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Experimental Investigation of the Compressive, Tensile and the Flexural Capacity of Beams made of Steel Fiber Reinforced Concrete (SFRC)

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Experimental investigations are conducted to study the increase in compressive, tensile and flexural capacity of fixed, cantilever and simply supported test beams made of Steel Fiber Reinforced Concrete (SFRC). In this research customized enlarged end fibers are used with a volume fraction of 1.5%. Fibers consists of low aspect ratio are used and sufficient capacity enhancement is observed by experimental testing in this study. Two different aggregate types are used to make the concrete i.e. stone and brick and the effects of steel fibers on these two types of concrete specimens are also evaluated. Stone and brick concrete specimens show significant increase in the compressive, tensile and flexural capacity and in some cases ductility due to the presence of steel fibers. Flexural test shows the increase in flexural capacity of about 8% to 60%, compressive strength is increased by about 8% to 19% and tensile strength by about 39% to 149%. This investigation proposes steel fibers as an additive for concrete to make flexural members of structures to increase the capacity as well as ductility which will reduce the risk of brittle failure during earthquake or any other load.
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The AUST Journal of Science and Technology, Volume 4, Issue 2, Page 52-69, July 2012
(Published in January 2014), ISSN 2072-0149, (DRAFT COPY)
1
Experimental Investigation of the Compressive, Tensile and the Flexural Capacity of
Beams made of Steel Fiber Reinforced Concrete (SFRC)
M. M. Islam
1
, M. A. Chowdhury
2
, A. Z. Mustafiz
3
, M. K. Uddin
3
, P. Mondal
3
, A. Siddique
1
Abstract
Experimental investigations are conducted to study the increase in compressive, tensile
and flexural capacity of fixed, cantilever and simply supported test beams made of Steel
Fiber Reinforced Concrete (SFRC). In this research customized enlarged end fibers are
used with a volume fraction of 1.5%. Fibers consists of low aspect ratio are used and
sufficient capacity enhancement is observed by experimental testing in this study. Two
different aggregate types are used to make the concrete i.e. stone and brick and the
effects of steel fibers on these two types of concrete specimens are also evaluated. Stone
and brick concrete specimens show significant increase in the compressive, tensile and
flexural capacity and in some cases ductility due to the presence of steel fibers.
Flexural test shows the increase in flexural capacity of about 8% to 60%, compressive
strength is increased by about 8% to 19% and tensile strength by about 39% to 149%.
This investigation proposes steel fibers as an additive for concrete to make flexural
members of structures to increase the capacity as well as ductility which will reduce the
risk of brittle failure during earthquake or any other load.
Keywords: Steel Fiber Reinforced Concrete (SFRC), flexural capacity, steel fiber
volume, aspect ratio of fiber, compressive strength, tensile strength, ductility.
1. INTRODUCTION
Fibers have been used to strengthen a weaken matrix for many centuries, such as straw in mud
bricks, a horse hair in gypsum plastering etc. For the last few decades, asbestos fiber is being
used to reinforce cement mortar in the asbestos cement industry. Recently other types of fibers
have been introduced in both research and industry fields. Steel, carbon, glass, polypropylene
and polyethylene short fibers are used to strengthen the concrete and cement mortar. For many
years, ACI 544.4R-88 has been working towards the development of standardized testing
techniques as applied to fiber reinforced concrete. The ACI committee suggested that the work is
not finished and a continuous research effort is needed to improve testing and reporting methods
for SFRC.
1
Assistant Professor, Department of Civil Engineering, AUST.
2
Lecturer, Department of Civil Engineering, AUST.
3
Graduate, Department of Civil Engineering, AUST.
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Ramakrishnan et al. (1980) stated that Steel fiber reinforced concrete can be considered as a new
and totally different concrete construction material. Fiber reinforcement has considerably
improved the flexural strength, direct tensile strength, fatigue strength, shear and torsional
strength, shock resistance, ductility and failure toughness (Uddin et al., 2013). According to
Ghalib (1980), fiber reinforcement presents several advantages such as superior crack control,
ductility, energy absorption capacity and improving the internal tensile strength of the concrete
due to bonding force between the fiber and the matrix. Steel fibers arrest the advancing cracks
and increase post cracking stiffness at all stages of loading, which results in narrow crack width
and substantially less deformation (Swamy and Al-Ta’an, 1981). Concrete inherently exhibits
low tensile strength and insufficient ductile behavior. These deficiencies are commonly
circumvented by providing conventional steel reinforcement or applying prestress in concrete
members. Alternatively, inclusion of steel fibers into concrete has been found to enhance tensile
strength and ductility of the material itself. Considering the importance of concrete in the
construction industry and its weakness in tension and against impact, steel fibers are best suited
to obtain desirable modifications in concrete properties (Dwarakanath and Nagaraj, 1991).
Based on past study, experimental investigations are conducted to study the increase in flexural
capacities of simply supported, cantilever and fixed beam using steel fiber reinforced concrete
(SFRC). Experimental evidences are gathered in this work and supported also by a few past
studies suggest that steel fiber mixed with concrete offer higher flexural, compressive and tensile
strengths. However beams made of such concrete must have larger ductile property under load.
