If columns have been modeled right up through the building they can be split at floor levels by using Copy/Monitor functionality.
Go to a 3D view and Isolate the Columns Category (so you can just see the Columns you want to split)
Select all of them and Save a Selection (this is so we can cleanup later)
Go to Collaborate tab and click Copy/Monitor - Use Current Project
Options - Columns tab, tick "Split Columns by Levels", Ok
Click Copy, tick Multiple, Select all the Columns, then click the little Finish button
Click the big Finish button
If you want to delete the old ones, load the Saved Selection from step 2 and press Delete
Done!