TIMBER / WOODTIMBER / WOOD

Timber StructureTimber Structure

TIMBERTIMBER

Wood is one of the Wood is one of the oldest known oldest known materials used in materials used in constructionconstruction

It is the only It is the only naturally renewable naturally renewable building materialbuilding material

Species of wood in Species of wood in Malaysia – more Malaysia – more than 2500than 2500

Names of woodNames of wood

Vernacular – Vernacular – given by given by the local community e.g. the local community e.g. Cengal – Cengai or Cengal – Cengai or PenakPenak

Botanical – Botanical – given by given by botanical member e.g. botanical member e.g. Balanorcarpus Heimeii Balanorcarpus Heimeii (Cengal)(Cengal)

Commerce – Commerce – given for given for trading e.g. Cengaltrading e.g. Cengal

Design ConceptDesign Concept

Wood popular for Lightweight Wood popular for Lightweight ConstructionConstruction

Simplicity in fabricationSimplicity in fabricationLightnessLightnessReusabilityReusabilityMaterial availabilityMaterial availabilitySimpler connectionsSimpler connectionsEnvironmental Environmental compatibilitycompatibilityAdaptability to Adaptability to modifications and modifications and remodelingremodeling

Wood in ConstructionWood in Construction

In the form of lumber – In the form of lumber – pieces of wood cut from tree pieces of wood cut from tree trunkstrunks

Wood products – Wood products – glue glue laminated timber, pressed laminated timber, pressed wood, chip board etc.wood, chip board etc.

Tree trunks → Log → LumberTree trunks → Log → Lumber

USE OF TIMBERUSE OF TIMBER

Classification of WoodClassification of Wood

Hardwood – Hardwood – tree has broad tree has broad leaves, seeds with hard leaves, seeds with hard shell, mostly grow in shell, mostly grow in tropical climate e.g. jatitropical climate e.g. jati

Softwood – Softwood – species that species that has needlelike leaves, has needlelike leaves, seed without hard shell, seed without hard shell, mostly grow in mostly grow in seasonal climate e.g. seasonal climate e.g. Pine treesPine trees

This classification is based on the Botanical aspects, not the hardness of the woodThis classification is based on the Botanical aspects, not the hardness of the wood

Cont.Cont.

Generally, most Generally, most hardwoods are harder to hardwoods are harder to work with than softwoodwork with than softwood

The term The term hardwoodhardwood and and softwoodsoftwood do not do not necessarily indicate the necessarily indicate the relative hardness or relative hardness or density between the two density between the two categoriescategories

Growth Ring/Annual RingGrowth Ring/Annual Ring

Growth ringGrowth ring = = earlywood + latewoodearlywood + latewood

Earlywood – Earlywood – cell cell with larger opening, with larger opening, during winterduring winter

Latewood – Latewood – cell with cell with smaller opening, smaller opening, during summerduring summer

Growth RingGrowth Ring

Growth RingGrowth Ring

Wood CellWood Cell

Cell Cavity

Cell Wall

Wood CellWood Cell

Forest Research Institute of Malaysia Forest Research Institute of Malaysia (FRIM)(FRIM)

Hardwood in Malaysia – classified Hardwood in Malaysia – classified based on the based on the density and durabilitydensity and durability

Three categoriesThree categoriesHeavyweight hardwoodHeavyweight hardwood – density – density greater than 880 kg/mgreater than 880 kg/m33, very durable , very durable e.g. balau, cengale.g. balau, cengalNormal/Intermediate weight hardwoodNormal/Intermediate weight hardwood – – density in the range of 720 to 880 kg/mdensity in the range of 720 to 880 kg/m33, , less durable compared to heavyweight less durable compared to heavyweight hardwood, e.g. kempas, keruinghardwood, e.g. kempas, keruingLightweight hardwoodLightweight hardwood – density less – density less than 720 kg/mthan 720 kg/m33, not durable except , not durable except being preserved, e.g. merantibeing preserved, e.g. meranti

Properties of WoodProperties of Wood

The most important properties The most important properties that affect strength and durability that affect strength and durability of wood are:of wood are:

1)1) Moisture contentMoisture content

2)2) Specific gravitySpecific gravity

Effect of Moisture ContentEffect of Moisture Content

Moisture contentMoisture content

The weight of water in wood expressed The weight of water in wood expressed as a percentage of its oven-dry weightas a percentage of its oven-dry weight

Determining moisture content – oven or Determining moisture content – oven or moisture metermoisture meter

Wood is a hygroscopic substance – it Wood is a hygroscopic substance – it can absorb water/moisturecan absorb water/moisture