This fundamental perception motivated the current research to evaluate the attainable flexural
capacity enhancement in concrete beams made concrete containing locally available fibers in
Bangladesh. In this context, Steel Fiber Reinforced Concrete (SFRC) beams made with two
different aggregates (i.e. stone and brick) are tested. According to ASTM C 1609/C 1609M–06
and ASTM C 78–02 specimen dimension is selected but two new different type of support
condition is introduced i.e. fixed and cantilever support in this research to be tested
experimentally.
The main objective of this research is to investigate the property enhancements using the steel
fiber reinforced concrete. Effect due to the fiber volume ratio on capacity enhancement is
analyzed. Besides these, this investigation also tends to examine failure patterns of the beams
made of SFRC and to investigate the member ductility by using SFRC. In the absence of a
reliable experimental results of the compressive strength, tensile strength and flexural strength
(with different support condition) of SFRC with the easily available fibers in context of
Bangladesh, the current research aims to investigate the capacity enhancement of SFRC from
experimental investigations.
The AUST Journal of Science and Technology, Volume 4, Issue 2, Page 52-69, July 2012
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2. MECHANISM BEHIND CRACK ARRESTING
Recent earthquake in different parts of the world have revealed again the importance of design of
reinforced concrete with high ductility. Strength and ductility of structures depend mainly on
proper detailing of the reinforcement in flexural members. Brittle failure of these members may
lead to catastrophic damages to the structure and the people living on these structures. To
increase the ductility of the flexural members, using Steel Fiber Reinforced Concrete (SFRC) can
be an efficient technique. Load carrying capacity of steel fiber at post-cracking stage made it
point of interest in modern research. Cracks are initiated due to the tension and propagate to the
neutral axis of the flexural member. Steel fibers arrest the micro-cracks and cracks are resisted
by the tensile property of the fiber. In the hardened state, when fibers are properly bonded,
they interact with the matrix at the level of micro-cracks and effectively bridge these
cracks thereby providing stress transfer media that delays their coalescence and unstable
growth (Figure 1). Steel Fibers are used as a volume percentage in the concrete mortar which
will create a matrix and bond strength will be increased. If the fiber volume fraction is
sufficiently high, this may result in an increase in the tensile strength of the matrix . Indeed,
for some high volume fraction fiber composite, a notable increase in the tensile as well as
flexural strength over and above the plain matrix has been reported. Once the tensile
capacity of the composite is reached and coalescence and conversion of micro-cracks to
macro-cracks has occurred, fibers, depending on their length and bonding characteristics
continue to restrain crack opening and crack growth by effectively bridging across macro-
cracks. This post peak macro-crack bridging is the primary reinforcement mechanisms of
steel fiber reinforced concretes (SFRC).
Figure 1: Mechanism of fibers in flexure (a) free area of stress, (b) fiber bridging area, (c) micro-
crack area and (d) undamaged area
3. TYPES OF STEEL FIBERS
There are different types, sizes and shapes of fiber that can be used as a construction material
(Figure 2). Steel fibers intended for reinforcing concrete are defined as short, discrete
lengths of steel having an aspect ratio in the range of 20-100, with any cross section
and that are sufficiently small to be randomly dispersed in an unhardened concrete
mixture using usual mixing procedures. According to ASTM A 820/A 820M – 06, five general
The AUST Journal of Science and Technology, Volume 4, Issue 2, Page 52-69, July 2012
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types of steel fibers are identified based upon the product or process used as a source of the steel
fiber material, they are, Type I: cold-drawn wire, Type II: cut sheet, Type III: melt-extracted,
Type IV: mill cut, Type V: modified cold-drawn wire and the fibers shall be straight or
deformed.
Figure 2: Different shape of steel fibers (a) steel fiber shapes, (b) steel fiber cross sections and (c)
fiber glued together into a bundle
4. EXPERIMENTAL PROGRAM AND DATA ACQUISITION
4.1 Properties of concrete
Steel Fiber Reinforced Concrete (SFRC) made with hydraulic cements and containing fine and
coarse aggregates along with discontinuous discrete steel fibers are considered in this research.
But ACI Committee (ACI 544.4R-88) believes that many other applications will be developed
once engineers become aware of the beneficial properties of the material and have access to
appropriate design procedures. Two types of aggregates i.e. brick and stone are chosen to make
the plain concrete and SFRC. The sizes of the aggregates are maintained 1in passing & 3/4in
retained and 3/4in passing & 1/2in retained with a weight ratio 1:1. The concrete mix ratio is
maintained 1:1.5:3 and water cement ratio is 0.45. The compressive and tensile (splitting)
strengths are measured according to ASTM C 39/C 39M–05 and ASTM C 496/C 496M–04
respectively with the concrete cylinder specimens of 4in (100mm) diameter and 8in (200mm)
height. The average compressive strength of brick and stone plain concretes are 3500 psi (24.5
MPa) and 4100 psi (28.7 MPa) respectively and tensile strengths are 648 psi (4.5 MPa) and 448
psi (3 MPa) respectively. Again the average compressive strength of brick and stone SFRC
(1.5% steel fiber volume) are 4100 psi (28.7 MPa) and 4800 psi (33.6 MPa) respectively and
tensile strengths are 944 psi (6.5 MPa) and 1104 psi (7.6 MPa) respectively. These results are
provided in Table 1. A steel fiber volume ration of 1.5% is selected for making SFRC after
parametric experimental investigation.
