Mechanical stress grading of dahurian larch structural lumber
Gupta, R. | Ethington, R.L. | Green, D.W.
The objective of this study was to test a method under development for assigning allowable properties to foreign species graded by American Lumber Standard machine-stress-rated (MSR) rules. The method was tested on dahurian larch (Larix dahurica), a major softwood species that grows in the Russian Far East and could be marketed in the United States. The relationship of tensile strength to bending strength for the test sample of dimension lumber was readily validated as similar to that for temperate softwoods from the United States and Canada. The results also showed a good relationship between bending strength and modulus of elasticity. Shear and compression perpendicular-to-grain strength values were weakly related to specific gravity, but barely met validation criteria. Edge-knot class and short-span flatwise modulus of elasticity were good sorting criteria for bending strength, as they are for MSR domestic lumber. Three published MSR grades representing a wide range of qualities were readily qualified. Tensile allowable stress was a limiting property. Achieving this property required the setting of boundaries that made the highest grade relatively rich in bending strength and stiffness and the lower grades relatively rich in tension. The sample could be sorted correctly into three selected grades nearly on the basis of edge-knot limitations alone. This study shows that this method can be used to machine stress rate dahurian larch into an array of existing domestic grades.
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