08-WOODS AND PLASTICS-2-60

Wood Classification

  • Major Classes:

    • Softwood: Derived from conifer trees (e.g. pine).

    • Hardwood: Comes from broad-leaved or deciduous trees, prevalent in the Philippines.

  • Grain Direction:

    • Grain direction affects wood's structural capabilities.

    • Improved handling of tensile and compressive forces when parallel to the grain.

    • Greater shear strength across the grain, but more susceptible to horizontal shear.

Wood in Architecture

1. Wood Classification

2. Structure

3. Properties

4. Defects

5. Sawing Methods

6. Philippine Wood

- Types: Strength classifications and applicable working stresses. - Weights and Physical Properties.

7. Lumber

- Classifications: Dimension lumber, timbers and beams. - Measure, Seasoning, Preservation, Treatment, and Deterioration.

8. Wood Composites

- Types: Plywood, Hardboard, Chipboard, Fiberboard, Gypsum Board, Fibercement Board, Particle Board.

9. Millwork

- Types: Mouldings, trims, and finishes.

10. Plastics in Architecture

- Types: Thermoplastics vs. Thermosetting plastics.

11. Plastic Sheets, Film, Foam, and Laminates.

Characteristics of Wood as a Construction Material

  • Strength & Durability:

    • Wood is strong yet light, offering advantages in structural applications like bridges and furniture.

  • Natural Aesthetics:

    • Contributes warmth and beauty through its unique grain and coloring.

  • Workability:

    • Easily shaped using basic tools.

  • Insulation:

    • Naturally insulates, providing energy efficiency.

  • Flexibility:

    • Able to bend under stress rather than shattering.

  • Fire Resistance:

    • Chars slowly without melting, providing limited flame spread.

Characteristics of Different Lumber

Plainsawn Lumber

  • Features:

    • Noticeable grain patterns; prone to twisting and cupping.

    • Uneven wear and fluctuating shrinkage.

Quartersawn Lumber

  • Features:

    • Consistent grain patterns and stable wear; less prone to warping compared to plainsawn.

Shrinkage and Moisture Content

  • Shrinkage:

    • Begins at fiber saturation point (approx 30% moisture content).

    • Radial Shrinkage: Less than Tangential Shrinkage.

  • Uniformity:

    • Vertical grain lumber shrinks uniformly while plainsawn cut develops cupping.

  • Thermal Expansion:

    • Generally less than volume changes due to moisture content.

Natural Properties Beneficial in Construction

  • Unique texture and color allowing for a variety of finishes.

  • Made of varying densities, with different mechanical properties.

  • Ability to accept various finishes.

Structural Components of Wood

1. Sapwood

  • Softer outer layer, high permeability, less durable, lighter in color.

2. Heartwood

  • Denser, more durable inner core providing mechanical support.

Wood Properties to Consider

a. Hardness

  • Assess strength based on compression under weight.

b. Flexibility

  • Softwoods are often brittle; hardwoods tend to be more flexible.

c. Strength and Durability

Wood Defects

a. Decay

  • Caused by fungal attacks, reduced in dry conditions.

b. Checks

  • Cracks formed by irregular shrinkage during drying.

c. Shakes

  • Cracks within the annual growth rings.

d. Knots

  • Irregular growths disrupting grain patterns.

e. Pitch pockets, Wane

  • Openings in annual rings; lack of wood on edges, respectively.

f. Warping Types

  • Crook, Bow, Cup, Twist—various distortions due to uneven shrinkage.

Sawing Methods: Plainsawing vs Quartersawing

Plainsawing

  • Tangential cuts yielding varied grain patterns, prone to distortion.

Quartersawing

  • Radial cuts ensuring tighter joints and uniform stability.

Lumber Specifications

Classification by Size

- Strips: Less than 2” thick, less than 8” wide. - Board Lumber: Less than 2” thick, at least 8” wide. - Dimension Lumber: More than 2” and less than 5” in any dimension. - Timbers: Pieces over 5” on the smallest dimension.

Treatment and Preservation of Lumber

  • Methods include:

    • Pressure treatment, hot/cold methods, dipping, and brushing.

  • Advantages of Seasoned Lumber: Enhances strength and durability, lessens fungi attack risk.

Wood Composites Overview

Plywood

  • Made from cross-layered veneers providing stability, various thicknesses available.

  • Types: Ordinary, Form, and Marine Plywood.

Other Composites

  • Includes Hardboard, Chipboard, Fiberboard, Gypsum Board, and Particle Board.

  • Each type has distinct applications based on density and properties.

Conclusion

  • Understanding the properties, classifications, and treatment of wood and wood composites is crucial in architecture for durability and aesthetic considerations.