Citation
Strengthening structural elements with CFRP : crack behavior

Material Information

Title:
Strengthening structural elements with CFRP : crack behavior
Creator:
Bhiri, Mohammed
Place of Publication:
Denver, CO
Publisher:
University of Colorado Denver
Publication Date:
Language:
English

Thesis/Dissertation Information

Degree:
Master's ( Master of science)
Degree Grantor:
University of Colorado Denver
Degree Divisions:
Department of Civil Engineering, CU Denver
Degree Disciplines:
Civil engineering
Committee Chair:
Kim, Yail Jimmy
Committee Members:
Chang, Nien-Yu
Li, Chengyu

Notes

Abstract:
Fracture-induced distress is a critical consideration in constructed civil structure. Such a problem typically takes place when a steel girder bridge is loaded by infinitely many vehicles that can generate fatigue loading. Once a fatigue crack initiated and propagated, the performance of the bridge is degraded and repair/strengthening work needs to be implemented. Use of carbon fiber reinforced polymer (CFRP) composite sheets is an alternative technology to enhance the behavior of damaged steel girders. Despite recent research endeavors, it is not known that the effect of CFRP-strengthening on mitigating the crack initiation and propagation of steel members under variation of temperatures. A two-phase experimental program is conducted to fill such a research gap to advance the state-of-the art, including plain steel elements and CFRP-strengthened counterparts that are loaded in axial tension with temperature 25, 75, 125, and 175. The development of cracks from their edges is monitored to establish a relationship between axial stress and crack propagation and debonding, and the effects of CFRP thermal behavior on the debonding area with load’s increase. The efficacy of CFRP-strengthening for steel members is elaborated. Moreover, this research presents behavior of reinforced concrete beams strengthening using carbon fiber-reinforced polymer (CFRP) sheets to carry monolithic and cycle load. An experimental program is conducted to study the improvement that will take place of adhesive both interface sides of concrete using C-grid FCRP. In order to test all beam with of different sizes of adhesive interface to increase and repair the shear capacity, then measuring the propagation of diagonal and flexural cracks, it has been shown that the use of C-grid has minimize prorogation of cracks over beams interface. Furthermore, the improved concrete bearing capacity using the C-grid gave similar results using CFRP sheet on the interface. DIC was used to analyze spread of cracks at different stages of the load during the tests, and to check shear stress distribution on the surface of the concrete.

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Source Institution:
University of Colorado Denver
Holding Location:
Auraria Library
Rights Management:
Copyright Mohammed Bhiri. Permission granted to University of Colorado Denver to digitize and display this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.

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i STRENGTHENING STRUCTU RAL ELEMENTS WITH CFRP: CRACK BEHAVIOR b y Mohammed Bhiri B.S., Sirte University, 20 10 A T hesis submitted to the Faculty of the Graduate School of the University of Colorado in Partial F ulfillment of the Requirements for the D egree of Master of Science Civil Engineering Program 2017

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ii ©2017 Mohammed Bhiri

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iii ALL RIGHTS RESERVED This T h esis for the Master of Science D egree by Mohammed Bhiri Has been approved for the Civil Engineering Program by Yail Jimmy Kim, Chair Nien Yin Chang Chengyu Li Date: December 16 , 2017

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iv ABSTRACT Fracture induced distress is a critical consideration in constructed civil structure. Such a problem typically takes place when a steel girder bridge is loaded by infinitely many vehicles that can generate fatigue loading. Once a fatigue crack initiated and propagated, the performance of the bridge is degraded and repair/strengthening work needs to be implemented. Use of carbon fiber reinforced polymer (CFRP) composite sheets is an alternative technology to enhance the behavior of damaged steel girders. Despite recent research endeavors, it is not known that the effect of CFRP strengthening on mi tigating the crack initiation and propagation of steel members under variation of temperatures. A two phase experimental program is conducted to fill such a research gap to advance the state of the art, including plain steel elements and CFRP strengthened counterparts that are loaded in axial tension with temperature 25, 75, 125, and 175 . The development of cracks from their edges is monitored to establish a relationship between axial stress and crack propagation and debonding, and the effects of CFRP therm al behavior on . The efficacy of CFRP strengthening for steel members is elaborated. Moreover, t his research presents behavior of reinforced concrete beams strengthening using carbon fiber reinforced polymer (CFRP) sh eets to carry monolithic and cycle load. An experimental program is conducted to study the improvement that will take place of adhesive both interface sides of concrete using C grid FCRP. In order to test all beam with of different sizes of adhesive inter face to increase and repair the shear capacity, then measuring the propagation of diagonal and flexural cracks, it has been shown that the use of C grid has minimize prorogation of cracks over beams interface. Furthermore, the improved concrete

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v bearing cap acity using the C grid gave similar results usi ng CFRP sheet on the interface . DIC was used to analyze spread of cracks at different stages of the load during the tests, and to check shear stress distribution on the surface of the concrete .

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vi DEDICATION First, all thanks and gratitude to Almighty God for all the grace and mercy that was given to me. Secondly to the first teacher to the man who was sent as to me, to you Prophet Mohammed. For you, my parents, who my Lord said "Your Lord has ordered you to worship none except Him, and to be good to your parents. If either or both of them attain old age with you, do not say: "Fie on you", nor rebuke them, but speak to them with words of respect, and lower to them the wing of humbleness out of mercy and say: 'My Lord, be merciful to them, as they raised me since I was little". My parents who have the greatest favor after Allah for anything good or any superiority. Finally, to my family, adviser, friends and all my teacher who support me durin g my life.

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vii ACKNOWLEDGEMENTS Over the past two years of working on strengthening the structural elements using CFRP composites I would like to express my gratitude to my parents and my family of their support during that period. Also, I want to thank my advisor Dr. Jimmy Kim for all his support, inspiration, and advice through my research period. I would like to show gratitude to Civil Engineering Department University of Colorado Denver and all technical staff at concrete Laboratory at civil engineering department of University of Colorado Denver for their assistance and help of the my experimental work. Also, I would like to recognize my friend and classmates of their contribution to the s uccess of my academic study. Finally, I would like to acknowledge University of Sebha and my county Libya for sponsoring me to study aboard and supporting me with a fully funded scholarship.

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viii TABLE OF CONTENT S 1. INTRODUCTION ................................ ................................ ................................ ...................... 1 1.1 Background ................................ ................................ ................................ ........................... 1 1.2 Problem Statement ................................ ................................ ................................ ................ 2 1.3 Objectives of Study ................................ ................................ ................................ ............... 2 1.4 Scope of Study ................................ ................................ ................................ ...................... 3 1.5 Research Outline ................................ ................................ ................................ ................... 3 2. LITERATURE REVIEW ................................ ................................ ................................ ........... 4 2.1 Introduction ................................ ................................ ................................ ........................... 4 2.2 Rehabilitation Steel Element wit h CFRP Composite ................................ ............................ 5 2.3 CFRP Characteristics and Efficiency ................................ ................................ .................... 6 2.4 Effects of Different Strengthening Systems of CFRP Composite on RC Beam Behavior. .. 7 2.5 Strengthening of Concrete Structures by CFRP Grids ................................ .......................... 8 3. COMPOSITE ST RENGTHENING OF STEEL MEMBERS IN FRACTURE INDUCED DISTRESS ................................ ................................ ................................ ................................ .... 11 3.1 Introduction ................................ ................................ ................................ ......................... 11 3.2 Experimental Tests ................................ ................................ ................................ .............. 12 3.2.1 Material for rehabilitation ................................ ................................ ............................. 12 3.2.1.1 Adhesive (epoxy) ................................ ................................ ................................ ... 12 3.2.1.2 CFRP strip ................................ ................................ ................................ .............. 12 3.2.2 Specimen detail and test setup ................................ ................................ ...................... 13 3.2.2.1 Surface preparation ................................ ................................ ................................ 13 3.2.2.2 Specimens' details ................................ ................................ ................................ .. 13 3.2.3 Test setup and instrumentation ................................ ................................ ..................... 13 3.3 Results and Discussion ................................ ................................ ................................ ........ 14 3.3.1 Load displacement behavior and ultimate load capacity ................................ ............. 14 3.3.2 Failure Modes ................................ ................................ ................................ ............... 15 3.3.3 Crack propagation and width opening ................................ ................................ .......... 15 3.3.4 Temperature effect on steel behavior under cyclic load ................................ ............... 16 3.3.5 CFRP debonding influence on cr ack propagation under temperature .......................... 17 3.3.6 Probabilistic prediction of crack propagation using Bayesian updating ...................... 18

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ix 4. BEHAVIOR OF RC BEAMS STRENGTHENED WITH CFRP AND C GRID U WRAP SHEETS AND SHEAR FACES. ................................ ................................ ................................ .. 51 4.1 Introduction ................................ ................................ ................................ ......................... 51 4.2 Experimental P rogram ................................ ................................ ................................ ......... 51 4.2.1 Specimens details ................................ ................................ ................................ ......... 51 4.2.2 Properties of materials ................................ ................................ ................................ .. 52 4.2.2.1 Concrete mix ................................ ................................ ................................ .......... 52 4.2.2.2 CFRP & C Grid properties ................................ ................................ .................... 52 4.2.2.3 Epoxy ................................ ................................ ................................ ..................... 53 4.3 Beams Preparation and Strengthening ................................ ................................ ................ 53 4.3.1 Beams preparation ................................ ................................ ................................ ........ 53 4.3.2 Applications of CFRP and C Grid sheets on the RC beams ................................ ........ 53 4.4 Test Setup and Instrumentation ................................ ................................ ........................... 5 4 4.5 Test Results and Discussions ................................ ................................ .............................. 54 4.5.1 Beams strengthening with CFRP U wrap ................................ ................................ .... 55 4.5.1.1 Load carrying capacity ................................ ................................ ......................... 55 4.5.1.2 Load displacement behavior of RC beam ................................ .............................. 55 4.5.1.3 RC beams strain response ................................ ................................ ...................... 56 4.5.1.4 CFRP strain of strain gages ................................ ................................ .................... 56 4.5.1.5 Failure mode ................................ ................................ ................................ .......... 57 4.5.2 Beams strengthening with CFRP U wrap (GEM) ................................ ........................ 58 4.5.2.1 Load carrying capacity of GEM beams ................................ ................................ 58 4.5.2.2 Load displacement behavior of GEM beams ................................ ........................ 59 4.5.2.3 RC beams strain response ................................ ................................ ...................... 59 4.5.2.4 CFRP strain of strain gages ................................ ................................ .................... 59 4.5.2.5 Failure mode ................................ ................................ ................................ .......... 60 4.5.3 Beams strengthening with C Grid U wrap and SMP hybrid (GHM) ........................... 60 4.5.3.1 Load carrying capacity ................................ ................................ ......................... 60 4.5.3.2 Load displacement behavior of RC beam ................................ .............................. 61 4.5.3.3 RC beams strain response ................................ ................................ ...................... 61 4.5.3.4 CFRP strain of strain gages ................................ ................................ .................... 62 4.5.3.5 Failure mode ................................ ................................ ................................ .......... 62 4.5.4 Beams strengthening with C Grid U wrap and SMP hybrid (GHC) ............................ 63

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x 4.5.4.1 Load carrying capacity ................................ ................................ ......................... 63 4.5.4.2 Load displacement behavior of RC beam ................................ .............................. 64 4.5.4.3 RC beams strain response ................................ ................................ ...................... 65 4.5.4.4 CFRP strain of strain gages ................................ ................................ .................... 65 4.5.4.5 Failure mode ................................ ................................ ................................ .......... 65 5. CONCLUSION ................................ ................................ ................................ ....................... 179 6. REFERENCES ................................ ................................ ................................ ....................... 182

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xi L IST OF TABLES Table 2.1 Mechanical 4 Table 3.1. Ultimate load and stress of unstrengthened and strengthened specimens with different 19 Table 3.2. Properties of CF RP s 19 Table 3.3. Properties 20 Table 3.4. De 21 Table 3.5. Tests Data of all steel specimens at dif ferent temperatur 22 Table 3.6. Crack propagation of steel strips strengthening without CFRP according to meas 23 Table 3.7. CFRP Debonding of specimens under monotonic load with temperature 40 C 2 4 Table 3.8. CFRP Debonding of specimens under cyclic load with temperature 40 C 25 Table 3.9. The crack length and width at different 26 Table 3.10. Bayesian updatin 26 Table 4.1 Nomenclature and detai 66 Table 4.2. Mix pro 67 Table 4.3 . Compressive strength of concrete cylinders 67 Table 4 . 4. Properties of C Grid composite strip from the manufacturer Table 4.5 . Summary of 69

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xii Table 4.6 . a. Failure modes of beams bonded at di . Table 4.6 . b. Failure modes of beams bonded at di fferent Table 4.6 . c. Failure modes of beams bonded at di fferent Table 4.6 . d. Failure modes of beams bonded at di

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xiii LIST OF FIGURES Fig. 3.4. Specimen S No CFRP 25 Fig. 3.5. Specimen S No CFRP 25 3 during tensile test with laser extometer and reflective tape Fig. 3.6. Specimen S CFRP 25 1 during tensile test with laser extometer and reflective tape to Fig. 3.7. Specimen S CFRP 75 1 subjected to thermal loading during tensile test with laser extometer and reflective tape to monitor the longitudina Fig. 3.8. Relation of stress level and crack length of specimens strengthened with CFRP at Fig. 3.9. Relation of stress level and crack width of specimens strengthened with CFRP at Fig. 3.10. Comparison between engineering strain and true stress of unstrengthened steel Fig. 3.11. Comparison between engineering stress and true strain of strengthened steel specim Fig. 3.12. Load Fig. 3.13. Stress strain behavior of steel specimens without CFRP. Fig. 3.14 Microscope picture of S No CFRP 25 3 of Fig. 3.15. Microscope picture of S No CFRP 25 Fig. 3.16. Microscope picture of S No CFRP 25 Fig. 3.17. Cracked specimen during tensile test Fig. 3.18. Load Fig. 3.19. Stress Fig. 3.20. Load displacement behavior of steel specimens without CFR Fig. 3.21. Stress

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xiv Fig. 3.22. Load displacement behavior of steel specimen 1 with CFRP under monotonic load at a temperature 40 Fig. 3.23. Infrared images of specimen 1 with CFRP under monotonic load at a temperature 40 Fig. 3.24. Load displacement behavior of steel specimen 2 with CFRP under monotonic load at a temperature 40 Fig. 3.25. Infrared images of specimen 2 with CFRP under monotonic load at a temperature 40 Fig. 3.26. Load displacement behavior of steel specimen 1 with CFRP under monotonic load at a temperature 40 Fig. 3.27. Infrared images of specimen 1 with CFRP under monotonic load at a temperature 40 F ig. 3.28. The response of steel specimens with CFRP under cyclic load at temperature of 40 C of three specimens: (a) load displacement behavior; (b) stress Fig. 3.29. Infrared images of specimen 1 with CFRP under cyclic load at a temperature 40 C: (a) Fig. 3.30. Infrared images of specimen 2 with CFRP under cyclic load at a temperature 40 C: (a) Fig. 3.31. Infrared images of specimen 3 with CFRP under cyclic load at a temperature 40 C: (a) Fig. 3.31. Comparison of failure probability of the Besaiyen updating model vs the crack % of steel specime Fig 4. 1.a. Beam preparation : (a) Steel cages; (b) Costing the concrete in wooden frame; (c) Fig.4.1. Concrete test se Fig.4.2. Beam CTB derail; (a) cross section; (b) strengthened beam with CFRP; (c) strain gages distribution; (d) reinforcements d Fig. 4.3. Test result for CTB: (a) load displacement; (b) PI gage strain in tension and c ompression; (c) CFRP strain at differen Fig. 4.4. Response of CFRP strain at different loading Fig 4.5. Failure mode of CTB: (a) flexural cracks at mid span at 49 kN; (b) CFRP debonding; (c) o verview final failure; (d) close view fina Fig.4.6. Beam UEM strengthened with CFRP details: (a) 100%; (b) 75%, (c) 50%; (d) 25%.....79

