TORSIONAL BEHAVIOR OF REPAIRED REINFORCED ......behavior of beams. Good agreement with the experimental test is obtain and this study shows that the optimum length of CFRP plate equal

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International Journal of Civil Engineering and Technology (IJCIET)

Volume 10, Issue 1, January 2019, pp.112–127, Article ID: IJCIET_10_01_012

Available online at http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=10&IType=1

ISSN Print: 0976-6308 and ISSN Online: 0976-6316

©IAEME Publication Scopus Indexed

TORSIONAL BEHAVIOR OF REPAIRED

REINFORCED CONCRETE BEAMS WITH

MULTI-BOUNDARY CONDITIONS

Hayder Al-Khafaji

Lecturer: Civil engineering Department

University of Babylon, Hilla, Iraq

ABSTRACT

This paper describes a finite element analysis for reinforced concrete beams of

multi-boundary conditions end repaired by CFRP and fc85 section tested under pure

torsion, classified according boundary conditions in two types cantilever and simply

supported beams every type include 13 beams divided according repaired to three

groups and control beam. The variables considered for group one and two included

the beam faces number that will be strengthened, the effect of CFRP Strips numbers

while the third group included repaired by fc85. The results of the repaired test beams

revealed that the technique of used thefc85very effective in simply supported beam

more than cantilever beam by about 97.5% while used repaired by CFRP more than

in cantilever. The torque resistance increased in all beams which repaired by

550.65%, 137% in cantilever beams and 11.78%, 139% in simply supported beams for

CFRP and fc85respectively, while the max twist decreased in all beams by 69.46%,

79.5% in cantilever beams and 26.5%, 62.19%in simply supported beams for CFRP

and fc85respectively.

Keywords: Reinforced Concrete Beam, Torsional Strengthening, CFRP strips,

Boundary Conditions, Repaired Beam.

Cite this Article: Hayder Al-Khafaji, Torsional Behavior of Repaired Reinforced

Concrete Beams with Multi-Boundary Conditions, International Journal of Civil

Engineering and Technology (IJCIET), 10 (1), 2019, pp. 112–127.

http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=10&IType=1

1. INTRODUCTION

The retrofitting of structures is promoted rather than demolishing and reconstruction of

deteriorated structures. Attention has also given to increase the load carrying capacity of

existing structures to increase the usage capacity or to change the intended usage so there is a

large need to strengthen concrete structures around the world. Retrofitting of structures using

fc85 and Carbon Fiber Reinforced Polymer materials is accepted as a sustainable and effective

method.

Hayder Al-Khafaji


High strength concrete was used to repair of all types of structural concrete elements in

buildings, water retaining structures, industrial plants, bridges, etc. where provide high

strength and extremely low shrinkage properties are required.

Externally bonded, CFRP sheets are currently being studied and applied around the world

for the repair and strengthening of structural concrete members [1]. CFRP materials are of

great interest to the civil engineering community because of their superior properties such as

high stiffness and strength has well as ease of installation when compared to other repair

materials.

David, E.,Djelal, C. and Buyle-Bodin , F. [2],using externally CFRP strips to bounded

beams and their results show that CFRP is very effective for flexure strengthening.

S. Panchacharam and A. Belarbi [3], makings experimental study to investigate the

torsional behavior of RC beams strengthened with externally bonded GFRP sheets. The

variables considered in this study are fiber orientation (parallel and perpendicular to the

longitudinal axis of the beam). The torsional reinforced concrete beams strengthened with

GFRP sheets exhibited significant increase in their cracking and ultimate strength as well as

ultimate twist deformations.

R.Dhanaraj and E.Chandrasekaran [4], investigated the numerical study on un retrofitted

and retrofitted reinforced concrete beams subjected to combined bending and torsion by

ANSYS. Then the study has been extended for the same reinforced concrete beams retrofitted

with carbon fiber reinforced plastic composites with ±45° and 0/90° fiber orientations. The

present study reveals that the CFRP composites with ±45° fiber orientations are more

effective in retrofitting the RC beams subjected to combined bending and torsion for higher

torque to moment ratios.

