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Timber Design
Section 4
4-2
an E of 1900 ksi and an allowable bending stress, F
b
, of 1450 psi.
A 5x5 Douglas Fir-Larch, Select Structural, Beam or Stringer
member has an E of 1600 ksi and an allowable bending stress, F
b
,
of 1600 psi. And a 5x5 Douglas Fir-Larch, Select Structural, Post
or Timbers member has an E of 1600 ksi and an allowable bending
stress, F
b
, of 1750 psi.
So, in the STAAD timber database for sawn lumber, for each
species and grade of timber, the section size, or properties are
associated with the Modulus of Elasticity and allowable stresses
for the cross-section. When a section is assigned, its E and
allowable stresses are automatically fetched along with its
properties. The material properties of Southern Pine members were
taken from Table 8.4 of the 1994 AITC manual. For all other
species with section sizes 2”-4” wide, the material properties have
been taken from Table 8.3. For all non-Southern Pine species with
section sizes greater than 5”x5”, the material properties are
obtained from Table 8.6 of the 1994 AITC Manual.
Please note that not all section sizes listed in Table 8.1 are
available in every species. Some sizes are not produced for
particular species. For example, the Aspen species only produces
sizes from 2”-4” wide. It does not produce sizes 5”x5” and larger.
This can be observed by comparing Table 8.3, where Aspen is
listed as an available species, to Table 8.6, where Aspen is not
listed as an available species. Also note that although 1” wide
members are listed in Table 8.1, there are no values available in
the species properties tables; Table 8.4, Table 8.5, and Table 8.6.
AITC does not allow for the structural design of these small
members.