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xv Fig. 4.7. Test result for UEM 100: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at differen Fig. 4.8. Response of CFRP strain at different loading s tages of specimen UEM Fig 4.9. Failure mode of UEM 100: (a) flexural cracks at mid span; (b) CFRP debonding; (c) overview final failure; (d) close view fina Fig. 4.10. Test result for UEM 75: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at differen Fig. 4.11. Res ponse of CFRP strain at different loading stages of specimen UEM Fig 4.12. Failure mode of UEM 75: (a) flexural cracks at mid span; (b) CFRP debonding; (c) overview final failure; (d) close view fina Fig. 4.13. Tes t result for UEM 50: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at differen Fig. 4.14. Response of CFRP strain at different loading stages of specimen UEM Fig 4.15. Failur e mode of UEM 50: (a) flexural cracks at mid span; (b) CFRP debonding; (c) overview final failure; (d) close view fina Fig. 4.16. Test result for UEM 25: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different locations. 95 Fig. 4.17. Response of CFRP strain at different loading sta ges of specimen UEM Fig 4.18. Failure mode of UEM 25: (a) flexural cracks at mid span; (b) CFRP debonding; (c) overview final failure; (d) cl ose view fina Fig.4.19. Beam GEM strengthened with C Grid details: (a) 100%; (b) 75%, (c) 50%; (d) Fig. 4.20. Test result for GEM 100: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at differen Fig. 4.21. Response of CFRP strain at different loading s tages of specimen GEM Fig 4.22. Failure mode of GEM 100: (a) flexural cracks at mid span; (b) CFRP debonding; (c) Fig. 4.23. Test result for GEM 75: (a) load displacement; (b) PI gage strain in tension and 95 Fig. 4.24. Response of CFRP strain at different loading stages of specimen GEM .....96 Fig 4.25. Failure mode of GEM 75: (a) flexural cracks at mid span; (b) CFRP debonding; (c) overview final failure; (d) close view fin al

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xvi Fig. 4.26. Test result for GEM 50: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at differ Fig. 4.27. Response of CFRP strain at different loading stages of specimen GEM Fig 4.28. Failure mode of GEM 50: (a) flexural cracks at mid span; (b) CFRP debonding; (c) overview final failure; (d) close view fin Fig. 4.29. Test result for GEM 25: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at differe Fig. 4.30. Response of CFRP strain at different loading st ages of specimen GEM Fig 4.31. Failure mode of GEM 25: (a) flexural cracks at mid span ; (b) CFRP debonding; (c) overview final failure; (d) close view fin Fig.4.32. Beam GEM strengthened with Grid details: (a) 100% 0.75*0.75; (b) 100% 1.5*3, (c) 100% Fig. 4.33. Test result for GEM 100 1.5*3: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different location Fig. 4.34. Response of CFRP strain at different loading stages of specimen GEM 100 Fig 4.35. Failure mode of GEM 100 1.5*3: (a) flexural cracks at mid span; (b) CFRP debonding; (c) overview final failure; (d) close view fina Fig. 4.36. Test result for GEM 100 3*1.5: (a) load di splacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different Fig. 4.37. Response of CFRP strain at different loading stages of specimen GEM 100 3*1.5. Fig 4.38. Failure mode of GEM 100 3*1.5: (a) flexural cracks at mid span; (b) CFRP debonding; (c) overview final failure; (d) close view fina Fig. 4.39. Test result for GEM 100 0.75*0.75: (a) load displacement; (b) PI gage strai n in tension and compression; (c) CFRP strain at dif Fig. 4.40. Response of CFRP strain at different loading stages of specimen GEM 100 0.75*0.75. Fig 4.41. Failure mode of GEM 100 0.75*0.75: (a) flexural cracks at mid span; (b) CFRP 11 3 Fig.4.42. Beams details GHM and GCM strengthened with C Grid and SMP hybrid: (a) 100%; (b) 75%, (c) 50%; (d) 25 4 Fig. 4.43. Test result for GHM 100: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different 5

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xvii Fig. 4.44. Response of CFRP strain at different loading stages of specimen GHM 6 Fig 4.45. Failure mode of GHM 100: (a) flexural cracks at mid span; (b) CFRP debonding; (c) overview final failure; (d) close view fi 7 Fig. 4.46. Test result for GHM 75: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different 8 Fig. 4.47. Response of CFRP strain at different loading stages of specimen GHM 9 Fig 4.48. Failure mode of GHM 75: (a) flexural cracks at mid span; (b) CFRP debonding; (c) overview final failure; (d) close view fi 0 Fig. 4.49. Test result for GHM 50: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different 1 Fig. 4.50. Response of CFRP strain at different loading stages of specimen GHM 2 Fig 4.51. Failure mode of GHM 50: (a) flexural cracks at mid span; (b) CFRP debonding; (c) overview final failure; (d) close view fi 3 Fig. 4.52. Test result for GHM 25: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at differen 34 Fig. 4.53. Response of CFRP strain at different loading stages of specime n GHM 5 Fig 4.54. Failure mode of GHM 25: (a) flexural cracks at mid span; (b) CFRP debonding; (c) overview final failure; (d) close view fi 6 Fig. 4.55. Test result for GHC 100: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different 7 Fig. 4.56. Effect of cyclic load on beam GHC 100: (a) stif fness; (b) damage index 8 Fig 4.57. Failure mode of GCM 100: (a) flexural cracks at mid span; (b) CFRP debonding; (c) overview final failure; (d) close view fi 9 Fig. 4.58. Test result for GHC 75: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP 0 Fig. 4.59. Effect of cyclic load on beam GHC 75: (a) st 1 Fig 4.60. Failure mode of GCM 75: (a) flexural cracks at mid span; (b) CFRP debonding; (c) overview final failure; (d) close view fi 2 Fig. 4.61. Test result for GHC 50: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different location. 3 Fig. 4.62. Effect of cyclic load on beam GHC 50: (a) st 4 Fig 4.63. Failure mode of GCM 50: (a) flexural cracks at mid span; (b) CFRP debonding; (c) overview final failure; (d) close view final failure. 5

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xviii Fig. 4.64. Test result for GHC 25: (a) load displacement; (b) PI gage strain in tensi on and compression; (c) CFRP strain at different 6 Fig. 4.65. Effect of cyclic load on beam GHC 25: (a) stiffness; (b) 7 Fig 4.66. Failure mode of GCM 25: (a) flexural cracks at mid span; (b) CFRP debonding ; (c) overview final failure; (d) close view fi 8 Fig. 4.67. Crack pattern of GEM 25 tested under monotonic load obtain Fig.4.68. Crack propagation with load of spe cimen GEM Fig. 4.69. Crack pattern of GEM 50 tested under monoton Fig.4.70. Crack propagation with load of specimen GEM 2 Fig. 4.71. Crack pattern of GEM 75 tested under monoton Fig.4.72. Crack propagation with load of sp ecimen GEM 4 Fig.4.74. Crack propagation with load of sp ecimen GEM Fig. 4.75. Crack pattern of GEM 100 0.75*0.75 tested under monotonic load obtained by Fig.4.76. Crack propagation with load of specime n GEM 100 Fig. 4.77. Crack pattern of GHM 25 tested under monotonic load with SMP hybrid obtained by Fig.4.78. Crack propagation with load of sp ecimen GHM Fig. 4.79. Crack pattern of GHM 50 tested under monotonic with SMP hybrid load obtained by Fig.4.80. Crack propagation with load of sp ecimen GHM .151 Fig. 4.81. Crack pattern of GHM 75 tested under monotonic with SMP hybrid load obtained by Fig.4.82. Crack propagation with load of sp ecimen GHM Fig. 4.83. Crack pattern of GHM 100 tes ted under monotonic with SMP hybrid load obtained by Fig.4.84. Crack propagation with load of specimen GH M Fig.4.85. Concrete beam area loss on beams surfac

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xix NOTATION S No CFRP Steel specimens without CFRP S CFRP Steel specimens strengthened with CFRP S UMD Unstren gthened steel specimens at tempera ture 40 C under monotonic load S CMD Strengthened steel specimens at temperature 40 C under monotonic load Random variable parameter Density function Crack length of unstrengthened specimens at a certain percent Crack length of strengthened specimens at a certain percent Random variable CTB Control beam strengthened with CFRP sheet.

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xx UEM Beam strengthened with CFRP sheet and CFRP U wraps with epoxy. GEM Beam strengthened with CFRP sheet and C Grid U wraps with epoxy GHM Beam strengthened with CFRP sheet and C Grid U wraps with epoxy and SMP (hybrid bonding) under monotonic loading. GHC Beam strengthened with CFRP sheet and C Grid U wraps with epoxy and SMP (hybrid bonding) under cyclic loading.

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xxi

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1 1. INTRODUCTION 1.1 Background Cracks problems in bridges have become one of the most significant issues that affect the operational life and load carrying capacity of bridges in the U.S., and the cites may resort to removing the bridge in case of not controlling the crack propagation of bridge. Some strategies were used in many bridges to control that cracks; these strategies include removing or fixing the damaged members or placing steel plates to bridge girders to race the beams load carrying capacity, also increase the number of girders between the damage ones (McRae & Ramey, 2003). Howe ver, these methods are expensive because of the needs of periodic maintenance as a result of corrosion. Strengthening of concrete and steel structures using CFRP has become widely known around the world for the features that characterize the CFRP composite which will be briefly explained in this introduction. The use of CFRP was limited in aerospace field to explore the environment and build space shuttles as a result of its durability and load capacity (Liu, Silva, & Nanni, 2001), but it extended to other areas including medical and construction. The first use of CFRP in the structural industry according to (Burgoyne, 1999) as in laboratory experiments filed in Switzerland. Although according to Nozaka, Sheild, & Hajjar 2005, the most important advantages of CFRP are durability, non corrosion, and lightweight, the main advantage of CFRP is the flexible response and strength of carbon fibers matrix and mechanical properties of epoxy that was used (Salama and Abd El Meguid, 2010). Many laboratories and analyt ical studies of using CFRP composite to support steel and concrete elements applied in previous studies. Also, Different types of fiber polymers composite such as GFRP and AFRP were studied using various applications such as sheets and bars. However, there are still research demands to explore in this area and study the behavior of concrete and steel supported by CFRP composite. In this research, many models and applications of using CFPR sheets were investigated and proposed like using CFRP with steel stri ps under effects of temperature variation, also; re distribution of stresses between concrete and CFRP sheets on stress reduction and crack control under monolithic and cycle loads.

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2 1.2 Problem S tatement Bridges girders that have a significant decrease in its cross section area as a result of corrosion in steel element or crack in the concrete. Surly bridge girders cross sections designed to carry specific truckloads, so the increase of traffic and exceeding load limits overload carrying capacity of the girders cause a crack and fatigue. That limits according to (AASHTO) American Association of State Highway, and Transportation Officials set dead stresses, live load stresses, deflection, and fatigue stresses. Loads transcending cause stresses pressure on the bridge girders in the short term, and fatigues and cracks in a long time. Recently, using CFRP composite as strengthening and rehabilitation became effective solution comparing with traditional reconstruction such as adding external prestressed tendons or steel plates. 1.3 Objectives of Study The objective of this research is to investigate the improvement and behavior of different CFRP strips bond applications and redistribution of stresses and crack control under monolithic and cycle loads using CFRP sheets. Also the influence of applying heat on depending on FCRP sheets with steel, and the impact of bonding CFRP grid (C grid) on the stresses field of concrete beams. The aims of this research can sum up as follows: Study strengthening steel and concret e with CFRP under the influence of monolithic and cycle loads with different CFRP applications. Study the growth of crack propagation regarding length and width with the temperature variation. Study the bond behavior of different CFRP bond length applicati on with reinforced concrete and examine the various failures modes. Conducting structural model of bridges girders using CFRP and FE analyses were evaluated using SAP2000. Provide design criteria for bridges girders rehabilitation bridges using CFRP compos ite.

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3 1.4 Scope of Study The scope of this study is strengthening of steel and concrete elements in shear and flexure area. In this study, two cases were taken. In one set is steel strips for tension tests with a variation of temperature and the other set is concrete beams with c grid. The primary focus was to raise beam's load carrying capacity of the using CFRP sheets during the testing process. 1.5 Research O utline The introduction discusses the background of the study and problem statement. Also, it shows the aims and scoop of the study performed to approach the research objectives. Chapter 1, Introduction with the research outline. Chapter 2, Literature Review, presents the previous researchers to repair and strengthening bridge girders and the efficiency of using CFRP on b ridges rehabilitating. Moreover, historical reviews about rehabilitate bridges and the previous researches evolution of repair methods using CFRP. Chapter 3, the experimental program of steel strips; this chapter focus on the specimens' details with CFRP a pplications and the test setup during the tension tests. Also, CFRP applications on specimens with applying different temperature on stiffness and strength properties. Probability analysis of the cracks growth under temperature variation using Bayesian upd ating. Chapter 4, concrete beams experimental program; this chapter presents a brief background of strengthening concrete using CFRP then the specimens' details with CFRP applications repair system; and the MTS machine test setup with specimens design. Als o, CFRP applications on specimens considering strengthening the damaged spots of the reference beam failure modes behavior under monolithic and cycle fatigue loads. This chapter includes the results analysis and efficiency of CFRP repair system that propos ed in this research. Chapter 5; that section showed a model of bridges girders strengthened with CFRP and FE analysis to simulate crack and failure model using SAP2000. Chapters 6, this contains a discussion of the research conclusions and suggestions for future work.

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4 2. LITERATURE REVIEW 2.1 Introduction The connotation of using CFRP composite in construction industry applications is a technique that was lately developing. This literature review will focus on previews researchers of using CFRP or other fi ber reinforced polymer (FRP) types to repair structural elements. This chapter will also address research that has not provided definitive solutions for the use of CFRP and applications proposed in some research. Initially, the properties of different type s of FRP will discussed. Secondly, the CFRP rehabilitation applications that were applied and compression of some research CFRP repair systems. Thirdly, bond and fatigue behavior of CFRP and failure mode will review. Finally, research results and FE analys is of elements strengthened externally with CFRP. Fiber reinforced polymer (FRP) reinforcement is a composite material Composed of a polymer matrix reinforced with fibers. The most used fiber reinforced polymer (FRP) are carbon, fiberglass, and aramid. The re are many differences between these types of FRP regarding flexibility and some properties, but the main difference is the mechanical properties and their ability to resist environmental conditions. As a result of the increasing academic research of usin g FRP for repairing and strengthening facilities, and bridges, and that results show the effectiveness of FRP application. Moreover, FRP use quickly moved to structures rehabilitation field, also; the use of FRP strap is comfortable to maintain bridges wit hout stopping traffic especially in seismic zones (Karbhari, 2005) The table 2.1 shows a compression of FRP types, and it showed that Young's modulus of CFRP is the highest which means higher stiffness. CFRP and AFRP have higher Young's modulus and strengt h comparing with GFRP. Also, the failure mode of all FRP has brittle failure mode.

