Prefered metod to attatch racks to floor ?

The company I used to work for used a Hilti drill & anchors, to secure racks to the floor.

I'd want to use threaded stud nails. Can be screwed down if the nail doesn't penetrate enough (irregular/old concrete), and can be unscrewed to remove rack.

-- Robert

I usually use tapcon screws (hex head) with an appropriate washer (if needed). If you go this route, I recommend blowing out the holes with compressed air before installing the screws. The tapping action of the screws tends to build up debris in the holes, and the screws can bottom out before they go in all the way.

Chances are you may have to move the racks later. People add racks, vertical wire managers, do all kinds of re-arrangements in their telecom rooms. You would have more options if you've opted to use less permanent way of immobilizing the racks.