EXPERIMENTAL STUDY ON POST REPAIR PERFORMANCE OF

REINFORCED CONCRETE BEAMS REHABILITATED AND STRENGTHENED

WITH CFRP SHEETS. A THESIS

Danish Javid under guide of Assistant Professor Mr Sathish Kumar.

Department of Civil Engineering, Bharath University in Chennai,INDIA

ABSTRACT

Beam is a major structural load transferring Member that support the transverse load

which usually rest on support at its ends. According to the revised codes, beams should have been

better flexural, shear and torsion strength in addition to the load transferring capacity. It is been a

major concern in construction industry in previous many years to increase the strength of the

newly constructed beams or already existing beam. The recent researches have led to various

innovations in high strengthening of beams due to developments, such as FRP NSMR (near

surface mounted reinforcement for concrete structures). Various other materials such as Fibre

Reinforced Concrete, Light Weight concrete and High Performance Concrete.

The present study examines the shear performance and modes of failure of rectangular

simply supported reinforced concrete (RC) beams designed with shear deficiencies. These

members were strengthened with externally bonded carbon fiber reinforced polymer (CFRP)

sheets and evaluated in the laboratory.

Toward that goal, twelve RC beams were fabricated and strengthened with hybrid FRPs

having different combinations of CFRP in shear. The beams were loaded with different

magnitudes prior to strengthening in order to investigate the effect of initial loading on the

behavior of the rehabilitated beam. Then beams were retrofitted with one layer as well two

layers of CFRPs, then the load was increased until the beams reach failure. The experimental

results showed that the shear strength of the beams was significantly increased by the CFRP

sheet and that it is beneficial to orientate the FRP at 450 to the axis of the beam. The shear

strength of FRP strengthened beams is usually calculated by adding individual components of

shear resistance from the concrete, steel stirrups and FRP.

The series of results indicated that there was considerable increase in shear capacity from

18% to 35% and also provided considerable horizontal restraint.

Keywords: rehabilitation; shear; carbon fiber reinforced polymer

INTRODUCTION

Fibre-reinforced polymer (FRP) composite materials typically used in civil engineering

consist of high-strength fibres (e.g., glass, carbon) embedded in a thermosetting polymer matrix

material (e.g., epoxy, polyester, vinyl ester). Fiber reinforced polymers _FRP_ have gained

importance in rehabilitation in recent years. The main reason is their high stiffness-to-weight ratio

over steel plates. Moreover, these materials are less affected by corrosive environmental

conditions and are known to provide longer life and require less maintenance. Large structural

deformations and significant load-carrying capacity prior to ultimate failure, typically seen in

ductile material structures, are critical in civil structures in which sudden failure, and especially

the lack of warning of this sudden and generally catastrophic failure, is unacceptable.

Fibre reinforced polymer (FRP) composite materials have been successfully used in new

construction and for the repair and rehabilitation of existing structures. It is the latter use where

Fibre-reinforced polymer materials hold the greatest promise. Strengthening or stiffening of

reinforced concrete and pre-stressed concrete structures may be required as a result of an increase

in load requirements, a change in use natural or man-made degradation of the structure, or design

or construction defects. Repair with externally bonded FRP reinforcement is attractive to owners,

engineers and contractors because of the ease and speed of installation, the structural efficiency of

the repair, the corrosion resistance of the materials, and the minimal effect that these materials

have on structural dimensions aesthetics, and versatility.

Properties of Carbon Fibers

o As Carbon Fibers are very fine in nature and moreover easily breakable by

stretching (by less than 2% elongation), the fibers can easily be made fuzz. Being crushed

and shortened in unit length, staple tends to become fly or dusts with ease and dispersed

into atmosphere.

o As most Carbon Fibers have high elastic modulus and are very fine in nature, micro fiber

is occasionally allergic to human skins or mucous membranes causing pain or itch.

o As Carbon Fibers have electric conductivity, fly or waste yarn can cause a short-

circuit at electric lines.

o As Carbon Fibers are solid-structured carbons and consequently are hard to be

burned. In incinerating Carbon Fiber products wastes, Carbon Fiber users are

recommended to carefully collect unburned staple dusts to avoid possible electric

troubles.

o CFRP materials are excellent for external strengthening because of their high tensile

strength, light weight, resistance to corrosion, superior durability, and cost-effective

installation process.

o As carbon itself is thought to have good compatibility with human body tissues,

Carbon Fibers or composites of the fibers are largely used as artificial human body parts.