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5 Table 2.1 Mechanical properties of fiber (fib, 2001) Type Tensile strength [N/mm ² ] [N/mm² ] Ultimate tensile strain [%] Carbon 2100 6000 215.000 700.000 0.2 2.3 Aramid 3500 4100 70.000 130.000 2.5 5.0 Glass 1900 4800 70.000 90.000 3.0 5.5 The focus of most studies that conducted of using FRP was concentrated on CFRP for repair system of bridge structures because significant improvement that was achieved (Tavakkolizadeh & Saadatmanesh, 2003). Carbon fibers reinforced polymer CFRP was preferred in this research because of CFRP mechanical properties such as high strength, high Young's modulus, non corrosive materials, lightweigh t, and durability. Also, for its suitability for use in infrastructure rehabilitation applications. 2.2 Rehabilitation Steel Element w ith CFRP Composite The researchers of the efficiency of strengthening structures with CFRP were measured in different stu died either analytically or experimentally to discover the methods of using CFRP types, and the most accurate applications of placing the CFRP sheets on the steel elements externally (Al Emrani & Kliger, 2006). Also, the different applications and combinat ions of CFRP with the adhesive materials such as epoxy illustrations change the behavior of the steel elements which means the applications of strengthening structures with CFRP sheets have a significant effect on the steel elements behavior. CFRP composit e is a current method of enhancing structures, and this technique is a modern engineering solution as a result of the advantages using of CFRP (Swaminathan, Pagano, & Ghosh, 2006). Such as high modulus of elasticity, high rupture resistance, high tensil e strength, lightweight, low coefficient of thermal expansion, impact resistance. Also, small elongation according to (Stoll, Saliba, & Laura, 2000). The unique elastic characteristic of the SMP resulted in the robust recovery of the interfaced form ation when the specimens failed, while such an effect was not achieved for those exposed to temperatures higher than175 1C due to thermal

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6 damage. Although the interfacial behavior was affected by the degree of thermal exposure, the occurrence of stress con centrations was virtually independent of the elevated temperatures et al . , 2014) 2.3 CFRP Characteristics and E fficiency (Salama & Abd El Meguid, 2010) According to Carbon fiber reinforced polymer (CFRP) is a matrix composite material streng thened by carbon fibers. The strengthening distributed phase could be in the procedure of both continuous and irregular carbon fibers, commonly knitted into a textile. CFRP is a costly material, but they have the essential specific mechanical characteristi cs per weight, such as ultimate strength and modulus of elasticity. CFRP used for strengthening the structures as a result of high modulus of elasticity, high rupture resistance, high tensile strength, low elongation, and low density. Moreover, CFRP is a m ore costly material than its corresponding item like GFRP and AFRP, although CFRP observed as having more significant properties. Many research was focused on using CFRP both for retrofitting and rehabilitation, and as an alternative to steel as a strength ening or prestressing structures elements. Cost of CFRP composite still a concern in the short term, but in long term durability and corrosion resistance low the cost of maintenance contrariwise of the traditional methods such as steel plate and mortar. H owever, design codes have been drawn up by organizations such as the ACI, some concern still some indecision in the engineering community in worries to applying CFRP composite as alternative materials. However, many pieces of research have approved the eff iciency of using CFRP in strengthening steel elements (Phares, Wipf, Klaiber, Abu Hawash, & Lee, 2003). Additionally, Al Saidy claims that (2001) the research showed the efficiency of CFRP sheets for enhancing the strength of steel structural elements. A study that involved experimental and field test that effectiveness of CFRP sheets was used to reinforce steel girder. Also, the study accomplished (Wipf et al . , 2005) show a significant augmentation in the load carrying capacity of bridges by using of CFRP sheets to the tension flange of a steel girder. Which support the conclusions that say the CFRP is an essential strengthening solution to repair steel structural element, and strengthening bridge girders with CFRP shows improvement of performance and response of the girders.

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7 2.4 E ffects of Different Strengthening Systems of CFRP Composite on RC Beam B ehavior . Flexural, flexural shear, and shear approaches of failures are the main failure styles for RC beams. Flexural failure is the ideal failure mode for the engineers than shear failure as a result of flexural failure is a ductile behavior shear failure characterize as a brittle mode. A ductile failure mode permits stress redistribution and gives notice to occupants, while a brittle failure mode i s rapid and consequently catastrophic. To create a flexure or shear resistance of RC beam durable enough strengthening is essential. Over last years, external reinforcement using CFRP composites increased the attractiveness of the elements because of sever al causes including material price, lightweight, and simplicity of application. Furthermore, CFRP has more dependable bond strength as compared to structural elements everywhere steel bars corrosion, and obvious cracks at the interface are unavoidable in t he occurrence of humidity and load (Mosallam & Banerjee,2007). The workability of using CFRP sheets to RC beams includes external bonding of CFRP sheets on the tension interface of RC beams using epoxy with six percent (1:3) hardener: resins. (Meier, 1987) Stated the usage of CFRP sheets as flexural strengthening support of RC beams, and displayed that CFRP can provide a solution which decreases overall cost savings in the order of 25%. Verified CFRP composites on full scale strengthened RC beams, and post ed the efficiency of the strain compatibility technique in the investigation of RC beam (Kaiser, 1989). It recommended that inclined damaging could lead to premature failure of strengthening CFRP sheet. The study involved the improvement of an analytical m odel for CFRP composite sheets, which was presented to agree with experimental results. Most of the research focused on response was obtainable in forms of load deflection and damage patterns and mechanical ductility of structures. Furthermore, all beams s howed significant growth in load carrying capacity and energy absorption ability of RC beams with strengthening (Alsayed et al., 2002). The ideas of rupture mechanics, and proposed an investigative model for the CFRP of shearing dowel engagements of both t he RC beams and the CFRP sheets is to investigate the flexural behavior of RC beams strengthened with CFRP sheets (Triantafillou & Plevris, 2000). It showed a summary of some shear design systems for RC beams strengthened with CFRP (Denianud & Roger Chen, 2001). Established a theoretical method depending on truss analogy system in combination with the concept of RC beams plasticity (Collotti et al., 2004), and that research

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8 described that the theoretical method gives an accurate association matrix with prev ious experimental work. (Adhikary, 2004) Presented an investigational test on shear behavior of RC beams property after externally strengthening them with unidirectional CFRP sheets. Many external strengthening systems calculated, and the system establish ed that the CFRP U stirrup arrangement is the most operational reinforcement procedure for shear strength development. (Zhang & Hsu, 2005) Described the data of experimental research showed on RC beams strengthened with both CFRP U wrap and CFRP sheets on the tension side. The tempryre have an eccects on the CFRP behavior with RC beam and accrding to (Siriwardanage & Kim, 2016) the transfer of stresses between the composite of beams and CFRP was influenced by the thermal growth which increase the relaxation of the CFRP the bonding, and the stresses behavior effected by thermal behavior of CFRP. The current edition of the ACI 440 (ACI, 2008) suggested a theoretical explanation to calculate the improvement of RC beams that strengthened externally with CFRP sh eets. (ACI, 2008) ACI 440 focused on the industrialized operational strain in CFRP, and RC beams composite during damage that changes relying upon the inconsistency of composites of CFRP properties, sizes, and the CFRP application systems. The previews of literature reviews explain that although extensive research has been concluding that reinforcing the RC beams with CFRP composite; however, it is still strengthening RC beams with several CFRP applications and patterns of reinforcement give a different beh avior that frequently not accurate. In this research, an experimental work through using CFRP sheets and also C grid composite have been designing to investigate the effectiveness of different application and size CFRP and C grid U wrap. 2.5 Strengthening of Concrete Structures by CFRP G rids The FRP composite can be transformed with several geometries and several mechanical fiber properties. Usual designs of FRP composites are one directional bar and strip or two dimensional fabrics or grids. When combining various binders/bonding representatives and various FRP composites a mineral based strengthening model is achieved as in figure (Blanksvärd, 2009)

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9 Table 2.2 Different geometries for fibre composites. Figures from (Möller et al., 2005), (Triantafillou a nd Papanicolau, 2006) and ( Han and Tsai, 2003). Inner filaments the textile fabric can be impregnated with epoxy resin. This will lead to a significant increase in the ultimate tensile strength of a system with textiles embedded in a mineral based bind er (Hegger et al., 2006). The FRP grid scheme includes using a carbon and glass grid of composite, and the assembly of the reinforcement concrete elements is objectively bric is that the grid is not woven. Grids can also be called meshes or nets. To produce a grid, the continuous fibers are braided or bundled into shape and then impregnated with a resin. Grids can be manufactured in a large variety of geometries, from dens e meshes for reinforcing boards and panels to reinforcing nets for slabs. The advantages of grids are that they have higher mechanical properties than consolidated woven fabric and smoother, better surface aspects. They are also considered to be highly the rmo be more adhesive by using epoxy resin. This can lead to a significant improvement in the tensile

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10 strength and the load carrying capacity of a composite between the concrete and CFRP grid (He gger et al., 2006).

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11 3. COMPOSITE STRENGTHENING OF STEEL MEMBERS IN FRACTURE INDUCED DISTRESS 3.1 Introduction As a result of the accumulation of damage in the steel girders under the influence of cyclic loads cause fatigue, and this ultimately leads to the formation of cracks due to the inability of steel girders to carry that fatigue loads. Strengthening bridge's steel girders with CFRP composite to withstand against the increase of traffic loads, and CFRP is a promising alternative to traditional solutions to repair steel elements exposed to fatigue failure. Also; rehabilitating bridges with CFRP increases the se rvice life of the bridge despite the inability of fatigue of these bridges (Kamruzzaman et al., 2014). Carbon Fiber CFRP is a creative and compelling technology that gives substantially higher static and fatigue repair and a different noncorroding option. However, the strength decreased of the steel beams was either initiation propagation or steady state. Corrosion of the beams effected on the overall load carrying capacity of the strengthened despite CFRP characterize as non corrosion material (Kim & Buma dian, 2016) , and to enhance the capacity and life service of steel girders the advantages of CFRP externally strengthening system were expanded (Huawen et al., 2010). In this research to simulate a realistic case, notched specimens adopted as results of proving the effectiveness of strengthening steel with CFRP that have notches according to several analyses such as (Jones and Civjan, 2003), (Tavakkolizadeh and Saadatmanesh, 2003). Bond length is an important factor, although it does not significantly inc rease the ability of structural elements, however; according to Lenwari, Thepchatri, & Albrecht 2006, region subjected to tensile stress should be strengthening for subsequent failure. The debonding is also clearly stimulated and occur under the direct eff ect tension compared with the cyclic loading. Also, the pattern of debonding failure studied in the short and long plates, where it observed that CFRP failure of small sheets was debonding while a failure of long sheets was rupture (Lenwari, Thepchatri, & Albrecht, 2005).

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12 3.2 Experi mental T ests 3.2.1 Material for rehabilitation In this section, the dimensions details of steel strips specimens and properties of the materials used in this research will be detailed. Then, use the CPRP sheets and epoxy as adhesive material. Adhesive length is an effective factor in the rehabilitation of steel with CFRP sheets. The epoxy glue is an important factor because if adhesive fails prematurely, the CFRP is no longer important and can not benefit from the strength an d stiffness of the CFRP sheets. CFRP strips with high strength can raise the stiffness of rehabilitated steel elements which also increase section moment of inertia. Moreover, use of CFRP strips having high quality epoxy glue can build strong combination s ystem that improves steel moment capacity and reduce cracks resulted by stress. 3.2.1.1 Adhesive (epoxy) In this study, two main parts of the epoxy mix were used. This mixture consisted of 1 resin to 3 hardeners, which manually mixed for five minutes. After making sure that the mixture is homogeneous, a thin layer of epoxy was placed on the steel surface. Then to assure that the distribution of epoxy layer is equal to about 2 mm thick, and immediately to ensure of avoiding any vacuum CPRP Sheet was susp ended in the epoxy layer. The steel specimens were placed inside the laboratory at a moderate temperature to cure for a week which is enough time according to manufacturer recommendations. Table 3.2 summarized the epoxy properties. 3.2.1.2 CFRP strip The significant mechanical properties of CFRP, such as the strength and strength mentioned earlier in this study were the main reason for the selection of CFRP, and although according to Nanni et al. 1997, the connection between CFRP and steel may cause co rrosion, and that can cause failure of connection prematurely. However, the developments of epoxy compound industry and its quality, which separates direct contact between CFRP and steel composite prevent corrosion (Shield et al., 2003). As previously ment ioned the adhesive length of CFRP sheets is not a significant factor in increasing the strength of steel element, but it is also important to reduce the early debonding. Length of the adhesive should be studied to ensure

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13 cohesion and adhesion to obtain the strongest possible bonding to the CFRP sheet. Sika Corp product CFRP sheet that was used for strengthening the steel strips, applied CFRP dimensions are the thickness of CFRP is 0.05 mm and 38.1 mm (1.5 in) width and the length 76.2 mm (3 in). 3.2.2 Speci men detail and test setup 3.2.2.1 Surface preparation To obtain a complete and strong bond between the CFRP composite and steel strips, to avoid undesirable debonding failure of the strengthening steel strips, surface cleaning to prepare and remove dust on the surface of steel specimens before of placing the epoxy. 3.2.2.2 Specimens' details The steel strips were cut lengthwise for all specimens to be analyzed and compared to the results obtained from the tensile test. (177.8, 127, 76.2) With widths of 1 m m with three specimens for each length. It noted that there was no difference in the tensile strength, as shown in table 3.1 where the average stress failure was almost 337 ksi for all length. That results of tensile stress were due to thickness and width constancy where they were 5 and 38.1 mm respectively. Therefore, specimen length is not effective with the constancy of width. For this reason, a specimen with (127, 38.1, and 5 mm) length, width, and thickness respectively were chosen during this experime ntal study, and notches were cut in the middle of the specimens to simulate the real steel bridge case with a depth about 2.5 mm. CFRP composite sheets used in reinforcement the steel specimens were unidirectional fiber with the tensile force direction wit h bond length 76.2 mm (3 in) on both sides. After that specimen was left for curing at the laboratory temperature for a week before testing. 3.2.3 Test setup and instrumentation As it is shown in Fig 3.3 tensile test setup of the specimens using MTS machin e with capacity 20 kips. The load cell connected to the clamp of the MTS machine using special spherical hinge. Also, to monitor strain laser extensometer was utilized to measure the longitudinal displacement by conducting the displacement between two spec ial tapes because the MTS displacement measurement is not accurate.

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14 Tensile tests of steel specimens under diffrent temperatures and the same load rate which is 0.5 mm/min were accomplished using a MTS 20 Kips hydraulic testing machine as presented in Fig 3.3 . , the valve of the hydraulic was released until the hydraulic bump achieved a constant rate predefined of its velocity, then and there the test specimens were fixed at upper and lower grips of spherical hinge . These grips have indented surfaces to ensu re an efficient hold of the specimens and to avoid any slippage of the specimens during the tensile force. The tests was performed at room temperature 25 °C . The strain rates was 0.5 mm/min which determined as the ratio of the applied velocity to the specimen's gauge length . Different temperatures was applied on the strengthened steel strips. Temperatures 25, 75, 125, and 1 75 °C were selected to study the temperature effects on CFRP debonding and the ultimate failure load. A lso, laser extometer wa s setup and focused on the specimens to measure and capture the deformation and failure behavior of steel specimens. 3.3 Results and D iscussion 3.3.1 Load displacement behavior and ultimate load capacity Table 3.4 summarize collected data of tests results of all strengthened and unstrengthened steel specimens, as presented in the table 3.4 average failure load of unstrengthened specimens (S No CFRP 25) is 41.91 kN with Stdev 0.35. However, strengthening specimens with CFRP enhanced the steel strips performa nce as described in Table 3.4 where average failure load of specimens strengthened with CFRP (S CFRP) 44.07 kN with Stdev 0.52. Fig 3.12 showed the behavior load displacement of S No CFRP 25 when the behavior was linear for all specimens up to the peak loa d then the load drop abruptly, the response of all specimens was similar with an average stiffness 147.32 kN/mm. While after strengthening the specimens with CFRP as shown in Fig 3.18 the behavior was also similar up to the peak then load abruptly with an average stiffness 269.78 kN/mm. Table 3.4 presents the temperature effects on ultimate failure load of strengthened steel specimens, and by inspecting the load displacement behavior, it can say that low increase in temperature has no significant e ffects on failure load where it was 42.36 kN at temperature 75 C. Conversely, when the temperature exceeds 100 C the epoxy loss its adhesive strength and CFRP will not carry applied load with steel strips, so the load carrying capacity of the specimens r educed, and failure loads were 39.32 and 38.49 kN at temperatures 125 and 175 C.

