Mdulus of Rapture

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DECLARATION OF THESIS / UNDERGRADUATE PROJECT PAPER AND COPYRIGHT

Authors full name : LIM CHIH WEN

Date of b irth : 29th NOVEMBER 1984

Title : BENDING BEHAVIOUR OF THE TIMBER BEAMS STRENGTHENED

WITH FIBRE REINFORCED POLYMER (FRP)

Ac adem ic Session: 2007 / 2008

I dec lare t ha t th is the sis is c lassified as :

I ac know ledged tha t Universiti Tekno log i Ma laysia reserves the right as follows :

1. The the sis is the p roperty o f Universiti Tekno log i Ma laysia.2. The Library of Universiti Tekno logi M a laysia has the righ t to ma ke c op ies for the purpose

of resea rc h only.

3. The Library has the right to ma ke c op ies of the thesis for ac ade mic excha nge .

Ce rtified b y :

SIGNA TURE SIGNATURE OF SUPERVISOR

841129-07-5553 EN. YUSOF BIN AHMAD(NEW IC NO. / PASSPORT NO.) NAME OF SUPERVISOR

Date : 23rd APRIL 2008 Date : 23rd APRIL 2008

NOTES : * If the thesis is CONFIDENTIAL or RESTRICTED, p lease a ttac h with the letter from

the o rganisa tion with p eriod and rea sons for confidentiality or restric tion.

UNIVERSITI TEKNOLOGI MALAYSIA

CONFIDENTIAL (Conta ins c onfidential informa tion under the Offic ial Sec retAc t 1972)*

RESTRICTED (Conta ins restric ted informa tion as spec ified by theorganisation w here resea rc h w as done )*

OPEN ACCESS I ag ree tha t my thesis to b e p ublished as online ope n acc ess(full text)


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I hereby declare that I have read this thesis and in my

opinion this thesis is sufficient in terms of scope and quality for the

award of the bachelor degree of Civil Engineering.

Signature : ...

Name of Supervisor : En. Yusof Bin Ahmad

Date : 23 APRIL 2008


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BENDING BEHAVIOUR OF THE TIMBER BEAMS STRENGTHENED WITH

FIBRE REINFORCED POLYMER (FRP)

LIM CHIH WEN

A thesis submitted in partial fulfilment of the

requirement for the award of the degree of

Bachelor of Civil Engineering

Faculty of Civil Engineering

Universiti Teknologi Malaysia

APRIL, 2008


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I declare that this thesis entitled Bending Behaviour of the Timber Beams

Strengthened with Fibre Reinforced Polymer (FRP) is the results of my own

research except as cited in the references. The thesis has not been accepted for any

degree and is not concurrently submitted in candidature of any other degree.

Signature :

Name : LIM CHIH WEN

Date : 23 APRIL 2008


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To my beloved mother and father


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ACKNOWLEDGEMENTS

Firstly, I would like to express my deepest gratitude to my supervisor, En.

Yusof Bin Ahmad, for his kind assistance and patiently guidance. Thanks you for all

your time and valuable experiences that you have shared with me regarding this

project.

Secondly, I want to appreciate my project partner, Mr. Lim Wei Han for

being so helpful and showing his great contribution and cooperation in the

completion of this project. I also want to thank my entire friends who directly or

indirectly assisted me in this project.

Last but not least, sincere gratitude and appreciation is forwarded to my

family for care, moral support and understanding during my four years studying in

Universiti Teknologi Malaysia.

LIM CHIH WEN

Faculty of Civil Engineering

Universiti Teknologi Malaysia


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ABSTRACT

Nowadays, construction industry is keen on finding a material to replace

concrete and steel due to the increment of cost. Therefore, timber, a renewable

construction material has been given more attention by researchers. The timber beam

can be upgraded to increase the strength capacity by using Fibre Reinforced Polymer

(FRP) bonding system. The FRP bonding system has been reported to be more

effective than steel bonding system among others due to its lightweight for easy

handling during construction. An experimental work was undertaken to study the

bending behaviour of timber beam strengthened with Carbon Fibre Reinforced

Polymer (CFRP) plate. Three timber beams with dimension 100 x 200 x 3000 mm

were tested to failure under four point loading. One beam is used as control beam

and the rest are strengthened with CFRP plate. The behaviour of the beams was

studied through their load-deflection characteristic upon loading, timber and FRP

strain, cracking history and mode of failure. The results showed that the strengthened

beams performed better than the control beam by having lower deflection at the same

load level and higher ultimate load. The percentage of increment is from 27 % to

36 %. It shows that the timber with CFRP bonding system is a suitable candidate in

many structural applications, including rehabilitation and strengthening as well as the

development of new wood members.


