IRJET-EXPERIMENTAL STUDY ON SHEAR BEHAVIOR OF DIFFERENT TYPES OF FIBERS IN REINFORCED CONCRETE BEAMS
Content
International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395 -0056
Volume: 02 Issue: 02 | May-2015
p-ISSN: 2395-0072
www.irjet.net
EXPERIMENTAL STUDY ON SHEAR BEHAVIOR OF DIFFERENT TYPES OF
FIBERS IN REINFORCED CONCRETE BEAMS
Dr.A.Vijayakumar1, Dr.D.L.Venkatesh Babu2, Mr.E.Prabakaran3
1Professor
2
and HOD of Civil Engineering, Coimbatore Institute of Engineering and Technology,
Coimbatore, Tamilnadu, India.
Professor and HOD of Civil Engineering, JSS Academy of Technical Education, JSS Campus,
Uttarahalli, Bangalore, India.
3Assistant
Professor. Department of Civil Engineering, KPR Institute of Engineering and
Technology, Coimbatore, Tamilnadu, India.
---------------------------------------------------------------------***---------------------------------------------------------------------
Abstract - This study presents a series of tests for
characterizing the structural behavior of fiber
reinforced concrete beams subjected to shear loading.
The experimental program involves two types of fibers,
steel fiber and a polypropylene fiber. As a reference,
plain concrete and conventionally reinforced concrete
specimens have also been casted and tested in the
laboratory as per ASTM standards. The ultimate shear
carrying capacities of the beams are calculated. The
study confirms that the shear crack resistance of the
material is greatly enhanced by the fibers. Fibers
reduced the crack width to approximately a fifth of that
in beams with stirrups. The use of steel fibers raises the
ductility and fracture energy of concrete. Addition of
steel fibers to concrete improves its post cracking
behavior in tension. The shear resistance increased
with increasing aspect ratio of fibers and volume
fraction of fibers.
Key Words: Steel fiber, Polypropylene fiber, Cracking,
Shear resistance.
1. INTRODUCTION
Both steel and polymeric fibers have been used to
reinforce concrete and consequently increase its
toughness and crack resistance. Fiber reinforced concrete
can be used in some structural applications with a reduced
amount or even without any conventional reinforcement.
One application of the fibers is to increase the loadcarrying capacity of concrete subjected to shear.
© 2015, IRJET.NET- All Rights Reserved
Several design methods have been proposed that
take into account the increase in shear strength due to
fibers (Al-Tann and Al-Feel, 1990; Casanova and Rossi,
1997; Campione and Mindess, 1999; RILEM 2000a;
Dupont and Vandewalle, 2000; Italian Guidelines CNR-DT
204/2006, 2006; among others). Each of the methods
accounts for the fiber contribution by means of an index
based on the toughness of the material. However, each
formula uses a different index, obtained from different
types of test conurations. Thus the application of the
design methods can be difficult. Moreover, most of the
design methods and test procedures have been developed
only for the evaluation of steel fiber reinforced concrete.
The purpose of this work is to present the results
of a study carried out to characterize the structural
behavior of FRC beams under shear loading, considering
fibers of different materials (steel and polymeric). Further,
the study aims to evaluate the ability of predicting the
ultimate shear capacity through code provisions or by
correlations with results from other tests. At the same
time, it is verified whether the design methods for SFRC
can be extrapolated to polypropylene fiber reinforced
concrete (PFRC).
2. MATERIALS
A concrete with 25 Mpa compressive strength was
considered for the mixes. Two types of fibers were
considered, Dramix 80/60 BN hook-ended steel fibers, and
polypropylene fibers. In all cases fiber volume was fixed at
0.4% based on literature review.
Page 269
International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395 -0056
Volume: 02 Issue: 02 | May-2015
p-ISSN: 2395-0072
www.irjet.net
τfd = 0.12 f (N/mm²) ; Where f is the equivalent residual
stress.
