Settlement calculations on eccentrically loaded footings 1

Moments change the soil bearing, generally increasing it on one side of the neutral axis and lessening it on the other. Of course that will have the corresponding effect on settlement and also result in rotation. Mc/I is added to P/A to account for eccentricity of loads.

SB = P/A + Mc/I

If there is uplift on one side, the Mc/I will increase the SB on one side by the amount it is reduced on the other. Soil bearing pressures must be recalculated under the part of the mat or footing that does not lift up.

It would be erroneous to ignore any significant increase in SB, rotation and settlement due to eccentricity.

Foundation mats centroid are often adjusted in location such that Dead load Moments are eliminated, in turn eliminating differential settlements between opposite edges.

Temporary live load settlements are often negligible, as wind loads act in one direction on one day and opposite on another, however their increase in soil bearing and potential to cause soil bearing failure as well as overturning must always be checked.

For additional info, you can try searching for "Calculation of soil bearing loads under eccentric loading conditions."

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."