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Wood Species: bending strength & stiffness

Classifying Wood Species by Bending Strength & Stiffness

Bending strength and stiffness are the most important properties for many plywood uses including concrete formwork.

Species of wood used to manufacture the plywood panel’s face and back are classified into five groups based on their bending strength and stiffness: group 1 being the strongest and group 5 the weakest.

For APA panels, the main species are:

  • Douglas-fir (Groups 1 & 2) for faces and back; with other species used only for inner plies – Western Larch, Western Hemlock, the true firs (Balsam, California Red, Grand, Noble, Pacific Silver and White), Ponderosa and Lodgeole Pine.
  • Southern Yellow Pine (Loblolly, Longleaf, Shortleaf, Slash) with some minor use of Sweetgum and Yellow Poplar for inner plies.
Five Group Species – grown in America
  • Group 1: Beech, American Birch (Sweet, Yellow) , Douglas-firª , Western Larch, Sugar Maple, Southern Pine ( Loblolly, Longleaf, Shortleaf, Slash), Tanoak
  • Group 2: Port Orford Cedar, Cypress, Douglas-fir a, Fir (Balsam, Calif. Red, Noble, Grand, Pacific Silver, White) Western Hemlock, Black Maple, Pine (Pond, Red, Virginia, Western White), Spruce (Black, Red, Sitka), Sweetgum, Tamarack, Yellow Poplar
  • Group 3: Red Alder, Paper Birch, Alaska Cedar, Subalpine Fir, Eastern Hemlock, Bigleaf Maple, Pine (Jack, Lodgeole, Ponderosa, Spruce), Redwood, Spruce (Engelmann, White)
  • Group 4: Aspen (Bigtooth, Quaking), Cedar (Incense, Western Red), Cottonwood (Eastern, Black Western Poplar, Pine (Eastern White, Sugar)
  • Group 5: Basswood, Balsam Popular.
Other Species –  not grown in America
  • Group 1:Apitong b,c, Kapur b, Keruing b,c, Pine (Caribbean, Ocote
  • Group 2: Lauan (Almon, Bagtikan, Mayapis, Red Lauan, Tangile, White Lauan)
  • Group 3: Mengkulang b, Meranti, Red b,d, Mersawa b
  • Group 4: Cativo.
Notes:
a.   Douglas-fir from trees grown in the states of Washington, Oregon, California, Idaho, Montana, Wyoming and the Canadian provinces of Alberta and British Columbia shall be classed as Group 1. Douglas fir from trees grown in the states of Nevada, Utah, Colorado, Arizona and New Mexico shall be classed as Group 2.
b.   Each of these names represents a trade group of woods consisting of a number of closely related species.
c.  Species from the genus Dipterocarpus marketed collectively: Apitong if originating in the Philippines, Keruing if originating in Malaysia or Indonesia.
d.  Red Meranti shall be limited to species having a specific gravity of 0.41 or more based on green volume and oven dry weight.