STRUCTURAL BEHAVIOUR AND DESIGN OF CONCRETE MEMBERS STRENGTHENED WITH EXTERNALLY BONDED FRP REINFORCEMENT

7/29/2019 STRUCTURAL BEHAVIOUR AND DESIGN OF CONCRETE MEMBERS STRENGTHENED WITH EXTERNALLY BONDED FRP

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Universiteit Gent, Faculteit Toegepaste Wetenschappen

Vakgroep Bouwkundige Constructies

Ghent University, Faculty of Engineering

Department of Structural Engineering

CONSTRUCTIEF GEDRAG EN ONTWERP VAN

BETONCONSTRUCTIES VERSTERKT MET

UITWENDIG GELIJMDE VEZELCOMPOSIETWAPENING

STRUCTURAL BEHAVIOUR AND DESIGN OF

CONCRETE MEMBERS STRENGTHENED WITH

EXTERNALLY BONDED FRP REINFORCEMENT

Stijn MATTHYS

LABORATORIUM MAGNEL VOOR BETONONDERZOEK

MAGNEL LABORATORY FOR CONCRETE RESEARCH

Proefschrift tot het verkrijgen van de graad van

Doctor in de Toegepaste Wetenschappen, richting Bouwkunde

Academiejaar 1999-2000

Thesis in fulfilment of the requirements for the degree ofDoctor of Applied Sciences, option Structural Engineering

Academic year 1999-2000


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CONSTRUCTIEF GEDRAG EN ONTWERP VAN BETONCONSTRUCTIES

VERSTERKT MET UITWENDIG GELIJMDE VEZELCOMPOSIETWAPENING

STRUCTURAL BEHAVIOUR AND DESIGN OF CONCRETE MEMBERS

STRENGTHENED WITH EXTERNALLY BONDED FRP REINFORCEMENT


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Universiteit Gent, Faculteit Toegepaste Wetenschappen

Vakgroep Bouwkundige Constructies

Ghent University, Faculty of Applied Sciences

Department of Structural Engineering

CONSTRUCTIEF GEDRAG EN ONTWERP VAN

BETONCONSTRUCTIES VERSTERKT MET

UITWENDIG GELIJMDE VEZELCOMPOSIETWAPENING

STRUCTURAL BEHAVIOUR AND DESIGN OF

CONCRETE MEMBERS STRENGTHENED WITH

EXTERNALLY BONDED FRP REINFORCEMENT

Stijn MATTHYS

LABORATORIUM MAGNEL VOOR BETONONDERZOEK

MAGNEL LABORATORY FOR CONCRETE RESEARCH

Proefschrift tot het verkrijgen van de graad van

Doctor in deToegepaste Wetenschappen, richting Bouwkunde

Academiejaar 1999-2000

Thesis in fulfilment of the requirements for the degree of

Doctor of Applied Sciences, option Structural Engineering

Academic year 1999-2000


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Promotor Supervisor

Prof. Dr. Ir. L. Taerwe

Universiteit Gent, Vakgroep Bouwkundige ConstructiesProf. Dr. Ir. L. Taerwe

Ghent University, Departement of Structural Engineering

OnderzoeksinstellingResearch institute

Universiteit Gent, Vakgroep Bouwkundige Constructies

Laboratorium Magnel voor Betononderzoek

Technologiepark-Zwijnaarde 9

9052 GentGhent University, Departement of Structural Engineering

Magnel Laboratorium for Concrete Research

Technologiepark-Zwijnaarde 9B-9052 Ghent

Beursverlenende instantie Research grant offered by

Vlaams Instituut voor de bevordering van het Wetenschappelijk-

Technologisch Onderzoek in de Industrie (IWT)

Bischoffsheimlaan 25

1000 BrusselInstitute for the Promotion of Innovation by

Science and Technology in Flanders (IWT)

Bischoffsheimlaan 25

B-1000 Brussels

Copyright Stijn Matthys 2000

Alle rechten voorbehouden. Dit werk of delen ervan, mogen onder geen enkele voorwaarde en ook

niet voor persoonlijk gebruik worden uitgeleend, gekopieerd of op n of andere manier

vermenigvuldigd, zonder voorafgaande, schriftelijke toestemming van de auteur en zijn promotor.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or

transmitted in any form or by any means, electronic, mechanical, photocopying, recording or

otherwise, without the prior written permission of the author and his supervisor.


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The thinking that we are has brought us to where we have already been.In order to go somewhere else, we must think in a different way.

Albert Einstein

Dedicated to Els, Tijmen and Siebe


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Preface

This doctoral study concerns advanced composite reinforcement for concrete structures

and more specifically its use as externally bonded reinforcement to repair and strengthen

existing structures. As a novel reinforcing material for concrete, these composites were

brought to my attention as an engineering student, reading an article about the house of the

future. A few years later, Prof. L. Taerwe offered me the opportunity to perform a graduation

thesis on the structural behaviour of prefabricated concrete slabs pretensioned with advanced

composites. As a result, I became active in this research field, first as a final year student,

after graduating in 1994 as a research assistant and in 1996 as a doctoral researcher.

The work presented in this report is based on the research I conducted over the last four

years with a doctoral research grant provided by the IWT (Vlaams Instituut voor de

bevordering van het Wetenschappelijk-Technologisch Onderzoek in de Industrie - Institute

for the Promotion of Innovation by Science and Technology in Flanders) of the Flemish

Community. The work has been carried out at the Magnel Laboratory for Concrete Research,

Department of Structural Engineering of Ghent University. In addition to the IWT, also the

Research Fund of Ghent University, the Volvo Fund, the Fund for Scientific Research

Flanders and the European Community (TMR Programme) are acknowledged for their

financial support. The companies B.K. International, ECC, Resiplast, Sika, Sumitomo Europe,

Syncoglas and S&P Clever Reinforcing Company are gratefully recognized for providing test

material.

During my doctoral study several persons gave me their support and contributed to the

experimental and analytical studies. First of all, I am very grateful to my supervisor Prof. Luc

Taerwe, director of the Magnel Laboratory for Concrete Research, who gave me the

opportunity to perform research on an innovative topic, yet closely related to building

practice. I appreciate very much his support and many suggestions during the whole research

project, as well as the useful discussions we had. Also, I am thankful for the international

dimension he gave to this research project, resulting in the participation of the author to

several conferences and workshops, membership in international task groups and study visits

to other research institutes. I want to thank Prof. Paul Thomas for being there with his

pragmatic ideas and thinking. A word of thanks is also addressed to the visiting researchers,

Paolo Serra, Hossam Khalil, and Ramiro Sanchez-Lopez and the graduation students, Jeroen

Depla, Peter De Meyer and Katrien Audenaert, who participated in some of the research.

