timber assigment

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LIST OF FIGURES Figure 1: Mpingo (African Blackwood).................................2 Figure 2: Mkongo (Pod Mahogany)......................................2 Figure 3: Mvule(African Teak)........................................3 Figure 4: Mninga(East African Padauk)................................3 Figure 5: Natural seasoning.......................................... 8 Figure 6: Kiln seasoning............................................. 8 Figure 7: Electric kiln.............................................. 9 Figure 8: Radial shake.............................................. 10 Figure 9: Heart shake............................................... 10 Figure 10: Cup shake................................................ 11 Figure 11:Star shake................................................ 11 Figure 12: Rind gall................................................ 11 Figure 13 : Wall formwork........................................... 15 Figure 14 :stair form work.......................................... 15

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timber introduction,characteristics ,defects,seasoning

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LIST OF FIGURESFigure 1: Mpingo (African Blackwood)2Figure 2: Mkongo (Pod Mahogany)2Figure 3: Mvule(African Teak)3Figure 4: Mninga(East African Padauk)3Figure 5: Natural seasoning8Figure 6: Kiln seasoning8Figure 7: Electric kiln9Figure 8: Radial shake10Figure 9: Heart shake10Figure 10: Cup shake11Figure 11:Star shake11Figure 12: Rind gall11Figure 13 : Wall formwork15Figure 14 :stair form work15

Table of ContentsLIST OF FIGURESiCHAPTER ONE11.0INTRODUCTION11.1DIFFERENT TYPES OF TIMBER FOUND IN TANZANIA11.2HARDWOODS/CONIFEROUS11.3SOFTWOODS11.4DIFFERENT TYPES OF TIMBER FOUND IN TANZANIA21.4.1MPINGO (AFRICAN BLACKWOOD)21.4.2MKONGO(Pod Mahogany)21.4.3MVULE(African Teak)31.4.4MNINGA(East African Padauk)3CHAPTER TWO52.0CHARACTERISTICS OF TIMBER52.1INTRODUCTION52.2MECHANICAL PROPERTIES52.2.1Stress strain relationship52.2.2Compressive strength52.2.3Tensile strength62.2.4Bending strength62.2.5Shear strength62.3PHYSICAL PROPERTIES62.3.1Density and specific weight62.3.2Moisture movement62.3.3Swelling72.3.4Heat conductivity72.3.5Sound conductivity72.3.6Resistance to action of acid and alkali72.4SEASONING OF TIMBER72.4.1Advantages of timber72.4.2Types of Timber Seasoning82.4.3Natural seasoning82.4.4Artificial seasoning82.4.5Water Seasoning:9CHAPTER THREE103.0DEFECTS OF TIMBER103.1INTRODUCTION103.2Defects due to abnormal growth103.3Defects due to conversion123.4Defect due to seasoning12CHAPTER FOUR134.0TIMBER PRESERVATION134.1INTRODUCTION134.2OIL TYPE PRESERVATIVE134.3ORGANIC SOLVENT PRESERVATIVES134.4ACETIC ANHYDRIDE TREATMENT134.5WATER SOLUBE PRESERVATIVES134.6Methods of applying preservatives144.7DIFFERENT USES OF TIMBER IN CONSTRUCTION154.8Challenges of using timber in construction165.0CONCLUSION176.0REFFERENCE18

