WOOD - Materials for Civil and Construction Engineers - page 432

Laminated strand lumber (LSL) and oriented strand lumber (OSL) are
extensions of the technology used to produce oriented strand board. They
are manufactured using similar processes, with the primary difference
being in the length of the strands—approximately 300 mm (12 in.) and 150
mm (6 in.) for LSL and OSL, respectively. As shown in Table 10.10, the
mechanical properties of LSL are somewhat less than those of PSL. The
mechanical properties of OSL are less than those of LSL (USDA-FS, 1999).

Glued-Laminated Timbers Laminated timbers are composed of two or more
layers of dimensional lumber glued together with the grain of all layers laid
parallel. Almost any species can be used when its mechanical and physical
properties are suited for the design requirements. However, softwoods, such
as Douglas fir and southern pine, are most commonly used for laminated
structural timbers.
Glued-laminated wood, commonly called “glulam,” is used for struc-
tural beams and columns, furniture, sports equipment, and decorative
wood finishes, as shown in Figure 10.19. In such cases, glued-laminated
wood is preferred over large one-piece members for many reasons, including
the following:

ease of manufacturing of large structural members from standard com-
mercial sized lumber

■

the opportunity to design large members that vary in cross section
along their length, as required by the application

■

specialized design to meet architectural appeal, opportunity to use
lower grades of wood within the less stressed areas of the member

■

minimization of checking and other seasoning defects associated with
curing large one-piece members

■

Assembly of the laminates into full-depth members is a critical stage
in manufacturing. Laminations are planed to strict tolerances just before
gluing to ensure the final assembly will be rectangular and that pressure

(a) (b)

FIGURE 10.19 Examples of glued-laminated wood.