Strengthening structures via external bonding of advanced fibre reinforced polymer (FRP) composite is becoming very popular worldwide during the past decade because it provides a more economical and technically superior alternative to the traditional techniques in many situations as it offers high strength, low weight, corrosion resistance, high fatigue resistance, easy and rapid installation and minimal change in structural geometry. Although many in-situ RC beams are continuous in construction, there has been very limited research work in the area of FRP strengthening of continuous beams.

1. 27
International Journal of Research and Innovation (IJRI)
International Journal of Research and Innovation (IJRI)
STRENGTHENING OF RC BEAMS USING FRP SHEET
Ketepalli Sravani 1
, K. Mythili2
, G.Venkat Ratnam3
1 Research Scholar, Department Of Civil Engineering, Aurora's Scientific Technological & Research Academy, Hyderabad, India
2 Associate Professor, Department Of Civil Engineering, Aurora's Scientific Technological & Research Academy,Hyderabad, India
3 Associate Professor, Department Of Civil Engineering, Aurora's Scientific Technological & Research Academy, Hyderabad, India
*Corresponding Author:
Ketepalli Sravani,
Research Scholar, Department of CIVIL Engineering,
Aurora's Scientific Technological & Research Academy,
Hyderabad, India
Published: October 27, 2014
Review Type: peer reviewed
Volume: I, Issue : II
Citation:Ketepalli Sravani,(2014)STRENGTHENING OF
RC BEAMS USING FRP SHEET
INTRODUCTION
General
To keep a structure at the same performance level,
it needs to be maintained at predestined time inter-
vals. Ifthe lack of maintenance has lowered the per-
formance level of the structures, the need to repair
up to the original performance level is required. In
case, when higher performance levels are needed,
upgrading of the structure is necessary. Perfor-
mance level means load carrying capacity, durabil-
ity and function. Upgrading refers to strengthening,
increased durability and change of function.
The fundamental aim of this work is to give clear
guidelines for the process of strengthening rein-
forced concrete beams using FRP materials. Types
and methods of FRP construction are described in
general. FRP properties and their effect on strength-
ening are illustrated.
External plate bonding is a method of strengthening
which involves adhering additional reinforcement to
the external faces of a structural member. The suc-
cess of this technique relies heavily on the physical
properties of the material used and on the quality
of the adhesive, generally an epoxy resin, which is
used to transfer the stresses between the flexural
element and the attached reinforcement. The first
reported case strengthened by this technique was in
1964. Epoxy-bonded mild steel plates were applied
to load bearing beams in the basement.
Frp Strengthening Of Beam:
Many existing buildings and bridges are in need
of repair or upgrade. A crumbling infrastructure
is areality that all communities are dealing with.
Existing beam members that are deficient with re-
spect toflexural capacity are costly to demolish and
reconstruct. An efficient, cost-effective means of-
strengthening existing concrete beams is needed so
an unsafe or unuseable structure can once again
beutilized.The method of epoxy-bonding steel plates
and fiberglass reinforced plastics to the tensile face
Abstract
Strengthening structures via external bonding of advanced fibre reinforced polymer (FRP) composite is becoming very
popular worldwide during the past decade because it provides a more economical and technically superior alternative
to the traditional techniques in many situations as it offers high strength, low weight, corrosion resistance, high fatigue
resistance, easy and rapid installation and minimal change in structural geometry. Although many in-situ RC beams
are continuous in construction, there has been very limited research work in the area of FRP strengthening of continu-
ous beams.
In the present study an experimental investigation is carried out to study the behavior of continuous RC beams under
static loading. The beams are strengthened with externally bonded glass fibre reinforced polymer (GFRP) sheets. Differ-
ent scheme of strengthening have been employed. The program consists of fourteen continuous (two-span) beams with
overall dimensions equal to (150×200×2300) mm. The beams are grouped into two series labeled S1 and S2 and each
series have different percentage of steel reinforcement. One beam from each series (S1 and S2) was not strengthened and
was considered as a control beam, whereas all other beams from both the series were strengthened in various patterns
with externally bonded GFRP sheets. The present study examines the responses of RC continuous beams, in terms of
failure modes, enhancement of load capacity and load deflection analysis. The results indicate that the flexural strength
of RC beams can be significantly increased by gluing GFRP sheets to the tension face. In addition, the epoxy bonded
sheets improved the cracking behaviour of the beams by delaying the formation of visible cracks and reducing crack
widths at higher load levels. The experimental results were validated by using finite element method.
KEYWORDS: continuous beam; flexural strengthening; GFRP; premature failure;
1401-1402

2. 28
International Journal of Research and Innovation (IJRI)
ofreinforced concrete beams has been studied ex-
tensively as a method to strengthen existing rein-
forcedconcrete structures. Experimental results
have proven that these techniques can be an effec-
tive means ofincreasing a beam’s flexural capacity
and stiffness. However, a problem that has been
encounteredduring the testing of reinforced beams
with epoxy-bonded plates is separation of the plate
from the beamat the plate termination prior to con-
crete compression failure. Furthermore, there is
some question as tothe loss of the ductile failure
mode usually associated with reinforced concrete
failure when carbon fibersheets and plates are used
for external reinforcement. The use of expansion
anchors has been examinedas a method of elimi-
nating epoxy-bonded plate tear off at termination.
Bonding of steel and fiber-reinforced plastics is the
most popular means of reinforcing existingconcrete
beams. However, applying epoxy can be a delicate
process requiring near perfect workingconditions.
The beam must be properly prepared for epoxy ap-
plication (smooth, flat, sandblasted, dustfree,clean
surface), and the thickness of the epoxy layer must
be uniform. Perfect conditions are not thenorm
when one is working in the field. This procedure can
be successful, but the quality controlmeasures can
be extreme. A solution to this problem is to take
advantage of the fact that bolts have beensuccessful
in stopping plate tear-off, and go one step further
and use anchor bolts as the main system ofanchor-
ing supplemental external steel reinforcement to the
beam. This method can be used underfrequently
encountered field conditions since the work envi-
ronment need not be ideal and prep work formount-
ing the reinforcement is minimal (aside from drilling
holes into the flexural member).
