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INTERNATIONAL JOURNAL OF CIVIL AND STRUCTURAL ENGINEERING
Volume 3, No 3, 2013
© Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0
Research article ISSN 0976 – 4399
Received on January 2013 Published on March 2013 564
Flexural behavior of strengthened and repaired R.C. beams by using steel
fiber concrete jacket under repeated load Yehia A. Hassanean
1, Kamal Abas Assaf
2, Shehata E. Abdel Raheem
3, Ahmed. N.M. Arafa
4
1- Professor, Civil Engineering Department, Faculty of Engineering, Assiut University, Egypt
2- Associate Prof., Civil Engineering Dept., Faculty of Engineering, Assiut University, Egypt
3- Associate Prof., Taibah University, Madinah, KSA. On leave, Assiut University, Egypt
4- Assistant Lecturer, Faculty of Engineering, Sohag University, Egypt
doi:10.6088/ijcser.201203013052
ABSTRACT
Strengthening and repairing of reinforced concrete beams by using thin fibers concrete jacket
have many advantages such as increasing of ultimate load, enhancement of serviceability
limit state, resistance to fire and avoiding of corrosion problems that appear in steel plate
jacket. The present work conducted to study the strengthening and repairing of reinforced
concrete beams subjected to short time repeated load by using mixed steel fibers concrete
jacket (MSFCJ). For this purpose fourteen reinforced concrete beams have a cross section
120×300 mm, total length 2300 mm were fabricated and tested under three point load. The
used concrete mix contains two mixed shape steel fibers, corrugated and end-hooked steel
fibers. Two of these beams were fabricated without strengthening, the first was tested under
static load up to failure and the second was tested under short time repeated loads up to
failure. The rest twelve beams, six of them were strengthened by U-shape MSFCJ with
various thickness and steel fibers content while the other six beams were loaded up to 0.5 the
ultimate static load and then repaired using MSFCJ. The twelve beams were tested under
short time repeated load. The tests results showed the effectiveness of the proposed technique
in both ultimate and serviceability limit state.
Keywords: Strengthening and repairing, Fiber concrete jacket, High-strength concrete,
mixed steel fiber, Repeated loading.
1. Introduction
The interest of strengthening and repairing of reinforced concrete structures has increased in
the last few years because of poor performance under service loading in the form of excessive
deflections and cracking, construction faults, design faults, excessive deterioration and the
changing in use of structure. In such circumstances, there are various methods for
strengthening and repairing of R.C beams such as externally bonded steel plates, R.C
jacketing and externally bonded fiber reinforced polymer (FRP). All these techniques can be
successfully used but have some limits. In particular, the use of R.C jacket is possible by
adding layers of concrete with thickness larger than 60 – 70 mm due to the presence of rebars
that require a minimum concrete cover (Fatih Altun; 2004). The use of externally glued steel
plates as well as FRP may have problems for fire resistance. Furthermore, the use of these
techniques may not satisfy minimum requirements for serviceability limit states.
During the last 10 years, the use of concrete reinforced with fibers has increased due to its
enhanced flexural, tensile, compressive and fatigue properties. Recently, a new technique has
been developed for strengthening and repairing beams under static loading (Byung Hwan;
Flexural behavior of strengthened and repaired R.C. beams by using steel fiber concrete jacket under
repeated load
Yehia A. Hassanean et al
International Journal of Civil and Structural Engineering 565
Volume 3 Issue 3 2013
1992, Giovanni Martinola et al.; 2007). This solution is based on the application of a thin
jacket in high performance fiber reinforced concrete (HPFRC) with a high compressive
strength and a hardening behavior in tension. This method has more advantages such as
increasing of ultimate load, enhancement of serviceability limit state, resistance to fire and
avoiding of corrosion problems that appear in steel plate jacket. This technique in
strengthening and repairing was undertaken to be the main object of this work by using high
strength concrete with steel fiber. Also all previous investigations conducted on SFC, single
shape of fibers has been used (Johnston and Zemp; 1991, Byung Hwan; 1992, Nasser Abdel
Salam; 2005) and there is no information available on performance of SFC containing fibers
of mixed shape. Therefore the present work was used mixed shape of steel fibers (end hooked,
corrugated) with the understanding that the end hooked fibers are effective in increasing the
ductility whereas, corrugated fibers are effective in increasing the bond between the
components of concrete.
