you have not to use two models for this.
You define one section cut for base shear wall, and anothere one for base columns. After calculation you can estimate if the ratio for the base shear is in the proportion of 25% or above for the columns using the value obtained for section cut..If not you...
the precision of calculation is better with small size mesh, and the only way to see the behavior of your slab is to put joint with spring between column and wall etc...
The precision increase with decrease of size mesh.
i think it's due to the p-delta effect. the added value for calculation of design biaxial moment and axial force make the value of rebar area too high.
i am using sap2000.
i want to know why SAP2000 design concrete columns with too high area of rebar?
the same section cheked with less area rebar is ok.