tavassoli arjang 201311 masc thesis

8/9/2019 Tavassoli Arjang 201311 MASc Thesis

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BEHAVIOUR OF GFRPREINFORCED CONCRETECOLUMNS UNDER COMBINED AXIAL LOAD AND

FLEXURE

by

Arjang Tavassoli

A thesis submitted in conformity with the requirements

for the degree of Masters of Applied Science

Department of Civil Engineering

University of Toronto

Copyright by Arjang Tavassoli (2013)


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Behaviour of GFRP-reinforced concrete columns

under combined axial load and flexure

Arjang Tavassoli

Masters of Applied Science

Department of Civil Engineering

University of Toronto

2013

ABSTRACTThis study presents experimental results from nine large-scale circular concrete columns

reinforced with longitudinal and transverse glass fiber-reinforced polymer (GFRP) bars. These

specimens were tested under lateral cyclic quasi-static loading while simultaneously subjected

to constant axial load. Based on the measured hysteretic loops of moment vs. curvature and

shear vs. tip deflection relationships, a series of parameters related to ductility and flexural

strength are used to evaluate the seismic behavior of each column. The results showed that

concrete columns reinforced with GFRP bars have stable post-peak branches and can achieve

very high levels of deformability. Longitudinal GFRP bars maintained their stiffness at high

strains and transverse GFRP spirals provided increasing confinement for the entire duration of

the test without any spiral damage. The tests showed that, as an innovative material with

excellent corrosion resistance GFRP bars can be successfully used as internal reinforcement in

ductile concrete columns.


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ACKNOWLEDGEMENTSThis research project has come together thanks to the help from both individuals at the

University of Toronto and members of my family. First and foremost, I would like to express

my sincere gratitude to Professor Shamim A. Sheikh for his support and guidance throughout

this project and on completing this thesis.

I am pleased to be a part of Professor Sheikhs knowledgeable structural research group at the

University of Toronto and would like to thank the members of the group (Dr. Jingtao Liu, David

Johnson, Dr. Michael Colalillo, Douglas Getzlaf, Lisa Vint, Alireza Khavaran and Zahra

Kharal) who helped me with different stages of this project. Special thanks are due to Jingtao

Liu for his presence and assistance on both theoretical and experimental portions of the project

and to David Johnson who I have learnt a lot from over the last four years. I acknowledge the

help I received from Trevor Hrynyk and David Ruggerio during the course of this project. I

would also like to thank the undergraduate students (Kanwar Johal, Edvard Bruun and Max Ho)

who helped me in the construction phase of the project.

The outcome of this research would not have been possible without the help of the technical

staff of the structural laboratory and machine shop. I would like to express my appreciation to

Renzo Basset, Giovanni Buzzeo, John MacDonald, Xiaming Sun, Bryant Cook, Michel Fiss,

Bob Manson and Alan McClenaghan.

Lastly, and most importantly, I wish to thank my parents for sacrificing their life to assure a

bright future for their children. I would also like to thank my brother Arsalan, who has always

been there for me, during both high and low points in my life.


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TABLE OF CONTENTSABSTRACT .............................................................................................................................................. II

ACKNOWLEDGEMENTS .................................................................................................................... III

TABLE OF CONTENTS ........................................................................................................................ IV

LIST OF TABLES .................................................................................................................................VII

LIST OF FIGURES ............................................................................................................................. VIII

NOTATIONS ........................................................................................................................................ XIII

1. INTRODUCTION .............................................................................................................................1

1.1 GENERAL ......................................................................................................................................... 1

1.2 PROBLEM......................................................................................................................................... 3

1.3 RESEARCH OBJECTIVES................................................................................................................... 5

1.4 THESIS ORGANIZATION ................................................................................................................... 6

2. LITERATURE REVIEW .................................................................................................................7

2.1 STEEL-REINFORCED CONCRETE COLUMNS...................................................................................... 7

2.1.1 Ductility parameters ...............................................................................................................7

2.1.2 Effect of axial load .................................................................................................................8

2.1.3 Effect of transverse reinforcement ratio ................................................................................. 8

2.1.4 Effect of concrete strength ......................................................................................................9

2.2 GFRP-REINFORCED CONCRETE COLUMNS ....................................................................................13

2.2.1 General .................................................................................................................................13

2.2.2 Tobbi 2012 ............................................................................................................................ 15

2.2.3 De Luca 2010 ....................................................................................................................... 172.2.4 Choo 2006 ............................................................................................................................18

2.2.5 Alsayed 1999 ........................................................................................................................ 21

2.3 DESIGN AND CONSTRUCTION OF BUILDING STRUCTURES WITH FIBRE-REINFORCED POLYMERS

(CSA-S806) ........................................................................................................................................... 23

2.3.1 CSA-S806-02 ........................................................................................................................ 23

2.3.2 CSA-S806-12 ........................................................................................................................ 24

3. EXPERIMENTAL PROGRAM .................................................................................................... 26

3.1 GENERAL....................................................................................................................................... 26

3.2 MATERIAL PROPERTIES................................................................................................................. 27

3.2.1 Concrete ...............................................................................................................................27

3.2.2 Patching Material ................................................................................................................. 29

3.2.3 Glass Fiber Reinforced Polymer .......................................................................................... 30

3.2.4 GFRP and CFRP sheets ....................................................................................................... 34

3.2.5 Steel reinforcement ............................................................................................................... 34

3.3 CONSTRUCTION PROCESS.............................................................................................................. 35

3.3.1 Stub formwork ...................................................................................................................... 35

3.3.2 Stub cages .............................................................................................................................35


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3.3.3 Column cages ....................................................................................................................... 36

3.3.4 Anchors placement .............................................................................................................. 37

3.3.5 Column formwork ................................................................................................................. 37

3.3.6 Concrete casting ................................................................................................................... 39

3.3.7 Column repair ...................................................................................................................... 40

3.3.8 FRP wrapping ...................................................................................................................... 42

3.4 INSTRUMENTATION ....................................................................................................................... 433.4.1 Strain gauges ........................................................................................................................43

3.4.2 Linear variable differential transformers (LVDT) ............................................................... 45

3.4.3 Light emitting diode (LED) targets ...................................................................................... 46

3.5 TEST SPECIMENS............................................................................................................................ 48

3.6 TESTING......................................................................................................................................... 52

3.6.1 Test set up .............................................................................................................................52

3.6.2 Test procedure ...................................................................................................................... 53

4. EXPERIMENTAL RESULTS AND DISCUSSION .................................................................... 57

4.1 COUPON TEST RESULTS ON GFRPBARS........................................................................................ 57

4.2 ANALYTICAL CALCULATIONS ON UNCONFINED COLUMNS........................................................... 63

4.3 TEST OBSERVATIONS..................................................................................................................... 70

4.4 TEST RESULTS AND ANALYSIS .......................................................................................................82

4.4.1 Shear vs.tip deflection ............................................................................................................. 82

4.4.2 Moment vs. curvature ...............................................................................................................89

4.4.3 Spiral strains ............................................................................................................................95

4.4.4 Deflected shape ........................................................................................................................ 97

4.5 DUCTILITY PARAMETERS............................................................................................................ 103

4.6 MOST DAMAGED SECTION........................................................................................................... 108

4.7DISCUSSION.................................................................................................................................... 109

4.7.1 Bar buckling ........................................................................................................................... 1094.7.2 Effect of axial load.................................................................................................................. 111

4.7.3 Type of GFRP ......................................................................................................................... 114

4.7.4 Effect of amount of transverse reinforcement, spiral spacing and size .................................. 117

4.7.5 Comparison with steel-reinforced columns ............................................................................ 128

5. CONCLUSION AND RECOMMENDATIONS ......................................................................... 136

5.1 SUMMARY ...................................................................................................................................136