The AUST Journal of Science and Technology, Volume 4, Issue 2, Page 52-69, July 2012
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Table 1: Engineering properties of concretes
Type of
concrete
Steel
fiber
volume
(%)
Compressive
strength
psi (MPa)
Tensile
strength
psi (MPa)
Brick concrete 0 3500 (24.5) 648 (4.5)
Stone concrete 0 4100 (28.7) 448 (3)
Brick SFRC 1.5 4100 (28.7) 944 (6.5)
Stone SFRC 1.5 4800 (33.6) 1104 (7.6)
4.3 Properties of Steel Fibers (SF)
An advantage of the pullout type of failure is that it is gradual and ductile compared with the
more rapid and possibly catastrophic failure that may occur if the fibers break in tension.
Generally, the more ductile the steel fibers are, the more ductile and gradual the failure of the
concrete. In this research customized enlarged end fibers are used to make SFRC specimens. The
average tensile strength of each fiber shall not be less than 345 MPa (50,000 psi) according to
ASTM A 820/A 820M–06. In this research tensile strength of each fiber is about 71,578 psi (494
MPa) at an average and attained maximum value of up to 80,619 psi (556 MPa) which satisfies
the ASTM code requirement. Since pullout resistance is proportional to interfacial surface area,
smaller diameter round fibers offer more pullout resistance per unit volume than larger diameter
round fibers because they have more surface area per unit volume. Thus, the greater the
interfacial surface area (or the smaller the diameter), the more effectively the fibers bond. The
diameter and cross-sectional area of the fibers are 0.083in (2.1mm) and 0.0054 in
2
(3.46 mm
2
)
respectively. The second factor which has a major effect on workability is the aspect ratio (l/d) of
the fibers. The length of the fiber is 2.5in (63 mm) and the diameter is 0.083in (2.1 mm) which is
given in Figure 3. The aspect ratio of this fiber is 21.16 considering the effective length 1.75in
(44.5mm).
The AUST Journal of Science and Technology, Volume
(Published in January 2014)
(a)
Figure: 3: (a) and (b) Size and
g
4.4 Strategy behind the
sizes and shapes of the flexural specimens
Usually flexural tests of concrete are done on simply supported beam. This research intends to
study the
flexural behaviours of cantilever and fixed supported beams in addition to simply
supported beam. To this end, t
he
tested in different support conditions. In this regard, the ends of fixed and c
made higher rigidity and
stiffness by gradual increase of cross sectional area in the vertical part.
Table 2 provides
in detail the considerations selected for sizes and shapes of flexural specimens.
The sizes of the simply supported tes
span of 18in (450mm), cantilever test beams are 4x4x12in
supported test beams are also 4x4x12in
beams are tested applying 2
point loading and the cantilever beams are tested applying 1 point
loading at the free end.
The AUST Journal of Science and Technology, Volume
4, Issue 2, Page 52-
69
(Published in January 2014)
, ISSN 2072-0149, (DRAFT COPY)
6
(b)
g
eometry of the customized enlarged ends
steel fiber
in this research.
sizes and shapes of the flexural specimens
Usually flexural tests of concrete are done on simply supported beam. This research intends to
flexural behaviours of cantilever and fixed supported beams in addition to simply
he
sizes and shapes of the
flexural specimens are selected to be
tested in different support conditions. In this regard, the ends of fixed and cantilever beam are
stiffness by gradual increase of cross sectional area in the vertical part.
in detail the considerations selected for sizes and shapes of flexural specimens.
The sizes of the simply supported test beams are 6x6x24in (150x150x600mm) with an effective
span of 18in (450mm), cantilever test beams are 4x4x12in
(100x100x300mm)
supported test beams are also 4x4x12in
(100x100x300mm).
The simply supported and fixed
point loading and the cantilever beams are tested applying 1 point
69
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steel fiber
s employed
Usually flexural tests of concrete are done on simply supported beam. This research intends to
flexural behaviours of cantilever and fixed supported beams in addition to simply
flexural specimens are selected to be
antilever beam are
stiffness by gradual increase of cross sectional area in the vertical part.
in detail the considerations selected for sizes and shapes of flexural specimens.
t beams are 6x6x24in (150x150x600mm) with an effective
(100x100x300mm)
and the fixed
The simply supported and fixed
point loading and the cantilever beams are tested applying 1 point
The AUST Journal of Science and Technology, Volume
(Published in January 2014)
Table 1: Experimental strategy on flexural beams
Type of
beam
Theoretical
Fixed
supported
beam
Cantilever
beam
Simply
supported
beam
4.5
Gathering the vertical and horizontal load and displacement data
A total of 24
short concrete cylinders
compression at constant displacement rate of 0.5mm/min, until the failure in a 1000 kN capacity
digital
Universal Testing Machine (UTM). Vertical displacement and axial loads are recorded
from the load cell of UTM. The lateral strai
histories obtained from High Definition (HD) video camera
employing an image analysis technique which is called Digital Image Correlation Technique
(DICT)
which is also done in
measurements are taken by using a customized
strain data acquisition system
conventional electric strain gauge measurement i.e. the failure location may not be predicted
(especially
in new specimens) so that actual strain data acquisition at failure location may be
failed which is not desired.
The strain is measured by selecting different frames from a test
video and measuring the
pixels of two definite points
loading.
