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O R I G I N A L A R T I C L E
Behavior of RC T-section beams strengthened with CFRP
strips, subjected to cyclic load
H. Murat Tanarslan Sinan Altin
Received: 2 January 2008 / Accepted: 19 May 2009
RILEM 2009
Abstract This paper presents results of an experi-
mental investigation on T-section reinforced concrete
(RC) beams strengthened with externally bonded
carbon fiber-reinforced polymer (CFRP) strips. Spec-
imens, one of which was the control specimen and the
remaining six were the shear deficient test specimens,
were tested under cyclic load to investigate the effect
of CFRP strips on behavior and strength. Five shear
deficient specimens were strengthened with side
bonded and U-jacketed CFRP strips, and remaining
one tested with its virgin condition without strength-ening. The type and arrangement of CFRP strips and
the anchorage used to fasten the strips to the concrete
are the variables of this experimental work. The main
objective was to analyze the behavior and failure
modes of T-section RC beams strengthened in shear
with externally bonded CFRP strips. According to test
results premature debonding was the dominant failure
mode of externally strengthened RC beams so the
effect of anchorage usage on behavior and strength
was also investigated. To verify the reliability of shear
design equations and guidelines, experimental resultswere compared with all common guidelines and
published design equations. This comparison and
validation of guidelines is one of the main objectives
of this work. The test results confirmed that all CFRP
arrangements differ from CFRP strip width and
arrangement, improved the strength and behavior of
the specimens in different level significantly.
Keywords RC beam Strengthening Shear CFRP Cyclic load
List of symbolsa Shear span
d Effective height of the cross section
fc Compressive strength of concrete
L Length of the beam
Vexp Experimental shear forces of specimens
Vcal Calculated shear forces of specimens
eCU Maximum strain of concrete
/ Diameter of reinforcement
Conversion factors
1 mm 0.039 in1 mm2 0.00152 in2
1 kN 0.2248 kips
1 MPa 145 psi
1 Introduction
Many existing reinforced concrete (RC) members are
deficient in strength and in need of strengthening.
H. M. Tanarslan (&)
Department of Civil Engineering, Dokuz Eylul
University, Buca, Izmir 35160, Turkey
e-mail: murat.tanarslan@yahoo.com
S. Altin
Department of Civil Engineering, Gazi University,
Ankara, Turkey
Materials and Structures
DOI 10.1617/s11527-009-9509-8
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Construction faults or poor construction applications,
changes in standards, and reduction or total loss of
shear or flexural reinforcements due to corrosion are
some of the factors that cause deficiency. In order to
take the full advantage of ductility and hinder sudden
failure, it is desirable that flexure behavior governs
the ultimate strength rather than the shear. Shearfailure is brittle in nature and comes without adequate
warning. Therefore strengthening of shear deficient
structures is essential to prevent unwanted failure.
Strengthening can be in the form of rehabilitation of
structural members, repairing the damaged structures
or retrofitting the seismic deficiencies. Using exter-
nally bonded carbon fiber-reinforced polymer
(CFRP) for strengthening has become popular in
recent years due to its mechanical advantages. CFRP
sheets are both cost effective and durable, they are
tailorable, non-magnetic, have excellent fatiguebehavior, ease of handling and installation, minimal
disruption to the structure function, good corrosion
resistance and high strength to weight ratio.
The effect of CFRP for flexural strengthening has
been studied both experimentally and analytically [1,
2]. But there is still need to study the problem of shear
because of the interacted parameters; static scheme,
shear span-to-depth ratio (a/d), concrete strength,
interaction of internal reinforcements with strength-
ening material. Many of the earlier studies were
concerned with the proof of CFRP for shear strength-ening [35]. These studies indicated that using CFRP
for shear strengthening is an effective method that
improves the members strength and/or stiffness [6
9]. In these studies also the overall behavior and
failure modes of CFRP strengthened structures were
investigated [1, 1016]. After proving the effect of
CFRP as strengthening material, researchers pursued
to improve the usage of CFRP. The developed
technique has to be more economical and easy usage
than wrapping. Using CFRP as strips cover in demand
features. After determination of the new technique,using CFRP as strips, first the efficiency and than the
performance as shear reinforcement was investigated
[17]. Afterwards the behavior and failure modes were
observed. Nevertheless, monotonic loading was
applied in all these studies and performance of CFRP
strips was not investigated under earthquakes. Thus,
previous studies have to be supported by new studies
in which cyclic loads, which act like earthquake to the
structure, were exposed.