CHAPTER ONE1.0 INTRODUCTIONTimber refer to the wood used for the construction work in fact the word timber is derived from an old English word TIMBRIAN which mean to build, on the other hand timber is material delivered from trees high plant gymnosperm and angiosperm division. Hundred year timber has been used as building material in the country, timber as the building material it used for varieties structural work such as trusses for roof construction, beam, column, railway bulk and bridges structural element. Timber can be highly being durable when properly treated been the case proper understanding of nature, limitations, properties of timber is required in order have a good safe timber structures1.1 DIFFERENT TYPES OF TIMBER FOUND IN TANZANIA There several types of timber found in the country, they names given as results of the trees names such as mninga , mpodo, mvule and Mpingo. Timber used for engineering works is divided into two classes1.2 HARDWOODS/CONIFEROUSThese are dicotyledonous plants characteristically with broad leaves, these tree give non resinous wood, the timber obtained from these trees are strong along and across fibers it is also flexible, Strong and tough capable of bearing tension, compression or shear.Examples of hardwood found in Tanzania are Mninga(East African padauk), Pangapanga, and Msenjele (African lignum vitae) which are normally found in Eastern South of Tanzania.1.3 SOFTWOODS Softwood is wood from gymnosperm trees such as conifers. Softwood is the source of about 80% of the world's production of timber, with traditional centers of production being the Baltic region. Softwoods are not necessarily softer than hardwoods. In both groups there is an enormous variation in actual wood hardness, with the range in density in hardwoods completely including that of softwoods.

1.4 DIFFERENT TYPES OF TIMBER FOUND IN TANZANIA1.4.1 MPINGO (AFRICAN BLACKWOOD)Mpingo is one of the most expensive timbers in the world and is preferred wood of the musical instrument trade because of its high density, fine texture and exceptional durability. Due to unsustainable extraction the tree is threatened with commercial extinction, but a sustainable trade is possible, providing a secure long term future for both woodwind musicians and communities who live around the forests where it grows and they are found in the southern part of Tanzania .

Figure 1: Mpingo (African Blackwood)1.4.2 MKONGO(Pod Mahogany) Although prized locally, pod mahogany is rare in international trade. Small quotas for the species restrict its application to specialist markets. The most suitable sectors for development are: (1) musical instruments, particularly in the manufacture of guitars and xylophones, and (2) furniture, where it could be used to substitute marabou, bubinga and/or rosewood. FSC 100% supplies of pod mahogany could also be used to replace doussie, merbau and bubinga in the construction, household and consumer goods, and flooring sectors (depending on the volumes required).

Figure 2: Mkongo (Pod Mahogany)1.4.3 MVULE(African Teak) African teak has strong dark brown hardwood resistant to termites and is used for construction, furniture, joinery, paneling, floors and boats. The tree can be used in the control of erosion. It makes a good shade tree and is useful as a roadside tree in urban areas. It grows rapidly, can be coppiced and is ready for cutting after about fifty years. The tree is nitrogen fixing and the leaves are used for mulching. Figure 3: Mvule(African Teak)1.4.4 MNINGA(East African Padauk) East African padauk is already used to manufacture flooring, furniture, construction materials, household and consumer goods, and musical instruments. It is easily worked and versatile which, together with the large quota available, permits its potential entry into numerous sectors, including large scale and structural applications (subject to the dimensions required). FSC 100% stocks could be pitched as a supplement or alternative to current supplies and similar species in all of the existing industries, as well as in the manufacture of windows and doors, musical instruments and boats and yachts. Figure 4: Mninga(East African Padauk)i. The system is not expensive to be implemented into offices.ii. It offers good records keeping in form of images because it has the memory card for storage purpose.iii. It provides enough evidence in lawsuits this is due to fact that the system is capable of saving the image of the victim.iv. It is easy to do the maintenance and repair

CHAPTER TWO2.0 CHARACTERISTICS OF TIMBER2.1 INTRODUCTIONThe principal characteristics of timber with which specifiers may be concerned on are strength, durability and finished appearance however timber can be characterized based on the following 2.2 MECHANICAL PROPERTIES Engineers, architects and carpenters must be well versed with the mechanical properties oftimber. In order that the engineer may properly design columns and beams for various partsof wooden structures, he must be thoroughly conversant with the strength and stiffness of theavailable classes of timber. The architect must not only appreciates the beauty of various species, the relative ease with which each may be worked, the tendency to shrink, warp, and check; but he must likewise be prepared to proportion joints and rafters to carry the imposed loads withoutexcessive deflection. The wheelwright must understand how the toughness and strength of hisaxles, spokes, and shafts are influenced by species, rate of growth, density, and defects. Thecarpenter and the craftsman must also have knowledge of the mechanical properties of woodin order that they may work it to best advantage. The mechanical properties of timber thatneed elaboration are as follows.

