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AHSANULLAH UNIVERSITY OF
SCIENCE AND TECHNOLOGY (AUST)
FINITE ELEMENT MODELING, ANALYSIS AND VALIDATION OF THE
SHEAR CAPACITY OF RC BEAMS MADE OF STEEL FIBER
REINFORCED CONCRETE (SFRC)
1
Presented by:
Md. Shahadat HossainDepartment of Civil Engineering
Ahsanullah University of Science
and Technology (AUST),
Dhaka-1208, Bangladesh
Co-Authors:
Md. Mashfiqul Islam
Saiful Amin
Zahidul Islam
Mana Bala
Md. Arman Chowdhury
Ashfia Siddique
Paper ID: SEE 075
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SFRC
STEEL FIBER REINFORCED CONCRETE
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OPC(Hydraulic cement &
Admixtures)
Fine & Coarse aggregates
Dispersion of Short Discrete
Steel Fiber
SFRC
components
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SFRC ADVANTAGES
Enhancement of ductility and energy absorption
capacity transforms failure modes from brittle
and dangerous shear failures into
more ductile flexural failures
Increase the flexural strength
, direct tensile strength and
fatigue strength.
Enhance shear and torsional strength
Shock resistance as
well as toughness of
concrete
Increasesstiffness , reduces
deflections
5
Applications of SFRC
• industrial or factory pavements, highways, roads, parking areas , airport runways
• tunnel linings,
• pre-cast structures, structures in high seismic risk areas, bridge decks
• off-shore platforms, water-retaining structures etc.
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PC
(reinforced) SFRC
Mechanism of SFRC
Fibers distribute randomly and act as crack arrestors.
Resistance to crack extension provided near a crack tip(zone a) by the bond stress between fibers and concrete
Increases the ductility by arresting crack and preventsthe propagation of cracks by bridging fibers.
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zone a: Free area of stress
zone b: Fiber bridging area
zone c: Micro-crack area
zone d: Undamaged area
When steel fibers are added to a
concrete mix :
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To investigate the performance of steel
fiber with three different aspect ratio,
i.e. 40, 60 and 80
To evaluate the shear capacities of SFRC RC beams due to aspect ratio of steel fibers.
To examine failure patterns of RC beams
made of SFRC.
To construct FE models for plain
reinforced concrete and SFRC in the FE platform of ANSYS
11.0 and also validate the models with the
experimental results.
Above all to
provide the
construction
industry of
Bangladesh
with reliable
experimental
data and
validated FE
modeling
about this
engineering
material.
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Experimental program and strategy
Experimental strategy
Experimental program
Specimen preparation
Testing and Data Acquisition
Investigation of failure
pattern
FE modeling through
optimizing the basic
engineering properties
FE analysis applying
experimental loading
environment and
displacement boundary
conditions
Validation of FE models and
analyses with experimental
results and failure modes
Strategy:Three different aspect ratio of steel fibers are selected
i.e. 40, 60 and 80 and prepared manually in thelaboratory. The beams are designed with 2-12mmφ
rebars(Figure-1) at bottom and without any web
reinforcement(Figure-2). The Rebars are connected to
provide anchorage at the end instead of making hook.The strategy is to estimate the shear capacity
increament due to steel fiber in the concrete mix and
also to evaluate the performance of fibers with respectto aspect ratio.
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Figure1: Longitudinal
reinforcement
Figure 2: Experimental strategy
on shear beams.
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Materials
Steel Fibers: Source types and shapes
According to ASTM A 820/A 820M – 06, five general 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.
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Typical Steel Fibers
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Selection of shape
Stress-strain curves for steel fiber reinforced mortars in
tension
(ACI 544.4R-88)
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Fiber preparation
The fibers are prepared manually in the laboratory.
The cold drawn wires are cut from the coil as desired
length to make the required aspect ratio. In this
research the ends of the fibers are bended 120˚ to
make enlarged ends which provide anchorage in the
concrete matrix. Figure 3 shows the fiber preparation
and images of the prepared fibers.