The load and displacement histories obtained from the load cell of
synthesized with the strain measurement results gathe
The AUST Journal of Science and Technology, Volume
4, Issue 2, Page 52-
69
(Published in January 2014)
, ISSN 2072-0149, (DRAFT COPY)
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Table 1: Experimental strategy on flexural beams
Theoretical
Strategical Experimental
Gathering the vertical and horizontal load and displacement data
short concrete cylinders
and 12 flexural members
are tested under axial
compression at constant displacement rate of 0.5mm/min, until the failure in a 1000 kN capacity
Universal Testing Machine (UTM). Vertical displacement and axial loads are recorded
from the load cell of UTM. The lateral strain in tension test is measured by analyzing the image
histories obtained from High Definition (HD) video camera
(60 frames per second)
employing an image analysis technique which is called Digital Image Correlation Technique
which is also done in
the work of Islam (2011) and Islam et
measurements are taken by using a customized
DICT simultaneous
vertical load and
(Figure 4).
There exists an extra advantage of DICT over
conventional electric strain gauge measurement i.e. the failure location may not be predicted
in new specimens) so that actual strain data acquisition at failure location may be
The strain is measured by selecting different frames from a test
pixels of two definite points
which change position due
The load and displacement histories obtained from the load cell of the
synthesized with the strain measurement results gathe
red from image analysis
outputs
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, July 2012
are tested under axial
compression at constant displacement rate of 0.5mm/min, until the failure in a 1000 kN capacity
Universal Testing Machine (UTM). Vertical displacement and axial loads are recorded
n in tension test is measured by analyzing the image
(60 frames per second)
and
employing an image analysis technique which is called Digital Image Correlation Technique
al. (2011). The
vertical load and
horizontal
There exists an extra advantage of DICT over
conventional electric strain gauge measurement i.e. the failure location may not be predicted
in new specimens) so that actual strain data acquisition at failure location may be
The strain is measured by selecting different frames from a test
which change position due
dilation under
the
digital UTM are
outputs
.
The AUST Journal of Science and Technology, Volume 4, Issue 2, Page 52-69, July 2012
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Figure 4: Digital Image Correlation Technique (DICT) for horizontal strain data acquisition.
5. EFFECTS DUE TO STEEL FIBER REINFORCEMENTS
5.1 Effect of steel fiber volume ratio
Concrete reinforced with low-volume fractions (up to 2 percent) of short fibers usually has a
compressive strength very similar to that of the plain unreinforced concrete, but exhibits much
greater resistance to crack formation and propagation. In the 1
st
phase of the investigation, the
compressive and tensile strength are evaluated with 1.0%, 1.5% and 2.0% steel fiber volume
with concrete by making cylinders. Figure 5 shows the legend style of different specimens. In
compression test, the compressive strength of brick SFRC is increased about 7%, 36% and 44%
for 1, 1.5 and 2 percent fiber volume respectively (Figure 6a), but for stone SFRC these
percentages are 5%, 20% and 26% respectively (Figure 6b) with respect to plain concretes. In
tension test, the tensile capacities of brick concretes are increased about 39%, 89% and 217% for
1, 1.5 and 2 percent fiber volume respectively (Figure 7a), but for stone aggregate these
percentages are 28%, 49% and 78% respectively (Figure 7b). The experimental results showed
that, tensile and compressive strengths increased with the increase in percentage of fiber volume.
From the view point of the above discussion a clear understanding is created i.e. fiber volume up
to 2 percent can give maximum strength. Emphasize is given in major two concerns, i.e. (i)
Economy and (ii) Strength. This investigation shows that, significant enhancement is achieved
using 1.5% steel fiber volume while 2% fiber volume become uneconomic. So, in the 2
nd
phase,
fiber volume of 1.5% is selected for preparing the flexural specimens as well as cylinder to get
representative compressive and tensile strengths.
Figure 5: Legend styles used in the figures (a) concrete compressive and tensile test specimens
(b) different flexural specimens.
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(a) (b)
Figure 6: Compressive stress-strain behaviour of concrete specimens made of 0%, 1%, 1.5% and
2% steel fiber volume ratio (a) brick concrete (b) stone concrete.
(a) (b)
Figure 7: Tensile stress-strain behaviour of concrete specimens made of 0%, 1%, 1.5% and 2%
steel fiber volume ratio (a) brick concrete (b) stone concrete.
5.2 Effect on compressive strength
The compressive strength of SFRC is evaluated according to ASTM C 39/C 39M–05. The steel
fiber has a significant effect on the enhancement of tensile strength but in case of compressive
strength the effects are found less significant. The concrete member under compression begins to
dilate laterally and it fails due to spalling of concrete as a result of Poisson’s effect. Crack
bridging by steel fibers resist the spalling which increases the compressive strength up to certain
limit (Figure 8). The concrete at the hoop direction suffers from extensive hoop tension which
0
1000
2000
3000
4000
5000
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
CBCC1
CBCC1SF1.0
CBCC1SF1.5
CBCC1SF2.0
Stress (MPa)
Strain
14
0
21
35
Stress (psi)
7
28
0
1000
2000
3000
4000
5000
0
0.001
0.002
0.003
0.004
0.005
0.006
CSCC1
CSCC1SF1.0
CSCC1SF1.5
CSCC1SF2.0
Stress (MPa)
Strain
14
0
21
35
Stress (psi)
7
28
0
500
1000
1500
0
0.005
0.01
0.015
0.02
0.025
CBCT1
CBCT1SF1.0
CBCT1SF1.5
CBCT1SF2.0
Stress (MPa)
Strain
3.5
0
7.0
10.5
Stress (psi)
0
500
1000
1500
0
0.005
0.01
0.015
0.02
0.025
0.03
CSCT1
CSCT1SF1.0
CSCT1SF1.5
CSCT1SF2.0
Stress (MPa)
Strain
Stress (psi)
3.5
0
7.0
10.5
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leads to failure of concrete under uniaxial loading. In SFRC the steel fibers with the volume of
1.5% are found not so efficient in enhancing the compressive strength of concrete by arresting
the hoop tension. The other reason may be the present concrete strength with this fiber volume
ratio is not enough to arrest the hoop tension. The compressive strength is increased by about 8%
for SFRC made of brick concrete compared to plain concrete (Figure 9a), while the increment is
about 19% for SFRC made of stone concrete (Figure 9b).