The ability to absorb or lose The ability to absorb or lose moisture depends on moisture depends on

environmental conditionsenvironmental conditions

Relative HumidityRelative Humidity

TemperatureTemperature

Variations of moisture content in Variations of moisture content in living treesliving trees

Moisture content 400%, specific gravity Moisture content 400%, specific gravity 0.20.2

Moisture content 100%, specific gravity Moisture content 100%, specific gravity 1.151.15

Typical trees contain water about two Typical trees contain water about two times the weight of its solid materialtimes the weight of its solid material

Water exist in woodWater exist in wood

FREE WATER – FREE WATER – in the cell in the cell cavitycavityBOUND or ADSORBED BOUND or ADSORBED WATER – WATER – in the cell wallin the cell wallThe amount of water in cell The amount of water in cell cavities varies with the cavities varies with the amount of dryingamount of dryingLumber has moisture Lumber has moisture generally in excess of 50% generally in excess of 50% at the time of its at the time of its manufacturemanufacture

FIBRE SATURETION POINT (FSP)FIBRE SATURETION POINT (FSP)

FSP is when the FSP is when the cell cavitycell cavity contains only air and the contains only air and the cell cell wallwall is saturated with water is saturated with water

Moisture content at FSP can Moisture content at FSP can vary from vary from 20 to 30%20 to 30% depending on the species ofdepending on the species of woodwood

Effect of Moisture ContentEffect of Moisture Content

Above FSP – Above FSP – volume volume and mechanical and mechanical properties unchanged properties unchanged or constant, although or constant, although the density of wood the density of wood decreasedecrease

Below FSP – Below FSP – wood wood shrink and strength shrink and strength increaseincrease

Amount of water in cell will affect:Amount of water in cell will affect:

Physical propertiesPhysical properties

Mechanical Mechanical propertiesproperties

DurabilityDurability

Dimensional Dimensional stabilitystability

Equilibrium Moisture ContentEquilibrium Moisture Content

The moisture content at The moisture content at which wood neither gains nor which wood neither gains nor loses moisture to the loses moisture to the surroundingsurrounding

Its values range between 5 Its values range between 5 and 17% at 70 °C and relative and 17% at 70 °C and relative humidity between 2 to 80%humidity between 2 to 80%

Specific GravitySpecific Gravity

Is the ratio of the weight of wood Is the ratio of the weight of wood (oven-dry) to the weight of an equal (oven-dry) to the weight of an equal volume of watervolume of water

Specific Gravity = (WSpecific Gravity = (Wss)/(w)/(wwwV)V)

WWss – oven-dry weight – oven-dry weight

wwww – density of water – density of water

V – volume of (green) woodV – volume of (green) wood

Wood is composed of:Wood is composed of:

Solid matterSolid matter

WaterWater

AirAir

Volume = VVolume = Vsolidsolid + V + Vwaterwater + V + Vairair

Specific gravitySpecific gravity

Determined in three conditions:Determined in three conditions:

1)1) Green (moisture content in excess Green (moisture content in excess of 19%)of 19%)

2)2) Air-dry (moisture content – 12%)Air-dry (moisture content – 12%)

3)3) Oven-dry (moisture content 0%)Oven-dry (moisture content 0%)

Cont.Cont.

Strength and stiffness of wood increase with Strength and stiffness of wood increase with the increase in specific gravitythe increase in specific gravity

Physical and mechanical properties of wood Physical and mechanical properties of wood are related to specific gravityare related to specific gravity

Density of wood is defined as the mass or Density of wood is defined as the mass or weight per unit volumeweight per unit volume

It is directly related to porosity or proportion It is directly related to porosity or proportion of voids and calculated using the total weight of voids and calculated using the total weight of woodof wood

PROPERTIES OF WOODPROPERTIES OF WOOD

Strength Strength is one of is one of the main properties the main properties that determines the that determines the suitability of wood suitability of wood in constructionin construction

Strength – Strength – the the ability of material to ability of material to resist external load resist external load without failurewithout failure

Strength of TimberStrength of Timber

Tensile strengthTensile strength

Compressive strengthCompressive strength

Flexural strengthFlexural strength

Shear strength hardnessShear strength hardness

Impact strengthImpact strength

Splitting strengthSplitting strength

Loading ConditionLoading Condition

Strength of woodStrength of wood

Varies according to the direction of Varies according to the direction of the applied loadthe applied load

1)1) Parallel to grainsParallel to grains

2)2) Perpendicular to grainsPerpendicular to grains

Wood grains – direction of wood Wood grains – direction of wood fibre with respect to the main axis fibre with respect to the main axis of woodof wood

Wood GrainsWood Grains

Straight grainStraight grain

Edge grainEdge grain

Flat grainFlat grain

Cross grainCross grain

Spiral grainSpiral grain

Diagonal grainDiagonal grain

The slope of grains will The slope of grains will affect the strength of affect the strength of woodwood

Effect of Wood GrainEffect of Wood Grain

Cont.Cont.

