IRJET- Effect of GFRP Rebars in RC Beams

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 06 Issue: 07 | July 2019 www.irjet.net p-ISSN: 2395-0072
© 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 1760
EFFECT OF GFRP REBARS IN RC BEAMS
A. M. Pardakhe 1, Dr. M. N. Bajad 2
1Reserch scholar, Sinhgad College of Engineering Vadgoan (Bk.), Pune
2Professor, Sinhgad College of Engineering Vadgoan (Bk.), Pune
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Abstract - This paper presents the findings of an
experimental work carried out on flexural behavior of RC
beam when reinforced with Glass Fiber Reinforced Polymer
(GFRP) as replacement ofsteelreinforcement. Underthisstudy
6 beam specimens were studied and the results are compared
to steel reinforcement. The results show good bond behavior
between GFRP and concrete. GFRP reinforced sectionsshowed
more deflection than steel-reinforced section, therefore the
design of such sections is governed by deflection.
Key Words: Crack patterns, Deflection, Flexure, GFRP bar,
RC elements.
1. INTRODUCTION
GFRP rebars are immerging as the replacement for the steel
rebars due to their non-corrosive nature, high tensile
strength and durability. In a region like India wherewehave
long coastal area and rainfall around two-three months,
corrosion of industrial and residential structure is a very
common problem due to which the structures are often
needed to retrofit. As the properties of GFRP reinforcement
differs from the steel reinforcement thedesigncriteria’salso
need to be changed. There are many types of bars available
in the market having a different configuration as the
research on this material will conduct they will gain more
focus and understanding leading to their use.
1.1 LITERATURE REVIEW
[1] O. Abdel Karim et.al (2019) they investigated the
strength, deformability,andserviceabilityofnormalandhigh
strength concrete reinforced with GFRP bars. Beams with
section 200 x 300 x2700 mm were cast and tested up to
failure. Two bars of sizes (12, 16, 20, 25mm) wereusedinthe
bottom. They found that the service moment of section
increases with decrease in bar spacing and the resisting
moment increase with the increase in the concrete strength.
[2] A. Araba et.al (2018) they studied the hybrid GFRP-
steel-reinforced continuous beam and compared them with
beam reinforced with either GFRP or steel reinforcement.
Amount of longitudinal reinforcement and area of steel to
GFRP bars mainly investigated. Results show that increasing
GFRP reinforcement increases load capacity, and less ductile
behavior, increasing steel reinforcement shows moreductile
behavior and less load carrying capacity increase.
[3] Ahmed El Refai et.al (2015) structural performance
of RC beams reinforced with steel-GFRP hybrid
reinforcementisstudiedandcomparedwithGFRPreinforced
beams for flexure. Hybrid beam showed higher ductility and
strength. Codal equations of CSA-S806-12 equation predict
the real deflection of these beams.
[4] S. Jabbar et.al (2018) compared mechanical
characteristics of GFRP and steel bars. Results show tensile
strength of GFRP as 593 MPa and steel bars as 760Mpa.
Flexural strength of unreinforced concrete was 3 MPa and
reinforced concrete with GFRP rebar, sand coated GFRP RC
exhibit flexural strength is 13.5 MPa, as a result, to increase
bonding with concrete and higher strain is 10.5 MPa at 28
days than that of steel-reinforced concrete at the expense of
flexural modulus.
[5] A. Khorasani et.al (2019) investigates the flexural
behavior, cracking, and deflection of concrete beams
reinforced with GFRP bars. 20 sections with 250 x 250 x
2200mm were tested. Arrangement of flexural and
transverse reinforcement was the parameters investigated.
Increaseinload-carryingcapacitywithincreasingtheamount
of transverse reinforcement. And decrease in the crack
widths and mid-span deflection until serviceload.Increasing
the load-carrying capacity by applying a small-diameter
transversereinforcement.Decreaseinthecrackwidths,using
a small-diameter transverse and tensile reinforcement.
2. MATERIAL
Following are the material used for the casting of specimens
2.1 GFRP Rebars
As shown in fig.1 Glass Fiber Reinforced Polymer bars
having with a helical wrapping surface the manufacturing
involves a combination of pultrusion and wrapping
processes.
• Manufacturer- ASLAN
• Density- 2100 kg/m3
• Modulus of elasticity- 45 Gpa
• Ultimate strength- >750Mpa
• Ultimate shear strength- >150
• Ultimate strain- 2.5%
The bars considered in the investigation had nominal
diameter 8mm, 12mm as shown in fig. 1.