Figure 8: Mechanism under compressive load (a) uniaxial loading, (b) crack initiation, (c)
spalling of plain concrete and (d) crack bridging by steel fibers in SFRC.
(a) (b)
Figure 9: Compressive stress-strain behaviour of plain concrete and SFRC made of (a) brick
concrete (b) stone concrete.
5.3 Effect on tensile strength
The tensile strength of the SFRC is evaluated according to ASTM C 496/C 496M–04 which
determines the tensile strength of concrete. Plain concrete is a brittle material which splits under
load as shown in Figure 10(a). Crack bridging of steel fibers arrests the initial cracks and
prevents the concrete from splitting (Figure 10b) and the concrete continue to carry load without
failure. Figure 11(a) shows that the tensile capacity of brick concrete with 1.5% steel fiber is
0
1000
2000
3000
4000
5000
0
0.0005
0.001
0.0015
0.002
0.0025
0.003
0.0035
0.004
CBOC1
CBOC1SF1.5
Stress (MPa)
Strain
14
0
21
35
Stress (psi)
7
28
0
1000
2000
3000
4000
5000
0
0.0005
0.001
0.0015
0.002
0.0025
0.003
0.0035
0.004
CSOC1
CSOC1SF1.5
Stress (MPa)
Strain
14
0
21
35
Stress (psi)
7
28
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increased 39% compared to the plain brick concrete. The increase for stone aggregate concrete is
significantly large and about 149% for 1.5% steel fiber compared to plain stone concrete.
Figure 10: Mechanism under tension (a) brittle failure of plain concrete (b) crack bridging of
SFRC
(a) (b)
Figure 11: Tensile stress-strain behaviour of plain concrete and SFRC made of (a) brick concrete
(b) stone concrete.
5.4 Effect of flexural capacity
Flexural capacity of the member is very important in case of concrete structures. As an
engineering material and in context of seismic consideration the concrete should be ductile with
a significant stiffness in flexure. To this end, three kinds of flexural members are considered in
this experiment, they are simply supported beam, cantilever beam and fixed supported beam.
Generally to evaluate the flexural capacity of concrete, simply supported beams are considered
so far in the previous researches. In this study, the effects of cantilever action and fixed
supported action are also extensively analyzed with both plain concrete and SFRC. For simply
supported beams, the flexural capacity is increased due to SFRC in brick concrete is about 55%
Figure 12(a) while 60% increased in stone concrete (Figure 12b). The increase in ductility is
almost 3 times for SFRC beams made of brick and stone concretes compared to plain concretes.
0
500
1000
1500
0
0.005
0.01
0.015
CBOT1
CBOT1SF1.5
Stress (MPa)
Strain
Stress (psi)
3.5
0
7
10.5
0
500
1000
1500
0
0.002
0.004
0.006
0.008
0.01
CSOT1
CSOT1SF1.5
Stress (MPa)
Strain
3.5
0
7
10.5
Stress (psi)
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(a) (b)
Figure 12: Evaluation of the load-displacement behavior of simply supported beams made of
plain concrete and SFRC (a) brick concrete and (b) stone concrete.
From the experimental investigation, it is found that the flexural capacity of cantilever beams are
increased about 8% and 10% in brick and stone concrete respectively (Figure 13 a & b), but in
ductility improvement concern stone SFRC showed more ductility in presence of steel fibers. In
stone SFRC the ductility is increased about 3 times while in brick SFRC is about 2 times than the
control specimens (steel fiber 0%). Investigation indicates that higher ductility can be achieved
by using steel fiber with stone concrete. The flexural capacity of SFRC increased in fixed
support beam is about 40% in brick concrete and 51% in stone concrete (Figure 14 a & b). The
ductility is increased 2 times and 5 times of brick and stone SFRC fixed supported beams
compared to control specimens.