SCOPE AND OBJECTIVE

Scope:

o CFRP was capable of increasing the strength and the flexural stiffness to a level

comparatively higher and CFRP sheets significantly extended the fatigue life of the

reinforced concrete beams.

o Strengthening and rehabilitation of existing reinforced concrete (RC) structures is

becoming an important issue in situations such as demand in the increase of service load

levels, repair due to degradation of a member, design/construction defects, and response

to requirements of newly developed design guidelines. Carbon fiber reinforced polymer

(CFRP) sheets continue to show great promise for use in these situations.

o CFRP are of interest to rehabilitation engineers because of their high-strength to weight

ratio, high fatigue resistance, ease of installation, and the fact that they do not corrode. In

addition to the structural benefits that may be of great use, when externally bonded to

repair corrosion damaged RC elements.

o The use of fiber-reinforced polymer CFRP composites in civil engineering has recently

emerged as an alternative to the traditional methods used for rehabilitation or

reinforcement of structures due to effective bonding to a flexural member, CFRP provide

increased strength in the tension zone of a section those , been determined to be deficient

because of inadequate design or structural damage.

o CFRP in the form of sheets composed of carbon yarns (CFRPs) can be applied to the

surface of a concrete beam by the use of epoxy adhesives, and these sheets are highly

resistant to peel stresses when compared with rigid CFRP plates. This can result in

significant enhancement of the flexural behavior of the member.

o It is shown that the static and the fatigue performance of members to which CFRP sheets

have been externally bonded are significantly improved with respect to strength and

stiffness. There are outstanding benefits observed in the use of external bonding of CFRP

sheets. They have been such that the method is already being used in the field for the

rehabilitation of large structural systems.

Objective:

The main aim is explore the correct application procedure that would result in an increase

in flexural capacity, shear strength, and stiffness. Also to exploit the advantage of high tensile

strength and it’s characteristic of low coefficient of expansion and excellent corrosion resistant.

The objective is to study the effectiveness of unidirectional CFRP fabric in increasing the

shear strength of concrete beam.

The objective is achieved by conducting the following tasks:

(i)Shear testing of concrete beam wrapped with three different configuration of CFRP fabric;

(ii)Calculating the effect of CFRP fabric different layers on the shear strength;

(iii) Evaluating the failure modes.

LITERATURE

Richard Andrew Barnes and Geoffrey Charles Mays (1991) examined the fatigue performance

of CFRP-strengthened concrete beams . Five reinforced concrete beams were tested in fatigue;

two control beams and three strengthened with externally bonded CFRP plates. Three loading

options were used: (1) apply the same loads to both plated and unplated beams, (2) apply loads to

give the same stress range in the rebar in both beams, and (3) apply the same percentage of the

ultimate load capacity to each beam. It appeared that fatigue fracture of the internal reinforcement

steel is the dominant factor governing failure in reinforced concrete beams strengthened in flexure

with CFRP plates. It is therefore recommended that the criteria for the fatigue design of CFRP

plated beams should be to limit the stress range in the rebars to that permitted in an unplated

beam.

Nikolaos Plevris, et al. (1995) analyzed reliability of reinforced-concrete beams strengthened

with CFRP laminates in flexure. They proposed that the effect of each design variable on the

reliability of the system and conclude that, except for the cross-section dimensions, the laminate

length, and the initial strain, all other variables (including the ratio of live to dead load) have

important effects on reliability against flexural failure. Also the flexural behavior is quite likely to

be the dominant response of CFRP-strengthened beams, the writers recommend that the

procedures employed here be applied to additional load effects such as shear.

