Parallel strand lumber
Parallel strand lumber (PSL) is a form of engineered wood made from clipped veneer strands laid in parallel alignment and bonded with adhesive. It is used for beams, headers, columns, and posts, among others uses.
Parallam is the brand name for the product invented, developed, commercialized and patented by MacMillan Bloedel (now Weyerhaeuser). It is the world's only commercially manufactured and marketed parallel strand lumber product. It is a member of the structural composite lumber (SCL) family of engineered wood products.
The product is manufactured as a 12" x 12" or 12" x 18" billet in a rectangular cross-section, which is then typically sawn and trimmed to smaller cross-sectional sizes. The beams are continuously formed, so the length of the beam is only limited to the maximum length that can be handled and transported. Typical thicknesses are 3½", 5¼” or 7"; typical depths are 9½", 11⅞" 14", 16" & 18". Typically the beams are made to a maximum length of 60 feet.
The design values for Parallam, in bending, tension parallel to grain and compression parallel to grain are greater than sawn lumber made from the same or similar species. This is because knots and other imperfections are randomly dispersed throughout the product so that strength variability from one piece to another is less than in solid-sawn wooden beams. Since materials are commonly graded to the lowest 5th percentile of the material's strength curve, this gives Parallam much higher usable strength. Parallam can be made from any wood species, but Douglas-fir, southern pine, western hemlock, and yellow-poplar are commonly chosen because of their superior strength.
- Kam-Biron, Michelle; Koch, Lori (Oct 2014). "The ABC's of Traditional and Engineered Wood Products". Structure Magazine.
- Stark, Nicole M.; Cai, Zhiyong; Carll, Charlie G., eds. (2010). Wood Handbook. Madison, WI: Forest Products Laboratory. pp. 11–21.
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