In the 1980s, fiber reinforced polymer (FRP) materi-
als began being used in civil engineering applica-
tions. The external strengthening of reinforced con-
crete members was an ideal use for preformed FRP
strips, which are lighter and easier to install than
steel strips. FRP strips do not rust when exposed
to moist environments as do steel strips. Currently
FRP strips are bonded to the concrete surface in the
same manner as the steel strips, and the concrete
substrate requires similar preparation as it would
for the bonding of a steel plate. The adhesive layer
between the concrete and strip can present prob-
lems for the behaviour of the strengthened flexural
member. Peeling stresses are induced in the ends of
the strip, which tend to pull the strip away from the
concrete. If these peeling stresses are larger than
the strength of the adhesive, the strip will peel away
from the beam suddenly. This results in the beam
losing the increase in strength provided by the strip,
and may cause a sudden and catastrophic failure.
Flexural members with attached steel strips often
have large anchor bolts on the ends of the strips.
These anchor bolts are provided to keep the steel
plate from falling and damaging people or prop-
erty in case the adhesive layer fails. Recently end
anchorages have been examined for use with FRP
strips as well.
Many researchers have been argued that the bond
is significantly affected by surface preparation and
general concrete quality, the degree and type of
external anchorage was found to be important in
maintaining the composite behaviour. This moti-
vates researches to find a more sustainable method
to bond CFRP and GFRP laminates with concrete
substrate using mechanical techniques.
A method of flexural strengthening reinforced con-
crete members with mechanically steel bolts is de-
veloped in this research study instead of an adhe-
sive to attach a specially designed FRP strip to the
concrete. This new technique has a potentially fast-
er installation time and a potentially more ductile
failure structural response than the sudden failure
of conventional bonded method with epoxy.
Fibre-Reinforced Plastic (FRP):
(also fibre-reinforced polymer) is a composite mate-
rial made of a polymer matrix reinforced with fibres.
The fibres are usually glass, carbon, basalt orara-
mid, although other fibres such as paper or wood or
asbestos have been sometimes used. The polymer
is usually an epoxy, vinyl ester or polyester thermo-
setting plastic, andphenol formaldehyde resins are
still in use.
Fibre Types:
Different types of fibres can be used in manufactur-
ing the FRP materials such as the following (Kend-
all, 1999):
E-Glass:
The most common reinforcing fibre is E-Glass,
which derives its name from its electrical resist-
ance. E-glass is available in a variety of forms such
as continuous rovings, woven rovings, stitched fab-
rics, unidirectional tapes and chopped fibre mats
or Chopped Strand Mat (CSM) as it is commonly
known. The fibre is very economical and of moder-
ate strength but low modulus (stiffness).
C, R and S Glass:
C glass is a chemical resistant grade mainly used
in the production of surface tissues to protect the
surface of a laminate. R glass and S glass are high
strength grades. Aramid Aramid, or Polyaramid fi-
bres such as Kevlar 49 are man-made organic fibres
offering very high tensile strengths and low density.
Aramid fabrics are very soft and easy to handle.
Carbon:
Carbon fibre is the most expensive of the more
common reinforcements, but due to its very high
strength and stiffness it is the most commonly used
fibre.

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International Journal of Research and Innovation (IJRI)
Advantages Of Fibre-Reinforced Plastics:
Fibreglass and other fibre-reinforced plastics (FRP),
such as carbon fibre and Kevlar, have many advan-
tages:
Low weight: even the cheapest fibreglass is much
less dense and therefore lighter than the equivalent
volume of steel or aluminium.
Mechanical strength: fibreglass is so strong and
stiff for its weight, it can out-perform most other
materials including steel, aluminium and timber.
Carbon-fibre and Kevlar can be used to make items
even lighter. The strength and stiffness per weight
of these exotic materials exceeds that of all known
materials.
High impact strength: in contrast to most metals,
fibreglass does not change shape even when it is
ruptured.
Resiliance: fibreglass products have a hard finish.
The gelcoat which covers and colours finished fi-
breglass products can be tailored to provide greater
hardness or more resiliance.
Formability: fibreglass can be moulded to almost
any desired shape. We can create or copy most
shapes with ease. Fibreglass moulds are cheap to
make compared with those for metal or plastic. It
is quite easy to change the weight and strength of a
product without having to make a new mould.
Chemical resistance: fibreglass is minimally re-
active, making it ideal as a protective covering for
surfaces where chemical spillages might occur. It
is useful in the construction of tanks, hoods, cov-
ers, pipes, ducts and other structures in the paper,
chemical, water treatment and petroleum indus-
tries.
Corrosion resistance: unlike metal, fibreglass does
not rust away and it can be used to make long-last-
ing structures.
Weatherproof: the chemical and corrosion resist-
ance of fibreglass combined with the gelcoat finish
on most products make fibreglass ideal for using
outdoors. If necessary, chemicals can be added to
provide additional protection against UV light.
Electrically insulating: for those working in the
power industry, materials such as fibreglass which
do not conduct electricity are essential for safety.
However, if required, we can adapt our fibreglass to
become electrically conductive.
Thermally insulating: fibreglass is not only long
lasting but maintains its temperature, thus reduc-
ing heating and cooling costs. The fibreglass sur-
face remains comfortable to touch, being neither
hot nor cold.
Fire resistance: by the addition of special addi-
tives, fibreglass can be made fire resistant to meet
most fire codes. The resins used conform to BS476
or ASTM-E-84.
Low thermal expansion: minimally affected by
changes in external temperature, fibreglass is ideal
for situations where temperatures fluctuate.
Anti-magnetic, no sparks: making it super safe for
the power industry, fibreglass has no magnetic field
and resists electrical sparks.
Low maintenance: once installed, fibreglass prod-
ucts require minimal maintenance.
Durable custom colours: fibreglass can be col-
oured, shiny or dull. We can even add patterns if
you wish. Your production costs are reduced as our
gelcoated products don't need further painting or
finishing. With care, the gelcoat finish on our auto-
motive parts can last for up to 20 years.
Long life: our fibreglass products are built to last.
Fibreglass has high resistance to fatigue and has
shown excellent durability over the last 50 years.