The bond between the CFRP and the concrete is
crucial in guaranteeing the effectiveness of strengthen-
ing when the structure is strengthened externally.
Previous tests subjected to monotonic loading indicated
that premature failure due to debonding was the major
problem for strengthened RC beams. Therefore, appro-
priate considerations must be given to hinder debond-ing. Particularly to prevent debonding researchers used
conventional anchorages. Actually, in literature very
limited amount of studies were encountered about
developed anchorages [18]. Therefore a new anchorage
detail was developed for the experimental program.
Then the performance of developed anchorages was
tested to investigate if it can advance the behavior of
CFRP strengthened RC beam.
This paper presents results of an experimental
study conducted on shear strengthening of RC
T-section beams with CFRP strips under cyclic loads.All seven beams except the flexural reference had no
internal shear reinforcements. Shear deficient speci-
mens were strengthened by using U-jacketed, and side
bonded CFRP strips while one of the shear deficient
specimen was tested with its virgin condition to serve
as a reference to shear deficiency. Developed mechan-
ical anchorage was applied to the U-jacketed speci-
men. The objective of this work was to investigate the
shear performance of strengthened specimens and to
determine the dominant factors that affect the behav-
ior and failure modes of the strengthened T-sectionRC beams under cyclic load. The parameters were
selected as to bear to the objective; (a) CFRP
distribution (b) CFRP orientation and (c) anchorage
usage. To evaluate enhancement of test results, on the
behavior, strength, stiffness and failure mode, were
compared with the control beams and then with each
other. In addition, to verify the reliability of shear
design equations and codes, experimental results were
compared with all common guidelines and published
design equations. This comparison and validation of
codes is one of the main objectives of this work.
2 Experimental program
2.1 Specimens and material properties
Seven T-section RC beams with various CFRP
schemes were manufactured and tested under cyclic
load in the experimental program. The cross-sectional
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procedure includes surface preparation, application ofpriming adhesive layer and bonding of the CFRP
sheets. First, the outer weak surface of the concrete
was removed with sand blasting. Afterwards, loose
particles on the surface of the specimens were
cleaned with compressed air. Once the surface has
been prepared for bonding, the epoxy resin was
prepared in accordance with manufacturers direc-
tions. The pores appearing on the concrete surface
was filled with pre-processed epoxy. Then epoxy
primer was coated at the designated places whereCFRP strips are going to be placed. Later on CFRP
sheets were placed on the coated epoxy primer and
constant pressure was applied on the sheet surface by
a roller to guarantee impregnation of the sheets by the
resin. Then another layer of epoxy was put on top of
the fabric and the extreme resin was cleaned. All
applications were performed at room temperature.
Specimen was cured for at least 15 days under
laboratory conditions before testing. The same
Specimens with w =50 mm (Specimen-7), with Anchorage
Specimens with w =100 mm (Specimen-5)
100
12
00
50x50x5 Steel Plates
50x50x5 L Shape Steel Plates 10 mm Dia. Bolt
1200
400 1675
50 Sf
Sf
50 Sf
Specimens with w =50 mm (Specimen-3, Specimen-4,
f
f
f
V
V
V
1200
285
360
75
285
360
75
28
5
75
3
60
Dimensions in mm.
400 1675
400 1675
Specimen-6)
ADETAIL
3020
25
25
12
12
10Steel bolt
CFRP
50x50x5Steel plate
Fig. 2 CFRP strip arrangements for specimen beams and anchorage detail
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strengthening procedure was carried out for all
strengthened specimens.