2.2.1 Stress strain relationship Wood has three principal axes, longitudinal, radial and tangential along which properties are fairly constant. Since wood is a noni tropic material, it has three values of modulus of elasticity varying by as much as 150 to 1, three shear moduli varying by 20 to 1, and six Poissons ratios varying by 40 to 1. There is no sharply defined elastic limit in wood but there is a proportional limit. However, the stress-strain diagram in any direction is fairly straight over a considerable range before it gradually curves off. It is a ductile material.The relative stress-strain curves for direct tension, direct compression and bending stress intensities parallel to the grain in Fig. 4.22 show that in both, direct compression and bending, the proportional limit is in the vicinity of 65 to 75 per cent of the ultimate strength2.2.2 Compressive strengthWhen subjected to compressive force acting parallel to the axis of growth, wood is found to be one of the strongest structural material. Columns and posts are, therefore, often fashioned of it. However, compressive strength perpendicular to fibres of wood is much lower than that parallel to fibres of wood. When wood is subjected to compression parallel to the grain, it may fail through collapsing of the cell walls or through lateral bending of the cells and fibres. In wet wood and in the hardwoods, which are composed of thick-walled fibres and vessels, incipient failure is due to bending of the individual fibres. In cross-grained pieces, the failure is likely to take place through shear parallel to the grain.2.2.3 Tensile strength When a properly shaped wooden stick is subjected to tensile forces acting parallel to the grain it is found to have greater strength that can be developed under any other kind of stresses. Indeed, the tensile strength of wood parallel to the grain is so great that much difficulty is encountered in designing end connections so that the tensile strength of a piece can be developed. Therefore, wood tension members are rarely used. Tensile strength parallel to the fibres is of the order 80.0 to 190.0 N/ mm2 . However, wooden parts restrained at their ends suffer from shearing stresses and crushing which wood resists poorly, and cannot be extensively used in structure working under tension2.2.4 Bending strength Wood well withstands static bending, owing to which it is widely employed for elements of buildings, e.g. beams, slabs, rafters, trusses, etc. The initial failure of long beams of uniform width is indicated by a wrinkling of the overstressed compression fibres, much like the failures which occur in compression prisms. Final failure of such beams is generally in tension. It is accompanied more or less by snapping as the individual fibres begin to break when the maximum load is reached. Very dry specimens sometimes fail very suddenly intension before any wrinkling of the compression fibres is noticeable. Short deep beams fail by horizontal shear suddenly, and this is more common in well-seasoned timber of structural sizes than in green timbers or in small beams2.2.5 Shear strengthWood has low shearing strength of 6.514.5 N/mm2 along the fibres. Resistance of wood to cutting across the fibres is 3 to 4 times greater than that along the fibres, but pure shear generally does not take place since the fibres are also subjected to crushing and bending.

2.3 PHYSICAL PROPERTIES2.3.1 Density and specific weight All the physical properties of clear wood are related to its density, which varies directly with the apparent specific gravity. The true specific gravity of wood is approximately equal for all species and averages 1.54, whereas the specific weight and apparent specific gravity vary with density of wood. The percentage of moisture in the wood has a very large effect upon the specific weight and hence true comparisons of this property can only be made on dry specimens2.3.2 Moisture movement Water is found in three portions of wood: (1) it constitutes over 90 percent of the protoplasm in the living cells; (2) it saturates the cell walls; (3) it fills, more or less completely, the pores of the life less cells. Timber is liable to shrink or swell with the movement of moisture. This movement is not the same in all the directions.

