Timber is defined as structural wood that is used in construction or in other engineering fields from the historical time. Even today there is certain work where timber is considered as the most ideal member. Types of timber are explained below:
Types of Timber:
i) Standing timber:
It is the timber available in living timber.
ii) Green timber :
It is the freshly fallen tree that has not lost much of moisture or timber which still contains free water in its cell.
iii) Rough timber:
It is the timber after falling off the tree.
iv) Converted timber:
It is the timber which has been sawn or prepared into various market sizes. Such as planks, Beams, Battens, etc.
v) Dressed timber:
It is the timber which has been sawn and worked to the exact required condition.
vi) Structural timber:
It is the timber used in framing and load-bearing structure.
vii) Clean timber:
It is the timber free from defects, deflects, blemishes.
Exogenous Tree and Endogenous Tree
i) Exogenous tree:
In this type of tree, plant growth takes place by the addition of new cells around though grown in the previous year.
This process naturally resolves an increase in height as well as the diameter of the plant.
It grows by the addition of a concentric ring every year.
Timber obtained from this class of tree is extensively used in the engineering work Eg. Deodar, saal, shisha, etc.
ii) Endogeneous tree:
In this type of tree, plant growth takes place by the addition of new cells only at the end of previous years. Such a tree grows upward without becoming much thicker. The stem of this tree is too flexible and thus they are not suitable for engineering work. Eg: Bamboo, Sugarcane, Coconut, Pine, etc.
Characteristics of a good timber:
~ It should have a uniform colour.
~ A freshly cut surface should provide a sweet smell.
~ It should have regular and annual rings.
~ It should give sonorous sound when struck together to each other.
~ It should have straight and closed fibre.
~ It should be free from dead knots.
~ A good timber should be durable and capable of resisting the action of fungi, insects, chemical, physical and mechanical agencies.
~ It should be fire-resistant.
~ It should have the property of elasticity.
~ It should be hard.
~ It should be strong for working as a structural member such as beam, rafter, purlin, etc.
(NOTE: The heavier and dark-coloured timber is usually strong.)
Uses of Timber:
~ It is generally used in the form of posts, beams, lintels, doors, windows frames, roof members, piles, etc.
~ It is used for flooring, ceiling, panelling.
~ It is used for the formwork for concrete, timbering for trenches, scaffolding, transmission poles, and fencing.
~ It is used in making furniture, musical instruments.
Parts of a Timber Tree:
i) Growth of tree:
The tree sucks its food from the soil through its roots in the form of sap as moisture. The sap is raised by cell and feed to the branches and leaves of the tree. The sap consists of moisture and mineral-like Phosphates and nitrates.
A young tree grows taller and thicker every year within the period of the rapid growth of each spring and slower growth summer.
ii) Pith (Medulla):
It is the innermost central portion of the tree. It feeds the sap from roots to leaves. It is larger in young trees then that in a mature tree. It has a dark colour. It is usually about 12.5 mm in diameter but sometimes they barely visible.
iii) Heart Wood:
The portion surrounding pith is called heartwood. It is compact, strong, durable and darker in colour.
The percentage of moisture is very less in the central part. The heartwood increases with the size of the tree & age of the tree too.
The heartwood provides the best timber for engineering work and instruction.
iv) Sap Wood:
The part of the trunk between the heartwood and cambium is known as sapwood. It is light in weight, softer and weaker part. It consists of high percentages of moisture. Due to this, the wood is prone to deflect so, it is not used for commercial purposes.
v) Cambium layer:
The thin layer adjacent to the bark is known as the Cambium layer. These are mainly responsible for the circumferential growth to the tree. If the bark is removed from any region the Cambium layer gets exposed and the cells cease to be active that is inactive resulting in the death of a tree.
vi) Inner bark:
It is the inner skin of the layer covering the cambium layer from the injury.
vii) Outer bark:
It consists of wood fibre and is the outermost cover or skin of a stream. It often shows fissures and cracks. It prevents the tree from injuries and weathering action.
viii) Medullary rays:
These are the radial rays starting from pith up to the cambium layer. This ray binds the annual rings together. Also, it carries sap to a various portion of the tree.
ix) Annual rings:
These are the concentric layer of wood around the pith. Every year’s such layer is added to the trunk of the tree. The number of annual rings indicates the number of the edge of trees.