ABE 102

Lecture 2.0 Construction Materials - Wood

By: Engr. Joan Jane J. Sanchez
Course Instructor
Department of Agricultural and Biosystems Engineering
College of Engineering and Geosciences
Caraga State University
ABE 102 – Materials and Processes

Introduction to Construction Materials

  • Overview of Construction Materials:

    • Materials are critical in the construction process and affect the quality, durability, and function of structures.

    • The lecture focuses on wood as a construction material among others like metal, ceramics, polymers, and composites.

Historical Context

  • Example of historical construction: The Great Pyramid of Giza:

    • Served as tombs for Pharaohs, notably King Khufu.

    • Symbolism: Pyramid shapes represented the sun's rays, believed to help the deceased rise to the heavens and join the sun God Ra.

    • Construction Facts:

    • Built with colossal stones weighing around 60 tons.

    • Included lost chambers: hidden or undiscovered rooms.

    • Questions about the builders and construction techniques for transporting and lifting such enormous stones.

Outline of Material Types

  1. Wood

  2. Metal

  3. Ceramics

  4. Polymers

  5. Composites

Construction Material Selection Considerations

  • Key considerations when selecting construction materials:

    1. Type and Function: Requirements of the building or structure and material characteristics.

    2. Economic Aspects: Original investment vs annual maintenance costs.

    3. Availability: Local sourcing of materials.

    4. Skilled Labor: Availability for installation.

    5. Quality and Durability: Long-term performance of materials.

    6. Transportation Costs: Cost implications of bringing materials to the site.

    7. Compatibility: Properties, dimensions, and installation methods must align.

    8. Cultural Acceptability: Community preferences for materials used in construction.

Wood as Construction Material

Characteristics of Wood

  • Wood is a widely used construction material for its:

    • Cost-effectiveness

    • Ease of Workability

    • Attractiveness

    • Adequate Lifespan (if protected from moisture and insects)

Types of Wood

  • Hardwood:

    • Composed mainly of angiosperms or deciduous trees.

  • Softwood:

    • Composed mainly of gymnosperms or coniferous trees.

  • Note: The terms "hardwood" and "softwood" relate to the density and hardness rather than the botanical classification.

Physical Properties of Wood

1. Nature of Wood

  • Wood is a cellular material derived from biological origins.

  • Key properties include:

    • Hygroscopic: Attracts moisture from the air.

    • Anisotropic: Shows variation in structure and properties in different directions.

2. Mechanical and Physical Properties

  • Mechanical Properties include:

    • Strength: Resistance to load.

    • Hardness: Ability to withstand indentation.

    • Stiffness: Resistance to deformation.

    • Toughness: Energy absorption and resistance to complete failure.

    • Warping: Distortion due to moisture content variation.

    • Nail-holding resistance: Ability of wood to hold nails.

    • Workability: Ease of fabrication.

    • Natural-decay resistance: Resistance against biological degradation.

    • •Physical Properties include:

    • Wood rings: Annual growth patterns.

    • Water content: Crucial for strength and dimensions.

    • Density: Influences strength and quality of wood (measured as weight per volume).

Water in Wood

1. Moisture Content (MC)

  • Defined as the amount of water in wood expressed as a percentage of the dry weight.

  • Calculated using:
    extMC=racextweightofwetwood−extweightofdrywoodextweightofdrywoodimes100ext{MC} = rac{ ext{weight of wet wood} - ext{weight of dry wood}}{ ext{weight of dry wood}} imes 100

  • Equilibrium Moisture Content (EMC): Commonly, wood is stable at around 12% MC for indoor applications.

2. Fiber Saturation Point (FSP)

  • Defined as the point where there is no free water left in cell lumens; only bound water in cell walls.

  • Below this point, wood shrinks; above it, wood dimensions are unaffected by moisture removal.

  • Typical FSP value is 30%.

3. Interaction With Water

  • Free Water:

    • Exists in cell cavities. Does not bond with cellulose.

  • Bound Water:

    • Held in cell walls, crucial for maintaining size, shape, and strength.

Shrinkage and Swelling

  • Causes various issues like splitting and warping.

  • Shrinkage and swelling calculations can minimize these effects.

  • Examples of problems:

    • Uneven shrinkage leads to: splitting, warping, and open joints.

Density and Specific Gravity

1. Density Calculations

  • Density (<br>ho<br>ho) defined as mass per unit volume:
    <br>ho=racmassvolume<br>ho = rac{mass}{volume}

  • Example:

    • A block of wood weighing 136 grams with a volume of 150 cm³ gives a density of:
      <br>ho=rac136extgrams150extcm3=0.907extg/cm3<br>ho = rac{136 ext{ grams}}{150 ext{ cm}^3} = 0.907 ext{ g/cm}^3

2. Specific Gravity (SG)

  • SG is the density relative to water:
    SG=racextDensityofwoodextDensityofwaterSG = rac{ ext{Density of wood}}{ ext{Density of water}}

  • Example calculation shows similar outcomes depending on wood species and treatment methods.

Summary of Physical Properties of Wood

  • Address key physical attributes such as color, grain, knots, and texture.

1. Wood Color

  • Affected by species, exposure to light, and age.

    • Ranges from light shades to dark hues.

2. Grain and Texture

  • Describes the direction, size, and arrangement of wood fibers.

    • Types of Grain Include:

    1. Straight grain

    2. Spiral grain

    3. Interlocked grain

    4. Wavy grain

    • Texture varies depending on grain and fiber structure.

3. Knots

  • Result from branches and can affect wood strength, cleavability, and aesthetic value.

    • Types of knots:

    1. Tight knots

    2. Loose knots.

Mechanical Properties of Wood

Overview

  • Mechanical properties define behavior under loads.

  • Factors influencing these properties include:

    • Environmental conditions (moisture, temperature)

    • Growth features (grain structure, knots)

Key Mechanical Properties

  1. Strength: Overall ability to resist forces.

    • Types: Bending, compressive, tensile, and shear strength.

  2. Stiffness: Resistance to bending, quantified by the Modulus of Elasticity (MOE).

  3. Toughness: Energy required for complete failure during bending.

  4. Hardness: Resistance to indentation measured using the Janka Hardness Test.

  5. Cleavability and Nail-holding Resistance: Important for construction applications.

  6. Natural-decay Resistance: Wood's durability against biological degradation.

Final Considerations

  • Understanding properties of wood is essential for effective construction practices.

  • Properties influence choices in design, construction methods, and material selection.

  • Questions and discussions encouraged for deeper understanding.