(a) (b)
0
10000
20000
30000
40000
50000
60000
0 1 2 3 4 5
FSCBO
FSCBOSF1.5
Load (kip)
Displacement. (in)
00
0.04
0.08
0.12
0.16
0.20
Load (N)
Displacement. (mm)
2
0
9
11
13.5
4.5
6.5
0
10000
20000
30000
40000
50000
60000
0 0.5 1 1.5 2 2.5 3
FSCSO
FSCSOSF1.5
Load (N)
Displacement. (mm)
2
0
9
11
13.5
Load (kip)
Displacement. (in)
0
0.04
0.08
0.12
0.16
0.20
4.5
6.5
0
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0 0.5 1 1.5 2 2.5 3
FCCBO
FCCBOSF1.5
Load (N)
Displacement. (mm)
Load (kip)
Displacement. (in)
0
0.04
0.08
0.12
0.16
0.20
0.24
0.28
0.2
0
0.6
0.8
1
0.4
0
1000
2000
3000
4000
5000
0 1 2 3 4 5 6 7
FCCSO
FCCSOSF1.5
Load (N)
Displacement. (mm)
0.2
0
0.6
0.8
1
Load (kip)
Displacement. (in)
0
0.04
0.08
0.12
0.16
0.20
0.4
0.28
0.24
The AUST Journal of Science and Technology, Volume 4, Issue 2, Page 52-69, July 2012
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13
Figure 13: Evaluation of the load-displacement behavior of cantilever beams made of plain
concrete and SFRC (a) brick concrete and (b) stone concrete.
(a) (b)
Figure 14: Evaluation of the load-displacement behavior of fixed supported beams made of plain
concrete and SFRC (a) brick concrete and (b) stone concrete.
0
10000
20000
30000
40000
50000
60000
70000
80000
0 0.5 1 1.5 2 2.5 3
FFCBO
FFCBOSF1.5
Load (N)
Displacement. (mm)
Load (kip)
Displacement. (in)
0
0.04
0.08
0.12
0.16
0.20
4.5
0
11
18
6.5
13.5
15.5
9
2
0
10000
20000
30000
40000
50000
60000
70000
80000
0 1 2 3 4 5
FFCSO
FFCSOSF1.5
Load (N)
Displacement. (mm)
4.5
0
11
18
Load (kip)
Displacement. (in)
0
0.04
0.08
0.12
0.16
0.20
6.5
13.5
15.5
9
2
The AUST Journal of Science and Technology, Volume 4, Issue 2, Page 52-69, July 2012
(Published in January 2014), ISSN 2072-0149, (DRAFT COPY)
14
Table 3: Failure patterns of plain concrete and SFRC specimens
Type of
Specimen
Plain concrete SFRC
Compression
Tension
Simply
supported
beam
Cantilever
beam
Fixed
supported
beam
Concrete can fail in two modes i.e. brittle and ductile. To this end, failure pattern of brick and
stone concrete are observed during experiment. Another objective of this study is to prevent the
brittle behavior of concretes by enhancing ductility without compromising the strength.
Experimental investigation shows attractive results that supports the concept of experimental
plan. Brittle failure of brick and stone aggregate is successfully resisted by using SFRC and
ductility is increased in a significant amount. Table 3 provides some images of failure after
experimental testing. Compression and tension testing of SFRC shows no indication of complete
separation or splitting as found for plain concrete. This is also factual for the flexural specimens.
Simply supported, fixed and cantilever beams made of plain concrete have failed by complete
separation whereas SFRC specimens showed no disconnection of parts. Failure occurred at the
The AUST Journal of Science and Technology, Volume 4, Issue 2, Page 52-69, July 2012
(Published in January 2014), ISSN 2072-0149, (DRAFT COPY)
15
root of cantilever in the cantilever specimens, at the mid span in the simply supported specimens
and at mid span & root of fixed support in the fixed supported beams.
6. CONCLUSION
In the absence of a reliable experimental investigation for predicting the compressive, tensile and
flexural strength (with different support condition) of SFRC made of easily available fibers in
context of Bangladesh, the current research successfully investigated the capacity enhancement
and stress field of the SFRC from experimental viewpoint to introduce this new engineering
material in the Bangladesh construction industry. In this research innovative kind of specimens
are introduced which unlock the new dimension in concrete flexure tests. The findings of this
research are as follows:
1. Previous researches worked with steel fibers consisting of high aspect ratio (50 and above) but
this research evaluates the performance of SFRC with available steel fibers of Bangladesh
with a low aspect ratio (only l/d =21.6).
2. After extensive testing it is found that steel fiber volume fraction of 1.5% is the most
acceptable and economic for capacity enhancement without compromising the strength.
3. The compressive strength is increased by about 8% for SFRC made of brick concrete
compared to plain concrete, while the increment is about 19% for SFRC made of stone
concrete.
4. Tensile capacity of brick concrete with 1.5% steel fiber is increased 39% compared to the
plain brick concrete. The increase for stone aggregate concrete is significantly large and about
149% for 1.5% steel fiber compared to plain stone concrete.
5. For simply supported beams, the flexural capacity is increased about 55% in brick SFRC
while 60% increased in stone SFRC. The increase of ductility is found almost 3 times for
SFRC beams made of brick and stone concretes compared to plain concretes. The flexural
capacity of cantilever beams are increased about 8% and 10% in brick and stone SFRC
respectively, but in the ductility improvement concern stone SFRC showed more ductility in
presence of steel fibers. In stone SFRC the ductility is increased about 3 times while in brick
SFRC is about 2 times than the control specimens (steel fiber 0%). The flexural capacity of
SFRC increased in fixed supported beam is about 40% in brick concrete and 51% in stone
concrete as well as the ductility is increased 2 times and 5 times of brick and stone SFRC
fixed supported beams compared to control specimens. Experimental investigations indicate
that higher ductility as well as capacity can be achieved by employing steel fiber in stone
concrete.