5.2 CONCLUSIONS ............................................................................................................................. 137

5.3 RECOMMENDATIONS FOR FUTURE WORK.................................................................................... 138

6. REFERENCES .............................................................................................................................. 140

APPENDICES ........................................................................................................................................ 144

APPENDIX A .........................................................................................................................................145

Glass transition temperature ........................................................................................................... 145

APPENDIX B .........................................................................................................................................148

Stub Formwork Design .................................................................................................................... 148

APPENDIX C .........................................................................................................................................154

Bar type B tension coupon test summary .................................................................................... 154


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Bar type C tension coupon test summary .................................................................................... 161

Bar type B compression coupon test summary ........................................................................... 167

Bar type C compression coupon test summary ........................................................................... 173

APPENDIX D .........................................................................................................................................177

Test Results (P-)............................................................................................................................. 177

Test Results (M-) ........................................................................................................................... 182

APPENDIX E ......................................................................................................................................... 187Strain variation in the spiral ........................................................................................................... 187

APPENDIX F .......................................................................................................................................... 196

Calculation of Ductility Parameters (,, , N, W).......................................................... 196


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LIST OF TABLES

Table 2-1: Steel-reinforced column database ............................................................................................. 11

Table 2-2: Tests results on GFRP bars (Almerich-Chulia et al, 2012).......14

Table 2-3: Results on GFRP- and Steel-reinforced square columns under axial load (Tobbi et al,

2012)...15

Table 2-4: Column properties and obtained results (De Luca et al., 2010)....17Table 2-5: Column group properties and obtained results (Alsayed et al., 1999) ......................................21

Table 3-1: Mechanical properties of LA repair mortar (BASF, 2007)....................................................... 29

Table 3-2: Mechanical properties of FRP sheets (Liu, 2013) .................................................................... 34

Table 3-3: Mechanical properties of two types of steel reinforcement ...................................................... 34

Table 3-4: Specimen details....50

Table 3-5: Specimen comparison ............................................................................................................... 51

Table 3-6: Number of direct comparisons.................................................................................................. 51

Table 4-1: Mechanical properties of GFRP straight bars and spirals in tension....58

Table 4-2: Mechanical properties of GFRP bars in compression...60

Table 4-3: Average glass transition temperatures for GFRP bars (Johal, 2013) ........................................ 61

Table 4-4: Modified nominal and nominal moment capacities for different GFRP bar types and differentaxial loads .................................................................................................................................................. 69

Table 4-5: Number of recorded cycles for column specimens..90

Table 4-6: Maximum measured spiral strain..96

Table 4-7: Ductility parameters................................................................................................................ 107

Table 4-8: Damaged region..108

Table 4-9: Euler buckling load, peak compressive load in the coupon and in the column ...................... 110

Table 4-10: Comparison of flexural strength enhancement in specimens...127

Table 4-11: Steel- vs. GFRP-reinforced column properties.....128

Table 4-12: Steel- vs. GFRP-reinforced column results .......................................................................... 128

Table C-1: Tensile mechanical properties of GFRP bar type B12 (Based on actual and nominal

diameter)...154

Table C-2: Tensile mechanical properties of GFRP bar type B 16 (Based on nominaldiameter)...157

Table C-3: Tensile mechanical properties of GFRP bar type B16 (Based on actual diameter) ............... 157

Table C-4: Tensile mechanical properties of GFRP bar type B 25 (based on nominal

diameter)...159

Table C-5: Tensile mechanical properties of GFRP bar type B25 (Based on actual diameter) ............... 159

Table C-6: Tensile mechanical properties of GFRP bar type C12 (Based on nominal

diameter)...161

Table C-7: Tensile mechanical properties of GFRP bar type C12 (Based on actual diameter) ............... 161

Table C-8: Tensile mechanical properties of GFRP bar type C16 (Based on nominal

diameter)...163Table C-9: Tensile mechanical properties of GFRP bar type C25 (Based on nominal

diameter)...............165Table C-10: Compressive mechanical properties of GFRP bar type B (Based on nominal

diameter).......167

Table C-11: Compressive mechanical properties of GFRP bar type B (Based on actual diameter) ........ 167Table C-12: Compressive mechanical properties of GFRP bar type C (Based on nominal diameter) .... 173


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LIST OF FIGURESFigure 2-1: Calculation of member and section ductility parameters (Sheikh and Khoury, 1993) .............. 7Figure 2-2: Load vs. drift ratio response of columns C100B60N25 (Left) and C100B130N25 (Right)

(Lgeron and Paultre, 2000).........................................................................................................................9

Figure 2-3: Moment vs. curvature response of columnsAS-18 (Left) and AS-18H (Right) (Sheikh et al.,

1994) .......................................................................................................................................................... 10Figure 2-4: Test setup to obtain the compressive response of GFRP bars (Deitz et al, 2003) ................... 13

Figure 2-5: Various tie configurations (Hany Tobbi, 2012) ...................................................................... 16Figure 2-6: Normalized axial stress vs. axial strain (Left), Dilation ratio vs. axial strain (Right) ............. 18Figure 2-7: Strength assumed for FRP bars (Choo et al., 2006) ................................................................20

Figure 2-8: Nominal moment-axial load interactions for Steel, AFRP, CFRP, and GFRP

(Choo et al., 2006) ......................................................................................................................................20Figure 2-9: Axial load vs. axial deformation for different column groups (Alsayed et al., 1999) ............. 22Figure 3-1: Concrete cylinder under compressive test ............................................................................... 28Figure 3-2: Compressive stress vs. strain relationship of concrete during column testing ........................ 28

Figure 3-3: Compressive stress vs. strain relationship for LA repair mortar .............................................30Figure 3-4: GFRP type C (Left), GFRP type B (Right) ......................................................................31

Figure 3-5: GFRP bars under tension test ..................................................................................................32Figure 3-6: GFRP bars under compression test ......................................................................................... 33Figure 3-7: Stub formwork .........................................................................................................................35

Figure 3-8: Circular wooden pucks for the correct placement of the column cage into the stub ............... 35Figure 3-9: Stub cage .................................................................................................................................36Figure 3-10: Column cage construction .....................................................................................................37Figure 3-11: Steel anchors ......................................................................................................................... 37Figure 3-12: Measuring the location of the 10 mm all threaded rods ........................................................ 38

Figure 3-13: Formwork before concrete casting ........................................................................................ 39Figure 3-14: Concrete casting .................................................................................................................... 40Figure 3-15: Columns P28-C-16-160, P42-B-12-160, and P28-B-12-50 (From left to right) ................... 40Figure 3-16: Column repair process ........................................................................................................... 41

Figure 3-17: Columns wrapped with FRP sheets and painted before testing ............................................. 42Figure 3-18: Strain gauge location on the longitudinal bars and spirals .................................................... 43Figure 3-19: Strain gauging the GFRP bars ............................................................................................... 45Figure 3-20: Location of the vertical LVDTs ............................................................................................ 46Figure 3-21: Location of the horizontal LVDTs and LED targets ............................................................. 46Figure 3-22: LED targets and the K610-CMM camera ............................................................................. 47

Figure 3-23: Specimen and cross section dimensions ................................................................................ 49Figure 3-24: Column Testing Frame (CTF) ............................................................................................... 52Figure 3-25: Installing steel plates at the ends of the specimen ................................................................. 53

Figure 3-26: Specimen in the CFT before testing ......................................................................................55Figure 3-27: Lateral displacement excursion protocol ............................................................................... 56

Figure 4-1: Tensile stress vs. strain relationship for GFRP bars used in this study ................................... 58

Figure 4-2: Compressive stress vs. strain relationship for GFRP bars used in this study .......................... 60Figure 4-3: Typical glass transition curve of a GFRP specimen (Johal, 2013) .......................................... 61

