finite element modeling and analysis of rc ... the behavior of rc beams with gfrp and steel bars....
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International Journal of Civil Engineering and Technology (IJCIET) Volume 8, Issue 9, September 2017, pp. 671–679, Article ID: IJCIET_08_09_076
Available online at http://http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=8&IType=9
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
© IAEME Publication Scopus Indexed
FINITE ELEMENT MODELING AND ANALYSIS
OF RC BEAMS WITH GFRP AND STEEL BARS
Dr. J. Premalatha
Professor and Head, Department of Civil Engineering,
Kumaraguru College of Technology, Coimbatore, India
R. Shanthi Vengadeshwari
Assoc. Prof, Department of Civil Engineering,
Dayananda Sagar College of Engineering, Bengaluru, India
Srihari P
PG student, Department of Civil Engineering,
Dayananda Sagar College of Engineering, Bengaluru, India
ABSTRACT
Infrastructural deterioration due to corrosion of reinforcing steel bars under
aggressive condition mainly in marine environment is a major challenge facing the
construction industry, which causes failure of most of the concrete structures. The
corrosion of steel bars can be controlled by replacing the steel bars with corrosive
resistance materials such as Fiber reinforced polymers (FRP). FRP bars are
emerging and promising alternative material to steel bars in concrete structures. Due
to non-corrosive nature of FRP, it improves the durability of RC structures.
Experimental based method is widely used to find the behavior of concrete structures
it gives a real life results, it is a time consuming process and material used for testing
is quite high cost. In this work a non-linear finite element analysis was carried out to
simulate the behavior of RC beams with GFRP and steel bars. Finite element
modelling was done using ANSYS software. Four beams were modeled in ANSYS. Two
beams taken as control beams each with Steel and GFRP bars used concrete beams.
Remaining Two beams were with the combination of Steel and GFRP bars used in
concrete beams by varying the reinforcement percentage. Structural performance like
Load-Deflection, crack pattern and flexural capacity were studied and results
obtained from the finite element analysis was validated with experimental test results
conducted by Wenjun et al [16].
Keywords: ANSYS, Concrete beams, Finite element analysis, GFRP and Steel bars,
Non-linear
Cite this Article: Dr. J. Premalatha, R. Shanthi Vengadeshwari and Srihari P, Finite
Element Modeling and Analysis of Rc Beams with Gfrp and Steel Bars, International
Journal of Civil Engineering and Technology, 8(9), 2017, pp. 671–679.
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=9
Finite Element Modeling and Analysis of Rc Beams with Gfrp and Steel Bars
http://www.iaeme.com/IJCIET/index.asp 672 [email protected]
1. INTRODUCTION
The use of advanced composite material such as fiber reinforced polymers (FRPs) for
reinforcing in concrete structures in place of steel reinforcement or rehabilitation of structural
members has started over the past few years ago. Understanding the response of composite
material in structural members during loading is crucial for the development of an economic,
efficient and safe design. The corrosion of steel reinforcement in concrete members leads to
failure of structures due to carbonation of concrete. Fiber reinforced polymers (FRPs) rebars
considered as alternative material to steel bars in concrete members in severe environmental
conditions. Apart from having a non-corrodible nature of FRPs, it has a high strength and
stiffness ratios to density. In RC structures, steel reinforcement is ductile material which is the
ratio of post-yield to yield deformation. This meaning of ductility cannot be defined for FRP
reinforced beams due to linear elastic behavior of fiber reinforced polymers and behave
linearupto failure. The design codes and guides specify to design as an over reinforced beam
failure because plastic deformation of concrete increase the ductility of beam (JSCE 1997,
CSA 2002, ACI 2006).Harris et al [1] tried to mimic the elastic plastic behavior of the steel
by using hybrid FRP rebars. Alsayed and Alhozaimy [2] examined 18 steel and FRP
reinforced concrete beams and found that with the addition of 1% steel fibers, the ductility
index can be increased by as much as 100%. ACI 440 [11] recommends that the FRP
reinforced structures should be over reinforced and concrete beams have to be designed so
that they fail by concrete crushing rather than by rupture FRP reinforcement. Li and Wang [3]
demonstrated that the GFRP rebars reinforcing engineered cementitious composite material
improved flexural practices and ductility of the concrete element. Wenjun et al [16] studied
GFRP bars are used in concrete beams with combination of steel bars can improve the
durability of structures. T.H Kim et al [8] worked on concrete beams prestressed with two
AFRP tendons and models are simulated in ANSYS to study the non-linear flexural response.
Prestressing level of beams were 60% and 55% of the ultimate strength of AFRP tendons.
ANSYS predicated maximum error less than 5%. The principle goal of this study is to build
up a nonlinear finite element model to investigate the behavior and strength of concrete beams
reinforced by GFRP and steel bars. Both GFRP and steel bars were used in combination as a
flexural reinforcement. The finite element commercial program ANSYS 16.2 [17] was
utilized in the analysis. Nonlinear material properties of the beam components were used. The
results obtained from the model were confirmed against the test results conducted by previous
experimental tests of Wenjun et al [16].
