spats: To counter the overturning due to the eccentricity, I mentioned in my post above a grade beam could be designed that connects the two frame foundations across the building width. This grade beam can be sized and designed to counter the overturning and the thrust.
More than 20 kips of uplift is not an uncommon metal building reaction in my area. There is usually a similarly large thrust to accompany this uplift. If you only have 5 kips of dead load from the roof and frame, a very large volume of concrete is needed to resist the uplift. Do not forget...
When P/A - M/S > 0 the eccentricity due to the moment is less than L/6 or the kern where L is the length of footing in the strong direction. A footing can be stable as long as the eccentricity does not exceed L/2 which will put the axial load outside the physical limits of the footing...
The force will be dependent on boundary conditions. If the steel member is not restrained against movement, the member will expand and no force will be generated.
Using ASCE7-10 C&C method for open pitched roof and assuming 120 MPH wind speed, exposure C, Kzt = 1, Kd = 0.85, Gust factor of 0.85, and a roof mean height of 15 feet, 4/12 slope, and clear wind flow ... Being that the tributary area of a post is greater than 4*a^2, I calculate the ultimate...