Structural Applications Of FRP:
FRP can be applied to strengthen the beams, col-
umns, and slabs of buildings and bridges. It is pos-
sible to increase the strength of structural members
even after they have been severely damaged due to
loading conditions. In the case of damaged rein-
forced concrete members, this would first require
the repair of the member by removing loose debris
and filling in cavities and cracks with mortar or
epoxy resin. Once the member is repaired, strength-
ening can be achieved through wet, hand lay-up of
impregnating the fibre sheets with epoxy resin then
applying them to the cleaned and prepared surfaces
of the member.
Two techniques are typically adopted for the
strengthening of beams, relating to the strength en-
hancement desired: flexural strengthening or shear
strengthening. In many cases it may be necessary to
provide both strength enhancements. For the flex-
ural strengthening of a beam, FRP sheets or plates
are applied to the tension face of the member (the
bottom face for a simply supported member with
applied top loading or gravity loading). Principal
tensile fibres are oriented in the beam longitudinal
axis, similar to its internal flexural steel reinforce-
ment. This increases the beam strength and its stiff-
ness (load required to cause unit deflection), how-
ever decreases the deflection capacity and ductility.
Disadvantages Of FRP:
The main disadvantage of externally strengthening
structures with fibre composite materials is the risk
of fire, vandalism or accidental damage, unless the
strengthening is protected. A particular concern for
bridges over roads is the risk of soffit reinforcement

4. 30
International Journal of Research and Innovation (IJRI)
being hit by over-height vehicles.
A perceived disadvantage of using FRP for strength-
ening is the relatively high cost of the materials.
However, comparisons should be made on the basis
of the complete strengthening exercise; in certain
cases the costs can be less than that of steel plate
bonding. A disadvantage in the eyes of many clients
will be the lack of experience of the techniques and
suitably qualified staff to carry out the work. Final-
ly, a significant disadvantage is the lack of accepted
design standards.
Experimental Study
Experimental Program:
A total of six rectangular beams were tested to find
the effectiveness of the strengthening process us-
ing GFRP laminates. Two beams were tested as con-
trolled beams for flexure, while the remaining four
beams were strengthened using GFRP mats and
tested with the goal of increasing their flexural ca-
pacities. The concept is based on the fact that the
force developed in the GFRP mat is due to contact
between the materials because of the bond which is
responsible for the increase in flexural capacities.
This paper provides information regarding
(i)Deformation characteristics of load versus deflec-
tion
(ii)Ductile capacity of composite beams.
Casting Of Specimen:
For conducting experiment, the proportion of 1: 1.9:
3.91 is taken for cement, fine aggregate and course
aggregate. The mixing is done by using concrete
mixture. The beams are cured for 28 days. For each
beam six concrete cube specimens were made at the
time of casting and were kept for curing. The uni-
axial compressive tests on produced concrete (150
× 150 × 150 mm concrete cube) were performed and
the average concrete compressive strength (fcu) af-
ter 28 days for each beam is shown in tables.
Descrip-
tion
Cement
Sand (Fine
Aggregate)
Course
Aggregate Water
Mix Pro-
portion
(by weight)
1 1.9 3.91 0.51
Quantities
of materi-
als
213 404.7 832.83 108.63
Materials For Casting:
Cement :
Portland Slag Cement (PSC) (Brand: Konark) is used
for the experiment. It is tested forits physical prop-
erties in accordance with Indian Standard specifica-
tions. It is having a specific gravity of 2.96.
(i)Specific gravity : 2.96
(ii)Normal Consistency : 32%
(iii)Setting Times : Initial : 105 minutes Final : 535
minutes.
(iv)Soundness : 2 mm expansion
(v)Fineness : 1 gm retained in 90 micron sieve.
Fine Aggregate:
The fine aggregate passing through 4.75 mm sieve
and having a specific gravity of 2.67are used. The
grading zone of fine aggregate is zone III as per In-
dian Standard specifications.
Coarse Aggregate:
The coarse aggregates of two grades are used one
retained on 10 mm size sieve and
another grade contained aggregates retained on 20
mm sieve. It is having a specific gravity of 2.72.
Water:
Ordinary tap water is used for concrete mixing in
all the mix.
Test Specimens:
All the six cast test specimens are rectangular RC
beamsof cross section 220mmx250mm and length
2000mm.six numbers of beams were tested for flex-
ure. It consists of two numbers of 10mmdiameter
and one number of 12mm diameter bars whichare
used in compression and tension sides. The ver-
ticalstirrups are provided with 6mm diameter bar
at aspacing of 225mm c/c as shown in Figure.
Thesebeams were designed to fail by flexure. Out
of sixbeams, two were used as control beams and
remainingfour were strengthened using GFRP mats.
The designmix adopted for all beams were 1: 1.9:
3.91 and watercement ratio of 0.51. The test speci-
mens were cured for28 days and they were tested.

5. 31
International Journal of Research and Innovation (IJRI)
GFRP Composites:
E-Glass fiber in the form of woven fabric of600gm/
sq.m is used for strengthening purposes. Forbond-
ing these fabric mats with RC beams, 45% byweight
of general purpose Iso resin is used.
Strengthening Configurations:
Two strengthening configurations were adopted us-
ingGFRP mats for flexure beams which are shown
in figure. Externally they are wrapped by a (i) Sin-
glelayer at two vertical sides, and tension bottom
face(GFRP1) and (ii) Double layer at two vertical
sides andtension bottom face(GFRP2).
ReinforcementOf Beam
Strengthening Of Gfrp Beams
Testing Arrangements:
The beams were tested in a steel loading frame ca-
pacityof 500kN. The arrangement is shown in Fig-
ure. Forgetting moment effect of the beam, an ex-
perimentalsetup has been arranged as shown in
Figure. Thesupport points were provided with a
hinge support atboth ends of steel rod welded to the
base plate. The loadwas applied by means of 500kN
capacity hydraulic jackpowered by hand operat-
ed hydraulic pump. The systematic Figure clearly
shows the loadingarrangement for getting the mo-
ment effect of the beam.
Deflections measured at important points. Three
number of dial gauges have used for recording the
deflection ofthe beams. One dial gauge has placed
just below thecenter of the beam and the remaining
two dial gaugeshave placed just near the middle of
the beam to measuredeflections as shown in Figure.
