WOOD - Materials for Civil and Construction Engineers - page 434

Architectural grade is suitable where appearance is an important
requirement.
Premium grade is the highest grade and is used when appearance is of
the utmost importance.
Appearance grades do not modify design values, grades of lumber used, or
other provisions governing the manufacture or use of glued laminate timber.
Glulams are specified by stress class, based on minimum values for their
flexural strength and elastic modulus, as shown in Table 10.11 (APA-EWS,
2004). The design values in this table are for members with four or more lam-
inations. The stress grade classification does not designate the species used

T ABLE 10.11 Stress Classes of Glulams (APA-EWS, 2004)

Extreme Fiber in Bending

Tension
Zone Compression Compression Shear

Stressed in Zone Stressed Perpendicular Parallel to Modulus of

in Tension 1 , Grain 3 Tension to grain Elasticity

10 6 psi Stress Class (psi) (psi) (psi) (psi) ( )

16F-1.3E 1600 925 315 195 1.3

5

20F-1.5E 2000 1100 425 210 1.5

24F-1.7E 2400 1450 500 210 1.7

2 4

24F-1.8E 2400 1450 650 265 1.8

4

26F-1.8E 2600 1950 650 265 1.9

6

28F-1.8E 2800 2300 740 300 2.1

7 6

30F-2.1E SP 3000 2400 740 300 2.1

8 9

30F-2.1E LVL 3000 3000 510 300 2.1

Notes:
1 For balanced layups, bending stress when compression zone is stressed in tension
shall be equal to the bending stress when tension zone is stressed in tension for the
stress class. Designer shall specify when balanced layup is required.
2 Negative bending stress, is permitted to be increased to 1850 psi for Douglas-fir and
to 1950 psi for southern pine for specific combinations. Designer shall specify when
these increased stresses are required.
3 For noon-prismatic members, notched members, and members subjected to impact
or cyclic loading, the design value for shear shall be multiplied by a factor of 0.72.
4 Shear Parallel to Grain

1 Horizontal 2 = 300 psi for glulam made of southern pine.

5 Modulus of Elasticity may be increased to

10 6 psi

1.8 * for glulam made of Canadian

spruce-fir-pine or Eastern spruce.
6 Modulus of

Elasticity = 2.0 * 106 psi for members with more than 15 laminations

except for 30F hybrid LVL glulam.
7 Limited to a maximum of 6 inches except for hybrid LVL glulam.
8 Requires the use of an outermost LVL lamination on the top and bottom.
9 Compressive perpendicular to grain stress can be increased to the published
value for the outer most LVL lamination.