Page 231 - Civil Engineering Formulas

TIMBER ENGINEERING FORMULAS 165

For shear, the adjusted design value F is computed from
V
(6.21)
F V F V C D C M C t C H
where F is the design value for shear and C is the shear stress factor 1—
V
H
pemitted for F parallel to the grain for sawn lumber members.
V
is
For compression perpendicular to the grain, the adjusted design value F c
obtained from
(6.22)
F c F c C M C t C b
where F c is the design value for compression perpendicular to the grain and C b
is the bearing area factor.
For compression parallel to the grain, the adjusted design value F c is given
by
(6.23)
F c F c C D C M C t C F C p

where F is the design value for compression parallel to grain and C is the col-
c p
umn stability factor.
For end grain in bearing parallel to the grain, the adjusted design value, F g is
computed from
(6.24)
F g F g C D C t

where F is the design value for end grain in bearing parallel to the grain.
g
The adjusted design value for modulus of elasticity, E is obtained from
E EC M C T C (6.25)

where E design value for modulus of elasticity
C buckling stiffness factor—applicable only to sawn-lumber truss
T
compression chords 2 4 in (50.8 101.6 mm) or smaller, when
subject to combined bending and axial compression and plywood
3
sheathing in (9.5 mm) or more thick is nailed to the narrow face
8
C other appropriate adjustment factors

Size and Volume Factors
For visually graded dimension lumber, design values F , F , and F for all
b t c
species and species combinations, except southern pine, should be multiplied
by the appropriate size factor C , given in reference data to account for the
f
effects of member size. This factor and the factors used to develop size-specific