Bonfiglioli et al (2004)[5], carried out an experimental and theoretical study to evaluate

the capability of dynamic testing to give useful information about the stiffness recovery due to

external CFRP strengthening of RC beams which were previously damaged. Specimens were

damaged under cycle loading until cracks appeared. Then CFRP used for repairing cracking

specimens. The theoretical results are in good agreement with the experimental ones. The

research suggests that dynamic testing can be used to obtain useful information about the

effectiveness of the strengthening system.

Ali (2007)[6], casted twenty eight reinforced concrete beams to investigate the behavior of

using CFRP to repaired and strengthened beams failed in flexure and shear zone. All beams

had been tested as a simply supported beam under two point of loading. From the results can

see the use of CFRP as external strengthening has significant effect on ultimate load, crack

pattern and deflection. The repaired beams reach (95% to 97%) of ultimate load in

comparison with those strengthened in the same way by CFRP.

AL-Saidy et al. (2007)[7], studied behavior of corroded damaged reinforced concrete

beams repair/strengthening with CFRP sheets. Ten beams were casted and tested up to failure.

Damaged beams were repaired by bonding CFRP sheets to the tension side to restore the

strength loss due to corrosion. From the results can see The use of CFRP sheets for

strengthening corroded reinforced concrete beams increasing the ultimate strength of repaired

specimens. Deflection was increased for all repaired beams as compared with control beam.

Abed Al-Amery (2009)[8], repaired ten damaged reinforced concrete beams at flexural

region. Steel and CFRP palates used for repairing work to investigate the effect of repairing

materials in restoring the original stiffness and capacity for damage beams. Beams tested as

simply supported beam under two point loading. It was observed that ultimate can be

increased up to (121.4%) in the case of using steel plates. While deflection was decreased to

Torsional Behavior of Repaired Reinforced Concrete Beams with Multi-Boundary Conditions


(15.4%) times .In case of using CFRP plates, the ultimate can be increased up to (64.3%).

While deflection was decreased to (28.6%) times of the original beams.

Nada S. Assi [9], using finite element method to adopted by ANSYS program for four

beams strengthened in flexure with different length of CFRP sheet to confirm the theoretical

calculations as well as to provide a valuable supplement to the laboratory investigation of

behavior of beams. Good agreement with the experimental test is obtain and this study shows

that the optimum length of CFRP plate equal to 83% of the full span length [10,11].

T.Abdo and R. Mabrouk[12],studied the behavior of simply supported RC beams with

openings subjected to pure torsion then verified using FEM analysis program ANSYS16.

Good agreement between the experimental and numerical results is found. The torque-rotation

relationship for all the beams under study was linear up to the cracking torque and after that it

became nonlinear.

2. MATERIALS CHARACTERISTICS:

The materials of the structural elements that analysis in this study include concrete, steel

reinforcing bars, Cempatch S and CFRP. The finite element models adopted have a number of

parameters, which are summarized in Table (1).

Table (1) Parameters for elements used in F.E. Model for beam

Representation Element Type Characteristics

Concrete Solid65

compressive strength (fc')=30 MPa

Poisson's ratio=0.2

modulus of elasticity=25742 MPa

ultimate strain=0.003

Steel Reinforcement Link180 Ø16, Ø12, Ø10

Yield strength=410 MPa

CFRP Shell41

Cempatch S Solid65

compressive strength (fc')=85 MPa

Poisson's ratio=0.17

modulus of elasticity=43332 MPa

ultimate strain=0.0045

Steel plate Solid185 modulus of elasticity=200000 MPa

Poisson's ratio=0.3

3. NUMERICAL ANALYSIS

The finite elements representation using ANSYS16.1 program has been applied in this study

to know the validate of the numerical representation of the reinforced concrete beams

strengthening with Cempatch S and CFRP subjected to pure torsion. Twenty six reinforced

concrete beams of 500*250 mm cross-section and 2550 mm length were tested in this study

Fig (1). Schematic representations of the repairing and strengthening schemes are shown in

Fig (2) and Table (2) shows the cases of beams.

