You always consider settlement of course - and as msucog indicates, there are very few cases (soft clays principally) where shear actually does govern. This is one reason why, in the many years I have practiced, I have done very few actually bearing capacity computations (other than 2xSu for a red light/green light for bearing in clays). If one looks at LRFD, etc., they make a big point of the shear strength reliability but then little shrift of settlement - which, we know governs most of the cases. Still, I think that we should get in the habit of using capacity for shear and pressure for settlement. Which, of course, is why 90% of the geotechnical reports say 'the allowable (net) bearing [blue]pressure[/blue]' can be taken as X kPa (or ksf). The other factor that always comes in and again, it is given very short shrift in codes and books is the influence of adjacent foundations on the allowable bearing pressure. Settlement is the primary concern of bearing pressures. The point is, sadly, that the building code doesn't given [brown]presumptive[/brown] capacities for a [brown]presumed[/brown] 25 mm, say, settlement of an [brown]isolated footing[/brown]. In such cases, such presumptive values would be far more useful and adequately annotated.