4. MATERIAL-SCALE CHARACTERIZATION TESTS
Fig- 1: Steel Fiber with Hooked-end and Polypropylene
Fiber
3. SHEAR RESISTANT MECHANISMS OF FRC BEAMS
In a FRC beam, it seems logical to consider that, during
failure; the shear force transferred along the web, due to
aggregate interlocking is increased since the crack
opening is reduced by the fiber action. Also, due to the
toughness of FRC, tensile stresses can be resisted across
the crack (through fiber bridging) once the shear crack
appears; giving rise to a vertical force component that
contributes to balancing the shear force acting on the
beam. For the shear design of beams, the European and
American Codes consider that the ultimate shear capacity,
Vu, is the sum of the contributions of the concrete and the
stirrups, Vcd and Vwd, respectively:
Vu = Vcd + Vwd
Accordingly, several authors (Al-Tann & Al-Feel, 1990;
Casanova & Rossi, 1997; Compione & Mindess, 1999;
RILEM, 2000a) have suggested the addition of another
factor, Vfd, to take into account the fiber contribution:
Vu = Vcd + Vwd + Vfd
Where Vfd is a function of different parameters. For
example, RILEM (2000) defines the contribution of steel
fibers to the ultimate shear capacity as:
Vfd = kf k1τfd bw d
Where kf = takes into account the contribution of the
flanges of a T-section:
Kf = 1+[hf/bw][hf/d] n ,
Kf ≤ 1.5
Hf = flange thickness (mm)
Bf = flange width (mm)
Bw = web width (mm)
N = Bf- Bw/ hf ;
K1 = 1600-d / 1000 k1 ≥ 1 ; (d in mm); k1 accounts for
the size effect
τfd = design value of the maximum tangential stress due
to fibers;
© 2015, IRJET.NET- All Rights Reserved
The concrete compressive strength was evaluated
for each mix by tests on 150×150×150 mm cubes. Twopoint loading tests were conducted on beam specimens of
150 × 250 × 2000 mm to study the shear capacity. Twopoint flexural tests were conducted on beam specimens of
100 × 100 × 500 mm according to the ASTM C1018 (1998)
standard. The test configuration and typical mean
responses can be observed in Figure..2
As it can be seen from .6 that toughness clearly increases
with the incorporation of fibers; to a greater extent with
steel fibers, followed by HPP fibers
Fig-2: Shear Test Configuration
5. TESTS RESULTS AND DISCUSSION
The structural-scale beams were tested under
shear loading through the two-point load conuration, with
a shear span to depth ratio equal to 2.67. The smaller
anchorage length provided for the longitudinal
reinforcement did not allow the development of arch
effect, which caused failure by debonding of the flexural
reinforcement in the case of beams without conventional
shear reinforcement.
Figure.6 shows the typical load-deflection
responses, where the shear ductility increase induced by
fiber action is appreciable. Beam PC-SR exhibited flexural
failure. In SFRC beams, the maximum load is higher by
approximately 20% of that of plain concrete, with increase
the deflection at maximum load. An increase of ductility
under shear loading can be clearly observed for all FRCs
with respect to plain concrete beam specimens, indicated
by the significant increase in the deformability of the
elements either at maximum load or along the post-peak
regime.
Page 270
International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395 -0056
Volume: 02 Issue: 02 | May-2015
p-ISSN: 2395-0072
www.irjet.net
Nevertheless, the load carrying capacity of beams
reinforced with fibers is always lower than that of the
beams with the same volume of steel in the form of
stirrups. This is attributed to the distributed nature of the
fiber reinforcement where only some fibers are favorably
oriented to resist cracking, whereas all the stirrups
actively prevent crack opening.
6. CONCLUSIONS
Compressive Strength in
N/MM^2
Compressive Strength of Concrete Cubes.