2.3.3 Swelling Is the capacity of wood to increase both its linear and volumetric dimensions when it absorbs water. Swelling of wood along the length of fibres ranges from 0.1 to 0.8 per cent, 3 to 5 per cent in the radial direction and 6 to 12 per cent in the tangential direction2.3.4 Heat conductivity Is quite low and the coefficient of heat conductivity along the fibres is 1.8 times greater than that across the fibres and averages 0.15 to 0.27 K cal /mhC. As the bulk density of wood increases and its moisture content decreases, the amount of air entrapped inside cavities decreases, the effect being greater heat conductivity of wood.

2.3.5 Sound conductivity The velocity of sound in wood is 2 to 17 times greater than that in air and as such wood may be considered to have high sound conductivity2.3.6 Resistance to action of acid and alkali Wood is not affected by weak alkali solution but decays in an acid medium (pH< 4).

2.4 SEASONING OF TIMBER As fresh timber which is obtained from trees contains about 30 to 40 % sap or moisture. This sap is very harmful for the life of a timber. Therefore, it is necessary to remove that sap by applying some special methods. All those methods which are used for removing the sap from timber are collectively termed as seasoning of timber2.4.1 Advantages of timber It has reduced weight, It is strong and durable It has resistance to decay or rot It takes high polish It is easier to work Its life is more.

2.4.2 Types of Timber Seasoning Natural Seasoning, Artificial Seasoning,a. Kiln Seasoning,b. Chemical Seasoning,c. Electric Seasoning, Water Seasoning2.4.3 Natural seasoning In the air seasoning or natural seasoning or natural drying, seasoning of timber, timber is dried by direct action of air, wind and sun. In this method, the timber logs are arranged one over the other, keeping some space or distance between them for air circulation of fresh air.Generally this type of seasoning requires few months to over a year, this is very slow process.

Figure 5: Natural seasoning2.4.4 Artificial seasoning Kiln Seasoning:In kiln seasoning timber is placed in a chamber with some special heating arrangement. In this process one thing should be kept in mind that heating system should be under control, otherwise timber will be crack or wrap. The time required for this seasoning is 3 to 12 days. This is quick process

Figure 6: Kiln seasoning

Chemical Seasoning:In chemical seasoning carbon dioxide, ammonium carbonate or urea are used as agents for seasoning, those are applied in dry state, the inter surface of timber dries first than outer side. This ensures uniform seasoning. The time required for this seasoning is 30 to 40 days Electric Seasoning:In this method electric current is passed through the timber logs. The time required for this seasoning is 05 to 08 hours Figure 7: Electric kiln2.4.5 Water Seasoning:In water seasoning, timber logs are kept immersed whole in the flowing water. The sap present in timber is washed away. After that logs are taken out from water and are kept in open air, so water present in timber would be dried by air. The time required for this type of seasoning is 2 to 4 weeks.

CHAPTER THREE3.0 DEFECTS OF TIMBER3.1 INTRODUCTION Defects can occur in timber at various stages, principally during the growing period and during the conversion and seasoning process. The defects in the wood as shown in Fig. 4.4 are due to irregularities in the character of grains. Defects affect the quality, reduce the quantity of useful wood, reduce the strength, spoil the appearance and favor its decay.3.2 Defects due to abnormal growth Following are some of the important defects commonly found in wood due to abnormal growth or rupture of tissues due to natural forces.

I. RADIAL SHAKEThese are similar to the star shakes and occur in felled timber when exposed to the sun during seasoning. Radial shakes are generally irregular, fine and numerous .In this many splits are appeared

Figure 8: Radial shake

II. HEART SHAKE Occurs due to shrinkage of heart wood, when tree is over matured. Cracks start from pith and run towards sap wood. These are wider at center and diminish outwards.