Figure 4-4: Cross section used for nominal sectional analysis .................................................................. 64Figure 4-5: Axial load-moment interaction curve using polar coordinate formulations (Everard, 1997) .. 64

Figure 4-6: Axial load-moment interaction curve using polar coordinate formulations (Davalath and

Madugula, 1987) ........................................................................................................................................65Figure 4-7: Layered cross section .............................................................................................................. 66

Figure 4-8: Axial load-moment interaction curve using layered analysis .................................................. 67Figure 4-9: Unconfined meoment vs. curvature responses for different bar types and axial loads ........... 69

Figure 4-10: P28-C-12-160 (Cycle 6, = 12 mm), P42-C-12-160 (Cycle 6, = 12 mm) ........................70


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Figure 4-11: Cover spalling in columns P28-C-12-50 and P28-C-12-160 after the 10thcycle ..................71Figure 4-12: Acceptable bond between the concrete and the LA repair mortar ........................................ 71

Figure 4-13: P28-C-12-50 (Cycle 35,L= 72 mm) ................................................................................. 73Figure 4-14: P28-C-12-50 (Most damaged region) .................................................................................... 73

Figure 4-15: P28-C-12-160 (cycle 24,L= 48 mm) ............................................................................... 74Figure 4-16: P28-C-12-160 (Most damaged region) .................................................................................. 74

Figure 4-17: P28-C-16-160 (cycle 24,L= 48 mm) ............................................................................... 75Figure 4-18: P28-C-16-160 (Most damaged region) .................................................................................. 75Figure 4-19: P28-B-12-50 (Cycle 35,L= 94 mm) ................................................................................. 76Figure 4-20: P28-B-12-50 (Most damaged region) .................................................................................... 76

Figure 4-21: P42-C-12-50 (Cycle 35,L= 72 mm) ................................................................................. 77Figure 4-22: P42-C-12-50 (Most damaged region) .................................................................................... 77

Figure 4-23: P42-C-12-160 (Cycle 25,L= 52 mm) ............................................................................... 78Figure 4-24: P42-C-12-160 (Most damaged region) .................................................................................. 78

Figure 4-25: P42-B-12-160 (Cycle 24,L= 48 mm) ............................................................................... 79Figure 4-26: P42-B-12-160 (Most damaged region) .................................................................................. 79

Figure 4-27: P42-B-16-160 (Cycle 25,L= 52 mm) ............................................................................... 80Figure 4-28: P42-B-16-160 (Most damaged region) .................................................................................. 80

Figure 4-29: P42-B-16-275 (Cycle 21,L= 44 mm) ............................................................................... 81Figure 4-30: P42-B-16-275 (Most damaged region) .................................................................................. 81Figure 4-31: Conversion from test set up used in this study to the cantilever column model ................... 83

Figure 4-32: Base shear calculation ........................................................................................................... 83Figure 4-33: Shear vs. tip deflection for column P28-C-12-50 .................................................................. 85Figure 4-34: Shear vs. tip deflection for column P28-C-12-160 ................................................................85

Figure 4-35: Shear vs. tip deflection for column P28-C-16-160 ................................................................86Figure 4-36: Shear vs. tip deflection for column P28-B-12-50 .................................................................. 86

Figure 4-37: Shear vs. tip deflection for column P42-C-12-50 .................................................................. 87Figure 4-38: Shear vs. tip deflection for column P42-C-12-160 ................................................................87Figure 4-39: Shear vs. tip deflection for column P42-B-12-160 ................................................................88

Figure 4-40: Shear vs. tip deflection for column P42-B-16-160 ................................................................88

Figure 4-41: Shear vs. tip deflection for column P42-B-16-275 ................................................................89

Figure 4-42: Moment vs. curvature for column P28-C-12-50 ................................................................... 91Figure 4-43: Moment vs. curvature for column P28-C-12-160 ................................................................. 91Figure 4-44: Moment vs. curvature for column P28-C-16-160 ................................................................. 92

Figure 4-45: Moment vs. curvature for column P28-B-12-50 ................................................................... 92

Figure 4-46: Moment vs. curvature for column P42-C-12-50 ................................................................... 93Figure 4-47: Moment vs. curvature for column P42-C-12-160 ................................................................. 93Figure 4-48: Moment vs. curvature for column P42-B-12-160 ................................................................. 94Figure 4-49: Moment vs. curvature for column P42-B-16-160 ................................................................. 94

Figure 4-50: Moment vs. curvature for column P42-B-16-275 ................................................................. 95Figure 4-51: Deflected shape of column P28-C-12-50 .............................................................................. 98Figure 4-52: Deflected shape of column P28-C-12-160 ............................................................................ 98Figure 4-53: Deflected shape of column P28-C-16-160 ............................................................................ 99

Figure 4-54: Deflected shape of column P28-B-12-50 .............................................................................. 99Figure 4-55: Deflected shape of column P42-C-12-50 ............................................................................100Figure 4-56: Deflected shape of column P42-C-12-160 ..........................................................................100Figure 4-57: Deflected shape of column P42-B-12-160 ..........................................................................101Figure 4-58: Deflected shape of column P42-B-16-160 ..........................................................................101Figure 4-59: Deflected shape of column P42-B-16-275 ..........................................................................102

Figure 4-60: Member ductility parameters ............................................................................................... 103

Figure 4-61: Procedure to obtain the displacement ductility factor () ............................................... 105Figure 4-62: Most damaged section/region .............................................................................................. 108Figure 4-63: Bar buckling in the compression zone................................................................................. 109


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Figure 4-64: Shear vs. tip deflection envelope curve for columns P28-C-12-50 and P42-C-12-50 ........ 112Figure 4-65: Shear vs. tip deflection envelope curve for columns P28-C-12-160 and P42-C-12-160 .... 112Figure 4-66: Moment vs. curvature hysteretic response for columns P28-C-12-50 and P42-C-12-50 .... 113

Figure 4-67: Moment vs. curvature hysteretic response for columns P28-C-12-160 and

P42-C-12-160113

Figure 4-68: Shear vs. tip deflection envelope curve for columns P28-B-12-50 and P28-C-12-50 ........ 115Figure 4-69: Moment vs. curvature hysteretic response for columns P28-C-12-50 and P28-B-12-50 .... 115

Figure 4-70: Shear vs. tip deflection envelope curve for columns P42-B-12-160 and P42-C-12-160.116Figure 4-71: Moment vs. curvature hysteretic response for columns P42-C-12-160 and

P42-B-12-160116

Figure 4-72: Shear vs. tip deflection envelope curve for columns P28-C-12-50 and P28-C-12-160..119

Figure 4-73: Shear vs. tip deflection envelope curve for columns P42-C-12-50 and P42-C-12-160..119

Figure 4-74: Shear vs. tip deflection envelope curve for columns P42-B-16-160 and P42-B-16-275.120

Figure 4-75: Moment vs. curvature hysteretic response for columns P28-C-12-50 and P28-C-12-160..120

Figure 4-76: Moment vs. curvature hysteretic response for columns P42-C-12-50 and P42-C-12-160..121

Figure 4-77: Moment vs. curvature hysteretic response for columns P42-B-16-160 and

P42-B-16-275121

Figure 4-78: Shear vs. tip deflection envelope curve for columns P28-C-12-160 and P28-C-16-160.123

Figure 4-79: Moment vs. curvature hysteretic response for columns P28-C-12-160 and

P28-C-16-160....123Figure 4-80: Shear vs. tip deflection envelope curve for columns P42-B-12-160 and P42-B-16-160.124


P42-B-16-160124

Figure 4-82: Shear vs. tip deflection envelope curve for columns P42-B-12-160 and P42-B-16-275.126