Especially, I want to recognize my colleagues and the foreign guests, for the friendly and the

professional contacts.

With respect to the experimental work, I am indebted to the technical staff of the

laboratory, who made it possible to perform quite a lot of large scale experiments. A special

word of thanks is also addressed to the administrative staff for their friendly support and for

being helpful when needed.

Preface v


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In the framework of this study I was able to meet many people abroad. In this respect, I

want to thank Drs. T. Triantafillou, S. Rizkalla, C. Burgoyne, B. Tljsten, G. Manfredi, R.

Tepfers, K. Pilakoutas and many others for the interesting conversations and feed-back I had

with them. Especially, I appreciate the pleasant and interesting time during the meetings of fib

(International Federation for Structural Concrete) Task Group 9.3 FRP Reinforcement forConcrete Structures and CUR (Civieltechnisch Centrum Uitvoering Research en

Regelgeving) Task Group C97B-1 Regelgeving voor versterken van betonconstructies met

behulp van uitwendige koolstofvezellijmwapening [Rules for the strengthening of concrete

structures using externally bonded carbon fibre reinforced polymer reinforcement], as well

as during my short study stays at the University of Manitoba (Canada), Chalmers University

(Sweden), the Royal Institute of Technology in Stockholm (Sweden) and the University of

Artois (France).

Finally, I want to thank my family, close friends and colleagues who encouraged and

supported me in a more personal way. Special thanks go to my wife Els, who supported me inso many ways.

Ghent, September 2000

Stijn Matthys

vi Preface


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Abstract

This thesis deals with several aspects of the structural behaviour and the design of

reinforced concrete members strengthened with externally bonded fibre reinforced polymer

reinforcement. Both analytical and experimental work are presented, focussing on the

development of design guidelines.

In the first chapter, an introduction is given on fibre reinforced polymer (FRP) materials as

structural reinforcement for concrete and more specifically as externally bonded

reinforcement to strengthen existing structures. Briefly, the use of FRP in concrete

construction, its history, benefits and some particular aspects of using this novel reinforcing

material are mentioned. The repair and strengthening with externally bonded FRP

reinforcement (FRP EBR) is discussed, demonstrating the efficiency and attractiveness of this

technique among which the advantages and disadvantages of this technique. The problem

statement and consequently the aim and the outline of this thesis are presented.

In Chapter 2, a description is given of FRP materials and their characteristics, the FRP

systems available for externally bonded reinforcement and the techniques to apply them to the

concrete. It is demonstrated that FRP reinforcement forms a group of materials, with high

performance characteristics, which strongly depend on the assembly of the constituent

materials. In general, the FRP EBR systems are very strong and durable. Nevertheless, when

evaluating the properties of different types of FRP, EBR systems based on carbon fibre

reinforced polymers (CFRP) exhibit the best characteristics.

The performed experimental and analytical studies concerning the structural behaviour of

concrete elements strengthened with FRP EBR are reported in Chapters 3 till 6. These

chapters correspond to the four test programmes which have been conducted, dealing with

flexural and shear strengthening of reinforced concrete beams, strengthening of tensile

members (to investigate tension stiffening and cracking behaviour) and confinement of

axially loaded columns. The experiments were mainly conducted on large scale elements,

varying several parameters with respect to the strengthening materials, the amount of external

reinforcement and the strengthening lay-out or configuration. Based on the experimental

work, an insight is obtained in the structural behaviour of the strengthened members. The

feasibility and efficiency of externally bonded FRP reinforcement to strengthen concrete

structures is clearly demonstrated. From the analytical verifications, existing models have

been verified and extended to predict the influence of externally bonded FRP reinforcement.

These calculation models deal with both the ultimate state and serviceability behaviour. It

appears that the structural behaviour of the strengthened concrete members can be predicted

in an accurate way.

Based on the derived models and a literature review regarding the models for FRP bond

failure, Chapter 7 gives detailed provisions for the design of the strengthened members. In

this extensive chapter, the basis of design, the safety concept, the design models and

procedures and some special design considerations are provided for concrete members

Abstract vii


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strengthened in flexure and shear, axially loaded confined columns and strengthened tensile

members. From this chapter it appears that, compared to new structures, the design of

concrete members strengthened with externally bonded reinforcement is more complex. To

assure structural safety, suggestions with respect to design failure modes, ductility and

accidental loss of FRP EBR are formulated. It is demonstrated that the design of strengthenedflexural members is often governed by the serviceability limit state and that special attention

should be paid to the ultimate limit state verification of bond failure. To gain better insight

into the design aspects, a parametric study concerning flexural strengthening is presented.

In the last chapter, the conclusions of the doctoral study are summarized and an outlook

on the future use and development of the FRP EBR technique is given. Some suggestions for

continued research are made.

viii Abstract


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Table of contents

Preface .................................................................................................................................................... v

Abstract................................................................................................................................................vii

Table of contents................................................................................................................................... ix

Notations ............................................................................................................................................. xix

SAMENVATTING................................................................................................................................ 1

1 Inleiding. ........................................................................................................................................... 1

1.1 Vezelcomposietwapening voor beton ........................................................................................... 1

1.2 Versterken van betonconstructies ................................................................................................. 1

1.3 Probleemstelling en internationale stand van zaken ..................................................................... 3

1.4 Doelstelling en onderwerp ............................................................................................................ 3

2 Uitwendige versterking met gelijmde vezelcomposietwapening.................................................. 4

2.1 Algemeen ...................................................................................................................................... 4

2.2 Voor- en nadelen van FRP EBR ................................................................................................... 5

2.3 Toepassingsmogelijkheden en FRP EBR systemen...................................................................... 6

2.4 Toepassingstechnieken.................................................................................................................. 7

3 Structureel gedrag van betonelementen versterkt in buiging...................................................... 7

3.1 Aard van de proeven ..................................................................................................................... 7

3.2 Voornaamste proefresultaten ........................................................................................................ 9

3.3 Analytische verificatie ................................................................................................................ 11

3.3.1 Bezwijktoestand...................................................................................................................... 11

3.3.2 Rekken in de wapening........................................................................................................... 13

3.3.3 Doorbuigingen ....................................................................................................................... 13

3.3.4 Scheuropeningen.................................................................................................................... 13

3.3.5 Rekken en schuifspanningen langsheen de FRP wapening.................................................... 14

3.4 Besluiten ..................................................................................................................................... 16

4 Structureel gedrag van betonelementen versterkt in dwarskracht ........................................... 16

4.1 Aard van de proeven ................................................................................................................... 16

4.2 Voornaamste proefresultaten ...................................................................................................... 18


4.3.1 Dwarskrachtsterkte ................................................................................................................ 20

4.3.2 Effectieve FRP breukrek ........................................................................................................ 21