2.3 Experimental setup
A schematic view of experimental set-up and the
arrangement of the measurement devices are shownin Fig. 3. All specimens (cantilever beams) were
supported to the strong wall by the help of two
45.0 mm diameter high strength steel mounting rods.
To perform cyclic load to the specimen, a loading
column was designed with hinges by the beams free
end. Loading column contained two hinges, a load
cell and a hydraulic jack. The capacity of the
hydraulic jack was 1000.0 kN while the load cells
capacity was 600.0 kN. Load was applied in cycles of
loading and unloading. Load cycles were selected as
they will help to evaluate the flexure and shear crackspropagations and their affect to behavior. Same
loading cycles were applied to all specimens at the
initial state. After couple of cycles in elastic region,
flexural and shear cracks were occurred. After the
appearance of these cracks, specimens behavior
Table 3 Properties of CFRP and resin
Properties of CFRP
and resin
Remarks
Fiber orientation 0 (Unidirectional)
Construction Warp: Carbon fibers (99% of total areal
weight), Weft: Thermoplastic heat-set
fibers (1% of total areal weight)
Areal weight 220 10 g/m2
Fiber density 1.78 g/cm3
Fabric design
thickness
0.12 mm (based on total carbon content)
Tensile strength of
fibers
4,100 N/mm2
(nominal)
Tensile E modulus
of fibers
231,000 N/mm2
(nominal)
Strain at break of
fibers
1.7% (nominal)
Resin Two component (A and B)Resin mixture ratio A/B = 4/1 (Weight)
Resin tensile
strength
30 N/mm2
Tensile E modulus
of resin
3,800 N/mm2
Rigid Floor
LVDT
Rigid
Wall
Dimensions in mm.
Hinge
Hinge
Load Cell
Hydraulic Jack
Strain Gauge
Fig. 3 Test setup and
instrumentation
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changed because of their distinct shear load carrying
capacities. Loading was increased up to yield load of
flexural reinforcements or until the fall of the
specimen. For each increment of load, the strains
from strain gauges and vertical displacements from
LVDTs were recorded by means of an automatic
data acquisition system. Four linear variable differ-ential transformers (LVDTs) were used to monitor
displacements. The LVTDs are located at the end of
the beam for maximum displacement, under the rigid
support to calculate the undesired displacement and
finally on the rigid support to calculate the rotation.
Measurement of strain is evident to designate the
contribution of CFRP strips to shear capacity. Strain
gauges also help to determine the shear cracks before
propagation by the help of increase at strains. As the
main aim was to designate the contribution of CFRP
strips, eight strain gauges were attached at the sectionmid-height along the fiber direction. The number and
places of strain gauges were designated with consid-
eration where the shear cracks are expected to be
developed, between 150.0 and 1000.0 mm apart from
the beams support [19].
3 Experimental results and evaluations
3.1 Observed behavior and failure modes
Experimental results are summarized in Table 4. All
the major cracks were visually examined at the
experimental program. Control specimen showed
ductile flexural behavior as expected. Large dis-
placements were developed, and specimen reached
at an ultimate load value that was 11% greater than
the yield load. Also a plastic hinge was developed at
the maximum moment region. Specimen-2, which
was fabricated to designate the shear deficiency, was
failed in shear. As the load reached to 39.5 kN,
three main shear cracks were developed in shearspan and the beam failed in shear as can be seen
from Fig. 4.
First crack always appeared as a flexural crack for
all specimens. A linear behavior was observed since
then. Due to the load increments, the initially
developed flexure cracks were advanced through the
sides and caused shear cracks between the CFRP
strips. Besides, shear cracks were also developed at
the unstrengthened part of the specimen, between Table4
Experimentalresults
Specimen#
Ultimate
load
(Vu
)(kN)
Failuredisp.