2. Experimental program
2.1 Details of the tested beams
Fourteen reinforced concrete beams with a cross section 120 × 300 mm and total length of
2300 mm were fabricated and tested under three point flexural test. The design of the flexural
and shear steel reinforcement ensured a flexural failure of the beams. The dimension and
details of reinforcement of the tested beams before the application of the proposed
strengthening or repairing techniques are shown in figure 1. Also properties of the tested
beams are given in table 1.Two beams (B0s and B0r) without jacket; B0s was subjected to a
static loading up to failure. Meanwhile B0r was subjected to a short time repeated loading up
to failure. The rest twelve beams, six of them were strengthened by using U-shape of MSFCJ
then divided into two groups (A, B) according to the studied parameters. The other six beams
were loaded up to 0.5 of the ultimate static load of beam B0s (50 KN). Eventually, the beams
were repaired using U-shape of MSFC jacket and divided into two groups (C, D). All
strengthened and repaired beams were subjected to short time repeated loading up to failure.
The details of the tested beams after the application of the proposed technique are shown in
figure 2.
Figure 1: Details of the tested beams
Flexural behavior of strengthened and repaired R.C. beams by using steel fiber concrete jacket under
repeated load
Yehia A. Hassanean et al
International Journal of Civil and Structural Engineering 566
Volume 3 Issue 3 2013
Figure 2: Strengthening and repairing scheme and shear connectors details for all
strengthened and repaired beams except BSB2, BRD2 without shear connectors
Table 1: Property of the tested beams
Group
No Parameter
Beam
No
Vf
%
Jacket Thickness Shear
Connector
s
Loading
Type tjb mm tjs (mm
----------
-
-----------------
--
B0s 0.0 0.0 0.0 ------- Static
B0r 0.0 0.0 0.0 ------- Repeated
A
Str
eng
then
ed B
eam
s
Effect of steel
fiber content
BSA1 1 40 30 with Repeated
BSA2 1.5 40 30 with Repeated
BSA3 2 40 30 with Repeated
B
Effect of the
jacket's
thickness
BSB1 1.5 30 30 with Repeated
BSB2 1.5 40 30 without Repeated
BSB3 1.5 50 30 with Repeated
C
Rep
aire
d
Bea
ms Effect of steel
fiber content
BRC1 1 40 30 with Repeated
BRC2 1.5 40 30 with Repeated
BRC3 2 40 30 with Repeated
D
Effect of the
jacket's
thickness
BRD1 1.5 30 30 with Repeated
BRD2 1.5 40 30 without Repeated
BRD3 1.5 50 30 with Repeated
2.2 Materials
The beams were cast with a concrete having a 28 day compressive strength of 27.5 N/mm2
and the constituent materials for 1 m3 are given in Table.2. A normal concrete resistance was
chosen in order to simulate the real case of existing beam and to better highlight the
strengthening and repairing effectiveness. Ordinary Portland cement and local natural sand
were used. The coarse aggregate was gravel with a maximum nominal size of 20 mm. All
Flexural behavior of strengthened and repaired R.C. beams by using steel fiber concrete jacket under
repeated load
Yehia A. Hassanean et al
International Journal of Civil and Structural Engineering 567
Volume 3 Issue 3 2013
used materials are match with ECP 203and ACI 215 limits (ACI Committee; 1974, Egyptian
Code of Practice: ECP 203; 2007).
The jacket was caste with a high strength concrete of cubic strength ranged from 82.5 to 93
N/mm2 after 28 days and the constitute materials for 1m3 are given in Table.2. Ordinary
Portland cement and local natural sand were used. The coarse aggregate was crushed basalt
with a maximum nominal size of 10 mm. To enhance the strength of concrete, silica fume
was used. The workability of the mix was improved by using a high–range water reduction
admixture under a commercial name of Sekament R 2004. The concrete mixes incorporated
two different shapes of steel fibers, corrugated and end-hooked steel fibers of size 0.6×2.0×30
mm in ratio 1:1 by weight and have a minimum tensile strength of 400 N/mm2.
The tension reinforcement used was made of 16 mm deformed bars of 430 N/mm2 yield
strength. Deformed bars of 10 mm diameter and 420 N/mm2 yield strength were used as
compression reinforcement. The stirrups used were made of 8 mm smooth bars of 310
N/mm2 yield strength. The used shear connectors were high tensile steel rivets of 520
N/mm2 yield strength have L shape of 50, 20 mm sides and 4 mm diameter and have end
screw with a length 25 mm.
