Wood is naturally engineered to
serve as a structural material.
The tree is fastened to the
earth with its roots, the foundation; the
trunk supports the weight of the branches,
as a column; and it bends when
loaded by the wind, as a cantilever
beam. Wood's mechanical properties are
complex, but if you understand a few
basics of lumber strength you can easily
size uniformly loaded joists and rafters
with span tables.
Stiffness and Strength
A good set of tables includes a number
of variables, the most basic of which
are stiffness and strength. A house frame
has to resist dead loads (the weight of
materials), live loads (the weights
imposed by use and occupancy), snow
loads, and wind