P42-B-16-275............................................................................................126

Figure 4-84: Hysteretic response of columns AS-19 and P42-B-16-160.129

Figure 4-85: Moment vs. curvature hysteresis response for columns AS-19 and P42-B-16-160131

Figure 4-86: Moment vs. curvature envelope response for columns AS-19 and P42-B-16-160..132

Figure 4-87: Shear vs. tip deflection hysteretic response of columns P27-NF-2 and P28-C-12-160..133

Figure 4-88: Shear vs. tip deflection envelope response of columns P27-NF-2 and P28-C-12-160134

Figure 4-89: Hysteretic response of columns P40-NF-6 and P42-C-12-160135Figure A-1: Heat flow vs. temperature for B12 spirals ............................................................................ 145Figure A-2: Heat flow vs. temperature for B16 spirals ............................................................................ 145Figure A-3: Heat flow vs. temperature for B25 high modulus straight bars ............................................ 146Figure A-4: Heat flow vs. temperature for C12 spirals ............................................................................ 146Figure A-5: Heat flow vs. temperature for C16 spirals ............................................................................ 147

Figure A-6: Heat flow vs. temperature for C25 straight bars ................................................................... 147Figure B-1: Stub formwork plan .............................................................................................................. 148Figure B-2: Wall A1................................................................................................................................. 149

Figure B-3: Wall A2................................................................................................................................. 149Figure B-4: Wall B ................................................................................................................................... 151

Figure B-5: Wall C ................................................................................................................................... 151

Figure B-6: Exterior plywood pieces ....................................................................................................... 153Figure C-1: Tensile stress vs. strain relationship for specimen B12-T-1 ................................................. 155

Figure C-2: Tensile stress vs. strain relationship for specimen B12-T-2 ................................................. 155

Figure C-3: Tensile stress vs. strain relationship for specimen B12-T-3 ................................................. 156Figure C-4: Tensile stress vs. strain relationship for specimen B16-T-1 ................................................. 157Figure C-5: Tensile stress vs. strain relationship for specimen B16-T-2 ................................................. 157Figure C-6: Tensile stress vs. strain relationship for specimen B16-T-3 ................................................. 158

Figure C-7: Tensile stress vs. strain relationship for specimen B25-T-1 ................................................. 159Figure C-8: Tensile stress vs. strain relationship for specimen B25-T-2 ................................................. 159Figure C-9: Tensile stress vs. strain relationship for specimen B25-T-3 ................................................. 160


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Figure C-10: Tensile stress vs. strain relationship for specimen C12-T-1 ............................................... 161Figure C-11: Tensile stress vs. strain relationship for specimen C12-T-2 ............................................... 161


Figure C-14: Tensile stress vs. strain relationship for specimen C16-T-2 ............................................... 164


Figure C-17: Tensile stress vs. strain relationship for specimen C25-T-2 ............................................... 166Figure C-18: Tensile stress vs. strain relationship for specimen C25-T-3 ............................................... 166Figure C-19: Compressive stress vs. strain relationship for specimen B25-C-1 ...................................... 168Figure C-20: Compressive stress vs. strain relationship for specimen B25-C-2 ...................................... 168Figure C-21: Compressive stress vs. strain relationship for specimen B25-C-3 ...................................... 169Figure C-22: Compressive stress vs. strain relationship for specimen B25-C-4 ...................................... 169

Figure C-23: Compressive stress vs. strain relationship for specimen B25-C-5 ...................................... 170Figure C-24: Compressive stress vs. strain relationship for specimen B25-C-6 ...................................... 170Figure C-25: Compressive stress vs. strain relationship for specimen B25-C-7 ...................................... 171Figure C-26: Compressive stress vs. strain relationship for specimen B25-C-8 ...................................... 171

Figure C-27: Compressive stress vs. strain relationship for specimen B25-C-9 ...................................... 172

Figure C-28: Compressive stress vs. strain relationship for specimen C25-C-1 ...................................... 174

Figure C-29: Compressive stress vs. strain relationship for specimen C25-C-2 ...................................... 174Figure C-30: Compressive stress vs. strain relationship for specimen C25-C-3 ...................................... 175Figure C-31: Compressive stress vs. strain relationship for specimen C25-C-4 ...................................... 175

Figure C-32: Compressive stress vs. strain relationship for specimen C25-C-5 ...................................... 176

Figure C-33: Compressive stress vs. strain relationship for specimen C25-C-6 ...................................... 176Figure D-1: Applied lateral load vs. displacement at load point for column P28-C-12-50 ..................... 177Figure D-2: Applied lateral load vs. displacement at load point for column P28-C-12-160 ................... 178Figure D-3: Applied lateral load vs. displacement at load point for column P28-C-16-160 ................... 178

Figure D-4: Applied lateral load vs. displacement at load point for column P28-B-12-50 ..................... 179

Figure D-5: Applied lateral load vs. displacement at load point for column P42-C-12-50 ..................... 179Figure D-6: Applied lateral load vs. displacement at load point for column P42-C-12-160 ................... 180Figure D-7: Applied lateral load vs. displacement at load point for column P42-B-12-160 ................... 180

Figure D-8: Applied lateral load vs. displacement at load point for column P42-B-16-160 ................... 181Figure D-9: Applied lateral load vs. displacement at load point for column P42-B-16-275 ................... 181Figure D-10: Moment vs. tip deflection for column P28-C-12-50 .......................................................... 182Figure D-11: Moment vs. tip deflection for column P28-C-12-160 ........................................................ 182

Figure D-12: Moment vs. tip deflection for column P28-C-16-160 ........................................................ 183Figure D-13: Moment vs. tip deflection for column P28-B-12-50 .......................................................... 183

Figure D-14: Moment vs. tip deflection for column P42-C-12-50 .......................................................... 184Figure D-15: Moment vs. tip deflection for column P42-C-12-160 ........................................................ 184Figure D-16: Moment vs. tip deflection for column P42-B-12-160 ........................................................ 185

Figure D-17: Moment vs. tip deflection for column P42-B-16-160 ........................................................ 185Figure D-18: Moment vs. tip deflection for column P42-B-16-275 ........................................................ 186

Figure E-1: Strain variation in the first spiral turn of specimen P28-C-12-50 ......................................... 187

Figure E-2: Strain variation in the second spiral turn of specimen P28-C-12-50 ....................................187Figure E-3: Strain variation in the first spiral turn of specimen P28-C-12-160 ....................................... 188

Figure E-4: Strain variation in the second spiral turn of specimen P28-C-12-160 .................................. 188

Figure E-5: Strain variation in the first spiral turn of specimen P28-C-16-160 ....................................... 189Figure E-6: Strain variation in the second spiral turn of specimen P28-C-16-160 .................................. 189Figure E-7: Strain variation in the first spiral turn of specimen P28-B-12-50 ......................................... 190Figure E-8: Strain variation in the second spiral turn of specimen P28-B-12-50 ....................................190

Figure E-9: Strain variation in the first spiral turn of specimen P42-C-12-50 ......................................... 191Figure E-10: Strain variation in the second spiral turn of specimen P42-C-12-50 .................................. 191Figure E-11: Strain variation in the first spiral turn of specimen P42-C-12-160 ..................................... 192


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xii

Figure E-12: Strain variation in the second spiral turn of specimen P42-C-12-160 ................................ 192Figure E-13: Strain variation in the first spiral turn of specimen P42-B-12-160 ..................................... 193Figure E-14: Strain variation in the second spiral turn of specimen P42-B-12-160 ................................ 193Figure E-15: Strain variation in the first spiral turn of specimen P42-B-16-160 ..................................... 194

Figure E-16: Strain variation in the second spiral turn of specimen P42-B-16-160 ................................ 194

Figure E-17: Strain variation in the first spiral turn of specimen P42-B-16-275 ..................................... 195Figure E-18: Strain variation in the second spiral turn of specimen P42-B-16-275 ................................ 195

