EXPERIMENTAL STUDY ON FLEXURAL STRENGTH OF ...

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EXPERIMENTAL STUDY ON FLEXURAL STRENGTH OF REINFORCED

CONCRETE BEAMS EXTERNALLY BONDED WITH CFRP SHEETS

M. Hemapriya1

, T.P.Meikandaan2

Assistant Professor1,2

, Department of Civil Engineering 1,2

BIST, BIHER, Bharath University

[email protected]

[email protected]

ABSTRACT

Fiber Reinforced polymer are commonly used for the Strengthening of Reinforced

Concrete Structures. In that CFRP plays a vital role in providing the strength, stiffness and

ductility of the Reinforced concrete Structures when compared with other fibers like GFRP, steel

and aramid fibers. Study on Flexural Strengthening of RC Beams with CFRP (Multiple Layers)

is carried out. The dimension of the beam specimens are 100mmx200mmx1500mm. Reinforced

concrete beams externally bonded with CFRP sheets were tested using a symmetrical two point

concentrated static loading system. Two beams were tested for Control Beam for Flexural (FB)

and two beams tested for it is preloading of 70% for FB. And after that it is tested by CFRP

bottom only multiple layers for preloading of 70% for FB. The result show in increasing strength

when compared to preloading of 70% for FB. Experimental data on load, deflection and ultimate

load of each of the beam were obtained. The load vs deflection curves were compared with

Control Beam for Flexural (FB), Preloading 70%FB and tested CFRP bottom multiple layer for

preloading of 70% for FB. In this investigation (CFRP) Carbon Fiber Reinforced Polymer gives

appreciable strength, stiffness and ductility in flexure.

Key words: Flexure strengthening of beams and carbon fiber Reinforced polymer

1.1 INTRODUCTION

A fiber Reinforced polymer (CFRP) composite is defined as a polymer (plastic) matrix, either

thermo set or thermoplastic, that is reinforced (combined) with a fiber or other reinforcing

material with a sufficient aspect ratio (length to thickness) to provide a discernible reinforcing

function in one or more directions. FRP composites are different from traditional construction

materials such as steel or Aluminum[1-7]. FRP composites are anisotropic (properties apparent

in the direction of the applied load) whereas steel or aluminum is isotropic (uniform properties in

all directions, independent of applied load)[46-50]. Therefore, FRP composite properties are

directional, meaning that the best mechanical properties are in the direction of the fiber

placement. Reinforced concrete buildings may be vulnerable to progressive collapse due to a

lack of continuous reinforcement. Carbon fiber reinforced polymer (CFRP) may be used to

International Journal of Pure and Applied MathematicsVolume 119 No. 12 2018, 8629-8645ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu

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retrofit existing reinforced concrete beams and provide the missing continuity needed to resist

progressive collapse. A fiber Reinforced polymer (FRP ) composite is defined as a polymer

(plastic) matrix, either thermo set or thermoplastic, that is reinforced (combined with a fiber or

other reinforcing material with a sufficient aspect ratio (length to thickness) to provide a

discernible reinforcing function in one or more directions[8-12].

The development of new material systems like carbon fiber reinforced polymers (CFRP)

used for strengthening and rehabilitation of existing structures are getting higher demands and

wide range of application in recent years. CFRP laminates gained importance over steel plate

bonding because they offer superior performance such as resistance to corrosion, and high

stiffness-to-weight ratio. Even though CFRP laminates are produced and utilized in different

applications, the most common form is built-up woven fabric that is externally bonded to

structural element by the wet lay-up method. Because the CFRP strengthening provides

additional flexural or shear reinforcement, the reliability for this material application depends on

how well they are bonded and can transfer stress from the concrete component to CFRP

laminates (1).

1.1.1 Need for carbon fibers

Carbon fibers are the predominant reinforcement used to achieve high stiffness and high

strength. The term carbon fiber covers a whole family of materials which encompass a large

range of strength and stiffness.Carbon fiber is the most commonly produced from a precursor of

polyacrylonitrile (PAN) fiber which is processed by first stretching it to achieve degree of

molecular orientation[13-17]. It is the stabilized in an oxidizing atmosphere while held under

tension. The fiber are then subjected to carbonizing regime at a temperature in the range of

1000-3500ºc. These fibers tend to be of lower performance than PAN-based fibers; they are also

cheaper due to their use of lower cost precursor. The dominant carbon fibers in current use have

a tensile modulus of about 230 GPa, a tensile strength of around 5000 MPa and a strain-to-failure

2% Unidirectional composites produced from them in either an epoxy or vinyl ester matrix have

the following typical properties. It has longitudinal tensile modulus 155- 165 GPa and

longitudinal strength 2500- 3000 MPa . The elongation break 1.2%-1.3% .

