WOOD - Materials for Civil and Construction Engineers - page 433

will be applied evenly. Prequalified adhesives, typically phenol-resorcinol,
are applied to the gluing face. The laminations are laid up and clamped
as an assembly while the glue cures. The adhesive is allowed to cure at
room temperature for 6 to 24 hours, or, in some newer processes, radio-
frequency curing is used to reduce the time to a few minutes (USDA-FS,
1999).
Glued-laminated wood is designed and produced to have consistent
and uniform properties. Due to the laminated structured, the glulam can be
laid up to optimize the use of the wood products. For example, glulams de-
signed as bending members are laid up with higher quality wood at the
edges of the beam and lower quality wood in the center, as shown in
Figure 10.20. Bending members used for cantilevers or continuous mem-
bers over multiple spans have a balanced layup, since both the top and bot-
tom of the beam carry tensile loads. However, glulams designed for simple
spans, which are designed to have only tension at the bottom and compres-
sion at the top of the beam, have unbalanced designs, with the higher quality
wood at the bottom of the member. This is an unbalanced design and these
members are carefully labeled to minimize the risk of installing the beam in
an incorrect orientation.
Glulams are produced in four appearance grades:
Industrial grade is suitable where the glulam will not be exposed to
view and appearance is not a concern.
Framing grade members match the width of conventional framing for
use as door and window headers.

Balanced Glulam Unbalanced Glulam

Lumber grades

Tension Laminate 2D

1 2

2 2

3 3

2 2

1 1

Tension Laminate Tension Laminate

FIGURE 10.20 Lay up arrangement for balanced and unbalanced

glulams.