Oral Buyukozturk and Brian Hearing (1998) proposed a review failure modes including

delamination with the use of FRP to rehabilitate various concrete structures. They discusses

methodologies used to characterize the failure processes of the system. Strengths were shown to

increase with the addition of FRPs, but the specimens were observed to fail through a variety of

mechanisms. Parameters affecting these failure modes were discussed, and techniques used in the

analysis of these modes were reviewed.

Mohsen Shahawy and Thomas E. Beitelman (1999) proposed the feasibility of using CFRP

fabric in the rehabilitation and strengthening of RC structures with respect to both static and

fatigue performance. This applies even to severely damaged beams. They concluded, from the

static test results that strengthening with fully wrapped systems is preferable to partially wrapped

systems. The main parameters in the static test study were the concrete compressive strength, the

number of CFRP laminates Comparisons were made for the standard section and equivalent

sections with two and three layers of CFRP involving the improvements in fatigue behavior,

stiffness, and capacity. The results from the fatigue study indicated that fatigue life of reinforced

concrete beams can be significantly extended through the use of externally bonded CFRP

laminates.

Alex Li, Jules Assih and Yves Delmas (2001) performed tests which Indicated that stiffness

increases while increasing the CFRP sheet area at the flanks. They concluded to strengthen the

RC beam in shear, it is necessary at the same time to strengthen the beam in flexure. The results

obtained by the strain gauges indicate that the first cracks are always found in concrete in the

tension zone causing the flexure. The appearance of the cracks in the beam end is later. Five types

of beams with different strengthening carbon-fiber–reinforced plastic sheets were used. The

experimental results show that it is not necessary to strengthen the entire concrete beam surface.

They also studied the effect of the shear strengthening of RC beams on the stress distribution,

initial cracks, crack propagation, and ultimate strength.

Ahmed Khalifa and Antonio Nanni (2002) presented a study on the shear performance and

modes of failure of rectangular simply supported reinforced concrete (RC) beams designed with

shear deficiencies. These members were strengthened with externally bonded carbon fiber

reinforced polymer (CFRP) sheets and evaluated in the laboratory. The experimental program

consisted of twelve full-scale RC beams tested to fail in shear. The variables investigated within

this program included steel stirrups, and the shear span-to-effective depth ratio as well as amount

and distribution of CFRP. The experimental results indicated that the contribution of externally

bonded CFRP to the shear capacity was significant. The shear capacity was also shown to be

dependent upon the variables investigated.

J. Barros and S. Dias (2002) studied Shear strengthening of reinforced concrete beams with

laminate strips of CFRP. They evaluated the influence of the beam height, they conducted two

series of tests with beams of distinct height. They proposed that these last reinforcing systems

were more effective than the one based on strips of CFRP sheet, not only in terms of increasing

the load bearing capacity, but also enhancing the beam ductility besides they are also much more

simple and faster to apply.

J. F. Chen and J. G. Teng (2003) presented a new shear strength model for RC beams shear-

strengthened with FRP which fail by FRP rupture .The key contribution of the study was the

realization of the fact that the stress distribution in the FRP along the shear crack is non uniform

at shear rupture failure, as a result of the non-uniform strain distribution in the FRP Also the

linear elastic brittle behavior is due to FRP rupture as well.

Abdo AbouJouadeh and Camille A. Issa (2004) proposed Strengthening of concrete with CFRP

results in an increase in load capacity as well as an increase in stiffness. Better performances and

serviceability measures are encountered when anchorage is taken into consideration. Stiffness and

rigidity of members progress with an increased application of CFRP laminates.