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ABSTRAK

Kini, industri pembinaan cenderung untuk mencari bahan pembinaan gantian

untuk konkrit dan keluli. Kayu, bahan pembinaan yang boleh dibaharui dengan

penanaman semula semakin diberi perhatian dalam kajian. Dengan penggunaan

sistem penguatan Polimer Bertetulang Gentian (FRP), kayu dapat meningkatkan

kekuatannya. Sistem penguatan FRP untuk kayu dan struktur adalah lebih berkesan

berbanding dengan sistem penguatan meggunakan keluli dari segi kesenangan dan

kemudahan membuat kerja. Kajian dijalankan dengan tujuan mengkaji kelakuan

kayu yang diperkuatkan dengan plat Polimer Bertetulang Gentian Karbon (CFRP).

Tiga batang rasuk padu berdimensi 100 x 200 x 3000 mm akan diuji hingga

kegagalan dengan ujian pembebanan empat titik. Sebatang rasuk akan digunakan

sebagai rasuk kawalan dan yang lain akan diperkuatkan dengan plat CFRP. Kelakuan

kayu akan dikaji berdasarkan ciri daya-pesongan dengan pembebanan, keterikan

kayu dan CFRP, serta mod kegagalan bagi rasuk kayu. Keputusan menunjukkan

bahawa rasuk kayu yang diperkuatkan mempunyai beban muktamad dan kekukuhan

yang lebih tinggi daripada rasuk kawalan. Peratuan pertambahan ialah di antara 27 %

hingga 36 %. Kesimpulan boleh dibuat bahawa sistem penguatan kayu dengan plat

CFRP adalah sesuai untuk diaplikasi dalam pembinaan dan pemulihan struktur kayu.


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TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES x

LIST OF FIGURES xii

LIST OF SYMBOLS xiv

1 INTRODUCTION 11.1 Introduction 1

1.2 Problem Statement 3

1.3 Objective 4

1.4 Scope of Research 4

1.5 Research Significance 5

2 LITERATURE REVIEW 62.1 Introduction 6

2.2 Timber 6

2.2.1 Hardwood 8

2.2.2 Mechanical Properties of Timber 9

2.2.3 Stress-Strain Behaviour of Timber 10

2.2.4 Factors Affecting Strength of Timber 11


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2.2.4.1 Moisture Content 11

2.2.4.2 Density 13

2.2.4.3 Defects 13

2.2.5 Failure Modes of Timber Beam 14

2.2.6 Timber as Structural Material 16

2.2.7 Yellow Meranti 17

2.3 Fibre Reinforced Polymer (FRP) 19

2.3.1 FRP as Building Material 20

2.3.2 Types of FRP 20

2.3.2.1 Carbon Fibre Reinforced Polymer(CFRP) 20

2.3.2.2 Glass Fibre Reinforced Polymer(GFRP) 21

2.3.3 Mechanical Properties of FRP 22

2.4 Adhesive 23

2.4.1 Sikadur -30 23

2.5 Past Studies 25

2.5.1 Research 1 25

2.5.2 Research 2 25

2.5.3 Research 3 26

2.5.4 Research 4 26

2.5.5 Research 5 27

3 METHODOLOGY 283.1 Introduction 28

3.2 Flow of Overall Testing 29

3.3 Lab Work and Testing 31

3.3.1 Moisture Content 31

3.3.2 Tensile Test Parallel to Grain 33

3.3.3 Tensile Test for CFRP Plate 35

3.3.4 Preparation of Timber Beam Strengthened with

CFRP Plate 38

3.3.5 Bending Capacity Test 42


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4 RESULT AND ANALYSIS 454.1 Introduction 45

4.2 Result from Lab Work 46

4.2.1 Moisture Content Measurement of Timber 46

4.2.2 Tensile Test of Timber Parallel to Grain 48

4.2.3 Tensile Test for CFRP Plate 50

4.2.4 Bending Capacity Test 52

4.2.4.1 Bending Behaviour 52

4.2.4.2 Ultimate Load Carrying Capacity 56

4.2.4.3 Modulus of Elasticity Stiffness 57

4.2.4.4 Ductility 58

4.2.4.5 Compare the Results with the Timber

Beam Strengthened with GFRP rod 59

4.2.5 Mode of Failure 61

5 CONCLUSIONS AND SUGGESTIONS 655.1 Conclusions 65

5.2 Suggestions 66

REFERENCES 68


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LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 The strength/density ratio for some structural materials 17

