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There is also another point in this discussion. The assumption of a fixed based for isolated foundations is not valid because these foundations are susceptible to rotation. That would mean no moment (there would be some as foundation has rotational stiffness) at column foundation interface and more moment at beam column interface - plastic hinging in beams column joint. Although the original discussion is about developing plastic hinge at foundation column interface but I think the fact that isolated foundations rotate makes these two conditions mutually exclusive (some degree). If the foundation rotates then it is a pinned end and the only forces there would be shear and axial.

I found another thread on the forum where isolated foundation rotation was discussed. The author (posted excerpt from Pauley and Priestley ) recommends modelling isolated foundation using a rotational spring to avoid unexpected column hinging at top of lower story columns. FYI, Thanks.

I posted the query because I recently read two articles: one is FOUNDATIONS FOR SHEAR WALL STRUCTURES by J.R. Binney and T Paulay, and the other one FOUNDATIONS FOR CAPACITY DESIGNED S T R U C T U R E S by P.W. Taylor and R.L. Williams. @Rana : This is not enough. These details ensure the development of column hinge at the bottom if it is possible. And that "if" depends on the soil-structure interaction and the strength of the soil. If the soil is strong enough to resist bearing pressure corresponding to forces (axial load + moment) that it may experience when the column will be in inelastic range (capacity design approach), and if you have designed the footing for the moment that it may experience when hinge (capacity design approach) will form in the column, which is, of course, greater than the moment that you will get from ETABS for the design Earthquake, then the hinge will form in the column. If the above scenario is not feasible then you may proportion the footing to allow the rocking behavior so that energy may be dissipated provided footing rotation is in permissible limits, which will depend on the soil-rotation relationship. @umer: In MAT, or other connected foundation types, the third option is to allow nonlinear behavior in the foundation. In that case, the foundation should be detailed for attaining necessary ductility levels. These things are not discussed in the ACI code. I have not read these things in RCC books as well.