timber (written report) for civil eng'g

8/10/2019 Timber (Written Report) for Civil Eng'g

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Timber

A. Introduction

Timber is wood in any of its stages from felling to readiness for use as structural material for construction orwood pulp for paper production. Timber is one of the oldest structural materials used by man. Temples and

monuments built several centuries ago but which still remain in excellent condition show the durability and usefulnesso timber. Wood used for structural purposes are timber. There is a lot of demand for primary species of timber like,deodhar, sissoo, sal etc. There are a large number of species of timber which can be used for construction and otherpurposes but are not well known in the market. In order to enhance and economize the utilization o wood, manywood based products have been developed in a big way like veneers, plywood, hard board, particle board, etc.

B. Sources of Timber

The source of timber supply is the trees in the forests. It is a part of the plant life that thrives in many forms.Though trees are different from other forms of plants life like herbs, they are basically of the same group, both in theirstructure and growth. They grow much taller than herbs and take a longer time to mature.

I. Tree and Its Growth

All plant life is basically made up of root, stem, leaves and branches. The roots anchor the tree to theground and take in mineral nutrients from the soil. The stem conducts the food materials to the leaves, stores themand also provides mechanically rigidity by supporting the leaves and branches. The leaves are the most importantpart of the tree for its existence because it is here that the complex substance required for the life processes aremanufacture the complex substances required for the growth of the tree.

II. Cross section of a Tree Stem

1. Bark outermost layer or the skin of the trunk. Its main function is to give protection to soft tissues of woodwithin.

2. Cambium a thin layer of thickened sap below the bark which is not yet converted into sap wood. This is mainlyresponsible for the circumferential of the tree.

3. Sapwood the food consumption and storage layer of the wood stem. The sap is light in color, light in weightand liable to decay. Sapwood being an active later in moist, rich in food material and less durable.

4. Heartwood innermost part of the tree. It is mainly concerned with providing mechanically stability andsupporting the heavy top part of the tree.

5. Pith also known as medulla. It is about 1.25 cm in diameter but sometimes barely visible. This is fibrous tissuerepresenting the original sapling.

6. Annual Rings / Growth Rings concentric layers of wood.7. Medullary Rays radial lines in the cross section and as small bands in the radial section.

III. Classification of Trees:

1. Exogenous Trees (exogens), which grow outward.2. Endogenous Trees ( endogens), which grow inward from a hard exterior shell or more commonly endwise

by the acquisition of new joints.

Other important classification:

Softwoods (gymnosperm) have needled shaped and grow in temperate regions and in high altitudes.


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- Obtained from coniferous trees having a characteristic of a Christmas tree type growth.- Light colored- Growth rings distinct- Usually light in weight- Resinous in nature and readily catch fire- Can be easily split- Strong along the grain but weak across

Hardwoods (angiosperms) broad-leaved trees.

- Called deciduous- Generally dark-colored- Growth rings are not as distinct as in softwoods- Usually heavier in weight- Non-resinous and do not catch fire readily- Cannot easily split- Strong in tension, compression and shear along across the grains

Other Methods of Classifications of Timber

1. Based upon the modulus of elasticity . The species of timber recommended for structural purposes areclassified into three groups A, B and C as:

Group A: Modulus of elasticity in bending above 125 t/cmGroup B: Modulus of elasticity in bending above 98 t/cm and below 125t/cmGroup C: Modulus of elasticity in bending above 56 t/cm and below 98 t/cm

2. Grading of structural timber. Structural timber can be graded into three classes. Select grade, Grade I andGrade II. This classification is based upon the structural design characteristics like permissible stresses defects,etc.

3. Based upon availability. According to availability, timber can be of three grades namely, X, Y and Z.

X Most common 1415m or more per yearY Common 335m to 1415m per yearZ Less common below 355m per year

4. Durability. Durability of timber is tested by the graveyards test conducted in the open. Timbers are classifiedbased upon such observations as of:

High Durability : Timbers having average life of 120 months and over.Moderate Durability : Timbers having average life less than 120 months but of 60 months or moreLow Durability : Timbers having average life less than 60 months

5. Seasoning Characteristics. Timbers are classified depending upon their behavior to cracking and splittingduring normal air-seasoning practice under three categories:

Highly Refractory (Class A) : These are slow and difficult to season free defects.Moderate Refractory (Class B) : These maybe seasoned free from surface defects, etc. if some protection is

given against rapid dying.Non refractory (Class C) : These can be rapidly seasoned free from defects.