30
25
20
O.C
15
SFRC
10
PFRC
5
0
7
28
No.of Days
Fig-3: Compressive Strength of Concrete
Cubes
Flexural Strength in N/MM^2
Flexural Strength
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
O.C
SFRC
PFRC
7
7. REFERENCES
1.Amir,A.,Mirsayah and Nemkumar Banthia., “Shear
Strength of Steel Fiber Reinforced Concrete”, ACI
Materials Journal.
28
No of Days
Fig-.4: Flexural strength of concrete
2.Balaguru,N&P.Shah “Fiber
composites”, pp 115-175.
Split Tensile Strength
Split Tensile Strength in
N/MM^2
It has been observed that the incorporation of
fibers to the mix increases the material
toughness both in tension and compression, as
represented by the toughness indexes of the
ASTM and JSCE standards.
The toughness increases results in higher shear
strength of the concrete and better
deformability, i.e. the deflection at maximum
load is significantly higher for FRC beams than
plain concrete specimens.
The compressive strength increase only
marginally due to fiber incorporation in
concrete.
First crack occurs earlier in PFRC when
compared to SFRC.
In SFRC beams, the maximum load increased by
approximately 20% of the plain concrete.
The length and width of the crack is reduced
due to the incorporation of fibers in the
concrete.
3.5
Reinforced
cement
3
2.5
O.C
2
SFRC
1.5
PFRC
1
0.5
3.“Design Considerations for Steel Fiber Reinforced
Concrete”. ACI 544.4R-88 (Reapproved 1999).
0
7
28
No.of Days
4.DuPont, D & Vandewalle L., “Shear Capacity of
Concrete
Beams
Containing
Longitudinal
Reinforcement and Steel Fibers”.
Fig 5: Split Tensile Strength of Concrete
Load vs Displacement Response for Shear Loading
90
80
Load (KN)
70
60
R.C-1
50
R.C-2
40
SFRC
PFRC
30
20
10
0
0
2
4
6
8
10
12
Displacement (mm)
Fig-6: Load-Displacement Response
Under Shear Loading
© 2015, IRJET.NET- All Rights Reserved
Page 271
e-ISSN: 2395 -0056
Volume: 02 Issue: 02 | May-2015
p-ISSN: 2395-0072
www.irjet.net
EXPERIMENTAL STUDY ON SHEAR BEHAVIOR OF DIFFERENT TYPES OF
FIBERS IN REINFORCED CONCRETE BEAMS
Dr.A.Vijayakumar1, Dr.D.L.Venkatesh Babu2, Mr.E.Prabakaran3
1Professor
2
and HOD of Civil Engineering, Coimbatore Institute of Engineering and Technology,
Coimbatore, Tamilnadu, India.
Professor and HOD of Civil Engineering, JSS Academy of Technical Education, JSS Campus,
Uttarahalli, Bangalore, India.
3Assistant
Professor. Department of Civil Engineering, KPR Institute of Engineering and
Technology, Coimbatore, Tamilnadu, India.
---------------------------------------------------------------------***---------------------------------------------------------------------
Abstract - This study presents a series of tests for
characterizing the structural behavior of fiber
reinforced concrete beams subjected to shear loading.
The experimental program involves two types of fibers,
steel fiber and a polypropylene fiber. As a reference,
plain concrete and conventionally reinforced concrete
specimens have also been casted and tested in the
laboratory as per ASTM standards. The ultimate shear
carrying capacities of the beams are calculated. The
study confirms that the shear crack resistance of the
material is greatly enhanced by the fibers. Fibers
reduced the crack width to approximately a fifth of that
in beams with stirrups. The use of steel fibers raises the
ductility and fracture energy of concrete. Addition of
steel fibers to concrete improves its post cracking
behavior in tension. The shear resistance increased
with increasing aspect ratio of fibers and volume
fraction of fibers.
Key Words: Steel fiber, Polypropylene fiber, Cracking,
Shear resistance.
