Behold the Beam

Part 3 — Types of Beams You Are Likely to Encounter If a surgeon doesn't possess a foundation of human anatomy and physiology knowledge, would you let that surgeon cut you open and probe around inside your body? Would you let a fire officer send you...


Part 3 — Types of Beams You Are Likely to Encounter If a surgeon doesn't possess a foundation of human anatomy and physiology knowledge, would you let that surgeon cut you open and probe around inside your body? Would you let a fire officer send you inside a burning structure if that...


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As with other engineered composite wood products, LSL is an alternative to flitch beams and steel lintels. LSL is also used as rim boards, intermediate span beams and purlins. LSL offers the added benefit of good resistance to a lateral force such as the wind (winds up to 120 mph!) Although not common, LSL can also be used as columns and wall studs. LSL wall studs can reach 30 feet.

Rather than run plumbing around an LSL beam, plumbers can run pipes through an LSL beam. A hole up to 4 5/8 inches in diameter can be drilled through a 14-inch LSL beam without compromising its structural integrity. The maximum length of an LSL beam is around 64 feet.

4. Parallel-Strand Lumber (PSL)

You're probably familiar with Weyerhaeuser's proprietary name for its PSL products: Parallam (correctly pronounced paral-lam, not para-lam). Introduced in 1988, Parallam is often made using waste material left over from the plywood manufacturing process. Structural applications include floors, walls and roofs.

Glulam, LSL, PSL and LVL all belong to a general category of engineered wood products known as structural composite lumber (SCL). SCL products are reliably straight and true, free of knots, resist twisting, shrinking, and bowing, and are split resistant and very strong.

Made from long, thin strands of wood bonded together in a microwave process, PSL is consistently straight and strong and resists shrinking, warping and splitting. The strength of PSL is similar to that of LVL. The PSL manufacturing process provides for the removal of natural wood growth defects such as knots. PSL beams are manufactured in widths up to seven inches and with depths up to 18 inches. Manufacturers claim that a PSL beam can span nearly 70 feet. To achieve additional strength and rigidity without increasing depth, PSL beams can be built up at the job site.

PSL is not designed to be appearance grade, so it is frequently left rough and unfinished, concealed within voids or behind sheetrock. However, "architectural-grade" PSL is offered that, after sanding and finishing, will provide "a unique architectural look and feel."

A significant environmental benefit of PSL is that the manufacturing process uses almost the entire log, making PSL an efficient use of a renewable resource: trees. PSL is used as beams and columns for contemporary post-and-beam structures, as well as for light framing beams and headers; PSL is often used for masonry wall lintels. You will find the use of PSL increasing throughout residential construction and as intermediate and large structural members in commercial building construction.

The strength properties of PSL are similar to those of a solid-sawn wooden beam of comparable dimension. PSL is more expensive than other LSL, LVL or a Glulam. PSL and LSL belong to a sub-category of SCL referred to as "long strand lumber."

5. Laminated-Veneer Lumber (LVL)

LVL is a composite consisting of several layers of wood veneer and adhesive. LVL is not new a technology; the LVL process was used during World War II to make airplane propellers. LVL has been used for beams and headers in building construction since the 1970s. You may hear LVL referred to by its proprietary name, MicroLam. LVL is also referred to as parallel-laminated veneer (PVL).

Although the face-side appearance of LVL resembles plywood, LVL is not plywood. LVL is engineered so that the grain of each veneer layer runs in the same direction (long) for uniform edge-load strength (on-edge, as a beam) or face-load strength (flat, as a plank). This "parallel lamination" provides increased uniformity and predictability compared with a material of the same dimension that is "cross laminated" (cross-banded) such as plywood.

Parallel lamination makes LVL an excellent choice for long-span load-bearing applications up to 80 feet. As with other structural composite lumber products, LVL is engineered to resist warping, shrinking, slitting, bowing, twisting and crowning. In other words, LVL — and its SCL kin — offer reliable dimensional stability. Pound-for-pound, a given LVL beam delivers greater load-bearing capacity than the most perfect solid-sawn lumber of the same dimension.