The AUST Journal of Science and Technology, Volume 4, Issue 2, Page 52-69, July 2012
(Published in January 2014), ISSN 2072-0149, (DRAFT COPY)
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REFERENCES
ACI 544.4R-88, Design Considerations for Steel Fiber Reinforced Concrete, American
concrete Institute, Reported by ACI Committee 544, 1988.
ASTM C 39/C 39M–05, Compressive Strength of Cylindrical Concrete Specimens,
American Society for Testing and Materials, 2005.
ASTM C 78–02, Standard Test Method for Flexural Strength of Concrete (Using Simple
Beam with Third-Point Loading), American Society for Testing Materials, 2002.
ASTM C 496/C 496M, Splitting Tensile Strength of Cylindrical Concrete Specimens,
American Society for Testing and Materials, 2004.
ASTM A 820/A 820M–06, Standard Specification for Steel Fibers for Fiber-Reinforced
Concrete, American Society for Testing Materials, 2006.
ASTM C 1609/C 1609M–06, Standard Test Method for Flexural Performance of Fiber-
Reinforced Concrete (Using Beam With Third-Point Loading), American Society for Testing
Materials, 2006.
Dwarakanath, H.V. and Nagaraj, T.S., Comparative Study of Prediction of Flexural Strength
of Steel Fiber Concrete, ACI Structural Journal, Title no: 88-S73, November- December, 1991.
Ghalib, M.A., Moment Capacity of Steel Fiber Reinforced Small Concrete Slabs, ACI
Journals, Title no: 77-27, July- August, 1980.
Islam, M.M., Interaction Diagrams of Square Concrete Columns Confined with Fiber
Reinforced Polymer Wraps, M.Sc. Engineering Thesis, Department of Civil Engineering,
Bangladesh University of Engineering and Technology (BUET), Dhaka, August 2011.
Islam, M.M., Choudhury, M.S.I., Abdulla M., & Amin, A.F.M.S., (), “Confinement Effect of
Fiber Reinforced Polymer Wraps in Circular and Square Concrete Columns”, 4th Annual Paper
Meet and 1st Civil Engineering Congress, Civil Engineering Division, Institution of Engineers,
Bangladesh (IEB), Dhaka, 22-24 December, 2011 (Awarded best paper).
Ramakrishna, V., Brandshuag, T., Coyle W.V. and Schrader E.K., A Comparative Evaluation
of Concrete Reinforced with Straight Fibers and Fibers with Deformed Ends Glued Together into
Bundles, ACI Journal, Title no: 77-17, May-June, 1980.
Swamy R.N., and Al-Ta’an S.A., Deformation and Ultimate Strength in Flexure of
Reinforced Concrete Beams Made with Steel Fiber Concrete, ACI Journal, Title no: 78-36,
September- October, 1981.
Uddin, M. K., Mustafiz, A. Z., Chowdhury, M. A. and Mondal, P., Investigation of the
Flexural Capacity of Beams Made of Steel Fiber Reinforced Concrete (SFRC), B.Sc.
The AUST Journal of Science and Technology, Volume 4, Issue 2, Page 52-69, July 2012
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17
Engineering Thesis, Department of Civil Engineering, Ahsanullah University of Science and
Technology (AUST), Dhaka, April 2013.
... According to Ghalib (1980), fiber reinforcement presents several advantages such as superior crack control, ductility, energy absorption capacity and improving the internal tensile strength of the concrete due to bonding force between the fiber and the matrix. Fiber reinforcement considerably improves the flexural strength, direct tensile strength, fatigue strength, shear and torsional strength, shock resistance, ductility and failure toughness of concrete (Uddin et al., 2013). For many years, ACI 544.4R-88 has been working towards the development of standardized testing techniques as applied to fiber reinforced concrete. ...
... All the specimens are tested in a 1000kN capacity digital universal testing machine (UTM). Strain data are measured by applying digital image correlation technique (DICT) using high definition (HD) images and high speed video clips and these data are synthesized with the load data from the load cell of UTM which is also followed in the work of Islam (2011), Islam et al. (2011), Uddin et al. (2013) and Dola et al. (2013). Flexural test shows the increase in flexural capacity of about 8% to 60% of beams due to SFRC which also showed an indication of increase in ductility of the flexural member. ...
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In recent years, brittle failures of so many reinforced concrete structures are observed during earthquakes and other deadly forces. In this regard, concrete researchers are intended to improve the ductility of the RC structure by using steel fiber to make concrete a composite material with enhanced capacities. To this end, this research concentrates on the applicability of steel fiber reinforced concrete (SFRC) in construction industry of Bangladesh by providing validated Finite Element (FE) models of experimental results. Experimental investigations show promising outcomes by using steel fibers in flexural specimens. Results of plain concrete and steel fiber reinforced concrete (SFRC) beam specimens are compared. SFRC beam specimens showed an increase of about 8% to 60% flexural capacity enhancement. Flexural specimens are then modeled in the Finite Element (FE) platform of ANSYS 10.0. Material property and boundary condition are applied on the basis of experimental data and test condition. Satisfactory agreement is observed between the test results and FE models. Critical investigations are done by evaluating different controlling parameters like Poisson's ratio, tensile strength, modulus of elasticity, shear transfer coefficients for open or close cracks etc. Tensile strength is one of the major governing parameters among all of those considered and it depends greatly on steel fiber aspect ratio and percentage volume of fiber. This study provides information on the parameter used in the FE model to get a realistic SFRC model which can be used to estimate flexural capacity enhancement of real structures made of SFRC. Keywords: Steel fiber reinforced concrete (SFRC), ANSYS, Finite Element (FE) modeling and analysis, flexural capacity, aspect ratio of fiber, steel fiber volume ratio.