Figure F-1: Displacement ductility factor and lateral drift ratio calculation (P42-C-12-50) ................... 196Figure F-2: Curvature ductility factor calculation for column P42-C-12-50 ........................................... 197Figure F-3: Cumulative ductility ratio and work damage indicator calculation (P42-C-12-50) .............. 198


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xiii

NOTATIONSa = Distance from the center of the left hinge to the location of the applied lateral loadA = Core area of a spirally reinforced compression member measured to the center of the spiral

A = Total area of longitudinal FRP reinforcementA = Total area of FRP hoop reinforcementA = Gross area of the sectionA = Total area of longitudinal steel reinforcementb = Distance from the center of the right hinge to the location of the applied lateral loadB = Width of rectangular/square column cross section

c = Distance from the center of the left/right hinge to the stub end/column tipD = Diameter of a circular column cross sectionD = Actual diameter of the GFRP bar measured in the lab excluding the ribbed or sand coatedregion

D = Distance from the column-stub interface to the beginning of the most damaged regionD = Distance from the column-stub interface to the most damaged sectionD = Nominal diameter of the GFRP bar provided by the manufacturer excluding the ribbed or sandcoated region

E = Energy damage indicatorE = Modulus of elasticity of GFRP reinforcement based on actual propertiesE = Modulus of elasticity of FRP reinforcement in compressionE = Modulus of elasticity of FRP reinforcement in tensionE = Modulus of elasticity of GFRP reinforcement based on nominal properties

E = Modulus of elasticity of steel reinforcementf = Specified compressive strength of concretef = Design stress in the spiral, hoop, or rectilinear FRP reinforcement in a columnf = Specified yield strength of longitudinal steel reinforcementf = Specified yield strength of steel hoop reinforcement


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xiv

f = Peak strength of steel reinforcementf = Ultimate tensile strength of a FRP bar/sheetf = Ultimate compressive strength of a FRP barh = Cross-sectional dimension of column core (center to center of spiral)H = Column heightk = Effective length factork = Confinement coefficientk = Stiffness of hysteretic loop of shear vs. tip deflection at cycle i averaged in two directionsk = Stiffness of the shear vs. tip deflection envelope curveL = Shear span of the specimenL = Length of the most damaged sectionL = Un-braced length of the GFRP compression sampleM = Moment at the most damaged sectionM = Nominal moment capacity of the column sectionM, = Modified nominal moment capacity of the column sectionM = Maximum moment measured in the most damaged section during the test

N = Cumulative ductility ratioP = Applied axial loadP = Critical axial load found using Euler buckling equationP = Nominal axial load resistance at zero eccentricity

For steel-reinforced columns: P f(A- A) + fAFor FRP-reinforced columns: P= f(A- A) + 0.002 EA

P = Lateral load capacity of the specimenP = Peak axial loadP = Factored axial load resistance at zero eccentricityP, = Ultimate compressive load in the GFRP bar during the coupon testP, = Ultimate compressive load in the GFRP bar during the column test


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xv

S = Spacing of transverse reinforcement or the spiral pitcht = Thickness of a FRP sheetT = Glass transition temperatureV = Shear at the base of the columnV = Maximum shear measured at the base of the column (column-stub interface) during the testV = Lateral reaction at the right hingeV = Nominal shear capacityw = Area enclosed by the hysteretic loop of shear vs. tip deflection at cycle iW = Work damage indicator = Ratio of average stress in rectangular compression block to the specified concrete strength = Column tip deflection = Peak tip deflection at cycle i averaged in both directions = Theoretical yield deflection = Ultimate deflection, = Axial deformation at peak load, = Maximum axial deformation at failure

= Design lateral drift ratio = Applied lateral displacement %= GFRP spiral strain when the base shear has dropped to 80% of peak shear = Maximum measured GFRP spiral strain = Ultimate GFRP spiral strain measured from tensile coupon tests = Yield strain of steel reinforcement = Ultimate tensile strain of a FRP bar/sheet = Strain at initiation of strain hardening of steel reinforcement = Rupture strain of steel reinforcement = Displacement ductility factor = Curvature ductility factor


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xvi

= Ratio of volume of hoop transverse steel reinforcement to total volume of concrete core (centerto center of hoop reinforcement)

= Ratio of volume of hoop transverse FRP reinforcement to total volume of concrete core (centerto center of hoop reinforcement)

= Ratio of total area of reinforcing steel to gross concrete section

= Ratio of total area of reinforcing FRP to gross concrete section = First peak stress reached by concrete = Second peak stress reached by concrete = Stress in the GFRP bar calculated based on actual properties = Stress in the GFRP bar calculated based on nominal properties = Curvature at the most damaged section

= Theoretical yield curvature = Ultimate curvature


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INTRODUCTION

1

1.INTRODUCTION

1.1

General

The use of Fibre Reinforced Polymers (FRP) started in the construction industry as early as

1970s. However, it was not until 1990s that non-metallic bars started to replace steel bars as

internal reinforcement in concrete structures. The main reason for this reinforcement

transformation was the costly issue of corrosion in steel-reinforced concrete structures. Over the

last 20 years, there has been a significant rise in the quality and the quantity of composite

reinforcement around the world. With advances in manufacturing technology leading to an

increase in production volume, the cost of high-strength FRP reinforcement has decreased and it

has become more readily available in the market.

Corrosion has cost billions of dollars in damages to concrete structures and specifically bridges

around the world. Meisen and Banthia (2009) reported that approximately 160,000 bridges are

rated deficient in the USA and are in need of immediate retrofit while in Canada the number of

deficient bridges is estimated at about 10,000. In Ontario alone, the repair cost of deficient

bridges and highways has been estimated as 57 billion dollars (Ministry of Transportation,

2009). FRP, as a high-strength non-corrosive material, has proven over the last few years to be

an optimal replacement to steel reinforcement if designed properly. Table 1-1, taken from a

report on FRP reinforcement in concrete structures published by the American Concrete

Institute (ACI) 440 committee, provides an extensive list of advantages and disadvantages of

FRP reinforcement (ACI Committee 440, 2006). Another disadvantage of the FRP material

which is not mentioned in Table 1-1 is its limitation in terms of constructability. As opposed to

steel bars, FRP bars cannot be bent, deformed or welded on the construction site. In terms of


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INTRODUCTION

2

durability problems associated with FRP reinforcement, research suggests that the accelerated

chemical tests conducted on the bars in the laboratory environment do not represent the actual

concrete environment in the field. Field tests conducted by researchers on GFRP samples taken

from bridges resulted in the conclusion that there was no degradation of Glass Fibre Reinforced

Polymer (GFRP) bars in the structures exposed to natural environmental conditions for periods

of 5 to 8 years (Mufti et al. 2007). The last advantage listed in Table 1-1 has been added by the

author, while the goal of this study is to determine the validity of this statement.

Table11:AdvantagesandDisadvantagesofFRPreinforcement(ACICommittee440,2006)

Advantages of FRP reinforcement Disadvantages of FRP reinforcement

High longitudinal tensile strength (varies with

sign and direction of loading relative to fibres)No yielding before brittle rupture

Corrosion resistance (not dependant on a coating)Low transverse strength (varies with sign and

direction of loading relative to fibres)

NonmagneticLow modulus of elasticity (varies with type of

reinforcing fibre)

High fatigue endurance (varies with type of

reinforcing fibre)

Susceptibility of damage to polymeric resins and

fibres under ultraviolet radiation exposure

Lightweight (about 1/5 to 1/4 the density of steel)Low durability of glass fibres in a moist

environment

Low thermal and electric conductivity (for glass

and aramid fibres)

Low durability of some glass and aramid fibres

in an alkaline environment

*High compressive strength and ability to

undergo cyclic loading without damage?