Table 2: Materials for 1 m3 of the used concrete
Type of
Concrete
Cemen
t kg/m3
Silica
Fume
Kg/m3
Sand
kg/m3
Grave
l
kg/m3
Crushed
Basalt
kg/m3
Additive
Litre/m3
Water
Litre/m3
Normal
Strength
Concrete
375 _______ 659 1076 _____ ______ 201
High Strength
Concrete 500 120 450 _____ 1200 17 132
2.3 Strengthening and repairing technique
The external strengthening and repairing system MSFCJ was performed as follows:
1. Preparations of concrete surface by grinding disk then loose particles and dust have
been removed by vacuum cleaner.
2. The bores to accommodate the shear connectors were drilled by using electrical drill.
3. Cleaning the bores by vacuum cleaner in order to have a good bond between the
epoxy and the concrete surface then epoxy resin was placed in the bores. After that,
the shear connectors were inserted into the bores at the indicated position. The
embedded length of shear connectors in concrete was 28 mm and the free length
outside the concrete surface was 22 mm.
4. Just before cast the jacket, the epoxy adhesive was mixed and applied to the concrete
surface to nominal thickness of about 0.5 mm.
5. Cast the MSFC jacket as mentioned before.
The installation process is given in figure 3.
Flexural behavior of strengthened and repaired R.C. beams by using steel fiber concrete jacket under
repeated load
Yehia A. Hassanean et al
International Journal of Civil and Structural Engineering 568
Volume 3 Issue 3 2013
2.4 Test procedures and instrumentations
The static and repeated loading of the tested beam were made using testing machine EMS 60
tons. All beams were tested as simple beams with a clear span of 2160 mm using a three
point loading system as shown in Figure 1. In static tests; the load was applied in increments
of 5 KN. In repeated tests, the fatigue loading was applied as stationary pulsating
concentrated load at the mid-span of the beam. The applied minimum load was constant at 14
KN (weight of steel tar of testing machine). The maximum load level was taken 0.95 of the
ultimate load of the reference beam tested statically (B0s). The frequency was chosen to be
500 cycles per minute and the chosen stroke was 0.5 mm, the loading scheme is shown in
Figure 4. For all tested beams, mid-span deflection, strain at the center of the main
reinforcement, strain in the compression zone of concrete surface at mid span section, first
crack load, and failure load were measured. Also, crack patterns and failure mode were
observed carefully.
Figure 3: Strengthening and repairing technique:
(a) exposed aggregate after grinding disk of concrete; (b) shear connectors after inserting into
their bores; (c) priming surface process; (d) cast the jacket; (e) beam after cast the jacket
Figure 4: Sketch of sequence of loading versus deflection (repeated tests)
Flexural behavior of strengthened and repaired R.C. beams by using steel fiber concrete jacket under
repeated load
Yehia A. Hassanean et al
International Journal of Civil and Structural Engineering 569
Volume 3 Issue 3 2013
3. Test results and discussion
The data in table 3 includes the cracking loads, the number of cycles to failure, maximum
deflections and strains. It also contains the failure mechanisms for the tested beams.
3.1 Pattern of crack and failure mechanism
For beam B0s which was subjected to static loading, the first crack was observed under point
of load application at section of maximum bending moment. With further increase in the
applied load, further flexural cracks are appeared and extended vertically upwards with the
development of new cracks between the earlier cracks. At the last stages of loading, the
cracks in the mid span zone continue to propagate vertically and few cracks developed in
between, while more cracks form in the shear span, then trended to progress towards the load
point diagonally (flexural-shear cracks) finally the beam failed by widening in the flexural
cracks accompanied by crushing of the concrete at the top compression side under the point
of load application. For "B0r" which tested under repeated load, the cracks are propagated in
the same manner of beam B0s up to the end of the static loading. When the beam is subjected
to the repeated loading the number and width of the cracks are increased dramatically. The
mode of failure as the same as "B0s", but the cracking pattern due to repeated loading was
more extensive.
