I helped out on a drive under barn once where the main floor was framed 12 inches oc, then topped with a t&g 2x floor and a 4 inch concrete slab on top of that.
What is the need of the concrete on top of the wood floor system?
I could see doing this in a house to get control over noise transfer whether airborne or transmitted through the structure but in a barn. This adds a lot of extra weight thus dicreasing the capacity of the floor.