The cracking patternwas also marked by drawing
lines along the crack. The tests are carried out till
the ultimate failure.
FABRICATION OF GFRP PLATE:
There are two basic processes for moulding: hand
lay-up and spray-up. The hand lay-up process is
the oldest and simplest fabrication method. The
process is most common in FRP marine construc-
tion. In hand lay-up process, liquid resin is placed
along with FRP against finished surface. Chemi-
cal reaction of the resin hardens the material to a
strong light weight product. The resin serves as the
matrix for glass fiber as concrete acts for the steel
reinforcing rods.
The following constituent materials were used for
fabricating plates:
1.Glass Fiber
2.Epoxy as resin
3.Diamine as hardener as (catalyst)
4.Polyvinyl alcohol as a releasing agent
A plastic sheet was kept on the plywood platform
Loading frame
Loading System
Shear Force Diagram

6. 32
International Journal of Research and Innovation (IJRI)
Bending Moment Diagram
Flexural Zone
and a thin film of polyvinyl alcohol was applied as a
releasing agent by the use of spray gun. Laminating
starts with the application of a gel coat (epoxy and
hardener) deposited in the mould by brush, whose
main purpose was to provide a smooth external sur-
face and to protect fibers from direct exposure from
the environment. Steel roller was applied to remove
the air bubbles. Layers of reinforcement were ap-
plied and gel coat was applied by brush. Process
of hand lay-up is the continuation of the above
process before gel coat is hardened. Again a plas-
tic sheet was applied by applying polyvinyl alcohol
inside the sheet as releasing agent. Then a heavy
flat metal rigid platform was kept top of the plate for
compressing purpose. The plates were left for mini-
mum 48 hours before transported and cut to exact
shape for testing.
Determination Of Ultimate Stress, Ultimate Laod
And Young’smodulus:
The ultimate stress, ultimate load and young’s mod-
ulus was determined experimentally by performing
unidirectional tensile test on the specimens cut in
longitudinal and transverse direction. The speci-
mens were cut from the plates by diamond cutter
or by hex saw. After cutting by hex saw, it was pol-
ished in the polishing machine.
For measuring the young’s modulus, the specimen
is loaded in INSTRON 1195 universal tensile test
machine to failure with a recommended rate of ex-
tension. Specimens were gripped in the upper jaw
first and then gripped in the movable lower jaw.
Gripping of the specimen should be proper to pre-
vent slippage. Here, it is taken as 50 mm from each
side. Initially, the stain is kept zero. The load as well
as extension was recorded digitally with the help of
the load cell and an extensometer respectively. From
these data, stress versus stain graph was plotted,
the initial slope of which gives the Young’s modulus.
The ultimate stress and the ultimate load were
Bonding epoxy
Universal Testing Machine
obtained at the failure of the specimen. The average
value of each layer of the specimens is given.
TESTING OF BEAMS:
All the six beams are tested one by one. All of them
are tested in the above arrangement. The gradual
increase in load and the deformation in the dial
gauge reading are taken throughout the test. The
load at which the first visible crack is developed is
recorded as cracking load. Then the load is applied
till the ultimate failure of the beam. The deflections
at midpoint of each span are taken for all beams
with and without GFRP and are recorded with re-
spect to increase of load. The data furnished in this
chapter have been interpreted and discussed in the
next chapter to obtain a conclusion.

7. 33
International Journal of Research and Innovation (IJRI)
Test Resultsand Discussions
Failure Modes Of Beams:
Peeling Failure:
The application of the GFRP fabrics to the soffit of
the concrete beam introduces shear transfer to the
concrete/epoxy interface. At the termination of the
GFRP fabric, a change in stiffness and discontinuity
of beam curvature creates a stress concentration in
the concrete, often initiating cracks that can lead
to debonding.
Based on the experimental observations, the mech-
anism of peeling failure can be described in
the following sequences:
1) uniformly spaced cracks developed in the con-
stant bending moment zone and some small cracks
in the shear span
2) as a result of shear stress and normal stress con-
centrations at the GFRP fabric end, the concrete
rupture strength was exceeded at this point and a
crack formed near the fabric end. This end Debond-
ing propagation to the CFRP fabric endDebond-
ingstarted here Loading point crack widened with
increasing load and propagated to the level of the
internal steel reinforcement
3) individual concrete cover blocks were formed be-
tween two adjacent cracks;
4) the end concrete cover block peeled away as the
load increased
5) This process continued sequentially for the rest
of the blocks
Due to the dowel action of the stirrups, the weakest
plane forms right under the longitudinal steel rein-
forcement, thus, the peeling failure always started
from the end of the plates and propagated along the
concrete cover parallel to the longitudinal steel re-
inforcing bars.
Debonding Failure
The beams with FRP fabric extending all the way to
the support are subjected to lower stress concentra-
tions at the FRP cutoff points and shear crack may
not developed at these points. On the other hand,
within the shear span, the shear stress concentra-
tion around the flexural or shear crack mouth dis-
placements may also lead to the local debonding of
the fabric along concrete-fabric interface.
Flexural cracks, located in regions of the beam with
large moment, can initiate interfacial fracture which
propagates between the concrete and FRP interface.
Crack mouths located in regions of the beam with
mixed shear and moments can subject an interfa-
cial crack to mixed mode loading.
For beam with a long fabric covering almost the
whole length of span, the debonding started at one
of the flexural cracks in vicinity of the point load.
The debonding propagated towards the sheet end
until total delamination occurred.
In general, peeling of the concrete cover at the level of
internal steel reinforcement occurred in beams with
shorter fabric length where significant shear cracks
were formed, indicating that significant stress con-
centration can occur at the sheet anchorage zone.
Debonding failure between FRP fabric and concrete
occurred due to susceptibility of the interface rela-
tive to vertical displacements of shear cracks in the
concrete beam.
BEAM SHEAR FAILURE MODES:
Three distinct modes of shear failure are observed,
which describe the manner inwhich concrete fails:
• Diagonal tension failure
• Shear compression failure
• Shear tension failure
DIAGONAL TENSION FAILURE:
This type of failure is usually a flexure-shear crack.
