A Project Report on

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submitted in partial fulfillment

for the award of the degree of

BACHELOR OF TECHNOLOGY IN

CIVIL ENGINEERING

(2007-2011)

C.V.MADHU BALA (Y7CE224) KARCHUNG (L8CE277)

M.D.SWATHI (Y7CE251) KELZANG LHUNDUP (L8CE278)

D.THARUN (Y7CE256) PENJOR DUKPA (L8CE279)

Under The Esteemed Guidance of

Sri. P. POLU RAJU (Asst. Prof.)

DEPARTMENT OF CIVIL ENGINEERING

KONERU LAKSHMAIAH COLLEGE OF ENGINEERING

(AUTONOMOUS)

2010-2011

KONERU LAKSHMAIAH COLLEGE OF ENGINEERING!

(AUTONOMOUS)

DEPARTMENT OF CIVIL ENGINEERING

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CERTIFICATE

This is to certify that the project entitled “EXPERIMENTAL EVALUATION OF

CONCRETE BEAMS USING CFRP AND GFRP” is the bonafied work done by

D.Tharun, with Register number Y7CE256 of IV/IV B.Tech submitted to Koneru

Lakshmaiah College of Engineering (Autonomous) for the partial fulfillment of the

completion of IV/IV B.Tech course for the award of the degree of BACHELOR OF

TECHNOLOGY in CIVIL ENGINEERING during the academic year 2010 – 2011.

_____________________ _________________________ _________________________

Mr. P.POLU RAJU Asst.Prof Dr. S.SIVA SHANKAR External Examiner

Project Guide I/C – Project

______________________________

Dr. CH.HANUMANTHA RAO

Head of the Department –CE

ACKNOWLEDGEMENT

We wish to express our sincere gratitude to our esteemed guide Mr. P. POLU

RAJU, Assistant Professor in Civil Engineering Department for his valuable guidance,

significant suggestions and help in every respect to accomplish the project work. His

persisting encouragement, everlasting patience and keen interest in discussions have been

benefited us to an extent, he have been a continuous source of inspiration to us

throughout the work.

We are very thankful to Dr. CH. HANUMANTHARAO, Head of the

Department of Civil Engineering for providing us necessary facilities. We also express

our thanks to Dr. K. RAJA SEKHAR RAO, Principal of our college for the facilities

provided.

We are highly indebted to our Project In charge, Dr. A. SIVA SANKAR,

Associate Professor, Department of Civil Engineering for his continuous

encouragement in successful completion of the work.

We thank the FOSROC company, Hyderabad for giving us FRP materials for

experimental enhancing research during our final project as desired.

We also express thanks to Mr. Y. Poorna Chandra Rao, Mr. V.L. Ganesh

Babu Structures lab technicians who have extended their help whenever needed. Our

acknowledgement would remain incomplete if we do not express our gratitude to the

staff of Civil Engineering for their help throughout this project.

With the completion of this project, we would like to thank all the people

involved in this project, who made the work possible to reach our expectations. Last but

not least we would like to thank our Parents and most of all The Almighty…

Project associates…

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CONTENTS

Acknowledgement

Contents

List of figures

List of tables

Nomenclature

1. INTRODUCTION

1.1 General …………………………………………………………………1

1.2 Importance of beam…………………………………………………….2

1.3 Retrofitting……………………………………………………………...3

1.4Fiber reinforced polymer composites.......................................................4

1.5Organization of the project……………………………………………...6

2. LITERATURE REVIEW

2.1 Introduction……………………………………………………………..7

2.2 Beam……………………………………………………………………8

2.3 Retrofitting…………………………………………………………….10

2.4 Outcomes of literature review and Objective of the

project………………...........................................................................10

2.5 Scope of the

study…………………………………………………………………..11

3. CHARACTERIZATION AND TESTING OF MATERIALS

3.1 Tests On Cement

3.1.1 Cement Consistency

Test…………………………………………………………..14

3.1.2 Setting Time

Tests…………………………………………………………15

3.1.3 Specific

Gravity………………………………………….……………16

3.1.4 Compressive Strength Of

Cement…………………………….………………………...17

3.2 Tests On Fine aggregate

3.2.1 Specific Gravity

………………………………………………………………17

3.2.2 Fineness

Modulus……………………………………………..………18

3.3 Tests On Coarse aggregate

3.3.1 Specific

Gravity………………………………………………………19

3.3.2 Fineness Modulus

………………………………………………………………20

3.4 Tests On Steel

Bars…………………………………………………………………21

3.5 Material Properties Of Composite Material

3.5.1 Adhesive (Epoxy resin based putty)

Properties…………………..………………………………..24

3.5.2 Primer (Nitrowrap 25)

Properties……………………………………………………24

3.5.3 Resin (Nitrowrap 410)

Properties……………………………………………………25

3.5.4 Carbon Fiber

Properties…………………………...……………………….25

3.5.5 Glass Fiber

Properties………………………..…………………………..25

3.5.6 Quality

test…………………………………………………………...26

3.5.7 Tests On Epoxy

Resin…………………………….…………………………...26

3.5.8 Tests On

Fibers………………………………………………………...27

3.6 Tests On Concrete

3.6.1 Cube Testing………………………………………………...28

3.6.2 Non Destructive Test (Rebound

Hammer)……..……………………………………………....31

4. EXPERIMENTAL PROGRAM

4.1 Scope Of The

Experiment…………..……………………………………………...33

4.2 Introduction……………………………………………………….....33

4.3 Material Properties…………………….………………………….....36

4.4 Control Specimen (Plain Cement Concrete)………………………...38

4.5 Control Specimen (Beam Weak-In-shear)………………..…………38

4.6 Control Specimen (Beam Weak-In-Flexure)..………………………39

4.7 Control Specimen (Balanced Section RCC Beam)…….……………40

4.8 Finishing works………………………………………...……………41

4.9 Retrofitting Procedure And Methodology

4.9.1 Surface Preparation

(specimen)....…………………….………………………….42

4.9.2 Preparation Of Retrofit Test

Specimens....………………………………………………..43

4.9.3 Primer Application (Nitowrap 25)………………………....43

4.9.4 Resin Application (Nitowarp 410).....………………………43

4.9.5 FRP Fixing....……………………………………………….43

4.9.6 Cutting of FRP Mat…………………....…………………....43

4.10 Test Specimens For Retrofit

4.10.1 Retrofitted Specimen (2 No. Plain Cement

Concrete)…………………………………………………….44

4.10.2 Retrofitted Specimen (2 No. Beam Weak-In-Shear)

……………………………………………………………….46

4.10.3 Retrofitted Specimen (2 No. Beam Weak-In-Flexure)

……………………………………………………………….47

4.10.4 Retrofitted Specimen

(2 No. Under Reinforced Section beam) ……………………47

4.10.5 Finishing

Works…………………………………………………..……48

4.11 Test Set-up………………………………………..………….48

5. RESULTS AND OBSERVATIONS

5.1 Experimental

Results……………………………………………..………………..51

5.2 Failures Observed In Various Cases………………………………...52

5.3 Comparison Of Results……………………………………………...56

5.4 Observations from Results………………..…………………………61

6. SUMMARY AND CONCLUSIONS

6.1 Summary…………………………………………………………….62

6.2 Conclusion…………………………………………………………..64

APPENDIX-I (Mix Design of M30 grade Concrete)

APPENDIX-II (Design of Reinforced Beam)

REFERENCES

Table No LIST OF TABLES Page No

1.1 Fiber content in composite material 5

3.1 Compressive Strength of Cement 17

3.2 Specific Gravity Of Cement 17

3.3 Sieve Analysis Of Sand 18

3.4 Zone III Sand Upper & Lower Limit values 18

3.5 Specific Gravity Of Aggregate 19

3.6 Sieve Analysis Of Aggregate 20

3.7 Material Properties Of Steel Rebars 22

3.8 Relative Density Of Epoxy Resin 27

3.9 Cube test Results of M30 30

3.10 NDT Test Results 32

4.1 Compressive Strength Of Concrete (M30) 34

4.2 Nomenclature of the Beams 35

5.1 Results 51

Figure No. LIST OF FIGURES P.No.

