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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


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


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.



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.



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



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.



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.



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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