2. FINITE ELEMENT MODELING
In order to accurately simulate the actual behavior of the concerned beam, all its components;
concrete beam, steel bars, GFRP bars and stirrups have to be modeled properly. Recent
experimental tests on concrete beam reinforced with steel and GFRP conducted by Wenjun et
al [16] were used to verify the developed finite element model.
Dr. J. Premalatha, R. Shanthi Vengadeshwari and Srihari.P
http://www.iaeme.com/IJCIET/index.asp 673 [email protected]
Figure 1 Beam Tested by Wenjun et al [16]
The four specimen tested by Wenjun et al [16] of length 2100mm with a rectangular
cross-section 180mm and 250mm width and depth respectively. B1 and B2 are reinforced
with steel and GFRP bars respectively. B3 and B4 were reinforced with steel and GFRP in
combination by varying a reinforcement percentage. The reinforcement details of all the four
beams are showed in Figure 1. A four-point static loading was applied to examine the simply
supported beams with a span of 1800mm as detailed in Figure 1. The dimensions and material
properties of the verified specimens are summarized in Table 1-2.
Table 1Concrete details for verified specimens
Beam No. ��� (MPa) ��� (MPa)
B1 & B2 30.95 24.76
B3 & B4 33.10 26.48
Table 2Reinforcement properties for verified specimen
Reinforcement Diameter
(mm)
Yield
strength (��)
MPa
Tensile
strength (���)
MPa
Modulus of
elasticity
(E) MPa
Steel 10 365
- 200000
12 16
- -
GFRP 12.7 - 782 45000
15.9 - 755 41000
2.1. Finite element type and mesh
To obtain an accurate simulation of the actual behavior of the concrete beam reinforced with
steel and GFRP bars, the elements composing the finite element model had to be chosen
properly. The mesh size was carefully selected to obtain high accuracy of results with
reasonable computational time. The aspect ratio of the used solid elements was kept as
possible within the recommended range between 1 and 3. The analysis was performed using
the ANSYS 16.2[17] program. Both material and geometric non-linearity were considered in
the analysis.
The 3-D eight node solid element SOLID65 is used to model concrete. Three translational
degrees of freedom are assigned for each node. Linear interpolation functions are utilized for
displacements and it simulates the cracking and crushing of brittle materials.
The LINK180 was used to simulate steel, GFRP rebars and the stirrups. Link180 is a two-
noded uniaxial tension-compression element with three translational DOF at each node.
Finite Element Modeling and Analysis of Rc Beams with Gfrp and Steel Bars
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Nonlinearity and plastic deformations are simulated in this element. In order to preclude early
warnings and premature failure messages due to concrete crushing at the positions of loading
and supports, eight-node solid element; solid185 are used to model the loading and support
plates. A typical figure of the three dimensional finite element mesh of the studied beams is
shown in Figure 2.
Figure 1 3D Finite element mesh (Concrete portion is removed to illustrate reinforcement)
2.2 Material Modelling
The material properties of the components of the pre-tested specimens were considered as
detailed in Table 1-2. In all cases, the ultimate strain of the concrete at failure was taken as
0.003 and the Poisson’s ratio of concrete was taken 0.2. A multi-linear isotropic stress strain
relation was used for modeling concrete material in compression. This relationship consists of
two portions. The first portion is an ascending curve represented by the numerical
expressions; Equations (1) and (2), [24] along with Equation (3). The curve starts at zero
stress and zero strain toward a value of0.25f�, calculated from Equation (3). The rest points
of the ascending curve are obtained from Equation (1). The strain at ultimate stress of
concrete is calculated using Equation (2).The descending branch which represents strain
softening of the ideal stress-strain curve of concrete was ignored as recommended in previous
studies [15, 19] in order to avoid convergence problems. A bilinear relationship was used to
represent the stress-strain curve of the steel reinforcement while a linear elastic behavior was
used for the GFRP rebars. The Poisson’s ratio was assumed to be 0.3 for steel reinforcement
and 0.2 for FRP. For support and loading plates, the stress-strain relation was considered
linear. Figure 3 shows the stress-strain relation of the concrete material.
Dr. J. Premalatha, R. Shanthi Vengadeshwari and Srihari.P
http://www.iaeme.com/IJCIET/index.asp 675 [email protected]
f E�ε1 � � ����
� (1)
ε� 2f��E�
(2)
E� fε (3)
Figure 3 Stress- Strain curve for concrete
2.3. Boundary condition and load application
Following the testing procedures conducted by Wenjun et al. [16], simply supported boundary
conditions were applied at the position of edge support. Due to symmetry of all the pre-tested
beams, only half of each beam was modeled, as shown in Figure 2. The nodes in the middle
symmetry surface were prevented to displace in Z- direction, while their movement in the
loading Y- direction was allowed. Till the failure load, the cracking and crushing of concrete
elements are monitored.