Figure 9: Heart shake

III. CUP SHAKEAppears as curved split which partly or wholly separates annual rings from one another. It is caused due to excessive frost action on the sap present in the tree, especially when the tree is young

Figure 10: Cup shakeIV. STAR SHAKEAre radial splits or cracks wide at circumference and diminishing towards the center of the tree. This defect may arise from severe frost and fierce heat of sun. Star shakes appear as the wood dries below the fiber saturation point. It is a serious fault leading to separated log when sawn

Figure 11:Star shake

V. RIND GALLCharacterized by swelling caused by the growth of layers of sapwood over wounds after the branch has been cut off in an irregular manner. The newly developed layers do not unite properly with the old rot, thereby leaving cavities, from where decay starts.

Figure 12: Rind gall

3.3 Defects due to conversion Conversion is the term used to describe the process whereby the felled tree is converted into marketable sizes of timber. Conversion defects are basically due to unsound practice in milling or attempts to economize during conversion of timber. A wane occurs in timber which contains, on one or more faces, part of the bark or the rounded periphery of the trunk. This reduces the cross sectional area, with consequent reduction in strength in the parts affected. Excessive slope of grains may also be classed as a conversion defect when conversion has not been done parallel to the axis of the trunk.

3.4 Defect due to seasoning These defects are directly caused by the movement which occurs in timber due to changes in moisture content. Excessive or uneven drying, exposure to wind and rain, and poor stacking during seasoning can all produce distortions in timber. These defects result in loosening of fixings or disruption of decoration, or both. The common types of seasoning defects are checkslongitudinal separation of fibres not extending throughout the cross-section of wood, splittingseparation of fibres extending through a piece of timber from one face to another , warp ageconsists of cupping, twisting and bowing.

CHAPTER FOUR4.0 TIMBER PRESERVATION4.1 INTRODUCTION Timber preservation generally refers to the application of treatments (chemicals) to timber to stop the attack of woodworm, fungal decay (wet rot/dry rot) and to protect it from the effects of dampness. Alternative methods of timber preservation can be employed without the use of chemicals, these could be to introduce a physical barrier (such as a membrane) between the timber and a source of moisture or even something as simple as increasing the airflow around timbers can prevent or arrest the causes of timber degradation. The following are the preservative methods4.2 OIL TYPE PRESERVATIVEApplied over outside of exposed timber, give unpleasant smell and are not suitable when timber is to be painted. The types in use are creosote, carbolinium, solignum etc. with or without admixture with petroleum or suitable oils having a high boiling range.4.3 ORGANIC SOLVENT PRESERVATIVESPreservatives Insoluble in Water) consists of toxic chemical compounds, e.g. pentachlorophenol, benzene-hexa-chloride, dichlorodiphenyl trichloro-ethane (D.D.T) and copper naphthenate. These are dissolved in suitable organic solvents like naphtha, or in petroleum products such as kerosene, spirit, etc. The treated timber can be painted, waxed or polished.4.4 ACETIC ANHYDRIDE TREATMENTIs used for protection of veneers, plywood and light lumbers against decay by acetylation. They are treated with acetic anhydride vapor, which minimizes swelling and improves resistance to decay and attack by insects4.5 WATER SOLUBE PRESERVATIVESAre odourless organic or inorganic salts and are adopted for inside locations only. If applied over outside surfaces, the salts can be leached by rainwater. Examples of leachable (3A-water soluble) type of preservatives are zinc chloride, boric acid (borax), etc. Zinc chloride, sodium fluoride and sodium-penta-chloro-phenate are toxic to fungi. These are expensive and odourless (except for sodium-penta-chloro-phenate). Benzenehexa-chloride is used as spray against borers. Boric acid is used against Lyctus borers and to protect plywood in tea chests.

