Volume 9, Issue 7, July – 2024 International Journal of Innovative Science and Research Technology

ISSN No:-2456-2165 https://doi.org/10.38124/ijisrt/IJISRT24JUL1964

Strengthening of RC Beam with GFRP

Composites in Shear N. B. Bhopale
N. B. Bhopale1 A.S. Manjarekar2
PG, Scholar Civil Engineering Department, Asst. Professor, Scholar Civil Engineering Department,
Sanjay Ghodawat University, Kolhapur, Maharashtra, India Sanjay Ghodawat University, Kolhapur, Maharashtra, India

Abstract:- The rehabilitation, repair and strengthening of retrofitting. Deciding for complete structural replacement may
existing reinforced concrete (RC) structures is essential entail certain drawbacks, including high material and labour
due to factors such as aging, steel reinforcement costs, heightened environmental consequences, and
corrosion, construction/design defects, increased service operational inconveniences stemming from the disruption of
loads demand, seismic events, and advancements in the structure's functionality. Hence, when feasible, repairing
design guidelines. Fiber-reinforced polymers (FRP) are or upgrading the structure through retrofitting is often
now being recognized as a promising material for the considered more favourable. Retrofitting has increasingly
rehabilitation of such structures, through strengthening emerged as the predominant approach in civil engineering,
or repairing. In buildings and bridges, RC sections are with applications including enhancing the load-bearing
commonly found in the form of beams and girders. Shear capacity of aged structures initially designed to withstand
failure of RC beams is particularly due to its sudden lower service loads than presently encountered, seismic
occurrence without warning. Therefore, the utilization of retrofitting, and the restoration of weakened structures. The
externally bonded (EB) FRP composites for shear degradation of concrete structures over time, particularly
strengthening of RC beams has gathered popularity as a accelerated in aggressive environmental conditions,
structural enhancement technique, primarily due to necessitates various methods for remediation, broadly
advantages of FRP composites, such as high strength-to- categorized as structural and non-structural repair. Structural
weight ratio and exceptional corrosion resistance. In repair involves the comprehensive refurbishment, renovation,
addition, FRP repair systems give a cost-saving choice to and retrofitting of the entire system to bolster structural
traditional repair methods and materials. A study was integrity for accommodating additional loads or retrofitting
performed to analyse the shear characteristics of RC purposes.
beams enhanced with continuous glass fiber-reinforced
polymer (GFRP) sheets. Reinforced concrete beams II. METHOD AND MATERIAL
externally bonded GFRP sheets subjected to failure using
a symmetrical two-point concentrated static loading  Literature Review
system. The experimental data obtained included load, The study by Hamid Saadatmanesh et al. (1991)
deflection, and failure modes of each beam, along with compared the strength of concrete girders before and after
the effect of the number of GFRP layers on the beams being reinforced with GFRP plates, showing that the plates
The failures observed in strengthened beams typically effectively enhanced the girders' performance [1]. Nanni, A
commence with the debonding of the FRP sheets, followed et.al (1993) explores on the lateral confinement of concrete
by brittle shear failure. The shear capacities of these using fibre-reinforced plastic (FRP) composites to enhance
beams were higher than that of the control beam. compressive strength, pseudo-ductility, and shear resistance.
Experimental and analytical studies were conducted on
Keywords:- Rehabilitation, RC, GFRP, Shear Strengthening, concrete specimens strengthened with FRP lateral
Externally Bonded (EB). confinement, including compression cylinders and column-
type specimens. Different types of FRP strips were used for
I. INTRODUCTION lateral reinforcement, such as braided aramid FRP tapes with
varying characteristics. The study aimed to demonstrate how
A considerable number of existing concrete structures in lateral confinement affects the behaviour of concrete
India fail to meet current design standards due to substandard specimens under different loading conditions, showing
design, construction, or the need for structural upgrades to increased compressive strength and pseudo-ductility. The
comply with new seismic design requirements arising from research also discusses the need for an analytical model to
evolving standards, corrosion-induced deterioration of steel predict the performance of confined concrete before
caused by exposure to aggressive environments, and developing design procedures for concrete members with FRP
occurrences like earthquakes. The inadequate performance of lateral confinement [2]. Kachlakev D., McCurry, D. D. (2000)
such structures poses a significant concern from a public Experimented on four full-scale reinforced concrete beams
safety perspective, leading to the necessity for reinforced were replicated from an existing bridge to test the
concrete structures to undergo modifications and effectiveness of using fibre reinforced polymer (FRP)
enhancements during their operational lifespan. In such composite for structural strengthening. The results showed
scenarios, two primary solutions emerge: replacement or that the use of FRP composites significantly increased the

