1. Classification and Structure of Wood 2. Properties of …civil.utm.my/mohammad/files/2012/09/K1-Kayu...Balau Merah Merbau Resak Bekak Berangan Dedali Kapur Bayur Bitangor Durian

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Department of Structures and Materials1

Lecturer:

Prof . Dr. Mohammad IsmailFaculty of Civil Engineering, UTM-Skudai,

Johor Darul Ta’zim,

MALAYSIA

December 6, 2013

TIMBER

1. Classification and Structure of Wood

2. Properties of Timber

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1. Classification and Structure of Wood

2. Properties of Timber

Prof Madya Dr. Mohammad IsmailFaculty of Civil Engineering, UTM-Skudai,

Johor Darul Ta’zim, MALAYSIA

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LEARNING OUTCOME

• At the end of the lecture, student should understand:

� General knowledge on timber

� Structure of wood

� Classification

� Properties

� Application

� Factors affecting strength

� Seasoning and preservative

� Timber product

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INTRODUCTION

• One of the oldest known construction materials

• Employed in many application

� Shipbuilding, bridges, railroad ties, flooring, cabinets,

nails

� Simple in fabrication, light, reuseable, insulation from

heat, electricity and sound, pleasing appearance,

� Resistance to oxidation, acid attack, salt water and

environmental compatibility

• Many wood product have been introduced

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STRUCTURE OF

WOOD


Growth Structures

Trees composed of three

discrete parts:

the roots,

the trunk and

the crown

which has a function to

perform

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Spread the root acts as

anchorage

Root:absorbs moisture and minerals from soil,

transferred via trunk to the crown

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• Trunk:� Provides rigidity and mechanical strength to maintain

the crown of leaves

� Provides transport system for moisture

� Store the sap and convert it to the form needed for

growth

• Crown� Capture as much energy from sunlight, to enable

photosynthesis process

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Bark

Relatively thin, rough, and

dense covering surround the

trunk

Cambium

A thin layer inside the bark, in

which the growth of wood takes

place continuously – eventually

results in growth ring (annual

ring)

Pith

Centre of the log, surrounded

by the annual rings, the number

of which approximately

represents the age of the tree

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• Heartwood

� Dead tissue/cell, provide mechanical support to the tree

� Darker, drier, and harder than the outer part

• Sapwood

� Contain living cell, density different with heartwood rather small

� Less durable and more permeable

� Impregnation with preservatives is easier

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Cell Structure of Wood

•Cells capable of carrying on the life process, make up

the structural element of wood

•Dry wood cells may be empty or partly filled with

deposits such as gums and resins

•Wood grain refers to the

arrangement of wood fibers

•Each cell has a hollow centre called

lumen or cell cavity

•Majority of wood cells are considerably elongated, commonly

called fibers

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CLASSIFICATION OF TIMBER

All commercial timbers classified into two groups, softwood and hardwood. The term hard and soft refer to botanical origin and not necessarily indicate the relative hardness or density of species

• Softwood

� Needle like leaves generally evergreen

• Hardwood

� Trees with broad leaves

� Most tropical hardwoods retain their leaves all year round

� In Malaysia hardwoods further classified into high density, medium and low

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High density Medium Low density

Balau 1000 kg/m3

Balau Merah 910

Bitis 1100

Chengal 980

Merbau

Resak

Giam

Keranji

Kapur 780kg/m3

Kasai

Kelat

Kempas 910

Keruing 830

Rengas

Simpoh

Tualang

Bintagor 710 kg/m3

Durian

Jelutong

Kedondong

Meranti 700 kg/m3

Pulai

Nyatoh 750

Ramin

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No Commercial

Name

Vernicular

Name

Botanical Name

1.

2.

3.

4.

Kempas

Merawan

Keruing

Nyatoh

Kempas

Merawan Jangkang

Keruing Bulu

Nyatoh Ketiau

Koompassia Malaccensis

Hopea nervosa

Dipterocarpus baudil

Ganua motleyana

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TAKE 5


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PHYSICAL PROPERTIES

Two most important physical properties are moisture

content and specific gravity

• Moisture Content

� Timber is hygroscopic, meaning it has affinity for water

in both liquid and vapour forms

� The ability to absorb or lose moisture depends on the

environmental such as temperature and humidity

� Moisture content = (weight of water/oven dry weight) x 100

� = mass of water present in a sample x 100

mass of sample when oven dry

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Department of Structures and Materials, Faculty of Civil

Engineering

UTM

16

Moisture content of newly cut timber is between 30-200% depend on the timber types and season

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Fibre Saturation PointAs wood dries, water is driven off the cell cavities. A point is reached when the cavities contain only air and the cell walls are saturated with water which is called Fibre Saturation Point

Saturation point

vary 24-30%,

depend on

species

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Density and Specific gravity

� Green wood is heavier than dry wood. Green sapwood

is heavier than green heartwood, whereas dry

heartwood is heavier than dry sapwood

� Density is defined – mass or weight per unit volume.