Bimal Babu Adhikary and Hiroshi Mutsuyoshi (2005) presented the results of a test program

for shear strengthening characteristics of continuous unidirectional flexible carbon-fiber polymer

sheets bonded to reinforced concrete RC beams. A total of eight 150 mm 200 mm 2,600 mm

concrete beams were tested. Various sheet configurations and layouts were studied to determine

their effects on ultimate shear strength of the beams. From the tests, it was found that the

externally adhesive bonded flexible carbon-fiber sheets are effective in strengthening RC beams

in shear. Further, it was observed that the strength increases with the number of sheet layers and

the depth of sheets across the beam section. Among the various schemes of wrapping studied,

vertical U-wrap of sheet provided the most effective strengthening for concrete beam,

strengthened using this scheme showed 119% increase in shear capacity as compared to the

control beam.

Amir Mofid, et al (2005) presented the results of an experimental investigation on reinforced

concrete (RC) T-beams retrofitted in shear with prefabricated L-shaped carbon fiber–reinforced

polymer (CFRP) plates. Shear strengthening of RC beams with L-shaped fiber-reinforced

polymer (FRP) plates has proved effective. The main objective of this investigation was to

evaluate the performance of the RC beams strengthened in shear with externally bonded (EB) L-

shaped plates as affected by the embedment length of the L-shaped FRP plates. the performance

of the beams strengthened with L-shaped CFRP plates was compared with that of a similar

specimen strengthened with EB FRP sheets without embedment. Results show that the

performance of the specimens strengthened with partially and fully embedded L-shaped CFRP

plates in the beam flange was superior to that of the beams strengthened with EB FRP sheets and

L-shaped CFRP plates with no embedment.

J. G. Teng, et al (2009) proposed shear resistance mechanism of beam. The nine beams were

tested in the present study: three as control specimens, three with bonded FRP full wraps, and

three with FRP full wraps left unbonded to the beam sides. The test results show that the

unbonded FRP wraps have a slightly higher shear strength contribution than the bonded FRP

wraps, and that for both types of FRP wraps, the strain distributions along the critical shear crack

are close to parabolic at the ultimate state.

Abukhari, et al (2010) presented paper that reviews existing design guidelines for strengthening

beams in shear with carbon fibre reinforced polymer (CFRP) sheets.They also proposed a

modification to Concrete Society Technical Report TR55. It goes on to present the results of an

experimental programme which evaluated the contribution of CFRP sheets towards the shear

strength of continuous reinforced concrete (RC) beams. A total of seven, two-span concrete

continuous beams with rectangular cross-sections were tested. The control beam was not

strengthened, and the remaining six were strengthened with different arrangements of CFRP

sheets. The experimental results show that the shear strength of the beams was significantly

increased by the CFRP sheet and that it is beneficial to orientate the FRP at 450 to the axis of the

beam. This led to the indication that strengthening of continuous RC beams in shear with CFRP

sheet can be highly effective and that the contribution of the CFRP depends on its configuration

and orientation.

Prashanth, et al (2012) proposed in their experimental investigation that the when RC beams

were preloaded up to 0 to 50 % of the ultimate capacity and were applied with CFRP sheets at the

soffit of the beam. Then when compared with control beam show characteristic increases in load

carrying capacity, ductility, flexure and shear. The Load vs deflection, and crack mechanism were

studied. Hence the use of CFRP sheets in the soffit of the beam has resulted in enhanced strength

and ductility.

Prashanth, et al (2012) proposed in their experimental investigation that the when RC beams

were preloaded up to 0 to 50 % of the ultimate capacity and were applied with CFRP sheets at the

soffit of the beam. Then when compared with control beam show characteristic increases in load

carrying capacity, ductility, flexure and shear. The Load vs deflection, and crack mechanism were

studied. Hence the use of CFRP sheets in the soffit of the beam has resulted in enhanced strength

and ductility.

Lakshmikandhan K. N, Sivakumar P, Ravichandran R (2013) They performed experimental

investigation to obtain recommendation to overcome the issues in assessment on the exact

damage for simulation. The stiffness degradation method has been developed to estimate and

simulate the exact damage level into beam performed well. They proposed that the repaired

reinforced concrete beam with damage levels (load level between first crack and ultimate load)

between 40 and 90 percent of ultimate load exhibited uniform behavior. The grade of concrete

used for the section design was 60 MPa and the grade of steel was 415 MPa. The repaired beams

restore the original strength with about 30 percentage additional load capacity. Levels Flexural

tests have been conducted with two point loading on 1.5 meter length of reinforced concrete beam

with size 100 mm width and depth of 200 mm.

