Maybe this will help:
I am remodelling the master bath on the second floor of our house. We've moved just about everything around in it. My question has to do with the corner whirlpool bath we are installing. This is a American Standard Lifetime Corner Model 6060L bath. It specs out at 846LB or 25Lb per square foot when filled with water. The floor joists are 2X10's, 16" on center, with a 3/4" plywood subfloor. The span on the joists is approximately 13'.
Do I need to reinforce the joists or will this be sufficient?
If you had a standard tub up there before, then the weight of the new tub should be ok. I switched from a standard one piece shower/bath unit 60 inches long, and put in a longer whirlpool bath from kohler, it is 6 inches longer and 6 inches wider, we have had our tub full, running and occupied and nothing shifted or sagged.