2.1 TEST PROGRAM

Table 2.1 Mix Proportion For M20

Water Cement Fine Aggregate Coarse Aggregate

186 litre 413.33kg

657kg

1140kg

International Journal of Pure and Applied Mathematics Special Issue

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0.45 1 1.59 2.75

The test program involves the casting of Specimens that are listed in the following steps below.

2.1.1 CASTING OF SPECIMENS

The dimension of beam to be prepared is 1500 mm with cross-section of 200mmx100mm

12 specimens will be prepared for this experiment using cement, fine aggregate and coarse

aggregate for which the designs mix proportion is arrived as shown .To investigate the ultimate

load carrying capacity of beam[18-24], specimens are prepared and designated as follows.

Figure 2.1 Typical Diagram Of Beam Dimension

2.2 CFRP WRAPPING

Carbon fiber reinforced polymer will be wrapped of the beam length of specimen for.

Out of the 12 specimens, 3 specimens will be used as control specimen for shear and 3 specimen

will be used for control specimen for flexural, 3 specimen will be wrapped for shear cracking

with multiple layer of preloading 90% U-wrapping and 3specimen will be wrapped for flexural

cracking with multiple layer of preloading 70% bottom only[25-33].


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Figure : 2.2 Reinforcement details for flexural

Figure : 2.3 Reinforcement details for shear

3.1 EXPERIMENTAL INVESTIGATION

The experimental investigation are conducted according to IS: 383-1970 for the fine aggregate

and coarse aggregate[34-41]. The test conducted are for fine aggregate are specific gravity, water

absorption, and for coarse aggregate are specific gravity, water absorption, Impact test Crushing

Test, Los Angel’s Abrasion test shown in table 4.1

Table 3.1 Test on Fine aggregate and Coarse aggregate

MATERIALS PROPERTIES VALUES

FINE AGGREGATE

Specific gravity 2.60

Water absorption 1.66%

Grading zone II

COARSE AGGREGATE

Specific gravity 2.65

Water absorption 0.80%

Impact test 20.0%

Crushing test 19.50%

Los angel’s abrasion test 6.25%


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Table 3.2 Test on fresh concrete (as per in 1199 – 1959)

TEST VALUE

Slump (mm) 31mm

Compaction factor 0.87

Vee-Bee (s) 5.1

4.1 TEST ON HARDENED CONCRETE

The experimental process comprises of specimen that has to be cube are cylinders and beams

for comparing the properties compressive strength splitting tensile strength and flexural strength

tests respectively[42-45].

The Casted specimens are cured for 7 days and 28 days . The tested values are listed below

Table 4.1 COMPRESSION TEST ON CONCRETE CUBES

Compressive Strength,N/mm2

(7 days)

Compressive Strength,N/mm2

(28 days)

14.22 26.49

Table 4.2 TENSION TEST ON CONCRETE CYLINDERS

Tensile Strength,N/mm2

(7 days)

TensileStrength,

N/mm2

(28 days)

1.01 2.44


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Figure 4.1 Experimental Two Point Loading Set Up


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Figure 4.2 Crack Pattern For Shear

Figure 4.3 Crack Pattern For Flexure

5.1 RESULTS AND DISCUSSION

The Results and Discussion consist of the following things:

Table 5.1Results of Control Beamss

Load

(Tonne)

Control Beam 1 Control Beam 2

Lvdt 1 (mm) Lvdt 2 (mm) Lvdt 1 (mm) Lvdt 2 (mm)

0 0 0 0 0

0.5 0.7 0 0.6 0.1

1.0 0.9 0.3 0.9 0.3

1.5 1.1 0.4 1.1 0.5

2.0 1.4 0.6 1.3 0.6

2.5 1.8 1.0 1.7 0.9

3.0 2.4 `1.5 2.3 1.4

3.5 2.8 1.7 2.8 1.6


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4.0 3.4 2.3 3.5 2.2

4.5 3.8 2.7 3.7 2.6

5.0 4.5 3.4 4.4 3.3

5.5 5.8 4.8 5.7 4.8

Figure 5.1 Load Vs Deflection Graph For Control Beam SB-I

Table 5.2 Preloading For 70% FB- I

Flexure Beam 1 Flexure Beam 2

Load (Tonnes) Lvdt1(mm) Lvdt2(mm) 0 0

0 0 0 0.5 0.5

0.5 0.3 0.3 0.7 0.6

1 0.4 0.4 1.1 1.0

1.5 0.8 0.9 1.4 1.4

2 1.1 1.2 2.0 1.8

2.5 1.7 1.5 2.5 2.2

3 2.2 2.0 2.9 2.6

3.5 2.6 2.4 3.4 3.1

4 3.2 3.0 3.5 3.2

4.16 3.3 3.1 0 0

0

1

2

3

4

5

6

0 2 4 6 8

Load

(Ton

ne)

Deflection (mm)

Load vs Deflection

lvdt 1 (mm)

lvdt2(mm)


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Figure 5.2 Load Vs Deflection Graph For Pre Loading 70% FB-I