Sang-Wook Bae, et al (2013) investigated the shear performance of an RC beam strengthened in

shear with externally bonded carbon fiber-reinforced polymer (CFRP) strips, subjected to a cyclic

loading.

The experimental results obtained in this study and a comprehensive review of the

existing literature showed that RC beams strengthened in shear with externally bonded CFRP

could survive 2 million cycles of cyclic loading without failure. Furthermore, the residual shear

strength of the FRP-strengthened beam appeared to be greater for almost 26.3% than the static

shear strength of the unstrengthened control beam.

Shamsher B Singh (2013) addresses the shear strengthening of deficient reinforced concrete

(RC) beams using carbon fiber-reinforced polymer (CFRP) sheets. The effect of the pattern and

orientation of the strengthening fabric on the shear capacity of the strengthened beams were

examined. Three beams with various lay-ups of strengthening fabric, 45°, 0°/90°, and 0°/90°/45°

were examined, in addition to an unstrengthened control beam. Experimental results showing the

advantage of beam strengthened using the various lay-ups of CFRP sheets are discussed. It is

concluded that Beam-45°, Beam-0°/90°, and Beam-0°/90°/45° show about 25%, 19%, and 40%

increases in shear-load carrying capacity in comparison to the control beam, respectively.He

proposed that the strengthened beams exhibited significant strength and stiffness even beyond the

critical value of the shear force.

A.Karthi and P.Easwaran (2015) investigated Analytical And Experimental Investigation On

Shear Strengthened Rc Beams By Using Frp .They provided a brief review on flexural and shear

strengthening of rectangular beams using CFRP/GFRP laminate of different thickness and

scheme. Different applications of FRP laminate for external strengthening of RC beams are

reviewed in this paper. Finally, a discussion on system of strengthening and conclusions are made

along with prospective outlook approach of research.

EXPERIMENTAL PROGRAM

Test Specimen and Materials

Twelve specimens of 1.5m length and cross-section 100mm x 200mm were cast in a

horizontal steel mould. All beams were designed as under reinforced sections.

To investigate the ultimate load carrying capacity of beam, specimens are prepared and

designated as follows.

CB– Control Beam specimens.

S1 – Beam specimen with inclined CFRP wrapping without spacing.

S2– Beam specimen with single layer inclined CFRP wrapping with spacing.

S3 –Beam specimen with double layer inclined CFRP wrapping with spacing.

Preliminary tests are carried as per IS standard on the material used for concrete like

specific gravity, fineness, consistency, and initial setting time for cement. For fine and coarse

aggregates tests such as sieve analysis, specific gravity, impact value, crushing value and abrasion

value (Los Angeles) are conducted as per standards and results are tabulated.

The ingredients of concrete such as cement, fine aggregate, coarse aggregate of

maximum nominal size of 20mm are weighed accurately using the platform weighing machine.

The ingredients are mixed manually and adequate amount of water is added to the constituents of

concrete .The mixing is done till to get uniform mix of concrete is obtained. Proper design mix

proportion is arrived and the mix design.

Reinforcements used in the specimen consists of 2, 10 mm φ bars which were provided

as the main longitudinal reinforcement and 2,8 mm φ bars were used at the top.

6 mm φbars were used as stirrups at a spacing of 200 mm center to center. The reinforcements are

placed inside the mould by giving side and bottom covers respectively. Thorough oiling of the

mould was done before placing the reinforcements. Cover blocks were used to keep the

reinforcements in position.

Strengthening Schemes

The single inclined layer of CFRP wrapping , of width of 100mm and spacing of 50mm

as shown in below figure was bonded along web face, with fibers inclined at 450 to longitudinal

direction of beam. So that they may act perpendicular to inclined shear cracks.