The diagonal crack starts from the last flexural
crack at mid span, where it follows direction of the
bond reinforcing steel and the concrete at the sup-
port. After that, few more diagonal cracks develop
with further load, the tension crack will extend
gradually until it reaches its critical point where it
will fail without warning. This type of shear failure
is always in the shear-span when the a/d ratio is in
the range of 2.5 to 6. Such beams fail either in shear
or in flexure.
Failure Plane
SHEAR COMPRESSION FAILURE:
This type of failure is common in short beams with
a/d ratio between 1 and 2.5. It’s called a web shear
crack, it’s crushing the concrete in the compression
zone due to vertical compressive stresses developed
in the vicinity of the load.
Compression Failure
SHEAR TENSION FAILURE:
This type of failure is also common in short beams
and it is similar to diagonal tension failure. First

8. 34
International Journal of Research and Innovation (IJRI)
we can see a shear crack that is similar to the di-
agonal crack that goes through the beam; the crack
extends toward the longitudinal reinforcement and
then propagates along the reinforcement that re-
sults in the failure of the beam.
Shear Torsion Failure
RESULTS OF EXPERIMENTS:
FAILURE PATTERN OF CONTROL BEAM:
The beam was so designed that it fails by flexure.
The beam was tested up to 42kN. The yield of steel
was found at 37kN. With further increase in the
load, regularly spaced flexure and shear cracks were
observed and they extended from the bottom of the
specimen towards the top fiber as shown in figure.
Failure Pattern OfControl Beam
FAILURE PATTERN FOR STRENGTHENING
BEAM:
The beam was strengthened with one layer of GFRP1
laminate on the bottom face and two vertical sides
completely. The ultimate load carrying capacity of
the beam was 66kN. The yield load was 57kN. The
load carrying capacity of this beam was increased
by 55%when compared to control beam as shown in
Figure. The failure was initiated by the stretching of
fiber wrap at the bottom in the flexure zone followed
by the crushing of concrete in compression zone as
shown in figure.
Failure Pattern Of Single Layer GFRP1 Beam
Failure Pattern OfDouble Layer GFRP2Beam
The beam was strengthened with two layers of
GFRP2 laminate on the bottom face and two verti-
cal sides completely. The ultimate load carrying ca-
pacity of the beam was 92kN. The yield load was
78kN. The load carrying capacity of this beam was
increased by 120% when compared to control beam
as shown in Figure. The failure was initiated by the
stretching of fibre wrap at the bottom in the flexure
zone followed by the crushing of concrete in com-
pression zone as shown in Figure.
Designation
of Beams
Failure Mode Pu(KN)
λ=Pu(strengthened beam)
Pu(Control beam)
Control beam Flexure failure 42 1
Single layer
GFRP1
Debonding failure
without concrete
cover
66 1.57
Double layer
GFRP2
Tensile rupture 92 2.19
LOAD DEFLECTION AND LOAD CARRYING
CAPACITY:
The GFRP strengthened beams and the control
beams are tested to find out their ultimate load
carrying capacity. The deflection of each beam un-
der the load point i.e. at the midpoint of each span
position is analyzed. Mid-span deflections of each
strengthened beam are compared with the control
beam. It is noted that the behavior of the flexure
deficient beams when bonded with GFRP sheets are
better than the control beams. The mid-span deflec-
tions of the beams are lower when bonded externally
with GFRP sheets. The stiffness of the strengthened
beams was higher than that of the control beams.
Increasing the numbers of GFRP layers generally
reduced the mid span deflection and increased the
beam stiffness for the same value of applied load.
The use of GFRP sheet had effect in delaying the
growth of crack formation.

9. 35
International Journal of Research and Innovation (IJRI)
Ductility:
A qualitative measure of ductility has to be with
reference to a load – deformation response. A duc-
tileresponse would be reflected in the deformation-
increasing at nearly constant load. The ratio of
theultimate deformation to the deformation at the-
beginning of the horizontal path can give a measure
ofductility.
Ductility has generally been measured by a ratio
calledthe ductility index or factor (μ). The ductil-
ity index isusually expressed as a ratio of rotation
(θ), curvature(φ), deflection (displacement) (M), and
absorbed energy(E) at failure (peak load) divided by
the correspondingproperty when the steel starts
yielding. In the presentstudy, ductility was obtained
based on displacement and absorbed energy meth-
ods.
Displacement Ductility:
Figure shows the response of a strengthened RC-
beam. Point A corresponds to initial concrete
cracking,point B to the first steel yielding, and point
C to failure.Based on Figure , the displacement duc-
tility index is defined by Eq. Where Mu is the mid
span deflection at ultimate beamload and My is the
mid span deflection at yielding loadof the tensile
steel reinforcement at the central support.
Table shows the experimental values of (Mu),
(My),the displacement ductility index value of (μM),
and percentage of increase of displacement ductility
in theBC. It can be seen that increasing the num-
ber of GFRPsheet layers led to increased mid span
deflection at yieldload level and ultimate load level.
Finite Element Analysis
Finite element method (FEM) is a numerical meth-
od for solving a differential or integral equation. It
has been applied to a number of physical problems,
where the governing differential equations are avail-
able. The method essentially consists of assuming
the piecewise continuous function for the solution
and obtaining the parameters of the functions in a
manner that reduces the error in the solution.
Formulation:
The governing equation for beam is given in Equa-
tion 5.1.
d2
y
M = EI
d x2
The displacement field v(x) assumed for the beam
element should be such that it takes on the
values of deflection and the slope at either end as
given by the nodal values
The v(x) can be given by,
v(x) = c0 + c1x + c2 x2
+c3x3
Type Of
Beam
(∆u) (∆y) (µ∆) Increase (Eu) (Ey) (µE) Increase
overthe
control
beam(%)
overthe
control
beam(%)
(mm) (mm) By
Eq.(1)
kN kN By
Eq.(2)
Control
beam
20 8 2.5 - 42 37 1.13 -
Sin-
glelayr
GFRP1
29 9.5 3.05 22 66 57 1.16 3
Double
layer
GFRP2
38 11 3.45 38 92 78 1.18 5
In solving the differential equations through integra-
tion, there will be constants of integration that must
be evaluated by using the boundary and continu-
ity conditions. The variables whose values are to be
determined are approximated by piecewise continu-
ous polynomials. The coefficients of these polynomi-
als are obtained by minimizing the total potential
energy of the system. In FEM, usually, these coef-
ficients are expressed in terms of unknown values
of primary variables. Thus, if an element has got n
nodes, the displacement field u can be approxi
Where ui are the nodal displacements in x-direction
and Ni are the shape functions, which are functions
of coordinates.