Related to porosity, or proportion of voids

� Both density and volume of wood vary with moisture

content

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• Wood density = (ovendry weight)/(vol. of green wood)

• Specific gravity = Ws (ovendry weight)/wwV (density of water and vol. of green wood)

• The specific gravity determined in three conditions

� Green

� Air-dry

� Oven-dry

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Movements in Service

• Timber in service experience movement or strain due to applied loads, changes in moisture content or changes in temperature

• Coefficient of thermal expansion

� Across grain 30-70 x 10-6 K-1

� Along the grain 3-6 x 10-6 K-1

• The deformation response of timber to load is quite complex. Under low level of load applied for short duration, timber deforms elastically

• Time-dependent deformation is referred to as creep

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TAKE 5

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MECHANICAL PROPERTIES

Wood has unique, independent properties in the

three mutually perpendicular axis: Longitudinal,

tangential, and radial

• Modulus of Elasticity

� MOE in the longitudinal direction is the highest,

depending on species

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Compressive Strength

• Strength parallel to the grain much higher than that

perpendicular to the grain

• Column, post, and members of a truss are

subjected to axial loads parallel to the grain of the

wood

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Bending/Flexural Strength

• Timber has very good bending strength, because

of this and its lightness, it remains one of the

important flexural materials in light construction

• It is used for joist, rafters, headers and other

members that are subjected to bending moments

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Tensile Strength

• Tensile strength parallel to grain is about 2 or 4

times the compressive strength parallel to grain

� Knot greatly reduced the tensile strength

• Tensile strength perpendicular to the grain is very

small

� Knot, shakes, and checks further reduce tensile

strength perpendicular to the grain

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Shear Strength

• A flexural member is always subjected to shear

forces.

• The resulting horizontal shear stress at the neutral

axis of a wood beam may cause shear failure

• Defects such as knot and shakes decrease the area

under shear, and the shear strength of lumber with

these defects is lower than that of clear wood

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• MECHANICAL PROPERTIES increase linearly with specific gravity and decrease with increase in moisture content

• Beyond the fiber saturation point the mechanical properties remain independent of changes in moisture content

• Knot weaken the lumber, and at section containing knots, most mechanical properties are lower than those in clear wood

� The effect of knots are more on axial tensile strength, less on bending strength, and very little on axial compressive strength

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GRADING

� Stress-grading rules incorporate a sorting criterion, a set of allowable values (mechanical properties for engineering design), and a grade name. Up to six allowable properties are associated with a stress grade

�Modulus of elasticity, tensile stress parallel to grain, compressive stress parallel to grain, compressive stress perpendicular to grain, shear stress parallel to grain and bending stress

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• Physical and mechanical properties of wood differ

from species to species and also within each

species

� It is influenced by condition of growth (climate,

density of surrounding forest, character of soil,

moisture content and defect)

• To simplify the structural design the species are

divided into several group

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Group

A

Group

B

Group

C

Group

DLasak

semulajadi

Need

curing

Lasak

semulajadi

Need

curing

Need

curing

Need

curing

Balau

Bitis

Chengal

Keranji

Kandis

Kempas

Kulim

Tualang

Balau

Merah

Merbau

Resak

Bekak

Berangan

Dedali

Kapur

Bayur

Bitangor

Durian

Kayu getah

Ara

Damar minyak

Geronggang

Jelutong

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FACTORS AFFECTING

STRENGTH

Moisture Content

• Main factor that affect strength

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Density and Specific Density

• This properties can be taken as an index to the

strength of timber.

• High strength timber means that the cell wall is

thick and the strength of timber is depend on the

thickness of the cell wall

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Defect

• The existence of defect such as knot, sloping

grain, cracks, fissures, wane, distortions, insect

damage, fungal decay, reaction wood and sapwood

will contribute to the weakness of timber

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ADVANTAGE AND

DISADVANTAGE OF TIMBER

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Thank You

1. Classification and Structure of Wood 2. Properties of …civil.utm.my/mohammad/files/2012/09/K1-Kayu...Balau Merah Merbau Resak Bekak Berangan Dedali Kapur Bayur Bitangor Durian

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