Bending properties of structural timber from a 28-year-old stand of New Zealand Pinus radiata

Seventy-eight upper logs taken from a 28-year-old stand of Pinus radiata D. Don in Kaingaroa State Forest, New Zealand, were sawn to maximise yields of 200 x 50-mm and 100 x 50-mm timber which was then dried, planed, visually and mechanically graded, and tested in bending. The timber was not as strong or as stiff as timber from older trees. Although the basic working stress in bending was higher than the code value, the modulus of elasticity was lower but not to an extent that is likely to cause problems in practice. A simplified grading rule was proposed which yields material with a basic working stress 50 % higher than No. 1 Framing grade. Relationships between log variables and the properties of timber from each log were derived, and it was shown that currently prescribed design moduli of elasticity for Engineering grade might be obtained only for timber from logs with a basic density in excess of 490 kg/m3