International Journal of Advanced Research in Engineering and Technology (IJARET ... ·...

International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –

6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 6, September – October (2013), © IAEME

153

BEHAVIOR OF TIMBER BEAMS PROVIDED WITH FLEXURAL AS WELL

AS SHEAR REINFORCEMENT IN THE FORM OF CFRP STRIPS

Javaid Ahmad1, Dr. Javed Ahmad Bhat

2, Umer Salam

3

1Graduate Student, National Institute of Technology, Srinagar

2Associate Professor, National Institute of Technology, Srinagar 3Graduate Student, National Institute of Technology, Srinagar

ABSTRACT

The aim of current study is to investigate the effect of tensile and shear reinforcement in the

form of Carbon Fiber Reinforced Polymer (CFRP) composites on flexural behavior of timber beams.

Five beams with cross section of 70mm x 120mm were tested, where one served as control beams

(without CFRP strengthening). Timber species used in this study was Cedrus Deodara (Deodar). An

experimental investigation was conducted on the behavior of FRP-reinforced wood section. The

strength of timber beams was significantly improved upon combined flexural and shear

strengthening with maximum percentage increase being 71.43%for Deodar beams. This study, in

turn, led to an empirical procedure based on modification factors, suitable for application in the

design of FRP reinforcement of existing timber beams under different configuration of strengthening

materials applied.

Keywords: Retrofitting, Fiber Reinforced Polymers, Flexural Strengthening, Timber Failures, Shear

Strengthening, Ductility Index, Flexural Rigidity.

1. INTRODUCTION

Rehabilitation of deteriorated civil engineering infrastructure such as buildings, bridge decks,

beams, girders, marine structures, roads etc. has been a major issue in last decade. The deterioration

of these structures might be due to aging, poor maintenance, corrosion due to unfavorable

environmental conditions, poor initial design or construction and accidental situations like

earthquakes. The need to upgrade the deteriorated civil engineering infrastructure is necessitated due

to the ever increasing demand e.g. unprecedented loads on buildings which have not been considered

in design and likewise.

New technology options in rehabilitation are being developed from polymers, metals,

ceramics and composites of these materials and some of these high performance materials are

already being utilized in construction. While the concept of composites has been in existence for

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154

several millennia, the incorporation of fiber reinforced polymer (FRP) is less than a century old.

These composites combine the strength of fibers with the stability of polymer resins.

Market penetration of timber and fiber composites within the construction industry will

ultimately be determined by final cost. CFRP is more expensive. However, material cost alone is not

the prime consideration for many applications using these materials. It is important to consider the

total built cost rather than just comparing the material component costs with traditional materials but

the costs of design, manufacture, fabrication and erection need to be considered as well. Building

owners, when looking at new construction, have not given a great deal of consideration to long term

rehabilitation methods, costs or effects on projected service. Although research has been done to

strengthen timber using FRP, but the comprehensive analysis and design are not established in detail.

This is one of the reasons why the application of FRP to timber is very limited.

In the plate bonding or externally bonded technique, the FRP is situated on the external

tensile surfaces of the concrete beam to improve the flexural strength or on the vertical surfaces of

the beam to increase its shear capacity (Allbones, 1999)[3]

. Arduini and Nanni (1997) have

investigated plates in the form of flexible carbon FRP sheets, to be externally bonded to the concrete

surfaces. The strengthening technology consisting of externally bonded CFRP sheets to concrete is

easy to perform and significant improvement was found for ultimate load capacity and to a lesser

extent in flexural stiffness.[5]

Plevris and Triantafillou (1992) provided an analytical study of the short-term flexural

behavior of timber beams and beam-columns reinforced on the tension face only with epoxy-bonded

unidirectional CFRP sheets. This work demonstrated that even a small amount of fibers, as low as

1% of the cross-sectional area, of thin carbon FRP bonded to timber beams could result in a strength

increase on the order of 60%.[18]

