We have a second story floor 12 ft long 2x12 16 on center. We want to put a 36 x 80 piece of equipment that's 400 lbs that vibrates. Looking for load specifically. Do we need to double 2x12 under the unit.
Each 2x12 spanning 12’ will support about 2250 lbs. depending on the species and grade of the joists.
So, total load is not an issue, but the strength of the subfloor and shear walls around this object could be a problem.
I’d check the subfloor and where the posts (if any) rests between the joists.