6. Treatability. This classification is based upon the behavior of timber to preservative treatment under pressure. Itcan be classified as:

-

Heartwood easily treatable.- Heartwood treatable but complete preservation is not easily obtained.- Heartwood only partially treatment.- Heartwood refractory to treatment.- Heartwood very refractory to treatment, penetration of preservative being practically nil from sides to ends.

C. Identification of Timber


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General Properties

1. Color. Color in wood shows a wide range o variation. The color of the same kind of timber changes dependingupon whether the surface us freshly cut or has been exposed.

2. Odor. The odor disappears on exposure and if present, is pronounced only when freshly cut.3. Hardness. Hardness is defined as the resistance of the material to indentation or penetration by a foreign body.

Soft to Very soft : Readily indented by finger nail.Moderate Hard : Not readily indented by finger nail but readily cut a knife.Hard to Very Hard : Not indented by finger nail and cut difficulty by knife.

4. Density. Density varies considerably depending upon:- The weight o wood substance- Any solid or dissolved substances- Moisture content- Any air cavities or walls

Of these, the weight of water in wood varies considerably. The timber may be grouped into three classes based upon

density:

Light to Very Light : Density below 550kg/cmModerate Heavy : 550 to 750 kg/cmHeavy to Very Heavy : Above 750 kg/cm

5. Grain. It refers to the general direction or alignment of wood cells.- Spiral grain is a natural defect due to the irregularities in the formation of the fibers themselves.- Interlocked grain in which grain changes direction to left and right more or less irregularly.- Wavy grain is produced by undulations in the course of wood.

6. Texture. Texture is due to the size of cells, distribution and proportion o various types of cells. Timber can be

classified into three main classes.- Fine texture- Medium coarse texture- Coarse texture

7. Lustre. It is due to the difference in the light reflecting property of the different cells. The rays reflect light muchmore than others.

Structures of Softwood

1. Tracheids. These are hollow, needle shaped units closely packed together so that a cross section through themresembles a honeycomb.

2. Storage Tissues (Rays and Wood Parenchyma Cells). The storage of food materials is done by two types ofcells rays and weed parenchyma. Rays are horizontally and radially aligned and can be seen as thin lines inthe cross section and as bands in the radial section.

3. Resin Canals. The resin formed in the parenchyma cells and in some species occur in special channels.4. Growth Rings. These are normally distinct in softwoods. In some woods, growth rings maybe distinct or faint

due to the similarity between early wood and late wood.

Structures of Hardwoods

1. Pores or Vessels. Pores are tubular elements running in a vertical direction and serve to conduct water andmineral nutrients.

2. Inclusions. These are sometimes colored deposits, white or chalky deposits and ingrowths of adjoining tissues

into the pore.3. Parenchyma. These are soft tissues and consist of small, thin walled, rectangular and brick-shaped cells.4. Rays. Their function is horizontal conduction and storage. In the cross section, rays can be seen as numerous

fine light-colored lines.5. Fibers. Fibers are too small to be seen individually but collectively, it form the ground mass in other tissues are

set.6. Cellular Canals. These are long tubular cavities seen in the horizontal or vertical direction.


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D. Felling and Conversion

Time for felling a timber A timber tree should be felled immediately after it has attained its full growth in order to obtain maximum

quality of wood at its most endurable state. If any tree is cut down prior to its maturity, it will yield more sap and lessquantity of heartwood.

Felling of TimberFelling is done by making clean saw cut as near to the base as possible. Felled timber should be converted

into smaller pieces as early as possible.

Conversion of TimberThe sawing of logs to form balks, boards, plank, deals, battens, etc. is called the conversion of timber.

During conversion, due allowance usually 3mm to 6mm should be kept for shrinkage, squaring and planning.

Conversion is done in several ways as discussed below:

1. Sawing. Is the use of any tool, either hand-operated or power-driven, having a thin metal blade or disk witha sharp, usually toothed edge, used for cutting wood, or ether hand materials.

Methods of Sawing:

1.1. Ordinary or Flat Sawing a very easy and quick method of sawing. The log is moved backward andforward on a saw which cuts parallel slices or cuts.