High coefficient of thermal expansion

perpendicular to the fibres, relative to concrete

May be susceptible to fire depending on matrix

type and concrete cover thickness

* This is added by the author. The goal of this study was to investigate this statement.


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INTRODUCTION

3

1.2

Problem

Despite the advances in the quality of the FRP bars over the last few years, many designers are

still reluctant to replace steel with FRP as the main reinforcement in concrete members.

However, this hesitation has been addressed to a great degree in the case of reinforced concrete

beams and slabs with large volumes of data available from tests performed on large specimens

in different research institutions around the world. Sufficient experimental data has led to the

addition of a chapter on the design of fibre-reinforced structures in the Canadian Highway

Bridge Design Code (CSA-S6-06). GFRP bars are confidently being used in bridge decks and

barrier walls where the presence of de-icing salts and potential for corrosion is the highest.

Halls Harbour Wharf Bridge in Nova Scotia, Joffre Bridge in Quebec and Crowchild Trail

Bridge in Alberta are some examples of Canadian bridges in which GFRP is used as the main

reinforcement (Mufti et al. 2007).

Contrary to the current understanding of the GFRP bars in tension, the compressive response of

these bars is not well-understood. Therefore many design codes in North America such as the

ACI440 prevent designers from using GFRP bars in members under compression while CSA-

S6-06 does not have any provisions regarding this application. Also, few studies have been done

regarding the behaviour of concrete columns reinforced with GFRP bars under pure axial load

while no experimental data exists on the response of concrete columns reinforced longitudinally

and transversally with GFRP under combined axial load and flexure. Steel reinforcement used in

bridge piers is susceptible to corrosion as a result of exposure to chlorides splashed by the

ongoing traffic during winters. The health of the pier reinforcement is critical to the structural

performance of the bridge as a whole and the lack of verification studies regarding the


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INTRODUCTION

4

behaviour of GFRP reinforced columns under realistic loading eliminates the chance of

identifying a more sustainable solution to this problem.


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INTRODUCTION

5

1.3

Researchobjectives

The experimental data presented here is part of a comprehensive research program which has

been active at the University of Toronto for more than 30 years (Sheikh, 1978; Sheikh and

Uzumeri, 1980, 1982; Sheikh and Yeh, 1986; Sheikh and Khoury, 1993, 1997; Sheikh et al.,

1994; Bayrak and Sheikh, 1997; Sheikh and Yau, 2002; Iacobucci et al., 2003; Memon and

Sheikh, 2005; Ghosh and Sheikh, 2007; Sheikh and Li, 2007; Sheikh and Liu, 2012). All

columns tested previously had steel as longitudinal and transverse reinforcement. Some of the

later work was carried out on columns internally reinforced with steel and externally retrofitted

with FRP wraps. The objective in this study is to investigate the behaviour of circular concrete

columns internally reinforced with GFRP bars and spirals under combined axial load and

flexure. Nine large-scale concrete columns were tested under quasi-static lateral cyclic loading,

while simultaneously subjected to a constant axial compression simulating seismic loading.

Each specimen consisted of a 356 mm (14 in.) diameter and 1473 mm (58 in.) long column cast

integrally with a 508762813 mm (203032 in.) stub. The testing variables included axial

load level, type of GFRP (manufacturer), spiral reinforcement ratio, size and spacing.


22/214


23/214

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24/214

LITERATURE REVIEW

8

2.1.2

Effectofaxialload

The level of axial load plays an important role in the behaviour of concrete columns especially

under seismic loading. As the axial load increases, the secondary effects become more

significant and therefore the column ductility decreases. This can easily be observed by looking

at the data presented in Table 2-1. For instance, the energy damage indicator for column S-2NT

is more than 10 times that of column S-1NT. These two columns are identical except that the

axial load on column S-1NT is twice the value for column S-2NT.

The Canadian concrete design handbook recommends the use of the following equation to

obtain the required amount of the spiral reinforcement in a concrete column.

Equation21 0.45( 1)

This equation does not take into account the level of axial load; however, for members subjected

to flexure and significant axial load the code recommends the use of the more general equation

given below to design the volumetric ratio of the circular hoop reinforcement.

Equation22 0.4

2.1.3

Effectoftransversereinforcementratio

Detailing in concrete columns plays a major role in the achieved ductility. The concrete

standards have strict provisions regarding spacing of the transverse reinforcement in columns.

Closely-spaced spirals or ties would increase the shear strength of the column, delay the

buckling of the longitudinal reinforcement and most importantly provide confinement to the

concrete core and therefore delay the crushing of the core. This statement can be verified from

the behaviour of columns C100B60N25 and C100B130N25 in Table 2-1. The former has spirals

spaced at 60 mm while the latter at 130 mm. Doubling the spiral spacing has caused the


25/214

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26/214

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27/214

11

Table21:Steelreinforcedcolumndatabase

Specimen

Column

size

B or D

mm

Column

length

mm

MPa

Lateral steelLongitudinal

steelAxial

load

level

P/P0

m

Size at

spacing, mm

%

MPa

%

MPa

AS-3H [1]

305 1473

54.1 9.5 @ 108 1.68 507

2.44 507

0.59

AS-18H 54.7 12.7 @ 108 3.06 464 0.61

AS-20H 53.6 12.7 @ 76.2 4.30 464 0.61

A-17H 59.1 9.5 @ 108 1.68 507 0.62

AS-3 [2]

305

1473 33.2 9.5 @ 108 1.68 507

2.44 507

0.50

AS-17 2438 31.3 9.5 @ 108 1.68 507 0.63

AS-18 1473 32.8 12.7 @ 108 3.06 464 0.63

AS-19 1473 32.3 9.5/6 @ 108 1.30 457 0.39

ES-1HT [3]

305 1473

72.1 15M @ 95 3.15 463

2.58 454

0.50

AS-2HT 71.7 10M @ 90 2.84 542 0.36

AS-3HT 71.8 10M @ 90 2.84 542 0.50

AS-4HT 71.9 15M @ 100 5.12 463 0.50 S-1NT [4]

356 1473

40.1 9.5 @ 80 1.12

507 3.00 507

0.54

S-2NT 40.1 9.5 @ 80 1.12 0.27

S-3NT 39.2 9.5 @ 300 0.30 0.54

S-4NT 39.2 9.5 @ 300 0.30 0.27

D60-7-4-2 5/8-0.2P [5]

305 1070

53.7 12.7 @ 67 2.73 414

2.44 414

0.2

D60-7-3C-1 5/8-0.2P 50.8 9.5 @ 41.3 3.82 414 0.2

D60-15-4-2 5/8-0.2P 100.8 12.7 @ 67 2.73 414 0.2

D60-15-3C-1 5/8-0.2P 100.2 9.5 @ 41.3 3.82 414 0.2

D120-15-3C-2 5/8-0.2P 101.6 9.5 @ 67 2.36 828 0.2

D120-15-3C-1 5/8-0.2P 101.7 9.5 @ 41.3 3.82 828 0.2

D60-4-3C-2 5/8-0.2P 26.2 9.5 @ 67 2.36 414 0.2

D60-4-3C-2 5/8-0.4P 27.0 9.5 @ 67 2.36 414 0.4

AS-1NSS [6] 305 1473 42.4 9.5 @ 300 0.61 457 2.58 465 0.56 C100B60N15 [7]

305 2150

92.4 10M @ 60 4.26 391

2.15 470

0.15

C100B60N25 93.3 10M @ 60 4.26 404 0.30

C100B60N40 98.2 10M @ 60 4.26 418 0.42

C100B130N15 94.8 10M @ 130 1.96 391 0.15

C100B130N25 97.7 10M @ 130 1.96 404 0.28

C100B130N40 104.3 10M @ 130 1.96 418 0.40


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12

Specimen

Column

size

B or D

mm

Column

length

mm

MPa

Lateral steelLongitudinal

steelAxial

load

level

P/P0

Ma

mom

kNSize at

spacing, mm

%

MPa

%

MPa

C100S100N15 [8]