(du
)(mm)
Initia
lstiffness
(kN/mm)
Stiffnessat
ultimateload
(kN/mm)
Increaseinultimate
displacementafter
strengthening(d
u,
n/d
u,
1)
Increasein
ultimate
loadafter
strengthening
(Vu,
n/V
u,
1)
Failuremode
atultimate
Specimen-1
Control
96.9
2
70.6
0
6.56
2.9
6
Flexure
Specimen-2
Control
39.5
2
8.7
0
6.15
3.6
2
Shear
Specimen-3
Sidebonding
61.6
3
17.7
5
6.33
3.3
3
2.0
4
1.5
6
Shear(debonding)
Specimen-4
Sidebonding
62.9
4
14.5
6
6.41
3.3
0
1.6
7
1.5
9
Shear(debonding)
Specimen-5
Sidebonding
68.4
8
17.7
3
6.70
3.0
1
2.0
4
1.7
3
Shear(debonding)
Specimen-6
U-jacketing
60.0
1
16.2
0
6.38
3.1
0
1.8
6
1.5
2
Shear(debonding)
Specimen-7
U-jacketing
80.6
7
29.8
9
6.89
2.9
3
3.4
4
2.0
4
Shear(rupture)
Forwardloadingstepwasconsideredforultimateloadandultimatedisplacement
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CFRP strips. These cracks then propagated towards
the CFRP strips and advanced along the interfacialconcrete. As the interfacial concrete started to
weaken, the bonds strength is reduced. Afterwards
the CFRP strips were separated from the concrete
surface. The same behavior was examined for all the
specimens that were failed because of debonding.
The failure mechanism of the debonded specimens
was presented in Fig. 5.
Because of debonding, all specimens except
Specimen-7 showed the same behavior until
50.0 kN load level. At about 20.0 kN, flexural cracks
appeared at the flange. Then, in the interval of 25.0and 35.0 kN, shear cracks were occurred at the
unstrengthened part, between the CFRP strips. After
exceeding 35.0 kN load level, shear cracks started to
develop faster, widen, propagate and undertake to the
body of the beam. This behavior was continued until
50.0 kN load level. After exceeding 50.0 kN load
level, dissimilar ultimate load levels were observed
due to the distinct load carrying capacities. However
the behavior and failure modes were exactly the
same. First some strips were separated from concrete
as can be seen from Fig. 6 (with a layer of concrete
adherent to them), then main shear crack waspropagated which is related to debonding. Hereafter,
specimens lost their load carrying capacities and
failed in shear consequently.
The behavior and failure mode of Specimen-7 is
totally different from formerly indicated specimens.
Specimen-7 strengthened in a manner similar to that of
Specimen-6. The main difference from the Specimen-
6 was the anchorage usage. The anchorage usage was
improved the behavior, therefore initial shear crack
propagation was delayed up to 80% when compared
with the specimens without anchorage. As the loadreached up to 80.7 kN and the deflection went up to
29.9 mm, 14th and 15th strips were compelled and
right after ruptured due to the stresses that were exceed
the limit that they can resist. As the strengthened part
lost its resistance against shear, a diagonal shear crack
was propagated abruptly at the decayed section as can
be seen from Fig. 7. The crack was advanced through
the top end of 10th strip and separated 11th, 12th and
13th strips from the concrete. Anchorage delayed the
strips from splitting at lower loads and also prevented
main shear crack propagation due to debonding.According to test results, the developed anchorage
worked so fine that U-jacketing with anchorage
denoted the best performance up to then.
Fig. 5 Failure mode, debonding
Fig. 4 Failure mode of Specimen-1
Fig. 6 Failure mode of Specimen-6
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3.2 Evaluation of the test results
To acquire strengthening effect, all strengthened
beams were compared with the control beams and
then with each other. Comparisons of specimens were
done by using response envelopes. Response enve-
lopes were drown by connecting peak points of
loading cycles and presented on Fig. 8. CFRP
reinforced specimens exhibited significantly higher
load-carrying capacity than that of the unstrength-
ened specimen, Specimen-2.To evaluate the contribution of strengthening
material strain activity of the strengthened specimens
was also evaluated. It must be point out that the strain
values, reported herein are not necessarily the max-
imum values. They are strictly related to the location
of the strain-gauges with respect to that of the shear
cracks. Actually, to be more realistic the largest strain
of the specimens is submitted here in Figs. 9 and 10.