Also to prevent debonding of CFRP layer at tension zone a supplement layer was provided,

whose fibres are along longitudinal axis of beam of width 50 mm and 1200mm length.

Another pattern in which one more inclined layer with 500mm width was inclined to

strengthen the beam in shear.

Note:If anchorages are not provided, it results in development of shear deformation at the

ends within the resins.This interfacial stress thus is responsible for peeling-off of cfrp from the

RC beam.

The two layer CFRP wrapping ,same as above, 100mm width was used but its fibres

oriented at inclination of 450 to the longitudinal axis, followed up with fibre oriented along the

longitudinal direction to be bonded to bottom edge on both sides of a specimen to prevent sheet

from prematurely peeling off from concrete surface. The spacing of 50mm was kept between

each inclined sheet as shown below. Thus giving a configuration of (450+0).

NOTE: Application of CFRP wraps has to be implemented prior to excessive damage of

concrete.So taking any value between given number will give percentage of damage.

Percentage Of Damage: The repaired RC beam with damage level (load level between

first crack and ultimate load) that is between 40% to 85% of ultimate load exhibit uniform

behavior i.e. From the previous journals, it is inferred that the damage level between about 40 and

85 percentage exhibits uniform trend.

Test setup and Instrumentation

Reinforced concrete beams are of three types as deep, intermediate-length and common.

Deep beams have shear span-to-effective depth (a/d) ratio less than two and resist the applied

load within arch action after web cracks. However, common beams have a/d ratio over six and

obey flexural mechanism.

Intermediate-length beams have a/d ratio between 2 to 6 range which leads to variable

angle web cracks generated in web zone. Incomplete generation of arch action leads to shear

strength deficiency of intermediate-length beams. Members with shear strength deficiency have

sudden and catastrophic failure behavior. In these members, wide diagonal cracks generate along

span, propagate toward load points and lead to rupture of transverse stirrups.

The test procedure consisted of loading monotonically until the failure of the beams

occurs. All test beams were tested under a two-point loading system. The span of the beams were

1.50 m, and the distance between the loads was 0.4 m. The shear span for both sides was 0.4 m.

The loads acting on the tested beams were measured by a load cell of 200-kN capacity.

Two linear variable displacement transducers (LVDTs) were used to measure the

deflection under both loading points of RC beams subsequent crack pattern were also marked on

the beam surface as they develop during the application of load from first crack appear until the

failure of the beam. The beams are designed to fail in shear (due to an inadequate number of

stirrups) .

TEST RESULTS AND DISCUSSION

12 RC beams with a rectangular cross-section of 100 mm by 200 mm and shear span-to-

depth ratio (a/d) of 2.28 were tested. To ensure shear failure must occur with in the beam, they

were made weak in shear by providing 200mm centre to centre spacing between 6 mm diameter

steel stirrups. Beam C1 was a control specimen so was not strengthened.

All other beams were to be strengthened. But before strengthening the load of 60% of

ultimate load of control beam was to be applied on rest of beams. After which the remaining tests

investigated the contribution of different arrangements of CFRP to the shear capacity of the

beams. In total three different type of pattern or CFRP orientations were used. In first case i.e. S1

specimen the CFRP was inclined at 450 to the longitudinal direction but with out spacing .In

second case S2 specimen CFRP was used with same configuration i.e. inclined but with spacing

of 50mm in single layer. In third case S3 specimen double layer CFRP pattern were used in a

same way as previous patterns with 50mm spacing. The CFRP sheet was 0.30 mm thick. The

elastic modulus of the carbon fibres was 285*103N/mm

2 and the ultimate tensile strength was

3500 N/mm2.

The experimental results indicate that strengthening of RC beams in shear with CFRP

sheet can be highly effective and that the contribution of the CFRP depends on its configuration

and orientation. Of the twelve beams tested, C1 was a control beam which was, consequently, not

strengthened. Beam C1 failed at total load of 58 kN as a result of a shear-tension failure. The

presence of CFRP sheets was found to alter the crack pattern from that observed in the control

beam.