There was another research done by Fiorelli and Antonio (2002) to evaluate the structural

behavior of timber beams strengthened with FRP. The research was focused on the experimental and

theoretical analysis of timber beams of the species Pinus Caribea Hondurensis which were reinforced

with GFRP and CFRP fabrics. The results of this research showed that the flexural stiffness (EI)

determined experimentally was greater than the theoretical values. These values are in favor of

structural safety. It shows that the increase of stiffness varied from 15% to 29% for beams

strengthened with glass and carbon fabric. The use of FRP provides better results in load capacity

and in the vertical displacement of the beam.[9]

Gentile et al. (2002) have investigated creosote-treated sawn Douglas Fir timber beams

strengthened with GFRP bars. The beams were obtained from a dismantled bridge that was in service

for over 30 years and were tested to obtain initial stiffness before strengthening. The percentage

reinforcement ratios were between 0.27 and 0.82%. The results have shown that the failure mode has

changed from brittle tension to compression failure. The flexural strength increased by 18 to 46%.[10]

Buell and Saadatmanesh (2005) have conducted research on creosote-treated solid-sawn

Douglas Fir strengthened with bidirectional CFRP fabric. The results show that applying carbon

fabric to the timber beams provides significant increase in the bending and shear capacity, and

nominal increase in the stiffness of the beams. The ultimate bending strength was increased between

40 to 53% and the horizontal shear strength was increased between 36 to 68%.[6]

The present study focuses on application of pre-fab CFRP strips for flexural and shear

strengthening of timber beams. The strips or plates are attached to beams by means of specified

adhesive. The flexural tests are carried out on timber beams strengthened with CFRP in varying

proportion with an object of studying the improvement in load carrying capacity, modulus of rupture,

flexural rigidity and ductility of these beams. However, the scope of this study is limited to seasoned

dry timber only which infers the applicability of research findings to beams used in dry condition or

in the interior of structure.



155

The timber species used in this research is Cedrus Deodara commonly known as Deodar. It

is being widely used in upper northern region (primarily Jammu and Kashmir) of India for structural

purposes due to its prime availability in this region. Besides, this it is having good mechanical

properties as compared to other timber species found in northern region of India. Having been widely

used in structures constructed decades ago, it has become necessary to rehabilitate the timber

structures which have suffered damage. Leaving the application of conventional rehabilitation

techniques aside, we are left with application of fiber composites as best alternatives for

rehabilitation of these structures. So, research has been conducted at National Institute of

Technology, Srinagar (NIT Srinagar) to study the feasibility of utilizing CFRP for rehabilitation or

design of new structures using Deodar.

2. METHODOLOGY

This section describes features of beam specimens, beam designation, loading equipment,

instrumentation and testing schemes. In the present study, ten timber beams were prepared for testing

among which eight beams were strengthened using CFRP Plates of different widths. The beams

without strengthening served as control beams and used as reference level for checking improvement

in properties of strengthened timber beams. As already mentioned timber species utilized for beams

is Cedrus Deodara. The ultimate tensile strength and modulus of elasticity of specimens of Deodar

were observed to be 35 MPa and 10 GPa respectively. The typical geometry and testing

arrangement is shown in Fig1.

Fig 1: Flexural Test – Loading Arrangement

The properties of materials used are summarized in Table 1 whereas beam designations are

shown in Table 2.

Table 1: Material Properties

Property Deodar CFRP

Ultimate tensile strength,

N/mm2

35 2000

Ultimate tensile strain, % 0.40 1.65

Tensile modulus of

elasticity, KN/mm2

10 175

P P

1524mm

480mm 70mm

120mm

CFRP Strip

480mm

Shear Reinforcement

International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976

6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 6, September

Beam Designation

Flexural Reinforcement

Width,

mm

Control Beam - D -

FPD-S-30-1 30

FPD-S-40-1 40

FPD-S-50-1 50

FPD-S-70-1 70

Bf = 30mm Bf = 40mm

ACFRP = 0.36% ACFRP

Fig 2: Graphical representation of Beam cross

Reinforcement was used in the form of CFRP strips of varying widths applied on the bottom

face and sides of the beams using adhesive

Technology (India), a New Delhi based supplier who imports it from Korea. The mechanical

properties of CFRP are shown in Table 1.