1. INTRODUCTION
Both steel and polymeric fibers have been used to
reinforce concrete and consequently increase its
toughness and crack resistance. Fiber reinforced concrete
can be used in some structural applications with a reduced
amount or even without any conventional reinforcement.
One application of the fibers is to increase the loadcarrying capacity of concrete subjected to shear.
© 2015, IRJET.NET- All Rights Reserved
Several design methods have been proposed that
take into account the increase in shear strength due to
fibers (Al-Tann and Al-Feel, 1990; Casanova and Rossi,
1997; Campione and Mindess, 1999; RILEM 2000a;
Dupont and Vandewalle, 2000; Italian Guidelines CNR-DT
204/2006, 2006; among others). Each of the methods
accounts for the fiber contribution by means of an index
based on the toughness of the material. However, each
formula uses a different index, obtained from different
types of test conurations. Thus the application of the
design methods can be difficult. Moreover, most of the
design methods and test procedures have been developed
only for the evaluation of steel fiber reinforced concrete.
The purpose of this work is to present the results
of a study carried out to characterize the structural
behavior of FRC beams under shear loading, considering
fibers of different materials (steel and polymeric). Further,
the study aims to evaluate the ability of predicting the
ultimate shear capacity through code provisions or by
correlations with results from other tests. At the same
time, it is verified whether the design methods for SFRC
can be extrapolated to polypropylene fiber reinforced
concrete (PFRC).
2. MATERIALS
A concrete with 25 Mpa compressive strength was
considered for the mixes. Two types of fibers were
considered, Dramix 80/60 BN hook-ended steel fibers, and
polypropylene fibers. In all cases fiber volume was fixed at
0.4% based on literature review.
Page 269
International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395 -0056
Volume: 02 Issue: 02 | May-2015
p-ISSN: 2395-0072
www.irjet.net
τfd = 0.12 f (N/mm²) ; Where f is the equivalent residual
stress.
4. MATERIAL-SCALE CHARACTERIZATION TESTS
Fig- 1: Steel Fiber with Hooked-end and Polypropylene
Fiber
3. SHEAR RESISTANT MECHANISMS OF FRC BEAMS
In a FRC beam, it seems logical to consider that, during
failure; the shear force transferred along the web, due to
aggregate interlocking is increased since the crack
opening is reduced by the fiber action. Also, due to the
toughness of FRC, tensile stresses can be resisted across
the crack (through fiber bridging) once the shear crack
appears; giving rise to a vertical force component that
contributes to balancing the shear force acting on the
beam. For the shear design of beams, the European and
American Codes consider that the ultimate shear capacity,
Vu, is the sum of the contributions of the concrete and the
stirrups, Vcd and Vwd, respectively:
Vu = Vcd + Vwd
Accordingly, several authors (Al-Tann & Al-Feel, 1990;
Casanova & Rossi, 1997; Compione & Mindess, 1999;
RILEM, 2000a) have suggested the addition of another
factor, Vfd, to take into account the fiber contribution:
Vu = Vcd + Vwd + Vfd
Where Vfd is a function of different parameters. For
example, RILEM (2000) defines the contribution of steel
fibers to the ultimate shear capacity as:
Vfd = kf k1τfd bw d
Where kf = takes into account the contribution of the
flanges of a T-section:
Kf = 1+[hf/bw][hf/d] n ,
Kf ≤ 1.5
Hf = flange thickness (mm)
Bf = flange width (mm)
Bw = web width (mm)
N = Bf- Bw/ hf ;
K1 = 1600-d / 1000 k1 ≥ 1 ; (d in mm); k1 accounts for
the size effect
τfd = design value of the maximum tangential stress due
to fibers;
© 2015, IRJET.NET- All Rights Reserved
The concrete compressive strength was evaluated
for each mix by tests on 150×150×150 mm cubes. Twopoint loading tests were conducted on beam specimens of
150 × 250 × 2000 mm to study the shear capacity. Twopoint flexural tests were conducted on beam specimens of
100 × 100 × 500 mm according to the ASTM C1018 (1998)
standard. The test configuration and typical mean
responses can be observed in Figure..2
As it can be seen from .6 that toughness clearly increases
with the incorporation of fibers; to a greater extent with
steel fibers, followed by HPP fibers
Fig-2: Shear Test Configuration
5. TESTS RESULTS AND DISCUSSION
The structural-scale beams were tested under
shear loading through the two-point load conuration, with
a shear span to depth ratio equal to 2.67. The smaller
anchorage length provided for the longitudinal
reinforcement did not allow the development of arch
effect, which caused failure by debonding of the flexural
reinforcement in the case of beams without conventional
shear reinforcement.
