MSR Lumber
The machine grading process sorts dimension lumber by strength and stiffness to improve consistency. The table below shows four common MSR grades and design values. For a comprehensive list, see Table 4C in Design Values for Wood Construction, a supplement to the National Design Specification® (NDS®) for Wood Construction.
Grade Designation | Bending (Fb) | Tension Parallel to grain (Ft) | Compression parallel to grain (Fc) | Modulus of Elasticity (E) |
---|---|---|---|---|
1650f-1.5E | 1650 | 1020 | 1700 | 1,500,000 |
1800f-1.6E | 1800 | 1175 | 1750 | 1,600,000 |
2100f-1.8E | 2100 | 1575 | 1875 | 1,800,000 |
2400f-2.0E | 2400 | 1925 | 1975 | 2,000,000 |
Design values in pounds per square inch (psi)
MSR lumber simplifies many design considerations because a grade such as 1650f-1.5E maintains the same Fb, Ft, Fc, and E values regardless of the species or size considered. Other properties, however, change by species as they relate to the specific gravity (density) of wood. A few examples are listed below; see Table 4C in the NDS supplement for more detailed information or refer to information produced by grade rules writing agencies.
Grade Designation | Species | Specific Gravity (SG) | Shear parallel to grain (Fv) | Compression perpendicular to grain (Fc⊥) |
---|---|---|---|---|
1650f-1.5E | SPF | 0.42 | 135 | 425 |
1650f-1.5E | HF | 0.43 | 145 | 405 |
2400f-2.0E | SPF | 0.50 | 170 | 615 |
2400f-2.0E | SYP | 0.57 | 190 | 805 |
Design values in pounds per square inch (psi)
Adjustment factors must be applied to the allowable design values presented here. Adjustments to values are taken for duration of load, repetitive member situations, beam and column stability, and other factors as summarized in Table 2.3.1 in the NDS supplement. Machine graded lumber enjoys specific advantages in beam stability, column stability, and buckling stiffness factors as a result of the consistency of E compared to visually graded lumber.
Machine graded lumber certification and quality control procedures are based on approved American or Canadian lumber standards (ALS or CLS), and QC testing takes place on a daily basis for all machine graded lumber products. Depending on the grade requirements, testing takes place for one or more of the following properties: E, Fb, and Ft. This testing process is established to verify that production meets design requirements for all product shipped to customers as MSR, MEL, or E-rated laminating grades.