Properties of Wood and Lumber Grades

1
Properties of Wood and Lumber Grades

• Sawn Lumber Wood members that have been
  manufactured by cutting a member directly from a
  log.
• Design values for sawn lumber depend on
• species group
• grade
• Load duration
• moisture content
• Size

2
Grading Structural Lumber

• Lumbers are graded based on size and number of
  growth (strength-reducing) characteristics they
  have (knots, checks, shakes, splits,...)

3
(No Transcript)
4
(No Transcript)
5
Grading Structural Lumber

• Visually Graded

6
Grading Structural Lumber

• Visually Graded
• WWP Lumber Grading Agency
• Western Wood Products Association
• 12 Mill Number
• SEL STR Lumber Grade
• DOUG FIR-L Lumber Species
• S-GRN Moisture Content
• Machine Stress Rated
• 1650Nominal Bending Stress, psi
• 1.5E Modulus of Elasticity, million psi

7
Sizes Categories

• There are three main size categories of lumber
• Boards 1 to 1 1/2 thick, 2 and wider
• Dimension lumber 2 to 4 thick, 2 and wider
• Timbers 5 and thicker, 5 and wider
• Note 1 Thickness is the smaller cross sectional
  dimension and width is the larger dimension.
• Note 2 Dressed dimensions (S4S, Surfaced four
  Sides) are less than nominal dimensions
  (1.5x3.5 for a 2x4). For stress calculations,
  dressed dimensions are used.

8
Design Values

• An important part of formwork design is being
  able to determine design values for the following
  mechanical properties
• Bending stress, Fb
• Shear stress, Fv
• Compressive stress parallel to grain, Fc
• Compressive stress perpendicular
• to grain, Fc?
• Modulus of Elasticity, E