Table 3: Results of tested beams
Bea
m N
o
Vf
%
tjb
mm
Concrete Strengths
for the jacket
( kg/cm2) Loading
type
Pcr
(KN)
N
×100
Deformations
Mo
de
of
fail
ure
fcu fct fr δcr
(mm)
δu
(mm)
εsu
×10-6
εcu
×10-6
B0s 0 0 ------ ----- ----- Static 20 195 2330 41 2.1 ــــــــــ F.C
B0r 0 0 ----- ----- ----- Repeated 20 25 2.36 45 2450 226 F.C
BSA1 1 40 825 56 75 Repeated 25 50 1.53 59.3 1850 197 F.C
BSA2 1.5 40 900 76 109 Repeated 28 90 1.04 53 1690 322 F.C
BSA3 2 40 930 80 115 Repeated 32 110 0.65 63.1 1250 174 F.C
BSB1 1.5 30 900 76 109 Repeated 25 55 0.97 49.23 1690 315 F.C
BSB2 1.5 40 900 76 109 Repeated 29 75 0.85 53.8 1205 280 F.C
BSB3 1.5 50 900 76 109 Repeated 35 130 0.7 42 1800 288 F.C
BRC1 1 40 825 56 75 Repeated 23 40 1.47 57.1 2009 291 F.C
BRC2 1.5 40 900 76 109 Repeated 27 75 1.76 48.4 1900 295 F.C
BRC3 2 40 930 80 115 Repeated 30 90 1.25 51.14 1495 320 F.C
BRD1 1.5 30 900 76 109 Repeated 25 45 1.83 46 2200 360 F.C
BRD2 1.5 40 900 76 109 Repeated 27 60 1.44 62 2442 250 F.B
BRD3 1.5 50 900 76 109 Repeated 33 100 1.39 65 2129 360 F.C
Flexural behavior of strengthened and repaired R.C. beams by using steel fiber concrete jacket under
repeated load
Yehia A. Hassanean et al
International Journal of Civil and Structural Engineering 570
Volume 3 Issue 3 2013
For the strengthened and repaired beams, it was observed that the strengthening and repairing
with MSFCJ decreased the number of cracks and all cracks concentrated in the middle third
of the tested beams in comparison the reference beam B0r. With increasing the steel fiber
content, more cracks with smaller width was observed. This was because the steel fibers
across cracks contributed in increasing the ductility of the tested beams and reducing the
stress in the tensile steel reinforcement. All mode of failure for the strengthened or repaired
beams was flexural accompanied by crushing of the concrete at the top compression side
under the point of load application except the repaired beam BRD2 suffered from the
debonding of the jacket at the last stage of loading. Meanwhile the identical strengthened
beam BSB2 failed without deponding. This may be reasonable for the absence of shear
connectors as well as the initial cracks existing in the cracked beam BRD2. Figure 5 shows
the cracking pattern and failure mechanisms for some tested beams.
Figure 5: Crack pattern and mode of failure for some tested beams
Flexural behavior of strengthened and repaired R.C. beams by using steel fiber concrete jacket under
repeated load
Yehia A. Hassanean et al
International Journal of Civil and Structural Engineering 571
Volume 3 Issue 3 2013
3.2 Fatigue life of the tested beams
The maximum number of cycles for the tested beams is presented in table 3. Generally, the
number of cycles for strengthened and repaired beams is larger than the reference beam; the
rate and value of increasing depend on the fiber content, jacket thickness and the interface
strength.
Figures 6 and 7 show a comparison between the reference beam and the strengthened or
repaired beams with a 40 mm jacket thickness and variable steel fiber content 1%, 1.5% and
2%. The increasing was 100%, 260% and 340% respectively for the strengthened beams with
respect to the reference beam. Meanwhile the increasing was 60%, 200% and 260%
respectively for the repaired beams. Also, it is clear from these figures that adding 1.5% fiber
content to the concrete used in jacket has a significant effect in increasing the maximum
number of cycles for the strengthened and repaired beams.
Figures 8 and 9 compare the maximum number of cycles for the reference beam and each of
strengthened or repaired beams with a 1.5% fiber content and variable jacket thickness 30, 40
and 50 mm jacket thickness. It can be noticed from these figures that the increase of jacket
thickness has a dramatic effect in increasing the number of cycles for the tested beams. The
enhancements were 120%, 260% and 420% respectively for the strengthened beams. At the
same time the enhancements were 80%, 200% and 300% respectively for the repaired beams.
20
40
60
80
100
120
Steel Fiber Content %
Ma
xim
um
Nu
mb
er o
f C
ycl
es x
10
0
0.0 1.0% 2.0 3.00.0 1.5% 2%
20
40
60
80
100
Steel Fiber Content %
Ma
xim
um
Nu
mb
er o
f C
ycl
es x
10
0
0.0 1.0% 1.5% 2%
Figure 6: Effect of fiber content on
maximum number of cycles for strengthened
beams.