Experimental results showed that shear strength is enhanced considerably if the CFRP

sheets are oriented with the main fibres at 450 The tests showed that the surface area of the CFRP

sheet can be minimised while maintaining a considerable increase in shear capacity.As already

mentioned CFRP sheets were applied with the main fibres oriented almost perpendicular to the

angle of the shear cracks at an angle of 450 to the longitudinal axis of the beam yielding of the

longitudinal reinforcement was observed at failure along with splitting of the concrete cover at

the bottom face of the beam.The failure cracks were inclined at a relatively steep angles running

from 690-83

0 to the longitudinal axis of the beams i.e. mostly at the centre part of a beam in all

cases.

The first cracking load for all beams has been observed to be same as it is function of

concrete strength alone.

The depth of cracking was 40mm. Shear cracks in the control specimen C1 were

observed close to the middle of the shear span when the load reached approximately 35kN. As the

load increased, additional shear cracks formed throughout, widening and propagating up to final

failure at a load of 58 kN with depth of cracking 135mm.

In specimen S1 strengthened with CFRP (450), no cracks were visible on the sides of the

test specimen due to the FRP wrapping, only longitudinal crack was formed from bottom of the

centre of beam to mid surface of the beam when the applied load was approximately 64 kN. The

crack also initiated close to the position of applied load from bottom portion and extended

towards the support at ultimate load of 78kN. The specimen failed by concrete splitting .This was

an increase of 35% in shear capacity compared to the control specimen C1. The load versus mid

span deflection curves for specimens are illustrated in Figure.

In beam S2, 100 mm wide and 50 mm spacing single layer CFRP sheet with was applied

with the main fibres oriented almost perpendicular to the angle of the shear cracks at an angle of

450 to the longitudinal axis of the beam as shown in Figure.

Beam S2 failed at a load of 68.5 kN, which is 18% greater than C1 i.e. control beam. As a

result of which the CFRP sheet ruptured in tension part at maximum bending point..Under the

loading point at first yielding of the longitudinal reinforcement was observed after further

increase in load , failure along with splitting of the concrete cover at the bottom face of the beam

occured. The failure crack again was inclined at a relatively steep angle.

Beam S3 was strengthened with the same configuration of CFRP sheet as beam S2 but in

double layer.The failure in beam occurred at 76kN which came out to be 31% greater than the C1

i.e. control beam.

Also it is observed that generally the deflection of beams increases with the increase in

load. But it was also noted that, as the number of CFRP layer increases, the deflection decreases

for a corresponding load.

CONCLUSIONS AND FURTHER RECOMMENDATION

An experimental investigation was conducted to study the shear behavior and the modes

of failure of simply supported rectangular section RC beams with shear deficiencies, strengthened

with CFRP sheets. This paper describes a series of tests on continuous beams strengthened in

shear with CFRP. The tests showed that it is beneficial to orientate the fibres in the CFRP sheets

at 450 so that they are approximately perpendicular to the shear cracks. The tests also support the

hypothesis that the efficiency of CFRP reduces with its axial rigidity. The parameters investigated

in this program were existence of steel shear reinforcement at spacing where beam will fail in

shear, shear span-to-effective depth ratio (a/d ratio), and CFRP amount and distribution.

The results confirmed that the strengthening technique using CFRP sheets can be used to increase

significantly shear capacity, with efficiency that varies depending on the tested variables. For the

beams tested in this program, increase in shear strength from 18% to 35% were achieved.

Conclusions that emerged from this study may be summarized as follows:

• The contribution of externally CFRP reinforcement to the shear capacity is influenced

by the a/d ratio.

• Increasing the amount of CFRP may not result in a proportional increase in the shear

strength. As the CFRP amount used to strengthen specimen S-3 was more however the strength of

that of specimen S-1 came out to be more. An end anchor is recommended if FRP debonding is to

be avoided.

• The test results indicated that contribution of CFRP benefits the shear capacity at a

greater degree for beam.