3.1 Cement Test 14

3.2 Vicat Mould Set-up 15

3.3 Vicat Mould Apparatus 15

3.4 Grading Limits for Sand in Zone III 19

3.5 Grading Limits For Coarse Aggregate

(IS 383-1970) 21

3.6 Rod Cutting Machine 21

3.7 Tensile Test by UTM 22

3.8 12mm & 8mm dia bars 22

3.9 Characteristic Average Stress/Strain Curve

of 8mm dia Fe500 grade steel rebars 23

3.10 Characteristic Average Stress/Strain Curve

of 12mm dia Fe500 grade steel rebars 23

3.11 Cube Casting 29

3.12 Compressive Test for Cube 29

3.13 Gauge Reading 30

3.14 Set up Rebound Hammer 31

4.1 Showing FRP materials with group members 37

4.2 RCC under reinforced section 37

4.3 Casted PCC with cubes 37

4.4 PCC Sections 38

4.5 Casted PCC specimen for testing 38

4.6 Section showing Weak-In-Shear 39

4.7 Shear reinforcement details 39

4.8 Weak-In-Shear specimen under test 39

4.9 Section showing Weak-In-Flexure 40

4.10 Reinforcement for Weak-In-Flexure 40

4.11 Weak-In-flexure under test 40

4.12 Reinforcement Details for RCC 41

4.13 RCC Balanced Section under test (UTM) 41

4.14 Surface preparing for FRP 42

4.15 Applying Nitowrap 25 (Primer) 42

4.16 Cutting CFRP 43

4.17 Cutting GFRP 44

4.18 Fixing CFRP 44

4.19 Fixing GFRP over CFRP 44

4.20 Showing CFRP details for PCCR1 45

4.21 Under Seasoning Condition 45

4.22 fSeasoning stage for CFRP 45

4.23 Showing CFRP & GFRP Details 46

4.24 Showing GRFP Wrapping over CFRP for

Improving Shear Strength 46

4.25 Curing stage After Nitowarp M25 47

4.26 CFRP Wrapping, Weak in Flexure 47

4.27 Application of Nitowrap 410 over CFRP

Material 48

4.28 Schematic representation of loading set up 49

4.29 Universal Testing Machine (UTM) 49

4.30 Different Kinds of Failure that are observed I 50

NOMENCLATURE

Fck - Target mean strength

Fck - characteristic strength of concrete

fy - Characteristic strength of the steel

ft - Flexural Strength

OPC - Ordinary Portland cement

t - Tolerance value

s - Standard Deviation

FA - Fine Aggregate

CA - Coarse Aggregate

W/c - water-cement ratio

P – Ratio of fine aggregate to total aggregate by absolute volume

S.FA - Specific gravity of Fine Aggregate

S.CA - Specific gravity of Coarse Aggregate

Z - Section Modulus

M.R. - Moment of Resistance

B.M. - Bending Moment

Mu - Ultimate moment

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c- Shear Stress in Concrete

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v- Nominal Shear Stress

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c max - Maximum Shera Stress in Concrete with Shear Reinforcement

Pt - Percentage of Steel

Ast - Cross Sectional area of the reinforcing steel

Asv - Total cross sectional area of stirrup legs

Sv - Spacing of the Stirrups

V - Shear Force

Vu - Shear Force due to Design Loads

b- Breadth of the section

D - Over all depth of the section

d - Effective depth of the section

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CHAPTER-I

INTRODUCTION

1.1 General

Recent earthquakes in urban areas such as the 1994 Northridge, the 1995

Hanshin-Awaji (Kobe) and the 1999 Kocaeli (Turkey) have repeatedly demonstrated

the disastrous consequences and vulnerability of existing structures to seismic

deformation demands. These structures were designed and detailed for gravity loads

and lateral forces that are lower than those specified by the current codes. The

objective of the beam retrofitting is to strengthen and to eliminate chances in the

structure so as to ensure that ductile hinging in the beam that takes place of very

severe seismic demand.

Many reinforced concrete (RC) framed structures located in zones of high

seismicity in India are constructed without considering the seismic codal provisions.

The vulnerability of inadequately designed structures represents seismic risk to

occupants and this fact explains a strong social need to retrofit the existing building

and upgrade the seismic code provisions. The seismic performance of RC moment

resisting frame mainly depends on the inelastic behavior of beams, columns and

beam-column joints. A Beam is defined as the horizontal members of the structure

that are responsible for carrying all vertical loads and transmitting the loads towards

the columns and helps in strengthening flexural stiffness and ductile capacity of the

beam. Earthquake generates ground motion both in horizontal and vertical directions.

Due to the inertia of the structure the ground motion generates shear forces and

bending moments in the structural framework. In earthquake resistant design it is

important to ensure ductility in the structure, i.e. the structure should be able to

deform in elastically without causing collapse.

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1.2 Importance of Beam

Recent earthquakes tested the vulnerability of existing reinforced concrete RC

structures to strong ground motions. Beams generally carry vertical gravitational

forces but can also be used to carry horizontal loads (i.e., loads due to an earthquake

or wind). The loads carried by a beam are transferred to columns, walls, or girders,

which then transfer the force to adjacent structural compression members. In light

frame construction the joists rest on the beam. Internally, beams experience

compressive, tensile and shear stresses as a result of the loads applied to them.

Typically, under gravity loads, the original length of the beam is slightly reduced to

enclose a smaller radius arc at the top of the beam, resulting in compression, while the

same original beam length at the bottom of the beam is slightly stretched to enclose a

larger radius arc, and so is under tension.

1.3 Retrofitting

Retrofitting of existing structures has become a major part of the construction

activity in many countries. Broadly, this can be attributed to aging of the

infrastructure and increased environmental awareness in societies. Some of the

structures are damaged by environmental effects, which include corrosion of steel,

variations in temperature, freeze–thaw cycles, exposure to ultra-violet radiation and

earthquake. There are always cases of construction-related and design-related

deficiencies that need correction. Many structures, on the other hand, need

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strengthening because the allowable loads have increased, or new codes have made

the structures substandard. This last case applies mostly for seismic regions, where

new standards are more comprehensive than the old ones. The bending moments and

shear forces are maximum at the joints. Therefore, the joints need to be ductile to

efficiently dissipate the earthquake forces. Most failures in earthquake-affected

structures are observed at the joints. Joint is combination of beam and column; beam

being an important element in the framework of a structure it should be strengthened

to maintain the stability. Traditional retrofitting techniques that use steel and

cementations materials do not always offer the most appropriate solutions.

Retrofitting with fiber-reinforced polymers (FRP) to strengthen and repair damaged

structures is a relatively new technique. Extensive researches are going on in the areas

of application of FRP in concrete structures for its effectiveness in enhancing

structural performance both in terms of strength and ductility.

Retrofitting with fiber-reinforced polymers (FRP) may provide technically

superior alternative to the traditional techniques in many situations. The FRPs are

lighter, more durable and have higher strength-to-weight ratios than traditional

reinforcing materials such as steel, and can result in less labor-intensive and less

equipment-intensive retrofitting work.

Structures were originally designed according to earlier codes to withstand

only gravity loads and the impacts of earthquake are not considered. Even if it was

considered the collapse might be due to the change in hazard level in that region.

The use of fiber-reinforced polymers (FRP) composite materials for

strengthening/ retrofitting of existing structure has increased in recent years. The FRP

products can be used for structural strengthening/ retrofitting of existing building and

bridges and for construction. Strengthening/ retrofitting is required when there are

increases in the applied loads, human errors in initial construction, accident event

such as earthquakes and when a structural member losses its strength due to

deterioration over time. The cost associated with replacing the structure back in

service immediately is relatively high that strengthening/ retrofitting becomes the

most efficient solution. There are different available materials like FRP, steel,

concrete etc. for retrofitting of the structure, but use of FRP is increasing rapidly. This

is due to the fact that FRP materials have several advantages over steel and other

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materials. They are lightweight with superior strength and stiffness-to-weight ratio,

they have relatively high corrosion resistance, and FRP laminates can be easily

bonded to concrete surfaces. Typical uses of FRP in construction are as follows:

1. FRP wraps are used on columns to increase the column ductility,

2. FRP plates are bonded to the surface of concrete members (beam, slab, walls)

to improve the flexure and shear capacity of the concrete members,

3. FRP reinforcing bars and pre-stressing strands are used as an alternative to

steel reinforcing.

The use of FRP laminates for this application offers several desirable attributes, such

as resistance to corrosion, high strength, lightweight, and ease of handling. Flexure

strengthening of concrete beams is ac- accomplished by epoxy bonding the FRP

plates to the tension face for shear & flexural strengthening; the FRP plates are

bonded to the beam.

The use of FRP laminates at the beam has many practical applications in the area of

repair. These include:

1. Retrofitting of an existing structure can be expansive and time consuming.

The uses of fiber laminates present a quick and economical method to

strengthen and repair beam.

2. The fiber composites are not adversely affected by weather and salt therefore,

the composites laminate will not be subjected to problems associated with

corrosion as in the case of steel reinforcing bars.

3. The laminate can act as a protective cover at the joint by reducing the exposed

concrete surface area where moisture or salts can penetrate into the joint and

cause corrosion of reinforcing bars.

1.4 Fiber reinforced polymer composites

Embedding continuous fiber in a resin matrix, which binds the fiber

together, forms them. Carbon fiber, glass fiber etc. are the common fiber and

depending upon the fiber used FRP composites are called as glass fiber reinforced

polymer (GFRP), carbon fiber reinforced polymers (CFRP). Fibers content (% by

weight) in different FRP Composites are as follows

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Table 1.1 Fiber content in composite material

Composites Fiber content

Materials (% By weight)

GFRP laminate 50-80

CFRP laminate 65-75

Polymeric resins are used as the matrix for the FRP and bonding adhesive

between the FRP and concrete.

In the case of a frame, plastic hinges may form either in the beam or in the

column depending on their relative stiffness. If hinge is first formed in the beam then

it is a case of strong column weak beam, whereas if hinge is first formed in column, it

can be regarded as a case of weak column strong beam. However, it is desirable to

design the frame such that the plastic hinges form in the beams, and not in the

columns. This is because

1. Plastic hinge in beams have larger rotation capacities than in columns.

2. Mechanics involving beam hinges have larger energy-absorption capacity on

account of the larger number of the beam hinges (with large rotation

capacities) possible.

