Bond and Harris - Decoding Eurocode 7 provides a good discussion on it. You may not be designing to Eurocodes but the theory is the same.

Horizongtal load is assessed using inclination factor i_c

The inclination factors are dependent on the ratio H/H_max, so you'll also need to know how to calculate H_max. That is basically the shear resistance along the base area. You can legitimately add some passive earth pressure if you have a skirted foundation too.

THIS MAY NOT BE AS TECHNICAL AS THE PREVIOUS SUGGESTED EQUATION, BUT I'VE ALWAYS LOOKED AT BEARING PRESSURE DUE TO VERTICAL LOAD AND MOMENT THEN DO A SEPARATE CHECK FOR SLIDING BASED ON FRICTION BETWEEN SOIL AND CONCRETE.

HERE IS A REFERENCE I HAVE USED IN THE PAST FOR LOOKING AT FOOTINGS WITH VERTICAL AND OVERTURNING LOADS

https://files.engineering.com/getfile.aspx?folder=...

Link

• https://files.engineering.com/getfile.aspx?folder=45ba3ff3-3910-4178-a686-4

I would transform the horizontal load to a moment (M= H x Df, I am assuming the horizontal load acting at ground level. Df is the depth of the footing embedment) and check eccentricity and that the maximum acting bearing pressure does not exceed the allowable bearing capacity/pressure.

TEDstruc:

Good publication.

Dik

The approaches above which suggest checking vertical/moment and horizontal capacities separately will not provide reliable results under combined loading as those checks would provide the maximum capacity under just vertical or just horizontal loading. Shallow foundations have their vertical, horizontal, moment and torsional (VHMT) reactions all coupled; that's what defines them as shallow foundations. As such, you cannot reliably check capacity under combined VHMT loading without considering the effect of the other capacity components.

Applied M will affect the V capacity (i.e. effective area concept). T can be considered as an additional horizontal load/reduction to the H part of the capacity envelope. The remaining VH envelope is curved - not rectangular - which shows interaction between the V and H components. If you have combined loading, you need to check all of the capacities together.

Incidentally, for drained conditions, the VH envelope is defined by H/V (rather than H/H_max) in some standards. Also, some standards recommend a drained sliding line to intercept the capacity envelope.