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Volume 9, Issue 7, July – 2024 International Journal of Innovative Science and Research Technology
ISSN No:-2456-2165 https://doi.org/10.38124/ijisrt/IJISRT24JUL1964

static capacity of the beams by approximately 150% Moreover, the efficiency of shear strengthening with GFRP is
compared to unstrengthen sections. Retrofitted beams with also dependent on the axial stiffness of the FRP, the existing
both carbon fibre reinforced polymers (CFRP) and glass fibre steel reinforcement ratio, and the concrete strength [13]. The
reinforced (GFRP) composites shows more load carrying externally bonded GFRP is a viable solution for increasing the
capacity minimizes deflection. Fibre optic gauges were shear capacity of RC beams, but the design must consider the
successfully used to monitor strain [3]. Externally bonded interaction between GFRP and internal reinforcement, as well
Glass Fiber Reinforced Polymer (GFRP) sheets have been as the specific characteristics of the beam and the GFRP
investigated as a method for shear strengthening of reinforced material. The complexity of the failure mechanisms and the
concrete (RC) beams by Dong et al., (2012) & Sundarraja & influence of various parameters on the efficiency of shear
Rajamohan, (2008). Research shows that this method can strengthening highlight the need for a comprehensive
effectively improve the shear capacity of RC beams up to understanding and careful design when implementing GFRP
50% [4]. M. A. A. Saafan (2006) Examines shear shear strengthening solutions[11], [13].
strengthening of RC beams using GFRP wraps and significant
improvement in shear strength was observed [5].  Materials
Pannirselvam, N et al. (2008) Develops strength models for
RC beams with externally bonded FRP and models provide  Cement:
accurate and reliable predictions for the strength of FRP- The properties of cement are determined in accordance
reinforced RC beams [6]. Khalifa, E. S (2013) studied with IS12269:2015[14], [15], with specifications outlined in
multilayer wraps which provide substantial improvement in IS4031-1988[16].
the flexural capacity of RC beams [7]. Compares the
effectiveness of CFRP and GFRP in strengthening RC beams.  Fine Aggregate:
Both CFRP and GFRP significantly improved the beam The fine aggregate passed through a 4.75 mm sieve and
strength, with CFRP showing slightly better performance [8]. exhibited a specific gravity of 2.65. As per Indian Standard
specifications, the fine aggregate belonged to zone III in
Dong et al. (2012) studied shear strengthening of RC terms of grading according to IS 383-1970 confirms Zone-III
deep beams with highly ductile fiber-reinforced concrete [17].
jackets, showing improved shear capacity by 13.6%–145.5%
through various reinforcement configurations [9].  Course Aggregate:
Todupunoori Shiva Sai et al. (2020) concluded in that the The maximum size of coarse aggregates is 20 mm, with
beams with a higher thickness of Glass Fiber Reinforced a relative density of 2.89. The choice of crushed stones with
Polymer (GFRP) and beams with a higher thickness of a maximum size of 20mm was made for the aggregates. The
Carbon Fiber Reinforced Polymer (CFRP) shows more tests on aggregate are conducted as per IS 2386 Part III-
deflections than Reinforced Cement Concrete (RCC) beam. 1963[18]. Aggregate comes under Grading zone III as per IS:
Results indicate that beams reinforced with CFRP sheets 383-1970 specifications [17].
demonstrate superior performance when contrasted with those
reinforced with GFRP. Specifically, the beam strengthened  Mix Proportions of Concrete:
with a 1mm thick GFRP sheet controls deflection by 17.09%, Concrete mix design as per IS 10262-1983 [19].Mix
while the 1mm thick CFRP sheet strengthens the beam to Proportion of concrete (by weight) was 1:1.51:3.56:0.5. Cube
control deflection by 22.49% in relation to the control beam. compressive strength after 28 days cube was 21.87Mpa.
Moreover, the beam enhanced with a 2mm thick GFRP sheet
manages deflection by 29.5%, while the beam supported by a  Steel Reinforcement:
2mm thick CFRP sheet controls deflection by 34.79% The longitudinal reinforcements that were used
compared to the control beam. In a similar fashion, the beam comprised of high-yield strength deformed bars with a
reinforced with a 3mm thick GFRP sheet limits deflection by diameter of 12mm at bottom and 8mm Dia. for top as a
41.5%, while the beam upheld by a 3mm thick CFRP sheet anchor bars. The stirrups were used from mild steel bars of
oversees deflection by 46.78% relative to the control beam. 6mm in diameter. The yield strength of the steel
The results indicate that beams strengthened with CFRP reinforcements has been determined by performing the
sheets have a greater ability to manage deflection compared to standard tensile test on three samples of each bar. The
those reinforced with GFRP sheets [10]. The behaviour of average proof stress at 0.2% strain for the 12mm and 8 mm
GFRP-strengthened beams in shear is complex and influenced diameter bars was 415 N/mm2, and for the 6mm diameter
by various factors such as the configuration of the bars, it was 245 N/mm2.The Tests are conducted as per IS
reinforcement, the interaction with internal steel 1786(2008) and IS 432-1(1982)[20], [21].
reinforcement, and the failure modes at ultimate load [11].
Junaid et al., (2021) Studies have shown that the effectiveness  Fiber Reinforced Polymer (FRP):
of GFRP for shear strengthening can be affected by the width Fibre sheet used in this experimental investigation was
and spacing of the strips, the presence of internal steel E-Glass, Bidirectional woven roving mat. It was not
stirrups, and the type of concrete used [12]. Additionally, the susceptible to atmospheric agents. It was also chemically
interaction between internal GFRP bars and stirrups and resistive and anticorrosive. The manufacturer of E-Glass
externally bonded CFRP sheets can influence the shear fiber woven sheet used for the experimental work.
strength gain, which may be reduced when internal and
external reinforcements are in close proximity [12].

