i

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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Table of Contents

LIST OF FIGURES ................................................................................................................................. i

CHAPTER ONE ....................................................................................................................................1

1.0 INTRODUCTION ...................................................................................................................1

1.1 DIFFERENT TYPES OF TIMBER FOUND IN TANZANIA ...............................................................1

1.2 HARDWOODS/CONIFEROUS .................................................................................................1

1.3 SOFTWOODS .......................................................................................................................1

1.4 DIFFERENT TYPES OF TIMBER FOUND IN TANZANIA ...............................................................2

1.4.1 MPINGO (AFRICAN BLACKWOOD) .........................................................................2

1.4.2 MKONGO(Pod Mahogany) ..........................................................................................2

1.4.3 MVULE(African Teak).................................................................................................3

1.4.4 MNINGA(East African Padauk) ....................................................................................3

CHAPTER TWO ...................................................................................................................................5

2.0 CHARACTERISTICS OF TIMBER...............................................................................................5

2.1 INTRODUCTION ...................................................................................................................5

2.2 MECHANICAL PROPERTIES....................................................................................................5

2.2.1 Stress strain relationship...................................................................................................5

2.2.2 Compressive strength .......................................................................................................5

2.2.3 Tensile strength ...............................................................................................................6

2.2.4 Bending strength ..............................................................................................................6

2.2.5 Shear strength .................................................................................................................6

2.3 PHYSICAL PROPERTIES..........................................................................................................6

2.3.1 Density and specific weight ...............................................................................................6

2.3.2 Moisture movement.........................................................................................................6

2.3.3 Swelling ...........................................................................................................................7

2.3.4 Heat conductivity .............................................................................................................7

2.3.5 Sound conductivity ...........................................................................................................7

2.3.6 Resistance to action of acid and alkali................................................................................7

2.4 SEASONING OF TIMBER ........................................................................................................7

2.4.1 Advantages of timber .......................................................................................................7

2.4.2 Types of Timber Seasoning................................................................................................8

2.4.3 Natural seasoning.............................................................................................................8

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2.4.4 Artificial seasoning ...........................................................................................................8

2.4.5 Water Seasoning: .............................................................................................................9

CHAPTER THREE ............................................................................................................................... 10

3.0 DEFECTS OF TIMBER........................................................................................................... 10

3.1 INTRODUCTION ................................................................................................................. 10

3.2 Defects due to abnormal growth ........................................................................................ 10

3.3 Defects due to conversion .................................................................................................. 12

3.4 Defect due to seasoning ..................................................................................................... 12

CHAPTER FOUR................................................................................................................................. 13

4.0 TIMBER PRESERVATION...................................................................................................... 13

4.1 INTRODUCTION ................................................................................................................. 13

4.2 OIL TYPE PRESERVATIVE ..................................................................................................... 13

4.3 ORGANIC SOLVENT PRESERVATIVES .................................................................................... 13

4.4 ACETIC ANHYDRIDE TREATMENT ........................................................................................ 13

4.5 WATER SOLUBE PRESERVATIVES ......................................................................................... 13

4.6 Methods of applying preservatives ..................................................................................... 14

4.7 DIFFERENT USES OF TIMBER IN CONSTRUCTION .................................................................. 15

4.8 Challenges of using timber in construction .......................................................................... 16

5.0 CONCLUSION ..................................................................................................................... 17

6.0 REFFERENCE ............................................................................ Error! Bookmark not defined.

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CHAPTER ONE

1.0 INTRODUCTION

Timber 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 structures

1.1 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 classes

1.2 HARDWOODS/CONIFEROUS

These 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.

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1.4 DIFFERENT TYPES OF TIMBER FOUND IN TANZANIA

1.4.1 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)

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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.

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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

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CHAPTER TWO

2.0 CHARACTERISTICS OF TIMBER

2.1 INTRODUCTION

The 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 of

timber. In order that the engineer may properly design columns and beams for various parts of wooden structures, he must be thoroughly conversant with the strength and stiffness of the available 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 without

excessive deflection. The wheelwright must understand how the toughness and strength of his axles, spokes, and shafts are influenced by species, rate of growth, density, and defects. The carpenter and the craftsman must also have knowledge of the mechanical properties of wood

in order that they may work it to best advantage. The mechanical properties of timber that need 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 Poisson’s 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 strength

2.2.2 Compressive strength

When 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

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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 tension

2.2.4 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 beams

2.2.5 Shear strength

Wood has low shearing strength of 6.5–14.5 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 PROPERTIES

2.3.1 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 specimens

2.3.2 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

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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 direction

2.3.4 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 /mh°C. 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 conductivity

2.3.6 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 timber

2.4.1 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.

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2.4.2 Types of Timber Seasoning

Natural Seasoning,

Artificial Seasoning,

a. Kiln Seasoning,

b. Chemical Seasoning,

c. Electric Seasoning,

Water Seasoning

2.4.3 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 seasoning

2.4.4 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

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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 kiln

2.4.5 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.

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CHAPTER THREE

3.0 DEFECTS OF TIMBER

3.1 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 SHAKE

These 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

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III. CUP SHAKE Appears 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 shake

IV. STAR SHAKE

Are 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 GALL Characterized 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

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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

checks—longitudinal separation of fibres not extending throughout the cross-section of wood, splitting—separation of fibres extending through a piece of timber from one face to another , warp age—consists of cupping, twisting and bowing.

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CHAPTER FOUR

4.0 TIMBER PRESERVATION

4.1 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

methods

4.2 OIL TYPE PRESERVATIVE

Applied 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 PRESERVATIVES

Preservatives 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 TREATMENT

Is 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 insects

4.5 WATER SOLUBE PRESERVATIVES

Are 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.

14

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 important

methods 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

15

4.7 DIFFERENT USES OF TIMBER IN CONSTRUCTION

i. wood frame work construction

In 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 formwork

ii. outdoor features construction

Construction 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 works

The 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 and

Installations 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

16

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.

17

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.