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Posted by RicodJour on October 7, 2008, 12:46 pm
On Oct 7, 12:32=A0am, mda53226_at_yahoo_dot_...@foo.com (mda) wrote:
> You're right, I'm a mechanical engineer. =A0I work in the world of steel =
and
> plastics. =A0I'm not familiar with estimating the strength of a nailed jo=
int
> in wood.
> Was thinking there must be a rule-of-thumb for estimating the strength of
> a 2x2 nailed to a 2x10. . . and a guideline for nail size and spacing to
> get a good joint without weakening the wood.
> Was also thinking it would be good to apply glue to the 2x2's before
> nailing. =A0The glue joint would carry the loaded with shear stress, and
> glue is very strong in that direction.
> I'm not totally clueless. =A0Am simply asking questions to collect the be=
st
> ideas before developing a plan. =A0(The "expert" at the building supply
> store told me I could only put a beam UNDER the ceiling. =A0There is no w=
ay
> to put it above the ceiling. =A0You folks are proving him wrong.) =A0I ca=
me
> here to ask because Google suggested this was a good place to get opinion=
s.
2x2s are problematic. The wood used in 2x2s is often sketchy. Solid
wood of a small cross section is prone to splitting when numerous
framing nails are used. In your situation you'll probably be using at
least five or six nails per 2x2 where it's attached to the 2x6 - in
5.5" you'll have six nails in a 1.5" wide area...not good. It would
be far preferable to use metal strapping - check the Simpson Strongtie
catalog.
Your question omits necessary information - joist span, attic height
(indicating probable load), etc. You first have to determine the
total design load per joist and use that to compute the size of the
beam. I no longer use solid sawn lumber for beam application in
remodeling. LVLs are far stronger and do not shrink. Shrinkage can
lead to cracked finishes and uneven settling.
Look into the LVLs and using metal strapping. The metal strapping
should preferably be wrapped over the top of the beam and under the
bottom of the joist. The number of nails is dependent on the load -
divide the total individual joist load by the shear loaded strength of
the nail and add one nail. Use the same number of nails on either end
of the strap. Simpson's web site will list the holding power of their
joist hanger nails.
R
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