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PSZ 19:16 (Pind . 1/ 07)
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