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Figure 3 : (a) Preparation of steel fibers (b) steel fibers of different
aspect ratio.
(a) (b)
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Three different types of steel fiber aspect ratio (l/d) i.e.
40, 60 and 80 are selected to be made. Their
corresponding measurements are given in the table-1
and shown in figure 4.
Aspect ratio
of steel fiber
Diameter
(mm)
Effective
length
(mm)
Original
length
(mm)
Angle
(Degree)
40 1.18 47.2 67.2 120
60 1.18 70.8 90.8 120
80 1.18 94.4 114.4 120
Aspect ratio:
Table1: Steel fiber size and geometry
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(a) (b)
Figure 4: (a) Size and geometry of steel fibers (b) image of fibers
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Aggregates
Crushed stone are used as coarse aggregate in this
research. Different types of aggregate are shown in
Figure 5.
Figure 5: (a) Stone aggregate (CA) and (b) Sand (FA)
(a) (b)
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Cement type OPC (ordinary Portland cement)
Coarse Aggregate Size 1 in passing and 3/4 in retain (50%)
3/4 in passing and 1/2 in retain (50%)
C: FA: CA 1:1.5:3
W/C 0.5
Slump 1in (25mm)
Fiber Volume 1.5%
Fiber Aspect ratio 40, 60 and 80
Fiber type End enlarged
Fiber Tensile strength 160000 psi (1100 MPa)
Fiber cross section Circular
Fiber dia 1.18 mm
Concrete comp. strength 3700 psi (25.5 MPa)
Type of coarse aggregate Stone
Table 2: Mix design of plain reinforced concrete and SFRC
Mix design
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Testing and Data Acquisition
A digital universal testing machine (UTM) of capacity
1000 kN is used in this experiment. This is a displacement
controlled machine. Load and displacement value can be
measured from this UTM. In this experiment displacement
rate of 0.5mm per minute is applied. Lateral
displacements/strain are measured by analyzing the
image histories obtained from high definition video
camera(Figure 6&7) and employing an image analysis
technique which is called Digital Image Correlation
Technique (DICT).
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Figure 7: Horizontal data acquisition
system via DICT.
Figure 6: Experimental setup for shear
critical beam in the UTM.
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Images of Experimental Testing of Simply Supported Beam
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0
1000
2000
3000
4000
5000
0 0.005 0.01 0.015
CSCCONCSC40CSC60CSC80
Co
mp
ressiv
e s
tress (
psi)
Compressive strain
0
7
14
21
28
35
Co
mp
ressiv
e s
tress (
MP
a)
2691 psi (19 MPa)
3741 psi (26 MPa)
4400 psi (30 MPa)
3733 psi (25.7 MPa)
Fig. 8: Experimental results of plain concrete and SFRC cylinder (a) compression
(b) splitting tension
0
200
400
600
800
1000
1200
1400
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08
CSTCONCST40CST60CST80
Tensile
str
ess (
psi)
Tensile strain
0
1.4
2.8
4.2
5.6
7.0
8.4
9.8
Tensile
str
ess (
MP
a)
(a) (b)
25
(a)
Fig. 9: Experimental results of plain reinforced concrete and SFRC beam (a) load
deflection behaviour of beams.
0
5
10
15
20
25
30
35
0 0.5 1 1.5 2
CSBSCCONCSBSC40CSBSC60CSBSC80
Lo
ad
(kip
)
Mid point deflection (in)
0 12.7 25.4 38.1 50.8
Mid point deflection (mm)
0
22
44
66
88
110
Lo
ad
(kN
)
132
154
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FE modeling
* Suitable element type
* Adequate mesh size
* Optimized material properties
* Appropriate boundary conditions
* Realistic loading environment
* Proper time stepping
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SOLID65 is used in ANSYS 11.0 to model the concrete and also SFRC, which is a three
dimensional (3D) solid element having eight nodes with three degrees of freedom at each
node, i.e., translational in the nodal x, y, and z directions. The element is capable of plastic
deformation, cracking in tension, crushing in compression and is also applicable for
reinforced composites (ANSYS 2005), such as, fibreglass, SFRC etc.
