Figure 6-1.-Examp1e of a laminated lumber.a board 1 ft long by 1 ft wide by 1 in. thick. Since thelength of lumber is usually measured in feet, the widthin inches, and the thickness in inches, the formula forthe quantity of lumber in board feet becomes thefollowing:Example: Calculate the board measure of a 14-ftlength of a 2 by 4. Applying the formula, you getLumber less than 1 in. thick is presumed to be 1 in.thick for board measure purposes. Board measure iscalculated on the basis of the nominal, not the dressed,dimensions of lumber. The symbol for board feet is bm,and the symbol for a unit of 1,000 is M. If 10,000 boardfeet of lumber were needed, for example, the quantitywould be 10Mbm.LAMINATED LUMBERLaminated lumber is commonly used whenincreased wood load-carrying capacity and rigidity arerequired. Usually made of several pieces of 11/2-in. -thick lumber, called laminations, the pieces arenailed, bolted, or glued together with the grain of allpieces running parallel (fig. 6-1). When extra length isneeded, the pieces are spliced with the splices staggeredso that no two adjacent laminations are spliced at thesame point. Built-up beams and girders are examplesof laminated lumber.Laminations may be used independently or withother materials in the construction of a structural unit.Trusses can be made with laminations for the chordsand sawed lumber for the web members (fig. 6-2).Special beams (fig. 6-3) may be constructed withlaminations for the flanges and sawed lumber for thewebs.Probably the greatest use of laminations is in thefabrication of large beams and arches. Beams withspans larger than 100 ft and depths of 8 1/2 ft have beenconstructed with 2-in. boards. Laminations this largeare factory-produced. They are glued together underpressure. Most laminations are spliced using scarfjoints (fig. 6-4), and the entire piece is dressed to ensureuniform thickness and width.PLYWOODPlywood is a panel product made from thin sheetsof wood called veneers. An odd number of veneers,such as three, five, or seven, is generally used so thegrains on the face and back of the panel run in the samedirection. Cross-lamination (fig. 6-5) distributes thegrain strength in both directions, creating a panel thatresists splitting and, pound for pound, one of thestrongest building materials available.Figure 6-2.-Truss using laminated and sawed lumber.6-8
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