Strength grading of Pine and Spruce

 of Pine and SpruceStructural wood is normally graded with a strength grading machine. See picture. The strength grading machine measures the strength of each piece of wood. Strength grades C18 andC24 are normally used for timber formwork beams, roof trusses and similar.
Example: C36 wood has a bending strength of 36 MPa, which is 360 kg/cm2, the same as high grade concrete. Wood resists both tension and compression. But concrete must be reinforced with steel to resist tension!

Strength Classes
C14 C18 C24 C30 C36 C40
Bending     Mpa 14 18 24 30 35 40
Tension     Mpa 8 11 14 18 21 24
Compression Mpa 16 18 21 23 25 26
E – modulus Mpa 7000 9000 11000 12000 13000 14000
Density   kg/m³ 290 320 350 380 400 420

Form for a bridge. The wood is of strength class C24. Hall with pillars and beams of laminated glued wood of strength class C14-C40. Wood of strength class C24 for rooftrusses. Joints with nailplates. T & G spruce panels.