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Volume 9, Issue 7, July – 2024 International Journal of Innovative Science and Research Technology
ISSN No:-2456-2165 https://doi.org/10.38124/ijisrt/IJISRT24JUL1964

 Epoxy Resin:
The success of the strengthening technique mostly
depends on the performance of the epoxy resin used for
bonding of FRP to concrete surface. Various types of epoxy
resins with a varying range of mechanical properties are
available in the market. These epoxy resins are generally
available in two parts, as resin and a hardener.

Fig 2 Hand Layup Method of Preparation of GFRP for Test

 Fabrication of GFRP Plate for Tensile Strength

The hand-made contact moulding in an open mould was
used to combine the plies of woven rope in the prescribed
sequence. A flat and rigid plywood platform has been
selected. A plastic sheet is placed on the plywood platform
and a thin polyvinyl alcohol film is applied as a release agent
Fig 1 Bidirectional Woven Glass Fiber Sheet using spray guns. The lamination begins with a brush-
deposited gel coating (Epoxy and Hardener) on the mould,
whose main purpose is to provide a smooth outer surface and
protect fibres from direct exposure to the environment. The
ply was cut from a roll of woven roving. The reinforcement
layer was placed on the form at the top of the gel layer and the
gel layer was again applied by brush. All air bubbles caught
were removed with serrated steel rollers. The hand laying
process is the continuation of the above-mentioned process
before the gel layer is completely hardened. The plastic sheet
was covered again with polyvinyl alcohol as a release agent,
applied to the top of the plate.

Table 1 Modulus of Elasticity of GFRP Specimens

Ultimate Stress Change In Ultimate
GFRP plate of Ultimate Load (N)
(MPa) Length mm Strain Modulus of elasticity
4500 310.34 4.00 0.027 11637.93
5250 362.07 4.50 0.030 12068.97
2 layers 5000 344.83 5.00 0.033 10344.83
4500 310.34 4.50 0.030 10344.83
4750 327.59 4.00 0.027 12284.48
Average 4800 331.03 4.40 0.029 11336.21

Subsequently, a heavy flat metal solid platform was number of 8mm φ was provided at top with 6mm φ 160 mm
mounted on the plate to compress. The plate was left for at spacing stirrups as shear reinforcement.
least 48 hours. and cut in size 150mmx25mm for the test, five
specimens were tested.  Strengthening of Beams with GFRP Sheet and testing
The concrete surfaces were prepared by chiselling and
 Casting of Beams roughening, followed by cleaning with an air blower. An
epoxy resin mixture, made by combining 100 parts resin with
 Description of Specimens : 10 parts hardener, was uniformly applied to the beam in shear
The experimental work consists of 8 number of RC zone. Glass fiber woven sheet was then positioned onto the
rectangular beams of same longitudinal reinforcement of epoxy layer, and pressure was applied with a roller to ensure
three numbers of 12mm φ as tension reinforcement and two resin penetration and eliminate air bubbles. Another resin
layer was applied before placing a second sheet, repeating the

