This work consists of fabrication and testing of sixteen reinforced concrete corbels. Fourteen of these corbels have been strengthened or repaired by various plies of Carbon Fiber Reinforced Polymer (CFRP) laminates. The experimental variables considered in the test program include, the CFRP pattern scheme (i.e. location, orientation, and number of layers), bond type (partial warping, full warping, and using CFRP anchors), and damaged ratio. Two modes of failure were observed, debonding and rupture of the CFRP laminates. Significant increase in ultimate capacity ranging from 17% to 71% was registered in the strengthening specimens and from 13% to 65% in repaired specimens.

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International Journal of Civil Engineering and Technology (IJCIET)
Volume 6, Issue 11, Nov 2015, pp. 11-20, Article ID: IJCIET_06_11_002
Available online at
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=6&IType=11
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
© IAEME Publication
___________________________________________________________________________
USE OF CFRP LAMINATES FOR
STRENGTHENING OF REINFORCED
CONCRETE CORBELS
Khalid K. Shadhan and Mohsen M. Mohammad Kadhim
University of Babylon
College of Engineering
ABSTRACT
This work consists of fabrication and testing of sixteen reinforced concrete
corbels. Fourteen of these corbels have been strengthened or repaired by
various plies of Carbon Fiber Reinforced Polymer (CFRP) laminates. The
experimental variables considered in the test program include, the CFRP
pattern scheme (i.e. location, orientation, and number of layers), bond type
(partial warping, full warping, and using CFRP anchors), and damaged ratio.
Two modes of failure were observed, debonding and rupture of the CFRP
laminates. Significant increase in ultimate capacity ranging from 17% to 71%
was registered in the strengthening specimens and from 13% to 65% in
repaired specimens.
Key words: CFRP, Reinforced Concrete and Corbels
Cite this Article: Shadhan, K. K. and Mohammad Kadhim, M. M. Use of
CFRP Laminates for Strengthening of Reinforced Concrete Corbels.
International Journal of Civil Engineering and Technology, 6(11), 2015, pp.
11-20.
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=6&IType=11
_____________________________________________________________________
1. INTRODUCTION
Corbels are structural members commonly used to support the reinforced concrete
beam element, especially in precast structures. Their primal function is to transfer the
horizontal and vertical forces to principal structural members. Corbels are cantilevers
having shear span-to-depth ratios not greater than unity, which tend to act as simple
trusses or deep beams, rather than flexural members (ACI 318-11, 2011),
thus they
need special provisions and act differently from the normal cantilever beams, this
difference in behavior is due to the steep inclination of tension cracks and influence of
compression strut.
While a significant number of researches had been made on ordinary reinforced
concrete corbels, a much fewer number were made for strengthening or repairing

2. Khalid K. Shadhan and Mohsen M. Mohammad Kadhim
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corbels using FRP composite materials (Elgwady et el. ,1999 ;Corry and Dolan, 2001;
Erfan et el. ,2010; Abed Attiah , 2010;Ahmed et. el. ,2013). This experimental
research is focused on the behavior of reinforced concrete corbels strengthened and
repaired with CFRP laminates.
2. Experimental program
2.1. Specimen description
The test specimen consisted of double corbels and a short column. Each side had a
total depth of 190 mm, 150 mm breadth and 200 mm length. The column supporting
the two corbels has a section of 200 mm ×150 mm and length of 440 mm as shown in
Figure (1). Two 10 mm bars were used as primary reinforcement, placed at the bottom
of the beam with an effective cover of 25 mm, and one 8 mm bars used as secondary
reinforcement. Column part is reinforced with six deformed bars having a 12 mm
diameter and supported with ties having a 10 mm diameter placed every 85 mm. The
usage of this high amount of column reinforcement is to assure the corbel failure in
the testing phase. The yield strength for the steel bar are 467, 589 and 536 MPa for 8,
10, and 12 mm, respectively.
Figure 1 Geometry and reinforcement details of the tested specimen
2.2. Concrete materials and mix design
During the design phase of the experimental program, 30 to 35 MPa concrete
compressive strength was chosen to mimic relatively real strength used in practice for
similar members. The mix was proportioned by weight at 1:1.7:2.2:0.45 for cement,
sand, gravel and water respectively. Locally available materials were used throughout
and showed conformity with the specifications required.
2.3. CFRP material description and application
Sika Wrap Hex-230C type was used as CFRP strengthening sheets. While, the epoxy
resin is of type Sikadur-330. The technical properties of the CFRP sheets and