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15 Strain response 3.3.2 Failure Modes As shown in Fig failure modes of some specimens at different temperatures where CFRP bonded to steel specimens and the load was applied wi th temperatures attached to specimens interface as in Fig 3.7 . By observing the failure during the tests, the failure was similar to most of the specimens where debonding failure was evident as shown in Fig. Fig a, b debonding was brittle behavior under te mperatures 25, 75 C, while with temperature increase the epoxy adhesive properties effected so the CFRP failure was ductile debonding. Also, the CFRP as shown in Fig d disintegrate as a result of temperature effects, and even by monitoring the specimens i t can conclude that the epoxy and CFRP properties are temperature are temperature depended materials especially with high temperatures. 3.3.3 Crack propagation and width opening Fig 3.9 presents the crack length of specimens under different temperatures where the crack was measured of unstrengthened specimens firstly by marking the specimen's surface with lines at every 10 percent of specimen's width as in Fig 3.9 , and the specimens notched at the middle of specimens as in Fig 3.1 . The crack propagation measured from the notches at three places 20, 40, and 60 % of specimen's width. By visual observation of unstrengthened specimens crack loads were 38.95, 34.91, and 26.95 kN at crack length 20, 40, and 60 % of specimens width, and Fig 3.14, 3.15 , and 3.16 presents the microscope view of cracked specimens at 20, 40, and 60 % crack of specimens width. Posteriorly, strengthened specimens tested at different temperatures, and as in Fig 3.12 at temperature 25 C it is obvious that the load carrying capacity of s pecimens improved, so the crack length decreased at the same crack load of unstrengthened specimens. Moreover, with an increase of temperature the epoxy started to lose its adhesive properties and that effect on the bond behavior of CFRP with steel strips surface, so the crack length increases at the same applied load of unstrengthened specimens. Also, the crack opening of strengthened and unstrengthened steel specimens was described in Fig 3.9 . Visual observation of specimens obtained the crack opening of unstrengthened specimens while applying the load, and when the crack length reached to three known crack length percent of specimen's width the test stopped to measure the crack width.

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16 Then co ntinue the test and applying the load to the next crack length percent up to the final failure. The crack opening behavior was similar to the crack length behavior where low temperatures increase have not important effects on crack width, and the crack ope ning increase of the three crack percent was around 0.2 mm of strengthened specimens at temperature 75 C comparing to specimens with temperature 25 C. While the crack opening increase to 0.55 and 0.85 mm at temperature 125 and 175 C comparing to specime ns with temperature 25 C. The failure of all unstrengthened specimens starts after steel strips yielding, and the cracks propagation started after ultimate failure load where the crack propagated slowly in the early crack stages; then, the crack propagat ion fell dramatically up to failure as a result of stiffness loss. Also, for CFRP strengthened specimens the debonding of CFRP refers of yielding failure of steel strips while with load increase CFRP is debonding behave in two cases. The first deboning typ e was a brittle behavior of specimens under temperature 25 and 75 C, and that debonding occurred as a sudden deboning, but when the temperature increased to 125 and 175 C the debonding happened slowly as ductile behavior. 3.3.4 Temperature effect on stee l behavior under cyclic load Crack length of unstrengthened steel specimens at cyclic loads was monitored during the test, and the crack length noted at every cycle. Also, to facilitate measurement process the unstrengthened specimens were marked on its su rface with lines as in Fig 3.4 , and to study the behavior of steel specimens under cyclic load. The load was applied up to peak then unload to zero loads with keeping the displacement form change, after that the load increased and this process continued up to final failure which is usu ally debonding or CFRP rupture. The cycles were counted after full amplitude, and if the failure happened during reduced amplitude, the cycle does not count. Table 3.5 explains the crack length of 10% of marked specimen's width under cyclic load where we c an note that most specimens 10% (3.06 mm) of crack length were at 6 cycle, and so on the cracks propagate with cycles increase up to the final failure occurred at average cycles 32. Subsequently, strengthened specimens were tested under 40 C as in Fig 3.2 8 it was clear that temperature effect on load carrying capacity. By comparing the results of unstrengthened specimens in table 3.5 with strengthened specimens table 3.4 it obvious that the number of cycles under temperature effects significantly reduced where the number of cycles that caused ultimate failure do not exceed 10 cycles despite

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17 strengthening the specimens with CFRP sheets, while the cycles that caused failure of unstrengthened specimens were 32 cycles. 3.3.5 CFRP debonding influence on crack p ropagation under temperature Debonding of CFRP under temperature effect by applying 40 C on the specimen's surface during the test using a hair dryer, and the temperature constancy on the specimen's surface was monitored using measuring gun ; however, the constancy of the temperature 40 C is on the CFRP surface during the test is not 100% uniform because the hair dryer moved up and down during the test . The tension load was applied after heating the strengthened specimen for a while to ensure that specime ns reached to 40 C which simulate the reality. Also, to analyze the debonding results FLIR camera was used as in Fig to measure thermal extension in specimen during the tests, and FLIR device data were analyzed using FLIR Tool software as in Fig. When the data were evaluated the notched area have high temperature and also at CFRP edges with the increase of load either in monotonic and cyclic load as in Fig 3.23, 3.25, 3.27 3.29, 3.30, and 3.31 . Furthermore, as in Fig the differences in temperature showed t hat the areas that have high temperature refers to debonding of CFRP, and this area becomes bigger, and there the debonding spread as far the load was applied. As presented in table 3.6 and table 3.7 the debonding at load up to 10 kN was not significant, but with the load increase the debondi ng spread suddenly. The tables 3.6, 3.7 summarize temperature effects on debonding area under monotonic and cyclic loads. However, to ensure that non bonded area has high temperature than the other places which is bon ded to the steel surface, and CFRP was bonded to steel specimen's surface and the plastic tape was placed at middle at different areas 25, 50, 75 % of CFRP area then the plastic tape removed. Subsequently, 40 C temperature was applied on the unloaded specimens for a while, and FLIR camera was used to obtain the thermal behavior, then the FLIR pictures were anal yzed using FLIR tool. As in Fig 3.32 , it is noticeable that non bonded areas have the higher temperature than the bonded places which approve that debonding can be getting by investigating thermal behavior of CFRP. In conclusion, most failure wa s as results of CFRP debonding and this debonding was brittle, and by monitoring temperature effects on CFRP sheets and epoxy behavior it was clear that the epoxy transformed from brittle to a ductile case which has an

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18 impact on load carrying capacity of s teel specimens, and the CFRP debonding. The results of failure mode were conducted from steel coupon tests may not give the same failure mode of bridge elemnts on the site because the steel girder will have lager strengthening area despite the expected fai lure mode will be CFRP debonding. According to (Zhang, 2016) failure properties of strengthened specimens with CFRP which usually was CFRP debonding, and debonding failure chance increase with temperature growth due to temperature effect on epoxy. 3.3.6 P robabilistic prediction of crack propagation using Bayesian updating The Bayesian updating idea of probability is utilizing available information to create a model and to use and analyze the data (Zhao, Haldar,2006). Bayesian updating can be beneficial to monitor and study structures repair and rehabilitation, and by using collected data from Bayesian updating theory, and probability can be simulated of crack propagation according to stresses (Zhang R, Mahadevan, 2000). Also, Model could found by mechanica l, statistical, probabilistic, and physical uncertainties. The probabilities conducting from integrating different elements provide random variable which can be estimated to describe the problems and every random that merged in function which affect final probability results simultaneously. The method of calculating the probability using Bayesian updating in this research was accomplished by; firstly, extracting the functions from previews studies and researches, then these functions were used on an examp le to explain the method of using the equations and ensure the effectiveness and applicability of the crack results that collected from experimental work. The Bayesian updating theory of probability can be applied to results analysis and monitor of structu res problem and chances of structural elements failure. Also, there are others methods could be used to study the probability of structures failures such as Paris model, Forman model, and Weertman model. To apply Bayesian updating theory to estimate the ef ficiency of strengthening steel elements using CFRP composite. Firstly, data were obtained from experimental investigations where the data were length or width cracks, applied load, and temperature. These parameters were considered as prior parameters in t he Bayesian model. The effectiveness of strengthening probability can be estimated depending on data collected from prior distribution parameters and

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19 new data assumption, and from all these parameters posterior density which can be described in (1) (Azad AK, Ahmed S, 2007) An example explained by (Zhang R, Mahadenan S, 2000) Model 1: Exponential distribution is random variable Model 2: Gamma distribution Assume P ( m1) = P (m2) = 0.5 , and t = 1.5 Table 3.8 presents the details of crack propagation of steel strips strengthened with CFRP, and three specimens were tested at every temperature and crack percent. For example, the crack length of the specimens at crack 20% of spec imens width at temperature 25 C were 5.1, 4.6, and 4.7 mm with an average 4.81 mm, and in this way, three specimens at every temperature were tested. Moreover, due to the difficulty of getting the crack length of specimens that strengthened with CFRP dur ing the test, every specimens were tested at known load specified previously, which is the load of unstrengthened specimens that caused crack 20, 40,

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20 and 60% of specimen's width. The loads were 38, 35.5, 27 kN at crack 20, 40, 60% of specimen's width resp ectively. After the load reached to the specified load, the test stopped and CFRP sheet removed, and the crack length and width was measured at every load as was explained previously. By using equation 2, 3 Montecarlo simulation was applied to calculate a ssumption values depending on the values collected from the experimental work of every category, so 100,000 assumption values were calculated using Montecarlo simulation of every crack present to provide an accurate probability model. Uncertainties of crac k probability model were calculated by applying equation 1. Equation 2 was used to calculate and analyze the specified crack that does not exceed crack limit to be studied, and the value obtained from equation 2 is assumed as conditional probability (2) After calculating the conditional probability from equation 2, and to obtain the prior probability using equation 3 at every crack category with variation of temperature, the average values of 100,000 assumed specimens were taken, and then the average value applied in equation 3 . ( 3) By applying the results presented in Table 3.8 in equation 1 the posterior probability was obtained which illustrated in Table 3.9 . It is notable that the crack propagation probability decreased as the load increase in linear behavior as in Fig 3.33 , as well as from observing and analyzing the crack data of each Bayesian updating model.

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21 Table 3.1. Ultimate load and stress of unstrengthened and strengthened specimens with different steel and bond length Without CFRP With CFRP Specimen Length mm Load (KN) Stress(Mpa) Load (KN) Stress(Mpa) 101.6 43.7 445.7 44.2 476.4 43.9 455.9 Table 3.2 . Properties of CFRP strip from the manufacturer. Property Value Fiber r einforcement Carbon High Tensile Fiber d ensity 1.7 g/cm ³ Fiber m odulus 240 GPa Roll length & w idth 100 m and 0. 5 m Fiber w eight 300 g/m² Thickness 0.176 mm Tensile strength 3,800 MPa Tensile modulus 124 GPa Tensile elongation, u ltimate strain 0.0155 Design tensile force @ 0.2% strain /m width 211 k N Coefficient of thermal expansion (transverse) 74 to 104 × 10 ( C) Coefficient of thermal expansion (longitudinal) 9 to 0 × 10 ( C)

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22 Table 3.3 . Properties of epoxy from the manufacturer. Property Value Mixed viscosity at 25°C [77°F] 1600 cps Pot life, 4 fluid ounces 2.5 to 3 hours Density 11,542 kg/m3 Tensile strength > 30 Mpa (52 Mpa) Elongation at break 1.5 % Tensile modulus > 1.5 × 10³ Mpa (2.62 × 10³ Mpa) Flexural strength > 40 Mpa (75 Mpa) Compressive strength > 7 0 Mpa (99 Mpa) Glass transition temperature 170°C Tear off strength > 2.5 Mpa (4.4 Mpa) Shear strength > 10 Mpa (16.6 Mpa)

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23 Table 3. 4 . Details of steel strip specimens Specimens category ID Presence of CFRP Loading Scheme Elevated Temperature 1 S No CFRPM Unstrengthened Monotonic 25 C S No CFRPM cyclic 25 C 2 S CFRPM Strengthened Monotonic 25 C, 75 C, 125 C , 175 C, 40 C. S CFRPC cyclic 40 C 3 S UMD Unstrengthened Monotonic 25 C at crack propagation 20%, 40%, 60% of specimens width 4 S CMD Strengthened Monotonic 25 C at crack propagation 20%, 40%, 60% of specimens width

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24 Table 3.5 . Tests Data of all steel specimens under monotonic at elevated temperature . ID Temperature ( C ) Failure Load (k N) Stdev (kN) Ave. (k N) S No CFRP 25 1 25 42.22 0.35 41.91 S No CFRP 25 2 25 41.68 S No CFRP 25 3 25 41.42 S No CFRP 25 4 25 42.16 S No CFRP 25 5 25 42.07 S CFRP 25 1 25 43.61 0.52 44.07 S CFRP 25 2 25 44.25 S CFRP 25 3 25 44.91 S CFRP 25 4 25 43.82 S CFRP 25 5 25 43.78 S CFRP 50 1 75 43.10 0.47 42.36 S CFRP 50 2 75 42.23 S CFRP 50 3 75 41.92 S CFRP 50 4 75 42.05 S CFRP 50 5 75 42.51 S CFRP 125 1 125 39.68 0.59 39.32 S CFRP 125 2 125 38.85 S CFRP 125 3 125 38.77 S CFRP 125 4 125 40.16 S CFRP 125 5 125 39.15 S CFRP 175 1 175 39.11 0.69 38.49 S CFRP 175 2 175 38.21 S CFRP 175 3 175 37.55 S CFRP 175 4 175 39.24 S CFRP 175 5 175 38.35

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25 Table 3.6 . Crack propagation of steel strips strengthening without CFRP according to measurements at known cycle counts. Crack % Crack length Number of Cycles Specimen 1 Specimen 2 Specimen 3 Specimen 4 10 3.05 6 5 5 6 20 6.10 9 6 9 11 30 9.15 11 15 14 16 40 12.19 15 22 20 21 50 15.24 17 24 23 25 60 18.29 20 27 25 28 70 21.34 24 33 28 32 80 24.38 33 34 30 36 90 27.43 35 35 31 37 100 30.48 36 36 33 37

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26 Table 3.7 . CFRP Debonding of specimens under monotonic load with temperature 40 C Load (kN) Specimen 1 Specimen 2 Specimen 3 Debonding a rea (mm²) Debonding ( % ) Debonding a rea (mm²) Debonding ( % ) Debonding a rea (mm²) Debonding ( % ) 10 274.09 9.44 175.99 6.06 232.73 8.02 15 818.52 28.19 804.80 27.72 895.35 30.84 20 1025.31 35.32 951.65 32.78 1065.98 36.72 25 1395.60 48.07 1106.50 38.11 1305.69 44.97 30 1940.14 66.83 1537.32 52.95 1594.66 54.92 40 2192.55 75.52 1962.40 67.59 2189.47 75.42 30 Down 2417.61 83.27 2325.36 80.10 2401.35 82.71 25 Down 2601.28 89.60 2542.45 87.57 2689.63 92.64 Down: Post peak load

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27 Table 3.8 . CFRP Debonding of specimens under cyclic load with temperature 40 C . Load (kN) Specimen 1 Specimen 2 Specimen 3 Debonding a rea (mm²) Debonding ( % ) Debonding a rea (mm²) Debonding ( % ) Debonding a rea (mm²) Debonding ( % ) 5 213.22 7.34 187.33 6.45 225.70 7.77 10 383.89 13.22 250.34 8.63 335.03 11.54 15 790.11 27.14 492.31 16.96 782.86 26.97 20 1003.15 34.55 964.67 33.23 1007.24 34.69 25 1368.66 47.14 1208.71 41.63 1340.36 46.17 30 1603.81 55.24 1497.96 51.60 1659.56 57.16 40 2012.75 69.33 1977.37 68.11 1956.23 67.38 30 2 nd cycle 2264.34 78.00 2137.23 73.62 2136.83 73.60 25 4 th cycle 2503.82 86.24 2379.93 81.98 2604.38 89.71

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28 Table 3.9. The crack length and width at different crack percent and temperature. value Crack length (mm) Crack width (mm) 20% 40% 60% 20% 40% 60% 25 C 4.81 9.22 14.56 1.10 2.16 3.31 75 C 5.52 11.36 17.43 1.32 2.33 3.43 125 C 6.54 12.37 18.47 1.67 2.63 3.73 175 C 7.83 13.51 20.67 2.12 2.87 3.77 Load (kN) 38 35.5 27 38 35.5 27 Average 6.16 11.57 17.76 1.51 2.48 3.56 Stdev (kN) 1.18 1.86 2.57 1.99 0.34 0.26 Table 3.10. Bayesian updating model at every crack percent . Value 20% 40% 60% Crack probability 0.089 0.075 0.041 0.499 0.478 0.498 0.501 0.522 0.502

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29 Fig 3.1. Steel specimens details : (a) without CFRP; (b) with CFRP.

