A S M Fahad Hossain. Assistant professor. Dept. of CE, AUST

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1 A S M Fahad Hossain Assistant professor Dept. of CE, AUST

2 Timber denotes structural wood obtained from tree. When a tree has been cut and its stems and branches are roughly converted into pieces of suitable lengths, it is known as rough timber. When a roughly converted timber is further sawn and converted into commercial size such as plank, log, batten etc. it is called Timber.

3 Stronger than other construction materials in proportion of weight Easily available everywhere. Workable: Can be easily worked to any size and shape Economical: wastage is minimum Durable Non conductor of heat and electricity. High salvage value. Can be transported easily by converting into commercial sizes. Can be easily jointed. Not corroded. Light weight. Good insulator of heat and electricity. Withstands shocks better than iron and concrete. Good sound absorbing material.

4 It should have uniform colour and regular annual rings. It should be from the heart of a sound tree and have straight fibres. It should have bright appearance with a silky luster when planned. It should be sweet to smell when freshly cut. It should be well seasoned and when cut with a saw, the surface should not clog the teeth of the saw. It should be free from natural defects. It should not be affected by wood rotting, fungi and other insects. It should have firm adhesion of fibres and compact medullary rays. It should be hard. It should be durable. It should be tough i.e., resistant to shocks. It should be elastic.

5 Structural works- Floor boards, Roof trusses, posts, door and window frames, electric poles, gates, railings, piles, wood stairs, scaffolding and formwork (temporary works during construction) etc. Furniture works- Cots, beds etc. Transportation works- Boats, launches, speed boats, ships, body frames of railway coaches, landing platforms, cart wheels etc. Commercial and industrial uses- toys, hardboard, particle board, fibre board, laminated board etc. Ornamental and decorative works- cabinet partition, table lamp holders, flower vases etc. Railway track sleepers Inform of piles, vertical posts, beams, lintels, doors and windows Making sports goods, musical instruments, agricultural implementations

A timber section consists of pith, heartwood, sapwood, cambium layer, inner and outer bark, medullar ray.

2) Cambium layer- A thin layer of sap lying between sapwood and inner bark. It is full of sap which is yet to convert into sapwood.

3) Medullar Ray- These are thin radial fibers extending from cambium layer right up to pith. These rays help in holding together annual rings of both heartwood and sapwood.

6 A timber section consists of pith, heartwood, sapwood, cambium layer, inner and outer bark, medullar ray. 1) Pith- Central part, dark colored and nourishes the plant in its young age. In old age, the pith dries up and decays. 2) Cambium layer- A thin layer of sap lying between sapwood and inner bark. It is full of sap which is yet to convert into sapwood. This is very sensitive layer, if it is exposed by removing the bark, cell stopped transmitting sap into the inner part and the tree dies. 3) Medullar Ray- These are thin radial fibers extending from cambium layer right up to pith. These rays help in holding together annual rings of both heartwood and sapwood. 4) Heartwood- Dark colored portion of the tree surrounding the pith. Almost dead portion of tree does not take part in its growth. It provides strongest and durable timber for various engineering purposes. 5) Sapwood- Light colored wood lying between heartwood and cambium layer. Light in weight and is of recent growth containing a lot of sap. This is the active part of the wood and thus helps in growth in the tree.

8 Cedar Oak Bamboo Palm

Uses - Oak is a hardwood and is used to make expensive furniture/flooring and strong framed structures.

9 Hardwood: This type of timber is produced from broad leaf trees that lose their leaves in winter a deciduous tree. The photograph opposite is of an oak tree which grows in this country. Uses - Oak is a hardwood and is used to make expensive furniture/flooring and strong framed structures. Softwood: This type of timber is produced from trees that do not lose their leaves (coniferous). Softwood trees grow much quicker than the hardwood ones, they are therefore cheaper to buy and far more available. Softwood is used for construction of houses and furniture, and outdoor uses such as fencing.

A tree absorbs CO2 as it grows and stores the carbon as wood. When it reaches maturity it stops absorbing extra carbon. Eventually, if not cutdown, it will die and gradually give off CO2 as it rots.

11 A tree absorbs CO2 as it grows and stores the carbon as wood. When it reaches maturity it stops absorbing extra carbon. Eventually, if not cutdown, it will die and gradually give off CO2 as it rots. If it is cut down and the wood is used for products such as furniture or buildings this locks up the carbon in the timber for the lifetime of the product. If the tree is replaced the new tree will start absorbing more CO2.

The process of drying timber or removing moisture or sap, present in a freshly felled timber, under more or less controlled conditions is called seasoning of timber.

15 The process of drying timber or removing moisture or sap, present in a freshly felled timber, under more or less controlled conditions is called seasoning of timber. Seasoning of wood is the first step in efficient utilization of timber Freshly felled timber contains a large quantity of moisture roughly from 100 % to 200 %, based on dry weight of wood A well seasoned piece of wood contains % moisture and will be in equilibrium with the atmospheric humidity The degree of moisture content is necessary for proper retention of shape and size of component parts Advantages of Seasoning: 1) Seasoned timber is light. 2) Improves strength properties. 3) Easy to transport and handle. 4) Timber less liable to be attacked by fungus and insects. 5) Reduces the tendency to shrink and warp.

16 Methods of Seasoning: 1. Natural Seasoning Sufficient space is left around each sawn piece for free air-circulation. Also known as air seasoning, natural air remains circulating around each piece of the stack and in due course of time, seasoning is brought about.

2. Artificial Seasoning Methods of Artificial Seasoning: Boiling : timber is immersed in boiling water for a certain period of time. Then it is dried slowly by natural air.