CFRP of thickness 1mm and different widths in all specimens varying from 30mm to 70mm.

The tests were carried on beam models in a loading frame of capacity 500KN. Prior to testing dial

gauges were set up at mid span and two alternate points. The loading was applied by means of

hydraulic jack till failure and deflections were noted every 4KN interval load. The failure pattern was

studied for each beam discussion regarding

flexural testing.

(a) Front View

International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976

6499(Online) Volume 4, Issue 6, September – October (2013), © IAEME

156

Table 2: Beam Designation

Flexural Reinforcement Shear Reinforcement

Thickness,

mm

Area of

CFRP,

%

Depth,

mm

Thickness,

mm

- 0 - -

1 0.36 120 1

1 0.47 120 1

1 0.59 120 1

1 0.83 120 1

= 40mm Bf = 50mm Bf = 70mm

CFRP = 0.47% ACFRP = 0.59% ACFRP

: Graphical representation of Beam cross-sections


of the beams using adhesive(Fig 2). The CFRP sheets were supplied by GSP Superb


properties of CFRP are shown in Table 1. Strengthened beams were provided with a single strip of

d different widths in all specimens varying from 30mm to 70mm.



ydraulic jack till failure and deflections were noted every 4KN interval load. The failure pattern was

studied for each beam discussion regarding which is given afterwards. Fig 3 shows schematics of

View (b) Side View

Fig 3: Testing Arrangement


(2013), © IAEME

Span of

Beam,

m

Thickness,

1.524

1.524

1.524

1.524

1.524

= 70mm

CFRP = 0.83%


. The CFRP sheets were supplied by GSP Superb


with a single strip of

d different widths in all specimens varying from 30mm to 70mm.



ydraulic jack till failure and deflections were noted every 4KN interval load. The failure pattern was

shows schematics of



157

3. RESULTS AND DISCUSSIONS

The results from laboratory testing for the strengthened beams are compared with control

beam (un-strengthened) in order to study the behavior of strengthened timber beams in terms of load

carrying capacity, bending strength, stiffness and ductility. In addition, the modes of failure for all

beams have been studied and discussed.

3.1 Unstrengthened Beam An unstrengthened timber beam (Deodar) was tested under two point loading. This is to

determine the initial bending stiffness whilst in the elastic zone. The Deodar Control beam started to

behave non-linearly when the load was 16.6 kN and the corresponding deflection was 10.5 mm. The

failure load was 29.05KN for Deodar Control Beam. Any non-linearity in the behavior of timber

beam was due to plasticity in the compression zone and the level of plasticity will determines

whether the beam fails in compression or otherwise.

Fig 4shows load versus deflection at mid-span of control beam for every 4 kN load interval.

It is clear that all beams exhibited linear elastic as expected. The gradients of the lines were

determined from which the stiffness of the beams can be calculated. This was done so that the

uniformity of initial stiffness could be judged. Table 3 contains other properties of control beams.

Moreover, Fig 5 shows failure pattern of control beam.

Fig 4: Load Deflection Curve for Control Beams

Table 3: Control beam test results

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30

Loa

d,

KN

Midspan Deflection, mm

Control Beam Deodar

Deodar Control Beam

Failure Load, Pu, KN 29.05

Maximum Midspan Deflection, δu, mm 23

Flexural Rigidity, EI, KNm2 76.40

Modulus of Rupture, N/mm2 41.5



158

Fig 5: Failure Pattern of Control Beam

3.2 Strengthened Beams The beams were tested under two point loading until failure. For comparison purposes, the

results of load-deflection curves for all beams are plotted. Main discussion from curves focuses on

load carrying capacity, bending strength, stiffness and ductility of the strengthened beams relative to

the un-strengthened beams (control beams). In addition deflection, crack patterns and failure

behavior are also discussed.