3. RESULTS AND DISCUSSION
The results obtained from the finite element model are correlated with the experimental test
results conducted by Wenjun et al [16]. The ultimate load and the corresponding maximum
deflection of the tested specimens and the finite element analysis as well as the load–
deflection curves, and deformed shapes after failure have been investigated and compared
with test results for all types of reinforced concrete beams. In addition, crushing and cracking
patterns for all the concrete beams are obtained in ANSYS 16.2 [17].
0
5
10
15
20
25
30
0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035
Strain
Str
ess
M
Pa
0.25f_c^′1
2
3
45
6 78
�_�〖f′〗_c^
Ultimate strain
Ultimate compressive strength
Finite Element Modeling and Analysis of Rc Beams with Gfrp and Steel Bars
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Table 3 Ultimate failure loads and Deflection values for all the Beams
Beam No. Failure loads of beam
!"# $%& '( )$
Deflection (mm)
*!"#*$%&
B1 120 107.9 108.9 105.8 19.52 20
B2 141.42 146.3 136.9 128.3 27.96 29
B3 130 127.6 134.8 126.5 29.25 28
B4 150 132.2 145.4 136.1 22.74 26
The results of the proposed 3-D nonlinear finite element model matched the experimental
results fairly well and the finite element model successfully predicted the behavior of the
beams. Table 3 shows the ultimate load and deflection values for all the beams.
Figure 4 Load-Deflection Curve and Crack patterns for B1
The ultimate capacity obtained from FEA is with in the 10% accuracy range, Figure 4
shows the load- deflection curve and crack patterns for B1 beam. The steel yielded at
midspan, the tension cracks were generated. The first crack occurred at 26kN near midspan as
the load is increased the crack propagates and diagonal cracks are developed. B1 is failed at
ultimate load 120kN due to concrete crushing after steel bars are yielded. This beam showed a
good ductile behavior by giving excessive cracks before failure of beam.
Figure 5 Load- Deflection curve and crack patterns for B2
Figure 5 shows the load-deflection and crack patters for B2 beam. It is noticed that beam
behaved linearly upto failure. At Initial load, there is a slight change in the slope of the curve.
Dr. J. Premalatha, R. Shanthi Vengadeshwari and Srihari.P
http://www.iaeme.com/IJCIET/index.asp 677 [email protected]
First crack observed in beam at a load 21.78kN as the load increases excessive cracks are
formed in midspan. Beam has a less stiffness compared to B1. At ultimate load 140.42kN
beam is failed due to concrete crushing in compression.
Figure 6 Load- Deflection curve and crack patterns for B3
In B3 beam Steel bars are introduced in tension zone to add a ductile behavior for the
beam. Compared to B2 beam, B3 has a more stiffness till the yielding of steel reinforcement.
The deformation is very less initially since stresses are taken by steel bars. After yielding of
steel bars, GFRP bars gave good response due to high tensile strength with increasing in
deformation. The first crack is observed at 23.9kN. After yielding of steel bars more diagonal
tensions cracks are developed and proceeding towards load points. At ultimate load 130kN,
beam is failed due to concrete crushing after yielding of steel reinforcement. Crack patters and
load- deflection curve is shown in Figure 6.
Figure 7 Load- Deflection curve and Crack patters for B4
Figure 7 shows the load-deflection curve and crack patterns for B4 beam. ANSYS 16.2
[17] predicted ultimate load 10% high than the experimental test results. The ultimate
capacity is increased due to increase in reinforcement ratio. The failure of beam is occurred at
150kN due to crushing of concrete after yielding of steel reinforcement.
Finite Element Modeling and Analysis of Rc Beams with Gfrp and Steel Bars
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4. CONCLUSION
A nonlinear finite element analysis of the flexural behavior of GFRP and Steel reinforced
concrete beams has been investigated in this paper. The study considered the ultimate load
carrying capacity, deflection and cracking pattern of the beams. The material as well as
geometric nonlinearities has been considered in the finite element model. The following
conclusions are outlined from this analysis.
1) The ANSYS16.2 FEA models are able to analyze reinforced concrete beams in
combination with steel and GFRP bars.
2) The results obtained from FEA are very close to results observed in the experiments.
3) The difference between FEA model results and experimental results are within 10%
range of accuracy in terms of ultimate load prediction.
4) The cracking behavior for all the beams are captured accurately in ANSYS and modes
of beam failure predicted from FEA is same as experimental test.
5) All the beams reinforced with Steel and GFRP bars are failed in ultimate load by
concrete crushing in compression zone after steel bars are yielded.
6) Beam2 reinforced with only GFRP bars failed in ultimate load by concrete crushing in
compression zone.
7) The beams reinforced with GFRP and Steel bars, steel reinforcement improves the
beam stiffness, ductility and load resistance after cracking.
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