to compile data. However, such standardized answers may frustrate users. Questionnaires are also sharply limited by the fact that respondents must be able to read the questions and respond to them.4.6 Methods of applying preservatives Before applying preservatives, the timber should be completely seasoned. There are some importantmethods of applying timber preservatives which are given below. Painting and dipping method Pressure process or full cell process Empty cell process Painting and dipping method: This is the most common method in which the preservative material is applied by means of a brush several times. The timber is also immersed in a tank full of liquid (preservative material). In both types the penetration hardly exceeds 1/16. The duration of immersion and temperature of solution is increased the penetration rate.Pressure process or full cell process: In this process, the timber is placed in an air tight chamber, from which air is withdrawn by creating a vacuum. The cells are full emptied to receive preservative material. After that preservative material is pumped under pressure of 100 to 200 psi and at a temperature of 120degreeF. As the timber contains required quantity of preservative a low vacuum is maintained to remove excess preservative. Such a timber is generally used in case of piles in salt water and railway sleepers.Empty cell process:This method is similar to the full cell process but initial vacuum is not to be maintained and no attempt is to be made to remove the air from cells. The preservative material is applied under pressure of 200 psi

4.7 DIFFERENT USES OF TIMBER IN CONSTRUCTIONi. wood frame work constructionIn certain part of the world such as Scandinavian countries, houses will be entirely built of timber because it is suitable for climatic conditions.Elsewhere, house builders can choose to support the house by wooden frames or stud walling. Roof Truss rafters are made entirely of wood and timber shuttering can be chosen for concrete work; in addition some construction plans require a massive bearing beam that will balance structure

Figure 13 : Wall formworkii. outdoor features constructionConstruction of commercial and some private projects will also include exterior work. Outside features such as patios and decking will be made of wood. Additionally, garden architects will require timber for raised plant containers and fencing, while garden shed and garages are often constructed of timber.iii. used in decorative worksThe most visible use of timber is displayed in the finishing process of a construction project. Stair case, door frames, skirting and floor boards as well as boiler, mater and pipe boxes are wooden. Custom-built cupboards are also mostly wooden as are fitted kitchen appliances

Figure 14 :stair form work

iv. Glued wood components e.g., beams, trusses, arches, frames and roofs of buildings andInstallations are very effective in chemically aggressive media because their service life is 1.5 times greater than that of steel or reinforced concrete. However, the use for wood should be economically justified and the possibility of replacing it with prefabricated concrete, asbestos cement, gypsum, plastics and other items should be carefully considered.

v. The use of fibreboard, ply-boards in building practice provides a substantial saving both in capital investments and running costs. The economy is provided, in the first place, by a more complete utilization of raw materials for the manufacture of building materials and items. The use of boards made of pressed wood shavings in dwelling house construction has a great economical effect. Currently, wood waste is utilized to manufactures polymer and cement based fibreboard and wood shavings board. This also allows manufacturing materials of better physical, mechanical and decorative properties than wood.

4.8 Challenges of using timber in construction Safety from Fire To provide an environment for the occupants inside or near a building that is reasonably safe from fire and similar emergencies. To provide reasonable safety for fire fighters and emergency responders during search and rescue operations.

Safety from Structural Failure Provide a high confidence of a low probability of structural failure resulting in local or global collapse, or the creation of falling debris hazards that could threaten life. Provide a high confidence that the structure will be capable of resisting regularly occurring loads and combinations of loads without significant damage or degradation.Shrinkage and Swelling of Timber Timber is a hygroscopic material. This means that it will adsorb surrounding condensable vapors and loses moisture to air below the fiber saturation point.

Safety during Building Use Provide an environment for the occupants of the building that is reasonably safe during the normal use of the building.

5.0 CONCLUSION

In modern building practice, timber and other wood product are extensively useful and normal they are used for walls and floors of buildings, carpentry and graded plank items, as well as prefabricated standard wooden cottages. This high usage of timber has brought great growth of economy of a country also growth of cities and town . A great quantity of wood is consumed in building and installation work for making piles, poles, various load-bearing components formworks, scaffolds. Currently, wood waste is utilized to manufactures polymer and cement based fibreboard and wood shavings board. This also allows manufacturing materials of better physical, mechanical and decorative properties than wood.