Tensile strength and Tensile strength and compressive strengths compressive strengths parallel to wood grains parallel to wood grains are higher than are higher than perpendicular to wood perpendicular to wood grains.grains.Compressive strength Compressive strength perpendicular to wood perpendicular to wood grains is between 12 and grains is between 12 and 18% of compressive 18% of compressive strength to wood grainsstrength to wood grains

Tensile strength parallel Tensile strength parallel to wood grains is to wood grains is approximately 2 to 4 approximately 2 to 4 times than compressive times than compressive strength parallel to strength parallel to wood grainswood grains

Shear strength Shear strength perpendicular to wood perpendicular to wood grains is higher than grains is higher than parallel to wood grains parallel to wood grains

Cont.Cont.

Hardness of wood is Hardness of wood is generally defined as generally defined as how easy the wood to how easy the wood to be work with i.e. cut, be work with i.e. cut, nailednailed

It depends on the It depends on the density, stiffness, and density, stiffness, and bonding between wood bonding between wood fibresfibres

Impact strength – Impact strength – the ability of wood the ability of wood to absorb sudden to absorb sudden external loadexternal load

It depends on the It depends on the hardness, elasticity, hardness, elasticity, plasticity of woodplasticity of wood

FACTORS AFFECTING STRENGTH FACTORS AFFECTING STRENGTH AND DURABILITY OF TIMBERAND DURABILITY OF TIMBER

Moisture contentMoisture content

DensityDensity

Wood grainsWood grains

DefectsDefects

Preservative Preservative TreatmentTreatment

Moisture ContentMoisture Content

Higher moisture Higher moisture content will reduce content will reduce the strength and the strength and durability of wooddurability of wood

Moisture will cause Moisture will cause wood to decaywood to decay

DensityDensity

Wood with higher Wood with higher density will have density will have higher compressive higher compressive strength and better strength and better durability durability due to due to dense microstructuredense microstructure

Wood DefectsWood Defects

Any irregularities in the Any irregularities in the structure of wood or structure of wood or lumber that will reduce lumber that will reduce the strength and the strength and durability durability

Types of defect:Types of defect:

1)1) Natural defectNatural defect

2)2) Defect during processingDefect during processing

3)3) Due to insects or fungusDue to insects or fungus

Natural DefectsNatural Defects

Natural DefectsNatural Defects

Design ConsiderationDesign Consideration

Effect of DefectEffect of Defect

Processing DefectsProcessing Defects

Generally is due to improper drying methodsGenerally is due to improper drying methods

Insects and FungusInsects and Fungus

Wood destroying insects – Wood destroying insects – termites, pin-hole borers, termites, pin-hole borers, beetlesbeetles

Fungi – Fungi – brown rot, white rotbrown rot, white rot

Conditions for fungal growthConditions for fungal growth

1)1) Proper temperatureProper temperature

2)2) Moisture greater than 19%Moisture greater than 19%

3)3) OxygenOxygen

4)4) Food (wood fibre)Food (wood fibre)

SEASONING OF WOODSEASONING OF WOOD

The process of controlled drying of The process of controlled drying of lumber (water in cell cavity and lumber (water in cell cavity and wall) to increase its structural wall) to increase its structural propertiesproperties

Reduction in moisture content:Reduction in moisture content:1)1) Increase strengthIncrease strength2)2) Reduce shrinkageReduce shrinkage3)3) Reduction in weightReduction in weight4)4) More durableMore durable

Methods of dryingMethods of drying

Air drying – Air drying – drying drying naturallynaturally

Kiln/Oven drying – Kiln/Oven drying – controlled drying controlled drying (temperatures and (temperatures and humidities)humidities)

Stacking lumberStacking lumber

Factors Affecting Drying ProcessFactors Affecting Drying Process

TemperatureTemperature

Relative humidityRelative humidity

Air circulationAir circulation

Duration of dryingDuration of drying

Types of wood – softwood, Types of wood – softwood, hardwoodhardwood

Size of lumberSize of lumber

Surrounding environmentSurrounding environment

Stacking methodStacking method

Air-drying vs Oven dryingAir-drying vs Oven drying

Preservative TreatmentPreservative Treatment

Is the process of Is the process of introducing or injecting introducing or injecting special chemicals into special chemicals into wood cell by special wood cell by special techniquestechniques