4.4 Besluiten ..................................................................................................................................... 22

5 Tension stiffening en scheuroverbrugging................................................................................... 23

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5.3.1 Tension stiffening effect ......................................................................................................... 26

5.3.2 Scheurafstand en scheuropeningen........................................................................................ 275.4 Besluiten ..................................................................................................................................... 29

6 Inrijgen van axiaal belaste kolommen.......................................................................................... 29



6.2.1 Drukproeven op omwikkelde cilinders................................................................................... 31

6.2.2 Drukproeven op omwikkelde kolommen ................................................................................ 32


6.3.1 Probleemstelling .................................................................................................................... 33

6.3.2 Steundruk ............................................................................................................................... 33

6.3.3 Spanning-vervorming gedrag van beton omwikkeld met FRP............................................... 34

6.3.4 Effectieve maximale steundruk............................................................................................... 35

6.3.5 Bezwijkbelasting .................................................................................................................... 36

6.4 Besluiten ..................................................................................................................................... 36

7 Ontwerprichtlijnen ........................................................................................................................ 37

7.1 Algemeen .................................................................................................................................... 37

7.2 Verloop van het ontwerp............................................................................................................. 38

7.3 Opvatting van het ontwerp met betrekking tot veiligheid........................................................... 387.3.1 Bezwijkgrenstoestand............................................................................................................. 38

7.3.2 Accidentele ontwerptoestand ................................................................................................. 39

7.3.3 Ductiliteit ............................................................................................................................... 39

7.4 Versterking in buiging ................................................................................................................ 39

7.4.1 Initile toestand...................................................................................................................... 39

7.4.2 Nazicht in de BGT bij volledige composietwerking ............................................................... 40

7.4.3 Nazicht in de BGT van FRP onthechting ............................................................................... 40

7.4.4 Nazicht van de gebruikgrenstoestand (GGT)......................................................................... 43

7.4.5 Parameterstudie en berekeningsprogramma ......................................................................... 43

7.5 Versterking in dwarskracht ......................................................................................................... 43

7.6 Kolommen omwikkeld met FRP................................................................................................. 44

7.6.1 Nazicht van de bezwijkgrenstoestand (BGT) ......................................................................... 44

7.6.2 Nazicht van de gebruikgrenstoestand (GGT)......................................................................... 46

7.7 Bijzondere aspecten van het ontwerp.......................................................................................... 46

8 Besluiten.......................................................................................................................................... 46

9 Referenties ...................................................................................................................................... 47

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Chapter 1 INTRODUCTION .......................................................................................................... 51

1 Advanced composites as structural reinforcement ..................................................................... 51

1.1 Fibre reinforced polymers........................................................................................................... 51

1.2 FRP reinforcement ...................................................................................................................... 52

1.3 FRP as structural reinforcement for concrete construction......................................................... 54

1.3.1 History and benefits of FRP reinforcement ........................................................................... 54

1.3.2 Particular aspects related to the use of FRP reinforcement.................................................. 54

2 FRP as externally bonded reinforcement for strengthening...................................................... 57

2.1 General ........................................................................................................................................ 57

2.2 Strengthening with FRP EBR ..................................................................................................... 58

2.3 Advantages and disadvantages of FRP EBR .............................................................................. 59

3 Problem statement ......................................................................................................................... 61

4 Aim and outline of the study ......................................................................................................... 61

4.1 Research objective and aim of the thesis .................................................................................... 61

4.2 Scope of the study ....................................................................................................................... 61

4.3 Outline of the thesis .................................................................................................................... 62

5 References ....................................................................................................................................... 62

Chapter 2 MATERIAL CHARACTERISTICS, FRP EBR SYSTEMS

AND TECHNIQUES...................................................................................................... 65

1 Constituent materials for FRP EBR............................................................................................. 65

1.1 General ........................................................................................................................................ 65

1.2 Fibres........................................................................................................................................... 66

1.2.1 Aramid fibres ......................................................................................................................... 66

1.2.2 Carbon fibres ......................................................................................................................... 67

1.2.3 Glass fibres ............................................................................................................................ 68

1.3 Polymer matrices......................................................................................................................... 68

1.3.1 Resins ..................................................................................................................................... 68

1.3.2 Fillers and additives .............................................................................................................. 71

1.4 Adhesives .................................................................................................................................... 71

1.4.1 General considerations.......................................................................................................... 71

1.4.2 Adhesive requirements ........................................................................................................... 71

1.4.3 Epoxy as structural adhesive ................................................................................................. 72

2 Material shapes, manufacturing and FRP EBR systems............................................................ 73

2.1 FRP reinforcement shapes .......................................................................................................... 73

2.2 Manufacturing............................................................................................................................. 74

2.2.1 Manufacturing of strips by means of pultrusion .................................................................... 74

2.2.2 Manufacturing of laminates by means of moulding............................................................... 752.2.3 Manufacturing of dry-fibre sheets and fabrics ...................................................................... 76

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2.2.4 Manufacturing of prepreg...................................................................................................... 77

2.3 FRP EBR systems ....................................................................................................................... 77

2.3.1 Prefab or pre-cured systems .................................................................................................. 78

2.3.2 Wet lay-up or in-situ curing systems...................................................................................... 78

3 Techniques, practical application and quality control................................................................ 79

3.1 FRP EBR strengthening techniques ............................................................................................ 79

3.1.1 Basic technique ...................................................................................................................... 79

3.1.2 Other techniques .................................................................................................................... 80

3.2 Practical execution and quality control ....................................................................................... 81

3.2.1 Practical execution ................................................................................................................ 81

3.2.2 Quality control ....................................................................................................................... 82

4 Material characteristics of FRP EBR systems............................................................................. 82

4.1 General ........................................................................................................................................ 82

4.2 Type of FRP EBR system and dimensions ................................................................................. 82

4.3 Physical properties ...................................................................................................................... 84

4.3.1 FRP reinforcement................................................................................................................. 84

4.3.2 Adhesive ................................................................................................................................. 85

4.4 Mechanical properties and behaviour under short-term loading................................................. 87

4.4.1 FRP reinforcement................................................................................................................. 87

4.4.2 Adhesive ................................................................................................................................. 90

4.5 Durability and long-term behaviour............................................................................................ 90

4.5.1 Environmental durability ....................................................................................................... 90

4.5.2 Mechanical behaviour under sustained loading.................................................................... 93

4.5.3 Cyclic loading ........................................................................................................................ 94

5 Conclusions..................................................................................................................................... 94

6 References ....................................................................................................................................... 95

Chapter 3 STRUCTURAL BEHAVIOUR OF RC BEAMS

STRENGTHENED IN FLEXURE................................................................................ 99

1 Introduction.................................................................................................................................... 99