Shape functions or interpolation functions Ni are
used in the finite element analysis to interpolate the
nodal displacements of any element to any point
within each element.
The beam element has modulus of elasticity E, mo-
ment of inertia I, and length L. Each beam element
has two nodes and is assumed to be horizontal as
shown in Figure. The element stiffness matrix is giv-
en by the following matrix, assuming axial deforma-
tion is neglected.
VALIDATION OF EXPERIMENTAL VALUE:
In the experimental work, the tested beams consist
of two spans of each 1000 mm as shown in Figure
is discritized as shown in Figure.
Test Beam
Finite Element Model

10. 36
International Journal of Research and Innovation (IJRI)
Beam Element Forces
The following sign convention is considered for the
deflection calculation.
(a)x is +ve towards right
(b)y is +ve upwards
(c)Anticlockwise slopes are +ve
(d)Sagging BM are +ve
Three element mesh is taken as shown in Figure.
Subdividing the span AD into three elements with
a node at the load point has the advantage that,
the nodal forces can be specified very easily. The
meshing has also ensured that all elements are of
uniform size, for easy hand calculation. Following
the standard procedure, the global stiffness matrix
and force vector is obtained as below,
{K}8x8
{U}8x1
= {F}8x1
Since there are four nodes and two d.o.f. per node,
the global stiffness matrix is of size (8x8) and {F} is
a column vector of size (8×1). The boundary condi-
tions stipulate that the vertical deflection be zero at
node 2 and 4.
Boundary conditions are the known values of de-
flection and slope at specified values of x. Here the
following boundary conditions are used for the ex-
act analysis of the beam.
At x =L/2; y=0
At x= 3L/2; y= 0
Thus reduced set of equations involving unknown
nodal d.o.f. is obtained in matrix form as,
{f}6x1
= [k]6x6
[u]6x1
Solving the Equation, the nodal displacement is
found out.
The Numerical and Experimental results are found
to be very near. The trend of the loads varying with
the deflection presents that the linear elastic state
exits in the structure, when the loads are equivalent
to about 48 KN.
CONCLUSIONS
Based on the Investigation the Following Conclu-
sions were made:
1.The provision in the ACI code can be used as
guidelines for the use of FRP in the repair and reha-
bilitation of structures.
2.Maximum percentage of increase in ultimate
strength was 55% for single layer GFRP and 120%
for double layer GFRP.
3.By the use of GFRP wrapping in the beams, the
initial cracks are formed at higher loads than in
their respective control beams. This shows that the
use of GFRP wrapping is more efficient in the case
of strengthening of shear and flexure.
4.The increase in the strength of the beam depends
upon the increasing number of laminates provided
to the beam.
5.The presence of GFRP laminate beam inhibits the
development of the diagonal cracks. There is a sig-
nificant difference in the load which causes this ini-
tial crack. The load –deflection behaviour was better
for beams retrofitted with GFRP laminate beams.
6.For the beams laminated with GFRP flexural fail-
ure was more prominent than shear failure.
7.When compared to control beams, displacement
ductility index of the strengthened beams is in-
creased by 22%, and 38% for Single layer of GFRP1
and Double layer of GFRP2 respectively.
8.The energy ductility index is increased by 3%
and 5% for Single layer of GFRP1 and Double layer
of GFRP2 respectively, when compared to control
beams.
9.In lower range of load values the deflection ob-
tained using Finite Element models are in good
agreement with the experimental results. For higher
load values there is a deviation with the experimen-
tal results because linear FEM has been adopted.
Scope Of The Future Work
It promises a great scope for future studies. Follow-
ing areas are considered for future research:
a.Experimental study of continuous beams with
opening
b.Non linear analysis of RC continuous beam
c.FEM modeling of unanchored U-wrap
d.FEM modeling of anchored U-wrap

11. 37
International Journal of Research and Innovation (IJRI)
REFERENCES:
[1] ACI Committee 440, “Starte-of-the-art report on fiber
reinforced plastic reinforcement for concrete structures”,
Report ACI 440R-96, USA: American Concrete Institute,
1996.
[2] Aiello MA, Valente L, and Rizzo A, “Moment redistribu-
tion in continuous reinforced concrete beams strength-
ened with carbon fiber-reinforced polymer laminates”,
Mechanicsof Composite Materials, vol. 43, pp. 453-466,
2007.
[3] Aiello MA, and Ombres L, “Cracking and deformability
analysis of reinforced concrete beams strengthened with
externally bonded carbon fiber reinforced polymer sheet”,
ASCEJournal of Materials in Civil Engineering, vol. 16,
No. 5, pp.292-399,2004.
[4] Akbarzadeh H, and Maghsoudi AA, “Experimental
and analytical investigation of reinforced high strength
concrete continuous beams strengthened with fiber rein-
forced polymer”, Materials and Design, vol. 31, pp. 1130-
1147, 2010.
[5] Arduini M, and Nanni A, “Behaviour of pre-cracked R.
C. beams strengthened with carbon FRP sheets”, ASCE
Journal of Composites for Construction, vol. 1, No. 2, pp.
63-70, 1997.
[6] Ashour AF, El-Refaie SA, and Garrity SW, “Flexural
strengthening of RC continuous beams using CFRP lam-
inates”, Cement and Concrete Composites, vol. 26, pp.
765-775, 2003.
[7] Bank LC, and Arora D, “Analysis of RC beams strength-
ened with mechanically fastened FRP (MF-FRP) strips”,
Composite Structures, vol. 79, pp. 180–191, 2006.
[8] Bousselham A and Chaallal O, “Behavior of reinforced
concrete T-beams strengthened in shear with carbon fiber
reinforced polymer - an experimental study”, ACI Struc-
tural Journal, vol. 103, pp. 339–347, 2006.