3. Eventually collapse of a beam generally results in a localized failure, whereas

collapse of a column may lead to a global failure

4. Column are more difficult to straighten and repair than beams, in the event of

residual deformation and damage

However due to inappropriate construction, human error factor, improper provision of

reinforcement on joint, weak column situation may exist. In the current study, effort

has been made to address the retrofitting strategies of beam. The appropriate

strategies required for each case has been studied in details through numerical

simulation.

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1.5 Organization of the Project

In chapter 2, the literature relevant to retrofitting of beam has been reviewed.

Chapter 3 deals with material properties used for casting of specimen (beam).

Chapter 4 deals with the detailed study of the experimental analysis of a under

reinforced beam & beam weak in shear and beam weak in flexure mode of failure.

Chapter 5 deals with the results and discussion for the case of a under reinforced

beam & beam weak in shear and beam weak in flexure in the beams with and without

FRP.

Chapter 6 deals with the summary and conclusions .The experimental evaluation

of load carrying capacities of both the specimens are detailed here in.

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CHAPTER - II

LITERATURE REVIEW

2.1 Introduction

Retrofitting of existing structures is one of the major challenges that modern

civil engineering structures has demonstrated that most of them will need major

repairs in the near future. Some of the structures are damaged by environmental

effects, which include corrosion of steel, variations in temperature, freeze–thaw

cycles and exposure to ultra-violet radiation. There are always cases of construction-

related and design-related deficiencies that need correction. Many structures, on the

other hand, need strengthening because the allowable loads have increased, or new

codes have made the structures substandard. This last case applies mostly for seismic

regions, where new standards are more comprehensive than the old ones.

Traditional retrofitting techniques that use steel and cementations materials do

not always offer the most appropriate solutions. Retrofitting with fiber-reinforced

polymers (FRP) to strengthen and repair damaged structures is a relatively new

technique. Extensive researches are going on in the areas of application of FRP in

concrete structures for its effectiveness in enhancing structural performance both in

terms of strength and ductility.

The use of fiber-reinforced polymers (FRP) composite materials for

strengthening/ retrofitting of existing structure has increased in recent years. The FRP

products can be used for structural strengthening/ retrofitting of existing building and

bridges and for construction. Strengthening/ retrofitting is required when there are

increases in the applied loads, human errors in initial construction, accident event

such as earthquakes and when a structural member losses its strength due to

deterioration over time. The cost associated with replacing the structure back in

service immediately is relatively high that strengthening/ retrofitting become the most

efficient solution. There are different available materials like FRP, steel, concrete etc.

for retrofitting of the structure, but use of FRP is increasing rapidly. This is due to the

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fact that FRP materials have several advantages over steel and other materials. They

are lightweight with superior strength and stiffness-to-weight ratio, they have

relatively high corrosion resistance, and FRP laminates can be easily bonded to

concrete surfaces.

The use of fiber reinforced plastic panels to strengthen and rehabilitate

concrete slabs, beams, and columns has been described in several articles in technical

reports, journals and trade magazines. A series of analytical and experimental studies

on various fiber reinforced plastic (FRP) strips and various authors have conducted

panels used to externally reinforce concrete beams. The overall objective in these

studies is to understand the structural response and interaction of the concrete and

FRP under loading condition.

2.2 Beam

Following literature has been studied and brief reviews of literature are given below.

Caltrans [1] (The California Department of Transportation) has developed

preliminary design recommendations for steel and FRP jackets, based on results of an

extensive experimental program. These studies proved the effectiveness of FRP

fabrics for the enhancement in ductility, energy dissipation, lateral load carrying

capacity, and ductile failure modes.

Beres A (1992) [2] used flat steel plates to confine the joint in an attempt to

prevent the spalling of concrete and to maintain the concrete integrity. Steel channels

were attached to the beam bottom face to prevent slip of the bars. This scheme was

found to be efficient in preventing the bars’ slippage, increasing the joint shear

strength and reducing the rate of strength deterioration.

Pellegrino et al [3] focusssed on experimental investigation on reinforced

concrete (RC) rectangular beams strengthened in shear with externally bonded U-

wrapped carbon fiber-reinforced polymer (CFRP) are presented and discussed. The

results provide some new insights into the complex failure mechanisms that

characterize the ultimate shear capacity of RC members with transverse steel

reinforcement and FRP sheets and show some mechanisms of interaction between the

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externally applied FRP sheets and the internal shear steel reinforcement with different

static schemes. This interaction is not considered in the actual code provisions but

strongly influences the efficiency of the shear strengthening rehabilitation technique

and, consequently, the calculation of the interacting contributions to the nominal shear

strength of the structural member. On the basis of the observation of the experimental

shear behavior, an analytical model, which allows the estimation of the interacting

contributions to the shear capacity of the strengthened beams, is proposed.

.

Hai H. Dinh et al [4] presented a simple model to estimate the shear strength of

steel fiber reinforced concrete (FRC) beams without stirrup reinforcement. The model

was developed based on observations from tests of 27 large-scale beams under

monotonically increased concentrated loading. Three types of hooked steel fibers

were evaluated in volume fractions ranging between 0.75% (59 kg/m3 or 100 lb/yd3)

and 1.5% (118 kg/m3 or 200 lb/yd3). All but one beam failed in shear either prior to

or after flexural yielding. In the proposed model, shear in steel FRC beams is assumed

to be resisted by shear stress carried in the compression zone and tension transferred

across diagonal cracks by steel fibers. Shear carried in the compression zone is

estimated by using the failure criterion for concrete subjected to combined

compression and shear proposed by Bresler and Pister. The contribution from fiber

reinforcement to shear strength, on the other hand, is tied to material performance

obtained through standard ASTM 1609 four-point bending tests. Comparison of

predicted versus experimental shear strengths for a large number of FRC beams tested

in this and other investigations indicate that the proposed model is capable of

predicting the shear strength of steel FRC beams with reasonable accuracy; mean and

standard deviation values of 0.79 and 0.12, respectively.

Mahmoud T. El-Mihilmy et al [5] proposed a simple and a direct approach for

analyzing and designing reinforced concrete beams strengthened with externally

bonded FRP laminates based upon equilibrium and strain compatibility was

presented. Design nomographs to facilitate implementation of the procedure were also

developed. Upper and lower limits for FRP cross-sectional area to ensure ductile

behavior of the strengthened beams were introduced. To verify the analytical

procedure, comparisons of results obtained by the section analysis with experimental

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results reported by different researchers were presented. Excellent correlation of the

predicted results with experimental results was noted.

2.3 Retrofitting

Weena P. Lokuge [6] et al proposed model formulation is based on the

experimental results reported by Candappa (2000). Although the proposed strain-

based model was developed for concrete with active con!nement, it is extended for

the case of passive con!nement using an iterative procedure.The proposed strain-

based stress–strain model is a new approach in predicting the behavior of HSC

subjected to active lateral con!nement. Proposed model can be applied to concrete

with active as well as passive con!nement. It is proven to be generally in close

agreement with the experimental test results for concrete con!ned by carbon !ber

wraps.

Mander and Priestley [7] proposed a stress-strain model for concrete

subjected to uniaxial compressive loading and confined by transverse reinforcement.

The concrete section might contain any general type of confining steel, either spiral or

circular hoops; or rectangular hoops with or without supplementary cross ties. These

cross ties might be having either equal or unequal confining stresses along each of the

transverse axes. The influence of various types of confinement was taken into account

by defining an effective lateral confining stress, which depended on the confinement

of the transverse and lateral reinforcement.

Bencardino et al. [8] provided the idea to find the moment curvature relations

for FRP wrapped sections. The equations had been developed for wrapped section

with strain compatibility method. Further, the quantitative relations of deflection,

curvature and energy ductility were presented.

Basu et al. [9] presented the overview of various aspects involved in the

seismic upgradation of buildings. They proposed the concept of seismic upgradation

based on performance bases criteria. Further, they described the seismic design

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methodology of structures and explained the various stages of seismic upgradation

such as seismic evaluation strategies, upgradation measures, verifications, etc.

Seth [10] discussed the conventional retrofit methods for retrofitting of

engineering concrete buildings in the light of the predominant failure patterns of

various structural systems in concrete and different parameters that governed the

choice of retrofit. She demonstrated the advantages and disadvantages of various

methods in terms of ductility.

Mukherjee and Joshi [11] presented a novel technique of rehabilitation of

earthquake-affected structures and retrofitting of structures against possible

earthquakes using fiber composites. They discussed about design methods, field

application techniques and their sustainability were also discussed.

The tests reported by Strickland and Hughes [12] done in a small laboratory

on plain concrete beams with CFRP laminates cemented to the bottom and sides of

these beams were tested at Wright Laboratory Pavements & Facilities Section in the

spring of 1992, and showed considerable strength enhancement over beams without

CFRP. These tests results showed bending load capacities could be increased rather

significantly by bonding CFRP panels on the tensile side of the beam. The objective

of this effort was to test evaluate the effect of environmental conditions on the

performance of concrete members strengthened by externally bonded advanced

composite materials. External bonding of very thin high-modulus, high-strength fiber

reinforced plastic panels to concrete structures has been shown to give increased

stiffness and larger load carrying capacity. Both non destructive and destructive test

methods show that laboratory CFRP/concrete beams show small detrimental effects

as a result of environmental exposure to freeze-thaw cycling and ultraviolet light. The

energy absorbing capacity of CFRP/concrete beams was increased by a factor of 50

over that of control beams, when tested statistically.

