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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
Fb
Tension
parallel
to grain Ft
Shear parallel
to grain
Fv
Compression
perpendicular
to grain
Fc⊥
Compression
parallel to
grain
Fc
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

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