[9] Brosens K, and Gemert D, “Anchoring stresses be-
tween concrete and carbon fiber reinforced laminates”,
Non-metallic (FRP) Reinforcement for Concrete Struc-
tures, Proc.of 3rd International Symposium, Sapporo, Ja-
pan, pp. 271–278, 1997.
[10] Ceroni F, “Experimental performances of RC
beams strengthened with FRP materials”,Construction
and Building Materials, vol. 24, pp. 1547-1559, 2010.
[11] Chahrour A, and Soudki K, “Flexural response of re-
inforced concrete beams strengthened with end-anchored
partially bonded carbon fiber-reinforced polymer strips”,
Journal ofComposites for Construction ASCE, vol. 9(2),
pp. 170–177, 2005.
[12] Concrete Society, “Design guidance for strengthen-
ing concrete structures using fibre composite materials”,
Report No. 55, 71p, 2000.
[13] El-Refaie SA, Ashour AF, and Garrity SW, “CFRP
strengthened continuous concrete beams”, Proceedings of
the ICE - Structures and Buildings, pp. 395 - 404, 2003.
[14] El-Refaie SA, Ashour AF, and Garrity SW, “Sag-
ging and hogging strengthening of continuous reinforced
concrete beams using carbon fibre-reinforced polymer
sheets”, ACIStructural Journal, vol. 100, pp. 446-453,
2003.
[15] El-Refaie SA, Ashour AF, and Garrity SW, “Sagging
strengthening of continuous reinforced concrete beams
using carbon fibre sheets”, The 11th BCA Annual Con-
ferenceon Higher Education and the Concrete Industry,
Manchester, UK, pp. 281–292, 3–4 July2001.
[16] El-Refaie SA, Ashour AF, and Garrity SW, “Strength-
ening of reinforced concrete continuous beams with CFRP
composites”, The International Conference on Struc-
turalEngineering, Mechanics and Computation, Cape
Town, South Africa, 2–4. , pp.1591– 1598, April 2001.
[17] El-Refaie SA, Ashour AF, and Garrity SW, “Tests of
reinforced concrete continuous beams strengthened with
carbon fibre sheets”, The 10th BCA Annual Conference
onHigher Education and the Concrete Industry, Birming-
ham, UK, pp. 187–198, Jun 2000.
[18] Eshwar N, Nanni A, and Ibell TJ, “Performance of
two anchor systems of externally bonded fiber-reinforced
polymer laminates”, ACI Materials Journal, vol. 105(1),
pp. 72– 80, 2008.
[19] Galati D, and De Lorenzis L, “Effect of construction
details on the bond performance of NSM FRP bars in con-
crete”, Advances in Structural Engineering, vol. 12(5), pp.
683– 700, 2009.
[20] Garden HN, and Hollaway LC, “An experimental
study of the influence of plate end anchorage of carbon
fibre composite plates used to strengthen reinforced con-
crete beams”, Composite Structures, vol. 42, pp. 175–
188, 1998.
[21] Garden HN, and Hollaway LC, “An experimental
study of the influence of plate end anchorage of carbon
fibre composite plates used to strengthen reinforced con-
crete beams”, Composite Structures, vol. 42, pp. 175–
188, 1998.
[22] Grace NF, “Strengthening of negative moment region
of reinforced concrete beams using carbon fiber- rein-
forced polymer strips”, ACI Structural Journal, vol. 98,
No. 3, pp. 347-358, 2001.
[23] Grace NF, Sayed GA, and Saleh KR, “Strengthening
of continuous beams using fibre reinforced polymer lami-
nates”, American Concrete Institute, Farmington Hills,
Mich, pp. 647-657, 1999.
[24] Grace NF, Wael R, and Sayed AA, “Innovative tri-
axailly braided ductile FRP fabric for strengthening struc-
tures”, 7th International Symposium on Fiber Reinforce
Polymer for Reinforced Concrete Structures, ACI, Kansas
City, MO, 2005.
[25] Grace NF, Abdel-Sayed G, Soliman AK, and Saleh KR,
Strengthening of reinforced concrete beams using fibre
reinforced polymer (FRP) laminates”, ACI Structural Jour-
nal, vol. 96, No. 5, pp. 865-874, 1999.
[26] Grace NF, Soliman AK, Abdel-Sayed G, and Saleh
KR, “Strengthening of continuous beams using fibre re-
inforced polymer laminates”, Proceedings of 4th Inter-
nationalSymposium on Fibre Reinforced Polymer Rein-
forcements for Reinforced Concrete Structures, SP-188,
American Concrete Institute, Farmington Hills, Michigan,
USA,pp.647-657, 1999.

12. 38
International Journal of Research and Innovation (IJRI)
[27] Jumaat MZ, and Alam MA, “Experimental and nu-
merical analysis of end anchored steel plate and CFRP
laminate flexurally strengthened R. C. beams”, Interna-
tional Journal ofPhysical Sciences, vol. 5, pp. 132-144,
2010.
[28] Jumaat MZ, Rahman MM, and Rahman MA, “Review
on bonding techniques of CFRP in strengthening concrete
structures”, International Journal of the Physical Scienc-
es, vol. 6(15), pp. 3567-3575, 4 August. 2011.
[29] Kadhim, “Effect of CFRP Sheet Length on the Behav-
ior of HSC Continuous Beam”, Journal of Thermoplastic
composite materials, Vol. 00, 2011.
[30] Khalifa A, and Nanni A, “Improving shear capacity
of existing RC T-section beams using CFRP composites”,
Cement and Concrete Composites, vol. 22, pp. 165–174,
2000.
[31] Khalifa A, Tumialan G, Nanni A, and Belarbi A,
“Shear Strengthening of Continuous Reinforced Beams
Using Externally Bonded Carbon Fiber Reinforced Poly-
mer Sheets”,In: Fourth International Symposium on Fiber
Reinforced Polymer Reinforcement for Reinforced Con-
crete Structures, Baltimore, MD, American Concrete In-
stitute, pp. 995–1008, November 1999.
[32] Lamanna AJ, Bank LC, and Scott DW, “Flexural
strengthening of reinforced concrete beams using fasten-
ers and fiber-reinforced polymer strips”, ACI Structural
Journal, vol. 98(3), pp. 368–76, 2001.
