D.-W. SEO ET AL. 867
grip adapters and cured for two weeks to ob tain the com-
pressive strength approximately 60 MPa. Figure 2 shows
the tensile test with the loading rate equal to 5 mm/min
[13].
Brittle fractures of GFRP bars, including Case A,
Asaln, and V-rod were seen in Figure 3 one of short-
comings of FRP was a brittle fracture and this issue was
improved by material hybridization proved in this study.
Table 3 summarizes the list of specimens that tested in
this study. 7 cases of tested specimens were selected for
tensile test associated with 4 types explained in Table 1.
A total of 21 samples consisting 3 specimens for each
case was tested.
Cases A through C were correspond ing to the types A,
B, and C in Table 1. For cases D-1 and D-2, type D in
Table 1 was subdivided into two types depending on a
steel type; Case D-1 with circular shape of rebar and D-2
with the deformed rebar. Cases A through D-2 were de-
veloped and fabricated by KICT [6]. Two commercially
available GFRP bars (i.e., Aslan and V-Rod, [9,10]) were
also considered and their tensile strength was compared
to other hybrid GFRP bars developed at KICT.
3.2. Results and Discussion
The tensile strength of the specimen can be calculated by
dividing the measured maximum load by the cross-sec-
tional area of the GFRP bar (Ahybrid). The elastic modulus
of the GFRP bar (Ehybrid) can be given by the following
expression as recommended in [13].
12
hybrid
12 hybrid
PP
EA
. (1)
In Equation (1) P1 and P2 are the applied loads corre-
sponding to 50% and 25% of the ultimate load respec-
tively, and ɛ1 and ɛ2 are the c o rresponding strains.
Table 4 and Figures 3 and 4 summarize the result of
tensile tests. Figure 3 shows a linear increment of elastic
The linear stress-strain relationship of the specimens was
found for Case A, Aslan and V-rod, in which no material
hybridization was considered.
In these cases the brittle fracture was occurred shown
Figures 1(c) and (d). Small change of the curvature was
Table 3. List of specimens for tensile test.
Case Description
A D13 with GFRP only
B
C
D-1
D-2
Aslan
V-Rod
D13 with GFRP and D4 steel wire inserted
D13 with GFRP and D2 × 13EA (steel wire) inserted
D13 with GFRP and D9 rebar inserted
D13 with GFRP and D9 deformed rebar inserted
D13 Aslan 100 [9]
D13 V-Rod GFRP [10]
Table 4. Results of tensile tests at the location L/2.
Elastic Modulus (E) Tensile Strength (P)
Case GPa N (E) MPa N (P)
A 49.6 1.00 754.4 1.00
B
C
D-1
D-2
Aslan
V-Rod
53.7
98.3
129.2
133.2
52.5
46.2
1.08
1.98
2.60
2.69
1.06
0.93
762.1
688.2
-
715.4
601.8
574.6
0.94
0.85
-
0.88
0.74
0.71
found for cases B and C after steel wire was likely
yielded earlier than GFRP. The bilinear type of fracture
behavior was detected for cases D-1 and D-2. In these
cases, failure mechanism is clearly dominated by steel
rebar in the initial stage and GFRP holds the applying
loads after approximately 350 MPa.
Most of the specimens failed in the gauge length, but
some of them presented ruptures at the grip adapters. The
averaged value of the three specimens for each case re-
sults, measured at the location L/2, was presented in Ta -
ble 4. A negligible difference of strains between the two
locations, L/2 an d L/4, was found. In Table 4, values for
both elastic modulus (E) and maximum tensile strength
(P) were normalized to case A for comparison purpose.
Case A was considered as a non-hybrid GFRP bar de-
veloped at KICT.
Enhancement in elastic modulus was investigated by
material hybridization up to 269%. However, regarding
the tensile strength, a small reduction was found for all
cases. This reduction may occur due to damage, the size
of specimen, the gripping method, or slip between two
materials (i.e., GFRP and steel). More detailed study for
this issue is planned by the authors.
Cases D-1 and D-2 shows the h ighest hybrid effect for
the GFRP bar in terms of elastic modulus with steel frac-
tion of 47.9%.
The commercial GFRP bars, Aslan and V-Rod pro-
vided maximum tensile strength approximately 30%
lower than “KICT GFRP bar” while elastic modulus was
a similar value supposed to be around 50 GPa.
4. Conclusions
In this study material hybridization of GFRP bar was
considered to overcome its low elastic modulus to be
used as reinforcement for concrete structures built in the
corrosive environment. The existing GFRP bar devel-
oped at Korea Institute of Construction Technology
(KICT [6]) was hybridized by adding steel as a high
strength material. Various combinations of mixing ratio
etween GFRP and steel were investigated.
b
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