Introduction to Timber

• Timber is a natural product obtained from a tree trunk, also known as wood, lumber, or stock.
• Trees mature enough to be cut are generally 20 to 25 years old or older.

Three Major Parts of a Tree

• Crown: Includes branches, twigs, and leaves.
• Trunk: Typically grows with a large diameter, stiff and straight.
• Roots: Anchor the tree in the ground and absorb minerals from the soil.
• Logs are produced by cutting and removing the crown and root parts of a tree.
• Lumber refers to logs cut into commercial thicknesses, widths, and lengths.
• Timber is wood that has undergone processing such as debarking, cutting, and drying.

Physical Properties of Timber

• Strength: The ability to resist stress and strain.

Types of Strength

• Compressive Strength: Ability to resist strain and stress along its fibers.
  • Compression perpendicular to the grain: Load applied at a right angle to the grain direction.
  • Compression parallel to the grain: Load applied to the ends of a column.
• Tensile Strength: Ability to resist lengthwise strain and stresses.
  • Static bending: Gradual application of a load causing beam deflection.
• Shearing Strength: Ability to resist rupture along or across the grain.
  • Shear strength parallel to the grain: Ability to resist internal slipping along the grain.
  • Shear strength perpendicular to the grain: Compressive force perpendicular to the grain causing splitting.
  • Impact bending or resistance: Measures the impact load required to cause failure.
• Stiffness: Ability to resist bending strains and stresses.
• Hardness: Resistance to indentation against cutting tools across the grain.
• Durability: Ability to resist decay and mechanical wear.
• Cleavability: Ability to split along the grain.
• Flexibility: Ability to be pliable, elastic, and resilient.
• Toughness: Ability to be firm and flexible but not brittle.
• Moisture: The amount of water affects its strength.
• Weight: Heavier timber is generally stronger.
• Wood defects: Irregularities that affect strength.

Common Timber Defects

Irregularities in timber can be due to:

• Abnormal growth:
  • Heart shakes: Radical cracks at the heart of the log.
  • Wind shake or cup shakes: Breaks across growth rings caused by excessive bending due to wind.
  • Star shakes: Several heart shakes radiating from the center of the log.
  • Knots: Bases of tree branches, resembling smaller cross-sections of a log.
• Deterioration:
  • Dry-Rot: Caused by fungi on seasoned timber with moisture.
  • Wet-Rot: Caused by water saturation during the tree's growth.

Classification of Timber

• Density: Quality of mass and volume.
  • Softwood: From coniferous or needle-leaved trees.
  • Hardwood: From deciduous or broad-leaved trees.
• Grain: Stratification of wood fibers.
  • Coarse grain
  • Fine grain
  • Straight grain
  • Cross grain
• Color: Shade of certain species.
  • Brown
  • Black
  • Orange
  • Yellow
  • White

Cross-Sectional Parts of a Tree-Trunk

• Bark: Dead covering of the tree.
  • Cortex: Corky outer covering.
  • Bast or PHLOEM: Inner bark that carries food from the leaves to branches, trunk, and roots.
• Cambium: Cell formation takes place to form more sapwood. Xylem cells transport nutrients from roots to other parts of the tree.
• Sapwood: Young, newer growth layer, lighter in color and softer.
• Heartwood: Mature part, darker in color, and hard layer.
• Growth rings or Annular growth rings: Concentric circles radiating from the center to the bark.
  • Summer wood: Slower growth due to heat and lack of moisture.
  • Tree's age can be determined by counting the rings.
• Medullary Rays: Cell-like structures that serve as passageways for food.
• Pith or Pitch: Porous, soft, and rotten material at the center of the tree.