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2.4 Outcomes of literature review and Objective of the project

Various techniques have been attempted to strengthen the Beam and the

ductility of the existing structure or the ability of the structure to dissipate the energy

generated during loading (due to dead as well as live load). After reviewing of

existing literature to the possible extent, it has been observed that FRP composites

have been used extensively due to its inherent advantages like light weight, more

durable, and higher strength-to-weight ratios, less labor-intensive and less equipment-

intensive retrofitting work.

The present work is aimed to compare the performance of a control specimen

of PCC beam, RC beam -balanced, weak in flexure, weak in shear with that of a

retrofitted specimen. The following is the major objective of the present study:

! To assess the strength, ductility and damage level of RC and retrofitted beam-

with control specimen of PCC beam, RC beam -balanced, weak in flexure,

weak in shear.

2.5 Scope of the study

In order to achieve the above-mentioned objectives the following tasks have been

carried out:

! Design and reinforcement detailing study has been carried out for the plain

cement concrete beam, beam as balanced section; beam weak in shear and beam

weak in flexure.

! Experimental studies have been carried out which helps us to know the behavior

of various classes of beam.

! Increasing the ductility and enhancing the energy dissipation capacity.

! Eliminating source of weakness/those produce concentration of stresses.

!

!

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CHAPTER – III

CHARACTERIZATION AND TESTING OF MATERIALS

Preview of Materials used in the Project are the following:

Cement Sand Aggregate

TMT bars Water GFRP

CFRP Nitowrap 25/410 Carborandum

Grinder Sand paper

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3.1. Tests on Cement

3.1.1. Cement Consistency Test

For finding out initial setting time, final setting time and soundness of cement, and strength a

parameter known as standard consistency has to be used. The standard consistency of a cement

paste is defined as that consistency which will permit a Vi cat plunger having 10 mm diameter

and 50 mm length to penetrate to a depth of 33-35 mm (5mm to 7 mm) from the top of the

mould. The apparatus is called Vi cat Apparatus. This apparatus is used to find out the

percentage of water required to produce a cement paste of standard consistency. The standard

consistency of the cement paste is some time called normal consistency (CPNC). This percentage

is usually denoted as ‘P’. The test is required to be conducted in a constant temperature (27° +

2°C) and constant humidity (90%).

The consistency obtained in this test of cement 53 grade is 32 percent.

Figure 3.1: Cement Test

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Figure 3.2: Vicat mould set up

3.1.2 Setting Time Tests:

3.1.2.1. Initial Setting Time Test:

Initial setting time is regarded as the time elapsed

between the moment that the water is added to the

cement, to the time that the paste starts losing its

plasticity. The time when water is added to the

cement and the time at which the needle penetrates the

test block to a depth equal to 33-35 mm (5.0 0.5

mm) from the top is taken as initial setting time.

Fig 3.3: Vicat mould apparatus

In this test, initial setting time of cement 53 grade is 45 minutes.

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3.1.2.2. Final Setting Time Test

The final setting time is the time elapsed between the moment the water is added to the cement,

and the time when the paste has completely lost its plasticity and has attained sufficient firmness

to resist certain definite pressure. This time should not be more than 10 hours. The paste attains

such hardness that the centre needle does not pierce through the paste more than 0.5 mm.

3.1.3. Specific Gravity

The specific gravity of the hydraulic cement has been found as per IS: 4031(part 11): 1988 using

le Chatelier Flask.

The following observations have been recorded.

Initial reading of le Chatelier Flask =0.5

Final reading le Chatelier Flask =21

Weight of cement taken 64 gms

Specific gravity of cement = 64/ (21-0.5) = 3.12

3.1.4. Compressive Strength of Cement

Compressive strength of the cement has been found as per IS 4031(part 6) 1988.The average

compressive strength of cement was obtained by testing the mortar cubes on 3rd

, 7th and 21st day.

The cement used satisfied the compressive strength a requirement according to IS 8112:1989.

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Table No. 3.1: Compressive strength of cement

Compressive strength (MPa) No of days

According to IS 8112:1989 Test Results

3 27 27.31

7 37 37.36

28 53 54.3

3.2. Tests on Sand

3.2.1. Specific Gravity

Specific gravity of the sand using the pycnometer as per IS 2386(part 3)-1963. The measured

values are shown in Table3.2. The specific gravity of sand is calculated as

Table No.e 3.2: Specific gravity of sand

Sl.no Description Weight (gms)

1 Empty Pycnometer (W1) 620

2 Pycnometer +3/4

th sand

(W2) 1465

3 Pycnometer + 3/4

th sand +

1/4th

water (W3) 1990

4 Pycnometer + water 1470

Specific Gravity = (W2-W1)/((W4-W1)-(W3-W2)) and is found to be 2.6

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3.2.2. Fineness Modulus

The fineness modulus of sand has been calculated as per IS: 383-1970. The percentage weight

retained in the sieves is shown in the Table no.3.3. The amount of sand taken is 1000gm.

Fineness modulus of aggregate is calculated as the percentage of the sum of cumulative

weight of sand retained in the sieves and found to be 2.33.

Table No.3.3: Sieve Analysis of Sand

Sl.

No Sieve Size

Wt.

retained

%

retained

Cumulative

retained % finer

Zone

Remark

1 4.75 mm 0 0 0 100

2 2.36 mm 43 4.3 4.3 95.7

3 1.18 58 5.8 10.1 89.9

4 600 285 28.5 38.6 61.4

5 300 414 41.4 80 20

6 150 200 20 100 0

Zone III

Table No.3.4: Zone – II sand upper and lower limit values

Sieve Size(mm) 0.15 0.3 0.6 1.18 2.36 4.75

% finer(test

value) 0 20 61.4 89.9 95.7 100

Std. lower limit 0 12 60 75 85 95

Std. upper limit 10 40 79 100 100 100

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Fig3.4: Grading limits for sand in zone – III

3.3. Test on Coarse aggregate:

3.3.1. Specific Gravity

Specific gravity of the aggregate has been found using the cylinder as per IS 2386(part 3)-1963.

Table No. 3.5: Specific gravity of aggregate

Sl.no Description Weight (gm)

1 Empty Cylinder (W1) 3972

2 Cylinder +2/3rd

aggregate (W2) 6740

3 Cylinder + 2/3rd

aggregate + water (W3) 8790

4 Cylinder + water 6990

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The specific gravity of aggregate is calculated as :

Specific Gravity = (W2-W1)/((W4-W1)-(W3-W2)) and is found to be 2.85

3.3.2. Fineness Modulus

The fineness modulus of aggregate has been calculated as per IS: 383-1970. The percentage

weight retained in the sieves is shown in Table no.3.6. The amount of aggregate taken is 2000

gms. The fineness modulus of aggregate is calculated as the percentage of the sum of the

cumulative weight of sand retained in the sieves and found to be 6.77.

Table No.3.6: Sieve Analysis of aggregate

S. No Sieve Size Wt. Retained % Retained Cumulative

Retained % Finer

1 80 mm 0 0 0 100

2 40 mm 0 0 0 100

3 20 mm 60 3 3 97

4 12.5 mm 120 6 9 91

5 10 mm 1080 54 66 34

6 4.75 mm 739 36.95 99.95 0.05

7 2.36 mm 0 0 99.95 0.05

8 1.18 mm 0 0 99.95 0.05

9 600 microns 0 0 99.95 0.05

10 300 microns 0 0 99.95 0.05

11 150 microns 1 0.05 100 0

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Fig 3.5: Grading limits for coarse aggregate IS: 383- 1970

3.4. Tests on Steel bars

The steel Fe500 supplied by TISCON were tested by using

UTM (Universal Testing Machine) properties like yield

stress ultimate stress, elongation, and reduction in area of

steel bars were found for 12mm and 8mm diameter steel

bars.

Fig. 3.6: Rod cutting machine

All the steel rebars used in the experiments were obtained from the same batch.12 mm and 8mm

diameter steel bars were used as longitudinal reinforcement in beam of the specimen. 6mm

diameter bars were used as transverse reinforcement in the form of closed rectangular hoops in

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specimen. Three rebars of 450 mm with gauge length 150 mm of each diameter of steel

as per IS 432(part 1): 1982 and IS 1608:1995.All test specimens failed in the middle portion with

formation of neck. The material properties of the specimens are shown in the Table no.3.7

The average stress/strain curves of 8 mm, 12 mm bars are shown in fig 3.7 and fig 3.8

respectively. The yield stress is calculated by 0.2% strain offset method.

Fig 3.7: Tensile test by UTM Fig 3.8: 12 mm and 8 mm dia bar

Table No.3.7: Material Properties of Steel Rebars

Sl.

No

Diameter of

the Rebar

(mm)

Yield

Stress

(MPa)

Ultimate

Stress

(MPa)

Young’s

Modulus

(MPa)

Elongation

(%)

%Reduction

in Area

1 12 565 745 2e+5 18.47 60.64

2 8 540 725 2e+5 16.3 71

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Fig 3.9: Characteristic Average Stress/Strain Curve of 8 mm Dia Fe500 Grade Steel Rebars

Fig 3.10: Characteristic Average Stress/Strain Curve of 12 mm Dia Fe500 Grade Steel

Rebars.

