SHEAR STRNGTHENING OF RC BEAMS WITH EXTERNALLY … · 1.2.1 Glass Fiber Reinforced Polymer (GFRP):...

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SHEAR STRNGTHENING OF RC BEAMS WITH EXTERNALLY BONDED

GFRP SHEETS

M. Hemapriya1

, T.P.Meikandaan2

Assistant Professor1,2

, Department of Civil Engineering 1,2

BIST, BIHER, Bharath University

[email protected]

[email protected]

ABSTRACT

The superior properties of polymers composite materials like high corrosive resistance, high

strength, high stiffness, excellent fatigue performance and good resistance to chemical attack etc,

has motivated the researchers and practicing engineers to use the polymers composites in the

fields of retrofitting of structures .strengthening the reinforced concrete beams has some

advantages namely, increasing durability and extending life span of the weakened reinforced

concrete beams. Study on Shear Strengthening of RC Beams with GFRP sheets is carried out.

The dimension of the Beam Specimen is 100mmx200mmx1500mm. The reinforced concrete

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

concentrated static loading system. The ultimate strength of three beams were tested and treated

as Control beams. Three more beams were tested after preloading of 80% of its ultimate strength,

Strengthened using GFRP sheets. In this study (GFRP) Glass Fiber Reinforced Polymer gives

appreciable strength, stiffness, and ductility in shear.

Key wards: Glass fiber, epoxy, and retrofitting

1.1 INTRODUCTION

A few agents took up solid shafts and sections retrofitted with glass fiber strengthened polymer

(GFRP) composites so as to study the improvement of quality and pliability, toughness, impact

of restriction, planning of configuration rules. By GFRP sheets, retrofitting of solid structures

give a more practical and in fact better option than the conventional strategies much of the time

since it offers high quality, low weight, erosion resistance, high exhaustion resistance.

Deterioration in concrete structures is a major challenge faced by the infrastructure and bridge

industries worldwide. The deterioration can be mainly due to environmental effects, which

includes corrosion of steel, gradual loss of strength with ageing, repeated high intensity loading,

variation in temperature[1-6], freeze-thaw cycles, contact with chemicals and saline water and

exposure to ultra-violet radiations. Along these lines, broad examination works are being

completed all through world on retrofitting of solid bars and sections with remotely reinforced

GFRP composites. A few specialists took up solid pillars and sections retrofitted with glass fiber

strengthened polymer (GFRP) composites to ponder the upgrade of quality and flexibility,

sturdiness, impact of imprisonment, readiness of outline rules. By GFRP sheets[35-43],

retrofitting of solid structures give a more sparing and in fact better option than the conventional

International Journal of Pure and Applied MathematicsVolume 119 No. 12 2018, 8647-8667ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu

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systems as a rule since it offers high quality, low weight, consumption resistance[7-14], high

weakness resistance.

RETROFITTING

Retrofitting refers to the addition of new technology or new features to older systems.

It is the modification of the existing structures to make them more resistant, durable and extend

their life span. Retrofitting is a technical intervention in the structural system of a structure that

improves the resistance by optimizing the strength, ductility and durability. Strength of the

structure is generated from the structural dimensions, materials, shape and number of structural

elements[15-22].

1.2 MATERIALS USED

1.2.1 Glass Fiber Reinforced Polymer (GFRP):

Glass Fibre is a material consisting of minerals extremely fine fibres of glass. It can be

used as a insulating material. Glass Fibres are also used as a reinforcing agent for many Polymer

products to form very strong and light fibre reinforced Polymer FRP Composite materials called

Glass Reinforced Plastic GRP popularily known as Fibre glass. Glass fibers are considerably

cheaper than carbon and aramid fibers[23-30]. Therefore glass fiber composites have become

popular in many applications. The moduli of fibers are 70-85 GPa with ultimate elongation 2-5%

depending on quality. The specialty AR-glass fibers are resistant to the alkaline environment

found in concrete but have much higher cost[44-50].

Table 1.1 Properties of GFRP

Properties of GFRP Value

Density of fibre 2.6 g/cc

Weight of fibre 920 g/mm2 Fibre thickness 4 mm Fibre orientation ±900 Nominal thickness per layer 1.5 mm Tensile strength 3400 N/mm2 Tensile modulus

Colour

Safety factor for static design

Ultimate strain

73000 N/mm2

White

1.5

4.5

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1.3 EXPERIMENTAL INVESTIGATION

The following tests are conducted on cement, fine aggregate and coarse aggregate and the

results are tabulated in the table[31-34].

1.3.1 TEST ON CEMENT

Portland Pozzolona Cement (PPC) is used for the experiment.