1.2. Tangential Sawing the cutting is tangential to the annual rings at right angles to the medullary rays.1.3. Radial Sawing sawing is done parallel to the rays and perpendicular to the rings. Radially sawn timber

shrinks and warps less than the ordinary sawn planks.1.4. Quarter or Rift Sawing the log is first cut into quadrants. Each quadrant may be further sawn by plain,

tangential or radial sawing.1.5. Combination Sawing it uses combination of one or two of the above methods to convert the log.

Lost of Timber in Conversion

There is 40% of the weight of the log wasted in conversion of timber by sawing.Bark sap, etc.: 10%, Trimmings: 18% - 20%, Saw dust: 10%

E. Moisture in Timber

One of the most important characteristics of timber that affects its use and on-the-site performance is itsmoisture content. This is very important factor in timber utilization and the technology of timber revolves aroundthe efficient methods of controlling the moisture content of timber.

1. Hygroscopic Nature of Timber

Timber is by nature hygroscopic, it absorbs water from the surrounding air. For efficient utilization, thetimber needs to be more or less dry, the permissible moisture content being from 6% to 20% depending uponthe use and the environment of use.

1.1. Water in Wood (Moisture Content)The moisture content of timber is the weight of water it contains, expressed as a percentage of the weight of

water in the timber when oven dried.

1.2. Fibre Saturation PointIt is the moisture content in percentage of timber when the cell walls are saturated with water and the cell

cavity contains no water.

1.3. Equilibrium Moisture Content A stage is finally reached after which there is no further interchange of moisture between the wood and air.

Such a state is called the state of equilibrium. The moisture content at this stage is called the equilibriummoisture content. Any subsequent change in temperature or moisture content of air upsets this balance and as aresult there is further exchange of moisture until a new stage of equilibrium is reached.


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2. Shrinkage of Timber

Drying of timber causes shrinkage while absorption of water causes the timber to swell. Timber is not ahomogenous material and hence, the shrinkage along different directions is not uniform.

Green timber shrinks least along its length, much more along the radial direction and maximum along thecircumference. The figures vary considerably for different species of timber, but on an average, the shrinkage isabout 0.1% along the circumference.

Permissible Moisture ContentIS: 287 1973 lays down the maximum permissible moisture content for different zones as per average

relative humidity as:

Zone I : Less than 40%, Zone II : 40% - 50%, Zone III : 50% - 67%, Zone IV : 67% and above

Determination of Timber

1. Oven Dry Method

Moisture content can be determined by the oven drying method. The wet timber is weighed (W) and driedin an oven weight, moisture content can be determined as:

F. Mechanical Properties of Timber

1. Tensile StrengthTension results when a pulling force is applied to opposite ends of a body. The result is an elongation or

stretching of the material in the direction of the applied force.

2. Compressive StrengthIt is determine from tests and two types of strength are identified, along the grain and across the grain.

3. Shear StrengthShear strength is determined only parallel to the grain as shear strength perpendicular to the grain cannot

be determined because of failure due to other causes before the ultimate shear strength is reached.

4. Bending StrengthBending Strength indicates both the ease with which a wood can be bent and the percentage of its strength

it retains after bending.

5. CleavabilityRefers to the splitting strength of the specimen. The property so as to be referred to directions such as

radial and tangential splitting.

6. BrittlenessThe property of suffering little deformation before breaking.

7. Torsion Strength A tough wood is one that will not rupture until it has deformed considerably under loads at or near its

maximum strength, or one which still hangs together after it has been ruptured and may be bent back and forthwithout breaking apart.

8. HardnessThe hardness is the ability of the wood surface to resist damage.

G. Defects in Timber

Defects are irregularities found in wood. Usually cause by climatic condition, nature of soil where tree growsand by natural calamities.

Defects cause in timber may be basically classified into two categories.


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- Internal defects which are due to factors affecting the growing tissue of the tree.- External defects due to external agents or subsequent treatment of timber.

The defect will be discussed under three headings. (Natural, Due to Seasoning, Due to Manufacturing or Use)

1. Natural

1.1. Knots A knot is a particular type of imperfection in a piece of wood. They are defects which weaken timber and

lower its value for structural purposes where strength is an important consideration.

Knots may be classified as follows:According to size:

1. Pin knot a knot not more than 6.5mm in diameter2. Small knot a knot more than 6.5mm, but not more than 20mm in diameter3. Medium knot a knot more than 20mm, but not more than 40mm in diameter4. Large knot a knot more than 40mm in diameter

According to form:1. Round and oval knot a knot cut more or less at the right angles to its long axis so that the exposed

section is round.2. Slay/Spike knot a knot cut approximately parallel to its long axis so that the exposed section has an

elongated shape.

