Wood material and timber

wood and its product
an important topic to study for interior and architecture students.
types of trees and product obtained from trees

1. WOOD TIMBER BY. PROF.SABERA CHAUS INIFD BORIVALI

2. The wood used for building or other engineering purposes is called timber. Timber is generally obtained from the trunk of a tree. The timber is in the form of living tree, The freshly felled tree and in the form of felled tree. INTRODUCTION

3. Standing timber : The timber in the form of living tree. Green timber : The freshly felled tree which has not lost moisture. Rough timber : The timber in the form of felled tree. Converted timber : The timber when sawn into various market sizes such as beams, battens, planks etc. Dressed timber : The timber which has been sawn, placed and worked to the exact required condition. Structural timber : The timber used in framing and load bearing structures . Clear Timber : Timber free from defects and stains. Important Technical Terms:

4. Characteristic of good timber.

5. Uniform color. Sweet smell if fresh cut. Regular annual ring. Sonorous when struck. S traight and close fibres . H eavy in weight. Free from shakes, flaws, dead knots or blemishes of any kind. F irm adhesion of fibres and compact medullary rays. The cellular tissue of the medullary rays should be hard and compact. When planed, its surface should present a firm bright appearance with a silky lustre . Characteristic of good timber.

6. Durable and Hard. Resisting the actions of fungi insects , chemicals, physical agencies and mechanical agencies. T he property of elasticity. Fire-resistant. (Wood having dense texture offers great resistance to fire .) S trong for working as structural member such as joint, beam, rafter , etc. It should be capable of taking loads slowly or suddenly . Note : The heavier and dark coloured timber is usually strong. Characteristic of good timber.

7. S tronger than other materials. E asily worked to any size and shape. C an be joined to the required form easily. Structural connections can be easily made in timberwork. Used for furniture and other decorative fittings . Timber construction is economical as the wastage is minimum. D urable . R e-sale value is good A non-conductor of heat and sound. Advantages of Timber over Other Materials :

8. The disadvantages of timber are few, but serious. These are : The greatest disadvantage is its ready combustibility, which can be diminished but not eliminated even by expensive treatment. Frame buildings built closely together present a serious conflagration hazard. D estroyed by decay induced by fungi, and by insects that feed upon the timber under favourable conditions. Timber swells and undergoes shrinkage with changing atmospheric humidity. Disadvantages :

9. Classification of Trees According to their manner of growth , the tree may be divided into two main classes Endogenous tree: These trees grow inwards. Fresh fibrous mass is in the inner most portion. e.g. bamboo and crane The stems of these trees are too flexible and thus they are not much suitable for engineering and structural works . They are found generally in tropical countries . They have their own limited applications for temporary construction.

10. 2. E xogenous trees: These trees grow outwards and increase in bulk by the formation of successive annular rings on the outside under the bark. E ach annual ring represents a layer of wood, deposited every year. The timber that is used for building and engineering purposes belongs to this variety. Examples: Deodar, chir , sal , kail , shishum , teak, etc Classification of Trees

11. Conifers trees : They remain evergreen and bear fruits in cone form with needle-pointed leaves. These trees yield soft woods which are generally light coloured , resinous, light in weight and weak. They show distinct annual rings. Types of Exogenous T rees

12. Deciduous trees : They shed their leaves in autumn and put on new leaves in the spring season . These trees yield hardwoods which are usually close-grained, strong, heavy, dark coloured , durable and non-resinous . They do not show distinct annual rings . The timber used for engineering purposes is mostly derived from deciduous trees. Types of Exogenous Trees

13. Comparison between Softwood and Hardwood S.no Aspects Soft Woods Hard Woods 1. Trees obtained Conifers trees Deciduous Trees 2. Annual Rings Distinct Indistinct 3. Medullary Rays Indistinct Distinct 4. Weight Light Heavy 5. Structure Resinous and splits easily Non- resinous and close grained 6. Strength Strong for direct pull and weak for resisting thrust or shear Equally strong for resisting tension, compression and shear 7. Colour Light Dark 8. Fire Resistance Poor Fair

14. A defect is an irregularity or abnormality occurring in or on wood which is responsible for its. Strength reduction. Lowering of durability. Lowering of utility Poor appearance D ecay Defects in Timbers

15. Classification of defect CAUSED DUE TO Natural force Fungi C onversion Seasoning Insects

16. S hakes : Defects in timber at the time of growth S tar Shake- Cracks wider at circumferences. Narrower towards the pith. (Reason)-exposure to axcess cold or Hot climate. While seasoning external layer is more Heate d than internal layer. Defects in Timber

17. 2. Heart shake Wider at pith. Narrower towards the circumference. (Reason)-over age of tree. 3. cup/ring shake Annual rings separates at a point. Irregular growth of a tree. Defects in Timber

18. 4. Radial shakes Type of star shake. Cracks stop at sap wood. (Reason)-temperature variation. Outer surface is more dry tha n inner surface. 5. Rind gall Swelling or injury on plant. Due to irregular cutting. Abnormal growth. Defects in Timber

19. 6. Upsets or rupture : due to crushing of fibers. due to unskillful felling. the result of violent wind . 7. Twisted fibers or wandering hearts : winds turn the tree constantly in one direction . tree are twisted longitudinally. if planks or any sections are cut , many fibers cut through, strength is reduced. twisted fibers is unsuitable for sawing. Defects in Timber

20. 8 .Burrs or excrescence : unsuccessful attempts at the formation of branches due to injuries inflicted when the tree was young , Technically , they are defects but , in practice, they produce valuable figure-wood for veneers . 9 .Wind cracks : when wood is exposed to atmospheric agencies, its exterior surface shrinks. Such a shrinkage results in cracks. Defects in Timber

21. 10. Knots Knots are the layer of nourishment form in the dark color on tree. Knots are formed when heartwood of tree comes in contact with atmosphere, when are branches cut. Knots are divided into two types: Live knots Does not affect strength and quality. Main timber is combined. b) Dry knots Not connected to the main timber. Affects the strenght . Defects in Timber

22. 11. Dry rot N ot natural. Due to fungi. Due to less air ventilation. Lack of light. Dampnes s in atmosphere. E.g. kitchen and bathroom. Changes wood into powder form. 12. Wet rot D ue to chemical decomposition. Get exposed to alternate wet and dry condition. Improper seasoning. Rain and wind Defects in Timber

23. 13. Heart rot Fungi affecting on heartwood Changes into powder form. Make the wood hallow. Reduces the strength. Damp sound when struck hammer Defects in Timber