It is obvious that maximum strain values that were
obtained from the specimens will give essential
information about the contribution of strengtheningmaterial to the shear resistance. When the measured
maximum strain values approach to the ultimate
Fig. 7 Failure mode of Specimen-7
-100
-80
-60
-40
-20
0
20
40
60
80
100
-40 -30 -20 -10 0 10 20 30 40
Displacement, mm
Shearforce,
kN
1
2
3
4
5
6
7
Specimen #
Fig. 8 Response envelopes
of specimen beams
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tensile strain, 0.017, the expected contribution to the
shear resistance is definitely achieved. Furthermore,
according to ACI-440 committee report, the effective
strain is the maximum strain that can be obtained in
the CFRP system at the ultimate load stage and is
governed by the failure mode of the CFRP system.
Loss of aggregate interlock of the concrete has been
observed to occur less than the ultimate tensile strain.To preclude this mode of failure, ACI-440 committee
report limited the maximum strain and proposes to use
0.004 mm/mm as maximum strain for design. Besides
if the measured strains are below the ACI-440
committee reports expected value that indicates the
expected contribution could not be obtained from the
strengthening material. With respect to that, when the
strain activity of the debonded specimens was
evaluated, it was observed that strain values were
definitely below the ACI-440 committee reports
expected value. Debonding, which cause prematurefailure, hinders to obtain the expected contribution
from the strengthening material.
The concrete strength of the test specimens plays
a great role especially when internal shear reinforce-
ments were omitted. Therefore while fabricating the
specimens extra care was conducted to achieve
similarity in concrete strength. Notwithstanding a
distinction with an interval of 6% less and 8% more
according to reference beam was materialized. While
-100
-80
-60
-40
-20
0
20
40
60
80
100
0,000 0,001 0,002 0,003 0,004
Strain, mm/mm
She
arforce,
kN
-100
-80
-60
-40
-20
0
20
40
60
80
100
0,000 0,001 0,002 0,003 0,004
Strain, mm/mm
Sh
earforce,
kN
-100
-80
-60
-40
-20
0
20
40
60
80
100
0,000 0,001 0,002 0,003 0,004
Strain, mm/mm
Shearforce,
kN
-100
-80
-60
-40
-20
0
20
40
60
80
100
0,000 0,001 0,002 0,003 0,004
Strain, mm/mm
Shearforce,
kN
Specimen-3
Specimen-5Specimen-6
Specimen-4
5060506050
Strain in-5 is maximum
795
5060506050
Strain in-2 is maximum
245
Strain in-8 is maximum
985
Strain in-7 is maximum
1090
(b)(a)
(d)(c)
Fig. 9 Load-maximum CFRP strain curves of Specimen-3, 4, 5 and 6
-100
-80
-60
-40
-20
0
20
40
60
80
100
0,000 0,001 0,002 0,003 0,004 0,005 0,006 0,007 0,008
Strain, mm/mm
Shearforce,
kN
Specimen-7
745
305030
5030
50
Strain in-6 is maximum
Fig. 10 Load-maximum CFRP strain curves of Specimen-7
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evaluating the below comparisons the effect of
concrete strength was not separately considered but
it must be point out that it will affect the evaluations.
However the comparisons will still give enough
knowledge to the researchers about the effect of
selected variables to the behavior. Specimen-3 was
strengthened with 50.0 mm wide CFRP strips, whichwere spaced at 60.0 mm, showed 57% less strength
than Specimen-1 and 56% more strength than Spec-
imen-2. Debonding was also affected the strain
behavior. The largest strain value of Specimen-3
was 0.002 mm/mm. That corresponds only to 50% of
the ACI-440 [20] committee reports expected value.
