Application of IBC Load Combinations to Footings

[CASALA]

I have a pretty straight forward problem, just not a very clear way to rectify it. I have a pre-engineered metal building that will essentially be a barn. The only concrete will be the individual footings that support (and anchor) each column, i.e. there will not be a slab or other element to resist uplift loadings. My dilema is that I feel as though the weight of the footings, i.e. the only element resisting the uplift tendency, should be reduced by 40% as dictated by ASCE 7-05 (and correspondingly IBC) equation 2.4.1.7. However, in doing so, the resulting footing sizes seem extremely oversized. On the other hand, by not reducing the weight of the footing, there is obviously no factor of safety regarding the uplift capacity of the foundation, not to mention seems to make the design not-code compliant.

With that said, does anyone know of a code that specifies how to address this issue, or can someone at least offer an opinion on whether or not the weight of the footing should be included as a deadload in ASCE 7-05 equation 2.4.1.7?

 

[civilperson]

D or dead load includes the weight of the foundation components and I also use the soil over burden weight as well. The equation 7 which uses 0.6 of dead load must equal the uplift from the wind to achieve stability. A clever shape of foundation with a large area under soil can shrink the required amount of concrete versus a drilled pier or auger cast pile which must use some component of skin friction and the self weight to resist uplift.