Hayder Al-Khafaji


Figure (1) Details of section beams for simply supported and cantilever

Repaired by CFRP

Repaired by strip CFRP

Repaired Cempatch S

Repaired by CFRP

Repaired by strip CFRP

Repaired Cempatch S

Figure (2) Distribution repaired of beams for simply support and cantilever



Designations:

C30= compressive strength fc'=30 MPa

C85= compressive strength fc'=85 MPa

CFRP= Carbon Fiber Reinforced Polymer

C=cut at the edge of beam

S =strip of beam length

4 , 3 =4edge and 3 edge

C4,C3 =Cover from 4 edge and 3 edge

Table (2) Details beams for simply supported

Group One

C30+CFRP4 C30+CFRP3 C30+CCFRP4 C30+CCFRP3

Group Two

C30+SCFRP4 C30+SCFRP3 C30+SCCFRP4 C30+SCCFRP3

Group Three

C85+C4 C85+C3 C85+C4+20 C85+C3+20

4. FINITE ELEMENT IDEALIZATION

A finite element analysis requires meshing of the model. In other words, the model is divided

into a number of small elements. Meshing, load and boundary conditions for beams are shown

in Fig (3).

Figure (3) Geometry of the numerical model for simply support and cantilever beams

Hayder Al-Khafaji


5. RESULTS AND DISCUSSIONS

In this section, the results obtained from ANSYS 16.1 are displayed for 26 beams divided

according boundary condition in two types cantilever and simply support each type include 13

beams. Because there is no experimental program for this research and compare it with the

results of the ANSYS. Therefore, the effectiveness of the program was verified through

another research that contains experimental results [3]. The general behavior of beams of

finite element represented in the torque-twist plots showed good convention with the data of

test from the experimentally tested. The torque-twist curves were show in Fig (4)to(6) and

Table(3).

Designations

A90W4:90 degree complete wrap

A0L4:0 degree, 4 sides

Table (3) Comparison between experimental and numerical ultimate torque and twist

Beam

Ultimate Torque (kN-m) Ultimate Twist (rad/mm)

Experimental Numerical Percentage

Difference % Experimental Numerical

Percentage

Difference %

reference 18 19.5 -8.3 110 104 5.45

A90W4 45 48 -6.67 70 63 10

A0L4 29 31.25 -7.76 168 152 9.53

Figure (4) Torque-Twist relationship of reference beam

Figure (5) Torque-Twist relationship of

beam(A90W4)

Figure (6) Torque-Twist relationship of

beam(A0L4)



The previous tables and figures present a comparison between experimental, numerical

results related to load, deflection. This comparison shows in general that the numerical

models are stiffer, and the numerical analyses give a smaller result for the deflection and

greater for ultimate load. These differences may be due to the following reasons:

The concrete of experimental samples is not perfectly homogeneous as assumed in the

numerical models.

The compressive strength of the tested concrete cubes may not represent exactly the actual

compressive strength.

Simply support

This type of boundary condition include 13 beams divided according repaired three groups

and control beam without repaired. The result of torque and twist for control beam was

(45kN.m) and twist (0.00196 rad/mm) as show in Fig (7).

Figure(7) Torque-Twist relationship of control beam

Group one:

This group consisted of four beams were repaired by CFRP along the length of beam. the

parameters of this group number of faces strengthened of beam. CFRP was continues around

the beam and was cut off in the area of cover for anther beams for four and three faces

respectively. Torque twist curve for all beams are shown Fig (8). The beast beam for this

group was (C30+CFRP4) by increase torque by (11.78%).