The flexural reinforcement is modelled using LINK8 element, which is a 3D spar element
as well as a uniaxial tension-compression element with three degrees of freedom at each
node same as SOLID65. The geometry and node locations for SOLID65 and LINK8
elements are shown in Fig.
FE element:
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FE models
(a)
(b)
Figure 9: Typical diagram of FE model of Shear-critical RC beam in ANSYS 11.0
(a) volume and (b) after meshing.
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FE governing parameters
Modulus of elasticity
Stress-strain behaviour
Poisson’s ratio
Density
Willum and Warke (1975) criterion
Shear transfer coefficient for open crack
Shear transfer coefficient for close crack
Tensile strength
Compressive strength
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Properties for FE
model
Beam specimen (SOLID65)
Rebar
(LINK8)CSBSCCON CSBSC40 CSBSC60 CSBSC80
Modulus of
elasticity3000000 psi 1870000psi 1400000psi 1400000psi
Density 2.69g/cm3 2.77g/cm3 2.72g/cm3 2.74g/cm3 7.8g/cm3
Tensile strength 4 Mpa 6 MPa 8 MPa 6.3 MPa -
Poisson’s ratio 0.325 0.325 0.325 0.325 0.3
Displacement
boundary
condition (-y
direction)
0.5mm 0.5mm 0.5mm 0.5mm
Shear transfer co-
efficient: closed
crack
0.25 0.5 0.5 0.5 -
Open crack 0.3 0.3 0.3 0.3 -
Yield stress- - - - 420 MPa
Table 3: FE input data for SOLID65 and LINK8 element
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0
5
10
15
20
25
30
35
0 0.5 1 1.5 2
ANSYS CSBSCCONCSBSCCON
Load
(kip
)
Mid point deflection (in)
0 12.7 25.4 38.1 50.8
Mid point deflection (mm)
0
22
44
66
88
110
Load
(kN
)
132
154
Fig. 4: Evaluation of load deflection behaviour FE and experimental
SC beams a) CSBSCCON i.e. control beam b) CSBSC40
0
5
10
15
20
25
30
35
0 0.5 1 1.5 2
ANSYS CSBSC40�CSBSC40
Load
(kip
)
Mid point deflection (in)
0 12.7 25.4 38.1 50.8
Mid point deflection (mm)
0
22
44
66
88
110
Load
(kN
)
132
154
(a) (b)
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Fig. 4: Evaluation of load deflection behaviour FE and
experimental SC beams a) CSBSC60 b) CSBSC80.
0
5
10
15
20
25
30
35
0 0.5 1 1.5 2
ANSYS CSBSC80CSBSC80
Load
(kip
)
Mid point deflection (in)
0 12.7 25.4 38.1 50.8
Mid point deflection (mm)
0
22
44
66
88
110
Load
(kN
)
132
154
0
5
10
15
20
25
30
35
0 0.5 1 1.5 2
ANSYS CSBSC60CSBSC60
Load
(kip
)
Mid point deflection (in)
0 12.7 25.4 38.1 50.8
Mid point deflection (mm)
0
22
44
66
88
110
Load
(kN
)
132
154
(a) (b)
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Fig. 6: Experimental and FE failure pattern (a) CSBFCCON
(b)CSBFC40
(a) (b)
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Fig. 6: Experimental and FE failure pattern (a) CSBFC60
(b) CSBFC80.
(b)(a)
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Shear strength of SC beams increased about 25%, 29%and 18% for the SFAR 40, 60 and 80 respectivelycompared to control specimen.The ductility isenhanced 1.33, 1.58 and 1.17 times respectively.
The FE models showed similar analyses resultcompared to experimental outcomes which ensuresgood agreements
The failure patterns are also similar which alsovalidated the FE models.
FE models showed conservative results which ensureadequate factor of safety as well as reliability of FEmodeling and analyses.
Further investigation shows the capability of themodels to predict capacity enhancements due to SFRCwhich ensures reliability of FE models.