300 2150

109 10M @ 100 1.43 440

2.55 560

0.16 16

C100SH100N15 101 9.5 @ 100 1.00 425 0.16 17

C100S70N25 103 10M @ 70 2.04 440 0.27 20

C100SH70N25 97 9.5 @ 70 1.43 425 0.26 19

C100S37N40 100 10M @ 37 3.85 440 0.43 22

C100SH37N40 103 9.5 @ 37 2.71 425 0.43 23

P27-NF-1 [9]

356 1473 40

9.5 @ 150 0.60 496

3.01 490

0.27 20

P27-NF-2 9.5 @ 100 0.90 496 0.27 22

P40-NF-5 9.5 @ 300 0.30 496 0.40 18

P40-NF-6 9.5 @ 100 0.90 496 0.40 20

P40-NF-7 9.5 @ 75 1.20 496 0.40 23

P56-NF-10 9.5 @ 300 0.30 496 0.56 18

P56-NF-11 10M @ 100 1.22 450 0.56 20P56-NF-12 10M @ 75 1.63 450 0.56 19

AS-1NS [10]

305 1473

31.4

9.5 @ 300 0.61 457 2.58 465

0.33 18

AS-7NS 37.0 0.33 20

AS-8NS 42.3 0.56 16

CI4 [11]

260 1650

56 10 @ 120 1.24

400

1.5

400 0.15

98

CI8 54 10 @ 120 1.80 3.0 14

CS4 54 12 @ 70 3.10 1.5 10

CS8 53 10 @ 70 3.20 3.0 14

[1] (Sheikh et al., 1994), [2] (Sheikh and Khoury, 1993), [3] (Bayrak and Sheikh, 1997), [4] (Sheikh and Yau, 2002),

(Memon and Sheikh, 2005), [7] (Lgeron and Paultre, 2000), [8] (Paultre et al., 2009) [9] (Sheikh and Liu, 2012) [10]

(Hosseini et al., 2005)

* Total energy dissipated until failure


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LITERATURE REVIEW

14

with a high accuracy. It was also concluded that the compressive modulus of elasticity of GFRP

was approximately equal to its tensile stiffness (Deitz et al, 2003).

Researchers at Instituto de la Construccion Eduardo Torrojo CSIC (Spain) tested more than

500 GFRP bars to obtain certification (Almerich-Chulia et al, 2012). The bars were made by the

pultrusion process and contained 75% fiber by volume. Table 2-2 summaries the results

attained. The un-braced length of bars tested in compression was not reported by the authors.

Table22:TestsresultsonGFRPbars(AlmerichChuliaetal,2012)

Diameter

(mm)

Tensile

Strength (MPa)

Tensile modulus of

elasticity (GPa)

Compressive

strength (MPa)

Compressive modulus

of elasticity (GPa)

8 856 38.3 464 39.910 779 42.6 450 46.3

12 638 41.1 470 41.9

16 696 42.5 449 50.8

20 724 43.6 444 44.9

25 723 39.9 372 42.0

32 720 39.7 319 40.8

AVG 733 41.1 424 43.8

Results provided in Table 2-2 verify the conclusions attained by Wu and Dietz regarding the

compressive strength and the stiffness of GFRP bars. Despite the presence of these data, due to

the uncertainty in the compressive response of GFRP bars and their low modulus of elasticity,

usage of these bars in columns is not recommended by most design codes. The ACI code (ACI

440.1R-06) specifically deters designers from using GFRP bars as longitudinal reinforcement in

columns or as compression reinforcement in flexural members. The Canadian Highway Bridge

Design Code (CSA-S6-06) does not have any provisions on the use of GFRP bars in

compression members. The latest version of the Canadian code (CSA-S806-12), on the other

hand, allows for the use of GFRP bars in columns, but conservatively advises the designer to

take the strength of the bar in compression as zero. Further discussion on the evolution of the

Canadian code provisions regarding this area is provided in section 2.3.


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LITERATURE REVIEW

15

A few studies have been conducted on the behaviour of internally GFRP-reinforced concrete

columns under pure axial load. Nevertheless, no experimental work has been reported on the

response of these columns under combined axial load and flexure.

The following sections summarize the existing experimental and theoretical studies on GFRP-

reinforced concrete columns available in the scientific literature.

2.2.2

Tobbi2012

Eight square columns with a cross section of 350 350 mm and a height of 1400 mm were

tested under concentric loading. One control specimen with no reinforcement, two steel-

reinforced columns and five GFRP-reinforced columns made up the eight specimens tested

(Tobbi et al, 2012). Table 2-3 summarizes the specimen details along with a few results.

Table23:ResultsonGFRP andSteelreinforcedsquarecolumnsunderaxialload(Tobbiet

al,2012)

Specimen Bar typeLongitudinal

reinforcement

Transverse

reinforcement

Tie spacing

(mm)

C-P-0-00 --- --- --- --- 0.94 ---

C-S-1-330 Steel 8 M15 M10 ties 330 (13.0) 0.98 ---C-S-1-120 Steel 8 M15 M10 ties 120 (4.72) 1.05 1.35

C-G-1-120 GFRP 8 No.19 No.13 ties 120 (4.72) 0.98 1.23

C-G-1A-120 GFRP 8 No.19 No.13 ties 120 (4.72) 1.00 1.21

C-G-2-120 GFRP 8 No.19 No.13 ties 120 (4.72) 1.00 1.27

C-G-3-120 GFRP 12 No.16 No.13 ties 120 (4.72) 0.98 1.36

C-G-3-80 GFRP 12 No.16 No.13 ties 80 (3.15) 1.02 1.68

Different tie configurations as shown in Figure 2-5 were used to investigate their effectiveness

for concrete core confinement (Tobbi et al, 2012). In Table 2-3, normalized first and second

peak stresses (, )relative to the compressive strength of each column are reported. It canbe seen that configuration 3 is the most effective way of confining the column core due to the

presence of more closely spaced longitudinal bars.


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.85 used fo

f a GFRP-r

ars as 35%

s

reinforce

column is

reaches its

e stress in

rain corres

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rs while the

inforceme

steel-reinf

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omposed o

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the longitu

ponding to

LI

obbi,2012)

y indicated

t in column

rced colum

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ty when the

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ERATURE

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rength leads

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concrete re

at the pea

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EVIEW

r further

opted to

king the

to close

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GFRP.

aches its

load is

by the


33/214


34/214

The

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1

2

3

Cho

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igure26:N

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- At low l

very simi

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-

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under axi

2.2.4

C

(2006) co

orced with l

rmalizedax

o vs. the a

l a strain of

h the typica

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nd B-3 wh

failure. The

ngitudinal

lar to that o

ibution of

aded colum

esearch is

al load and

oo2006

ducted a st

ongitudinal

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0.0025 all c

l value for

significantl

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following c

einforceme

steel reinfo

GFRP bars

. (P0= 0.85

eeded to u

lexure

dy that foc

FRP bars. F

18

axialstrain(

or all the c

olumns mai

oncrete. As

y for colu

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nt ratios, th

rced colum

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fc(Ag A

derstand t

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or different

Left),Dilati

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rp)).

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calculatin

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ERATURE

ialstrain(R

igure 2-6.

around 0.2

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cing. How

s of up to

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EVIEW

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umns is

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columns

columns

ial load


35/214

LITERATURE REVIEW

19

interaction curves were calculated for different FRP bar types. In the analysis, the following

assumptions were made (Choo et al., 2006):

1- A parabolic relationship until the peak strain and linear response after peak for concrete

in compression

2- The strength of concrete in tension was ignored in the analysis

3- Linear elastic response for FRP bars was assumed in both tension and compression.

