LAMINATED LUMBER

Laminated lumber (figure 3-29) is made of several pieces of lumber held together as a single unit, a process called lamination. Usually 1 1/2-inches thick, the pieces are nailed, bolted, or glued together with the grain of all pieces running parallel. Laminating greatly increases the load-carrying capacity and rigidity of the weed. When extra length is needed, the pieces are spliced-with the splices staggered so that no two adjacent laminations are spliced at the same point. Built-up beams and girders are examples. They are built as shown in figure 3-30, usually nailed or bolted together, and spliced.

Lamination can be used independently or with other materials in the construction of a structural unit. Trusses can be made with lamination for the chords and sawed

Figure 3-30.-Built-up beam.

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 placed in a horizontal position and is usually the full width of the beam (figure 3-35).

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