[33] Lee TK, and Al-Mahaidi R, “An experimental investi-
gation on shear behaviour of RC T-beams strengthened
with CFRP using photogrammetry”, Composite Struc-
tures, vol. 82, pp. 185–193, 2008.
[34] Leung CKY, and Cao Q, “Development of strain hard-
ening permanent formwork for durable concrete struc-
tures”, Materials and Structures, vol. 43(7), pp. 993–
1007, 2009.
[35] Leung CKY, “Delamination failure in concrete beams
retrofitted with a bonded plate”,Journal of Materials in
Civil Engineering, vol. 13, pp. 106–113, 2001.
[36] Leung CKY, “FRP debonding from a concrete sub-
strate: Some recent findings against conventional belief”,
Cement and Concrete Composites, vol. 28, pp. 742–748,
2006.
[37] Maghsoudi AA, and Bengar H, “Moment redistribu-
tion and ductility of RHSC continuous beams strength-
ened with CFRP”, Turkish Journal of Engineering and
EnvironmentalSciences, vol. 33, pp. 45-59, 2009.
[38] Micelli F, Anniah RH, and Nanni A, “Strengthening
of short shear span reinforced concrete T joists with fiber
reinforced plastic composites”, Journal of Composites for-
Construction, vol. 6, pp. 264–271, 2002.
[39] Nguyen DM, Chan TK, and Cheong HK, “Brittle
failure and bond development length of CFRP-concrete
beams”, Journal of Composites for Construction, vol. 5(1),
pp. 12–17,2001.
[40] Niemitz CW, James R, and Berña SF, “Experimental
behavior of carbon fiber-reinforced polymer (CFRP) sheets
attached to concrete surfaces using CFRP anchors”, Jour-
nal ofComposites for Construction, vol. 12(2), pp. 185–
194, 2010.
[41] Obaidat YT, Susanne H, Ola D, Ghazi A, Yahia A,
“Retrofitting of reinforced concrete beams using compos-
ite laminates”, Construction and Building Materials, vol.
25, pp. 591-597, 2010.
[42] Oehlers DJ, Liu IST, and Seracino R, “Shear deforma-
tion debonding of adhesively bonded plates” Proc. Institu-
tion of Civil Engineers, vol. 158(1), pp. 77–84, 2005.
[43] Orton, SL, Jirsa JO, and Beyrak O, “Design consid-
erations of carbon fiber anchors.”Journal of Composites
for Construction, vol. 12(6), pp. 608–616, 2008.
[44] Pan JL, and Leung CKY, “Effect of concrete composi-
tion on FRP/concrete bond capacity.” Journal of Compos-
ites for Construction, vol. 11(6), pp. 611–618, 2007.
[45] Rahimi H, and Hutchinson A, “Concrete beams
strengthened with externally bonded FRP plates.” Jour-
nal of Composites for Construction, vol. 5(1), pp. 44–56,
2001.
[46] Ritchie PA, Thomas DA, Lu LW, and Connelly GM,
“External reinforcement of concrete beams using fiber re-
inforced plastic”, ACI Structural Journal, vol. 88(4), pp.
490– 500,1991.
[47] Smith ST, and Teng JG, “Debonding failures in FRP-
plated RC Beams with or without U strip end anchorage”,
Proc. FRP Composites in Civil Engineering, vol. 1, pp.
607–615, 2001.
[48] Panda KC, Bhattacharyya SK, and Barai SV, “Shear
behaviour of reinforced concrete T-beams with U-bond-
ed glass fibre reinforced plastic sheet”, Indian Concrete
Journal, vol. 84, pp. 61–71, 2010.
[49] Riyadh A, “Coupled flexural retrofitting of RC beams
using CFRP straps”, CompositeStructures, vol. 75, pp.
457-464, 2006.
[50] Ross CA, Jerome DM, Tedesco JW, and Hughes ML,
“Strengthening of reinforced concrete beams with exter-
nally bonded composite laminates”, ACI Structural Jour-
nal, vol. 96. No. 2, pp. 65-71, 1999.
[51] Sebastian WM, “Significance of mid-span de-bond-
ing failure in FRP-plated concrete beams”, ASCE Journal
of Structural Engineering, vol. 127, No. 7, pp.792-798,
2001.
[52] Sheikh SA, “Performance of concrete structures
retrofitted with fibre reinforced polymers”, Engineering
Structures, vol. 24, pp. 869-879, 2002.
[53] Smith ST, and Teng JG, “FRP-strengthened RC
beams I: Review of debonding strength models”, Engi-
neering Structures, vol. 24, No. 4, pp. 385-395, 2002.
[54] Spadea G, Bencardino F, and Swamy RN, “Structural
behaviour of composite RC beams with externally bonded
CFRP”, Journal of Composites for Construction, ASCE,
pp. 132– 7, 1998.
[55] Teng JG, Smith ST, Yao J, and Chen JF, “Interme-
diate crack-induced debonding in RC beams and slabs”,
Construcion and Building Materials, vol. 17(6–7), pp.
447–462, 2003.

13. 39
International Journal of Research and Innovation (IJRI)
[56] Yang ZJ, Chen JF, and Proverbs D, “Finite element
modelling of concrete cover separation failure in FRP plat-
ed R. C. beams”, Construction and Building Materials,
vol. 17, No.1, pp. 3-13, 2003.
[57] Yao J, and Teng JG, “Plate end debonding in FRP-
plated RC beams—I: Experiments”,Engineering Struc-
tures, vol. 29(10), pp. 2457–2471, 2007.
[58] Yao J, Teng, JG, and Lam L, “Experimental study
on intermediate crack debonding in FRP-strengthened RC
flexural members”, Advances in Structural Engineering,
vol. 8(4), pp. 365–396, 2005.
AUTHOR
Ketepalli Sravani
Research Scholar, Department Of Civil Engineering,
Aurora's Scientific Technological & Research Academy,
Hyderabad, India
K. Mythili
Associate Professor, Department Of Civil Engineer-
ing, Aurora's Scientific Technological & Research
Academy,Hyderabad, India
G.Venkat Ratnam
Associate Professor, Department Of Civil Engineer-
ing, Aurora's Scientific Technological & Research
Academy,Hyderabad, India