3. Use of CFRP Laminates for Strengthening of Reinforced Concrete Corbels
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impregnation resin used in this study as given by the manufacturer are presented in
Table (1) and (2), respectively. A two-part impregnation resin (Sikadur®
-330) is
mixed in required proportion, until the color is a uniform grey, and then applied with
a special tool to the concrete surface to a thickness of ~1.5 mm. The adhesive is also
applied to the CFRP sheet to the same thickness. The CFRP sheet is then placed on
the concrete ,epoxy to epoxy, and a rubber roller is used to properly seat the CFRP
sheet by exerting enough pressure so the epoxy is forced out on both sides of the
CFRP sheet and the adhesive line did not exceed 2mm in thickness. After the
specimens are confined, they are left in laboratory conditions for 7 days after gluing
to be completely cured.
Table 1 Technical properties of CFRP Laminates
Type
Tensile
strength
(MPa)
Elongation
at Break
(%)
Tensile
modulus
(GPa)
Thickness
(mm)
Weight
(g/m2
)
SikaWarp®
Hex-230C
>3500 >1.8 238 0.131 225
Table 2 Technical properties of impregnation resin
Type
Tensile
strength
(MPa)
Elongation
at Break
(%)
Flexural
modulus
(MPa)
Pot live
(minute)
Density
(kg/l)
Sikadur-330 30 0.9 3800
at 15Co
:90min
at
35Co
:30min
1.31
2.4. Specimens identification and strengthening schemes
The CFRP strengthening patterns were chosen to modeling the possibilities in the
field, i.e. some of the CFRP patterns that cannot apply in the field had been neglected.
Two control specimens of CON1 and CON2 with no strengthening had been applied.
Table (3) in conjunction with Figure (2) illustrates the specimen identification and
CFRP strengthening schemes.
For investigation of influence of number of layers and the bond type six different
specimens had been made, three of which H1P,H2P and H3P with CFRP bond only
on the face of the corbels and the other three H1F, H2F, and H3F with full bonded
CFRP over all the faces of specimens. All of the strips in the six specimens were
horizontally applied. The specimen H2A had two horizontal strips partially bonded on
the shear face of the corbels. This specimen had upgraded bond strength with the
usage of four CFRP anchor (two for each of strips) applied near the edge of corbel.
The applying of anchors was after the casting and curing of the specimens.
Specimens 2H2F and 3H2F had two and three layers of pair horizontal CFRP
strips respectively, the two specimens V6F and IF had fully warped CFRP strips with
orientation of 90 and 45 degrees, respectively. The last three specimens were for
measuring the efficiency or repair technique. Specimens H3V6F-0%, H3V6F-35%,
and H3V6F-70% are tested with damage ratio of 0%, 35%, and 70% respectively. All
of these three specimens were repaired with three full warped horizontal strips, and
had additional of six fully warped vertical strips.

