For the structure that I am working on, I am finding that the IBC 06 ASD Basic combinations yield larger “lateral” foundations to resist seismic, and the Alternate combinations yield larger “gravity only” foundations to resist the D + L + S combination.
Does the code prohibit, or is there anything wrong with designing the building’s isolated footings only for IBC 06 ASD “Basic” load combinations which include Gravity and Wind (Equations 16-8 to 16-14 with W), and only the “Alternate” load combinations which include seismic (Equations 16-20 and 16-21)?
This will achieve the least size footings, but at a factor of safety under seismic that appears to meet code but is less than what would be achieved if all the Basic combinations (including Equation 16-15) were used for design.
Looking for opinions … thanks,
John Gares
A. W. Lookup Corp.