Building Design and Construction Handbook - Merritt - Ventech!

10.90 SECTION TEN
Narrow boards may be edge-glued, and short boards may be end-joined to create
greater lengths. The resultant wide and long laminations are then face-glued into
large, manufactured timbers. Figure 10.26 shows different types of glulam beams.
Recommended practice calls for lumber of nominal 1- and 2-in thicknesses for
laminating. The lumber is dressed to 3 ⁄4-, 1 3 ⁄8- and 1 1 ⁄2-in thicknesses, depending
on the species before gluing. The thinner laminations are generally used in curved
members.
Virtually any species of wood can be used in the laminating process if the design
values have been determined. Different species can be intermixed within the depth
of a section to achieve optimum resource utilization. Higher-strength species are
positioned in a beam in zones that will be subjected to high stresses under design
loads. Lower-strength species can be placed in zones with lower in-service stresses.
Similarly, manufacturer of glulam beams can be based on a graded layup concept.
This requires that laminations with a higher lumber grading be used in zones subjected
to high design stresses, and lower grades, in lower-stressed areas of the
member. As a consequence, glulam members are a resource-efficient wood product,
since varying grades and species can be used to achieve desired performance.
Constant-depth members normally are a multiple of the thickness of the lamination
stock used. Variable-depth members, because of tapering or special assembly
techniques, may not be exact multiples of these lamination thicknesses.
Nominal width of stock, in 4 6 8 10 12
Standard member finished width, in 3 or 3 1 ⁄8 5or5 1 ⁄8 6 3 ⁄4 8 1 ⁄2 or 8 3 ⁄4 10 1 ⁄2 or 10 3 ⁄4
Standard widths as listed above are most economical, since they represent the maximum
width of board normally obtained from the stock used in laminating. Other
widths, such as 3 1 ⁄2 or 5 1 ⁄2 in, which fit well with conventional 2 � 4 and 2 � 6
framing, are also available in many market areas.
FIGURE 10.26 Types of glued-laminated beams.