In general, all control beams and strengthened beams behaved linearly elastic initially and as

the load increased, the flexural cracks increased in number, width, and depth, and the beams tend to

behave non-linearly until failure. There are some slight drops observed in some of the curves as a

result of internal cracking of the beam, which is hardly recognized through the observation with eyes

and ears. All figures clearly indicate that all the strengthened beams have higher ultimate load

carrying capacity than control beam. When there is significant failure, the corresponding load will be

taken as ultimate load carrying capacity. Besides that, the strengthening beams with FRP also

enhance the flexural stiffness. In other words, the strengthened beams experienced lower deflection

than the un-strengthened control beam at the same load level. This low deflection phenomenon is

desirable in the aspect of serviceability limit state in design to ensure comfortability of timber

structures. In timber design, generally the deflection will govern the design.

Beams were strengthened using CFRP plates with of thicknesses 1mm and four different

widths i.e. 30, 40, 50 and 70 mm. The span of Deodar beams was 1.524m. In this study, the same

control beam was used for comparison. The beams were tested and the graphs of load versus mid-

span deflection were plotted in Fig 6.

Fig 6: Load Deflection curves for Deodar beams strengthened using CFRP

0

10

20

30

40

50

60

0 10 20 30 40 50

Loa

d,

KN


Control Beam Deodar

FPD-S-30-1

FPD-S-40-1

FPD-S-50-1

FPD-S-70-1



159

The behavior exhibited by beams under combined flexure-shear tests is similar to that of

beams provided with only tension reinforcement but these differ in the level of improvement in terms

of strength stiffness and ductility. It is observed that providing flexural and shear reinforcement does

not improve the behavior to the desired level as observed in earlier tests.

Beam FPD-S-30-1 starts to behave non-linearly when the load was 14.11KN and

corresponding mid span deflection was 8.78mm. This point was the limit for proportionality and then

beam shows non-linear behavior where from the stiffness decreased gradually. When the load was

increased to 39.01 kN, the mid span deflection was 18.74 mm, beam stopped to take any extra load,

however no de-bonding occurred. Beyond 39.01KN, the load decreased abruptly. A tensile crack

occurred with impressions on CFRP strip acting as shear reinforcement. Shear cracks were restrained

by virtue of shear reinforcement. In fact, this beam failed in tension. The CFRP plate was not

ruptured indicating that the yield or ultimate stress was not reached.

For beam FPD-S-40-1 the proportionality limit was 16.6 kN which was slightly higher

compared to beam FPD-S-30-1. This beam has shown good performance at the beginning of the

testing where the slope of the curve was greater than the slope for beam FPD-S-301. When the load

was increased to 45.65 kN, there was large deflection of 29.1mm in the beam and failure took place.

It is very common to timber beams that when the beam fails in tension, the compression fiber fails

too and vice versa due to large deflection. Thus, by increasing the CFRP area, it helps the beam to

reduce the serious crack but the strengthened area was not sufficient to prevent the beam from

tension failure. When compared to FPD-40-1 the failure load was 41.5KN. The increase in load

capacity in FPD-S-40-1 was due to presence of shear reinforcement which prevented the shear cracks

and thus increased the load capacity. In this case the main function of CFRP plate as shear

reinforcement was to prevent shear cracks and that of CFRP plate as tension reinforcement was to

share the stress at the tension fiber and reduced the deflection and to delays the formation of tensile

crack. In this test, the beam failed in tension. There was no de-bonding of the plates.

When the beam was strengthened with more area of CFRP plate such as beam FPD-S-50-1,

the load-carrying capacity was increased to 49.8KN. The cracks occurred at the beam corner at

midspan where the maximum bending stress occurred. Corners or edges are weak zone for timber

beams. Hence, the cracks were considered not serious because the main timber fibers were not

cracked. The beam failed at the ultimate load 49.8KN. At failure, de-bonding occurred between

CFRP plate and the beam surface. It seems that the maximum tensile and compressive capacity of

timber was fully utilized. The tensile strength of CFRP plate was too high relative to the tensile

timber capacity, hence the CFRP plate was not fully utilized.