Figure (8) Torque-Twist relationship of group one

Hayder Al-Khafaji


Group two:

This group consisted of four beams also repaired by CFRP. CFRP was shaped strips each

150mm along length of beam. Parameters of this group like group one. Torque twist curve for

all beams are shown Fig (9). The beast beam for this group was (C30+SCFRP4) by increase

torque by (9.11%).

Figure(9) Torque-Twist relationship of group two

Group three

This group consisted of four beams also repaired by Cempatch S. the parameters of this group

number of faces repaired and depth of repaired inside the beam. Torque twist curve for all

beams are shown Fig (10). The beast beam for this group was (C85+C4+20) by increase

torque by (139%).

Figure(10) Torque-Twist relationship of group three



Table (4) ultimate torque, percentage variation of maximum of ultimate torque and twist for simply

support beams

Beams T(kN.m) Percentage% θ(rad/mm)

Control beam simply support 45 ------- 0.00196

Group one

C30+CFRP4 50.3 11.78 0.00214

C30+CFRP3 48.2 7.11 0.00235

C30+CCFRP4 49.4 9.78 0.002

C30+CCFRP3 46.7 3.78 0.0016

Group two

C30+SCFRP4 49.1 9.11 0.00201

C30+SCFRP3 47.3 5.11 0.00161

C30+SCCFRP4 48.6 8 0.00177

C30+SCCFRP3 45.9 2 0.00156

Group three

C85+C4 78.4 74.22 0.00208

C85+C3 70.4 56.44 0.00203

C85+C4+20 107.55 139 0.00324

C85+C3+20 88.1 95.78 0.00212

Cantilever

This type of boundary condition include 13 beams divided according repaired three groups

and control beam without repaired. The result of torque and twist for control beam was

(22.9kN.m) and twist (0.00678rad/mm) as show in Fig (11).

Figure (11) Torque-Twist relationship of control beam

Group one

Parameters in this group like group one in simply support only different in boundary

condition . Torque twist curve for all beams are shown Fig (12).the beast beam for this group

was (C30+CFRP4) by increase torque by (550.6%).

Hayder Al-Khafaji


Figure (12) Torque-Twist relationship of group one

Group two

Parameters in this group like group two in simply support only different in boundary

condition. Torque twist curve for all beams are shown Fig (13). The beast beam for this group

was (C30+SCFRP4) by increase torque by (514.6%).

Figure(13) Torque-Twist relationship of group two

Group three

Parameters in this group like group three in simply support only different in boundary

condition. Torque twist curve for all beams are shown Fig (14). The beast beam for this group

was (C85+C4+20) by increase torque by (137.8%).



Figure(14)Torque-Twist relationship of group three

Table (5) ultimate torque, percentage variation of maximum at ultimate torque and twist for simply

support beams

Beams T Percentage% θ

Control beam Cantilever 22.9 -------- 0.00678

Group one

C30+CFRP4 149 550.655 0.0319

C30+CFRP3 113.85 397.16 0.0479

C30+CCFRP4 146 537.55 0.0308

C30+CCFRP3 107.55 369.65 0.045

Group two

C30+SCFRP4 140.7375 514.57 0.0291

C30+SCFRP3 103.95 353.9 0.0427

C30+SCCFRP4 127.0125 454.64 0.0245

C30+SCCFRP3 95.5125 317.08 0.0385

Group three

C85+C4 40.275 75.87 0.00367

C85+C3 38.25 67.03 0.00775

C85+C4+20 54.45 137.77 0.00408

C85+C3+20 48.15 110.26 0.00650

Effect of variable Parameters

Through the following Fig (15) to (18), the effect of each parameter, in the present study, on

the beams behavior is studied.