4. Khalid K. Shadhan and Mohsen M. Mohammad Kadhim
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Table 3 Characteristics of Corbel specimens
Specimen
identification
Compressive
strength, fcu
No. of CFRP
strips
No. of CFRP
layers
CFRP Bond
type
Damaged
ratio, (%)
CON1 33.5 Nil Nil Nil Nil
CON2 32.3 Nil Nil Nil Nil
H1P 33.1 1 1 Partial warp 0
H2P 34.2 2 1 Partial warp 0
H3P 30.4 3 1 Partial warp 0
H1F 32.5 1 1 Full warp 0
H2F 34.6 2 1 Full warp 0
H3F 27.7 3 1 Full warp 0
H2A 33.7 2 1 CFRP anchors 0
2H2F 31.3 2 2 Full warp 0
3H2F 34.1 2 3 Full warp 0
V6F 34.2 3 1 Full warp 0
IF 32.8 3 1 Full warp 0
H3V6F-0 31.1 3 1 Full warp 0
H3V6F-35 30.8 3 1 Full warp 35
H3V6F-70 32.2 3 1 Full warp 70
3. EXPRIMENTAL RESULTS
The main objective of this research is to investigate the efficiency of CFRP when used
as strengthening and/or repairing material for reinforced concrete corbels, and its
influence on the load carrying capacity and behaviors of the corbels. Test results were
analyzed based on ultimate load carrying capacity, load-deflection curve, crack
patterns and failure mode. Table (4) in conjunction with Figure (3) and (4) shows test
results for all corbels specimens.
The results show that the CFRP strips can delay the formation of first crack .This
delay is mainly depending on the CFRP existence near the weak points (i.e. corbel-
column junction) and the amount of CFRP in the specimens. This is due the high
moment at this point. After this crack a shear crack began to develop at the loading
area from the end of the bearing plate continuing toward the corbel face with an angle
varied from 40 to 60 degrees. This was the typical case in all of the tested specimens
except the specimen with inclined CFRP strips, specimen IF, which the typical first
crack did not took place at column-corbel junction point due to existence of CFRP
strips exactly at the very point of junction. In this specimen the first crack was a shear
crack at the loading area.
While all control and strengthened specimens failed suddenly and exhibited no
ductility. Generally, the deflections of the specimens strengthened with CFRP were
lower than the deflections of the corresponding control beam, Figure (3).
The application of CFRP strips proved to be an effective method of strengthening
reinforced concrete corbels. The test results show that the increase varied from 16% in
specimen H1P to 71% in specimen V6F in load carrying capacity of un-strengthened

5. Use of CFRP Laminates for Strengthening of Reinforced Concrete Corbels
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corbels. These increases are depending on many factors such as number of CFRP
strips, Types of bonding, Angle of bonding, damage ratio, and CFRP pattern.
Figure 2 Specimens identification and strengthening schemes

6. Khalid K. Shadhan and Mohsen M. Mohammad Kadhim
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Figure 2 Continued
The crack patterns after the failure of the specimens were different from specimen
to another. While some specimens had several miner crack, others had few major
ones. It has been found that the application of CFRP strips restrained the cracking
propagation; however the quantity and location of the CFRP strips had been found to
have a great influence on the crack pattern. Figure (4) gives illustrated figures of

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cracking pattern in the tested specimens. The black lines in the figure represent the
cracks while the gray areas represent the crushing of the concrete
The CFRP pattern showed a great influence on the failure mechanism of the tested
specimens. While the un-strengthened control specimens had elastic failure with
widening of shear cracks, all of the strengthened specimens, except one specimen, had
sudden failure. This specimen was H3P that failed in semi-ductile way. That is
because this specimen failed by debonding of CFRP accompany with concrete cover
separation , and due to elastic characteristics of concrete – that influence the failure
mechanism – this specimen failed in this unique way.
The specimens H1P, H2P, H3P, H1F, H2F, 2H2F, 3H3F, and H2A failed by
debonding of one (or more) CFRP strip from concrete surface, although the position
of debonding differ in the specimens. For the specimens that had increased bond
strength i.e. H1F, H2F, 2H2F, 3H2F, and H2A, the debonding was at the mid- span of
the specimen, while for other specimens that had no bonding strengthening, i.e. H1P,
H2P, and H3P the debonding was at the sides of the specimen. For the specimens IF
and V6F the failure was due to rupture in one of CFRP strips. For specimens H3F,
H3V6F0%, H3V6F35%, and H3V6F70% the failure was by combined factor of
CFRP strips deboning and rupture.
Table 4 Ultimate load capacity and failure mode for tested beams
Specimen
Cracking
load , (kN)
*Increase in
cracking load, (%)
Ultimate
load ,(kN)
*Increase in
ultimate load, (%)
Failure mode
CON1 90 Nil 211 Nil Concrete crushing
CON2 83 Nil 242 Nil Concrete crushing
H1P 101 12.2 265 17.0 CFRP debonding
H2P 105 16.7 280 23.6 CFRP debonding
H3P 118 31.1 270 19.2 CFRP debonding
H1F 105 16.7 284 25.4 CFRP debonding
H2F 105 16.7 305 34.7 CFRP debonding
H3F 125 38.9 298 31.7 CFRP rupture
H2A 108 20.0 294 29.8 CFRP debonding
2H2F 108 20.0 302 33.3 CFRP debonding
3H2F 110 22.2 312 37.7 CFRP debonding
V6F 132 46.7 388 71.3 CFRP rupture
IF 131 45.6 325 43.5 CFRP rupture
H3V6F-0 118 31.1 374 65.1 CFRP rupture
H3V6F-35 111 23.3 322 42.2 CFRP rupture
H3V6F-70 90 --- 256 13.0 CFRP rupture
*compared with the average of the control specimens