Beam FPD-S-70-1 was strengthened using wider and thicker section where the cross section

dimension was 70 mm by 1 mm. The proportionality limit was 14.11 kN. The beam started to crack

when the load reached at 33.2 KN, however the cracks were prevented to propagate to wider area by

the help of CFRP plate and shear reinforcement. The tensile cracks were small and only the bottom

layer at midspan was affected. The total failure occurred at the ultimate load of 41.5 KN. It very

obvious that the compression zone has reached it ultimate capacity. Any CFRP area of more than

0.59% of beam cross section will not give enhancement to the ultimate capacity unless the

compression zone is strengthened. Thus, when the beam was strengthened using more area or wider

plate, the ultimate load as well as the slope of load-deflection curve was increased and the failure

mode was changed from tension to compression.

The application of CFRP plate as shear reinforcement in addition to tension reinforcement

gives advantage where failure occurs due to shear cracks. Besides, the presence of shear

reinforcement increases the load carrying capacity relative to beams with tension reinforcement

alone.



160

3.2.1 Effects on Load Carrying Capacity

The load carrying capacity of all beams is shown in Table 4. The strengthened beams have

greater load carrying capacity when compared to control beam only up to a limit beyond which it

decreases. Generally, the ultimate and service load carrying capacity was increased as the percentage

of CFRP increased up to CFRP area of 0.59%. The ultimate load was increased significantly when

the percentage of CFRP plate was 0.36%. This percentage was considered small when compared to

beam cross section but the strength achievement was very encouraging where the increase in ultimate

load was 34.28%. The highest increment for ultimate load among these beams was 71.43% i.e. when

the beams were strengthened using 0.59% of CFRP.

Table 4: Load carrying capacity of Deodar beams provided with flexural and shear reinforcement

Beam

Area of

CFRP

(%)

Ultimate

Load

Pu

(KN)

Midspan

Deflection,

δu

(mm)

Increase in

Load

Capacity

(%)

Control Beam- D 0 29.05 23 0

FPD-S-30-1 0.36 39.01 18.74 34.286

FPD-S-40-1 0.47 45.65 29.1 57.143

FPD-S-50-1 0.59 49.8 40.32 71.430

FPD-S-70-1 0.83 41.5 38.22 42.85

To get a better and clearer understanding regarding this relationship, ultimate loads were

plotted against percentage area (tensile reinforcement) of CFRP as shown in Fig 7. The relationship

is not linear. When the beam was strengthened using more than 0.59% CFRP, it would not enhance

the load carrying capacity as the compression zone has achieved maximum capacity. Thus, it can be

concluded that the beam experiences over-reinforced if the percentage of CFRP is greater than

0.59%. This is clearly shown by the curve in Fig 7.

Fig 7: Load Vs Area of tension reinforcement

These results indicate that beams were over reinforced beyond FPD-S-50-1. The increases the

load carrying capacity for this beam was 71.43%. In summary, the load carrying capacity of the

strengthened Deodar beams increases between 34.28 % to 71.43%, when the CFRP area is between

0

10

20

30

40

50

60

0 0.2 0.4 0.6 0.8 1

Loa

d,

KN

Tensile Reinforcement Area, %

Load Vs CFRP Area



161

0.36% to 0.59%. Beyond CFRP area of 0.59% the beams showed decrease in load carrying capacity

owing to compression failure of over reinforced section.

3.2.2 Effects on Flexural Rigidity (EI) The flexural rigidity of beams strengthened using CFRP plate are tabulated in Table 5.

Generally, the flexural rigidity was increased as the percentage of CFRP plate increased up to a limit.

It seems that strengthening using wider plate was efficient to enhance the stiffness. The effect of

plate width can be confirmed by comparing beams FPD-S-30-1, FPD-S-40-1, FPD-S-50-1 and FPD-

S-70-1. Wider plate is more effective to prevent the initial crack at bottom layer because most of the

tensile cracks started at the unstiffened portion. The flexural rigidity of the beams could be increased

to 65% for Deodar, when the timber beams were strengthened using CFRP plate of area of 0.36%.