Figure 7: Effect of steel fiber content on
maximum number of cycles for repaired
beams.
20
40
60
80
100
120
140
Jacket Thickness (mm)
Ma
xim
um
Nu
mb
er o
f C
ycl
es x
10
0
0.0 30 40 50
20
40
60
80
100
120
Jacket Thickness (mm)
Ma
xim
um
Nu
mb
er o
f C
ycl
es x
10
0
0.0 30 40 50
Figure 8: Effect of jacket thickness on
maximum number of cycles for strengthened
beams.
Figure 9: Effect of jacket thickness on
maximum number of cycles for repaired
beams.
Beam without Shear
Connectors Beam without Shear
Connectors
Flexural behavior of strengthened and repaired R.C. beams by using steel fiber concrete jacket under
repeated load
Yehia A. Hassanean et al
International Journal of Civil and Structural Engineering 572
Volume 3 Issue 3 2013
Investigating figures 10 and 11, it can be observed that the absence of shear connectors lead
to decreasing the maximum number of cycles and preventing the strengthened or repaired
beams to reach its predicted maximum number of cycles. This may be reasonable for the
separation of the jacket from the main beam especially at the last stages of loading.
10
20
30
40
50
60
70
80
90
100
Maxim
um
Num
ber o
f Cycle
s x 1
0
Reference
Beams
Beam with Shear
Connectors
Beam without
Shear Connectors 20
30
40
50
60
70
80
Maxim
um
Num
ber
of C
ycl
es x
10
2
Reference
Beams
Beam with Shear
Connectors
Beam without
Shear Connectors
Figure 10: Interface effect on maximum
number of cycles for strengthened beams.
Figure 11: Interface effects on maximum
number of cycles for repaired beams.
3.3 Deformation response
3.3.1 Deflection
The changes of the mid-span deflections with the increase of the number of cycles for all
beams tested under short time repeated loading are given in figures 12 to 15. It can be
observed that in all beams there was an initial increase of the mid-span deflection, followed
by a stable region where the deflection remained relatively constant through many number of
cycles followed by a dramatic increase of deflection just before failure. Also, it can be
observed that with increasing the fatigue life of the tested beams, the deflections increases
significantly. A greater number of cracks resulting from cycling may cause this.
For the strengthened or repaired beams with a constant jacket thickness and variable steel
fiber content 1%, 1.5% and 2%, it is clear that at the same number of cycles, the mid-span
deflection decreases as the fiber content increases. For strengthened beams, the increasing of
steel fiber from 1% to 1.5% decreased the deflection by 58% at 5000 cycle while at the same
number of cycles the decreasing was 70% when the steel fiber increased from 1% to 2% as
shown in figure 16. For repaired beams, the Increasing of steel fiber content from 1% to 1.5%
decreased the mid-span deflection by 41% at 4000 cycle. Meanwhile at the same number of
cycles, the increasing of steel fiber content from 1% to 2% decreased the mid-span deflection
by 63% as shown in figure 17. It is clear that the slope of line from 1% to 1.5% is larger than
the slope of line from 1.5% to 2%.
For the beams that were strengthened or repaired by MSFC jacket with a constant steel fiber
content and variable jacket thickness, it is obvious that at the same number of cycles,
increasing the jacket thickness causes a significant decreasing in the mid-span deflection. For
example, the increasing of jacket thickness for strengthened beams from 30 mm to 40 mm
decreased the deflection by 44% at 5500 cycle while at the same number of cycles the
increasing of jacket thickness from 30 mm to 50 mm decreased the deflection by 62% as
shown in figure 18. For repaired beams, the increasing jacket thickness from 30 mm to 40
mm decreased the mid-span deflection by 28% at 4500 cycle. Meanwhile at the same number
of cycles, the increasing of jacket thickness from 30 mm to 50 mm decreased the mid-span
Flexural behavior of strengthened and repaired R.C. beams by using steel fiber concrete jacket under
repeated load
Yehia A. Hassanean et al
International Journal of Civil and Structural Engineering 573
Volume 3 Issue 3 2013
deflection by 39% as shown in figure 19. Figures 20 and 21 show the effect of shear
connectors between the main beam and the jacket. The absences of the shear connectors
decreased the effectiveness for each strengthened beams and repaired beams.