The recorded CFRP strain was indicated that the
failure was occurred at an average effective stress
level below the nominal strength due to debonding.
Specimen-4 showed 54% less and 59% more
strength than the flexural control specimen andunstrengthened shear deficient specimen, respec-
tively. The maximum vertical strain at the time of
failure was 0.0031 mm/mm (i.e. 78% of the ultimate
strain). By increasing the amount of strengthened area
(decreasing the spacing of CFRP strips from 60.0 to
30.0), an increase of 55% at contribution to the shear
resistance was obtained according to Specimen-3.
However debonding was still governing the behavior.
Debonding hindered to achieve the expected contri-
bution to the shear resistance as can be seen from the
recorded maximum CFRP strain value.Specimen-5 had reached 68.5 kN load level in
forward loading step but failed in that cycle while
backward loading. Specimen showed 73% more
strength than Specimen-2 and 42% less strength than
Specimen-1. The maximum localized CFRP strain
was in the order of 0.0036 mm/mm, which corre-
sponds to 89% of the ACI-440 committee reports
expected value. CFRP strips were contributed well to
the shear resistance, as be seen from the strain level.
Ultimate strain almost reached the ACI-440 commit-
tee reports expected value. However, debondingfrustrated to get the accurate contribution from the
strengthening material.
Specimen-6 was strengthened with 50.0 mm width
U-jacketed CFRP strips which were spaced at
60.0 mm. While planning the strengthening scheme
of Specimen-6, the main aim was to prevent
debonding by the help of orientation. According to
studies, debonding is rarely faced in which
specimens strengthened with U-jacketed CFRP [3].
However, Specimen-6 was still associated with a
rapid, sudden, and unstable separation of the bonded
CFRP strips at the upper ends. Specimen showed
62% less strength than Specimen-1 and 52% more
strength than Specimen-2. The maximum localized
CFRP strain was in the order of 0.0016 mm/mm,which corresponds to 40% of the ACI-440 committee
reports expected value. U-jacketed specimens
behavior was not obtained as planned due to
debonding of the CFRP at the upper ends. If
debonding at the upper ends could be prevented a
better utilization can be obtained from CFRP and
consequently a higher increase in shear capacity
could be obtained.
Specimen-7 was strengthened with U-jacketed
CFRP strips with end anchors. End anchors showed
significant performance for preventing CFRP frompeel off. By preventing peel of CFRP strips was
subjected to higher loads and therefore some CFRP
strips were ruptured. Actually, specimen almost
reached its ductile behavior if we compare with the
yield load of Specimen-1. Specimen-7 showed an
increase in capacity of 104% over reference. Spec-
imen-7 also measured the largest strain up to then,
which was 50% larger than ACI-440 committee
reports expected value, 0.006 mm/mm. Ultimate
load level and strain behavior clearly proved the real
effect of CFRP to shear capacity when debondingwas prevented.
In order to evaluate the contribution of CFRP
strips to shear capacity, initial and ultimate load
stiffness of the test specimens were also evaluated.
Initial stiffness were calculated by using the slope of
the lines that was connecting to origin and the load,
at which first flexural crack was occurred. When the
initial stiffness of CFRP strengthened specimens
were observed, it was seen that the initial stiffness
were shifted in an interval of 3% and 12% more than
that of the shear deficient reference specimen. If thestrengthening material provides less crack propaga-
tions until the ultimate load was reached, minor
decrease at ultimate load stiffness will be material-
ized. However as it was also visually examined,
many cracks were occurred at the shear span until the
fall of the specimens. Therefore the stiffness was
decreased to up to 25% less than that of the reference
specimen.
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4 Comparison of test results and design equations
The use of CFRP composites for shear strengthening
is a widely preferred method in recent years.
