ASD/LRFD Manual - American Wood Council

M3: Design Provisions and Equations
M3.7 Solid Columns
Slenderness Considerations and
Stability
The user is cautioned that stability calculations are
highly dependent upon boundary conditions assumed in
the analysis. For example, the common assumption of a
pinned-pinned column is only accurate or conservative if
the member is restrained against sidesway. If sidesway is
possible and a pinned-free condition exists, the value of
K e in NDS 3.7.1.2 doubles (see NDS Appendix Table G1
for recommended buckling length coefficients, K e ) and the
computed adjusted compression parallel to grain capacity
decreases.
M3.8 Tension Members
This section covers design of members stressed
primarily in tension parallel to grain. Examples of such
members include shear wall end posts, truss members, and
diaphragm chords.
The designer is advised that use of wood members
in applications that induce tension perpendicular to grain
stresses should be avoided.
M3.8.1 Tension Parallel to Grain
is:
where:
The basic equation for design of tension members
T′ ≥ T (M3.8-1)
T′ = adjusted tension parallel to grain
capacity, lbs
T = tensile force, lbs
The equation for calculation of adjusted tension capacity
is:
Net Section Calculation
Design of tension members is often controlled by the
ability to provide connections to develop tensile forces
within the member. In the area of connections, one must
design not only the connection itself (described in detail
in Chapter M10) but also the transfer of force across the
net section of the member. One method for determining
these stresses is provided in NDS Appendix E.
M3.8.2 Tension Perpendicular to
Grain
Radial Stress in Curved Members
Stresses induced in curved members under load include
a component of stress in the direction of the radius
of curvature. This stress is traditionally called radial tension.
Radial stress design is a specialized consideration
that is covered in NDS 5.4.1 and is explained in detail in
the American Institute of Timber Construction (AITC)
Timber Construction Manual.
T′ = F t ′A (M3.8-2)
where:
A = area, in. 2
F t ′ = adjusted tension design value, psi.
See product chapters for applicable
adjustment factors.
American Wood Council