According to position on the surface of the wood: 1. Knot cluster group of two or more knots such that the wood fibres are deflected around the group.2. Branches knot two or more knots emanating from the same base.

According to quality:1. Live knot a knot whose fibres are completely intergrown with those of the surrounding wood.

2. Sound knot live knot free from decay3. Decayed knot knot soften than the surrounding wood and containing decay4. Tight knot lice or dad knot held firmly in place5. Dead knot knot whose fibres are not intergrown with those of the surrounding wood6. Loose knot a dead knot which is not held firmly in place7. Knot hole a hole left as a result of the removal of a knot

1.2. Cause by Abnormal Growth

1. Wind Cracks shakes or cracks on the outside of a log due to the shrinkage of the exterior surface caused byatmospherics influence.

2. Rind Galls peculiar curve swellings cause generally by the growth of layers of wood over the shump formed

by the imperfect cutting off of a branch.3. Twisted Grain of Spiral Grain caused by the twisting of the fibres due to wind.4. Upset facture of the fibres across the log so that there is very likelihood of a break occurring. Caused by

excessive compression due to bending of shock during the growth of the tree.5. Shakes caused by rapture of tissues resulting to partial or complete separation of the fibres along the grain.

- Heart shake A crack starting at the heart and extends in a radial direction (along the medullar rays) and atthe right angles to the annual rings.

- Star shakes A number of shakes occurring at or near the pith of the tree giving the appearance of a star onthe end of a piece.

- Ring/Cup shake crack developed between the growth rings either over the whole circumference or part of it.- Radial shake Split are fine, numerous and irregular. Occurs when felled timber in kept expose to sun.

6. Compression wood and Abnormal wood which formed on the lower side of branch or inclined stems of

conifers.7. Sap Stain discoloration of sap wood mainly due to fungi.8. Burr/Burl large excrescence on a tree trunk or an enlarge root stock with hilly contorted grain.

2. Defects due to Seasoning

1. Twist spiral distortion along the length of the timber.2. Cup curvature in the transverse direction of the timber.


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3. Honey Combing separation of the fibres in the interior due to drying stresses.4. Bow curvature of the timber in the direction of the timber.5. Check rupture along the grain during seasoning.6. Split separation of the fibres along the grain and extends from one end of the plank to the other.7. Compression failure buckling or collapse caused by compression.8. Case Hardening due to the unequal drying of the exterior surfaces under compression and the interior surface

under tension due to rapid drying.9. Spring cultivate of the timber in its own plane.

3. Due to Manufacturing or Use

1. Chipped/Torn Grain caused by the breaking away of timber below the surface of the dressing by the action ofthe planning tool.

2. Chip Mark indentation on the finished surfaced caused by chips.3. Wane original round surface of a tree which remains on a finished plank.4. Boxed Heart pith at the center fully enclosed within one piece in the process of conversion.5. Diagonal Grain caused due to improper sawing of wood.

Evaluation of DefectsKnots tend to weaken the timber in tension but may improve the strength in compression.Check, Splits and Shakes reduce the shearing resistance of wood.Tension Wood it has high longitudinal shrinkage tending it to warp and split.Sap Rot chances of fungal attack are high if wood has this defect if not well-seasoned.Slope of Grain lower the tensile strength parallel to the grain and the modulus of rupture which increase in thecase of radial slope of grain.Loose Grain - reduction in structural.Wane - reduce the mechanical properties and volume.Worm Hole spoil the appearance and reduce mechanical strength.Pith Pockets affect the appearance and destroy the integrity of wood.Mould essentially spoils the appearance of wood.

H. Decay of Timber

Decay usually caused by the presence of sap or by alternate dry and wet condition of timber.

Causes of decay9. Alternate moisture and dryness10. Fungi and molds11. Insects and warms12. Heat and confined air

The detection of incipient decay may be done as follows:

1. Abnormal color.2. Areas showing a range of brown colors different from the normal color of wood indicate the presence of fungus.3. Abnormal mottled appearance often indicates decay.4. Softness and brashness of woods.5. Roughness of surface.6. Few or numerous small pits and presence of soft spots of intense discoloration.

Diseases of timber1. Foxiness it disfigures the timber by reddish brown stains around the pith denoting growth in a marshy soil and

indicating the commencement of decay in a matured tree.2. Plethora disease caused by non-uniform supply of nutrients to all portions of the tree.3. Quaggywood center of the tree found to be full of shakes and clefts.