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3.5. Material properties of composite materials

3.5.1. Adhesive (Epoxy resin based putty) properties

Nitocote VF is a thixotropic, solvent free, three-component compound based on

epoxy resins, graded fillers and thixotropic agents. It is applied directly to concrete

for filling cracks, blow holes etc., which cures to a surface ready for subsequent

coatings. For filling blow holes, making good slightly damaged concrete, eliminating

minor irregularities on floors and walls prior to applying primer and resin coatings.

Density: 1.6g/cc

Volume solids: 100%

Minimum application temperature: 10 C

Compressive strength: 50

Pot life: 40 min at 27 C

Drying time: 8 hrs at 27 C

Recoatable: 24 hours

Full cure: 7 days at 27 C

Flash point: 40 C

Shelf life: 12 months in unopened container when stored under normal warehouse

conditions.

3.5.2. Primer (Nitowrap 25) properties

Nitowrap 25 is solvent free, two component compound based on epoxy sealer cum

primer.

Density - 1.14 g/cc

Pot life - 25 min. @ 27 C

Full cure - 7 days

Flashpoint 25 C

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3.5.3. Resin (Nitowrap 410) properties

Niotwrap 410 is solvent free, two component compound based on a high build epoxy

which is used as resin.

Viscosity – Thixotropic

Colour - Pale yellow to amber

Application temperature - 15 C - 40 C

Density - 1.25 - 1.26 g/cc

Pot Life - 2 hours at 30 C

Cure time - 5 days at 30 C

Flash Point - 33 C

3.5.4. Carbon fiber properties

Fibre orientation – Unidirectional

Weight of fibre - 200

Density of fibre - 1.80

Fibre thickness - 0.30

Ultimate elongation (%) - 1.5

Tensile strength - 3500

Tensile modulus - 285 x103

3.5.5. Glass fiber properties

Weight of fibre 920

Density of fibre 2.6

Fibre thickness 0.36

Fibre orientation 90

Nominal thickness per layer 0.36

Tensile strength 3400

Tensile modulus 73,000

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3.4.6. Quality Test

The range of quality test on FRP materials are conducted such as

1. Pressure test

2. Elongation test

3. Hydraulic pressure test

4. Glass to resin ration test

5. Spark test

6. Tensile test

7. Acetone test

8. Specific gravity test

9. Weight accuracy test

10. Dimensional accuracy

11. Tensile strength test

12. Leak proof testing

13. Flawless welding test

3.5.7. Test on Epoxy Resin

Characterization of resin, reinforcement and GFRP composite are essential for the

analytical study and to ensure the quality of the resin and reinforcement used for

retrofitting. Epoxy compatible glass fiber fabric WRM with area density of

360gsm is used as reinforcement. The following test is conducted on the epoxy

resin as per Bureau of Indian standards (BIS), British Standards (BS) and

International Standards Organization (ISO).

3.5.7.1. Specific Gravity (!e)

Specific gravity (!e) of the epoxy resin was calculated using the pycnometer as per

IS 6746:1994. The room temperature during the test was 33.10C and hence the

temperature correction was applied. The measured values are shown in Table 3.8.

The relative density of the epoxy resin at 33.10C is 1.159. The temperature of

6.10C was more than the specified temperature of 27

0C. A correction factor of

0.00065 per degree should be added to the value of the relative density obtained at

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the test temperature. The relative density of the epoxy resin with the correction is

1.164

Table No. 3.8 Relative Density of Epoxy Resin

SL. No. Description Weight (g)

1 Empty Pycnometer (B) 33.1

2 Pycnometer + Water (C) 82.7

3 Pycnometer + Resin (A) 91.6

3.5.7.2. Gel time

The epoxy resin and hardener was mixed thoroughly as per the IS 6746-1994 in

the ratio of 1:0.1 by weight for finding the gel time. The epoxy resin in glass

container was kept below the plunger of the gel timer. The gel timer was

switched on as soon as the hardener was added to the resin. The time was counted

till the movement of the plunger stopped and was noted as the gel time.

3.5.8 Tests on Fibers

3.5.8.1. Tensile Test of GFRP Composites

The tensile strength of the GFRP composite was determined as per procedures

given in standard BS 2782-Part 10-Method 1003-1997 along the wrap (00), weft

(900) and forty five degree (45

0) directions. The testing of GFRP composite is

done in Universal testing machine. The shear strength and shear modulus of the

GFRP composites was determined from the specimens with fibers oriented at

ninety-degree (900) direction under tension. Glass fiber fabric tabs were bonded at

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the ends of specimens per the BS 2782-Part 10-Mwthod 1003-1997. Strain along

longitudinal and transverse direction was measured using linear electrical

resistance strain gauges. Test specimen failed due to the rupture of fabric near the

grips. The GFRP composite materials were brought in two batches. The tensile

strength of GFRP composite of batch (1) along the wrap (00), weft (90

0) and forty

five (450) directions are provided by the competent companies.

3.5.8.2. Tensile Test of CFRP Composites

The tensile strength of the CFRP composite was determined as per procedures

given in standard BS 2782-Part 10-Method 1003-1997 along the wrap (00), weft

(900) directions. The testing of CFRP composite is done in Universal testing

machine. The shear strength and shear modulus of the CFRP composites was

determined from the specimens with fibers oriented at Zero degree (00) direction

under tension. Carbon fiber fabric tabs were bonded at the ends of specimens per

the BS 2782-Part 10-Mwthod 1003-1997. Strain along longitudinal and transverse

direction was measured using linear electrical resistance strain gauges. Test

specimen failed due to the rupture of fabric near the grips. The CFRP composite

materials were brought in two batches. The tensile strength of CFRP composite of

batch (1) along the wrap (00), weft (90

0) is provided by the competent companies.

3.6. Tests on Concrete

3.6.1 Cube test

Two cube specimens from each batch of concrete mixed were tested to acquaint

strength and to maintain consistency in quality in each mix as designated below for

M30 concrete. Total of sixteen cubes of 150mm 150mm 150mm have been casted.

Two cubes from each mix batch have been tested and the average compressive

strength on 3rd

, 7th

and 28th

day of casting has been calculated. The average

compressive strength of concrete in the trial mix design is shown in table 3.8.The mix

1:1:2.2, having an average mean strength 39mpa has been used in casting.

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Fig.3.11: Cube Casting

Fig.3.12:Compressive Test for Cube

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Fig.3.13: Gauge Reading

Table No. 3.9: Cube Test Results of M30

Average compressive strength at (MPa)

Sample

Mix Ratio

w/c 3rd

day 7th

day 28th

day

S1 1:1:2.2 0.4 20 27 48

S2 1:1:2.2 0.4 21 26 52

S3 1:1:2.2 0.4 17 28 45

S4 1:1:2.2 0.4 19 29 42

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3.6.2. Non destructive Test (Rebound Hammer)

This category of products comprises the range of instruments utilized to evaluate

construction material strength. The range of instruments is typically considered to be

two parts. The first are non-destructive field tests of compressive strength. The second

are tensile field tester systems to either determine the tensile strength of an overlay or

bond material, or tensile strength of anchors embedded in the concrete. The first

group is pure Non-Destructive Testing where the strength of the material is

determined by correlation to another parameter more easily available and readily

apparent. This is typically the hardness of the concrete or the resistance to penetration

by either a pin or probe. The Windsor Probe, Windsor Pin and our line of Rebound

Hammers all fall within this category. These are widely used standard tests and as

such have seen use throughout the world. The second set of instruments is our

concrete tensile testers. These have been optimized to both test the strength of the

anchors and repair overlay material. They can be used to test until failure or to simply

verify that the material will not be affected by a specific amount of force. A number

of considerations were taken into account when designing this line of products

includes viscous damping of the resultant failure backlash, portability, and

ruggedness.

Fig 3.14: Set up rebound hammer

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Table No. 3.10: NDT test result as tabulated below

Sl. no. Particular NDT value n/mm2

1 Plain cement concrete (PCC) 44

2 Reinforced concrete (RCC) 52

3 Weak in Flexure (WF) 51

4 Weak in shear (WS) 50

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CHAPTER - IV

EXPERIMENTAL PROGRAM

4.1. Scope of the Experiment

“ To develop economical and practical method to upgrade beam’s loading capacity

and to delay or to eliminate brittle failure mode within the structure ”.

4.2. Introduction

The experimental study represented here in was carried out at the Structural

Laboratory, Civil Engineering Department, K L University, Vaddeswaram, Andhra

Pradesh, India.

The test program consisted of casting and testing of sixteen (16) beams, using M30

grade of concrete and Fe 500 (TMT) grade steel. Ordinary Portland cement, natural

river sand and the crushed aggregates of 10 mm and 20 mm maximum sizes were

used.

I. Four (4) were control beams, all having size of 150 x 150 x 700 mm length

and designed as the Plain Cement Concrete section.

II. Four (4) were designed as Under reinforced, reinforced with 2-12mm diameter

at bottom, 2–8mm diameter at top using 6mm diameter stirrups @ 90 mm c/c

III. Four (4) were designed as weak-in-shear, reinforced with 2-12 mm diameter at

bottom, and reduced 50% of shear stirrups @ 150mm c/c

IV. Four (4) were designed as weak-in-flexure, reinforced with reduction of 70%

main bottom steel and shear stirrups maintaining same as Under reinforced.