Table 5.3 Test Result Of CFRP Bottom Wrapping Multiple Layer For Pre Loading For

70% FB-I

Load (Tonnes) Flexure Beam 1 Flexure Beam 2

Lvdt 1 (mm) Lvdt 2(mm) Lvdt 1 (mm) Lvdt 2(mm)

0 0 0 0 0

0.5 0.3 0.3 0.3 0.2

1 0.4 0.4 0.4 0.3

1.5 0.7 0.6 0.7 0.5

2 1.1 1.0 1.0 0.8

2.5 1.6 1.4 1.5 1.3

3 2.1 1.8 2.0 1.7

3.5 2.5 2.4 2.4 2.3

4 3.1 2.9 3.0 2.8

4.5 4.2 4.1 4.1 3.9

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 0.5 1 1.5 2 2.5 3 3.5

Lo

ad

(T

on

ne)

Deflection (mm)

Load vs Deflection

lvdt1(mm)

lvdt2(mm)


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5 5.1 4.9 4.9 4.7

5.5 6.2 5.9 6.1 5.8

6 8.0 7.8 7.9 7.7

6.5 9.2 8.8 9.1 8.7

7 10.4 9.8 10.3 9.6

7.5 12.2 10.4 12.1 10.3

8 14.5 13.8 14.5 13.5

Figure 5.3 Load Vs Deflection Graph For Test Result Of CFRP Bottom Wrapping Multiple

Layer For Preloading 70% For FB-I

5.2 LOAD AT INITIAL CRACK FOR SB

Under two point static loading of beam specimens, at each increment of load, deflection and

crack development were observed .In CB initiation for SB I, SB II,SB IIIof crack takes place at a

load of 1.5Tonne.

5.2.1 RESULT OF ULTIMATE LOAD FOR SB

The Beam Specimen for CB for SB-I, SB-II, SB-III goes the ultimate load breaking point of 5.5

tonnes. After that the beam specimens SB I, SB II and SB III are then applied to the Pre

Loading of 90% that is 4.95 Tonne. After then it was wrapped for CFRP U-wrapping Multiple

layer for SB-I, SB-II,SB-III. The Test Result show the ultimate strength for SB-I, SB-II, SB-III

were found to be 10 tonnes.

5.3 LOAD AT INITIAL CRACK FOR FB

0

2

4

6

8

10

0 5 10 15 20

Load

(T

on

ne)

Deflection (mm)

Load vs Deflection

lvdt1(mm)

lvdt2(mm)


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Under two point static loading of beam specimens, at each increment of load, deflection and

crack development were observed .In CB initiation for FB I, FB II,FB IIIof crack takes place at a

load of 2.0 Tonne.

5.3.1 RESULT OF ULTIMATE LOAD FOR FB

The Beam Specimen for CB for FB-I, FB-II, FB-III goes the ultimate load breaking point of 6

tonnes. After that the beam specimens FB I, FB II and FB III are then applied to the Pre

Loading of 70% that is 4.16 Tonne. After then it was wrapped for CFRP U-wrapping Bottom

only Multiple layer for FB-I, FB-II,FB-III. The Test Result show the ultimate strength for FB-I,

FB-II, FB-III were found to be 8 tonnes.

TABLE 5.4 TEST RESULTS OF ULTIMATE LOAD FOR FB

Type of Beam Wrapping Layers Ultimate

Load(Tonnes)

Control Beam for FB ________________ ________________ 6

Preloading of 70%

FB

________________ ________________ 4.16

CFRP for FB Bottom Wrapping Multiple Layer 8

Figure 5.20 Ultimate Load For Different FB

6.1 CONCLUSION

The Following conclusion is drawn from the test result:

i. It is concluded that from Control Beam for FB Ultimate Breaking point is 6 Tonne.

0

1

2

3

4

5

6

7

8

9

1

Ult

imate

Load

(T

on

ne)

FB

Ultimate load for SB

Control Beam for FB

Preloading of 70% for FB

CFRP Bottom only multiple layer for Preloading 70% for FB


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After Preloading 70% for FB of 4.16 Tonne. Then after CFRP bottom only wrapping

multiple layer for Preloading 70% for FB the test result for FB has been got 8 Tonne.

Therefore after test result for CFRP U Wrapping Bottom only multiple layer for

preloading 70% for FB it is increased by 3.84 Tonne.

ii. The Deflection of Reinforced Concrete Beams increase with increase in elastic range.

Hence from the Study on Flexural Strengthening of RC Beams with CFRP (Multiple layers)

conclude the strength of the RC Beams in shear is increased after wrapping Carbon Fiber

Reinforced Polymer with multiple layers and also the strength of the RC Beams in flexural is

increased after wrapping Carbon Fiber Reinforced Polymer with multiple layers.

REFERENCE

1. Abdeldjeli Belarbi ,Sang-Wook Bae, Michael Murphy and Amir Mirmiran(2011 ) “

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