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Volume 9, Issue 7, July – 2024 International Journal of Innovative Science and Research Technology
ISSN No:-2456-2165 https://doi.org/10.38124/ijisrt/IJISRT24JUL1964

pressure application with steel roller. This process ensured the Specimens were tested using a universal testing machine.
composite laminate was well-affixed, with consistent pressure Beam tested under two-point loads to measure shear
maintained to expel excess resin and ensure proper bonding. capacities. Deflection readings were taken two dial gauges
The beams, bonded with glass fiber fabric in shear zone, were placed at center at center of beam specimen and L/3 distance
cured at room temperature for at least a week before testing. from end support.

Table 2 Beam Strengthening Systems

Beam ID Sheet Thickness (mm) No. of layers of sheet Strengthening system with GFRP sheets
CB Control Beam (No sheets)
SSB1 0.58 1 U warping with one layer on shear zone
SSB2 0.58 2 U warping with two layers on shear zone
SSB3 0.58 3 U warping with three layers on shear zone

III. RESULTS AND DISCUSSION reinforcement with GFRP. SSB3 displays the most significant
advancement in ultimate load (1.82 times that of the reference
The beam U warped with three layers of GFRP beam) and the greatest shear contribution from GFRP. The
performed better than the Control beam and all other beams advancement in ultimate load carrying capacity and shear
strengthen (SSB1, SSB2, and SSB3). It is observed from contribution escalates with multiple layers of GFRP The
above fig.5 that, the ultimate load carrying capacity of all utmost shear contribution is evident in SSB3 at 45.06%,
strengthened beams is higher than the control beam. All whereas the minimum is in SSB1 at 21.47%. The reference
reinforced beams (SSB1 to SSB3) demonstrate superior beam (CB) failed exclusively in shear. All reinforced beams
ultimate capacities in comparison to the reference beam (CB). failed due to delamination of GFRP in conjunction with
concrete crushing followed by shear collapse. From the fig.4
SSB1 and SSB2 demonstrate the most effective reduction in
deflection at midspan, each showing an 11% reduction
compared to the control beam. SSB3, although having the
highest ultimate load capacity, shows a lesser reduction in
deflection at midspan (5%).The reinforcement technique
utilizing GFRP proves to be efficacious in amplifying both the
ultimate load capacity and shear effectiveness of the beams.

Fig 3 Test Setup

Fig 5 Ultimate Load Vs Warping System

Fig 4 Load Vs Deflection

The enhancement ratio of ultimate load (λ) varies from

1.27 (SSB1) to 1.82 (SSB3), signifying a noteworthy
advancement in load-bearing ability as a result of the
Fig 6 Shear strength Vs Warpping System

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Volume 9, Issue 7, July – 2024 International Journal of Innovative Science and Research Technology
ISSN No:-2456-2165 https://doi.org/10.38124/ijisrt/IJISRT24JUL1964

Table 3 Ultimate Load, Shear Contribution by Fiber and Load Enchancement Pattern, Natureof Failuer
Experimental Results Load Enhancement Nature of Failure
Load at Vn, Vc,test (Vf,test/ Factor = P
Specimen Vf,tes
failure test +Vs,tes Vn,test)* (Strengthen Beam) /
t (kN)
P in (KN) (kN) t (kN) 100 (%) P(Control Beam)
CB 69.5 34.75 - - - Shear failure
Delamination of GFRP followed by
SSB1 88.5 44.25 34.75 9.5 21.47% 1.27
crushing of concrete & shear failure
Delamination of GFRP followed by
SSB2 110.5 55.25 34.75 20.5 37.10% 1.59
crushing of concrete & shear failure
Delamination of GFRP followed by
SSB3 126.5 63.25 34.75 28.5 45.06% 1.82
crushing of concrete & shear failure

IV. CONCLUSION Engineering,” Volume, vol. 45, no. 1, pp. 1432–1440,

2013, doi: 10.1016/j.compositesb.2012.08.021.
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compared to the control beam: as 27%, 59%, and 82% 2014, doi: 10.1155/2014/967964.
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