• The series of results indicated that there was considerable increase in shear capacity

from 18% to 35% and also providing considerable horizontal restraint. Recommendations for

future research are the follows:

• Experimental and analytical investigations are required to link the shear contribution of

FRP with the load condition. These studies have to consider both the longitudinal steel

reinforcement ratio and the concrete strength as parameters. Laboratory specimens should

maintain practical dimensions.

• The strengthening effectiveness of FRP has to be addressed in the cases of short and

very short shear spans in which arch action governs failure.

ACKNOWLEDGEMENT

Prima facie, I am grateful to the God for the good health and well being that is necessary

to complete a project. I wish to express my sincere thanks to P.Dayakar, Head of Department, for

providing me with all the necessary facilities for the research. I place on record, my sincere

thanks to Dean of the Faculty, for continue encouragement.

I am also grateful to guide Mr Sathish Kumar, Assistant Prof , in the Department of Civil

engineering. I am extremely thankful and indebted to him for sharing expertise, and sincere and

valuable guidance and encouragement extended to me.

I take this opportunity to express gratitude to all of the Department faculty members, for

their help and support. I also thank my parents for the unceasing encouragement, support and

attention.

I am also grateful to my colleagues who supported me through this venture.

REFERENCES

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5. Amir Mofid, Sébastien Thivierge, Omar Chaallal and Yixin Shao.(2005) “Experimental

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List of Tables and Figures

Tables

Table 1: CFRP Properties

Table 2: Preliminary Test Results

Table 3: Cement Tests

Table 4: Tests on Fresh Concrete

Table 5: Compression test on Concrete cubes

Table 6: Results of Tensile tests on Concrete Cylinders

Figures

Figure 1: Configuration and reinforcement details for beam specimens

Figure 2: Schematic representation of CFRP strengthening schemes

Figure 3: Schematic representation of test set-up

Figure 4: Failure modes of series S specimens

Figure 5: Applied load versus deflection (kN vs mm)

Figure 6 :Applied load versus deflection for specimens C1,S1,S2 and S3

Table 1- CFRP Properties

PROPERTIES CARBON FIBRE

Fibre Orientation Unidirectional

Weight of Fibre 200g/m2

Density of fibre 1.80 g/cc

Fibre thickness .30mm

Ultimate elongation(%) 1.5

Tensile strength 3500 N/mm2

Tensile modulus 285*103 N/mm

2

Table 2- Preliminary Test Results

MATERIALS FINE AGGREGATES COARSE AGGREGATES

PROPERTIES

Specific Gravity 2.61 2.71

Water Absorption % 1.7 .91

Grade Zone II

Impact Value % 19.2

Crushing Value % 20

Los Angles’ Abrasion 9

Value %

Table 3 - Cement Tests

PROPERTIES VALUES

Consistency 33.5%

Fineness test .8%

Initial and Final Setting Time 55,245(min)

Table 6 - Results of Tensile tests on Concrete Cylinders

TENSILE STRENGTH(7 DAYS) TENSILE STRENGTH(28DAYS)

2.97 N/mm2

5.1 N/mm2

Table 4 - Tests on Fresh Concrete

TESTS VALUES

Slump 49

Compaction Factor .85

Vee-Bee Time (sec) 8

Table 5 - Compression test on Concrete

cubes

COMPRESSIVE STRENGTH(7 DAYS) COMPRESSIVE STRENGTH(28DAYS)

21.7 N/mm2

36.4 N/mm2

Figure 1- Configuration and reinforcement details for beam specimens

Figure 2 - Schematic representation of CFRP strengthening schemes

Figure 3 - Schematic representation of test set-up

(a) Specimen C-1

(b) Beams Subjected to 60% of ultimate load of C-1

Figure 4 - Failure modes of control beams

(a) Specimen S-1

(b) Specimen S-2

(c) Specimen S-3

Figure 4 Failure modes of series S specimens

Specimen C-1 Specimen S-2

Specimen S-3 Specimen S-1

Figure 5 Applied load versus deflection (kN vs mm)

Figure 6 Applied load versus deflection for specimens C1,S1,S2 and S3