Figure.6 shows the typical load-deflection
responses, where the shear ductility increase induced by
fiber action is appreciable. Beam PC-SR exhibited flexural
failure. In SFRC beams, the maximum load is higher by
approximately 20% of that of plain concrete, with increase
the deflection at maximum load. An increase of ductility
under shear loading can be clearly observed for all FRCs
with respect to plain concrete beam specimens, indicated
by the significant increase in the deformability of the
elements either at maximum load or along the post-peak
regime.
Page 270
International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395 -0056
Volume: 02 Issue: 02 | May-2015
p-ISSN: 2395-0072
www.irjet.net
Nevertheless, the load carrying capacity of beams
reinforced with fibers is always lower than that of the
beams with the same volume of steel in the form of
stirrups. This is attributed to the distributed nature of the
fiber reinforcement where only some fibers are favorably
oriented to resist cracking, whereas all the stirrups
actively prevent crack opening.
6. CONCLUSIONS
Compressive Strength in
N/MM^2
Compressive Strength of Concrete Cubes.
30
25
20
O.C
15
SFRC
10
PFRC
5
0
7
28
No.of Days
Fig-3: Compressive Strength of Concrete
Cubes
Flexural Strength in N/MM^2
Flexural Strength
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
O.C
SFRC
PFRC
7
7. REFERENCES
1.Amir,A.,Mirsayah and Nemkumar Banthia., “Shear
Strength of Steel Fiber Reinforced Concrete”, ACI
Materials Journal.
28
No of Days
Fig-.4: Flexural strength of concrete
2.Balaguru,N&P.Shah “Fiber
composites”, pp 115-175.
Split Tensile Strength
Split Tensile Strength in
N/MM^2
It has been observed that the incorporation of
fibers to the mix increases the material
toughness both in tension and compression, as
represented by the toughness indexes of the
ASTM and JSCE standards.
The toughness increases results in higher shear
strength of the concrete and better
deformability, i.e. the deflection at maximum
load is significantly higher for FRC beams than
plain concrete specimens.
The compressive strength increase only
marginally due to fiber incorporation in
concrete.
First crack occurs earlier in PFRC when
compared to SFRC.
In SFRC beams, the maximum load increased by
approximately 20% of the plain concrete.
The length and width of the crack is reduced
due to the incorporation of fibers in the
concrete.
3.5
Reinforced
cement
3
2.5
O.C
2
SFRC
1.5
PFRC
1
0.5
3.“Design Considerations for Steel Fiber Reinforced
Concrete”. ACI 544.4R-88 (Reapproved 1999).
0
7
28
No.of Days
4.DuPont, D & Vandewalle L., “Shear Capacity of
Concrete
Beams
Containing
Longitudinal
Reinforcement and Steel Fibers”.
Fig 5: Split Tensile Strength of Concrete
Load vs Displacement Response for Shear Loading
90
80
Load (KN)
70
60
R.C-1
50
R.C-2
40
SFRC
PFRC
30
20
10
0
0
2
4
6
8
10
12
Displacement (mm)
Fig-6: Load-Displacement Response
Under Shear Loading
© 2015, IRJET.NET- All Rights Reserved
Page 271
