Engineering Properties Structural Lumber Douglas-Fir-Larch, Hem-Fir, Spruce-Pine-Fir

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Engineering Properties Structural Lumber Douglas-Fir-Larch, Hem-Fir, Spruce-Pine-Fir

Civil Engineering and Design
Engineering Material Properties

Engineering Properties of Visually Graded Structural Lumber Douglas-Fir-Larch, Hem-Fir, Spruce-Pine-Fir.

Stress-graded structural lumber is produced under two systems: visual grading and machine grading. Visual structural grading is the oldest stress grading system. It is based on the premise that the mechanical properties of lumber differ from those of clear wood because many growth characteristics of lumber affect its properties; these characteristics can be seen and judged by eye (ASTM D245). The principal growth features affecting lumber properties are the size and location of knots, sloping grain, and density.

Grading rules for lumber nominally 2 x 4 in (standard 38 x 89 mm) thick (dimension lumber) are published by grading agencies (listing and addresses are given in ‘‘National Design Specification,’’ American Forest & Paper Association, 1992 and later). For most species, allowable properties are based on test results from full-size specimens graded by agency rules, sampled according to ASTM D2915, and tested according to ASTM D4761. Procedures for deriving allowable properties from these tests are given in ASTM D1990. Allowable properties for visually graded hardwoods and a few softwoods are derived from clear-wood data following principles given in ASTM D2555. Derivation of the allowable strength properties accounts for within-species variability by starting with a non parametric estimate of the 5th percentile of the data. Thus, 95 of 100 pieces would be expected to be stronger than the the assigned property. The allowable strength properties are based on an assumed normal duration of load of 10 years.

Lumber Visually Graded Dimension, Engineering Design Properties - Engineering design values are for normal load duration and dry service conditions

Design values, (lb/in²)
Species and commercial grade	Size classification, in	Bending F_b	Tension parallel to grain F_t	Shear parallel to grain F_v	Compression perpendicular to grain F_c⊥	Compression parallel to grain F_c	Modulus of elasticity E	Grading rules agency
Douglas-Fir-Larch
Select structural	-	1,000	1,000	95	625	1,700	1,900,000	WCLIB WWPA
No. 1 and better	2 – 4 thick	1,150	775	95	625	1,500	1,800,000
No. 1	-	1,000	675	95	625	1,450	1,700,000
No. 2	2 and wider	875	575	95	625	1,300	1,600,000
No. 3	-	500	325	95	625	750	1,400,000
Stud	-	675	450	95	625	825	1,400,000
Construction	2 – 4 thick	1,000	650	95	625	1,600	1,500,000
Standard	-	550	375	95	625	1,350	1,400,000
Utility	2–4 wide	275	175	95	625	875	1,300,000
Hem-Fir
Select structural	-	1,400	900	75	405	1,500	1,600,000	WCLIB WWPA
No. 1 and better	2 – 4 thick	1,050	700	75	405	1,350	1,500,000
No. 1	-	950	600	75	405	1,300	1,500,000
No. 2	2 and wider	850	500	75	405	1,250	1,300,000
No. 3	-	500	300	75	405	725	1,200,000
Stud	-	675	400	75	405	800	1,200,000
Construction	2 – 4 thick	975	575	75	405	1,500	1,300,000
Standard	-	550	325	75	405	1,300	1,200,000
Utility	2–4 wide	250	150	75	405	850	1,100,000
Spruce-Pine-Fir
Select structural	-	1,250	675	70	425	1,400	1,500,000	NLGA
No. 1–No. 2	2 – 4 thick	875	425	70	425	110	1,400,000
No. 3	2 and wider	500	250	70	425	625	1,200,000
Stud	-	675	325	70	425	675	1,200,000
Construction	2 – 4 thick	975	475	70	425	1,350	1,300,000
Standard	-	550	275	70	425	1,100	1,200,000
Utility	2–4 wide	250	125	70	425	725	1,100,000

Reference: Reproduced with permission of the American Forest and Paper Association