I built my wife a hanging day bed and need to hang it from the porch ceiling.
I figure the bed with mattress and pillows weighs around 100 lbs. Knowing my friends, at some point there will be up to 5 adults on it for a photo op. (No, we are not swingers and the 5 adults will be clothed and not engaged in vigorous motion, Aklim.) 5 adults at an average of 180 lbs (the girls are more likely 110 to 140, the guys may push 200) total up around 800 lbs. So this contraption may at some point be close to a 1000 lb live load.
I built my porch with 2x6 #2 grade SYP ceiling joists on 16 in centers spanning right at 10 feet. Span tables tell me that dimension joist will span 12' 0" with a 20 lb per square foot live load.
The ceiling joists run perpendicular to the orientation of the swing in the picture above.
I plan to attach 4x4's above the joists and perpendicular to them and attach heavy duty through bolted eye bolts to the 4X4's. The 4x4's will be long enough to span three joists, so essentially the weight will be shared by three joists on each side.
How can I calculate how much weight three of my joists will carry?
Note: My original plan was to double up the key 2x6's with plywood and construction adhesive, but I have figured out it is not possible to get new 10 foot long joists into the space without unreasonable additional demolition.