0
10
20
30
40
50
60
70
0 10 20 30 40 50 60 70 80 90 100 110 120 130
Number of Cycles x102
Def
lect
ion
(m
m)
B0r - Reference BeamBSA1 - 1 % FiberBSA2 - 1.5 % BSA3 - 2 %
0
10
20
30
40
50
60
0 10 20 30 40 50 60 70 80 90 100 110 120 130
Number of Cyclesx102
De
fle
cti
on
(m
m)
B0r - Reference Beam
BSB1 - 3 cm Jacket Thickness BSB2 - 4 cm
BSB3 - 5 cm
Figure 12: Effect of steel fiber content on
variation of mid span deflection with
number of cycles for strengthened beams
Figure 13: Effect of jacket thickness on
variation of mid span deflection with number
of cycles for strengthened beams
0
10
20
30
40
50
60
0 10 20 30 40 50 60 70 80 90
Number of Cycles x 102
De
fle
cti
on
(m
m)
B0r - Reference Beam
BRC1 - 1 % Fiber
BRC2 - 1.5 % BRC3 - 2 %
0
10
20
30
40
50
60
70
0 10 20 30 40 50 60 70 80 90 100
Number of Cycles x 102
Def
lect
ion
(m
m)
B0r - Reference Beam
BRD1 - 3 cm Jacket Thickness
BRD2 - 4 cm
BRD3 - 5 cm
Figure 14: Effect of steel fiber content on
variation of mid span deflection with
number of cycles for repaired beams
Figure 15: Effect of jacket thickness on
variation of mid span deflection with number
of cycles for repaired beams.
10
20
30
40
50
60
1 1.5 2Steel Fiber Content
Defl
ecti
on
(m
m)
20
30
40
50
60
1 1.5 2Steel Fiber Content
Defl
ecti
on
(m
m)
Figure 16: Effect of steel fiber content on
mid-span deflection of strengthened beams
after 5000 cycles
Figure 17: Effect of steel fiber content on
mid-span deflection of repaired beams after
4000 cycles
Flexural behavior of strengthened and repaired R.C. beams by using steel fiber concrete jacket under
repeated load
Yehia A. Hassanean et al
International Journal of Civil and Structural Engineering 574
Volume 3 Issue 3 2013
10
20
30
40
50
30 40 50Jacket Thickness (mm)
Def
lecti
on
(m
m)
20
30
40
50
30 40 50
Jacket Thickness(mm)
Defl
ecti
on
(m
m)
Figure 18: Jacket thickness effect on mid-
span deflection of strengthened beams after
5500 cycles
Figure 19: Effect of jacket thickness on mid-
span deflection of repaired beams after 4500
cycles
10
15
20
25
30
35
40
45
50
Defl
ecti
on (m
m)
Reference
Beams
Beam with Shear
Connectors
Beam without
Shear Connectors
20
25
30
35
40
45
50
Deflection (m
m)
Reference
Beams
Beam with Shear
Connectors
Beam without
Shear Connectors
Figure 20: Effect of interface strength on
mid-span deflection of strengthened beams
after 2500 cycles
Figure 21: Effect of jacket thickness on mid-
span deflection of repaired beams after 2500
cycles
3.3.1 Strain response
The recorded strains on the main steel reinforcement and concrete (top surface) for the
strengthened and repaired beams are given in Figures 22 to 29. In both beams, the strain in
main steel increased suddenly before failure, indicating yielding of the reinforcement. At that
point, strain in the concrete increased but remained lower than strains corresponding to
expected ultimate behavior (0.003 micro-strain). It can be also seen that there is a more
gradual increase in the steel and concrete strain as the beam approaches its fatigue life. This
may be due to increasing the deflection resulting from increased cycling
Figures 30 to 33 show a comparison between the strains in main steel and concrete for those
beams which were strengthened or repaired by 40 mm jacket thickness and variable steel
fiber content. It is clear that at the same number of cycles, the strains decrease as the steel
fiber content increases. It can also be observed that the increasing of steel fiber content from
1% to 1.5% has a significant decreasing in the strains in both main steel and concrete.
Figures 34 to 37 show the effect of jacket thickness in strains for strengthened and repaired
beams. It can be observed that at the same number of cycles, the strains decrease as the jacket
thickness increases. From the same figures, it is clear that the absences of the shear
connectors increased the strains for the strengthened and repaired beams.