Table 1.2 Test on cement

TEST VALUES

Specific Gravity 3.15

Fineness 99.7%

Consistency 34%

Initial setting Time 40 min

1.3.2 TEST ON FINE AGGREGATE

Locally available sand is used as fine aggregate.

Table 1.3 Test on fine aggregate

TEST VALUES


Gradation(sieve analysis)(IS: 383) Zone II

1.3.3 TEST ON COARSE AGREGATE

The coarse aggregates of two grades are used one retained on 12.5 mm size sieve and another

grade contained aggregates retained on 20 mm sieve.

Table 1.4 Test on coarse aggregate

TESTS VALUES


Aggregate Impact Value 13.20%

Aggregate crushing value 5.809%

Aggregate Abrasion Value (LOS ANGELES) 5.52%


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1.4 MIX PROPORTIONS OF M20 GRADE CONCRETE

Table 1.5 Mix proportion

Water Cement Fine aggregate Coarse aggregate

191.58(lit) 425.73 (kg) 662.367 (kg) 1159.98 (kg)

0.45 1 1.55 2.72

1.5 CASTING OF BEAM

Width=100mm

Length =1500mm

Depth =200mm

Fig-1.1 Typical diagram of a beam

Table 1.6 : Quantity of materials for casting

Materials One Mould (in Kg) Six Mould (in Kg)

Cement 15 90

Fine Aggregate 22 132

Coarse Aggregate 37 222

Water 6.5 39


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1.6 TESTING THE SPECIMEN

Fig 1.2 Test setup

Fig 1.3 Testing on specimen

2.1 WORKABILITY TEST ON FRESH CONCRETE-

Table 2.1 Slump test

Water cement ratio (%) Workability measured slump (mm)

0.45 38

Table 2.2 Compaction factor

Water cement ratio (%) Compaction factor

0.45 0.824


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2.2 ANALYSIS OF BEAM FOR 28 DAYS:

Table 2.3: Load in Tonnes for 28 Days

Beam no. Control beam (Ultimate load)

at 28 days (Tonnes)

(Tonnes)

Preloaded beam of 80% at

28 days (Tonnes)

B 1 5.5 4.4

B 2 5.6 4.48

B 3 5.45 4.36

Avg Load

(Tonnes) 5.51 4.45

2.3 CONTROL BEAM TEST (ULTIMATE LOAD) AT 28 DAYS:

Table 2.4: Ultimate load and deflection

Testing of beam (Controlled beam CB 1)

Load (tonnes) LVDT 1 (mm) LVDT 2(mm)

0 0 0

0.5 0.7 0.1

1 0.9 0.3

1.5 1.1 0.45

2 1.4 0.6

2.5(initial crack) 1.8 1

3 2.4 1.50

3.5 2.8 1.7

4 3.4 2.3

4.5 4.5 2.7

5 4.5 3.4

5.5 (ultimate) 5.8 4.8


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0

1

2

3

4

5

6

7

0 1 2 3 4 5 6

Lo

ad

Deflection

Testing of beam (C.B 1)

LVDT 1 (mm)

LVDT 2(mm)

Fig 2.1 Load and deflection graph for C.B 1


Testing of beam (Controlled beam C.B 2)


0 0 0

0.5 0.3 0.1

1 0.52 0.31

1.5 0.7 0.5

2 1.2 0.85

2.5(initial crack) 1.5 0.9

3 1.9 1.36

3.5 2.35 1.9

4 2.9 2.4

4.5 3.45 2.8

5 4.4 3.7

5.6 (ultimate) 5.6 4.8


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Fig 2.2 Load and deflection graph for C.B 2

Table 2.6: ultimate load and deflection

Testing of beam (Controlled beam CB 3)


0 0 0

0.5 0.6 0.1

1 1 0.4

1.5 1 0.5

2 1.3 0.45

2.5(initial crack) 1.6 1.1

3 2.5 1.6

3.5 2.6 1.8

4 3.2 2.2

4.5 4.5 2.7

5 4.6 3.5

5.45 (ultimate) 5.7 4.7


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0

1

2

3

4

5

6

0 1 2 3 4 5 6

Lo

ad

Deflection

Testing of beam (CB 3)

LVDT1 (mm)

LVDT2(mm)

Fig.2.3 Load and deflection graph for C.B 3

2.4 PRELOADED BEAM TEST OF 80% AT 28 DAYS :


Testing Of Beam( Preloaded Beam (P.B 1) with 80% of load)

load (tonnes) LVDT 1 (mm) LVDT 2 (mm)

