into compacted soil. I'd put far more stock in that than I would rotational stiffness of a strip footing. Is that not the case here?
If you want to base fixity on the restraint provided by the footing, the soil has to work, the footing has to work (transverse steel), the starter dowels need to be developed into the footing and lapped with the vertical bars, and the dowel hooks need to extend across the wall rather than away from it. It takes a fair bit to get the job done right.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
Pinned is the conservative assumption, but it is neither pinned nor fixed. The connection is rigid, not fixed, but the amount of rigidity is dependent on a lot of things.
I vote for pinned also unless there a reason to justify the time trying to figure out a reasonable rotational spring or subgrade modulus to account for the footing/wall interaction.
Pinned here too. Although I have seen instances when engineers assume fixed because their rebar was undersized or the wall too thin. But they don't carry their assumptions into foundation design.
