International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue5- May 2013
Strengthening Of RC Beam Using GFRP Wraps
T.Manikandan 1. G.Balaji ponraj2
1
2
Assistant Professor in Civil Engineering, PSNA College of Engineering and Technology, Dindigul, Tamilnadu.
Assistant Professor in Civil Engineering, PSNA College of Engineering and Technology, Dindigul, Tamilnadu.
Abstract - Fiber reinforced polymer materials are
continuing to show great promise for using strengthening
reinforced concrete structures. These materials are an
excellent option for use as external reinforcing, because of
their light weight, resistant to corrosion and high strength.
The main aim of this study is to investigate the flexural
characteristic of RC beams using GFRP sheets and strips.
This paper presents experimental results of the RC
beams strengthened in flexure with various externally
bonded GFRP configurations, here in order to delay the
GFRP debonding as well as to increase the efficiency of the
GFRP strips, additional U jacket strip or sheets
located in the debonding initiation region have been
proposed. Ten rectangular RC specimens were tested to
evaluate the effect of using the additional U shaped GFRP
sheets and spaced U strips on the intermediate
crack debonding of the laminate. The fiber orientation
effects of the side bonded sheets were also investigated.
The beam specimens to be rehabilitated are initially
loaded to 75% of estimated ultimate load, treated and
tested to failure. The parameters consider for the study
are ultimate load carrying capacity load deflection
failure modes and flexural stiffness of the strengthened
beams.
I. INTRODUCTION
The strengthening of concrete structures with
externally bonded reinforcement is generally done
by using either steel plates or Fibre Reinforced
Polymer (FRP) laminates. Each material has its
specific advantages and disadvantages. The plate
bonding technique is now established as a simple
and convenient repair method of enhancing the
flexural, shear and compressive performance of
concrete structures. Fibre reinforced polymers offer numerous
beneficial
characteristics
over
steel
including
excellent corrosion resistance, non magnetic, non
conductive, generally resistant to chemicals, good
fatigue
resistance,
low
coefficient
of
thermal
expansion, and high strength to weight ratio as well
as being lightweight. FRPs also possess a high
specific stiffness and an equally high specific strength in the
direction
of
fibre
alignment.
Use
of
FRPs provides a high structural efficiency and their
low density makes physical implementation much
easier. Unfortunately, FRPs are also expensive, but
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the higher costs of FRP materials are often offset by
savings in reduced periodic maintenance, longer life
spans and of reduced labour costs.
II. CONCRETE
For concrete the maximum aggregate size used was
20 mm. the concrete mix proportion designed by IS
method to achieve the strength of 20 N/mm2 and
was 1: 1.62:3.8 by weight. the design water cement
ratio was 0.55. Three cube specimens were cast and
tested at the time of beam test (at the age of 28
days) to determine the compressive strength of concrete. The
average
compressive
strength
of
the
concrete was 30 N/mm2.
III. REINFORCING STEEL
The yield of steel reinforcement used in this
experimental
program
was
determined
by
performing
the standard tensile test
on three
specimens of each bar diameter. The average yield
stresses of steel bars were 400 N/mm2 for 10 mm
diabar.
IV. EPOXY RESIN
The success of the strengthening technique critically
depends on the performance of the epoxy resin
used. These epoxies are generally a two part
systems, a resin and a hardener. The resin and
hardener used in this study were Araldite GY 257
and Hardener HY 840 respectively. The properties
of epoxy resin and hardener supplied by the
manufacturer are summarized in Table 1.
V. TENSILE TEST ON FIBRE COMPOSITES
To determine the tensile tests on composites,
different resin to fibre ratios and thicknesses of
GFRP were cast. Tensile tests were conducted as
per the ASTM D 638 - 1968.The tensile test
specimen is shown in figure.3 and the optimum
resin to fibre ratio was found.
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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue5- May 2013
Table.l - Properties of Epoxy Resin and Hardener
S.NO
1
2
3
Properties
Density at
25°C
g/cm3
Specific
gravity
Flectural
strength
Kg/cm2
Araldite
Hardener
HY 840
1.15
0.98
1.8
2.0
450-550
300-400
VI. FRP LAMINATES
Fibre reinforced polymer material systems
composed of fibre embedded in a polymeric matrix,
exhibit
several
properties
which
create
the
opportunity for their use as structural reinforcing
elements.
They
are
characterized
by
excellent
tensile strength in the direction of the fibers. FRP
composites do not exhibit yielding, but instead are
elastic upto failure. They are also characterized by
relatively low modulus of elasticity in tension and
low compressive properties. FRP composites are
corrosion resistant and should perform better than
other construction materials in terms of weathering
behavior.
In
this
study,
bidirectional
glass
reinforced polymer laminate are used.
Table.2 – Properties of FRP
PROPERTIES
E-GLASS
Density of fiber
2.6 x lO-5N/mm3
Fiber thickness
0.3mm
Tensile strength
3450N/mm2
Tensile modulus
62000 N/mm2
epoxy resin was applied to the concrete surface. The
resin mixture flowed and filled the cracks by
gravity. After bonding of FRP to concrete plastic sheets
were wrapped tight around the FRP to enhance the
confinement. Over the plastic sheets weights were
applied to ensure good bonding and removal of
entrapped air from the confinement of FRP. After a
curing time of 2-3 days, the rehabilitated specimens
were tested until failure. The cracking pattern,
ultimate loads and deflected shape of the specimens
were noted.