2.2 The strength group of timber 18

2.3 Wey grade of timber (N/mm2), moisture content > 19% 19

2.4 Mechanical properties of CFRP, GFRP and mild steel 22

2.5 Qualitative comparison between carbon fibers and E-glass 23

2.6 Characteristic of Sikadur

-30 24

3.1 Dimensions of test pieces (unit: mm) 36

3.2 Information of the timber beams 39

4.1 Initial moisture content of timber beams 47

4.2 Moisture content of timber beams after four-point loading test 48

4.3 Elastic modulus of the timber samples 50

4.4 Elastic modulus of the CFRP samples 52

4.5 Comparison of strength increase over control beam for

strengthened beams 56

4.6 Comparison between unstrengthened modulus of elasticity

and strengthened modulus of elasticity 57


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4.7 Comparison between the ductility of control beam and the

ductility of strengthened beams 58

4.8 Comparison of strength increase over control beam for beams

strengthened with GFRP rods 60

4.9 Comparison between unstrengthened modulus of elasticity and

strengthened modulus of elasticity with GFRP rods 60

4.10 Comparison between the ductility of control beam and the

ductility of beams strengthened with GFRP rods 61

4.11 Mode of failure for all tested beam 62


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LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1 Typical cross section of tree 7

2.2 Stress-strain relationship for timber 10

2.3 Relationship between longitudinal compressive strength and

moisture content 12

2.4 Failure of beam 15

3.1 Flow Chart of Overall Testing 30

3.2 Sample for moisture content 32

3.3 Air jet use to remove dust 32

3.4 Oven-dry 32

3.5 Test piece for tension Parallel to grain test 34

3.6 Sample for tensile test 34

3.7 Tensile test with Machine Dartec 35

3.8 Shape of test pieces 36

3.9 Sample of CFRP for tensile 37

3.10 CFRP samples in Machine Dartec 38


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3.11 Sikadur

-30 39

3.12 Cross section for beam strengthened with CFRP plate 40

3.13 Timber beams strengthened with CFRP plates 41

3.14 Position of the strain gauge 41

3.15 Standard set up for bending 43

3.16 Real setting during lab testing 43

3.17 Machine of data recording system 44

3.18 Display screen of data recording system 44

4.1 Stress strain curves for all timber samples tested 49

4.2 Stress strain curves for all CFRP plate samples tested 51

4.3 Load-deflection curve for control beam (Beam 18) 53

4.4 Load-deflection curve for beam strengthen with CFRP

plate S2512 54

4.5 Load-deflection curve for beam strengthen with CFRP

plate S3014 54

4.6 Load-deflection curves for all tested beams 55

4.7 Load-deflection curves for all beams strengthened with

GFRP rods 59

4.8 Failure modes for beam 63

4.9 Failure modes for beam 29 63

4.10 Failure modes for beam 15 64


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LIST OF SYMBOLS

P - Maximum applied load

ft - Tensile stress of timber

ffu - Tensile stress of CFRP plate

A - Minimum area of cross-section of test length

Ar - Ratio of cross section between CFRP plate and timber beam

t - Thickness of CFRP plate

w - Width of CFRP plate

a - Half of shear span

h - Height of timber beam

max - Maximum strain

max - Maximum stress

E - Modulus of elasticity of the beam

dmax - Maximum elongation


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CHAPTER 1

INTRODUCTION

1.1 Introduction

Timber is one of the earliest materials used in construction. Human use it to

construct houses, bridges and many other structural buildings. It is the most popular

building material before the emergence of modern structural material such as

concrete and steel due to its high strength to weight ratio (Marco Corradi and

Antonio Borri, 2006). The timber is easy to mobilize and construct (cut, nailed,

bolted and level). It does not require any fabrication of formwork and curing time

like concrete do. Therefore, using timber in the construction can reduce the use of

heavy machinery, shorten the construction period and save up construction cost.

Beside that, timber can resist oxidation, acid, saltwater and other corrosion agents

(Regis B. Miller, 1999).

However, timber has some drawbacks in its usefulness in construction.

Problems such as design failure, insect attack, rot, decay, weathering and mechanical

damage will occur during the design life of the structure. Timber by nature is a very

inhomogeneous building material (Regis B. Miller, 1999). Unlike the steel and

concrete, the material properties of timber cannot be designed or produced according

to the recipe. Their material properties are very much depend on factors such as the

age, the diameter of the timber logs, the number of knots, the orientation of timber

grain and the moisture content (Frederick F. Wangaard, 1950). Even the timbers


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taken out from the same log will have different degree of strength. This will increase

the difficulty in design of the structure. Furthermore, some timber may require pre-

treatment before they can be used for construction. All these factors have affected the

marketability of the timber in the construction industry.

