I have a project coming up where I'll be sawing
white ash logs into 5" X 8" x 14' to 16' timbers for
use in timber frame trusses of sorts - the loading
will be the same as roof rafters. The unsupported
span is in the neighborhood of 10 feet.
My question has to do with pith located in
the timber. I have a number of straight tree stems
that could easily produce one 5 X 8, and some that
could produce two 5 X 8 timbers, and I'm looking
for input on how the location of the pith effects
the strength/grade of the member.
I'm familiar with the basic grading rules for
structural timbers (from FPL tech notes), and it
appears that pith centered in the timber does not
lower the grade .... defects(knots) on the faces
are what influence grade the most.
In a situation where two timbers (5X8's) can be
sawn from the log/stem, is there a preferred
or recommended approach? My first instinct would
be to saw either timber a bit away from the pith
to avoid having the associated pith defects on
the face of the timber - in essence, sawing a
thin plank that contains the pith, from the center
of the log.
As and aside, I believe I've read in one of the
FPL documents that anything 5" or wider can be/is
considered a timber ...
Thoughts appreciated
Carl