0

10

20

30

40

50

60

0 0.002 0.004 0.006 0.008 0.01

To

rqu

e(k

N.m

)

Twist(rad/mm)

C85+C4 Cantilever

C85+C3 Cantilever

C85+C4+20 Cantilever


Hayder Al-Khafaji


Figure(15) the effective area of CFRP for simply supported beams

Figure(16) the effectivedepth of Cempatch S for simply support

Figure(17) the effective area of CFRP for cantilever

0

10

20

30

40

50

60

0 0.001 0.002 0.003

To

rqu

e(k

N.m

)

Twist(rad/mm)

Simply supportC30+CFRP4C30+CCFRP4C30+SCFRP4C30+SCCFRP4

0

10

20

30

40

50

60

0 0.0005 0.001 0.0015 0.002 0.0025

To

rqu

e(k

N.m

)

Twist(rad/mm)

Simply support

C30+CFRP3

C30+CCFRP3

C30+SCFRP3

0

20

40

60

80

100

120

0 0.001 0.002 0.003 0.004

To

rqu

e(k

N.m

)

Twist(rad/mm)

Simply supportC85+C4C85+C4+20 0

20

40

60

80

100

0 0.0005 0.001 0.0015 0.002 0.0025

To

rqu

e(k

N.m

)

Twist(rad/mm)

Simply supportC85+C3C85+C3+20

0

20

40

60

80

100

120

140

160

0 0.01 0.02 0.03 0.04

To

rqu

e(k

N.m

)

Twist(rad/mm)

CantileverC30+CFRP4 CantileverC30+CCFRP4 CantileverC30+SCFRP4 CantileverC30+SCCFRP4 Cantilever

0

20

40

60

80

100

120

0 0.01 0.02 0.03 0.04 0.05 0.06

To

rqu

e(k

N.m

)

Twist (rad/mm)

CantileverC30+CFRP3 CantileverC30+CCFRP3 CantileverC30+SCFRP3 CantileverC30+SCCFRP3 Cantilever



Figure(18) the effectivedepth of Cempatch S for cantilever

A conclusion the curves of torque-twist which is presented in Fig (15) to (18) indicates the

following points:

The increase in ultimate torque in the case of 4 faces by (11.78 and 9.11)%for beams

(C30+CFRP4 and C30+SCFRP4,) respectively for simply supported, and (550.6 and

514.5)% for beams (C30+CFRP4cantilever and C30+SCFRP4 cantilever) respectively for

cantilever.

The increase in ultimate torque in the case of 3 faces by (7.11 and 5.11)% for beams

(C30+CFRP3 and C30+SCFRP3) respectively for simply supported, and (397and

353.9)% for beams (C30+CFRP3cantilever and C30+SCFRP3 cantilever) respectively for

cantilever.

The decrease in twist at the same torque of control beam in the case of 4 faces by (26.53

and 25.5)% for beams (C30 + CFRP4 and C30 + SCFRP4, C30) respectively for simply

support, and (67.216)% for beams (C30+CFRP4cantilever) for cantilever.

The decrease in twist at the same torque of control beam in the case of 3 faces by (25.5

and 25)% for beams (C30 + CFRP3and C30 + SCFRP3) respectively for simply support ,

and (69.16 and 69.46)% for beams (C30+CFRP4 cantilever and C30+SCFRP4 cantilever)

respectively for cantilever.

When repaired by fc85 the ultimate torque increase (74.22 and 139)% and the twist at the

same torque of control beam decrease(55.76 and 62.2)% for beams(C85+C4 and

C85+C4+20) respectively for simply support, and (75.87 and 137.77)%, (75.6 and 79.5)%

for beams (C85+C4cantilever and C85+C4+20cantilever) respectively for cantilever.

Repaired from 4 edge by CFRP have given better results from 3 edge and more stiffness

in two types of boundary conditions, but were more effective in the case of cantilever

from the simply support by (196%).

The technique of used the Cempatch S material very effective in simply support more than

cantilever of 97.5% and then when increase the depth of Cempatch S material inside the

beam was become more stiffness.