The elastic modulus of the concrete is 2.4 x 104 N/mm

2. After 3 day curing, 7 days

curing and 28-days curing, companion cubes (150 x 150 x 150 mm) casted along with

the beams were tested in compression to determine the 3 day, 7 day and 28-day

compressive strength and modulus of elasticity.

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Table No.4.1: Compressive Strength of Concrete

Sl.No Cubes

(150x150x150)

3 days

Strength(N/mm2)

7 days

Strength(N/mm2)

28 days

Strength

(N/mm2)

Remarks

1. Specimen 19 26.6 39.02 Satisfied

We experimented two beams each from control specimen PCC, Under reinforced and

Weak in flexure bonded with CFRP fabric in single layer from tension face, which is

parallel to beam axis subjected to static loading.

For two beams Weak-in-shear was bonded with CFRP fabric in single layer, parallel

to beam axis from the tension face subjected to static loading and bonded with GFRP

strips of 5 cm wide with 85 cm c/c of two pieces each at the two ends, where shear is

maximum under loading condition. Sample were tested under virgin condition and

tested until failure.

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The details of test beams & nomenclature are presented below:

Table No. 4.2: Nomenclature of Beam

Sl. No Specimen

Designation

No. of

Specimens Remarks

A PCC 4 Control PCC A

1 PCC1 2 Control Specimen

2 PCC2

3 PCCR1 2 Retrofitted Specimen

4 PCCR2

B RCC 4 Control RCC balance section B

5 RCC1 2 Control Specimen

6 RCC2

7 RCCR1 2 Retrofitted Specimen

8 RCCR2

C WS 4 Control Beam Weak in Shear C

9 WS1 2 Control Specimen

10 WS2

11 WSR1 2 Retrofitted Specimen

12 WSR2

D WF 4 Control Weak in Flexure D

13 WF1 2 Control Specimen

14 WF2

15 WFR1 2 Retrofitted Specimen

16 WFR2

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4.3. Material Properties

Similar concrete mix of M30 grade was used for all beams. The proportions in the

concrete mix were 1.0 (cement) : 1.0 (sand) : 2.2 (gravel) by weight. The

water/cement ratio was 0.4 and type I Portland cement was used. The average

compressive strength was determined from concrete cubes tested after 28 days of

curing and given in Table 4.1. The average yield stress of main steel bars used in all

experiments was 500 MPa and an elastic modulus of 200 GPa. One type of FRP sheet

was used during the tests: a bidirectional CFRP with the fibers oriented in both

longitudinal and transverse directions.

The fiber-composite material consisted of glass bonded together with an epoxy

matrix. The sheet was subjected to longitudinal tensile tests to determine elastic

modulus and ultimate strength. The CFRP exhibited a linear elastic behavior up to

failure. The method of testing utilized to determine the properties of CFRP sheets was

performed according to ASTM D 3039-76 to evaluate the tensile properties of

oriented fiber composites. The test results gave an average ultimate strength of 600

MPa and elastic modulus of 30 GPa for the CFRP sheets. The construction epoxy

adhesive used in bonding the GFRP sheets to the surface of the beam was of two-

component cold-curing type. The ultimate tensile strength of the adhesive was about

25 MPa and the elastic modulus was 8.5 GPa.

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Fig.4.1 Showing FRP materials with group members.

As per the mix design of M30 grade concrete and Fe500 grade steel (TMT) re-bars,

we scheduled to cast each specimen of 4 beams, for Control PCC, RCC Under

reinforced, Weak in shear and Weak in Flexure, out of which we used 2 each

specimen for control testing and 2 for retrofitting. The mix proportion achieved was

1:1:2.2 (1 part of cement, 1 part of natural sand and 2.2 of crushed aggregates).

During casting we followed weigh batching method so as to curtail unnecessary

hindrance and poor quality. After the 28 days curing period we have kept them under

natural conditions until the test periods in the lab.

Fig.4.2. RCC Under reinforced Fig.4.3. Casted PCC with cubes

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4.4. Control Specimen (Plain Cement Concrete)

The dimensions of two numbers control PCC specimen cast for testing was 150mm x

150mm x 700mm, and it was designed for M30 grade concrete and casted with utmost

care through proper workability. The curing was given for best soaked in portable

water for 258 days then kept in natural atmospheric condition until the test was

conducted.

700

L- Section

PLAIN CEMENT CONCRETE

150

C-section

15

0

Fig.4.4 PCC Sections

Fig.4.5. Casted PCC specimen for testing

4.5 Control Specimen (Beam weak in shear)

We have casted two numbers of beams weak in shear with its dimension of

control specimen cast for testing was 150mm x 150mm x 700mm, and adequately

designed as per the IS code 456, provision. The overall dimension of beam

specimen is shown below. Three number of 10 mm diameter Fe500 bar have been

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used as main reinforcement in beam, with 2-6mm diameter bars as hanging bar on

top with 4 numbers of 6mm diameter stirrups, reducing 50% of the Under

reinforced.

700

L- Section

CONTROL SPECIMEN - WEAK IN SHEAR

150

C-section

Hanger 2-6mm

2-12mm dia

stirrup-6mm @208mm c/c

150

Fig.4.6. Section showing Weak in Shear

Fig.4.7 Shear reinforcement details Fig.4.8 Weak in shear specimen under test

4.6. Control Specimen (Beam weak in Flexure)

The design and casting for the beams weak-in-flexure were executed for two numbers

of beams with it ruling dimensions as 150mm x 150mm x 700m. It was designed

based on IS 1026, 1982 and IS 456 codes with a provision of 2 numbers of 12mm

diameter from the tension face and 2 numbers at 6 mm diameter on top as hanging

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bars, with the reduction of 70% of the Under reinforced. The stirrup provided remains

unchanged in under reinforced.

700

150

L-Section

CONTROL SPECIMEN - WEAK IN FLEXURE

150C-section

stirrup-6mm @90mm c/c

Hanger 2-6mm

3 - 10mm dia

Fig.4.9. Section Showing Specimen Weak in Flexure

Fig.4.10 Reinforcement for Weak in Flexure Fig.4.11 Weak in Flexure under test

4.7. Control Specimen (Under reinforced RCC beam)

Beams for Under reinforced were designed by using IS 456 code provision

with M30 grade of concrete for two beams. It was calculated that the three numbers of

12mm diameter bars and stirrups of eight numbers provided @ 90mm c/c of Fe500

(TMT) bars. The casting was done with utmost care so as to achieve its good

workability and proper compaction was also given to eliminate the air voids in the

concrete mass. Thorough curing by soaking in portable water for 28 days was

genuinely provided for gaining the required

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strength.

700

15

0

L- Section

RCC BALANCE SECTION

150

C-section

stirrup-6mm @90mm c/c

Hanger 2-6mm dia

2nos -12mm dia

Fig.4.12. Reinforcement Details for RCC

Fig.4.13. RCC under reinforced Section under Test (UTM)

4.8. Finishing Works

For the control specimen we tried to give good finishing during casting after that we

have done white washing so as to clearly identify the hair cracks development at

cracking loads during the time of testing.

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4.9. Retrofitting procedure and methodology

4.9.1. Surface Preparation (specimen)

As per recommendations of retrofitting work to get strengthening of structural

elements, Surface preparation is an important task in our experimental work. This task

was done with the help of grinding machine (To avoid undulation on surface of

specimen), Emery cloth, Carborandum stone (for smooth surface), Blower machine

(cleaning the dust).

4.9.2. Preparation of Retrofit Test Specimens

The CFRP sheets were bonded to the tension face of the specimens after 28 days of

casting. Before applying the epoxy, the concrete surface was smoothened and cleaned

to insure a good bond between the epoxy glue and the concrete surface. The epoxy

was hand-mixed and hand-applied at an approximate thickness of about 1 mm. The

bond thickness was not specifically controlled, but the excess epoxy was squeezed out

along the edges of the sheet, assuming complete epoxy coverage. More details about

the methodology utilized to fix the CFRP sheets to the different beams are discussed

in chapter.

Fig.4.14. Surface preparing for FRP Fig.4.15. Applying Nitowrap 25 (Primer)

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4.9.3. Primer Application (Nitowrap 25)

As mentioned above after surface preparation, Primer coat (Nitowrap 25) has been

applied on surface thickness of 100!, for bonding with concrete and fibers, then it

was left for at least 24 hours to get set. We allowed no disturbances to the prepared

areas after the application of primer.

4.9.4. Resin Application (Nitowrap 410)

Resin has been applied on primer coat after 24 hours, prior to fixing the fibers at

recommended areas on prepared bottom surface of beams. Beam, then allowed for 30

minutes to achieve sufficient hardness to attract the newly cut CFRP materials for

proper bonding.

