Introduction to Timber as a construction material
The need of constructing a place to live, or a shelter was originated long back when human used to live his life as a wanderer in forest. Hence, finding the various available construction material and its suitability was necessitated long back.
As a civil engineer, one must know all types of construction material that are available. He must also know the advantages and disadvantages of each type of construction materials. By knowing so, he can use that knowledge to take the maximum advantages of a material.
Concrete the current king in the construction market is a new product. In far earlier days timber was one of the primary construction material.
Therefore here we are discussing about timber/wood as a available construction material and its suitability for using in construction, along with its properties.
- Timbers is nothing but wood logs.
- They are used for building or other engineering purposes.
- These timbers are obtained from trunk of a tree.
Structure of a tree
- It is the innermost part or core having soft tissues.
- Found near about the centre of log of a timber.
- Varies from 1.5 to 10mm in diameter.
2. HEART WOOD:-
- Inner part surrounding the pith.
- Imparts rigidity to tree.
- Provides strong and durable timber for various engineering purposes.
3. SAP WOOD:-
- Outer annual rings bet, heart wood and cambium layer.
- Light in colour.
- Light in weight.
- Contains living cells and takes active part in growth of trees.
4. CAMBIUM LAYER:-
- Thin layer bet, sapwood and inner bark.
- It indicates that which is yet to be converted into sapwood.
5. INNER BARK:-
- Inner skin or layer covering the cambium layer.
- Gives protection to cambium layer.
6. OUTER BARK:-
- Outermost protective layer.
- Consists of cells of wood fibre and it is also known as cortex.
7. MEDULLARY RAYS:-
- Thin radial fibres extending from pith to cambium layer.
- Holds together the annual rings of heartwood and sapwood.
- One ring is added every year which decides the age of the tree.
Defects in Timber
The various defects that are found in the timber or wood are as follows:-
- Defects due to conversion
The various marks or signs placed by chips on the finished surface of a timber is the defect due to conversion.
- Defects due to fungus
Fungi attacks the timber or wood under the following cases:-
- When voucher content of the timber or would is more than 20%
- When there is a presence of air and warmth in the timber or wood
The important defects due to fungus are:-
- Dry rot:- Certain types of fungi attack on wood and convert them into dry powder form. Dry rot usually occurs when there is no free circulation of air, or in the absence of sunlight, or if the wood is unseasoned. Dry rot can be prevented by using well seasoned timber free from sap.
- Wet rot:- Certain type of fungi causes chemical decomposition of wood and convert timber into greyish brown powder and this process is called as wet rot.Again wet rot occurs due to unseasoned timber exposed to rain and wind, other reasons for occurring of wet rot might be alternate wet and dry conditions. Wet rot can be prevented by well seasoned timber usage. Also in many cases wet rot is prevented by covering the timber with tar or paint for protection against moisture.
- Defects due to insect
The insects responsible for decay of timber are:-
- Marine bores.
- Defects due to seasoning
- Case hardening.
- Honeycomb being
- Defects due to natural forces
- Rind galls.
- Knots., etc.
Requirement of a good Timber
- A good Timber must have uniform color.
- Also it should have regular annual rings
- A good timber should also have bright appearance and silky lustre
- Timber must give a clear sound when struck
- Importantly, timber should be well seasoned
- Timber should not be affected by wood rotting fungi etc
- Hardness, durability and toughness speaks a lot about quality of timber for a civil engineer.
- Timber should not split when nail is driven into it.