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30 Fig. 3.2. Cleaning steel strip . Fig. 3.3. Test setup.

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31 Fig. 3.4. S pecimen S No CFRP 25 3 during tensile test. Fig. 3.5. S pecimen S No CFRP 25 3 during tensile test with laser extometer and reflective tape to monitor the longitudinal displacement.

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32 Fig. 3.6. Specimen S CFRP 25 1 during tensile test with laser extometer and reflective tape to monitor the longitudinal displacement.

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33 . Fig. 3.7. Specimen S CFRP 75 1 subjected to thermal loading during tensile test with laser extometer and reflective tape to monitor the longitudinal displacement.

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34 Fig. 3.8. Relation of stress level and crack length of specimens streng thened with CFRP at elevated Fig. 3.9. Relation of stress level and crack width of specimens streng thened with CFRP at elevated temperatures: 6 12 18 4.8 9.37 14.5 5.5 11.3 17.4 6.5 12.3 18.4 7.83 13.83 20.43 0 5 10 15 20 25 425.76 381.73 294.78 Crack length (mm) Stress (MPa) Crack length without CFRP Crack length with CFRP W @ 75 c W @ 125 c W @ 175 c (a) (b) (c) 1.38 2.4 3.57 1.07 2.1 3.3 1.3 2.33 3.43 1.67 2.63 3.73 2 2.87 3.77 0 0.5 1 1.5 2 2.5 3 3.5 4 425.76 381.73 294.78 Crack width (mm) Stress (MPa) Crack width without CFRP Crack width with CFRP W @ 75 c W @ 125 c W @ 175c (a) (b) (c)

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35 Fig. 3.10. Comparison between engineering strain and true stress of unstrengthened steel specimens. Fig. 3.11. Comparison between engineering stress and true strain of strengthened steel specimens. 0 100 200 300 400 500 600 700 800 0 0.002 0.004 0.006 0.008 0.01 0.012 Stress (MPa) Strain Eng. Stress vs Strain W/o cFRP True Stress vs Strain W/o cFRP 0 100 200 300 400 500 600 700 800 0 0.01 0.02 0.03 0.04 0.05 Stress (Mpa) Strain Eng. Stress vs Strain W/o cFRP True Stress vs Strain W cFRP

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36 Fig. 3.12 . L oad displacement response of steel specimens without CFRP.

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37 Fig. 3.13. Stress strain behavior of steel specimens without CFRP .

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38 Fig. 3.14 Microscope picture of S No CFRP 25 3 of 20% crack of specimen width. Fig. 3.15. Microscope picture of S No CFRP 25 2 of 40% crack of specimen width. Fig. 3.16. Microscope picture of S No CFRP 25 5 of 60% crack of specimen width.

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39 Fig. 3.17. Cracked specimen during tensile test.

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40 Fig. 3.1 8. L oad displacement response of steel specimens with CFRP.

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41 Fig. 3.19 . S tress strain response of steel specimens with CFRP

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42 Fig. 3.20. Load displacement behavior of steel specimens without CFRP under cyclic load .

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43 Fig. 3.21. Stress strain behavior of steel specimens without CFRP under cyclic load.

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44 Fig. 3.22. Load displacement behavior of steel speci men 1 with CFRP under monotonic load at a temperature 40 C. (a) 10 kN up (b) (a) 30 kN up (b) (a) 4 0 kN up (b) (a) 30 kN dwon (b) Fig. 3.23 . Infrared images of speci men 1 with CFRP under monotonic load at a temperature 40 C : (a) temperature ; (b) CFRP debonding. 0 10000 20000 30000 40000 50000 0 1 2 3 4 5 6 7 Load (N) Displacement (mm)

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45 Fig. 3.24 . Load displacement behavior of steel speci men 2 with CFRP under monotonic load at a temperature 40 C. (a) 10 kN up (b) (a) 30 kN up (b) (a) 4 0 kN up (b) (a) 30 kN dwon (b) (b) Fig. 3.25. Infrared images of specimen 2 with CFRP under monotonic load at a temperature 40 C: (a) temperature; (b) CFRP debonding. 0 10000 20000 30000 40000 50000 0 1 2 3 4 5 6 7 Load (N) Displacement (mm)

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46 Fig. 3.26 . Load displacement behavior of steel speci men 1 with CFRP under monotonic load at a temperature 40 C. (a) 10 kN up (b) (a) 30 kN up (b) (a) 40 kN up (b) (a) 30 kN dwon (b) Fig. 3.27. Infrared images of specimen 1 with CFRP under monotonic load at a temperature 40 C: (a) temperature; (b) CFRP debonding. 0 10000 20000 30000 40000 50000 0 1 2 3 4 5 6 7 Load (N) Displacement (mm)

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47 a b Fig. 3.28. The response of steel specimens with CFRP under cyclic load at temperature of 40 C of three specimens: (a) load displacement behavior; (b) s tress strain behavior.

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48 (a) 10 kN up (b) (a) 30 kN up (b) (a) 40 kN up (b) (a) After 4 th cycle (b) Fig. 3.29. Infrared images of specimen 1 with CFRP under cyclic load at a temperature 40 C: (a) temperature; (b) CFRP debonding. (a) 10 kN up (b) (a) 30 kN up (b) (a) 40 kN up (b) (a) After 4 th cycle (b) Fig. 3.30. Infrared images of speci men 2 with CFRP under cyclic load at a temperature 40 C: (a) temperature; (b) CFRP debonding.

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49 (a) 10 kN up (b) (a) 30 kN up (b) (a) 40 kN up (b) (a) After 4 th cycle (b) Fig. 3.31. Infrared images of speci men 3 with CFRP under cyclic load at a temperature 40 C: (a) temperature; (b) CFRP debonding.

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50 Fig. 3.31. Comparison of failure probability of the B esaiyen u pdating model vs the crack % of 0 0.02 0.04 0.06 0.08 0.1 0 20 40 60 80 Failure probability Crack % of specimen's width

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51 4. BEHAVIOR OF RC BEAMS STRENGTHENED WITH CFRP AND C GRID U WRAP SHEETS AND SHEAR FACES. 4.1 Introduction In this research experimental studies were conducted on concrete beams strengthened with CFRP under the effect of monolithic and cyclic load, and the tests were accomplished using hinge support by four point loads. The beams experimental work was divided into two main phases, the first phase R C beams strengthened with CFRP sheets from the bottom and CFRP U wrap from the side face to strengthing shear region. The second phase also RC beams were reinforced with CFRP sheets from the bottom and C Grid U wrap from the side face to strengthing shear region. The work divided in this chapter to five main parts. Firstly, properties and specifications of materials that used either concrete, epoxy, CFRP, or C Grid. Secondly, instrumentation test setup, then test results were discussed and analyze failure r easons of every category. Next, the failure mode of some beams was inspected depending on DIC system; finally, a brief summary of benefits of using CFRP and C Grid on R.C beams in this research. 4.2 Experimental Program 4.2.1 Specimens details Twenty beams in this chapter were divided to main five categories as mentioned in Table 4.1 . All the 20 RC beams have the same dimensions as shown in Fig 4.2 . Where the length was 1200 mm, 165*100 mm height and width. The reinforcements of RC beams designed using ACI 318 design code considering the simply support as a support condition. Fig 4.1.b shows the reinforcement details of RC beam that conducted from ACI 318 where the main steel reinforcement No.3 with diameter 9.5 mm bent along beam length of tension side at the bottom with 20 mm left as a concrete cover; also steel reinforcement bent up at beam edges to increase the beam strength to resist stresses. Moreover, the shear reinforcements of RC beams were distributed along the beam with stirrups every 3 in as shown in Fig 4.2.d . After connecting steel bars in steel cage form as in F ig 4.1.a st eel and wooden frame was set up as in Fig 4.1.b .

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52 4.2.2 Properties of materials 4.2.2.1 Concrete mix The concrete was mixed according to mix quantities that mentioned in Table 4.2 with W/C ratio 40% according to ACI recommendations in case of using an elec tronic mixer. Sand and gravel gradation have been confirmed through sieve analysis as shown in Fig; also, Fig all the sand were placed in the oven for more than three days to make sure that the sand is nonmoisture. Cement type III used in the concrete mi x to its ability to reach 98 hardness in about a week. Concrete cylinders specimens with dimensions 100 mm in diameter and 200 mm in height. 6 concrete specimens were tested with an average c ompression strength 22.62 MPa Fig 4.1.d . Illustrates the failed specimens, and after casting the concrete curing RC beams ensured by placing the beams in the curing room for at least a month before testing the specimens. 4.2.2.2 CFRP & C Grid properties As it was mentioned at the beginning of this chapter two type of CFRP strengthen composites was used to strengthening the RC beams where CFRP sheets were placed at the tension side of the beams which is the bottom face. While CFRP and C Grid sheets glued to the shear stress flow side of RC beams, and that to strength the beams and work as U stirrups (U wrap) as shown in Fig 4.2.d the U wrap starting from the supports and increase with percent up to the applying load point which covers the whole shear region. Table 3.1 &Table 4.4 explain the mechanical properties of CF RP and C Grid sheets according to specifications and characteristics of manufacturers. The main aim of the section is to study the efficiency of using C grid composites at a different size of C Grid applications, and that to study the best C Grid applicat ion size to cover the shear region and compare it with beams results of using CFRP sheet. This comparison is to investigate if there are no significant differences in the load carrying capacity of using CFRP and C Grid that means using C Grid is more effic ient because it will accumulate more CFRP and epoxy materials.

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53 4.2.2.3 Epoxy The properties and uses of epoxy were explained in chapter 3 as described in Table 3.2 where all specimens strengthened with CFRP glued on concrete using resin: epoxy with mix r atio 1:3. The curing time of epoxy was more than one week to reach the required adhesive strength according to the manufacturing specifications. In this research, the curing time of epoxy exceeds 10 days to ensure that the epoxy has reached the required ad hesive strength . 4.3 Beams Preparation and S trengthening 4.3.1 Beams preparation After casting the concrete with mixing ratio as explained in Table 4.2 , and placing it in the curing room for a month to acquire the required strength. Posteriorly, RC beams took out from curing room, and cleaned of dust on RC beams using an air compressor and metallic brush, then beams corners filleted and smoothed out at the U wrap place using grinding machine to avoid stresses concentrations at the beams corners. Also , to ensure a strong bon d between RC beams and C Grid because the C Grid materials is not a smooth bent material such as CFRP sheets. 4.3.2 Applications of CFRP and C Grid sheets on the RC beams A s shown in Fig 4.2 . All RC beams strengthened with CFRP sheets at tension region with 1000 mm length, 100 mm width, and 2 mm epoxy thickness. Strengthening of RC beams as three styles as described in Table 4.1 ; firstly, one beam as a control beam which strengthened with CFRP sheet at the bottom side. Other grou p strengthening RC beams with CFRP sheets at beam's bottom and at the same time gluing RC beams 4 with CFRP U wrap and 7 with C Grid U wrap at the shear region with 25, 50, 75, and 100 at a distance between support and applied point load. Thirdly, 8 RC bea ms CFRP sheet was placed at the bottom and leaving them 7 days to cure the epoxy after that SPM rubber glued at C Grid sheets put at beam corner. Also, the 8 beams were left SMP to cure for 10 days that because the SMP may effect epoxy resin, then C Grid U wrap sheets placed with different strengthening sizes 25, 50, 75, and 100 as presented in Fig 4.6 & 4.19 .

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54 4.4 Test Setup and I nstrumentation Experimental tests of all RC beam were done under the effects of four points load with boundary conditions hinge hinge as simply support tests at span 1050 mm as shown in Fig 4.1 . Fig 4.1 describe load support conditions of RC beams and test setup, as shown MTS 55 kips machine was used with a rigid frame to apply the two points load at a distance 450 mm between load points. Rigid frame weight neglected to facilitate the calculation of applied load. As in Fig 4.1 Load cell placed to read applied load during tests, also two PI gages installed to get the horizontal stress in RC beam at mid span in the tension region at bottom and compression at the top. MTS 55 kips machine procedure was set up at loading rate 0.5 mm /min, and that to facilitate monitoring failure modes and CFRP debonding in RC beams by controlling applied load speed. Moreover, Potentiometers device was placed at beam mid span to capture beam's vertical displacement, and to read horizontal strain of C FRP sheet 5 strain gages were glued at CFRP bottom as shown in Fig 4.2.c . Furthermore, Failure mode and crack propagation of RC beams monitored closely during tests using digital image correlation camera (DIC). Fig clarify DIC system and how the camera ins talls to monitor RC beams behavior during the tests. To simplify setup explanations of DIC system firstly the camera was headed for a spot on RC beam that required to be studied of cracks and strains on the surface, and place, where the camera headed on RC beam, was painted using ink roller as in Fig. After it was confirmed that all instrumentations and setups were mentioned above installed and connected with collecting data devices using Mydata software, and DIC system installed and set up to capture the c racks and surface strains. 4.5 Test Results and D iscussions The focus in this section will cover analysis and discussion of the tests result in data that collected from RC beams strengthened with CFRP sheets at the bottom and CFRP and C Grid U wrap tests at the shear region. In this section, the test results will be discussed for every category separately where the curve of the load will be displayed with displacement, tension, and compression of RC beam. Also, Failure modes for every beam will be discuss ed, the discussion of failure mode include failure type of the beam at every stage of load stages, and using DIC system the crack propagation of RC beams will be displayed and then load vs crack length will

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55 be extracted from the DIC pictures. Moreover, to study CFRP response load strain curve using strain gages will be presented for every beam to clarify the load influence on CFRP sheets. As in Table 4.1 the RC beams divided into five categories, and every category will be discussed and will be compared wit h the other category according to strengthening and load condition. 4.5.1 Beams strengthening with CFRP U wrap Tests results in this category detailed in Fig 4.6 , also tables 4.5 and 4.6 include test data of this section. 4.5.1.1 Load carrying capacity The tests results presented in table 4.5 explained tests data of RC beams either control beam (CTB) and beams strengthening with CFRP U wrap indicating the failure loads, Stdev, and COV; also table 4.6 described the failure load at every stage of the load stages, and clarified failure mode and cracks propagation. Firstly, for CTB beam as in table 4.5 failure load was 91.17 kN under monolithic load influence, and by monitoring CTB specimen when the load was applied the first failure was observed as flexura l cracks then with the increase of applied load shear flexural cracks start to appear. Finally because of beam displacement increase CFRP debonding occurred at beams edges. After that, RC beams that strengthened with CFRP U wrap at shear face sides were t ested which described in Table 4.1 , and Fig 4.6 RC beams strengthened with CFRP U wrap at four different sizes of CFRP 25, 50, 75, and 100% of the shear face between the support and point load. Table 4.5 indicates to the observed improvement in load carryi ng capacity of the strengthened beam with CFRP U wrap where the ultimate load of beams increased around 24.97, 18.8, 16.31, and 12.21 kN to beams strengthened with CFRP U wrap 100 , 75, 50 , and 25% respectively. Also, the failure of all beams occurred as a result of flexural and flexural shear failure while CFRP sheets failure was as results of rupture, and with noting that no debonding happened to CFRP U wrap as it is obvious in Fig 4.9, 4.12, 4.15, and 4.18 . 4.5.1.2 Load displacement behavior of RC beam A s displayed in Fig 4.1 the displacement was taken at beam mid span using a linear potentiometer. According to Fig 4.3.a, 4.7.a, 4.10.a, 4.13.a and 4.16.a the load displacement