4.9.5. FRP Fixing

As mentioned above after applying resin coat immediately fix the FRP as per

dimensions, after a minimum of 30min again resin coat has been applied on to

maintain composite of Fibers

4.9.6. Cutting of FRP Mat

Fig.4.16. Cutting CFRP

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Fig4.17. Cutting GFRP (white)

Fig.4.18. Fixing CFRP Fig.4.19. Fixing GFRP over CFRP

4.10. Test Specimen for Retrofitting

4.10.1. Retrofitted Specimen (2 Nos. Plain Cement Concrete)

Similarly, the dimensions of retrofitted PCC specimen cast for testing was 150mm x

150mm x 700mm, and it was designed for M30 grade concrete and casted with utmost

care through proper workability. The curing was given for best soaked in portable

water for 28 days and then kept in natural atmospheric condition until the test was

conducted. Proper specification and design data from IS code: 10262, 1982.

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700

Longitudinalview with CFRP

150

C-section

500

Single layer CFRP wrapping

50

Single layer CFRP

wrapping

50

100 100

15

0

Fig.4.20. Showing CFRP Details For PCCR1

Fig.4.21. Under seasoning Condition for Nitowrap 25

Fig.4.22. Seasoning Stage for CFRP

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4.10.2. Retrofitted Specimen (2 Nos. Beam weak in shear)

We have cast beams weak in shear with its dimension as 150mm x 150mm x 700mm,

and adequately designed as per the IS code 456, provision. The overall dimension of

beam specimen is shown below. Three number of 12 mm diameter Fe500 bar have

been used as main reinforcement in beam, with 2-8mm diameter bas as hanging bar

on top with 4 numbers of 6mm diameter stirrups, reducing 50% of the Under

reinforced. Workability and curing was given top priority so as to gain its desired

strength.

500

GFRP Strip

650

700

Longitudinal view with CFRP

C-section

50

100 100

50

CFRP size for one beam

250

50

50

150

GFRP Strip all around

CFRP Wrapping

500

85230

Fig.4.23. Showing CFRP & GFRP Details

Fig.4.24. Showing GFRP Wrapping over CFRP for Improving Shear Strength

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4.10.3. Retrofitted Specimen (2Nos. Beam weak in Flexure)

The design and casting for the beams weak in flexure was executed for beams with it

ruling dimensions as 150mm x 150mm x 700m. It was designed based on IS 1026,

1982 and IS 456 codes with a provision of 2 numbers of 12mm diameter from the

tension face and 2 numbers of 8 mm diameter on top as hanging bars, with the

reduction of 70% of the Under reinforced. The stirrups provided remain unchanged as

under reinforced. Curing of 28 days soaked in clean water was also given after that it

was kept in natural atmospheric condition until test time. Sample shown below.

Fig.4.25.Curing Stage After Nitowarp 25 Fig.4.26.CFRP Wrapping, Weak in Flexure

4.10.4. Retrofitted Specimen (2Nos. under reinforced beam)

Beams for balanced section were designed by using IS 456 code provision with M30

grade of concrete. It was calculated that the three numbers of 12mm diameter bars and

stirrups of eight numbers provided @ 90mm c/c of Fe500 (TMT) bars. The casting

was done with utmost care so as to achieve its good workability and proper

compaction was given to eliminate the air voids in the concrete mass. Thorough

curing by soaking in portable water for 28 days was genuinely provided for gaining

the required strength.

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Fig.4.27. Application of Nitowrap 410 over CFRP Wrapping

4.10.5. Finishing Works

Once the retrofitting work is completed it was allowed for seasoning 7 days under the

natural atmospheric conditions and finally painted with white wash for those empty

surfaces especially two sides, so that we could see the hair cracks development very

clearly during testing. We have also noted the first cracking loads and the ultimate

loads that the specimen could carry under sustained loading condition.

4.11. Test Set-Up

The specimens were tested by using the Beam Testing machine (BTM) which has the

loading capacity of 15 tonnes by keeping the beam in the horizontal position with two

loading system of 20 cm internal loading distance and hinges at a distance of 5 cm

from the end support as shown in Fig.4.28. The standard testing machine was used for

testing of control specimen of Plain Cement Concrete. Then the Beam Testing

Machine was found not supporting to our desired strength then we have shifted to

Universal Testing Machine (UTM) for testing the remaining specimen as desired.

The sustained loading was applied from top of the beams until we could identify the

hair cracks and we have noted down the first cracking loads, further the loading is

continued until we get the ultimate load that the steel in tension face can take no more

up coming loads and transfers it to the concrete section ultimately.

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Fig.4.28 Schematic Representation of Loading setup

!

Fig.4.29 Universal Testing Machine (UTM)

Photograph of Test Set-Up

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Fig.4.30. Different kinds of failure that are observed in retrofitted concrete

beams

(a) Steel yield and FRP rupture; (b) Concrete compression failure; (c) Shear

failure; (d) De-bond of layer along rebar; (e) De-lamination of FRP plate; (f)

Peeling due to shear crack

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CHAPTER - 5

RESULTS AND OBSERVATIONS

5.1. Experimental Results:

Table No. 5.1: Results

Sl.

No

Beam

Designation

Designed Load

(KN)

Cracking

Load

(KN)

Ultimate

Failure Load

(KN)

% Increase in

Strength

1. PCC1 10.78

0 11.35 317.9

(Ultimate

Failure Load)

2. PCC2 0 10.9

3. PCCR1 31 48

4. PCCR2 28 45

5. RCC1 47.65

48 90 162.5

(Cracking

load)

6. RCC2 49 75

7. RCCR1 85 150*

8. RCCR2 125 150*

9. WS1 29.2

30 75 250.7

(Cracking

load)

10. WS2 37 90

11. WSR1 135 190*

12. WSR2 100 150*

13. WF1 31.79

37.5 75 111.6

(Cracking

load)

14. WF2 40 75

15. WFR1 100 145*

16. WFR2 64 125*

*Note: Ultimate load capacity of the beam is greater than the given value.

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5.2. Failures observed in various cases:

Fig 5.1(a): PCC Controlled beam

Fig 5.1(b): PCC retrofitted beam

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Fig 5.2 (a): RCC Under Reinforced beam

Fig 5.2(b): RCC Retrofitted beam

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Fig 5.3(a): RCC beam weak in flexure-controlled beam

Fig 5.3(b): RCC beam weak in flexure-retrofitted beam

Fig 5.3(c): RCC beam weak in flexure-retrofitted beam

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Fig 5.4(a): RCC beam weak in shear-controlled beam

Fig 5.5(b):RCC beam weak in shear-retrofitted beam

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5.3. Comparison of results:

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5.4. Observations from Results:

1. PCC

! PCC beams under go pure bending at an average load of 11.125 KN for the design

load of 10.78 KN, where as PCCR under go pure bending at an average value of

46.5 KN.

! In PCCR, due to de-lamination of FRP failure load was observed at 28 KN.

Widening of crack was observed up to 3-4 mm till 37 KN applied load.

2.RCC

! In RCC beam, as steel is introduced failure was in the tension zone i.e., at the

bottom zone. Cracking load was observed to be 40KN for the design load of 47.65

KN.

! In RCCR, failure was observed in tension zone itself only but observed at the

cracking load of 105 KN. Cracks got widened at a load of 150 KN.

3. Beam Weak-In-Shear

! In beam weak in shear (WS) cracking was observed at an average load of 33.5

KN for the design load of 29.2 KN. Diagonal cracks were observed at the

supports of the beam which shows that it failed in shear.

! In WSR, Failure started at an average load of 117.5 KN.

! Due to de – lamination of FRP, failure sound was observed. Cracks got widened

at 177.5 KN. Cracks were observed widened up to 2-3mm. Then spalling of

concrete took place.

4. Beam Weak –In-Flexure

! In beam weak in flexure (WF) cracking was observed at an average load of 39

KN for the design load of 75 KN. Flexural cracks were observed. In WFR, the

cracking load of 82 KN.

! Due to de-lamination of FRP, failure sound was observed after the application of

cracking load. Later on spalling of concrete also took place at load of 125 KN.

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CHAPTER - VI

SUMMARY AND CONCLUSIONS

6.1. Summary

In the present study, for better understanding the performance of Beam model

behavior we have taken the following steps:

• A beam model of 150 X 150 X 700 mm was considered.

• M 30 grade concrete and Fe 500 steel were used.

• FRP materials named Nitowrap 25, Nitowrap 410, CFRP and GFRP were

acquired.

• Tests for the materials used were conducted and results were used for designing.

• Four controlled specimens of PCC, RCC balanced, Weak-In-shear and Weak-In-

Flexure were casted and four retrofitted specimens of corresponding types were

prepared.

• Tests with the help of UTM were conducted and load carrying capacities of all the

specimens were taken after the period of curing.

• Finally, comparative study was carried out between controlled and retrofitted

specimens from the results and observations.

• Graphical representation of the comparative study is shown.

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Therefore, percentage increase in cracking load and ultimate load are considered.

They are

CRACKING LOAD:

PCC: Percentage increase in Load 447.05% i.e, 5.47 times than controlled beam

RCC: Percentage increase in Load 162.5% i.e, 2.62 times than controlled beam

WS: Percentage increase in Load 250.7% i.e, 3.51 times than controlled beam

WF: Percentage increase in Load 111.6% i.e, 2.12 times than controlled beam

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6.2. CONCLUSION

In the present study, four-point bending test was conducted in the laboratory on four

specimens, viz. control specimen of PCC beam, RC beam -balanced, weak in flexure,

weak in shear with that of a retrofitted specimen.

Based on the experimental and numerical results, the following conclusions are drawn.

1. Effective procedure of wrapping enhances the strength considerably including the

change of failure mode as well as the change the location of failure plain.