4.

Doatiness form of incipient decay.

Damage due to Fungal Attack

Fungi a system of plant organisms which live on and attack timber and caused rot and decay.

Two groups of destroyer:Bacteria smallest living organism


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Fungi are mainly responsible for the decay of timber

Life cycle of Fungus:

Control Fungal AttackThe following points are to be kept in mind with reference to rot-causing fungi:

1. The timber should not be subjected to alternate wet and drying conditions. This can be ensured by paintingor varnishing after drying the timber thoroughly.2. Where alternative wet and drying conditions are unavoidable and painting is too costly, as in the case of

railways sleepers, a proper preservative treatment should be made.3. No timber used in a structure should have sap wood present in it.4. It should be ensured that adequate ventilation is there around the timber, particularly where it is built into

masonry.

Damage due to InsectsDamage in timber by insects are quiet considerable particularly in warm countries.

Important categories of Insects1. Termites or White ants it completely excavate the wood at the center leaving the outer shell intact.2. Beetles13. Long horn beetles are small beetles 6mm to 20mm in size and mainly thrive on timber in the forest and can

attack any wood.14. Pin hole beetles are very small, 3mm to 6mm in size and also called ambrosia beetles.15. Powder post beetles are small beetles which normally attack only starchy hardwoods with large pores.16. Furniture beetles are the common beetles that attack the furniture and other wood works in the house.17. Death watch beetles (Xestobium) are beetles that varies from 6mm to 20mm in size, and chocolate brown in

color.

Control of Insect PestsSince insects do not attack and destroy the whole timber before it is apparent, it is possible to do in situ

prevention. The tunnels made by the insects further help in the deep penetration of toxic elements that are used to

destroy them.

I. Seasoning of TimberThe process by which the moisture content of timber is reduced to a suitable level depending upon the use.

Objectives of seasoning3. To reduce movement the tendency to split, warp and shrink4. To make it immune from attacks of insects

HYPHEA

MYCELIUM

FRUIT BODY

SPORE

EGG

LARVA ORCATERPILAR

PUPATIONSTAGE ORCHRYSALIS

BUTTERFLY ORMOTH


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5. To increase the strength, durability, workability and resilience6. Ta make it receptive to finish like preservatives, paints and varnish7. To reduce the weight to minimize cost of transportation8. To make the timber burn readily (if used as fuel)

Three factors that control this process: Humidity, Rate of air circulation, Temperature of the surrounding air.

Seasoning characteristics of timber

All timber does not respond to seasoning the same way. Some are very sensitive and tend to twist, warp,and check at even a slow rate of drying while other timbers do not react so violently to even higher rate of drying.

Timber Classification Depending upon their BehaviorClass A Highly refractory woodsClass B Moderate refractory woodsClass C Non-refractory woods

Methods of Seasoning

Kiln Seasoning - quicker method to the desire moisture content under highly controlled conditions.

Two main method of artificial seasoning :1. Compartment Kiln consists of closed-air tight shed in which the timber is kept. The timber remains stationary

while the environment is changed as the seasoning progresses.2. Progressive Kiln has the stack on trolleys that progressively travel through chambers that change the

conditions as it travels through the varying atmospheres.

Natural/Air Seasoning slow process and the reduction in moisture content to the desired level mat not beattainable by air seasoning is adopted.

Methods of Stacking Timber1. One in Nine Stacking Nine sleepers laid each allow gap between adjacent sleepers.2. Close Crib Stacking Solid stack without gaps with sleepers alternate layer, places in criss-cross manner,

slower rate of seasoning and reduces the air circulation.3. Open Crib Stacking Gaps between adjacent sleepers in this layer allow the more air circulation. The affect of

during in this method resembles the one and nine method.

Three Types of Air Seasoning Shed1. Shed Type 1 consists of a roof and walls on four sides with doors at ends, adjustable shutters at the top and

bottom of walls provide controlled circulation.2. Shed Type 2 consists of a roof with walls on three sides, th north side being open.3. Shed Type 3 consists of roof on a four pillars all sides being open.

Chemical Seasoning consists of immersing timber in solution of salt, also known as Salt Seasoning.Electrical Seasoning the principle is to be subject the wood by the use of plates or electrodes at the ends to anelectric current.

