Construction Material Timber

Construction Material Timber, Timber “Wood suitable for buildings or engineering purposes is called timber”

What Is Timber

Timber is a multipurpose building material that is available in both hardwood and softwood varieties. Softwoods, such as pine and cedar, are characterized by their low density. Examples of hardwood with a high density are mahogany and oak.

Wood, or timber, is a renewable, adaptable natural resource that is extensively used in building and furniture manufacturing. The main sources of wood in India include different tree species like teak, sal, and Sheesham.

As a building material, timber has several benefits. It has good insulating qualities and is robust and long-lasting. Furthermore, as wood is a renewable resource that can be restored with appropriate forest management, it is a sustainable option.

Recent data indicates that India has a sizable timber sector, with over 85 million cubic meters of yearly production predicted in 2020. Thousands of people are employed by this industry, which also boosts the national economy.

Classification of Trees

ON THE BASIS OF MODE OF GROWTH:-
- Endogenous Trees:-Trees that grow inward by depositing every year of fresh layer internally, instead of on the outside of tree is known as endogenous ( Example * Bamboo, cane, palm ) They have very limited Engineering applications.
- Exogenous Trees:-
  - Trees grow outside from the center by depositing annually a new layer of material between the previous year’s growth in the bark.
  - The cross-section of such tree is having a series of consecutive concentric rings. These rings are called annual rings and each ring represent the growth of one year.
  - Such trees grow bigger in diameter.
  - The timber which is mostly used for engineering purposes belongs to the Exogenous tree.

Exogenous trees are further divided into two groups:-

Conifers or Evergreen Trees ⟹ They have pointed leaves, They are tall and cone-shaped fruit and hence are referred to as Conifer. These trees yield softwoods, light in color, light in weight, and weak wood. Timber obtained from these trees is suitable as tension members, as they have straight grains and distinct annular rings.
Examples:- Deodar, Pine, kail, Chir, spruce.

Deciduous trees⟹ They have broad leaf. The leaves of these trees fall in autumn and new ones appear in spring seasons. The timber for engineering work is mostly derived from deciduous trees. Timber obtained from these trees is strong, durable, dark in color, heavy, and non-resinous. Examples: Teak, Sal, Shisham, Walnut, mahogany, babul, oak, etc.

Commercially trees are also classified as soft and hard woods Soft wood.

ON THE BASIS OF DURABILITY:-

Highly durable (avg. life span>10 years).
Moderately durable (5-10 years).
Low durable (<5 years).

ON THE BASIS OF ELASTIC MODULUS:-

Group A: E = 12.5 GPa
Group B: E = 9.8 GPa to 12.5 GPa
Group C: E = 5.6 GPa to 9.8 Gpa.

ON THE BASIS OF EASE OF SEASONING:-

Non refractory (can be seasoned easily)
Medium refractory (liable to twist and warp)
Highly refractory (liable to undergo severe damage).

Structure of Tree

(a) Pith: The innermost central portion or core of the tree is called the pith or medulla. Having different sizes from tree to tree. It mainly represents the decayed part of the wood hence does not give any strength to it.

(b) Heartwood: The inner annual rings surrounding the pith are known as heartwood. It is also dark in color and hence does not take an active part for the growth of the tree. But timber has strength because of this part.

(c) Sapwood: The outer annual rings between the heartwood and cambium layer is known as sapwood. Also known as alburnum. Its color is generally light which indicates that through this layer trees take their food and nutrients from the soil. Does not give any strength to it.

(d) Cambium layer: The thin layer of sap between sapwood and the inner bark is known as the cambium layer. We can say it is the past of sapwood because by the time it gets converted into sapwood. Hence is responsible for the future growth of the trees.

(e) Inner bark: The inner skin or layer covering the cambium layer is known as inner bark.

(f) Outer Bark: The outer skin or cover of the tree is known as outer bark.

(g) Medullary rays: The thin radial fibers extending from the pith to the cambium layer are known as medullary rays. Its main function is to hold the annual rings of sapwood and heartwood in position and thereby impart strength to it.

PROCESSING OF TIMBER:-

FELLING OF TREES:-

The process of cutting down or felling down the trees is known as the felling of trees.
cutting must be done at an appropriate age when it will achieve sufficient maturity.
If over mature tree is cut it would have a large portion of decayed wood i.e. pith and if under matured tree is cut then a large percentage of sap wood would be present. In both cases, we will get poor timber.
The optimum age for the cutting of the tree is 5-100 years.
Cutting should be done when the sap is at rest. Not in autumn or spring because in that season movement of nutrients will be greater.
Cutting should be done in summer in hilly areas and winter in plain areas.

SEASONING OF TIMBER :-

The process of drying timber upto the optimum level of moisture is termed as seasoning of timber.
A newly fell timber has almost 50% water by weight hence it cannot be used directly. This water may present either in cell cavities or cell walls and may be either as sap or as moisture. Removing sap from timber is a difficult task.
During the drying process, a condition occurs when entire cavity water is lost but wall water is still present this stage is termed as fibre saturation point.

Significance of seasoning of timber:-

To remove moisture, so that its uniform burning can be done.
To increase its workability and resistance against deforming agencies like insects, fungi etc.
To reduce its weight so that transportation costs can be optimized.
Removing moisture prevents warping and twisting during burning. Hence, helps in maintaining uniform shape and size.
It also permits decorative treatments over it.