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56 behavior of RC beams was almost similar despite the improvements in load carrying capacity at strengthened beams with CFRP U wrap. Comparing the results of load displacement curves, it could be observing that stiffness at early load stage up to 48 kN stiffness improves of beams strengthened with CFRP U wrap comparing with CTB b eam. While when load exceeds 50 kN yielding stage started, and the interior cracks at beams mid span appeared according to DIC system as shown in Fig 4.5, 4.9, 4.12, 4.15, and 4.18 . where the failure happened and growth in RC beam up to the ultimate load. Retaining to load displacement curve it obvious that the increase in load is compatible with displacement, but when load exceeds more 85 kN the displacement increase was significant despite the load increase was slight, and that as a result of a drop in of RC beam's stiffness and crack in concrete as shown in DIC Fig. 4.5.1.3 RC beams strain response Two PI gages at RC beam mid span install at one side of RC beam, one at the top to read compression response and the other PI gage at the bottom to read tension response at a distance 25 mm from the beam edge. As presented in Fig. 4.3.b, 4.7.b, 4.10.b, 4.13 .b and 4.16 .b the increase in load up 47 kN cause a slight RC beam response in tension and compression, but with the stress increase, the tension respon se was higher than the compression. The results of all beams in this category were compared, and it was observed that the behavior of all the RC beams was similar regardless the differences in the values, but the RC beams tension and compression response d iffers with load increase as a result of beam failure. Even though the RC beams that strengthened with CFRP U wrap tension and compression response is similar to the CTB beam's tension and compression response, the results of stress refer that strengthen t he beams increase the load carrying capacity which increase beam ability to displace more according to mentioned figures. 4.5.1.4 CFRP strain of strain gages To measure the strain in CFRP, all beams have five stains along CFRP sheets. As shown in Fig 4.2. c every beam was glued with 5 strain gages where one glued at beam mid span of CFRP, and two strain gages spread at every 2 in from the mid span of the beam, and the other two strain gages were spread on the other side of the beam at distance 2 in. The str ain gages were glued at the center of 100 mm which is CFRP sheet width. The aim of using the stain gages is to measure the elongation response along of the CFRP. As clarified in Fig 4.7.c, 4.10.c, 4.13 .c and

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57 4.16 .c strain gage response at beam mid span was the highest while the strain gages response of CFRP reduces whenever strain gages place are farther than beam mid span, and it observed that the strain gages response increase with load rise where the behavior of all strain gages have similar although the strain value different. As in Fig 4.7, 4.10, 4.13 and 4.16 response of strain gages number 7, 11 was slightly low compared with a response of strain gages number 9 at mid span, and that as a result of maximum displacement and flexural failure at RC beam m id span. 4.5.1.5 Failure mode Experimental tests of RC beams monitored while applying the load by using DIC system and optical observation of RC beams specimens through the tests, and as in table 4.6 the failure mode of every stage of load stages. According to Fig failure mode of CTB beam starts at load 48 kN and the crack growth as a flexural failure, then cracks start to propagate and increase as the flexural failure, flexural shear failure when th e load exceeds 85 kN. As a result of the increase of beam deflection at mid span which cause increasing of spread cracks, and final failure of the beam happened as CFRP debonding and concrete crushing between applied load points at load 91.17 kN. Even thou gh RC beams strengthened with CFRP U wrap have failure similar to CTB beam failure at the beginning where the failure was the flexural failure, the CFRP U wrap started to resist the failure with the increase of load. Where there are no obvious flexural she ar failures of RC beams strengthened with CFRP U wrap with 100 and 75 % and with less percent of RC beam strengthened with 50 and 25 %. The final failure of CFB beams group was as results of concrete crushing at load points, and CFRP rupture after the plac e of CFRP U wrap as shown in Fig 4.9, 4.12, 4.15, and 4.18 . load carrying capacity of CFB RC beams improve 25, 19, 16, and 12 kN of beams strengthened with CFRP U wrap 100, 75, 50 and 25 %. It can be concluded that the failure pattern of all beams is simil ar at all early stages of load, but with load increase, RC beams strengthened with CFRP U wrap showed a development in beam's performance where the failure was prevented due to the flexural shear and improve load carrying capacity significantly. Also, noth ing the debonding of specimens, strengthening RC beams with CFRP prohibit direct debonding, and in case of debonding, it happened as the CFRP rupture which approves that CFRP U wrap has a strong strengthening as in DIC picture Fig.

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58 4.5.2 Beams strengthen ing with CFRP U wrap (GEM) Tests results in this category detailed in Fig 4.20, 4.23, 4.26, and 4.29. , also T ables 4.5 and 4.6 include test data of this section. 4.5.2.1 Load carrying capacity of GEM beams According to results shown in T able 4.5 explained tests data of RC beams both control beam (CTB) and beam s strengthening with C Grid U wrap (GEM) indicating the failure loads; also table 4.6 described the failure load at every stage of the load stages, and clarified failure mode and cracks pro pagation. Firstly, for CTB beam as in mentioned T able 4.5 failure load was 91.17 kN under monotonic load influence, and by monitoring CTB specimen while applying the load. It was observed that beginning failure was flexural cracks then with the applied loa d increase shear flexural cracks appeared, and finally because of beam displacement increase CFRP debonding occurred at beams edges. Subsequently, RC beams that strengthened with C Grid U wrap (GEM) at shear face sides were tested which described in Table 4.1 , and Fig 4.19 GEM beams at four different sizes of C Grid 25, 50, 75, and 100% of the shear face between the support and point load. Table 4.5 indicates to the observed improvement in load carrying capacity of the strengthened beam with C Grid U wrap where the ultimate load of beams increased as in the case of strengthening with CFRP U wrap. Through comparing the results of failure load of UEM and GEM beams, it was obvious that there is a noticeable convergence in the results between most the beams tha t have the same strengthening size. For example, the failure load does not exceed 2 kN of beams strengthened with CFRP and C Grid U wrap 100%. As in UEM beams, the failure mode of GEM beams started as the flexural failure at 48 kN, and with load increase, flexural shear failure can be seen using DIC camera. Moreover, the final RC failure happened at ultimate load as results of CFRP debonding which leads to C Grid U wrap rapture Fig 4.22, 4.25, 4.28, and 4.31 . That indicates that despite improvement in the u ltimate load of RC beams by using C Grid U wrap, it is clear that C Grid U wrap is weak comparing with CFRP U wrap because of C Grid U wrap rapture.

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59 4.5.2.2 Load displacement behavior of GEM beams According to Fig 4.20.a, 4.23.a, 4.26.a, and 4.29.a the lo ad displacement behavior of GEM beams was almost similar despite the improvements in load carrying capacity at strengthened beams with C Grid U wrap. Comparing the results of load displacement curves, it was observing that stiffness improve of GEM beams an d have a similar stiffness of UEM beams. However, with load increase, the load displacement behavior started to change from linear behavior which indicate that the beams in yielding stage. After the load exceeds 50 kN, the interior cracks at beams mid span appeared according to DIC system as shown in Fig 4.22, 4.25, 4.28, 4.31 . Where failure happened and growth in RC beam up to the ultimate load. Retaining to load displacement curve it evident that the increase in load is compatible with displacement as sho wn in DIC Fig. 4.5.2.3 RC beams strain response As presented in Fig. 4.20. b , 4.23. b , 4.26. b , and 4.29. b the increase in load up 50 kN cause a slight RC beam response in tension and compression, but with the stress increase, the tension response was h igher than the compression. The results of all beams in this category were compared, and it was observed that the behavior of all the RC beams was similar regardless the differences in the values, but the RC beams tension and compression response differs w ith load increase as a result of beam failure. Even though the RC beams that strengthened with C Grid U wrap tension and compression response is similar to the CTB beam's tension and compression response, the results of stress refer that strengthen the bea ms increase the load carrying capacity which increase beam ability to displace more according to mentioned figures. 4.5.2.4 CFRP strain of strain gages To measure the strain in CFRP, all beams have five stains along CFRP sheets. As shown in Fig 4.2.c every beam was glued with 5 strain gages where one glued at beam mid span of CFRP, and two strain gages spread at every 2 in from the mid span of the beam, and the other two strain gages were spread on the other side of the beam at distance 2 in. The strai n gages were glued at the center of 100 mm which is CFRP sheet width. The aim of using the stain gages is to measure the elongation response along of the CFRP. As clarified in Fig. 4.20.c, 4.23.c, 4.26.c, and 4.29.c strain gage response at beam mid span wa s the highest while the strain gages response

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60 of CFRP reduces whenever strain gages place are farther than beam mid span, and it observed that the strain gages response increase with load rise where the behavior of all strain gages have similar although th e strain value different. As in Fig. 4.20.c, 4.23.c, 4.26.c, and 4.29.c response of strain gages number 7, 11 was slightly low compared with the response of strain gages number 9 at mid span, and that as a result of maximum displacement and flexural failur e at RC beam mid span. 4.5.2.5 Failure mode Experimental tests of RC beams monitored during applying the load by using DIC system and optical observation of RC beams specimens through the tests, and as in table 4.6 the failure mode of every stage of load s tages. Even though beams strengthened with C Grid U wrap GEM beams have similar failure mode at first failure stages comparing with beams strengthened with CFRP U wrap which was the flexural failure, the C Grid U wrap started to resist the shear stresses w ith the increase of load. However, at the final failure concrete crushing at load points occurred, and deboning of CFRP sheet at the bottom cause C Grid rapture as a result of stress concentration at beams corners. It can be concluded that the failure pat tern of all beams is similar at all early stages of load, but with load increase, RC beams strengthened with C Grid U wrap showed a development in beam's performance. Where the failure was prevented due to the effect of the flexural shear, and improvements load carrying capacity significantly similar to the beams strengthened with CFRP U wrap. Also, deboning the CFRP sheets resulted in C Grid U wrap rapture because of stress concentration at beams corners. Therefore, it can be concluded that using C Grid is an efficient solution to strengthen RC beams, but C Grid is a weak material to resist stress concentrations rapture. 4.5 .3 Beams strengthening with C Grid U wrap and SMP hybrid (GHM) Tests results in this category detailed in Fig 4.43, 4.46, 4.49, and 4.52 , also tables 4.5 and 4.6 include test data of this section. 4.5.3.1 Load carrying capacity The tests results presented in table 4.5 explained tests data of RC beams either control beam (CTB) and beams strengthening with C Grid U wrap and SMP hybrid (GHM) to release

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61 stress concentrations indicating the failure loads. Also, table 4.6 described the failure load at every stage of the load stages, and clarified failure mode and cracks propagation. Next, GHM beams that strengthened with C Grid U wrap at s hear face sides and SMP at the beams corner were tested which described in Table 4.1 , and Fig 4.42 presents GHM beams at four different C Grid strengthening sizes area 25, 50, 75, and 100% of the shear face between the support and point load. Table 4.5 ind icates that load carrying capacity of a strengthened beam with C Grid was similar to load carrying capacity of GEM and UEM beams where the ultimate load of beams was 111.82, 107.65, 106.13, and 100.13kN of beams strengthened with C Grid U wrap 100, 75, 50, and 25% respectively. 4.5.3.2 Load displacement behavior of RC beam As displayed in Fig 4.2 the displacement was taken at beam mid span using a linear potentiometer. A ccording to Fig 4.43.a, 4.46.a, 4.49.a, and 4.52.a the load displacement behavior of GH M beams was almost similar to UEM and GEM beams despite differences in load carrying capacity values. Moreover, by comparing the results of failure load of GHM and GEM beams, it was clear that there is an obvious difference in the results between most the beams that have the same strengthening size. As in GHM beams the failure mode of GHM beams started as flexural failure at 48 kN, and with load increase, flexural shear failure can be seen using DIC camera 4.5.3.3 RC beams strain response Two PI gages at RC beam mid span install at one side of RC beam, one at the top to read compression response and the other PI gage at the bottom to read tension response at a distance 25 mm from the beam edge. As presented in Fig. 4.43.b , 4.46.b, 4.49.b and 4 .52.b the increase in load up 50 kN cause a slight RC beam response in tension and compression, but with the stress increase, the tension response was higher than the compression. The results of all beams in this category were compared, and it was observed that the behavior of all the RC beams was similar regardless the differences in the values, but the RC beams tension and compression response differs with load increase as a result of beam failure. Even though the RC beams that strengthened with C Grid U wrap tensi on and compression response is similar to the CTB beam's tension and compression response, the results of stress refer that strengthen the beams increase the load carrying capacity which increase beam ability to displace more according to mentioned figures .

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62 4.5.3.4 CFRP strain of strain gages To measure the strain behavior of CFRP, all beams have five stains along CFRP sheets. As shown in Fig 4.2.c every beam was glued with 5 strain gages where one glued at beam mid span of CFRP, and two strain gages spread at every 2 in from the mid span of the beam, and the other two strain gages were spread on the other side of the beam at distance 2 in. The strai n gages were glued at the center of 100 mm which is CFRP sheet width. The aim of using the stain gages is to measure the elongation response along of the CFRP. As clarified in Fig 4.43.c, 4.46.c, 4.49.c, and 4.52.c strain gage response at beam mid span was the highest while the strain gages response of CFRP reduces whenever strain gages place are farther than beam mid span, and it observed that the strain gages response increase with load rise where the behavior of all strain gages have similar although the strain value different. As in Fig 4.43.c, 4.46.c, 4.49.c, and 4.52.c response of strain gages number 7, 11 was slightly low compared with the response of strain gages number 9 at mid span, and that as a result of maximum displacement and flexural failure at RC beam mid span. 4.5.3.5 Failure mode Experimental tests of RC beams monitored while applying the load by using DIC system and optical observation of RC beams specimens through the tests, and as in table 4.6 the failure mode of every stage of load stag es. Even though beams strengthened with C Grid U wrap and SMP hybrid GHM beams have a flexural failure, the C Grid U wrap started to resist the shear stresses with the increase of load. Also, the concrete failure of all beams occurred as a result of flexur al and flexural shear failure while CFRP sheets failure was as global debonding of beams that have strengthening area 100, 75, 50% while the SMP prevented C Grid rapture. With noting that debonding failure of beam strengthened with 25% was local debonding and C Grid rapture because of the limited C Grid and SMP coverage area in Fig 4.54 . In conclusion, the failure pattern of all beams is similar at all early stages of the load. However, with load increase, RC beams strengthened with C Grid U wrap showed a development in beam's performance where the failure was prevented due to the flexural shear and improve load carrying capacity significantly similar to the beams strengthened with CFRP U wrap. Also, SMP hybrid improves the U wrap performance which prevents deboning the

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63 CFRP sheets as result of using SMP hybrid that allows C Grid U wrap to work better which stress concentration at beams corners. 4.5 .4 Beams strengthening with C Grid U wrap and SMP hybrid (GHC) In this category cyclic load was applied to simu late the real case of load that RC beams are subjected to an FEMA 2007 protocol were used an according to ( Krawinkler , 2009 cited from FEMA, 2007 ) for testing of drift sensitive nonstructural components, but is applicable in general also to drift sensitive structural components. It uses a targeted maximum deformation amplitude , m, and a targeted smallest deformation amplitude, 0, as reference values, and a predetermined number of amplitude ai of the step wise increasing deformation cycles is given by the equation ai+1/an = 1.4(ai/an), where a1 is equal to 0 (or a value close to it) and is equal to m (or a value close to it). Two cycles are to be executed for each amplitude. If the last damage state has not yet occurred at the target value m, the loading history shall be continued by using further increments of amplitude of 0.3 Tests results in this category detailed in Fig 4.55, 4.58, 4.61 and 4.64 , also tables 4.5 and 4.6 include test data of this section. 4.5.4.1 Load carrying c apacity The tests results presented in table 4.5 explained tests data of RC beams either control beam (CTB) and beam strengthened with CFRP U wrap indicating the failure loads, Stdev, and COV; also table 4.6 described the failure load at every stage of the load stages, and clarified failure mode and cracks propagation. Firstly, for CTB beam as in the table 4.5 failure load was 91.17 kN under monolithic load influence, and by monitoring CTB specimen when the load was applied the first failure was observed as flexural cracks then with the increase of applied load shear flexural cracks start to appear. Finally because of beam displacement increase CFRP debonding occurred at beams edges.