0 0 0

0.5 0.5 0.1

1 0.7 0.3

1.5 0.9 0.4

2 (initial crack) 1.3 0.7

2.5 1.7 0.9

3 2 1.3

3.5 2.6 1.5

4 3.1 1.9

4.4 (ultimate) 3.7 2.3


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Fig 2.4 Load and deflection graph for P.B 1

Table 2.8 : Ultimate load and deflection



0 0 0

0.5 0.2 0.1

1 0.4 0.35

1.5 0.7 0.5

2 1.1 0.84

2.5 (initial crack) 1.4 0.9

3 1.7 1.3

3.5 2.15 1.8

4 2.6 2.2

4.48 (ultimate) 3.3 2.8


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0

0.5

1

1.5

2

2.5

3

3.5

0 1 2 3 4 5

Load

Deflection

Testing Of Beam(P.B 2)

LVDT 1 (mm)

LVDT 2 (mm)

Fig 2.5 Load and deflection graph for P.B 2

Table 2.9 : Ultimate load and deflection



0 0 0

0.5 0.6 0.1

1 0.8 0.2

1.5 1 0.5


2.5 1.6 1

3 2.1 1.2

3.5 2.7 1.4

4 3 1.8

4.45 (ultimate) 3.6 2.2


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0

0.5

1

1.5

2

2.5

3

3.5

4

0 1 2 3 4 5

Load

Deflection

Testing Of Beam(P.B 3)

LVDT 1 (mm)

LVDT 2 (mm)

Fig.2.6 Load and deflection graph for P.B 3

3.1 COMPRESSIVE STRENGTH ON CUBE :

1. It is found that after 7th day test on cube the compressive strength achieved was 13.78 N/mm

2

2. It is found that after 28th day test on cube the compressive strength achieved was 22.54

N/mm2

Fig 3.1 Compression Test on Cube.

3.2 SPLIT TENSILE STRENGTH OF CYLLINDER:

1. Testing done for tensile strength for cylinder after 7th day was 3.98 N/mm

2

2. Testing done for tensile strength for cylinder after 28th day was 8.85 N/mm

2


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Fig 3.2 Split tensile test on Cylinder

4.1 WRAPPING RESULTS FOR SPECIMEN

Table 4.1 Wrapped specimen 1

GFRP SINGLE LAYER WRAPPING 'U'- PATTERN FOR BEAM 4


0 0 0

0.5 0.3 0.4

1 0.6 0.7

1.5 0.9 1

2 1.1 1.2

2.5 1.4 1.5

3 1.7 1.8

3.5 2 2.1


4.5 2.7 2.8

5 3.2 3.3

5.5 4.9 5.5

5.9(ultimate) 6.9 7.3


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Fig. 4.1 wrapped beam 4

Table 4.2 wrapped specimen 2



0 0 0

0.5 0.2 0.3

1 0.6 0.5

1.5 0.9 0.8

2 1 0.9

2.5 1.2 1

3 1.5 1.1

3.5 1.9 1.7


4.5 2.5 2.1

5 2.9 2.7

5.5 3.4 3.2

6 4.1 3.8

6.1 (ultimate) 5.8 5.2


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Fig 4.2 Wrapped beam 5

Table 4.3 wrapped specimen 3



0 0 0

0.5 0.5 0.3

1 0.8 0.5

1.5 1.1 0.8

2 1.3 1

2.5 1.5 1.2


3.5 2 1.9

4 2.3 2.1

4.5 2.5 2.3

5 2.9 2.7

5.5 3.4 3.2

6 (ultimate ) 3.9 3.5


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Fig 4.3 wrapped beam 6

Table 4.4 Comparison

BEAM FIRST CRACK LOAD ULTIMATE LOAD

Control beam 1 2.5 5.5



Beam 4 with single layer wrapping 4 5.9

Beam 5 with single layer wrapping 4 6.1

Beam 6 with single layer wrapping 3 6

5.1 CONCLUSIONS

The study on the effect of GFRP bonding with beams and working can still be a

promising work as there is always a need to strengthening of the beams.

The following conclusions could be drawn from the present investigation

1. It was found that the ultimate load of the beam wrapped with single layer of GFRP sheet

resulted in the increment by 9% by shear strengthening.

2. It was observed that the crack pattern in the beam specimen was in the vertical direction i.e the

crack progressed from the bottom towards the top of the beam .

3. The wrapped beam resisted more load than the control beams.

4. Hence, it was found that by strengthening the beam using wrapping in “U” manner increase

the strength of the beam.


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SHEAR STRNGTHENING OF RC BEAMS WITH EXTERNALLY … · 1.2.1 Glass Fiber Reinforced Polymer (GFRP):...

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