Therefore, methods or techniques to overcome these disadvantages are

developed. One of the most popular methods to do so is reinforcing the timber with

the use of other material such as steel. However, steel corrosion will deteriorate the

loading capacity of the strengthen timber. Therefore, in recent years, the increased

availability and reduced cost of fibre reinforced polymer (FRP) material has

stimulated increased research into strengthening timber structures (Chris Gentile,

Dagmar Svecova, and Sami H. Rizkalla, 2002). FRP is formerly developed for the

aerospace industry but now is becoming more widely used in the construction

industry. Its high strength to weight ratio and good durability has made it suitable to

replace steel in strengthening the timber beam (Ted W. Buell and Hamid

Saadatmanesh, 2005). It can be used either to enhance flexural and shear strength of

existing structures or decrease the size of new structures for the given required

strength. FRP reinforcement is bonded to the surface of timber with the used of

adhesive, generally epoxy resin. The most commonly used fibre types are glass

(GFRP) and carbon (CFRP).

The main focus of this research is to determine the effectiveness of FRP to

strengthen and increase loading capacity of the timber beam. Several tests will beconducted with different arrangement of the FRP reinforcement to determine the

most effective way to strengthen the timber beam. Timber beam without any

reinforcement is used as a control beam for the comparison.


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1.2 Problem Statement

Nowadays, due to high demand, the prices of cement and steel have increased

drastically. Many researchers are looking for an alternative material to replace

concrete and steel as building materials. One of the options is timber. The used of

timber as a building material has a long history. However, due to the inhomogeneous

material properties, limited capacity and vulnerable towards insect attack, the usage

of timber as building material has decrease. The concrete and steel are subsequently

replace the timber to become the main material in construction.

However, with the progressive technology development, several methods and

techniques are suggested to overcome the drawbacks in the used of timber as

building materials. Reinforcing the timber beam with other material is one of the

popular methods. In the early stage of development, steel has been used to strengthen

the timber beam. The steel plate is bonded to the tension surface in order to pre-stress

the wood. This will increase the bending and shear capacity of the beam (Chris

Gentile, Dagmar Svecova, and Sami H. Rizkalla, 2002). However, there are some

mechanical limitations for the use of steel as timber reinforcement such as:

Heavy weight that will increase the transportation cost and the difficulty ofinstallation.

High thermal conductivity that might create problem in case of fire. Oxidation which will make the steel rusty.

Therefore, innovative techniques by employing FRP glued-in with resin to

replace steel as the reinforcement offer more benefits. It has high strength to weight

ratio and good durability. Furthermore, it is free from oxidation. The use of

composite material in wood reinforcement was first proposed in the 1980s by Meier,

Triantafillou, Triantafillou and Plevris, Kropf and Meierhofer, Gentile et al., Borri et

al., who applied composites based on glass (GFRP) or carbon fibre sheets (CFRP)


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epoxy-bonded externally on the tension zones and studied their effect on the

mechanical characteristics (Marco Corradi and Antonio Borri, 2006).

However, wood technology in Malaysia is still left behind if compare with the

advance country such as US and Japan. Researchers in Malaysia are lack of interest

in developing new wood technologies. Thus, hopefully this research can give some

contribution to the development of wood technology in Malaysia and help increase

the popularity of using the timber beam in the local construction industry.

1.3 Objectives of Research

The objectives of this research are:

i. To determine whether FRP strengthening increase the stiffness and bendingstrength of the timber beams.

ii. To study the ductility of timber beams strengthen with FRP.iii. To study the failure mode of the timber beams strengthened with FRP.iv. To determine the most suitable material and technique in the strengthening of

the timber beams.

1.4 Scope of Research

The main focus for this research is to analysis the bending behaviour of

timber beam strengthen with Carbon Fibre Reinforced Polymer (CFRP) plate.

Therefore, timber beams and CFRP plates are the main materials being used. For the


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type of timber, Yellow Meranti is selected to use in this research. The adhesive used

for this research is Sikadur

30. Furthermore, the test results of this research will be

compared with the results from the experimental work done by Lim Wei Han (2008)

using GFRP bars to strengthen the timber beam.

1.5 Research Significance

Generally, the strengthening technique developed in this research will

increase the overall strength and stiffness of timber beam. Moreover, effective

strengthening technique can reduce the size of beam while increase their strength,

thereby creating a more efficient use of timber supply. This technique is suitable for

both new construction and rehabilitation of existing structures. For existing timber

structure, this strengthen techniques may save the cost of replacing the structure by

allowing it to withstand higher loads.