Figure 1 GFRP Rebars
2.2 Mix proportions for M30 grade concrete
Cement = 340 kg/m3
Fly ash = 60 kg/ m3
Water = 190 kg/ m3
Fine aggregates = 810 kg/ m3
Coarse aggregate = 1112 kg/ m3
Water-cement ratio = 0.475
3. METHODOLOGY
Both GFRP and steel-reinforced beams were designed using
design manual 3 ISIS, Canada and IS 456-2000 respectively.
Table 1 shows the details of the beam specimens.
Table -1: Details of beam specimens for four-point
bending test
Beam
designat
ion
Size of beam
No. of
specim
ens
Reinforce
ment
provided
Reinforce
ment type
B1
150x150x70
0mm
3 2-8mm φ Steel
B2
150x150x70
0mm
3
1-8mm 2-
12mm φ
GFRP
These specimens were then cured for 28 days and tested for
four-point bending test on a universal testing machine as
shown in fig 2.
Fig. 2 setup for four-point bending test
4. RESULTS AND DISCUSSION
Results of the four-point bending test are shown below
Table -2: Experimental results of beams reinforced with
steel and GFRP rebars
S.N
Load
(KN)
Deflection of
beams with
GFRP rebars
(mm)
Deflection of
beams with
steel rebars
(mm)
Percentage
increase in
deflection of
the beam with
GFRP rebars
w.r.to beam
with steel
rebar
1 0 0 0 0
2 2 0.3 0.4 -33.33
3 4 0.65 0.7 -7.7
4 6 1.1 1.1 0
5 8 1.35 1.25 +7.4
6 10 1.55 1.45 +6.45
7 12 1.8 1.6 +11.11
8 14 2 1.7 +15
9 16 2.1 1.8 +14.28
10 18 2.25 1.85 +17.77
11 20 2.85 1.95 +31.58
12 22 3.05 2 +34.43
13 24 3.8 2.05 +46.05
14 26 3.95 2.1 +46.83
15 28 4.15 2.2 +46.99
16 30 4.3 2.3 +46.51
17 32 4.55 2.35 +48.35
18 34 4.65 2.4 +48.38
19 36 5.2 2.5 +51.92
20 38 5.4 2.6 +51.85
21 40 5.9 2.75 +53.39
22 42 6.2 2.85 +54.03
23 44 6.35 2.9 +54.33
24 46 6.5 2.95 +54.61
25 48 6.7 3.05 +54.47
26 50 7 3.15 +55
27 52 7.15 3.25 +54.54
28 54 7.3 3.35 +54.1
29 56 7.5 3.4 +54.66
30 58 7.75 3.5 +54.83
31 60 7.9 3.65 +53.80
32 62 8.15 3.7 +54.60

33 64 8.3 3.75 +54.80
34 66 8.6 4 +53.48
35 68 8.8 4.1 +54.05
36 70 9.25 4.25 +55.15
37 72 9.7 4.35 +55.40
38 74 10.2 4.55 +55.40
39 76 10.85 4.7 +56.68
Table 3 shows the first crack and service load and chart 1
shows Comparison of load vs deflection curves for steel and
GFRP.
Chart -1: Comparison of load vs deflection curves for steel
and GFRP
Table -3: First crack and Service load for GFRP and steel
RC beams
Material First crack load (KN)
Service load (KN)(@
1.66mm)
GFRP 20 13
Steel 58 19
4.1 Influence of GFRP rebarsonthedeflectionofRC
beams
The deflection of GFRPreinforced beams wasmore bynearly
40-50% than in steel-reinforced beam. GFRP reinforced
beams results in higher deflections (10-12mm). More stiff
curves are obtained in term of the steel-reinforced beam
than GFRP reinforced. As the cracks are formed the GFRP
section the slip between bar and concrete is occurring
resulting in more deflection at lower loads which was not
seen in case of the steel-reinforced beams. The first crack
was observed at a load of 20KN. Service load calculated was
13 KN.it is happening because of the low modus of elasticity
of GFRP bars which is nearly 45 Gpa and also the bond
strength of GFRP with concrete is not as strong as steel bars.
For the steel-reinforcedbeamverylessdeflection(1-1.5mm)
was seen at lower loads (1-12KN)whichthenturnedinto the
first crack at the load of 58 KN. The service load calculatedat
the deflection of 1.66mm was observed to be 19 KN (The
service load calculated is for the maximum allowable
deflection as per the limit state of serviceability which is
(length/360). For the GFRP reinforced beams, large
deflections as compared tosteel reinforcedbeamswereseen
at comparatively smaller loads. The first crack wasobserved
at a load of 20KN. Service load calculated was 13 KN.
4.2 Effect of GFRP rebars on cracking pattern of
RC beam
The crack propagation was markedandmonitoredmanually
throughout the beam testing. As shown in Table 3 which
show the first crack load and service load for steel and GFRP
reinforced section. The difference of first crack load was
nearly60- 65% more in case of steel-reinforced beams. As
there was more deflection occurring in case of GFRP
reinforced beams it was obvious to form cracks at a lower
load as compared to the steel-reinforced sections where
there was not much of deflection.
As shown in fig. 3 and fig. 4 which shows the cracking
pattern for steel and GFRP reinforced sections, In case of
GFRP, reinforced beams some moreminorcrackedspacedat
a lesser distance was then observed. The crack observe was
below the loading points these cracks then propagated into
the compression zone rapidly as the bar slip was occurring
at the interface of bar and concrete. Wider cracks such as
1.5mm were seen in the GFRP reinforced beam at smaller
loads such as 15-20KN, while the deflections for steel-
reinforced beam was seen very less for steel-reinforced
beam cracking started at some higher loads i.e. 58KN.
Fig. 3 cracking pattern of the steel-reinforced beam
Fig. 4 cracking pattern of GFRP reinforced beam

