On Jul 12, 8:37 pm, "Art" wrote:
Please excuse me for starting a fresh thread on the subject but I got a lot
more info on how the floor is constructed.

We removed an old whirlpool made by Jacuzzi. Jacuzzi says the floor needs
to be 55 lbs/ sq ft. For some reason the new Sanijet tub recommends 100
lbs/sq ft. The latter number seems to make more sense.

So I want to strengthen the floor and plan on using a sheet of 3/4" plywood
on top of the old floor.

Here is the new information. The portion of the floor with the tub is
cantilevered out 2 feet. There is basically a box made up of 10 inch
joists that are 8 feet long with the last 2 feet of them sticking out the
side of the house to make the cantilever. That means that some of the tub
will be sitting on the sill plate. That is good, I would think. However
the parallel joists that make up the cantilever portion terminate at a
single perpendicular joist which is fastened to another long joist which is
part of the main floor system. So imagine a house of parallel joists with
a box attached to the middle of one joist consisting of one parallel joist
for the attachment and perpendicular joists that stick out beyond the sill
plate 2 feet.

The part on the sill plate should be plenty strong. I am worried about the
part that attaches to the long joist in the main part of the floor system.
I am thinking all of the weight is on that one joist (except for what is on
the sill plate). I cannot put posts underneath. I am thinking of sistering
that joist and bolting all 3 joists together (the joist that is the end of
the box, the joist that the box is attached to, and the new sister joist.)
I will probably have an engineer look at it but I know you guys have great
ideas, and I rather verify your ideas with the engineer rather than asking
him to come up with a fix.

Thanks again for your assistance.

Art-

Quick answer....if I'm understanding the existing conditons

you've got 8 ft 2x10 joist that span ~6ft & cantilever ~2ft and a
"rim" joist that collects the ends of the cantilevers

since deflection goes as span^3 the 2 ft cantilever section is
actually stiffer than the 6 ft span section.

Of course the actual loading (edge of tub or a real distributed load)
depends on how the tub bears on the floor


anyway based on my rough calcs (assuming worst case 100 psf
distributed load all concentrated at the end) the 2 ft cantilever
looks ok stress ~300 psi & deflection 1/64"

the 6ft span (again with all the 100 psf distributed load concentrated
at midspan..assumed worst case) again looks ok stress ~660 psi &
deflection 1/16"

looks ok as is, no mods needed

sistering the rim joist IMO won't really do much,

but if you WANT to stiffen the floor, sister the 8 ft joists, use
glue & small dia (.113 to .131) nails..forget the bolts, you want
good shear transfer & its hard to beat glue & lots of small nails (~4"
oc)

Your joist to sill bearing loads (~100psi) look ok so the sisters
don't really have to bear on the sill. Non-bearing sisters will be
easier to install & they'll be there just to stiffen the spans

I spent more time typing than doing the design or calcs...so hopefully
someone will check my concepts.
Its all about checking the load path so if I'm not understanding the
existing condition...oops!

cheers
Bob