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Default Fir lumber load ratings?


noxpurt wrote:
How can I determine or lookup the load ratings or the load failure point for
a fir plank that is 2 (1.5)" x 12 (11)" x 40"? The plank is oriented widest
side up and level and the load is against the flat side while being
supported with 1.5" ledges on each side.

thank for any tips


Point load or distributed load?

GIven the ineffective orientation it may be that the deflection of the
beam
will be unacceptable long before it breaks, unless you are intentionlly
using it as a spring. If it is loaded to failure, it will fail in
tension, starting
near the middle of the lower surface, uness a point load crushes
fibers in the upper sruface sufficiently to precipitate compressive
failure.

Regardless, it is a simple rectangular beam. You can look up formulas
online for calculating the maximum tensile stres at the extereme fiber
abd the deflection at the center.

Is it construction lumber? 'Fir' is ambiguous. It can be hem-fir or
Doug Fir.

You can look up the minimum strength in bending for hem-fir online,
as well as the modulus of rigidity (Young's modulus).
Then use the formulas for a rectangular beam to determine how much
it will deflect under the intended load and your factor of safety.

If it is Douglas Fir, then use the minimum values for the species group
Doug Fir or Larch.

If you know the particular species, then use the minimum values for
that species.

It is doubtful you will find useful values in any look-up table as no
one uses beams in that orientation for obvious reasons. One
wonders if you should not reconsider what you are doing--will
this be a ramp?

Now, if you want to know what time is is you start by scribing a circle
on the ground out where it will be indirect sunlight for most of the
day...

--

FF