J. Preservation of Timber

Apart from structural wood preservation measures, there are a number of different(chemical) preservatives and processes (also known as timber treatment, lumber treatment or pressure treatment)that can extend the life of wood, timber, wood structures or engineered wood. These generally increasethe durability and resistance from being destroyed by insects or fungus.

Types of Preservatives1. Type 1 (Oil Type) Coal tar creosote with or without admixture of petroleum, coal tar, fuel oil or other suitableoils having boiling range.

2. Type 2 (Organic Type) consists of toxic substances dissolved in volatile spirits.3. Type 3 (Water Soluble leachable Type) inorganic or organic salts soluble in water.4. Type 4 (Water Soluble fixed Type) water soluble salts with fixative salt.

Characteristics of Good Preservative


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1. It should be strongly toxic to insects, fungi, etc.2. It should penetrate readily into timber.3. It should cover large surface areas with a comparatively small quantity of preservative.4. It should have no destructive influence on strength of the timber.5. It should be harmless to human being.6. It should not render the timber treated with it more flammable.7. It should be non-corrosive to metals.8. It should be pleasant in color and give an attractive appearance to the woodwork.9. It should be highly resistant to water and dampness.10. It should be economical and available readily.

Methods of Treatment:

1. Surface Application done by brushing, spraying or dipping in the preservative solution for a short period.2. Soaking timber is debarked thoroughly and submerged in the preservative solution for sufficiency long period

till absorption is obtained.3. Hot and Cold Process the timber is kept submerged in the preservative solution which is maintained in at the

temperature of 90 degrees Celsius for suitable period depending upon the change.

4. Boucherle Process carried out by attaching to the butt end of a pole, a hose is connected to the reservoir ofthe preservative at higher level.

5. Diffusion Process can be adopted in the ffg manner:18. Momentary dipping of timber in concentrated solution and close stacking under cover.19. Prolonged immersion in dilute solution and close stacking under cover.20. Application of preservatives paste over all surface of the timber and then close stacking under water.21. Injecting suitable paste into timber through incisions spread on the surface.6. Pressure or Pneumatic Processes - require great changes of pressure and are essentially commercial

processes in which a large quantity of timber is treated. 7. Full Cell Or Bethel Process this process is useful when maximum absorption of the preservative is desired. 8. Empty Cell Process aims at a maximum penetration of the preservative with minimum net retention.

a. Lawry Process

b. Rueping Process

Fire Proofing of TimberThe chemicals used in general act by producing non-flammable gasses which reduce the availability of

oxygen to the interior.22. The melting point of the chemical is low so that it melts and forms a barrier to the supply of oxygen to the inside.23. The chemical decomposes under heat, yielding non-flammable gasses that dilute the inflammable gasses. The

retards the ignition of inflammable point.24. The chemical vaporizes at sufficiently low temperature, absorbing sufficient hat so that the temperature of wood

dos not rise to decomposition point.

K. Availability and Uses of Timber

Commonly use timbers worldwide1. Teak one of the most valuable timber tree in the world. 2. Deodar non-porous wood. Commonly used for construction purposes, furniture and cabinet making, light

and heavy packing, railways sleepers and carriages. 3. Chir is a coniferous tree found in temperate regions. It is similar with deodar but is inferior in quality.4. Kail similar to chir the only difference is the color in their sapwood. Chirs sapwood is creamy white while

kails is white to pale-yellowish white. 5. Sissoo(Shishan) moderate and sized tree, having a short trunk and large brancher with round leaves. 6. Sai straight-growing upright tree with dark large leaves. 7. Mango moderate straight tree and found almost in all region in India.

Timber in Philippines

First Group:1. Banuyo large tree with a short trunk that is usually about 30 40 ft (9 12 m) long and in a diameter of 48

72 in (120 180cm).2. Dungon producing a regular or irregular bole with a merchantable length of 40 60 ft (12 18m) and a trunk

diameter of up to 100 in (40cm) above large buttresses.3. Ipil developing boles that are often short and thick, and are made up to 50ft (15m) in length.4. Molave trunk diameter is about 28in (70cm) at maturity. The wood is high in density.


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5. Narra - reached a height up to 100 ft (30cm) or more, trunk diameter of 24 36 in (60 -90 cm).6. Supa unusually wide sapwood is light grayish brown in color and is clearly demarcated from the heartwood.7. Tindalo fast growing tree. Rarely attacked by termites.

