Go Bars...(Material)

[William R. Monroe]

>Again, I think this is breaking strength rather than shear strength - but
I'm not an >engineer - any engineers out there to set us straight?
>
>Terry Farrell


I think it is important to note that the strength of any given wood species
can be measured most commonly as:

Compression strength parallel to the grain, or,
Compression strength perpendicular to the grain, or,
Tension strength parallel to the grain, or,
Tension strength perpendicular to the grain, or,
Shear strength perpendicular to the grain, or,
Shear strength parallel to the grain, or,
Bending strength perpendicular to the grain, or,
Bending strength parallel to the grain.

Suffice to say, I do not think this is a single strength principle we are
dealing with.  When go bars are installed, they are subjected to some amount
of "Compression Stress" parallel to the grain - force pressing into the bar
from top and bottom, and some amount of "Bending Stress" perpendicular to
the grain.  This is usually measured by applying a force to the middle of a
piece of wood which is supported on its two ends.

I would think this is mostly a measure of Bending Strength (bending stress).
For the real engineering types:

Max Bending Stress for a simply supported, center-loaded beam of rectangular
cross section (also referred to as the Modulus of Rupture (MR))

= 1.5(Pmax x l)/(bd^2).

Where Pmax = maximum load; l = span of beam; b = width of beam; d = depth of
beam.

With assistance from R. Bruce Hoadley.

BTW, shear strength is a "breaking strength" and is most often measured
parallel to the grain.  Picture holding a square block of wood, and trying
to slide one half past the other.  That is (roughly) shearing.

Regards,
William R. Monroe