Therefore, almost all design standards have propa-
gated provisions to calculate the contribution of
CFRP. Additionally, due to lack of design standards,several researchers have also developed new analyt-
ical models to predict the nominal shear resistance for
CFRP.
In general, truss analogy was considered to find the
contribution of CFRP to shear capacity which is
similar to determine the contribution of steel shear
reinforcement. While predicting the CFRP contribu-
tion, tensile strength of CFRP, strain distribution in the
CFRP along the shear crack and the shear crack angle,
were considered as the effective parameters. Accord-
ing to these models all CFRP strips, intersected by themain shear crack, are assumed to contribute the same
average stress. The differences from one method to
other lies on how much effective stress developed at
ultimate state. Furthermore, shear crack angle gener-
ally assumed to be 45 in all provisions.
To predict the shear resistance due to CFRP,
Concrete Society [21] and ACI 440 are based on
work of Khalifa et al. [22], and fib [23] and Canadian
Standards Association (CSA-S806-02) [24] are based
on the work of Triantafillou [11]. Apart from them,
Chen and Teng [25, 26] developed a strip model,combined with the shear friction approach, based on
the bond mechanism observed from the tests. The
model used empirical expressions based on curve-
fitting of test results to define the effective stress of
CFRP. Analytical model made also clear distinction
between rupture failure and debonding, and devel-
oped two separate models.
For all these methods, total shear resistance of a
strengthened RC section is found as the sum of the
three components.
Vn Vc Vs Vf 1
where Vc is the contribution of concrete, Vs is the
contribution of internal steel shear reinforcement andfinally Vf is the contribution of CFRP at Eq. 1. In this
study only the concrete was contributed to shear force
carrying capacities because specimens do not include
internal shear reinforcements.
The analytical shear contributions of known models
and design standards were compared with the test
results and presented in Table 5. As can be seen from
Table 5, shear resistance due to CFRP, which were
calculated by CSA-S806-02, performed well with the
experiments except Specimen-7. As the predicted
shear resistances of all codes were compared, Chenand Tengs method produced the closest result to the
experimental results for specimen with anchorage.
Analytical shear resistance of the strengthened
specimens with respect to ACI-440 was found in the
interval of 5% and 11% less than the experimental
results. Concrete Societys analytical results were not
well-matched to the experimental values. Neverthe-
less, analytical shear load carrying capacities for fib
TG9.3 were denoted the biggest difference with the
range of 24% and 41% from experimental results. A
significant deviation between experimental andguidelines values for all predictions were observed
for Specimen-7 except Chen and Tengs proposal. To
prevent premature failure, anchorage was applied.
Due to the measures, specimen reached its maximum
shear capacity. The positive influence of anchorages
to shear capacity was not included in the ana-
lytical equations that were suggested by guidelines.
Table 5 Comparison of experimental and analytical results
Specimen # Calculated strengths Experimentalstrengths (kN)
Experimental/calculated
ACI 440
(kN)
fib
(kN)
Concrete
Society (kN)
CSA
(kN)
Chen and
Teng (kN)
Specimen-3 Side bonding 55.9 49.7 62.7 62.3 68.6 61.63 1.10 1.24 0.98 0.99 0.91
Specimen-4 Side bonding 57.6 48.0 66.6 62.94 71.8 62.94 1.09 1.31 0.95 1.00 0.88
Specimen-5 Side bonding 61.7 48.7 59.7 68.48 76.2 68.48 1.11 1.41 1.15 1.00 0.90
Specimen-6 U-jacketing 56.9 47.4 81.8 58.71 69.8 60.01 1.05 1.27 0.73 1.02 0.86
Specimen-7 U-jacketing 64.5 53.0 100.8 65.9 78.2 80.67 1.25 1.52 0.80 1.22 1.03
CSA Canadian Standards Association, CSA-S806-02
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8/7/2019 behaviour RC Tbeam under cyclic load
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Therefore, the experimental results and analytical
provisions were not brought out close results. Con-
sequently, the proposed design equations can conser-
vatively predict the experimental test results. But the
influence of the ratio a/d and interaction of internal
shear reinforcement to shear capacity due to CFRP
was not included in the guidelines. The proposeddesign results will be more realistic if the parameters
that affect behavior have captured by the guidelines.
