ASD/LRFD Manual - American Wood Council

30 M5: structural glued laminated timber
M5.2 Reference Design Values
Reference design values of structural glued laminated
timber are affected by the layup of members composed of
various grades of lumber as well as the direction of applied
bending forces. As a result, different design values
are assigned for structural glued laminated timber used
primarily in bending (NDS Supplement Table 5A) and
primarily in axial loading (NDS Supplement Table 5B).
The reference design values are used in conjunction with
the dimensions provided in Table 1C (western species) and
Table 1D (southern pine) of the NDS Supplement, but are
applicable to any size of structural glued laminated timber
when the appropriate modification factors discussed in
M5.3 are applied.
Reference design values are given in NDS Supplement
Table 5A for bending about the X-X axis (see Figure
M5.2‐1). Although permitted, axial loading or bending
about the Y-Y axis (also see Figure M5.2-1) is not efficient
in using the structural glued laminated timber combinations
given in NDS Supplement Table 5A. In such cases, the
designer should select structural glued laminated timber
from NDS Supplement Table 5B. Similarly, structural glued
laminated timber combinations in NDS Supplement Table
5B are inefficiently utilized if the primary use is bending
about the X-X axis.
The reference design values given in NDS Supplement
Tables 5A and 5B are based on use under normal duration
of load (10 years) and dry conditions (less than 16%
moisture content). When used under other conditions,
see NDS Chapter 5 for adjustment factors. The reference
bending design values are based on members loaded as
simple beams. When structural glued laminated timber is
used in continuous or cantilevered beams, the reference
bending design values given in NDS Supplement Table 5A
for compression zone stressed in tension should be used
for the design of stress reversal.
Figure M5.2-1
X
Y
Y
X-X Axis Loading
Loading in the X-X
and Y-Y Axes
X
Y
X
X
Y-Y Axis Loading
Y
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