Second Group:1. Guijo very tall reaching the height of 200 ft, with straight cylindrical stems, and trunk diameter up to 72 in.2. Malugai it reached the height of 100 150 ft at maturity. Trunk diameter of 24 36 in.3. Manggachapui lighter in color of sapwood and is somewhat distinct from the heartwood.4. Narig lighter color of sapwood than heartwood and is not clearly demarcated.

Third Group:1. Amugis height of 120 ft with a trunk diameter of 24 30 in.2. Apitong tree size is reported to vary with species but heights are commonly about 100 200 ft.3. Mayapis tall tree that is sometimes buttressed often develops straight, clear trunks.4. Palosapis sapwood is pale yellow and is not distinct from the heartwood in appearance.5. Red Lauan pinkish color of sapwood and is not clearly demarcated from the heartwood.6. Tangile large and tall tree with straight, cylindrical trunks above fairly large and high buttresses.

Fourth Group:1. Almon sapwood and heartwood have the same color but is lighter and usually has grayish tinge.2. White Lauan sapwood is usually very wide, 2.5 3 in and is lighter in color than the heartwood.

Advantages of Timber in Construction1. It can be easily worked with tools and required shape can be given.2. Joints, joinery works and structural connections can be easily made in timber construction.3. This is suitable for attractive interior decorations.4. Light in weight, strong in durable if well-protected.5. Close-grained fibres and natural color of timber impact beauty to the construction.6. As timber is a heat-resistant material, the houses built of timber are warm in winter and cool in summer.7. Timber houses can easily be dismantled without getting damage and loss and can suitably be shifted from one

place to other.8. Timber construction material is economical, when it is locally available.9. Strength of timber construction is more than any other material of construction in proportion to weight.

Disadvantages of Timber in Construction1. Timber is not suitable for cyclonic weather and natural calamities.2. It is costly if it is not locally available.3. Subjected to fire risk.4. It is not suitable for dump or wet places.5. Its liable to crack, warp and decay if not properly seasoned and not treated with preservatives. 6. It needs regular care and maintenance.

8. Wood Based Products

Advantages of these materials:1. Many secondary species of timber can be extensively used for certain applications.2. All kinds of wood waste can be used.3. By their cross-grained construction, these materials have less shrinkage and are sufficiently strong.4. They can be made very aesthetic to show attractive figures on the exterior despite using inferior wood in the

interior.5. With additional plastic coatings, they can become functionally very superior.6. They have better insulation properties.

VeneersVeneers are thin sheets of wood, 0.4 mm to 6mm thick. Obtained by different knife cutting processes.

Veneers can be classified as:25. Rotary Veneers26. Sliced Veneers


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PlywoodPlywood is made up of veneers that glued together. The outside layers of plywood are called faces, the

central layer is called core, and those between the faces and core are called cross bands.

The advantages of plywood are:1. It has a good strength both across as well as along the grains unlike wood, from which it is made, have greater

stiffness and strength along the grain that across it. The more the number of piles, the more uniform is strengthalong the across grains.

2. Wood shrinks and expands more across grain as it loses or absorbs water. In plywood, because of the cross-grained construction, the tendency to shrink and swell is considerable reduced.

3. Plywood has better splitting resistance due to grains in adjacent layers running at right angles and nailing thescrewing even close to the edges is safe. It has also greater shock resistance than ordinary wood.

4. Plywood can be easily bent to a curvature limited by the tensile and compressive strength of the outer piles.5. The face piles made of different heartwoods show great aesthetic variety in grain pattern and color. These can

also be made artificially by sand blasting or etching.

Plywood Grades and Sizes

Plywood for general purposes shall be on the following grades depending upon the type of adhesive used forbonding of the veneers:1. Boiling water proof (BWP) grade2. Boiling water resistant (BWR) grade3. Warm water resistant (WWR) grade4. Cold water resistant (CWR) grade*The classification of plywood for general purposes shall be of the types like AA, AB, AC, AD, BB, BC, BD, CC, CD,and DD base on their quality of surfaces.Permissible defects per square meter given by (no. of defects) A=3, B=6, C=9, D=no limit.

THICKNESS

BOARD THICKNESS (mm)

3-ply 3,4 5,6

5-ply 5,6 8,9

Above 11-ply As ordered

Dimensions and Tolerance

(cm x cm) (cm x cm)240x120 180x90

210x90 150x120210x120 180x90210x90 120x120180x120 90x90

The dimensions of plywood boards should be specified as the first dimension to represent the length to the grain onthe faces, the second the width and the thickness.