2 Outline of the experiments .......................................................................................................... 100

2.1 Test specimens and material properties .................................................................................... 100

2.2 Specimen preparation and test procedure ................................................................................. 101

3 Test results .................................................................................................................................... 103

3.1 Behaviour at ultimate load ........................................................................................................ 103

3.1.1 Failure mode........................................................................................................................ 103

3.1.2 Strengthening effect, ultimate FRP strain and ductility....................................................... 103

3.2 Load-deflection behaviour ........................................................................................................ 104

3.3 Cracking behaviour ................................................................................................................... 106

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3.4 FRP strain distribution .............................................................................................................. 107

4 Analytical verification.................................................................................................................. 108

4.1 Prediction of the failure load and failure mode......................................................................... 108

4.1.1 Verification assuming full composite action........................................................................ 108

4.1.2 Verification of anchorage failure......................................................................................... 108

4.1.3 Verification of bond failure due to crack bridging .............................................................. 109

4.2 Moment-strain behaviour.......................................................................................................... 112

4.3 Moment-curvature and moment-deflection behaviour.............................................................. 114

4.4 Cracking.................................................................................................................................... 117

4.5 Strains and bond shear stresses along the FRP EBR................................................................. 119

4.6 Service load, safety and ductility .............................................................................................. 121

4.6.1 Service load.......................................................................................................................... 121

4.6.2 Ratio of ultimate to service load .......................................................................................... 122

4.6.3 Ductility ............................................................................................................................... 122

5 Conclusions................................................................................................................................... 123

6 References ..................................................................................................................................... 124

Chapter 4 STRUCTURAL BEHAVIOUR OF RC BEAMS

STRENGTHENED IN SHEAR................................................................................... 127

1 Introduction.................................................................................................................................. 127

2 Outline of the experiments .......................................................................................................... 1272.1 Test specimens and material properties .................................................................................... 127


3 Test results .................................................................................................................................... 130

3.1 Failure load and mode of failure ............................................................................................... 130

3.2 FRP strains ................................................................................................................................ 132

3.3 Contribution of the internal and external shear reinforcement ................................................. 132

3.4 Midspan deflection.................................................................................................................... 134

4 Analytical verification.................................................................................................................. 1354.1 Shear capacity of the reference beams and diagonal tension shear crack ................................. 135

4.2 Shear capacity of the strengthened beams ................................................................................ 136

4.3 Effective ultimate FRP strain .................................................................................................... 137

5 Conclusions................................................................................................................................... 140

6 References ..................................................................................................................................... 141

Chapter 5 SERVICEABILITY BEHAVIOUR: TENSION STIFFENING

AND CRACK BRIDGING .......................................................................................... 143

1 Introduction.................................................................................................................................. 143

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2 Outline of the test programme.................................................................................................... 144



3 Test results .................................................................................................................................... 147

3.1 Behaviour at ultimate load ........................................................................................................ 147

3.2 Mean tensile strain .................................................................................................................... 148

3.3 Crack pattern ............................................................................................................................. 150


4.1 Cracking load and load at which the steel starts yielding ......................................................... 150

4.2 Tension stiffening effect ........................................................................................................... 151

4.3 Crack spacing and crack width ................................................................................................. 154

5 Conclusions................................................................................................................................... 158

6 References ..................................................................................................................................... 159

Chapter 6 CONFINEMENT OF AXIALLY LOADED COLUMNS......................................... 161

1 Introduction.................................................................................................................................. 161

2 Outline of the experiments .......................................................................................................... 161



3 Test results .................................................................................................................................... 1653.1 Compression tests on wrapped cylinders .................................................................................. 165

3.1.1 Behaviour at ultimate load................................................................................................... 165

3.1.2 Stress-strain behaviour ........................................................................................................ 167

3.2 Tests on confined columns........................................................................................................ 168

3.2.1 Behaviour at ultimate load................................................................................................... 168

3.2.2 Stress-strain behaviour and effectiveness of wrapping configuration................................. 169


4.1 Problem statement..................................................................................................................... 173

4.1.1 Constant versus increasing confining action ....................................................................... 173

4.1.2 Effective circumferential failure strain ................................................................................ 173

4.1.3 Axial failure strain ............................................................................................................... 174

4.2 Lateral confining pressure exerted by the FRP ......................................................................... 174

4.2.1 Fully wrapped cylindrical specimens with fibres perpendicular to longitudinal axis......... 174

4.2.2 Influence of partial wrapping .............................................................................................. 176

4.2.3 Influence of fibre orientation ............................................................................................... 176

4.2.4 Influence of column shape ................................................................................................... 177

4.3 Stress-strain relationship of FRP confined concrete ................................................................. 178

4.3.1 General ................................................................................................................................ 178

4.3.2 Analytical verification.......................................................................................................... 179

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4.4 Confined concrete strength and ultimate strain......................................................................... 182

4.4.1 Ultimate state ....................................................................................................................... 182

4.4.2 Confined concrete strength .................................................................................................. 183

4.4.3 Effective FRP failure strain ................................................................................................. 184

4.5 Load carrying capacity of the wrapped members ..................................................................... 186

5 Conclusions................................................................................................................................... 187

6 References ..................................................................................................................................... 188

Chapter 7 DESIGN OF CONCRETE MEMBERS STRENGTHENED WITH

EXTERNALLY BONDED FRP REINFORCEMENT............................................. 191

1 Introduction.................................................................................................................................. 191

2 Basis of design............................................................................................................................... 191

2.1 General ...................................................................................................................................... 191

2.2 Limit states and design situations ............................................................................................. 192

2.2.1 Ultimate and serviceability limit state (persistent situation) ............................................... 192

2.2.2 Accidental situation ............................................................................................................. 192

2.2.3 Special design considerations.............................................................................................. 193

2.3 Models for the constituent materials and partial safety factors................................................. 193

2.3.1 SLS verification.................................................................................................................... 193

2.3.2 ULS verification, full composite action between concrete and FRP EBR ........................... 193

2.3.3 ULS verification of bond failure .......................................................................................... 195

2.4 Safety concept ........................................................................................................................... 195

2.4.1 Safety concept with respect to the ultimate limit state ......................................................... 195

2.4.2 Safety concept with respect to accidental situation ............................................................. 196

2.4.3 Ductility ............................................................................................................................... 196

3 Flexural strengthening................................................................................................................. 197

3.1 General ...................................................................................................................................... 197

3.2 Initial situation .......................................................................................................................... 197

3.3 ULS verification assuming full composite action ..................................................................... 198

3.3.1 Principle of calculation and basic assumptions .................................................................. 198

3.3.2 Steel yielding/concrete crushing .......................................................................................... 199

3.3.3 Steel yielding/FRP fracture.................................................................................................. 199