The purpose is to prevent The purpose is to prevent the destruction from fungi the destruction from fungi and insects and to inhibit and insects and to inhibit combustion combustion

Classes of Wood PreservativesClasses of Wood Preservatives

Creosote oilCreosote oil

Water-borne wood preservativesWater-borne wood preservatives

Light organic solvent preservativesLight organic solvent preservatives

It is important that the preservatives It is important that the preservatives must penetrate into the wood and to must penetrate into the wood and to such extent it is effectively protect the such extent it is effectively protect the woodwood

Attributes of Ideal Wood Attributes of Ideal Wood PreservativesPreservatives

Easy penetration into wood cellEasy penetration into wood cellPermanent in the wood cellPermanent in the wood cellToxic to insect and fungiToxic to insect and fungiSafe to handleSafe to handleColourlessColourlessCompatible with coatings and Compatible with coatings and finishesfinishesCheapCheap

Ease of Injecting PreservativesEase of Injecting Preservatives

Wood densityWood density

Microstructure of woodMicrostructure of wood

Chemical composition of cell Chemical composition of cell wallwall

Size of lumberSize of lumber

Moisture contentMoisture content

Methods of Treatment ProcessMethods of Treatment Process

Non-Pressure MethodNon-Pressure MethodBrushingBrushingImmersion Immersion Hot and cold open tank Hot and cold open tank treatmenttreatmentPressure TreatmentsPressure Treatments

1)1) Full cellFull cell2)2) Empty cellEmpty cell

Cont.Cont.

The only method to achieve any The only method to achieve any worthwhile degree of penetration is by worthwhile degree of penetration is by way of way of pressure treatmentpressure treatment

BrushingBrushing – not very effective, chemical – not very effective, chemical will not be able to penetrate into wood will not be able to penetrate into wood cell, need to repeat the processcell, need to repeat the process

ImmersionImmersion

Cold immersion – lumber is immersed in Cold immersion – lumber is immersed in tank for few weekstank for few weeksHot immersion – immersed in tank at Hot immersion – immersed in tank at higher temperature 90 °Chigher temperature 90 °C Hot-Cold immersion – immersed in tank at Hot-Cold immersion – immersed in tank at 90 °C, during heating air in cell cavity will 90 °C, during heating air in cell cavity will expand and pushed out, during cooling expand and pushed out, during cooling the cell will shrink and absorb the the cell will shrink and absorb the chemicalchemical

Pressure (full cell)Pressure (full cell)

Lumber is put in containerLumber is put in containerHalf vacuum (to pull out air)Half vacuum (to pull out air)Spray hot chemical, increase pressure Spray hot chemical, increase pressure (chemical enters wood cell)(chemical enters wood cell)Half vacuum to push out extra chemical from Half vacuum to push out extra chemical from the cellthe cellCell wall and cavity filled with chemicalCell wall and cavity filled with chemicalSuitable for construction in damp soilSuitable for construction in damp soilIn buildings, chemical may leach outIn buildings, chemical may leach out

Pressure (empty cell)Pressure (empty cell)

Lumber placed in containerLumber placed in containerApply pressure (compressed the air)Apply pressure (compressed the air)Spray chemicalSpray chemicalIncrease pressure (forcing chemical to Increase pressure (forcing chemical to penetrate into cell wall but air in cell cavity is penetrate into cell wall but air in cell cavity is compressed)compressed)Reduce pressure, half vacuum, air in cell Reduce pressure, half vacuum, air in cell cavity will expand pushing out extra cavity will expand pushing out extra chemicalchemicalCell wall filled with chemical but cell cavity is Cell wall filled with chemical but cell cavity is emptyemptyMore economical, cleaner lumberMore economical, cleaner lumber

TIMBER STRESS GRADETIMBER STRESS GRADE

Divided into two Divided into two categories:categories:

Wet condition – Wet condition – moisture greater moisture greater than 19%than 19%

Air-dry condition – Air-dry condition – moisture equal to or moisture equal to or less than 19%less than 19%

Design PurposesDesign PurposesFRIM divides stress timber into several FRIM divides stress timber into several gradesgrades

Basic stress – Basic stress – stress that can be sustained stress that can be sustained by timber without failureby timber without failure

GradeGrade Design stressDesign stress

SelectedSelected 80% of basic stress80% of basic stress

ParticularParticular 63% of basic stress63% of basic stress

GeneralGeneral 50% of basic stress50% of basic stress

Strength of TimberStrength of Timber

Divided into four groups i.e. Divided into four groups i.e. A, B, A, B, C, and DC, and D

