I have a marble bathtub that weights around 2400lbs which I have calculated is about 42 cubic feet; capacity of 314 gallons of water (@8.3lbs=2600lbs).
The total weight of the bathtub with water and two people would be about 5300 lbs. The tub is approximately 20.10 square feet. The load per square foot is approx 259-264PSF.
The floor is concrete. The joists are 3x8x14 and they are sistered (doubled along their length) as well as with perpendicular supports in between (2x4s). The tub would sit on approximately 4 of these sistered joists (it has a width of approx 3ft).
I am unfamiliar with calculating the PSF supported by the beams.
Is this sufficient support for the bathtub?