17 2. Artificial Seasoning Methods of Artificial Seasoning: Boiling : timber is immersed in boiling water for a certain period of time. Then it is dried slowly by natural air. Steaming: Steam is passed and then dried in natural air. Steam is usually passed for 4 to 6 hours. Kiln Seasoning: Chemical Seasoning: salt seasoning, 1st soaked in salt, then passed through kiln seasoning Electrical Seasoning: high frequency alternating currents are passed through timber in a closed chamber and the resistance caused by the passage of the currents produces heat which dries the timber.

Indicates an increase in life by developing resistance to insect attack, fungal infection and disease of timbers A preservative acts like a disinfectant.

19 Indicates an increase in life by developing resistance to insect attack, fungal infection and disease of timbers A preservative acts like a disinfectant. A seasoned timber, since dried, is hygroscopic and to prevent re-absorption of moisture, the tissues of seasoned wood have to be soaked with some type of preservative. Seasoning, therefore, prepares a timber for preservative treatment by driving away moisture Choice of Preservative is governed by 1. Their toxicity and poisonous effects 2. Permanency in their effect in treated wood 3. Should not be injurious to wood tissues 4. Cheaply available and safe to handle 5. Should allow a decorative treatment 6. Should not disfigure exposed surface of timber 7. Non-inflammable 8. Should have a good covering quality

20 Methods of Preservation 1. Charring : Crude method, a coal layer is formed on the surface, used at lower ends of posts of timber. 2. Tarring: Application of a layer of hot tar on the surface, applied to a embedded ends of posts 3. Painting: both aesthetic and preservative purposes 4. Creosoting :distillation of coal, petroleum or wood substances, used on piles, poles and railway sleepers. 5. Water soluble chemical salts : cheaper than creosote treatment, e.g. Zinc chloride treatment 6. Ascu-Treatment: Mixture of 3CuSO4.5H2O +4 K2Cr2O7.2H2O+ As2O5.2H20

21 Types of preservatives

26 Timber Rot It is a sort of timber decay. During rot, disintegration takes place and gases like H2S and CO2 are generated Two types :

Wood-equivalent Products These types of composite woods are manufactured by binding together wood strands, fibers or veneers with adhesives to form composite materials.

Veneer layers are usually glued and pressed onto core panels of different materials (such as particle board, fiberboard) b) Plywood- It is made from thin sheets of wood veneers.

27 Wood-equivalent Products These types of composite woods are manufactured by binding together wood strands, fibers or veneers with adhesives to form composite materials. (a) Veneer It is thin slices of wood, usually thinner than 3 mm. (1/8 inch). Veneer layers are usually glued and pressed onto core panels of different materials (such as particle board, fiberboard) b) Plywood- It is made from thin sheets of wood veneers. These are stacked together with the direction of ea s grain differing from its neighbors by 900. The piles are bonded under heat and pressure with strong adhesives (i.e. phenol formaldehyde resin) making plywood a type of composite material. It has greater resistance to cracking, shrinkage, twisting and high strength.

c) Particle Board- These are made from leftover waste-wood products such as wood

resin is pressed and extruded to form it.

alternative, is made using small wood fibers rather than wood dust.

28 c) Particle Board- These are made from leftover waste-wood products such as wood scraps or shavings from sawmills, wood chips or even saw dust and a synthetic resin is pressed and extruded to form it. d) Medium density Fiberboard- Medium-density fiberboard, or MDF, a costlier alternative, is made using small wood fibers rather than wood dust. c) Plastic Wood- It is a combination of 50% of recycled plastics and 50% of wood fiber. It is used for outdoor furniture and plat structures.

29 Important Varieties of Timber available in Bangladesh 1. Teak or Segun : Chittagong Hill Tracts 2. Sal : Chittagong Hill Tracts and Sunderbans 3. Garjan : Chittagong Hill Tracts and Sunderbans 4. Gazari: Bhowal Garr, Madhupur jungles, Chittagong Hill Tracts and Sunderbans 5. Sundary: Sunderbans 6. Shisham or Shisso : small quantities in all over the country 7. Shiris: Chittagong Hill Tracts, Sylhet, Khulna, Mymensingh and Dhaka 8. Gamhari: Chittagong Hill Tracts 9. Debdaro : all over Bangladesh 10. Arjun: Chittagong Hill Tracts 11. Shilkarai : Thoughout Bangladesh 12. Chaplash : Chittagong Hill Tracts 13. Neem : all over the country 14. Sandal or Chandan : Chittagong Hill Tracts and the Sunderbans Important Foreign Timbers Imported in Bangladesh: 1. Burma Teak: from Burma 2. Iron Wood: from Burma 3. Mahogany: from Burma, U.S.A. and U.K

PINE WOODS OAK METALS POLYMERS ASH SOFTWOODS CHIPBOARD MAHOGANY MAN MADE HARDWOOD WOODS MDF PLYWOOD BEECH HARDBOARD THERMOSET FERROUS METALS CARBON

PINE WOODS OAK METALS POLYMERS ASH SOFTWOODS CHIPBOARD MAHOGANY MAN MADE HARDWOOD WOODS MDF PLYWOOD BEECH HARDBOARD THERMOSET FERROUS METALS CARBON ASH PINE MAHOGANY SOFTWOODS CHIPBOARD HARDWOOD MAN MADE WOODS OAK WOODS MDF PLYWOOD BEECH HARDBOARD RESISTANT METALS MATERIALS ALUMINIUM POLYMERS NON-FERROUS METALS UREA FORMALDEHYDE COPPER ZINC THERMOSET