Timber “Wood suitable for buildings or engineering purposes is called timber” Classification of Trees They have pointed leaves, They are tall and cone-shaped fruit hence is referred to as Conifer. and such types of trees Endogenous Trees, Exogenous Trees, Conifers or Evergreen Trees
Classification of Trees:-
>>ON THE BASIS OF MODE OF GROWTH:-
A. Endogenous Trees:-Trees that grow inward by depositing every year of fresh layer internally, instead of on the outside of the tree is known as endogenous ( Example * Bamboo, cane, palm ) They have very limited Engineering applications. which comprise the great majority of modern trees (all conifers, and all broadleaf trees), grow by the addition of new wood outwards, immediately under the bark. Endogenous trees, mainly in the monocotyledons grow by the addition of new material inwards.
B. Exogenous Trees:-
- Trees that grow outside from the center by depositing annually a new layer of material between the previous year growth in the bark.
- The cross-section of such a tree is having a series of consecutive concentric rings. These rings are called annual rings and each ring represents the growth of one year.
- Such trees grow bigger in diameter.
- The timber which is mostly used for engineering purposes belongs to an Exogenous tree.
Exogenous trees are further divided into two groups:-
- Conifers or Evergreen Trees ⟹ Classification of Trees They have pointed leaves, They are tall and cone-shaped fruit hence is 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 having straight grains and distinct annular rings.
Exa:- Deodar, Pine, kail, Chir, spruce.
2. Deciduous trees⟹ They have broadleaf. They include oaks, maples, and beeches, and they grow in many parts of the world. 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. Example: Teak, Sal, Shisham, Walnut, mahogany, babul, oak, etc. Deciduous trees are giant flowering plants. The word deciduous means to “fall off,” and every fall these trees shed their leaves. Most deciduous trees are broad-leaved, with wide, flat leaves.
Commercially trees are also classified as soft and hardwoods Softwood.
Hardwood is not necessarily a harder material (more dense) and a softwood is not necessarily a softer material (less dense).
Different types of construction projects call for different kinds of timber, both hardwood and softwood are used for everything from structural to decorative pine, redwood, spruce, and yew. Most hardwoods have a higher density than most softwoods..
Softwood and hardwood are distinguished botanically in terms of their reproduction, not by their end-use or appearance. All trees reproduce by producing seeds, but the seed structure varies.
In general, hardwood comes from a deciduous tree that loses its leaves annually and softwood comes from a conifer, which usually remains evergreen. Hardwoods tend to be slower growing, and are therefore usually denser.
Examples of hardwood trees include alder, balsa, beech, hickory, mahogany, maple, oak, teak, and walnut. Examples of softwood trees are cedar, Douglas fir, juniper, pine, redwood, spruce, and yew. Most hardwoods have a higher density than most softwoods.
>>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:-
- Nonrefractory (can be seasoned easily)
- Medium refractory (liable to twist and warp)
- Highly refractory (liable to undergo severe damage).