Foundation Walls at Braced Frames (analysis + design)

[P205]

I wanted to get some input from the community regarding foundation wall design at braced frame locations. Newman’s book Foundation and Anchor Design for Metal Building Systems doesn’t cover this area.

In sketch 1, I have sized the foundation wall between the braced frame columns (neglecting the foundation wall beyond, see sketch 2). I’ve resolved the OT moment and restoring moment using factored loads. (If you’re wondering, I’m using the Canadian codes, so this is seismic forces amplified xRd).

Could you comment on my approach to the design?
1- Restoring moment > OT moment
2- Check shear in the wall for the tension load
3- check bending of the wall+footing for moment of (956 x 2.1 = 2027 kN-m) 2.1m being the distance between the columns.

Additional info:
I've design the footing for the pressure of: 956kN/(3m x 3m) = 106 kPa as cantilevers.
I've design the piers for tension in order to get the load into the bottom of the footing.

Question, as for the bearing pressure on the soil, if I turn the tension and compression loads into a moment (956 x 2.1 = 2027 kN-m), the e=M/P >> L/6. Using the equation for when the pressure is not over the whole footings length, I get a very very small pressure. Doesn’t quite feel right. But given that the restoring moment is greater than the OT moment, and the building is so light, I’m not entirely surprised that there is little bearing pressure. Am I looking at this completely wrong?

As for sketch 2, what happens when there IS foundation wall beyond the braced frame? How does it change the whole analysis and design? I’ve design the wall between the columns to be 600 thick, and plan to have the walls beyond it back to my regular 250 wall.

Thank you in advance for your input. I really appreciate the help here, and hopefully this can help other in the future because I wasn’t able to find threads here, or references in books on dealing with this situation.

EDIT: I moved the pictures to a second post for clarity.

 

[P205]

Sketch 1

Sketch 2

 

[KootK]

That all sounds pretty reasonable to me and, frankly, your treatment strikes me as being more rigorous than what most folks will do.

In my experience, the weak spot in this system is getting anchorage to work at the base connection that wants to pull away from the end of the wall. 600 mm is pretty thick though so you've probably got space to do something robust there.

Engaging more wall beyond the frame yields two benefits which will come as little surprise:

1) Improved OT resistance.

2) A better anchorage situation per the concern that I raised above.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[P205]

Thank you KootK, your input is much appreciated.