Beam without Shear
Connectors
Beam without Shear
Connectors
Flexural behavior of strengthened and repaired R.C. beams by using steel fiber concrete jacket under
repeated load
Yehia A. Hassanean et al
International Journal of Civil and Structural Engineering 575
Volume 3 Issue 3 2013
0
500
1000
1500
2000
2500
0 10 20 30 40 50 60 70 80 90 100 110
Number of Cycles x 102
Ma
in S
teel
Str
ain
(M
icro
str
ain
)
B0r - Reference Beam
BSA1 - 1 % Fiber
BSA2 - 1.5 %
BSA3 - 2 %
0
500
1000
1500
2000
2500
0 10 20 30 40 50 60 70 80 90 100 110 120 130
Number of Cycles x 102
Ma
in S
teel
Str
ain
(M
icro
Str
ain
) B0r - Reference Beam
BSB1 - 3 cm Jacket Thickness BSB2 - 4 cm
BSB3 - 5 cm
Figure 22: Effect of steel fiber content on
variation of strain in main steel with number
of cycles for strengthened beams
Figure 23: Effect of jacket thickness on
variation of strain in main steel with number
of cycles for strengthened beams
0
500
1000
1500
2000
2500
0 10 20 30 40 50 60 70 80 90
Number of Cycles x 102
Ma
in S
teel
Str
ain
(M
icro
Str
ain
)
B0r - Reference Beam
BRC1 - 1 % Fiber
BRC2 - 1.5 %
BRC3 - 2 %
0
500
1000
1500
2000
2500
0 10 20 30 40 50 60 70 80 90 100
Number of Cycles x 102
Ma
in S
teel
Str
ain
(M
icro
Str
ain
)
B0r - Reference Beam
BRD1 - 3 cm Jacket Thickness
BRD2 - 4 cm
BRD3 - 5 cm
Figure 24: Effect of steel fiber content on
variation of strain in main steel with number
of cycles for repaired beams
Figure 25: Effect of jacket thickness on
variation of strain in main steel with number
of cycles for repaired beams
0
100
200
300
400
0 10 20 30 40 50 60 70 80 90 100 110
Cycles x 102
Co
nc
rete
str
ain
(M
icro
Str
ain
)
B0r - Reference Beam
BSA1 - 1 % Fiber
BSA2 - 1.5 %
BSA3 - 2 %
0
100
200
300
400
0 10 20 30 40 50 60 70 80 90 100 110 120 130
Cycles x 102
Co
nc
rete
str
ain
(M
icro
Str
ain
)
B0r - Reference Beam
BSB1 - 3 cm Jacket Thickness
BSB2 - 4 cm
BSB3 - 5 cm
Figure 26: Effect of steel fiber content on
variation of strain in concrete with number
of cycles for strengthened beams
Figure 27: Effect of jacket thickness on
variation of strain in concrete with number of
cycles for strengthened beams
Flexural behavior of strengthened and repaired R.C. beams by using steel fiber concrete jacket under
repeated load
Yehia A. Hassanean et al
International Journal of Civil and Structural Engineering 576
Volume 3 Issue 3 2013
0
100
200
300
400
0 10 20 30 40 50 60 70 80 90
Number of Cycles x 102
Co
nc
rete
str
ain
(M
icro
Str
ain
)
B0r - Reference BeamBRC1 - 1 % FiberBRC2 - 1.5 % BRC3 - 2 %
0
100
200
300
400
0 10 20 30 40 50 60 70 80 90 100
Number Cycles x 102
Co
nc
rete
str
ain
(M
icro
Str
ain
)
B0r - Reference Beam
BRD1 - 3 cm Jacket Thickness
BRD2 - 4 cm
BRD3 - 5 cm
Figure 28: Effect of steel fiber content on
variation of strain in concrete with number
of cycles for repaired beams
Figure 29: Effect of jacket thickness on
variation of strain in concrete with number of
cycles for repaired beams
500
1000
1500
2000
1 1.5 2Steel Fiber Content
Ma
in S
teel
Str
ain
(M
icro
stra
in)
500
1000
1500
2000
1 1.5 2Steel Fiber Content
Ma
in S
tee
l S
tra
in (
Mic
ro
stra
in)
Figure 30: Effect of steel fiber content on
main steel strain for strengthened beams
after 5000 cycles
Figure 31: Effect of steel fiber content on
main steel strain for repaired beams after
4000 cycles
50
100
150
200
1 1.5 2Steel Fiber Content
Co
ncrete
Str
ain
(M
icro
stra
in)
100
150
200
250
300
1 1.5 2Steel Fiber Content
Co
ncr
ete
Str
ain
(M
icro
stra
in)
Figure 32: Effect of steel fiber content on
concrete strain for strengthened beams after
5000 cycles
Figure 33: Effect of steel fiber content on
concrete strain for repaired beams after 4000
cycles
Flexural behavior of strengthened and repaired R.C. beams by using steel fiber concrete jacket under
repeated load
Yehia A. Hassanean et al