Table 5: Effect of CFRP area on flexural rigidity of Deodar beams provided with flexural and shear

reinforcement

Beam

Percentage of

CFRP Area,

%

Flexural

Rigidity,

EI,

KNm2

Increase in

EI,

%

Modification

Factor

Control Beam-D - 76.36 - 1

FPD-S-30-1 0.36 126 65 1.65

FPD-S-40-1 0.47 94.85 24.21 1.24

FPD-S-50-1 0.59 74.68 -2.20 0.98

FPD-S-70-1 0.83 65.65 -14.02 0.87

Fig 8 shows the relationship between the flexural rigidity and the area of CFRP plates. The

graph shows that there is decrease in flexural rigidity of beam when the area of CFRP exceeds

0.36%. It is observed that there is a limiting value for the elasticity after certain area of CFRP which

pertains to optimum value for CFRP area.

Fig 8: Flexural Rigidity Versus CFRP Area

0

20

40

60

80

100

120

140

0 0.2 0.4 0.6 0.8 1

Fle

xu

ral

Rig

idit

y,

EI,

KN

m2

Tensile Reinforcement, %

Flexural Rigidity Vs

Tensile Reinforcement



162

3.2.3 Effects on Ductility

Beam FPD-S-50-1 was taken as a typical example for discussion of ductility. The Load-

deflection curve for the beam is shown in Fig 9. From the curve, the maximum elastic load and

ultimate load, and the corresponding deflections were determined.

Fig 9: Load Deflection Curve for the beam FPD-S-50-1

In this study none of the CFRP plate has yielded because the yield strain for CFRP is higher

than the yield strain of the timber. Hence the compressive zone of the timber will reach its yield

point before CFRP. From the curve, the elastic deflection, and the ultimate deflection were

∆e = 13.23 mm, and ∆u = 42.32 mm, respectively. The curve was very smooth exhibiting no sudden

crack or crush occurred. The total failure occurred when the deflection at mid-span was 42.32 mm

which is considered high. This value provides good performance in the ductility point of view where

the people will have ample time to escape from the building before collapse.

Using the same procedures mentioned earlier, the ductility indices were calculated based on

energy methods and the summary of the results is shown in Table 6.

Table 6: Ductility Index for Deodar beams provided with flexural and shear reinforcement

Beam CFRP

Area, %

Energy Ductility index

Elastic

We

Nm or J

Ultimate

Wtot

Nm or J

Based on Energy

�� 0.5 �� 1�

Control Beam - D 0 96.30 392.28 2.53

FPD-S-30-1 0.36 64.52 380.98 3.45

FPD-S-40-1 0.47 68.32 418.61 3.56

FPD-S-50-1 0.59 110.60 1099.44 5.47

FPD-S-70-1 0.83 138.61 858.91 3.60

The polynomial regression equations for the other beams are shown in Table 7. There was

significant increase in ductility when the timber beams are strengthened using CFRP plates. Even

y = -3E-07x6 + 4E-05x5 - 0.001x4 + 0.032x3 - 0.294x2 + 2.342x -

0.195

R² = 0.994

0

10

20

30

40

50

60

0 10 20 30 40 50

Loa

d,

KN


FPD-S-50-1

Poly. (FPD-S-50-1)



163

after ultimate failure, the beams still held together. By taking control beam as a reference, the highest

ductility index based on energy method was 5.47 where the percentage increase was 116.20%.

From these results, there is a relationship between the CFRP area and the ductility index. The

relationship is shown graphically in Fig 10. The curves indicate that ductility index increases

nonlinearly as the area of CFRP plates increased. When the area of CFRP is about 0.59%, we get

maximum value for the ductility index and any increases in CFRP area beyond this value will not

improve the ductility.

Fig 10: Ductility index Vs Tension reinforcement

Table 7: Polynomial Regression Equations of load deflection Curves of Beams

Deodar Beams

Control Beam-D y = -0.0007x3 - 0.0096x2 + 1.7841x + 0.3608;

[R² = 0.9959]

FPD-S-30-1 y = -9E-05x6 + 0.0049x5 - 0.0989x4 + 0.9152x3 - 3.7661x2 + 6.8676x - 0.0591;

[R² = 0.9971]

FPD-S -40-1 y = -5E-06x5 + 0.0004x4 - 0.0132x3 + 0.1421x2 + 1.0356x + 0.5485;

[R² = 0.9915]

FPD-S -50-1 y = -5E-07x6 + 6E-05x5 - 0.0024x4 + 0.0481x3 - 0.4583x2 + 3.1226x - 0.0458;

[R² = 0.9948]

FPD-S -70-1 y = -7E-07x6 + 8E-05x5 - 0.0036x4 + 0.0719x3 - 0.672x2 + 3.2474x - 0.2069;

[R² = 0.9968]

4. CONCLUSIONS

I. In general, the percentage increase in load carrying capacity in all these beams was found to

be more than that in beams provided with flexural reinforcement only.