3.3.4 Brittle failure at first cracking ............................................................................................. 200

3.3.5 Shear failure ........................................................................................................................ 200

3.4 ULS verification with respect to loss of composite action........................................................ 201

3.4.1 Bond failure modes .............................................................................................................. 201

3.4.2 Bond behaviour.................................................................................................................... 202

3.4.3 Design bond shear strength ................................................................................................. 203

3.4.4 Anchorage zone.................................................................................................................... 203

3.4.5 Force transfer between FRP and concrete .......................................................................... 211

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3.4.6 Crack bridging ..................................................................................................................... 212

3.5 SLS verification ........................................................................................................................ 214

3.5.1 Basis of calculation.............................................................................................................. 214

3.5.2 Stress limitation ................................................................................................................... 216

3.5.3 Verification of deflections .................................................................................................... 2163.5.4 Verification of crack widths ................................................................................................. 217

3.5.5 Verification of bond interface cracking ............................................................................... 219

3.6 Influence of design parameters and governing design aspects ................................................. 219

3.6.1 Influence of characteristics of the existing RC element ....................................................... 219

3.6.2 Governing design aspects .................................................................................................... 225

3.7 Summary of design process ...................................................................................................... 231

4 Shear strengthening ..................................................................................................................... 232

4.1 General ...................................................................................................................................... 232

4.2 ULS verification........................................................................................................................ 233

4.2.1 Shear capacity...................................................................................................................... 233

4.2.2 Effective FRP failure strain ................................................................................................. 233


4.4 Spacing requirements................................................................................................................ 237

4.5 Summary of the design process................................................................................................. 237

5 Confinement of axially loaded columns ..................................................................................... 237

5.1 General ...................................................................................................................................... 237

5.2 ULS verification........................................................................................................................ 2385.2.1 Load carrying capacity ........................................................................................................ 238

5.2.2 Stress-strain relationship and compressive strength of confined concrete.......................... 238

5.2.3 Effective ultimate FRP strain and corresponding lateral confining pressure ..................... 240

5.2.4 Anchorage and bond quality ................................................................................................ 242


5.4 Summary of the design process................................................................................................. 244

6 Strengthened tensile members .................................................................................................... 245

6.1 General ...................................................................................................................................... 245

6.2 ULS verification........................................................................................................................ 245


6.3.1 Stress limitation ................................................................................................................... 246

6.3.2 Verification of deformations ................................................................................................ 246

6.3.3 Verification of crack widths and bond interface cracking ................................................... 246

7 Special design considerations...................................................................................................... 247

7.1 General ...................................................................................................................................... 247

7.2 Influence of environmental conditions...................................................................................... 247

7.2.1 Temperature effects and freeze-thaw action ........................................................................ 2477.2.2 Moisture ............................................................................................................................... 248

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7.2.3 Chemical resistance ............................................................................................................. 248

7.2.4 UV light exposure ................................................................................................................ 248

7.2.5 Lightning.............................................................................................................................. 249

7.3 Fire protection ........................................................................................................................... 249

7.4 Long-term loading..................................................................................................................... 2497.5 Cyclic loading ........................................................................................................................... 250

7.6 Impact and vandalism ............................................................................................................... 251

8 References ..................................................................................................................................... 251

Chapter 8 CONCLUSIONS AND OUTLOOK............................................................................ 257

1 General.. ........................................................................................................................................ 257

2 Conclusions................................................................................................................................... 257

2.1 FRP materials and FRP EBR systems....................................................................................... 257

2.2 Structural behaviour of RC elements strengthened with FRP EBR.......................................... 258

2.3 Design guidelines for concrete structures strengthened with FRP EBR................................... 259

3 Outlook on the use and development of the FRP EBR technique ........................................... 259

3.1 The use of externally bonded FRP reinforcement wit respect to steel plate bonding ............... 259

3.2 The use of externally bonded FRP reinforcement in practice ................................................... 259

3.3 New developments.................................................................................................................... 260

4 Continued research needed ......................................................................................................... 261

Appendix A PRACTICAL EXECUTION AND QUALITY CONTROL..................... 263

Appendix B MATERIAL PROPERTIES........................................................................ 271

Appendix C RC BEAMS STRENGTHENED IN FLEXURE .......................................279

Appendix D RC BEAMS STRENGTHENED IN SHEAR.............................................291

Appendix E TENSION STIFFENING AND CRACKING BEHAVIOUR ..................297

Appendix F FRP CONFINED CONCRETE .................................................................. 307

Appendix G CALCULATION PROGRAMME USED FOR

THE PARAMETRIC STUDY..................................................................... 319Appendix H CALCULATION PROGRAMME FOR

FLEXURAL STRENGTHENING.............................................................. 329

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Notations

Roman upper case letters

Ac cross-sectional area of concrete

Ac,eff effective concrete area in tension

Ae cross-sectional area of effectively confined concrete

Af cross-sectional area of FRP reinforcement

Ag gross cross-sectional area

Ar cross-sectional area of reinforcement

As cross-sectional area of longitudinal steel reinforcement

As1 cross-sectional area of longitudinal tensile steel reinforcement

As2 cross-sectional area of longitudinal compressive steel reinforcementAu cross-sectional area of unconfined concrete

Awf cross-sectional area of FRP shear reinforcement

Aws cross-sectional area of steel shear reinforcement

Ci constant

D diameter of cylinder or column

Di constant

Ea modulus of elasticity of adhesive

Ec modulus of elasticity of concrete

IIc

El

modulus of elasticity of concrete at origin of second branch (circumf. direction)

1cE l modulus of elasticity of concrete of first branch (circumferential direction)

2cE l modulus of elasticity of concrete of second branch (circumferential direction)

EcII modulus of elasticity of concrete at origin of second branch

Ec1 modulus of elasticity of concrete of first branch

Ec2 modulus of elasticity of concrete of second branch

Ec modulus of elasticity of concrete for long-term loading

Eel elastic energy

Ef modulus of elasticity of FRP

Ef,comp modulus of elasticity of FRP in compressionEfib modulus of elasticity of fibres

Efk characteristic value of modulus of elasticity of FRP

Efk0.05 lower bound characteristic value (5 % fractile) of E-modulus of FRP

Efk0.95 upper bound characteristic value (95 % fractile) of E-modulus of FRP

Ef,tens modulus of elasticity of FRP in tension

Efu modulus of elasticity of FRP at ultimate stage

Ei tangent modulus of elasticity of concrete at origin in the axial (i = c) or

circumferential (i = c ) directionl

EiII modulus of elasticity of concrete at origin of second branchEi1 modulus of elasticity of concrete of first branch

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Ei2 modulus of elasticity of concrete of second branch