5 Conclusions
In this study, the shear performance of T-section RC
beams with shear deficiencies (without stirrups)
strengthened with different configurations of CFRP
strips were investigated. The test results indicated
that the shear strengthening effectiveness with CFRPstrips on the RC beams varies in function of the
spacing of CFRP strips, CFRP strips widths, strip
orientation and anchorage usage. But all in all an
increase in strength was seen in every specimen to
which CFRP applied, regardless of CFRP application.
The arrangement of CFRP strips was among the
effective parameters directing the strength of the
specimens. Experimental results of the Specimen-
3 and Specimen-4 showed that the ultimate
strength increased 3% when the spacing of CFRPstrips was decreased from 60.0 mm to 30.0 mm.
Specimen-4s ultimate shear capacity was
62.9 kN, corresponding to an increase of 59%
over the control beam. By increasing CFRP strips
width from 50.0 to 100.0 mm, a gain of 14% over
Specimen-4 was obtained. Increasing the strength-
ened area on the shear span delayed the initial
shear cracks propagations and a better utilization
was obtained from the strengthening material.
The effect of CFRP orientation to shear capacity
can be evaluated by investigating the behavior ofSpecimen-3 and Specimen-6. Specimen-3s ulti-
mate shear capacity was 61.6 kN that corresponds
to an increase of 56% over the control beam.
Although it is expected to obtain a better contri-
bution from Specimen-6, strengthened by U-
jacketed CFRP, only an increase of 56% over
the control beam was obtained.
Side-bonded and U-jacketed specimen beams,
without anchorage, were collapsed with brittle
shear failure because of debonding. In addition,
the recorded CFRP strain was also indicated that
the failure was occurred at an average effective
stress level below the nominal strength due to
debonding. This is one of the main problems of
CFRP strengthened RC structures. To overcome
debonding, a new mechanical anchorage wasdeveloped in the experimental program. New
developed mechanical anchorage was behaved
efficient under cyclic load. Although there were
no shear reinforcements in the specimens that tied
the beam web and flange together, top anchorages
prevented the separation of beam flange and web.
Top anchorages were also prevented peeling of
the CFRP strips from concrete. In addition, the
function of the end-anchors was to prevent the
premature peeling of the CFRP strips and it was
enormously prosperous under cyclic load. Anchorage application increased the ultimate
strength by 52% according to experimental results
of the Specimen-6 and Specimen-7. It also
prevented debonding at initial state and changed
the failure mode from debonding to rupture. It is
obvious that anchorage usage is the dominant
parameter to achieve the required strength and
behavior from the shear strengthened RC beam.
Shear resistance due to CFRP, which were
calculated by CSA-S806-02, performed well with
the experiments except Specimen-7. As thepredicted shear resistances of all codes were
compared, Chen and Tengs method produced the
closest result to the experimental results for
anchoraged specimen. All analytical results from
guidelines indicated that the used expression to
estimate the contribution of CFRP strips to the
shear capacity is acceptable.
The initial and ultimate load stiffness of Speci-
mens was up to 12% and up to 19% which more
and less than that of the shear deficient control
specimen, respectively. As the strength of spec-imen was increased specimens initial stiffness
was also increases. However, because of the
propagated cracks at the beam web, ultimate load
stiffnesss were decreased when compared with
the unstrengthened specimen, Specimen-2.
The tests performed in the presented series should
be the starting point for designating the behavior and
strength of strengthened RC beams with CFRP strips
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under cyclic loads. It is hoped this study also helps to
understand the shear mechanism of a RC beam
strengthened with externally bonded CFRP strips.
Still further tests and more in depth study are needed
for confirming the degree of effectiveness of each
orientation and arrangement.
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