II. The maximum increase in load carrying capacity was 71.43% when area of tensile

reinforcement was 0.59%.

III. The balanced reinforced occurred when the CFRP was about 0.59%.

0

1

2

3

4

5

6

0 0.2 0.4 0.6 0.8 1

Du

ctil

ity

In

de

x

Tension Reinforcement, %

Ductility Index



164

IV. Ductility index obtained from energy method was observed to vary in the range 2.53 – 5.47

for Deodar beams.

V. The failure mode was debonding of CFRP plate in some cases.

VI. Combined flexure-shear reinforcement is effective as compared to flexural reinforcement

alone.

VII. All beams in this study did not fail due to peel off and also no de-bonding occurred between

CFRP plate and the bonding agent and between bonding agent and timber substrate because

the bonding length for all beams (1.5 m) was sufficient.

VIII. When FRPs were bonded to the timber, randomization of defects (e.g., timber knots and

drying cracks) reduces the variability of properties and consequently increases the tensile

strength. Other effect was that the "bridging effect" exerted by the FRP composite skin on

the bonded timber also increases the tensile strength.

IX. Although steel bars or plates are still used for strengthening works, but if high strength,

modulus and ductility of FRP are used, the FRP could be the right choice provided the

overall price is considered.

5. REFERENCES

[1] A Borri, Dr M Corradi, Andrea Grazini (2003), FRP Reinforcement of Wood Elements

Under Bending Loads.

[2] Alann André and Robert Kliger, (2009), Strengthening Of Timber Beams Using Frp, With

Emphasis On Compression Strength: A State Of The Art Review. The second international

conference of International Institute for FRP in construction for Asia-Pacific Region.

[3] Allbones, C. (1999). The Use of Pultruded Composites in the Civil Engineering and

Construction Industry.Proceedings of Composites and Plastics in Construction. 16-18 Nov.

Watford, UK, pp (5) 1-3.

[4] A Yusof and A. L. Saleh, (2010), Flexural Strengthening Of Timber Beams Using Glass

Fibre Reinforced Polymer Electronic Journal of Structural Engineering

[5] Arduini, M. and Nanni, A. (1997).Behaviour of Precracked RC beams Strengthened with

Carbon FRP Sheets. Journal of Composites for Construction. Vol. 1, pp 39-80.

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[28] Dr. Salim T. Yousif, “New Model of CFRP-Confined Circular Concrete Columns: Ann

Approach”, International Journal of Civil Engineering & Technology (IJCIET), Volume 4,

Issue 3, 2013, pp. 98 - 110, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.

[29] A.S Jeyabharathy, Dr.S.Robert Ravi and Dr.G.Prince Arulraj, “Finite Element Modeling of

Reinforced Concrete Beam Column Joints Retrofitted with GFRP Wrapping”, International

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ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.

[30] Javaid Ahmad, “Seismic Evaluation & Retrofit Assessment of Jlnm Hospital, Rainawari

Srinagar”, International Journal of Civil Engineering & Technology (IJCIET), Volume 4,

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[31] Shaikh Zahoor Khalid and S.B. Shinde, “Seismic Response of FRP Strengthened RC Frame”,

International Journal of Civil Engineering & Technology (IJCIET), Volume 3, Issue 2, 2012,

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[32] Wani Ahmad and Javed Ahmad Bhat, “Pre-Tensioned Precast Elements as a Replacement to

Wooden Bracings in the Armature Cross Wall System: An Abstract Attempt to Revive the

Forgotten Heritage”, International Journal of Civil Engineering & Technology (IJCIET),

Volume 3, Issue 2, 2012, pp. 181 - 187, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.

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