huangyhg

modelling column stiffness
i believe the normal method is to model the column as pinned at mid height between floors and then use a stiffness of half the gross section stiffness of the concrete. if you want to be more accurate in your model you'll have to work out a cracked section stiffness allowing for the steel in the column. but there won't be any point in doing that unless you are modelling your slab with the same accuracy.
carl bauer
my suggestion would be follow the necessary stiffness method used in formulating the dof for the column element. this seems appropriate, pending the direction of forces, as the slab deformations under gravity loading will effect the axial and lateral deformations and pending the supporting layout of the columns and any lateral loadings, torsion deformations will be effected.
as carlbauer noted, this is only as accurate as you method of modelling the slab.
bjr,
for 2-d flat slab analysis for vertical gravity loadings i use the "equivalent frame method" (ref aci 318) where the column stiffness and the stiffness of the transverse torsional
bjr...we do what ingenuity stated.

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