... Steel fiber-reinforced concrete (SFRC) is a composite material whose components include the traditional constituents of Portland cement concrete (hydraulic cement, fine and coarse aggregates, and admixtures) and a dispersion of randomly oriented short discrete steel fibers (Islam et al. 2012, Islam et al. 2014a. The development of SFRC began in the early 1960s when researchers first studied the concept of using steel fibers to improve the mechanical properties of concrete . ...
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Reinforced concrete (RC) columns are often designed and assessed under the assumption that axial loads and bending moments are applied simultaneously. In this case, the actual loading history varies from the assumed design loading history. While this deviation from the design loading history may be inconsequential, cases may exist in which this new loading history results in a significant reduction of the reliability of the column. The reason for this is easily explained by studying the column’s P-M Interaction Diagram. A typical PM Interaction Diagram depicts all combinations of axial loads and bending moments which correspond to a prescribed limit state. These limit states may indicate column failure, or they may simply identify critical material or geometric states. To this end, this study attempts to construct the P-M Interaction Diagram for short square column made of steel fiber reinforced concrete (SFRC) experimentally and via finite element (FE) approach. The columns are modelled and analyzed in the FE platform of ANSYS 11. The use of SFRC in the construction industry of Bangladesh is not yet started for reliable experimental results and FE modelling. This study will provide real experimental data as well as FE analysis on P-M Interaction Diagram of square RC columns for predicting the axial load as well as bending capacity.
... Steel fiber-reinforced concrete (SFRC) is a composite material whose components include the traditional constituents of Portland cement concrete (hydraulic cement, fine and coarse aggregates, and admixtures) and a dispersion of randomly oriented short discrete steel fibers (Islam et al. 2012, Islam et al. 2014a. The development of SFRC began in the early 1960s when researchers first studied the concept of using steel fibers to improve the mechanical properties of concrete . ...
Conference Paper
Full-text available
Reinforced concrete (RC) columns are often designed and assessed under the assumption that axial loads and bending moments are applied simultaneously. In this case, the actual loading history varies from the assumed design loading history. While this deviation from the design loading history may be inconsequential, cases may exist in which this new loading history results in a significant reduction of the reliability of the column. The reason for this is easily explained by studying the column’s P-M Interaction Diagram. A typical PM Interaction Diagram depicts all combinations of axial loads and bending moments which correspond to a prescribed limit state. These limit states may indicate column failure, or they may simply identify critical material or geometric states. To this end, this study attempts to construct the P-M Interaction Diagram for short square column made of steel fiber reinforced concrete (SFRC) experimentally and via finite element (FE) approach. The columns are modelled and analyzed in the FE platform of ANSYS 11. The use of SFRC in the construction industry of Bangladesh is not yet started for reliable experimental results and FE modelling. This study will provide real experimental data as well as FE analysis on P-M Interaction Diagram of square RC columns for predicting the axial load as well as bending capacity.
... All the specimens are tested in a 1000kN capacity digital universal testing machine (UTM). Strain data are measured by applying digital image correlation technique (DICT) using high definition (HD) images and high speed video clips and these data are synthesized with the load data from the load cell of UTM which is also followed in the work of Islam (2011), Islam et al. (2011), Uddin et al. (2013) and Dola et al. (2013). The tensile capacity enhancement is found 253%, 204% and 182% compared to control specimen for brick SFRC made of end enlarged fibers, straight fiber and 50-50 mixed fibers respectively. ...
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... The stress strain relationship of normal concrete (NC, considering stone concrete), steel fiber reinforced concrete (SFRC) and reinforcements used in this investigation are shown in Figure 3. The tensile strength of SFRC is applied 1100psi (Uddin et al 2013 andDola et al 2013) considering 1.5% volume fraction. The density of NC, SFRC and steel rebar are considered 0.086, 0.089 and 0.283 lb/cft respectively. ...
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Several methods are available for predicting flexural strength of steel fiber concrete composites. In these methods, direct tensile strength, split cylinder strength, and cube strength are the basic engineering parameters that must be determined to predict the flexural strength of such composites. Various simplified forms of stress distribution are used in each method to formulate the prediction equations for flexural strength. In this paper, existing methods are reviewed and compared, and a modified empirical approach is developed to predict the flexural strength of fiber concrete composites. The direct tensile strength of the composite is used as the basic parameter in this approach. Stress distribution is established from the findings of flexural tests conducted as part of this investigation on fiber concrete prisms. A comparative study of the test values of an earlier investigation on fiber concrete slabs and the computed values from existing methods, including the one proposed, is presented.
4R-88, Design Considerations for Steel Fiber Reinforced Concrete
ACI 544.4R-88, Design Considerations for Steel Fiber Reinforced Concrete, American concrete Institute, Reported by ACI Committee 544, 1988.
Interaction Diagrams of Square Concrete Columns Confined with Fiber Reinforced Polymer Wraps
  • M M Islam
Islam, M.M., Interaction Diagrams of Square Concrete Columns Confined with Fiber Reinforced Polymer Wraps, M.Sc. Engineering Thesis, Department of Civil Engineering, Bangladesh University of Engineering and Technology (BUET), Dhaka, August 2011.