Based on strengthBased on strength

Selection of timber Selection of timber based on based on strengthstrength from different groups from different groups

MANNER OF CUTTING A LOGMANNER OF CUTTING A LOG

The method of cutting a log will affect The method of cutting a log will affect shrinkageshrinkageShrinkage occurs in three mutually Shrinkage occurs in three mutually perpendicular directions:perpendicular directions:

1)1) Along its axisAlong its axis2)2) Along a radial directionAlong a radial direction3)3) Along tangent to the radiusAlong tangent to the radius

Tangential shrinkage Tangential shrinkage is the highest, about is the highest, about two times the radial shrinkagetwo times the radial shrinkageThe longitudinal shrinkage The longitudinal shrinkage is negligibleis negligible

WOOD PRODUCTSWOOD PRODUCTS

Wood in construction Wood in construction can be divided into two can be divided into two formsforms

1)1) In the form of lumberIn the form of lumber

2)2) In the form of wood-In the form of wood-based panel based panel

Two types of panels: Two types of panels: veneered panels and veneered panels and non-veneered panelsnon-veneered panels

PanelsPanelsVeneered panels – Veneered panels – also called plywood, also called plywood, made from thin sheet of woodmade from thin sheet of woodNon-veneered panels – Non-veneered panels – manufactured manufactured from wood particles or fibresfrom wood particles or fibres

Used for Used for structuralstructural applications such applications such as floor and wall panels, as floor and wall panels, non-structuralnon-structural applications such as in furniture and applications such as in furniture and cabinetscabinets

Wood-Based ProductsWood-Based Products

Manufactured by Manufactured by bonding together bonding together using using resin under resin under heat and pressureheat and pressure

Non-Veneered PanelsNon-Veneered Panels

Divided into two major Divided into two major categories:categories:

ParticleboardsParticleboards

FibreboardsFibreboards

ParticleboardParticleboard

Manufactured from Manufactured from discrete discrete pieces of wood pieces of wood particles particles (chipboard, flakeboard, splinterboard),(chipboard, flakeboard, splinterboard), combined with a synthetic combined with a synthetic resinresin or glue, bonded or glue, bonded together together under heat and pressureunder heat and pressure in a hot press in a hot press in which an entire interparticle bond is createdin which an entire interparticle bond is created

ParticlesParticles – piece of wood smaller than veneer – piece of wood smaller than veneer sheets but larger than wood fibresheets but larger than wood fibre

ClassificationsClassifications

Low-density particleboard – Low-density particleboard – density 590 density 590 kg/mkg/m33 and specific gravity of 0.59 and specific gravity of 0.59Medium-density particleboard – Medium-density particleboard – density density between 590 and 880 kg/mbetween 590 and 880 kg/m33 and specific and specific gravity between 0.59 and 0.80gravity between 0.59 and 0.80High-density particle board – High-density particle board – density density greater than 800 kg/mgreater than 800 kg/m33 and specific and specific gravity of 0.80gravity of 0.80

FibreboardFibreboard

Is a generic term for a Is a generic term for a homogeneous panel made homogeneous panel made from from wood fibreswood fibres

Fibreboard panels have Fibreboard panels have density between 160 and 500 density between 160 and 500 kg/mkg/m33, and specific gravity , and specific gravity between 0.16 and 0.50 between 0.16 and 0.50

Cont.Cont.

Veneer, plywood, and Veneer, plywood, and blockboard are blockboard are natural wood panelsnatural wood panels

Particleboard and Particleboard and fibre building board – fibre building board – are reconstituted are reconstituted wood panels which wood panels which are manufactured are manufactured mainly from mainly from various various wood wasteswood wastes

Wood PlyWood Ply

PlywoodPlywood

Is a panel comprising an assembly of plies Is a panel comprising an assembly of plies bonded togetherbonded together

Glulam or Glue-Laminated TimberGlulam or Glue-Laminated Timber

Consists of Consists of sawn sawn lumber laminations lumber laminations bonded with an bonded with an adhesiveadhesive so that the so that the grain of all laminations grain of all laminations runs parallel with the runs parallel with the long directionlong direction

Can be manufactured Can be manufactured in a in a variety of shapes variety of shapes and sizesand sizes

GlulamGlulam

Structural SectionStructural Section

Application of TimberApplication of Timber

Structural – Structural – column, beam, trusscolumn, beam, truss

Non-structural – Non-structural – frame, partitionframe, partition

Application in ConstructionApplication in Construction

Floor TileFloor Tile

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