Relationship between apparent modulus of elasticity, gage length, and tensile strength of lumber
Tóm tắt
The percent explained variation (r2) of tensile strength (T) of dimension lumber can be accounted for primarily by apparent modulus of elasticity (Ea). Tensile strength ratio, a good index of T of structural lumber, and Ea are both dependent on relative knot size, making T a function of Ea. This theoretical relationship helps to increase r2 when T is regressed on Ea and gives the “cause and effect” for some multiple regression analyses. An independent variable was identified on the basis of this theory. Shortening the gage length enhances ability to predict T when flatwise bending Ea or tension Ea is used as an independent variable, but not when edgewise bending Ea is used. Two single variables not previously reported, Ea measured in flatwise bending on 16-inch gage length (EF 16) and Ea measured in tension on 6-inch gage length (ET 6) (based solely on deformation measurements), are individually able to explain approximately as much variation of T (r2=0.75) as the combination of Ea measured flatwise on 48-inch gage length (span length for the existing American grading machines), and ASTM bending strength ratio. The combination of EF 16 and ET6 can explain 85% of the variation of T. The highest r2 (0.87) was obtained when a modified bending strength ratio was added to these new variables.
Tài liệu tham khảo
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