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64 After that, RC beams tha t strengthened with C Grid U wrap at shear face sides tested which described in Table 4.1 , and Fig 4.42 RC beams strengthened with C Grid U wrap at four different sizes of C Grid 25, 50, 75, and 100% of the shear face between the support and point load. Ta ble 4.5 indicates to the observed improvement in load carrying capacity of the strengthened beam with C Grid U wrap where the ultimate load of beams increased with the increase of strengthening area 93.71, 91.76, 88.19, 86.23 kN to beams strengthened with C Grid U wrap 100 , 75, 50 , and 25% respectively. Also, the failure of all beams occurred as a result of flexural and flexural shear failure while CFRP sheets failure was as results of rupture . Also, it was noted that no debonding happened to C Grid U wrap as it is obvious in Fig 4.57, 4.60, 4.63 and 4.66 , and that duo to using the SMP hybrid which release the stress concentration, and as mentioned before the stress concentration at the beams corners are the main cause of C Grid U wrap rupture. 4.5.4.2 Load displacement behavior of RC beam The displacement was taken at beam mid span using a linear potentiometer as shown in Fig 4.1. According to Fig 4.55.a, 4.58.a, 4.61.a, and 4.64.a , the load displacement behavior of RC beams was almost similar with improvem ent in ultimate load with an increase of strengthening the area. Comparing the results of load displacement curves of beams under cyclic load, it could be observing that stiffness is higher at first cycle, but with an increase in cycles the beam loss its s tiffness signi ficantly as in Fig 4.56.a, 4.59.a, 4.62.a, , and 4.65.a . Moreover, it is noticeable that stiffness improved by strengthening RC beams with C Grid were 16.29, 14.38, 13.22, and 11.94 kN/mm at C Grid strengthening area 100, 75, 50, 25%. Also, i nterior textural cracks at beams mid span appeared after the 10th cycle in all the beams according to DIC system. Where failure happened and growth in RC beam with cycles increase. Strengthening RC beam daily the failure depending on strengthening the area , whereby monitoring the failure in the beam the first crack was at 14th, 12th, 11th, 11th cycle at strengthening area 100, 75, 50, 25. Besides, the damage index of the beam increases rapidly with the load cycles increase as observed in Fig 4.56.b, 4.59.b, 4.62.b, , and 4.65.b . The increase strengthening area effect on damage index where it was 0.64 at 100 C Grid U wrap strengthening area while strengthening area 75, 50, 25 % have almost same damage index with 0.74.

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65 4.5.4.3 RC beams strain response As presented in Fig. 4.55.b, 4.58.b, 4.61.b, and 4.64.b increase in cycles number cause a much RC beam response in tension and compression, but tension response was more compatible in all the beams than the compression. The results of all beams in this catego ry compared, and it observed that the tension behavior of all the RC beams was similar regardless the differences in the values, but the RC beams tension response differs with an increase in cycles as a result of beam failure. However, the compression resp onse was the difference in some beam as a result of differences of beams capacity under cycles load. 4.5.4.4 CFRP strain of strain gages As clarified in Fig 4.55.c, 4.58.c, 4.61.c and 4.64.c strain gage response at beam mid span was the highest while the s train gages response of CFRP decrease whenever strain gages place are farther than beam mid span, and it observed that the strain gages response increase with load increase where the behavior of all strain gages have similar although the strain value diffe rent. As in Fig 4.55.c, 4.58.c, 4.61.c and 4.64.c response of strain, gage number 7 was slightly low compared with the response of strain gages number 9 at mid span, and that as a result of maximum displacement and flexural failure at RC beam mid span. 4.5.4.5 Failure mode Experimental tests of RC beams monitored while applying the load by using DIC system and optical observation of RC beams specimens through the tests, and as in table 4.6 the failure mode of every stage of load stages. According to Fig 4.57, 4.60, 4.63, and 4.66 failure mode of all GHC beams starts at after the 10th cycle and the crack growth as a flexural failure, then cracks start propagate and increase as a flexural failure, flexural shear failure happened after 17th, 15th, 14th, 12th . And as a result of the increase of beam deflection at mid span which cause increasing of spread cracks, and final failure of the beam happened as CFRP debonding after C Grid U wrap and concrete crushing between applied load points directly before the ult imate load. Even though RC beams strengthened with C Grid U wrap and SMP hybrid at corner have failure similar to CTB beam failure at the beginning where the failure was the flexural failure, the C Grid U wrap started to resist the failure with the increas e of load. Where there are no obvious shear failures of RC beams strengthened with C Grid U wrap with 100, 75,

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66 50, and 25 %. SMP hybrid release the stress concentrations at RC beams corners which prohibit local CFRP debonding and C Grid U wrap rapture. The final failure of GHC beams group was as results of concrete crushing at load points, and CFRP global debonding after the place of C Grid U wrap as shown in Fig 4.57, 4.60, 4.63, and 4.66 . Load carrying capacity of GHC RC beams improves with the increase o f C Grid U wrap strengthening area. T o sum up, that the failure pattern of all beams is similar at all early stages of load, but with load increase, RC beams strengthened with C Grid U wrap showed a development in beam's performance where the failure was p revented due to the flexural shear and improve load carrying capacity significantly. Also, nothing SMP hybrid prevented CFRP local debonding of strengthened RC beams as in DIC picture Fig.

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67 Table 4.1 . Nomenclatu re and details of concrete beam specimens . Category Number of beams Beam description Load type CTB 1 Control beam strengthened with CFRP sheet . M onoton ic UEM 4 Beam strengthened with CFRP sheet and CFRP U wrap s with epoxy. M onoton ic GEM 7 B eam strengthen ed with CFRP sheet a nd C Grid U wrap s with epoxy M onoton ic GHM 4 Beam strengthen ed with CFRP sheet and C Grid U wrap s with epoxy and SMP (hybrid bonding) under m onoton ic loading. M onoton ic GH C 4 Beam strengthen ed with CFRP sheet and C Grid U wrap s with epoxy and SMP (hybrid bonding) under cyclic loading. Cyclic Table 4.2. Mix p roportions of concrete . Component Value Cement 380 (kg/m 3 ) Water 205 (kg/m 3 ) Gravel 1200 (kg/m 3 ) Sand 700 (kg/m3) W/C (%) 40%

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68 Table 4.3 . Compressive strength of concrete cylinders. Specimen Compressive Load at 28 days (kN) Compressive Stress at 28 days ( MPa ) C1 173.7 24.54 C2 187.98 23.8 4 C3 139.9 22 . 1 8 Average compressive stress 23.52 Table 4 . 4 . Properties of C Grid composite strip from the manufacturer ( Chom arat, 2010). Property Value Fiber r einforcement Carbon High Tensile Roll length & w idth 25.9 m & 0 .914 m Fiber w eight 300 g/m² Thickness 0.135 mm Individual strand cross sectional area 0.46 mm² Tensile strength per strand 1.03 kN Area o f strand per unit width 12.12 (mm²/m) Average number of strand per unit width 26.25 (strands/m) Tensile strength per unit width 27.08 (kN/m) Tensile modulus 238 GPa Strand strain at rupture 0.013

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69 Table 4.5 . Summary o f test results of concrete beams . Spec. ID Anchorage Pu (kN) Average P u (kN) CTB 91.11 91.11 UEM 100 Strengthening with 100% CFRP U wrap 116.08 109.18 UEM 75 Strengthening with 75% CFRP U wrap 109.91 UEM 50 Strengthening with 50% CFRP U wrap 107.42 UEM 25 Strengthening with 25% CFRP U wrap 103.32 GEM 100 Strengthening with 100% C Grid U wrap 113.65 107.53 GEM 75 Strengthening with 75% C Grid U wrap 107.17 GEM 50 Strengthening with 50% C Grid U wrap 104.24 GEM 25 Strengthening with 25% C Grid U wrap 101.50 GEM 100 1.5*3 Strengthening with 100% C Grid U wrap (1.5*3 grid size) 104.38 GEM 100 3*1.5 Strengthening with 100% C Grid U wrap (3*1.5 grid size) 107.02 GEM 100 0.75*0.75 Strengthening with 100% C Grid U wrap (0.75*0.75 grid size) 114.77 GHM 100 Strengthening with 100% C Grid U wrap and SMP 111.82 106.45 GHM 75 Strengthening with 75% C Grid U wrap and SMP 107.65 GHM 50 Strengthening with 50% C Grid U wrap and SMP 106.21 GHM 25 Strengthening with 25% C Grid U wrap and SMP 100.13 GHC 100 Strengthening with 100% C Grid U wrap and SMP 93.71 89.97 GHC 75 Strengthening with 75% C Grid U wrap and SMP 91.76 GHC 50 Strengthening with 50% C Grid U wrap and SMP 88.19 GHC 25 Strengthening with 25% C Grid U wrap and SMP 86.23

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70 Table 4.6 . a. Failure modes of beams bonded at different Load stage on the beam. Beam No. Load level (kN) 45 60 60 75 75 80 80 90 90 100 100 110 >110 CTB Flexural cracks at 47 kN at midspan Flexural cracks increase and propagate and flexural shear cracks start Flexural shear cracks propagate Cracks propagate and CFRP sheets start debond Concrete crush and CFRP sheets debond beam fail at 91 kN ..... UEM 100 Flexural cracks at 55 kN at midspan Flexural cracks propagate Flexural shear cracks appear Cracks propagate CFRP sheets start debond at some points Cracks propagate Concrete crush and CFRP sheets rupture beam fail at 116 kN UEM 75 Flexural cracks at 52 kN at midspan Cracks increase and propagate Cracks propagate flexural shear cracks start CFRP sheets start debond at some points Concrete crush and CFRP sheets rupture beam fail at UEM 50 Flexural cracks at 49 midspan Cracks increase and propagate flexural shear cracks start Flexural shear cracks propagate flexural shear cracks Concrete crush and CFRP sheets rupture beam fail at UEM 25 Flexural cracks at 50 kN at midspan Cracks increase and propagate Flexural shear cracks appear Cracks propagate CFRP sheets start debond at some points CFRP sheets start debond at some points

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71 Table 4.6.b. Failure modes of beams bonded at different Load stage on the beam. Beam No. Load level (kN) 45 60 60 75 75 80 80 90 90 100 100 110 >110 GEM 100 Flexural cracks at 48 kN at midspan Cracks propagate Flexural shear cracks start and propagate Cracks propagate Shear cracks CFRP sheets start debond at some points Concrete crush and CFRP debond and C Grid rupture beam fail at 112 kN GEM 75 Flexural cracks at 50 kN Cracks increase and propagate Cracks propagate Cracks propagate and CFRP sheets start debond CFRP sheets start debond at some points Concrete crush and CFRP debond and C Grid rupture beam fail at 107 kN GEM 50 Flexural cracks at 49 kN at midspan Flexural cracks increase and propagate flexural shear cracks start Flexural shear cracks propagate Shear cracks Concrete crush and CFRP debond and C Grid rupture beam fail at 112 kN GEM 25 Flexural cracks at 47 kN at midspan Cracks propagate Flexural shear cracks appear Cracks propagate Flexural shear cracks propagate Concrete crush and CFRP debond and C Grid rupture beam fail at 112 kN GEM 100 1.3*3 Flexural cracks at 51 kN Flexural cracks increase and propagate Cracks propaga te Flexural shear cracks propagate Shear cracks Concrete crush and CFRP debond and C Grid rupture beam fail at 112 kN GEM 100 3*1.5 Flexural cracks at 50 kN Flexural cracks increase Cracks propagate Shear cracks Cracks propagate CFRP debond and C Grid rupture beam fail at 112 kN GEM 100 0.75*0.75 Flexural cracks at 53 kN Flexural cracks Flexural cracks propagate Cracks propagate C Grid resist Flexural cracks and shear cracks Flexural cracks increase and propagate Concrete crush and CFRP debond and C Grid rupture beam fail at 112 kN

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72 Table 4.6.c. Failure modes of beams bonded at different Load stage on the beam. Beam No. Load level (kN) 45 60 60 75 75 80 80 90 90 100 100 110 >110 CHM 100 Flexural cracks at 48 kN at midspan Flexural cracks propagate and flexural shear cracks start Cracks propagate Flexural cracks propagate Cracks propagate SMP release stress concentration Concrete crush and CFRP debond at midspan beam fail at 112 kN CHM 75 Flexural cracks at 50 kN Flexural cracks propagate Flexural shear cracks appear Cracks propagate SMP release stress concentration Concrete crush and CFRP debond at midspan beam fail at 107 kN CHM 50 Flexural cracks at 54 kN at midspan Flexural cracks propagate and flexural shear cracks start Cracks propagate Flexural cracks propagate SMP release stress concentration Concrete crush and CFRP debond at midspan beam fail at 105 kN CHM 25 Flexural cracks at at 48 kN Cracks propagate Flexural cracks propagate CFRP sheets start debond at some points Cracks propagate Concrete crush and CFRP debond and C Grid rupture beam fail at 102 kN

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73 Table 4.6. d . Failure modes of beams bonded at different Load stage on the beam. Beam No. Load level (kN) 45 60 60 75 75 80 80 90 90 100 100 110 >110 GHC 100 Flexural cracks at 12 th cycle Cracks propagate Flexural shear cracks start Cracks propagate SMP release stress concentration Concrete crush and CFRP debond at midspan beam fail at 112 kN GHC 75 Flexural cracks at 9 th cycle Flexural cracks propagate SMP release stress concentration SMP release stress concentration Concrete crush beam fail at 107 kN GHC 50 Flexural cracks at 10 th cycle Flexural cracks propagate and flexural shear cracks start Cracks propagate SMP release stress concentration Concrete crush and CFRP debond at midspan beam fail at 104 kN GHC 25 Flexural cracks at 10 th cycle midspan Flexural cracks propagate Cracks propagate SMP release stress concentration Concrete crush beam fail at 107 kN

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74 ( a ) Fig 4. 1.a . Beam preparation : (a) Steel cages; (b) Costing the concrete in wooden frame; (c) Concrete mixer; (d) tested concrete cylinder . ( b ) ( c ) ( d )

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75 Fig.4.1. b. Concrete test setup

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76 Fig.4.2. Beam CTB derail; (a) cross section; (b) strengthened beam with CFRP; (c) strain gages distribution ; (d) reinforcements details .

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77 Fig. 4.3. Test result for CTB: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different locations. 0 20 40 60 80 100 120 0 5 10 15 20 Load (kN) Displacemant (mm) 0 20 40 60 80 100 120 -0.002 0 0.002 0.004 0.006 Load (kN) Strain Tension Compressi on 0 20 40 60 80 100 120 -0.001 0.004 0.009 0.014 Load (kN) Strain G1 G2 G3 G4 G5 (a) (b) (c)

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78 Fig. 4.4. Response of CFRP strain at different loading stages of specimen CTB. 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 -150 -100 -50 0 50 100 150 Strain Distance from CL (mm) 20% Pu 40% Pu 60% Pu 80% Pu 100% Pu

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79 ( a ) Fig 4. 5. a. Failure mode of CTB : (a) flexural cracks at mid span at 49 kN; (b) CFRP debonding; (c) overview final failure; (d) close view final failure. ( b ) ( c ) ( d )

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80 Fig.4. 5. b . Global failure of beam CTB . Fig 4.5.c . Failure mode of beam CTB.

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81 Fig.4.6 . Beam UEM strengthened with CFRP details: (a) 100 % ; (b) 75 % , (c) 50 % ; (d) 25 % .

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82 Fig. 4.7 . Test result for UEM 1 00 : (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different locations. 0 20 40 60 80 100 120 0 5 10 15 20 Load (kN) Displacemant (mm) 0 20 40 60 80 100 120 -0.002 0 0.002 0.004 0.006 Load (kN) Strain Tension Compressi on 0 20 40 60 80 100 120 -0.001 0.004 0.009 0.014 Load (kN) Strain G1 G2 G3 G4 G5 (a) (b) (c)

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83 Fig. 4.8 . Response of CFRP strain at differe nt loading stages of specimen UEM 1 00 . 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 0.011 0.012 -150 -100 -50 0 50 100 150 Strain Distance from CL (mm) 20% Pu 40% Pu 60% Pu 80% Pu 100% Pu

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84 ( a ) Fig 4 .9 .a . Failure mode of UEM 100 : (a) flex ural cracks at mid span ; (b) CFRP debonding; (c) overview final failure; (d) close view final failure. ( b ) ( c ) ( d )

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85 Fig.4. 9. b . Global failure of beam UEM 100 . Fig.4.9.c . Failure mode of beam UEM 100.