8. Khalid K. Shadhan and Mohsen M. Mohammad Kadhim
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Figure 3 Load-Deflection curve for tested specimens
(e): H2P, H2B and H2F (f): H3V6F (0), H3V6 (35) and H3V6F (70)
(a): H1P, H2P and H3P (b): H1F, H2F and H3F
(c): H2F, 2H2F and 3H3F (d): H3F, IF and V6F

9. Use of CFRP Laminates for Strengthening of Reinforced Concrete Corbels
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Figure 4 Crack patterns after failure for corbels specimens

10. Khalid K. Shadhan and Mohsen M. Mohammad Kadhim
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4. CONCLUSIONS
1. Using carbon fiber reinforced polymer (CFRP) strips is an effective technique for
strengthening of reinforced concrete corbel. The ultimate carrying capacity is
increased by 16% to 71%.
2. The orientation of CFRP strips found to have the largest effect on increased load
carrying capacity, the percentage of increase differ from 35% for horizontal strips to
71% for vertical strips.
3. The presence of CFRP laminates can increase the cracking load of R.C corbels by
acceptable amount. This increase is found to vary from 12% in specimen with
horizontal CFRP strips to 46% for specimen with vertical CFRP strips.
4. The damage ratio of the specimen has reverse effect on the effectiveness of the repair.
Thus for corbels with high damage ratio (greater than or equal 70%), the application
of CFRP laminates are not an effective technique to improve the characteristics of the
corbels.
5. The debonding in the CFRP laminates (which is the main mode of failure) is sudden
and have a brittle nature. Thus for more effective strengthening, using of CFRP
anchors to improve the bond strength is recommended.
REFERENCES
[1] Abed Attiah M., (2010), ‘‘Behavior of reinforced concrete corbels strengthened
with carbon fiber reinforced polymer strips’’, PhD thesis, Basrah University.
[2] Ahmad, S., Elahi, A., Kundi, S., and Haq, W. (2013), “Investigation of shear
behavior of Corbel beams strengthened with CFRP”, Life Science Journal 2013.
[3] American Concrete Institute, ACI Committee 318. (2011) “Building code
requirements for structural concrete (ACI 318-11) and commentary”, American
Concrete Institute, Farmington Hills, MI 48331.
[4] Corry, R. W. and Dolan, C. W. Strengthening and repair of a column bracket
using a carbon fibre reinforced polymer (CFRP) fabric. Journal of PCI Journal,
January-February, 2001, pp. 54–63.
[5] Elgwady, M. A., Rabie, M., and Mosatafa, M. T. Strengthening of corbles using
CFRP, an experimental program, Cairo university, Giza, Egypt, 1999.
[6] Erfan, A. M., Abdel-Rahman, G. T., Nassifand, M. K. and Hammad, Y. H.
Behavior of reinforced concrete corbels strengthened with CFRP fabrics, Benha
University, 2010.
[7] Ivanova, I., Assih, J., Li, A. and Delmas, Y. Influence of Fabrics Layers on
Strengthened Reinforced Concrete Short Corbels. International Journal of Civil
Engineering and Technology, 5(11), 2014, pp. 33–43.