Anchor Bolt Depth

That depends on a lot of information that you did not provide:

1. Loads on column/baseplate (due to live, dead, seismic, wind, ........... loads)
2. Strength/depth of concrete
3. Type/size/strength of anchor bolts
4. Size/thickness of baseplate

The manufacture of the mezzanine should be able to answer your question. They should be able to make recommendation size and type. The manufacture of the anchor will be able to give you instructions as to how to apply it.

It also depends on applicable code in your area as well as the type of analysis.

A standard A307 bolt with standard hex head will develope it's full strength when embedded 10diameters into the concrete (3000psi concrete). It must be at least 4diameters from the nearest vertical edge. This is for pull out strength only. For lateral loads, it takes a seperate analysis. For example. a 1 inch A307 bolt can safely withstand a pull-out force of it's area times 20000 pounds (safe allowable stress),i.e., .785 square inches x 20000pounds per square inch allowable equals 15700 pounds, when embedded 10 inches into 3000psi concrete.

Most engineering offices that must size anchor bolts have tables that have allowable loads for various size bolts.