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CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

Through out history, the unique characteristic and comparative abundance of

wood have made it a natural material for homes and other structures, furniture, tools,

vehicles and decorative object. Although concrete and steel have replace timber as

main construction materials, it is still prized for a multitude of uses.

Modern technology has help improve the natural characteristic and loading

capacity of timber, make it more useful in the construction industry. Reinforcing the

timber beam with FRP is one of the methods to do so. By bonding the FRP plate or

rod in the tension surface of the timber beam with adhesive such as epoxy, its

bending strength and stiffness will gradually increase.

2.2 Timber

Malaysia has more than 2500 species of wood, but only 10% are suitable to

be used as construction material. Timber is primarily composed of hollow, elongate,


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spindle-shaped cells that are arranged parallel to each other along the trunk of the

tree. When the lumber is cut from the tree, the characteristic and arrangement of

these fibrous cells will affect its properties such as the strength, shrinkage and the

grain pattern. A typical cross section of a tree is shown in Figure 2.1.

Basically, tree can be divided into two broad classes: hardwood and softwood.

The term hardwood and softwood do not stand for the hardness or density of the

timber. It is just refer to the botanical origin of the particular plant. Some softwood is

actually harder than some hardwood. The easiest way to differentiate these two

categories is trees with broad leaves are hardwoods and trees with needle like leaves

are softwoods.

(A) Outer bark - dry dead tissue served as a protective coating(B) Inner bark - living tissues which carries food from the leaves to the other

part of the tree

(C) Cambium - microscopic layer inside the inner bark where new timberand bark cells are formed

Figure 2.1: Typical cross section of tree(Regis B. Miller, 1999)


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(D) Sapwood - light in colour, functioned to carry sap from the roots to theleaves

(E) Heartwood - dark in colour, formed by a gradual change in sapwood andis inactive in the tree

(F) Pith - it is where new timber growth for twigs take place(G) Wood rays - connect the various part of the tree for the storage and

movement of food

2.2.1 Hardwood

Most of the timbers in Malaysia are hardwood and basically hardwood has

better strength and durability compare with softwood. Sawn section of hardwoods is

relatively free from knots, wane and fairly straight grain. However, it has the

tendency to distort and crack. The Forest Department of Malaysia has classified

hardwoods in Malaysia into three groups according to the density and durability of

the woods. The durability of the wood will decrease if the density decreases.

The classification is done under the Peraturan Penggredan Malaysia (1984):

Heavy Hardwood for density more than 880 kg/m3 Medium Hardwood for density from 720 kg/m3 to 880 kg/m3 Light Hardwood for density less than 720 kg/m3


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2.2.2 Mechanical Properties of Timber

Mechanical properties of timber most commonly measured and represented

as strength properties for design purposes. This research is intended to improve the

strength and load capacity of timber by strengthening it with FRP.

The following are some common properties used to measure the wood (Regis B.

Miller, 1999):

Modulus of ruptureIt reflects the maximum load carrying capacity of a member in

bending and is proportional to maximum moment carried by the

specimen. The assumption made in the calculation is that the timber

behaves elastically.

Work to maximum load in bendingIt reflects the ability to absorb shock with some permanentdeformation and more or less injury to a specimen. Work to maximum

load is a measure of the combined strength and toughness of wood

under bending stresses.

Compressive strength parallel to grainMaximum stress sustained by a compression parallel-to-grain

specimen having a ratio of length to least dimension of less than 11.

Compressive stress perpendicular to grainIt is reported as stress at proportional limit. There is no clearly defined

ultimate stress for this property.

Tensile strength parallel to grainMaximum tensile stress sustained in direction parallel to grain. In the

absence of sufficient tension test data, modulus of rupture values are

sometimes substituted for tensile strength of small, clear, straight


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grained pieces of wood. The modulus of rupture is considered to be a

low or conservative estimate of tensile strength for clears specimens.

Tensile strength perpendicular to grainResistance of wood to forces acting across the grain that tends to split

a member. Values presented are the average of radial and tangential

observations.

Shear strength parallel to grainIt is an ability to resist internal slipping of one part upon another along

the grain. Generally, the shear strength of timber can be classified into

two types: shear strength parallel to grain and shear strengthperpendicular to grain. Values presented are average strength in radial

and tangential shear planes.

2.2.3 Stress-Strain Behaviour of Timber

Typical stress-strain relationship for timber is shown in Figure: 2.2. When

timber is tested to failure under axial tension, the stress-strain relationship is linear

up to maximum load and the timber will fail in brittle tension. In axial compression,

Figure 2.2: Stress-strain relationship for

timber Buchanan, 1990

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