One can see that the beam of all beams for two type of boundary condition, for simply

supported (C85+C4+20) which repaired by Cempatch S material from four side and for

cantilever (C30+CFRP4 cantilever) Which repaired by CFRP.

0

10

20

30

40

50

60

0 0.002 0.004 0.006 0.008

To

rqu

e(k

N.m

)

Twist (rad/mm)

Cantilever

C85+C4 Cantilever

C85+C4+20 Cantilever0

10

20

30

40

50

60

0 0.002 0.004 0.006 0.008 0.01

To

rqu

e(k

N.m

)

Twist (rad/mm)

Cantilever

C85+C3 Cantilever


Hayder Al-Khafaji


6. CRACK PROPAGATION

The ANSYS16.1 program registers the crack propagation at each applied load step. Cracks

patterns obtained from the finite element analysis by using the Crack/Crushing plot option, as

shown in Fig (19).

Torsional reinforced concrete beams were repaired by CFRP sheets and fc85 the

distribution of cracks has changed about the control beam this indicates that the behavior of

the beams and the distribution of the stresses have changed, where the repaired of the simply

support beams led to the decrease of cracks that was it clear through a small percentage

increase of ultimate torque (11.78%) for CFRP and (139%) for fc85 for beams (C30+CFRP4)

and(C85+C4+20)respectively while the cantilever beams increase the number of cracks due to

increase the ultimate torque high percentage (550.6%)for CFRP and (137%) for fc85 for

beams (C30+CFRP4) and (C85+C4+20)respectively.

simply supported beams Cantilever beams

Figure(19) Crack propagation at ultimate load for simply supported and cantilever beams

7. STRESS AND MODE OF FAILURE

Fig (20) to (21) show the stress and mode of failure.

Simply

supported

beams

Cantilever

beams

Figure(20) stress at ultimate load for simply supported and cantilever beams



Simply

supported

beams

Cantilever

beams

Figure (21) mode of failure for simply supported and cantilever beams

8. CONCLUSIONS

The beams of repaired with CFRP and Cempatch S material whether, four or three faces for

two type of boundary condition were proved that an effective way, if not give the improved

properties return beam to the control beam.

The repaired with CFRP led to increase of ultimate torque force by (11.78%) for simply

support and (550.6%) for cantilever.

The repaired with Cempatch S material led to increase of ultimate torque force by (139%) for

simply support and (137.7%) for cantilever.

Torsional reinforced concrete beams were repaired by CFRP sheets and Cempatch S the

distribution of cracks has changed about the control beam this indicates that the behavior of

the beams and the distribution of the stresses have changed, where the repaired of the simply

support beams led to the decrease of cracks that was it clear through a small percentage

increase of ultimate torque while the cantilever beams increase the number of cracks due to

increase the ultimate torque high percentage.

For simply support beams were repaired with Cempatch S material were the best and which

reaches up to (91.36%), higher than beams were repaired with CFRP which reaches an

increase to (7.1%).

For cantilever beams were repaired with CFRP were the best and which reaches up to

(436.9%), higher than beams were repaired with Cempatch S material which reaches an

increase to (97.7%).

For the same torque decrease the twist deformations in beams which repaired by CFRP and

Cempatch S material (26.53%), (62.2%)respectively for simply support and (69.46%),(79.5%)

respectively for cantilever

Hayder Al-Khafaji


REFERENCES

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Analysis", Vol. 32, Part (A), No.7, Eng. & Tech. Journal, pp. 1671-1683, 2014.

[10] Kadhim Naief Kadhim and Ghufran A. (The Geotechnical Maps For Gypsum By Using

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http://www.vbt.bme.hu/

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TORSIONAL BEHAVIOR OF REPAIRED REINFORCED ......behavior of beams. Good agreement with the experimental test is obtain and this study shows that the optimum length of CFRP plate equal