Figure 3-31.-Truss using laminated and sawed lumber.
lumber, or for the web members (figure 3-31).
Special beams can be constructed with lamination for
the flanges and plywood or sawed lumber, for the
web, as shown in figure 3-32. Units, such as plywood
box beams and stressed skin panels, can contain both
plywood and lamination (figure 3-33).
Probably the greatest use of lamination is in the
fabrication of large beams and arches. Beams with
spans in excess of 100 feet and depths of 8 1/2 feet
have been constructed using 2-inch boards.
Laminations this large are factory produced. They are
glued together under pressure. Most laminations are
spliced using scarf joints (figure 3-34), and the entire
piece is dressed to ensure uniform thickness and
Figure 3-32.-Laminated and sawed lumber or plywood beam.
width. The depth of the lamination is
horizontal position and is usually the full
placed in a
width of the
beam (figure 3-35).
Plywood is constructed
number of layers (plies) of
by gluing together a
wood with the grain
direction turned at right angles in each successive
layer. This design feature makes plywood highly
resistant to splitting.
It is one of the strongest
building materials available to Seabees. An odd
number (3, 5, 7) of plies is used so that they will be
balanced on either side of a center core and so that the
grain of the outside layers runs in the same direction.
The outer plies are called faces or face and back. The
next layers under these are called crossbands, and the
other inside layer or layers are called the core
(figure 3-36). A plywood panel made of three layers
would consist of two faces and a core.
Figure 3-33.-Stressed skin panel.