Properties of Timber | Civil Engineering Optional Notes for UPSC PDF Download

Timber is a type of wood which has been processed into beams and planks. It is also known as “lumber” in US and Canada. Basically, timber or Lumber is a wood or firewood of growing trees. Any wood capable of yielding a minimum dimensional size can be termed as a timber or lumber. It is a stage in the process of wood production. Timbers are used for the structural purpose. Those woods which are adapted for building purposes are timbers. Finished timber is supplied in standard sizes for the industry. Timber is used for building houses and making furniture.

There is high demand for timber as a building material. From building construction to furniture making, timbers have numerous uses. These uses have made timber an important building material.

Properties of Timber

• Colour
• Appearance
• Hardness
• Specific Gravity
• Moisture Content
• Grain
• Shrinkage and Swelling
• Strength
• Density
• Toughness
• Elasticity
• Warping
• Durability
• Defectless
• Workability
• Soundness
• Free of abrasion

While selecting timbers for use, one must check these properties to ensure the quality. At the same time, it is also essential to ensure that the timber is defectless.

These properties are briefly discussed below:
Colour

• Timber color varies significantly among different tree species. For instance, freshly cut teak has a golden yellow hue, Deodar is whitish, and Walnut is dark brown. Generally, lighter-colored timber is considered weaker.

Appearance

• The smell is a distinctive feature of certain timbers, aiding in their identification. Freshly cut timbers often have a pleasant aroma, such as the resinous scent from pine.

Hardness

• Hardness determines timber's resistance to damage. Harder timber is more resistant to wear and tear.

Specific Gravity

• Timber's specific gravity ranges from 0.3 to 0.9, influenced by the presence of pores. Light timber has a specific gravity of less than 1 (lighter than water), while dense timber can reach up to 1.5.

Moisture Content

• Timber is hygroscopic, absorbing or releasing water based on atmospheric humidity. High moisture content indicates lower quality and increases the risk of fungal attack.

Grain
Grain structure impacts timber quality:

• Straight Grain: Vascular tissues run parallel to the timber's length.
• Coarse Grain: Vascular tissues and fibers are widely spaced.
• Interlocked Grain: Vascular tissues twist in a spiral arrangement.

Shrinkage and Swelling

• Timber shrinks when cell walls release water and swells when they absorb water. High-quality timber swells less. Thicker-walled timbers swell more than thinner ones.

Strength
Timber strength varies due to its anisotropic nature:

• Compressive Strength: Ranges from 500 kg/cm² to 700 kg/cm².
• Tensile Strength: Timber resists tensile force, with a range of 500-2000 kg/cm².
• Transverse Strength: Indicates good bending strength.

Density

• Higher density timber has thicker cell walls, indicating better quality.

Toughness

• Timber must withstand shocks and jerks, possessing anti-bending and anti-splitting properties. Older timbers with annual rings are generally tougher.

Elasticity

• Elastic timber returns to its original shape after use, making it ideal for items like sports bats.

Warping

• Good quality timber resists environmental changes and seasonal effects.

Durability

• High-quality timber resists fungal and insect attacks, enhancing its longevity.

Defectless

• Timber from sound trees is free from sap, shakes, and dead knots. Defect-free timber is stronger.

Workability

• High-quality timber is easy to work with, saw, and finish.

Soundness

• Good quality timber produces a pleasing sound when struck.

Texture

• Fine and even texture indicates good quality timber.

Free of Abrasion

• Timber should resist external damage and protect its surface effectively.