Since the authors were uncertain regarding the response of FRP bars in compression, the

compressive strength as recommended by Deitz was taken as half of the tensile strength,

while various modulus of elasticity ratios were used in the analysis

4- Linear strain profile was assumed through the height of the section during bending

5- Perfect bond was assumed between reinforcement and surrounding concrete

6- Confinement effects from transverse reinforcement were not included in this study

Stress vs. strain relationships for different FRP bars used in this study are shown in Figure 2-7.

The moment-axial load interaction curves were calculated for a rectangular section using a

crushing concrete strain of 0.003 and a compressive strength of 35 MPa. Figure 2-8 shows these

curves for grade 60 steel, AFRP, CFRP and GFRP. Moment and axial load are normalized using

the following expressions:

Equation23 =

Equation24 =


36/214

Figure2

Figure27

8:Nominal

:Strengthas

omentaxia(

20

sumedforF

loadinteraChooetal.,2

Pbars(Cho

tionsforSte006)

LI

oetal.,2006

el,AFRP,CF

ERATURE

)

P,andGFRP

EVIEW


37/214

LITERATURE REVIEW

21

It is evident that steel-reinforced columns exhibit a balance point since steel reaches its yield

strain at the same time as concrete reaches its peak strain. However, FRP-reinforced columns do

not show a balance point and for reinforcement ratios equal to or greater than 3%, moment

resistance increases as the axial load decreases from maximum to zero. For FRP-reinforced

columns with low reinforcement ratios, there is potential for brittle tension failure. In other

words, at low axial loads the FRP bars can reach their ultimate tensile strength before concrete

in compression crushes. This has to be noted by the designers and authors believed that the ACI

318-05 reinforcement ratio limits needed to be adjusted for columns reinforced with FRP bars

(Choo et al., 2006). Ignoring the contribution of FRP bars in compression, as recommended by

many codes, is conservative and further research is needed in this area.

2.2.5

Alsayed1999

Fifteen concrete columns with a cross sectional dimensions of 450 250 mm and a height of

1200 mm were tested under concentric axial compression using an Amsler testing machine with

a capacity of 10,000 kN (Alsayed et al., 1999). Columns were divided into five groups of three

specimens each. The first group did not have any reinforcement while the other four groups had

steel/GFRP as longitudinal and transverse reinforcement as seen in Table 2-5 which shows the

details of the specimens and some of the results.

Table25:Columngrouppropertiesandobtainedresults(Alsayedetal.,1999)

Groupf'c

(MPa)

Longitudinal

Reinforcement

Transverse

Reinforcement

Max Load

Measured

(kN)

Overall

shortening

(mm)Quantity Type Quantity TypeA 38.6 0 - 0 - 2997 3.54

B 38.3 6 16 mm Steel 6 @ 250 Steel 3681 3.99

C 38.8 6 16 mm Steel 6.35 @ 250 GFRP 3380 4.54

D 39.0 6 15.7 mm GFRP 6 @ 250 Steel 3285 4.14

E 38.5 6 15.7 mm GFRP 6.35 @ 250 GFRP 3301 3.84


38/214

The l

and

stiff

confi

achi

The

capa

GFR

reinf

failu

bars.

The

the c

oad vs. def

showed a

ess of the

ning the col

ved was ne

authors co

ity by 13%

P results in

orced speci

e for GFR

It is not cl

atio of un-

olumn is 16

igure29:A

rmation res

less stiff b

FRP ties c

umn core a

gligible for

cluded that

and conver

a 10% loss

ens failed

-reinforced

ar what the

raced lengt

which indic

ialloadvs.

onses for a

ehaviour th

ompared to

early stage

all column

replacing

ting the tra

in axial ca

y buckling

columns

authors m

over diam

ates the like

xialdeform

22

ll the colum

an groups

that of the

s of loading

groups due

steel bars

sverse rein

acity of th

of the steel

as initiated

an by the

eter for the

lihood for b

tionfordiff

n groups ar

and D, w

steel ties. S

than GFRP

to the low

ith GFRP

orcement f

e column (

bars at the

by concret

reakage of

longitudina

uckling.

rentcolum

LI

shown in

ich could

teel ties we

ties. Howe

transverse

bars in col

om steel to

lsayed et a

id-height

e crushing

the GFRP

GFRP bar

groups(Als

ERATURE

igure 2-9.

e due to t

re more eff

er, the con

reinforcem

umns redu

the same a

l., 1999). T

f the colu

nd breakag

ars in com

in the mid-

ayedetal.,1

EVIEW

roups C

e lower

ctive in

inement

nt ratio.

es their

ount of

e steel-

n, while

e of the

ression.

eight of

999)


39/214

LITERATURE REVIEW

23

2.3Design and construction of building structures withfibre

reinforcedpolymers(CSAS806)

The Canadian code has gone through considerable changes regarding the use of FRP bars in

concrete structures over the last few years. These changes are more visible in terms of

compression members and members under combined axial load and flexure. This section briefly

summarizes code provisions in 2002 and introduces adjustments and additions made in 2012.

Since circular columns are used in this research study, only provisions regarding the use of

spirals are discussed here.

2.3.1

CSAS80602

Clause 8.4.3.1 states that FRP reinforcement shall not be used as longitudinal reinforcement in

members subjected to compressive axial load and flexure. FRP can be used as transverse

reinforcement if the following limitations are taken into account (Canadian Standards

Association, 2002).

For spirally reinforced columns (Clause 8.4.3.2):

- Spiral reinforcement shall have a diameter of at least 6 mm

- Pitch of the spiral shall not exceed 1/6 of the core diameter of the column

- Clear spacing between the successive turns of the spirals must be between 25 and 75 mm

- The volumetric spiral ratio must not be less than the value given by:

Equation25 =0.6

( 1)

Where,

Equation26 = ()+


40/214

LITERATURE REVIEW

24

0.2 and

1 0.3

FRP is not permitted to be used as longitudinal reinforcement in columns in this code and FRP

reinforcement in the compression zone shall be deemed to provide no compressive resistance in

design (Clause 8.6.2). For structures in seismic zones, the transverse FRP reinforcement shall be

larger of the amounts given by Eq. 2.5 and Eq. 2.7 (Clause 12.7.1):

Equation27 =14s

( 1)

is the design lateral drift ratio which shall not be less than 3%. Transverse reinforcement

spacing shall not be greater than the minimum of of the minimum member dimension, 150

mm and 6 times the diameter of the smallest longitudinal bar. According to the requirements of

clause 8.4.3.2, k, the confinement coefficient, is equal to 1 for circular hoops or spirals.

2.3.2

CSAS80612

In the ten years between the 2002 to 2012 codes, research was conducted around the world and

specifically in Canada on GFRP-reinforced concrete structures yielding positive results

regarding the behaviour of GFRP-reinforced columns. The Canadian code in 2012 thus relaxed

the stringent condition on using GFRP bars in compression members. Some of the changes in

the 2012 code are discussed below.

CL 8.4.3.1 states that the longitudinal FRP reinforcement may be used in members subjected to

compressive axial load and flexure. However, the code still conservatively states that strength

and stiffness of FRP bars in compression shall be ignored in design (Canadian Standards

Association, 2012). In clause 8.4.3.7, the code prevents the designers from using a longitudinal

reinforcement ratio of less than 1% in compression members to avoid the brittle tension failure

discussed earlier in Section 2.2.4.


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LITERATURE REVIEW

25

The volumetric ratio of spiral reinforcement is found using the equation below:

Equation28 =

( 1)

Where,

Equation29 Although the reduction factor of 0.6 is removed here compared to Eq 2.5 of the 2002 code, the

stress in the spiral () has been increased from 0.004 to 0.

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