SCBF

[Ducla]

I am designing a one story SCBF with a zipper column to resist unbalanced loads. Is there something in the code that says I don't need to design the pad footing under the zipper column for the material overstrength of the capacity of the braces? The footing would be very large if I have to design for this unbalanced load.

 

[amendale]

You do not have to design for it if the overturning forces are less than this effect. See this reference:

http://www.sefindia.org/rangarajan/SEISMIC/7290994-Seismic-Detailing-Genera.pdf

 

[amendale]

"If the foundation is allowed to uplift
or rock, as might occur in shallow foundations, then
the foundation only needs to develop the weight
associated with the foundation (spread footing, grade
beams, slab-on-grade, soil wedge along side of
footing, etc). A factor of safety should also be
considered regarding the calculated foundation mass
since you may not be accounting for all mass present.
The author recommends a 1.3 factor of safety
multiplier on the calculated mass since it is hard to
predict precisely how the foundation will behave.
If the foundation is considered fixed, or not subject
to uplift movement (pile foundation or large
subterranean structure) then the brace tensile yield
vertical component needs to be developed into the
foundation."