Emat modulus of elasticity of matrix

Er modulus of elasticity of reinforcement

Es modulus of elasticity of steel

Esec

secant modulus of elasticity

Esec,M = fccM/cc1M

Esec,Md = fccMd/ccMd

Esec,u secant modulus of elasticity at ultimate stage

Esec,ud secant modulus of elasticity at ultimate limit state

Esec1 = fcc/cc1

(EA) axial stiffness of the tension reinforcement

Ga shear modulus of adhesive

Gf fracture energy

Ic moment of inertia of transformed (cracked) section

Ico moment of inertia of transformed (cracked) section before strengthening

If moment of inertia about the centroid of FRP

Io2 moment of inertia of transformed cracked section before strengthening

I1 moment of inertia of transformed uncracked section

I2 moment of inertia of transformed cracked section

Kconf parameter expressing the stiffness and effectiveness of the confining device

Kconfx Kconfin x-direction

Kconfy Kconfin y-direction

K flexural stiffness

L distance between support and end of FRP

M moment line of a beam with a point load Q = 1 at midspan

M(x) moment at distance x

MAd design value of resisting moment of the accidental situation

Mcr cracking moment

Md design value of moment

MdS design value of moment of strengthened member

Mfib fibre mass per area

Mk characteristic value of moment

Mkg moment due to dead loadMkq moment due to life load

MRbd resisting design moment corresponding with VRbd

MRd resisting design moment

MRdS resisting design moment of strengthened member

MRdU resisting design moment of unstrengthened member

MRpd design value of moment corresponding with VRpd

MSd acting design moment

Mx=0 moment acting on section corresponding to end of EBR

My moment at which internal steel starts yieldingMyd design value of moment at which internal steel starts yielding

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Mo acting moment during strengthening

MserS service moment of stengthened beam under rare load combination, obtained

from MRdS

MserU service moment of unstengthened beam under rare load combination, obtained

from MRdU

N applied tensile force or acting load

Nc force in concrete

Ncr cracking load

Ncr,exp cracking load (experimental)

Ncr,m = (Ncr,n + Ny)/2

Ncr,n load beyond which concrete element is in stabilized cracking phase

Nf force in FRP

Nfa FRP force to be anchored

Nfad design value of FRP force to be anchored

Nfa,max maximum FRP force which can be anchored

Nfad,max design value of maximum FRP force which can be anchorage

Nfd acting design force in FRP

)(N max,tfQu l acting force at distance from end of FRP, when reaching ultimate loadmax,tl

NRd resisting design force

NRfd resisting design force in FRP

NRsd resisting design force in steel

Nr = Ns + Nf

Nrd = Nsd + Nfd

Nref (ultimate) load of reference specimen

Nrk = Mk/ze

NSd acting design force

NSrd acting design force in reinforcement

Ns force in steel

Nsd acting design forcein steel

Ns1 force in tensile steel reinforcement

Ns2 force in compressive steel reinforcement

Nu ultimate load

Nu,exp ultimate load (experimental)Ny load after yielding of the internal steel reinforcement

Ny,exp load after yielding of the internal steel reinforcement (experimental)

Q point load

Qana ultimate load (analytical verification)

Qcal ultimate load (calculated)

Qcr cracking load

Qcr,exp cracking load (experimental)

Qexp ultimate load (experimental)

Qf force in FRP

Qk1 service load, from ultimate limit state assuming full composite action

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Qk2 service load, from ultimate limit state verifying loss of composite action

Qk3 service load, from stress limitations

Qk4 service load, from deflection limitations

Qk5 service load, from crack width limitations crack width

Qmax

maximum load

Qref (ultimate) load of reference specimen

Qser service load

Qu ultimate load

Qu,ref ultimate load of reference specimen

Qy load at which the steel starts yielding

Qo load at which the FRP EBR is applied

R curvature of the helix, or

radius of cylinder or column

T temperature

Tg glass transition temperature

Vc shear capacity of concrete

Vck concrete shear contribution at service load

Vcr shear force causing shear cracking

Vd acting design shear force

Vf,exp FRP shear contribution (experimental)

Vk shear force at service load

VR resisting shear capacity

VRbd resisting design shear force at which bond failure is initiated

VRd resisting design shear capacityVRd1 resisting design shear capacity of the concrete

VRd2 resisting design shear capacity of the concrete in diagonal compression

VRp resisting shear force at which shear crack peeling is initiated

VRpd resisting design shear force at which peeling initiates

VSd acting design shear force

Vu ultimate shear capacity

Vu,ref ultimate shear capacity of reference specimen

Vwf resisting shear capacity of FRP shear reinforcement

Vwfd resisting design shear capacity of FRP shear reinforcement

Vws resisting shear capacity of steel stirrups

Vwsd resisting design shear capacity of steel stirrups

Vx=0 shear force acting on section corresponding to end of EBR

Roman lower case letters

a maximum deflection, or

shear span

ac length governing critical flexural shear crack of unstrengthened memberag maximum deflection due to self weight

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aL fictitious shear span

la horizontal distance over which the moment line is shifted

alim maximum allowable deflection

aQ maximum deflection due to the point loads

av distance from major load to supporta1 deflection in uncracked state

a2 deflection in fully cracked state

max)/a( l ratio of the allowable deflection over the span length l

b width of concrete member

b clear width between the rounded corners

bf total width of the bonded FRP

bw minimum width of the section (width of the web)

bo constant

cF factor related to the fracture energyd effective depth of the member, or

thickness of the bond layer

d clear depth between the rounded corners

d1 distance between tension face and tensile steel reinforcement

d2 distance between compression face and compressive steel reinforcement

fc concrete compressive cylinder strength

fcb bond shear strength of the concrete

fcbd design bond shear strength of the concrete

fcbk characteristic bond shear strength of the concrete

fcc compressive strength of the confined concrete

fccd design value of the confined concrete compressive strength

fccM confined concrete strength assuming constant confining pressure ul

fccMd confined concrete strength assuming constant confining pressure udl

fc,cube concrete compressive strength measured on cubes

fcd design value of concrete compressive strength

fck characteristic value of concrete compressive strength

fcm mean concrete compressive cylinder strength

fc,prism concrete compressive strength measured on prismsfct concrete tensile strength

fctk characteristic value of concrete tensile strength

fctk0.05 lower bound characteristic tensile strength

fctk0.95 upper bound characteristic tensile strength

fctm mean concrete tensile strength

fco unconfined concrete strength

ff FRP tensile strength

ff,comp FRP compressive strength

ffd design value of the FRP tensile strength

ff,eff effective strength of the FRP

ffd,eff effective design strength of the FRP

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ffib tensile strength of the fibres