2. Retrofitting for shear may enhance the ductility to a considerable extent due to

additional confinement effect.

3. By adopting appropriate methodology, retrofitting a plain concrete structure, having

no steel at all exhibits enhanced strength in line with theoretical estimation.

4. Flexural retrofitting also increases the shear strength of concrete and could be shown

in terms of equivalent percentage of mild steel.

5. The beam Weak-In-shear exhibited greater cracking load compared to all the other

specimens.

6. The beams failure mode was as expected i.e., beam Weak-In-Flexure produced

flexural mode of failure, beam Weak-In-Shear produced shear mode of failure, PCC

beam admitted pure bending starting with the flexural cracks, and RCC balanced

section also exhibited flexural cracks.

7. Therefore modes of failure that were observed significantly were FRP rupture, shear

failure, de-bond of layer along rebar, de-lamination of FRP plate and peeling due to

shear crack.

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APPENDIX-I

Mix Design Of M30: -

(1) Design stipulations:

a) Characteristic strength Fck = 30 N/mm2

b) Maximum size of aggregate = 20mm

c) Degree of workability = 0.90

d) Degree of Quality control = Good

e) Type of Exposure = mild

(2) Test Data for Materials:

a) Cement used = OPC

b) Specific gravity of cement = 3.15

c) Specific gravity of

(i) Coarse aggregate = 2.6

(ii) Fine aggregate = 2.6

d) Water absorption

(i) Coarse aggregate = 0.5%

(ii) Fine aggregate = 1.0%

e) Free Surface Moisture

(i) Coarse aggregate = Nil

(ii) Fine aggregate = 2.0%

f) Sieve Analysis

(3) Target mean strength of concrete:

Fck = fck + t(s)

! 30 + 1.65*6 = 39.9 N\mm2

(4) Selection of water cement ratio = 0.375

(5) Selection of water & sand content

(i) Water content = 186 Kg/m3

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(ii) Sand content = 35%

(6) Adjustment Of Values In Water Content & Sand Percentages For Other Condition

Adjustments

Change in condition Adjustment required

Water content Sand content

For decreasing water content ratio 0 -1.7

For increasing compacting factor

i.e 0.1

+3 0

For sand conforming zone -3 0 -1.5

Total Adjustments +3.0 -3.2

Therefore Sand Content =35-6=29%

Water content = 186+(186*3)/100=191.6c/m3

DETERMINATION OF CEMENT CONTENT

W/c ratio = 0.4

Water content = 191.6 Kg/cum

Thus, Cement content = 511 Kg/cum

DETERMINATION OF COARSE & FINE AGGREGATE

V=(W+C/SC + FA/P*S.FA)*(1/1000)

0.98=(191.6+162.2+FA/0.81)*(1/1000)

FA=512 kg/m3

V=(W+C/SC + CA/P*S.CA)*(1/1000)

0.98=(191.6+162.2+CA/1.781)*(1/1000)

CA=115 kg/m3

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Mix Proportions:

Water Cement Fine aggregate Coarse aggregate

191.6 511 512 115

0.4 1.0 1.0 2.2

Cement : Sand: Coarse Aggregates = 1 : 1 : 2.2

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APPENDIX-II

Calculation of load carrying capacity of

PCC beams

The F.B.D. and bending moment diagram

of P0 is shown in Fig. A1.

Max. B.M. = 200W

Z =1

6bD

2 = 562.5!103mm

3

f

t= 0.7 f

ck= 0.7 30 = 3.834N/mm

2 : IS 456 Fig. A1

M.R. = Zf

t=2.156625

!10

6N-mm

Equating B.M. =M.R.

W= 10.78 KN.

Ultimate failure load =2W=21.56 KN.

Beam with under reinforced section

Analysis of beam: -

C

u= T

u

Where

Cu= Resultant compressive force in concrete,

uT =Resultant tensile force in tension steel,

x u=Neutral axis depth.

Cuc= 0.36 ! fck ! b ! xu

=0.36 ! 30 !150 ! 0.46 !120

= 89424N

Tu =0.87 ! fy ! Ast

=0.87 ! 500 !Ast

=435!Ast

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Cu=T

u

89424 = 435!Ast

Ast = 206mm2

No of bars =

2 bars of 12mm dia

Moment carrying capacity of beam:-

Mu =0.87 ! f y ! Ast ! (d " (0.42 ! xu ))

Mu = 0.87 ! 500 ! 266.19 ! (120 " (0.42 ! 0.46 ! d))

Mu = 9.53!106 N " mm

P = 47.65KN

Shear reinforcement

V=W=47.65 K

!v= v / bd

!v= 47.65"10

3/ 120 "150

!v= 2.65N / mm

2

!c max

= 3.5N / mm2

For!c,

Pt = 100Ast / bd

Pt = (100 " # "122" 2) / (120 "150)

Pt = 1.26

$!c= 0.712N / mm2

Load carrying capacity of beam:-

Mu =WL/3

P =Mu ! 3/L

P =9.53!106! 3/600

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!

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!c max

> !v> !

c

vus= v

u" !

cbd

vus= 47.65#103

" (0.712 #120 #150)

vus= 34.684KN

vus= 0.87 f

yA

svd / S

v

34.684 !103= 0.87 ! 500 ! " ! 2 ! 62

!120 / Sv

Sv= 85.10mm< 0.75d& < 300mm

#Sv= 0.75d = 90mm

No of stirrups = (650/90) + 1

= 8 stirrups of 6mm dia bars

RCC beam weak in flexure

Ast = 206mm2

If 50% decreased (206/2)=103mm2

Instead of 12mm bars 8mm are used

No of 8mm bars =

Load carrying capacity of RCC beam weak in flexure

Ast =151mm2

Mu = WL/3

L = 600mm

W=31.79KN

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RCC beam weak in shear

No of stirrups = 8Nos of 6mm dia bars

If 50% decreased 4 stirrups

Spacing = 180mm

Load carrying capacity of RCC beam weak in shear

No of stirrups = 4 Nos of 4mm dia bars

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!

REFERENCES

[1] California Department of Transportation, “Memo to Designers 20-4 Attachment

B”, State of California, USA 1996

[2] Beres A., El-Borgi S., White R., Gergely P., Experimental results of repaired and

retrofitted beam- column joint tests in lightly RC frame building. Technical Report

NCEER-92-0025, 1992.

[3] Pellegrino, C., and Modena, C. (2002). “Fiber Reinforced Polymer Shear

Strengthening of Reinforced Concrete Beams with Transverse Steel Reinforcement.”

J. of Composites for Construction,. 6(2), 104-111

[4] A shear strength model for steel fiber reinforced concrete beams without stirrup

reinforcement by Hai h. Dinh1, Gustavo j. Parra-Montesinos2, and James k. Wight3

[5] Analysis of reinforced concrete beams strengthened with frp laminates by

mahmoud t. el-mihilmy1 and Joseph w. tedesco, 2 members, ASCE

[6] Stress–Strain Model for Laterally Con!ned Concrete ---Weena P. Lokuge1; J. G.

Sanjayan2; and Sujeeva Setunge3

[7] Mander J B, Priestley M J N, Park R (1988), “Theoretical stress-stain model for

confined concrete", Journal of structural Engineering, ASCE, vol. 114, No. 8, pp.

1804-1826.

[8] Francesco Bencardino, Giuseppe Spadea and R.N.Samy (2002), “Strength and

Ductility of Reinforced Concrete Beams Externally Reinforced with Carbon Fiber

Fabric”, ACI Structural Journal, vol. 99, pp.163-171

[9] Basu P. C, (2002), “Seismic Upgradation of Buildings: An Overview”, The

Indian Concrete Journal, The Associated Cement Companies Ltd., pp. 461-475.

[10] Seth A (2002), “Seismic Retrofitting by Conventional Methods”, The Indian

Concrete Journal, The Associated Cement Companies Ltd., August, pp.489-495.

[11] Mukherjee A. and Joshi M. V (2002), “Seismic Retrofitting Technique Using

Fiber Composites”, The Indian Concrete Journal, The Associated Cement Companies

Ltd., August, pp.496-502.

[12] RC beams and slabs externally reinforced with fiber reinforced plastic (FRP)

panels by C. A. Ross, L. C. Muszynski, D. M. Jerome, J. W. Tedesco, R. L.

Sierakowsk

[13] Foreign Journal, use of FRP fabric for strengthening of reinforced concrete beam-

column joints by Dr. D. D’Ayala, University of Bath, UK.

[14] Seismic Retrofit of Historic building structures, by T. Jeff Guh, Ph. D., S.E. and

Arash Altoontash, Ph. D., P.E.

[15] Seismic retrofitting of reinforced concrete buildings using traditional and

innovative techniques, by Giuseppe Oliveto and Massimo Marletta.

[16] Seismic evaluation and retrofitting of buildings and structures by N. Lakshmanan.

[17] Retrofitting of structures, IIT, Roorkee, 2003

[18] IS 456:2000, “Indian Standard Plain and Reinforced Concrete – Code of Practice

(fourth revision)”, Bureau of Indian Standards, July 2000.

[19] IS10262:1982,”Indian Standard Recommended Guidelines for Concrete Mix

Design (fifth revision)” Bureau of Indian Standards, March 1998