4.3 Effect of GFRP rebars on the failure pattern of
RC beam
As shown in Chart 1which shows the comparison of load vs
deflection curves for steel and GFRP, both the material
shows nearly linear behavior up to failure. The curve for
steel RC beams was stiffer then GFRP beams, as the
deflection was more in case of GFRP beams. The failure of
the steel-reinforced beam was by yielding of steel followed
by the crushing of concrete which was expected failure for
under reinforced beams as they were designed as under
reinforced sections.
The failure in GFRP reinforced beams was by crushing of
concrete in the compression zone as they were designed as
over reinforced sections.Barslipwithminoryieldingofglass
fibers was also seen at the failure of GFRP reinforced beams.
The failure in GFRP reinforced beam wasnotsuddenaswere
reported by many of the researchers; it was more of the
desired failure. in case of the sand coated bar, the sand
coating contributes to the bond strengthofGFRPsectionand
the slip which is occurring in helically wrapped bars in the
present study is not that much and the sudden deboning of
the sand coated layer occurs leading to the sudden failure of
GFRP sections.
5. CONCLUSIONS
Based on the experimental investigation conducted
following conclusions are made.
1. GFRP reinforced beams shows 40-50% more
deflection as compared to steel reinforced beams.
2. The failure of GFRP reinforced sections is not
sudden it is more of a desired failure.
3. Design of GFRP beam is mainly controlled by
deflection and cracking due to the low modulus of
elasticity of GFRP rebar.
4. Results show that GFRP can be used as internal
reinforcement with some modification to design
compared to steel design.
ACKNOWLEDGEMENT
The authors wish to acknowledge Aslan for supplying FRP
rebars used in this study as well as JK concrete for providing
concrete material. The authors would also like to thank the
authorities of the department of Civil Eng. SCOE, Pune for
their kind help and support.
REFERENCES
[1] O. I. Abdelkarim, E. A. Ahmed, H. M. Mohamed, and B.
Benmokrane, “Flexural strength and serviceability
evaluation of concrete beams reinforced with deformed
GFRP bars,” Eng. Struct., vol.186,no.May2018,pp.282–296,
2019.
[2] A. M. Araba and A. F. Ashour, “Flexural performance of
hybrid GFRP-Steel reinforced concrete continuous beams,”
Compos. Part B Eng., vol. 154, pp. 321–336, 2018.
[3] A. El, F. Abed, and A. Al-rahmani,“Structural performance
and serviceability of concrete beams reinforced with hybrid
( GFRP and steel ) bars,” Constr. Build. Mater., vol. 96, pp.
518–529, 2015.
[4] S. A. Jabbar and S. B. H. Farid, “Replacement of steel
rebars by GFRP rebars in the concrete structures,” Karbala
Int. J. Mod. Sci., vol. 4, no. 2, pp. 216–227, 2018.
[5] A. M. M. Khorasani, M. R. Esfahani, and J.Sabzi,“The effect
of transverse and flexural reinforcement on deflection and
cracking of GFRP bar reinforced concrete beams,” Compos.
Part B Eng., vol. 161, pp. 530–546, 2019.
BIOGRAPHIES
Author is a PG student perusing Masters in
Structural Engineering at Sinhgad College
of Engineering, Vadgaon, Pune.
Author is Professor at Sinhgad College of
Engineering, Vadgaon, Pune.

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