ffk characteristic value of the FRP tensile strength

ffm mean value of the FRP tensile strength

ff,tens = ff

fwy

yield stress of the stirrups

fwyd design value of yield stress of the stirrups

fy yield stress of the steel reinforcement

fyd design value of the yield stress of the steel reinforcement

fyk characteristic value of the yield stress of the steel reinforcement

fo,c intercept stress

lc,of intercept stress (circumferential direction)

fo,i stress at the intercept of the second slope with the stress axis

g self weight

h total depth of the member

hf flange depth

k constant

kb size factor

kc factor relating to compaction of concrete

ke confinement effectiveness coefficient

ke1 confinement effectiveness coefficient, for partial wrapping

ke2 confinement effectiveness coefficient, for account fibre orientation

ke3 confinement effectiveness coefficient, for shape of cross-section

kf = (sin f+ cos f)

kM coefficient depending on the loading type

ks = (sin s + cos s)

kv factor relating maximum moment and shear force

k factor relating crack width assumed tensile member to maximum crack width

k1, k2 coefficients

l span length of the beam, or

overlap joint length

bl bonded length

n,crl transfer length at stabilized cracking

fl transfer length of FRP reinforcement (based on mean bond stress)

rl transfer length

rfl transfer length of FRP reinforcement

sl transfer length of steel rebars (based on mean bond stress)

tl available anchorage or transfer length

max,tl maximum anchorage or transfer length

1l distance between the point load Q and the support

l /d ratio of span length to effective depth( /d)l max maximum ratio of span length to effective depth

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m = Mkq/Mkg, for unstrengthened (U) or strengthened (S) member

mi mass fraction of constituent i

n power

nc curve-shaped parameter

lcn curve-shaped parameter (circumferential direction)ni curve-shaped parameter that mainly controls the curvature in the transition

zone between the first and second branch

p pitch of the helix

r radius, or

= Ec/(Ec-Esec1)

rc radius of rounded corners

1/r curvature

1/ru curvature at failure

1/ry curvature at start of yielding of steel reinforcement

s centre to centre spacing of the FRP, or

slip, or

adhesive thickness

s clear spacing between the FRP reinforcement

sf spacing of FRP shear reinforcement

sf,max maximum allowable spacing of the FRP reinforcement

srm mean crack spacing

srmexp mean crack spacing (experimental)

sr,max maximum crack spacing

sr,maxexp maximum crack spacing (experimental)

ss spacing of steel stirrups

su ultimate slip

s1 slip corresponding to b,max

t (total) thickness of FRP reinforcement

tdf equivalent dry-fibre thickness

u bond perimeter

uf bond perimeter of the FRP reinforcement

us bond perimeter of the steel reinforcement

v vertical crack displacementvfib fibre volume fraction

vi volume fraction of constituent i

vmat matrix volume fraction

w horizontal crack displacement

wcrit critical crack width at which there is no longer aggregate interlock contribution

wf crack width at level of FRP reinforcement

wh horizontal component of the crack width

w'i clear distance between the rounded corners

wk characteristic value of the crack width

wlim maximum allowable crack width

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wm mean crack width

ws crack width at level of steel reinforcement

wv vertical component of the crack width

x depth of the compression zone, or

= c/cc1, ordistance

xe depth of the compression zone (linear elastic analysis)

xlim maximum allowable depth of compression zone (ductility requirement)

xo neutral axis depth before strengthening

yu ultimate deflection at midspan

yref ultimate deflection at midspan of reference specimen

z lever arm between total tensile force and compression force

ze lever arm between (linear elastic analysis)

zf lever arm between FRP tensile force and compression force

zs lever arm between steel tensile force and compression force

Greek upper case letters

reduced moment of inertia of transformed cross-sectionf parameter

o reduced moment of inertia of transformed cross-section, prior to strengthening

1 reduced moment of inertia of transformed cross-section, uncracked state

2 reduced moment of inertia of transformed cross-section, cracked state

Md variation of the design moment

Nf variation of the FRP force

Nfd variation of the design value of the FRP force

T temperature change

x small distance

f,cr FRP stress increase at first cracking

(mean) diameter of the steel reinforcement

r global load safety factor for the rare load combination

qp global load safety factor for the quasi-permanent load combination

Greek lower case letters

reduction factor, or

angle of shear reinforcement with respect to longitudinal axis

f = Ef/Ec, or

angle of FRP shear reinforcement with respect to longitudinal, or

fibre orientation with respect to the circumferential direction

xxvi Notations


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s = Es/Ec, or

angle of steel stirrups with respect to longitudinal axis

T,CFRP coefficient of thermal expansion of FRP

T,concrete coefficient of thermal expansion of the concrete

1, 2 parameter expressing confined concrete strength1d, 2d parameter expressing the design value of confined concrete strength

coefficient which relates mean and characteristic value of crack width, or= 12, or

parameter depending on the unconfined concrete properties

fe coefficient which relates mean and characteristic value offue

t factor taking into account the type of loading

1 coefficient taking into account the bond characteristics of the reinforcement

2 coefficient taking into account the loading type

c material safety factor for the concretec,axial material safety factor for the concrete under uniaxial compression

g load safety factor for the dead load

f material safety factor for the FRP

M partial safety factor for the materials

q load safety factors for the life load

s material safety factor for the steel

s,axial material safety factor for the steel under uniaxial compression

G distance from the compression face to the centroid of the compression force

divided by the depth of the compression zone (stress block centroid coefficient)

1/r curvature ductility index

1/r,min minimum curvature ductility index

c concrete strain at the extreme compression fibre

ccMd axial strain of confined concrete corresponding with fccMd

ccu ultimate axial strain of confined concrete

ccud design value of ultimate axial strain of confined concrete

cc1 axial strain of confined concrete at maximum load

cc1M axial strain of confined concrete corresponding with fccM

c,exp measured axial concrete strain

lc circumferential concrete strain

IIcl circumferential concrete strain at the origin of second branch

1cl circumferential concrete strain at maximum load

ucl circumferential ultimate concrete strain

fit,ucl circumferential ultimate concrete strain, calculated to fit experimental results

cm mean concrete strain

cr1 tensile strain of the uncracked state, with N= Ncr

cr2 tensile strain of the fully cracked state, with N= Ncr

Notations xxvii


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cu ultimate concrete strain at the extreme compression fibre

cII concrete strain at the origin of second branch

co initial concrete strain

c1 axial concrete strain at maximum load

f FRP reinforcement strainf,eff effective FRP tensile strain

fm mean FRP reinforcement strain

f,min minimum required ultimate FRP strain to assure sufficient ductility

fQu midspan FRP strain at ultimate load

fu ultimate FRP strain

fu,c FRP strain in the critical section at ultimate stage

fud design value of the ultimate FRP strain

fue effective ultimate FRP strain

fue,d design value of the effective ultimate FRP strain

fu,eff effective failure strain of the FRP wrapping reinforcement

fum mean value of the ultimate FRP strain

i strain of the concrete in the axial (i = c) or circumferential (i = ) directionlc

