Comparison of Various Standards for the Characteristic Strength and Stiffness of Timber

G B Walford, Forest Research, Rotorua

Comparing published design stresses for radiata pine with those for both visual and machine grades from Australia, USA, UK and ISO, in the nominal 150×50 mm dimension, it was found that:

  • Radiata pine has a relatively high assigned strength compared to other visual grades.
  • For US visual grades radiata pine No. 1 Framing is closest to the Ponderosa #1 grade, Redwood #2 grade and Douglas fir – south #1 grade.
  • For US machine stress rated (MSR) timbers, No. 1 Framing radiata equates closest to 1200/1.2 grade while Engineering grade radiata equates closest to 1950/1.5 grade.
  • The MGP system tracks very closely with the ISO system for softwoods, with MGP8 grade equating to the ISO S14 grade.
  • The Australian F-grade system clearly does not suit softwoods.
  • No. 1 Framing radiata is closest to C16 grade in the EN 338 (Eurocode) system.

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