International Journal of Civil and Structural Engineering 577
Volume 3 Issue 3 2013
0
500
1000
1500
2000
30 40 50Jacket Thickness(mm)
Ma
in S
teel
Str
ain
(M
icro
stra
in)
500
1000
1500
2000
2500
30 40 50Jacket Thickness (mm)
Main
Ste
el S
train
(M
icro
stra
in)
Figure 34: Effect of jacket thickness on
main steel strain for strengthened beams
after 5500 cycles
Figure 35: Effect of jacket thickness on main
steel strain for repaired beams after 4500
cycles
50
100
150
200
250
300
350
30 40 50Jacket Thickness (mm)
Co
ncrete
Str
ain
x 1
0-6
100
150
200
250
300
350
400
30 40 50Jacket Thickness (mm)
Con
cret
e S
train
(M
icro
stari
n)
Figure 36: Effect of jacket thickness on
concrete strain for strengthened beams after
5500 cycles
Figure 37: Effect of jacket thickness on
concrete strain for repaired beams after 4500
cycles
4. Conclusions
Based on the test results and discussions above, the following conclusions can be drawn.
1. The strengthening and repairing with MSFC jacket decreased the number of cracks
and they were concentrated in the middle third avoiding the forming of shear cracks.
2. Presences of shear connectors in the jacket play a role in enhancing the bonding
between the main beam and the jacket and prevent the debonding failure. While the
absence of shear connectors lead to prevent the strengthened and repaired beams to
reach its predicted maximum number of cycles.
3. The application of MSFC jacket on a R.C beam provides a significant increase in the
strengthened and repaired beams stiffness.
4. The application of MSFC jacket on a R.C. beam provides an increase of the maximum
number of cycles from 2 to 5 times for strengthened beams and from 1.6 to 4 times for
repaired beams depending on the fiber content, jacket thickness and the interface
strength.
5. Adding 1.5% fiber content to the concrete used in the jacket has a significant effect in
increasing the number of cycles and decreasing both the deflections and strains. This
content may be the economic steel fiber content that can be added.
Beam without Shear
Connectors Beam without Shear
Connectors
Beam without Shear
Connectors
Beam without Shear
Connectors
Flexural behavior of strengthened and repaired R.C. beams by using steel fiber concrete jacket under
repeated load
Yehia A. Hassanean et al
International Journal of Civil and Structural Engineering 578
Volume 3 Issue 3 2013
6. The proposed technique provides a significant structural enhancement at the
serviceability limit state; due to the remarkably increase of the beam stiffness and
decrease the measured deformations.
5. References
1. ACI Committee 215, (1974), Consideration for Design of Concrete Structures
Subjected to Fatigue Loading, ACI Journal, 71(3), pp 97-121.
2. Byung Hwan, (1992), Flexural Analysis of Reinforced Concrete Beams Containing
Steel Fibers, Journal of Structural Engineering, 118(10), pp 2821-2836.
3. Egyptian Code of Practice: ECP 203-2007, (2007), Design and Construction for
Reinforced Concrete Structures, Ministry of Building Construction, Research Center for
Housing, Building and Physical Planning, Cairo, Egypt.
4. Fatih Altun, (2994), An Experimental Study of the Jacketed Reinforced Concrete
Beams under Bending, Construction and Building Materials, 18, pp 611-618.
5. Giovanni Martinola, Alberto Meda, Giovanni A. Plizzari and Zila Rinaldi, (2007),
Strengthening and Repairing of RC Beams with Fiber Reinforced Concrete, Cement،
Concrete Composites, 32, pp 731-739.
6. Johnston, C.D., Zemp, R.W., (1991), Flexural Fatigue Performance of Steel Fiber
Reinforced Concrete Influence of Fiber Content, Aspect Ratio and Type, ACI Materials
Journal, 88(4), pp 374-383.
7. Nasser Abdel Salam, (2005), Repair and Strengthening of Reinforced Concrete Beams
Using Fiber Reinforced Concrete, M.Sc. Thesis, Zagazig university, Egypt.