iII strain at the origin of the second branch

m mean value of the strain

mu mean ultimate strain

r reinforcement strain

rm,r mean strain of the reinforcement with respect to the surrounding concrete

r2 reinforcement strain in the cracked section

s steel reinforcement strain

sm mean steel reinforcement strain

s,min minimum required ultimate steel strain to assure sufficient ductility

su ultimate strain of the steel reinforcement

s1 steel tensile reinforcement strain

s2 steel compressive reinforcement strain

y yield strain of the steel reinforcement

yd design value of the yield strain of the steel reinforcement

yk characteristic value of the yield strain of the steel reinforcement

o initial strain at the extreme tensile fibre before strengthening

1 strain corresponding to the uncracked state

2 strain corresponding to the fully cracked state

, , b distribution or tension stiffening coefficients

l boundary condition

= h/da = MserS/MAk

e effectiveness factoreffd design value of the effective FRP strength of the confining reinforcement

xxviii Notations


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S = MRdS/MRdU

o = Mo/MserU

angle between the diagonal shear crack and the member longitudinal axisf ratio of the recorded mean tensile strain at ultimate load mu to the mean

ultimate FRP strain fu obtained from tensile tests parameterdS reduced acting design moment of the strengthened member

RdS reduced resisting design moment of the strengthened member

RdU reduced resisting design moment of the unstrengthened member

u dilation rate (change of circumferential strain with respect to the axial strain)

coefficient taking into account the load configuration and span of the beam Poisson ratio

f Poisson ratio of the FRP

fib Poisson ratio of the fibres

mat Poisson ratio of the matrix

= x/d

b bond parameter

reinforcement ratio

c,eff ratio of the effective concrete area in tension

eq equivalent reinforcement ratio

f volumetric ratio of the FRP wrapping reinforcement, or

density of the fibre compositefx ratio representing the quantities of transverse confining reinforcement in

the x direction

fy ratio representing the quantities of transverse confining reinforcement in

the y direction

i density of the constituent i

l longitudinal reinforcement ratio

r reinforcement ratio for either steel (r = s) or FRP reinforcement (r = f), or

= As/Ac,eff

s steel reinforcement ratiosg = As/Ag

s,min minimum reinforcement ratio of the internal steel

w,eq equivalent shear reinforcement ratio

wf FRP shear reinforcement ratio

ws steel shear reinforcement ratio

stress

c concrete stress

ccu ultimate compressive stress of confined concrete

ccud design value of the ultimate compressive stress of confined concrete

c,exp measured axial concrete stress

Notations xxix


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cII concrete stress at the origin of the second branch

f FRP stress

fib fibre stress

l lateral confining stress on the concrete

circ,l confinement stress per unit width exerted by circular FRP wrapping reinf.

spiral,l confinement stress per unit width exerted by helicodal FRP wrapping reinf.

ul maximum lateral confinement stress

udl design value of maximum lateral confinement stress

uxl maximum lateral confining stresses in the x direction

uxdl design value of maximum lateral confining stress in the x direction

uyl maximum lateral confining stresses in the y direction

uydl design value of maximum lateral confining stress in the y direction

xl lateral confining stress in the x direction

yl lateral confining stress in the y direction

mat matrix stress

max maximum stress

r stress in the tensile reinforcement (steel or FRP)

s stress in the tensile steel reinforcement

s2 stress in the compressive steel reinforcement

ws tensile stress in the steel stirrups shearstressad design value of mean shear strength obtained through lap shear tests

am mean shear strength obtained through lap shear tests

b bond shear stress

bm mean bond shear stress

b,max maximum bond shear stress

c,max maximum shear stress in the concrete

cza shear stress mobilised in compression zone and in shear crack (aggregate

interlock)fm mean bond stress of the FRP reinforcement

m mean shear stress

max maximum shear stress

sm mean bond stress of the steel reinforcement

Rd1 design value of resisting shear stress of concrete

Rm mean resisting shear stress

Rp resisting shear stress corresponding with initiation of peeling

Rpd design value of resisting shear stress at initiation of peeling

Rpk characteristic value of resisting shear stress at initiation of peeling

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ratio of the critical crack width at which there is no longer an aggregateinterlock contribution to the mean crack spacing

creep coefficient coefficient relating the dowel action to the axial stiffness of the reinforcement ratio of the average over the maximum concrete compressive stress (stressblock area coefficient)2 load combination factor with respect to the quasi-permanent load combination

constant

Important abbreviations

FRP fibre reinforced polymer

FRP EBR externally bonded FRP reinforcement

AFRP aramid fibre reinforced polymer

CFRP carbon fibre reinforced polymer

GFRP glass fibre reinforced polymer

HFRP hybrid fibre reinforced polymer

RC reinforced concrete

SLS serviceability limit state

ULS ultimate limit state

AS accidental situation

EC1 Eurocode 1

EC2 Eurocode 2

Notations xxxi


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SAMENVATTING

Deze samenvatting geeft een overzicht van de voornaamste aspecten van het proefschrift,

dat handelt over de versterking van structurele betonelementen met uitwendig gelijmde

vezelcomposietwapening (externally bonded fibre reinforced polymer reinforcement of FRP

EBR). De voor- en nadelen, de eigenschappen en de toepassing van deze versterkingstechniek

worden besproken, alsook het uitgevoerd experimenteel onderzoek en de analytische

verificaties. Ontwerprichtlijnen worden voorgesteld voor gewapend betonelementen versterkt

in buiging en dwarskracht en axiaal belaste kolommen omwikkeld met FRP EBR.

1 Inleiding

1.1 Vezelcomposietwapening voor beton

De ontwikkeling van lichte vezels met hoge sterkte en stijfheid in de jaren veertig was het

begin van een sterke opgang van de vezelcomposietmaterialen. Aanvankelijk slechts

aangewend voor hoogwaardige toepassingen binnen de ruimtevaart en vliegtuigindustrie,

groeide de interesse voor vezelcomposietmaterialen ook binnen een groter aantal sectoren van

de industrie, waaronder de bouwsector. In de betonbouw is de aanwending van

vezelcomposiet- of fibre reinforced polymer (FRP) elementen, voornamelijk als structurele

wapening, uitgegroeid tot n van de meest veelbelovende nieuwe technieken [1-4]. Immers,

uitgesproken voordelen zoals o.a. een hoge axiale sterkte, een uitstekende corrosie

Documents

STRUCTURAL BEHAVIOUR AND DESIGN OF CONCRETE MEMBERS STRENGTHENED WITH EXTERNALLY BONDED FRP REINFORCEMENT