Dimension Nominal size Tolerance(a) Length Up to and including 120cm

Above 120cm

+3mm0mm

+6mm0mm

(b) Width Up to and including 90cm

Above 90cm

+3mm0mm

+6mm0mm

(c) Thickness Up to and including 5mm6 to 9mm Above 9mm

10%7%5%

Hardboard

BOARD THICKNESS (mm)7-ply 9,12 15,16

11-ply 19,22 25


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Hardboard is manufactured from raw materials like wood waste obtained from saw mills, veneermanufacture, furniture making, etc.

3 Types of Hardboard1. Medium Hardboard which is homogeneous fiber building board having a density exceeding 480kg/m2 2. Normal Hardboard is one with the density exceeding 800kg/m2 but not exceeding 1200kg/m2 3. Tempered Hardboard- is a fiber board which is especially treated to give increased density strength and

water resistance.Type of Board Average Density

g/cm3

Thickness

mm

Bending Strength(modulus of rapture)

AverageMPa

Water absorption(by mass) after

immersion, max.%

Medium Board Min. 0.35

Max. 0.80

691012

6 40

StandardHardboard

More than 0.80 34

567

30

30

40

30

TemperedHardBoard

- 34569

50 20

Typemm

Nominal Thicknessmm

Tolerance

Medium Hardboard 681012

0.50.70.70.9

Standard Hardboard 345

69

0.4

0.50.5

Width and Length of HardboardsType Width (m) Tolerance on width

(mm)Length (m) Tolerance on Length

(mm)Medium HardboardStandard HardboardTempered Hardboard

1.21.21.2

31.2, 1.8, 2.4, 3.0,

3.6, 4.8, 5.5 5

Particle BoardIt is a board manufactured from particles of wood or other lingo cellulose materials which are agglomerated,

formed and pressed together by the use of an organic binder together with one or more agents such as heat,pressure, moisture, etc.

Dimensions and ToleranceThe size of particle boards in mm should be as follows.

Length(mm) : 4850, 3650, 3000, 2750, 2400, 2100, 1800, 1500, 1200,1000Width(mm) : 1850, 1800, 1500, 1200, 1000, 900, 600, 450Thickness(mm) : 6, 9, 12, 15, 19, 22, 25, 27, 30, 35, 40

Tolerance Length : 8mm


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Width : 8mThickness : 2.5mm Above 25mm : 2.5mmUp to 25mm : 5mm

Density : Mean density of particle boards shall be between 500-900kg/m2

Block boards These boards are extensively used for construction of railway carriages, bus bodies, and marine and river

crafts and for furniture making, partitions, paneling, prefabricated houses, etc.Block board grading is done as follows

Grade 1: Exterior for bus bodies, railway coaches, pre-fabricated houses, etc.Grade 2: Interior grade for furniture, partitions, paneling ceiling, etc.

DimensionsThickness (mm) : 12, 16, 20, 25, 30, 32, 35, 38, 40, 45, 50Length (mm) : 300, 270, 240, 210, 180, 150, 120Width (mm) : 150, 120, 90

Other boards:

Batten boardThe core is made up of strips of wood usually 8cm wide, each laid separately or glued to form a slab.

Lamin BoardBoard having one core of strips, each not exceeding 7mm in thickness glued together to form slab.

Adhesives

Synthetic Resins A synthetic resin adhesive has a composition consisting substantially of phelonic (obtained from the reaction

of phenol with an aldehyde) or amino plastic resins(obtained from the reaction of urea, thio-urea, melamine, with

formaldehyde) including a hardening agents, fortifier, filler or extender.

Depending upon thie use, they may be also be classified as:1. Gap filling adhesive suitable for use in situations where the surfaces to be joined may or may not be

continuous contact.2. Close contact adhesive where the surface to be joined can be brought into close contact by means of

adequate pressure. Animal Glue

Generally obtained from hides and bones of animals.

Vegetable GlueIt is made from natural grains and starch-bearing roots, potato, corn, wheat with acids like NaOH.


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NATURAL FORCES:

Oval Knot Spike Knot Branched Knot Live Knot Dead Knot

Loose and Tight Knot Knot Cluster Knot Hole Wind Cracks

Twisted Grain Upset Shakes

Sapstain

Burr Coarse Grain Druxiness

DUE TO SEASONING:

Split Honey Combing Check Warp

Case Hardened

Diseases of Timber


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timber (written report) for civil eng'g

Documents