VIII. TESTING FOR BEAMS
A two-point flexure bending system was adopted
for the tests. All the beams were designed to fail
flexure only, premature failure by shear was
avoided by providing adequate number of stirrups at
2D distance from both ends, after mounting the test
beams over two supporting pedestals kept at the two
ends, the concentrated loads consisting the two
point loading scheme was applied by means of SOT
hydraulic jack, using distributor made of steel box
section.
For
measurements
of
deflection,
dial
gauges were located at three places, one at mid span
and other two under the load points. At the end of each load
increment, observations were recorded for under load
deflection, midpoint deflection, crack development and its
propagation on the beam surfaces. The load at first crack,
ultimate load, type of failure etc., were carefully
observed and recorded
VII. BONDING PROCEDURE
Before bonding the composite fabric onto the
concrete surface, special consideration was given to
the surface preparation. The concrete surface was slightly
grinded
off
to
remove
material
for
enhancing good bonding and cleaned with air
blower to remove all dirt and debris. Once the
surface had been prepared to the required standard, the epoxy
resin had to be mixed in
accordance with
manufacturer's instructions. Mixing was carried out
in a metal container (Araldite GY 257 - 100 parts
by weight and Hardener HY 840 - 50 parts by
weight) and was continued until the mixture was of
a uniform colour. When this was completed, the
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IX.TEST SPECIMENS
The tests were carried out on ten simply supported
reinforced concrete beams with square cross section
of 150* 150 and a span length of 1000 mm. The beams were
strengthened
with
external
U
wraps
bonded to to tension side. The continuous GFRP
reinforcement which give delay in debonding of
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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue5- May 2013
bottom longitudinal GFRP laminates. In this out of ten beams
two were controlled specimen, two beams were treated as
continuous U jacketed wraps, two beams were treated as
partially U jacketing wraps, remaining four beams were
treated and GFRP strips were bonded at different spacing.
X. CRACK PATTERN
The crack concentration area was located in the
pure bending region. The application of GFRP
continuous U - shaped sheets caused a shifting of
the cracked region towards the supports. Due to the
utilization of the side- bonded sheets in the beams,
it was not possible to monitor the crack pattern of
the beams.
XI. LOAD TO DEFLECTION BEHAVIOUR
The load carried by tested beams for all groups of
beams at initial and ultimate load levels. The initial
load was taken at which the deflection of the control beams
was measured at above 35% of their ultimate
load. The initial crack fore the control beams was
about 12 kN and the corresponding deflection at the
level was about 0.35 mm. The ultimate load
obtained is higher for fully and partially wrapped
beams as compared to controlled beams.
XII. COMPARISON OF LOAD VS DEFLECTION
The increase in load carrying capacity of
rehabilitated beams proves the effectiveness of the
strengthened system in upgrading the RC beam
capacity. The test result indicates that the beams
strengthened with GFRP laminates have more load
carrying
capacity
as
compared
to
controlled
specimen. This can be attributed to the high tensile strength
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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue5- May 2013
and modulus of elasticity of GFRP laminates. The
effectiveness
of
bonded
external
reinforcement
becomes
more
apparent,
when
compared to control specimen. As a result the
proportion, increase in strength with control beam
was less than that obtained in the GFRP wraps.
XIII. FAILURE MODES
Normally two failure modes are possible with the
FRP
externally
strengthened
reinforced
concrete
beams: (i) rupture of frp laminates on the bottom of
the beam 2.crushing of concrete at the top of the
beam. both failure modes occur after considerable
flexural cracking and vertical deflection. The mode of failure
was
found
flexure
zone
as
load
increased
higher. These cracks gradually increase in height
with an increase in load.
3.
4.
XV. REFERENCES
[1.]
Azadeh
Parvin
and
Wei
Wang
(2001)
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of FRP
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XIV. CONCLUSION
This research work included the testing of ten
reinforced concrete beams, each having a span of 1000 mm
and
strengthened
in
flexure
using
various
externally bonded GFRPconfigurations based on the
specific findings of this research , the following
conclusions may be drawn
1. For all of the tested specimens, the mode of the
failure was characterized by intermediate crack
debonding
of
the
bottom
FRP
flexural
strengthening reinforcement.
2.
Using an additional transverse FRP continuous U- wrap
ISSN: 2231-5381
system
with
the
fibre
direction
parallel
to the beam axis, increase the ultimate load carrying
capacity,
mainly
because
of
the
flexural
contribution
of
the
GFRP
reinforcement.
There was a significant effect of the width of
the flexural GFRP laminates on the debonding
mechanism. In the case of the narrow laminates
, the debonding plane was observed inside the
concrete cover, along the steel reinforcement.
Not extending the length of the U - shaped
distance to cover the ends of the laminates
limited
the
effectiveness
of 'the
anchorage
techniques as far as the ultimate load capacities
were concerned.
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