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86 Fig. 4.10 . Test result for UEM 75 : (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different locations. 0 20 40 60 80 100 120 0 5 10 15 20 Load (kN) Displacemant (mm) 0 20 40 60 80 100 120 -0.002 0 0.002 0.004 0.006 Load (kN) Strain Tension Compressi on 0 20 40 60 80 100 120 -0.001 0.004 0.009 0.014 Load (kN) Strain G1 G2 G3 G4 G5 (a) (b) (c)

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87 Fig. 4.11 . Response of CFRP strain at differe nt loading stages of specimen UEM 75 . 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 0.011 0.012 -150 -100 -50 0 50 100 150 Strain Distance from CL (mm) 20% Pu 40% Pu 60% Pu 80% Pu 100% Pu

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88 ( a ) Fig 4. 12. a. Failure mode of UEM 75 : (a) flexural cracks at mid span; (b) CFRP debonding; (c) overview final failure; (d) close view final failure. ( b ) ( c ) ( d )

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89 Fig.4. 12. b . Global failure of beam UEM 75 . Fig 4.12.c . Failure mode of beam UEM 75.

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90 Fig. 4.13 . Test result for UEM 50 : (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different locations. 0 20 40 60 80 100 120 0 5 10 15 20 Load (kN) Displacemant (mm) 0 20 40 60 80 100 120 -0.002 0 0.002 0.004 Load (kN) Strain Tension Compre ssion 0 20 40 60 80 100 120 -0.002 0.003 0.008 0.013 Load (kN) Strain G1 G2 G3 G4 G5 (a) (b) (c)

PAGE 112

91 Fig. 4.14 . Response of CFRP strain at differe nt loading stages of specimen UEM 50 . 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 0.011 0.012 -150 -100 -50 0 50 100 150 Strain Distance from CL (mm) 20% Pu 40% Pu 60% Pu 80% Pu 100% Pu

PAGE 113

92 ( a ) Fig 4. 15. a. Failure mode of UEM 50 : (a) flexural cracks at mid span; (b) CFRP debonding; (c) overview final failure; (d) close view final failure. ( b ) ( c ) ( d )

PAGE 114

93 Fig.4. 15. b . Global failure of beam UEM 50 . Fig 4.15.c . Failure mode of beam UEM 50.

PAGE 115

94 Fig. 4.16 . Test result for UEM 25 : (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different locations. 0 20 40 60 80 100 120 0 5 10 15 20 Load (kN) Displacemant (mm) 0 20 40 60 80 100 120 -0.006 -0.004 -0.002 0 0.002 0.004 0.006 Load (kN) Strain Tension Compressi on 0 20 40 60 80 100 120 -0.001 0.004 0.009 0.014 Load (kN) Strain G1 G2 G3 G4 G5 (a) (b) (c)

PAGE 116

95 Fig. 4.17 . Response of CFRP strain at differe nt loading stages of specimen UEM 25 . 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 -150 -100 -50 0 50 100 150 Strain Distance from CL (mm) 20% Pu 40% Pu 60% Pu 80% Pu 100% Pu

PAGE 117

96 ( a ) Fig 4. 18. a. Failure mode of UEM 25 : (a) flex ural cracks at mid span ; (b) CFRP debonding; (c) overview final failure; (d) close view final failure. ( b ) ( c ) ( d )

PAGE 118

97 Fig.4. 18. b . Global failure of beam UEM 25 . Fig 4.18.c . Failure mode of beam UEM 25.

PAGE 119

98 Fig.4.19 . Beam GEM strengthened with C Grid details: (a) 100 % ; (b) 75 % , (c) 50 % ; (d) 25 % .

PAGE 120

99 Fig. 4.20 . Test result for GEM 1 00 : (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different locations. 0 20 40 60 80 100 120 0 5 10 15 20 Load (kN) Displacemant (mm) 0 20 40 60 80 100 -0.002 0 0.002 0.004 0.006 Load (kN) Strain Compressio n Tension 0 10 20 30 40 50 60 70 80 90 100 110 -0.002 0.003 0.008 0.013 Load (kN) Strain G1 G2 G3 G4 G5 (a) (b) (c)

PAGE 121

100 Fig. 4.21 . Response of CFRP strain at differen t loading stages of specimen GEM 1 00 . 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 -150 -100 -50 0 50 100 150 Strain Distance from CL (mm) 20% Pu 40% Pu 60% Pu 80% Pu 100% Pu

PAGE 122

101 ( a ) Fig 4. 22. a. Failure mode of GEM 100 : (a) flex ural cracks at mid span ; (b) CFRP debonding; (c) overview final failure; (d) close view final failure. ( b ) ( c ) ( d )

PAGE 123

102 Fig.4. 22. b . Global failure of beam GEM 100 . Fig 4.22.c . Failure mode of beam GEM 100.

PAGE 124

103 Fig. 4.23 . Test result for GEM 75: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different locations. 0 20 40 60 80 100 120 0 5 10 15 20 Load (kN) Displacemant (mm) 0 20 40 60 80 100 120 -0.002 0 0.002 0.004 0.006 Load (kN) Strain Tension Compressi on 0 20 40 60 80 100 120 -0.002 0.003 0.008 0.013 Load (kN) Strain G1 G2 G3 G4 G5 (a) (b) (c)

PAGE 125

104 ( a ) Fig 4. 25. a. Failure mode of GEM 75 : (a) flex ural cracks at mid span ; (b) CFRP debonding; (c) overview final failure; (d) close view final failure. ( b ) ( c ) ( d )

PAGE 126

105 Fig.4. 25. b . Global failure of beam GEM 75 . Fig 4.25.c . Failure mode of beam GEM 75.

PAGE 127

106 Fig. 4.26 . Test result for GEM 50: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different locations. 0 20 40 60 80 100 120 0 5 10 15 20 Load (kN) Displacemant (mm) 0 20 40 60 80 100 120 -0.001 -0.0005 0 0.0005 0.001 Load (kN) Strain Tension Compressio n 0 20 40 60 80 100 120 -0.002 0.003 0.008 0.013 Load (kN) Strain G1 G2 G3 G4 G5 (a) (b) (c)

PAGE 128

107 Fig. 4.27 . Response of CFRP strain at different loading stages of specimen GEM 50. 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 -150 -100 -50 0 50 100 150 Strain Distance from CL (mm) 20% Pu 40% Pu 60% Pu 80% Pu 100% Pu

PAGE 129

108 ( a ) Fig 4. 28. a. Failure mode of GEM 50 : (a) flexural cracks at mid span; (b) CFRP debonding; (c) overview final failure; (d) close view final failure. ( b ) ( c ) ( d )

PAGE 130

109 Fig.4. 28. b . Global failure of beam GEM 50 . Fig 4.28.c . Failure mode of beam GEM 50.

PAGE 131

110 Fig. 4.29 . Test result for GEM 25: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different locations. 0 20 40 60 80 100 120 0 5 10 15 20 Load (kN) Displacemant (mm) Load-dis0 0 20 40 60 80 100 120 -0.002 0 0.002 0.004 0.006 Load (kN) Strain Tension Compressi on 0 20 40 60 80 100 120 -0.001 0.004 0.009 0.014 Load (kN) Strain G1 G2 G3 G4 G5 (a) (b) (c)

PAGE 132

111 Fig. 4.30 . Response of CFRP strain at different loading stages of specimen GEM 25 . . 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 -150 -100 -50 0 50 100 150 Strain Distance from CL (mm) 20% Pu 40% Pu 60% Pu 80% Pu 100% Pu

PAGE 133

112 ( a ) Fig 4. 31. a. Failure mode of GEM 25 : (a) flexural cracks at mid span; (b) CFRP debonding; (c) overview final failure; (d) close view final failure. ( b ) ( c ) ( d )

PAGE 134

113 Fig.4. 31. b . Global failure of beam GEM 25 . Fig 4.31.c . Failure mode of beam GEM 25.

PAGE 135

114 Fig.4.32 . Beam GEM strengthened with Grid details: (a) 100 % 0.75*0.75; (b) 100 % 1.5*3, (c) 100 % 3*1.5.

PAGE 136

115 Fig. 4.33 . Test result for GEM 100 1.5*3: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different locations. 0 20 40 60 80 100 120 0 10 20 Load (kN) Displacemant (mm) 0 20 40 60 80 100 120 -0.002 0 0.002 0.004 0.006 0.008 Load (kN) Strain Tension Compressi on 0 20 40 60 80 100 120 -0.001 0.004 0.009 0.014 Load (kN) Strain G1 G2 G3 G4 G5 (a) (b) (c)

PAGE 137

116 Fig. 4.34 . Response of CFRP strain at different loading stages of specimen GEM 100 1.5*3. 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 -150 -100 -50 0 50 100 150 Strain Distance from CL (mm) 20% Pu 40% Pu 60% Pu 80% Pu 100% Pu

PAGE 138

117 ( a ) Fig 4. 35 .a . Failure mode of GEM 100 1.5*3 : (a) flexural cracks at mid span; (b) CFRP debonding; (c) overview final failure; (d) close view final failure. ( b ) ( c ) ( d )

PAGE 139

118 Fig.4. 35. b . Global failure of beam GEM 100 1.5*3. Fig 4.35.c . Failure mode of beam GEM 100 1.5*3.

PAGE 140

119 Fig. 4.36 . Test result for GEM 100 3*1.5: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different locations. 0 20 40 60 80 100 120 0 10 20 30 Load (kN) Displacemant (mm) 0 20 40 60 80 100 120 -0.002 0 0.002 0.004 0.006 Load (kN) Strain Tension Compres sion 0 20 40 60 80 100 120 -0.001 0.004 0.009 0.014 Load (kN) Strain G1 G2 G3 G4 G5 (a) (b) (c)

PAGE 141

120 Fig. 4.37 . Response of CFRP strain at different loading stages of specimen GEM 100 3*1.5. 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 0.011 0.012 -150 -100 -50 0 50 100 150 Strain Distance from CL (mm) 20% Pu 40% Pu 60% Pu 80% Pu 100% Pu

PAGE 142

121 ( a ) Fig 4. 38. a. Failure mode of GEM 100 3*1.5 : (a) flexural cracks at mid span; (b) CFRP debonding; (c) overview final failure; (d) close view final failure. ( b ) ( c ) ( d )

PAGE 143

122 Fig.4. 38. b . Global failure of beam GEM 100 3*1.5. Fig 4.38.c . Failure mode of beam GEM 100 3*1.5.

PAGE 144

123 Fig. 4.39 . Test result for GEM 100 0.75*0.75: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different locations. 0 20 40 60 80 100 120 0 10 20 30 Load (kN) Displacemant (mm) Load-dis0 0 20 40 60 80 100 120 -0.002 0 0.002 0.004 0.006 Load (kN) Strain Tension Compressi on 0 20 40 60 80 100 120 -0.001 0.004 0.009 0.014 Load (kN) Strain G1 G2 G3 G4 G5 (a) (b) (c)

PAGE 145

124 Fig. 4.40 . Response of CFRP strain at different loading stages of specimen GEM 100 0.75*0.75. 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 0.011 0.012 0.013 0.014 0.015 -150 -100 -50 0 50 100 150 Strain Distance from CL (mm) 20% Pu 40% Pu 60% Pu 80% Pu 100% Pu

PAGE 146

125 ( a ) Fig 4. 41 .a . Failure mode of GEM 100 0.75*0.75 : (a) flex ural cracks at mid span ; (b) CFRP debonding; (c) overview final failure; (d) close view final failure. ( b ) ( c ) ( d )

PAGE 147

126 Fig.4. 38. b . Global failure of beam GEM 100 3*1.5. Fig 4.41.b. Failure mode of beam GEM 100 0.75*0.75.

PAGE 148

127 Fi g.4.42 . Beams details GH M and GCM strengthened with C Grid and SMP hybrid : (a) 100 % ; (b) 75 % , (c) 50 % ; (d) 25 % .

PAGE 149

128 Fig. 4.43 . Test result for GHM 100: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different locations. 0 20 40 60 80 100 120 0 5 10 15 20 Load (kN) Displacemant (mm) 0 20 40 60 80 100 120 -0.002 0 0.002 0.004 0.006 Load (kN) Strain Tension Compre ssion 0 10 20 30 40 50 60 70 80 90 100 110 -0.002 0.003 0.008 0.013 Load (kN) Strain G1 G2 G3 G4 G5 (a) (b) (c)

PAGE 150

129 Fig. 4.44 . Response of CFRP strain at different loading stages of specimen GHM 100. 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 -150 -100 -50 0 50 100 150 Strain Distance from CL (mm) 20% Pu 40% Pu 60% Pu 80% Pu 100% Pu

PAGE 151

130 ( a ) Fig 4. 45. a. Failure mode of GHM 100 : (a) flexural cracks at mid span; (b) CFRP debonding; (c) overview final failure; (d) close view final failure. ( b ) ( c ) ( d )

PAGE 152

131 Fig.4. 45. b . Global failure of beam GHM 100. Fig 4.45.c . Failure mode of beam GHM 100.

PAGE 153

132 Fig. 4.46 . Test result for GHM 75: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different locations. 0 20 40 60 80 100 120 0 5 10 15 20 Load (kN) Displacemant (mm) 0 20 40 60 80 100 120 -0.002 0 0.002 0.004 0.006 Load (kN) Strain Tension Compressi on 0 20 40 60 80 100 120 -0.001 0.004 0.009 0.014 Load (kN) Strain G1 G2 G3 G4 G5 (a) (b) (c)

PAGE 154

133 Fig. 4.47 . Response of CFRP strain at different loading stages of specimen GHM 75. 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 -150 -100 -50 0 50 100 150 Strain Distance from CL (mm) 20% Pu 40% Pu 60% Pu 80% Pu 100% Pu

PAGE 155

134 ( a ) Fig 4. 48. a. Failure mode of GHM 75 : (a) flexural cracks at mid span; (b) CFRP debonding; (c) overview final failure; (d) close view final failure. ( b ) ( c ) ( d )

PAGE 156

135 Fig.4. 48. b . Global failure of beam GHM 75. Fig 4.48.c . Failure mode of beam GHM 75.

PAGE 157

136 Fig. 4.49 . Test result for GHM 50: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different locations. 0 20 40 60 80 100 120 0 5 10 15 20 Load (kN) Displacemant (mm) 0 20 40 60 80 100 -0.002 0 0.002 0.004 0.006 Load (kN) Strain Tension Compression 0 10 20 30 40 50 60 70 80 90 100 110 -0.001 0.004 0.009 0.014 Load (kN) Strain G1 G2 G3 G4 G5 (a) (b) (c)

PAGE 158

137 Fig. 4. 5 0 . Response of CFRP strain at different loading stages of specimen GHM 50. 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 0.011 0.012 -150 -100 -50 0 50 100 150 Strain Distance from midspan (mm) 20% Pu 40% Pu 60% Pu 80% Pu 100% Pu

PAGE 159

138 ( a ) Fig 4. 51. a. Failure mode of G HM 50 : (a) flex ural cracks at mid span ; (b) CFRP debonding; (c) overview final failure; (d) close view final failure. ( b ) ( c ) ( d )

PAGE 160

139 Fig.4. 51. b . Global failure of beam GHM 50. Fig 4.51.c . Failure mode of beam GHM 50.

PAGE 161

140 Fig. 4.52 . Test result for GHM 25: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different locations. 0 20 40 60 80 100 120 0 5 10 15 20 Load (kN) Displacemant (mm) 0 20 40 60 80 100 -0.002 0 0.002 0.004 0.006 Load (kN) Strain Tension Compression 0 10 20 30 40 50 60 70 80 90 100 110 -0.001 0.004 0.009 0.014 Load (kN) Strain G1 G2 G3 G4 G5 (a) (b) (c)

PAGE 162

141 Fig. 4.53 . Response of CFRP strain at different loading stages of specimen GHM 25. 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 -150 -100 -50 0 50 100 150 Strain Distance from CL (mm) 20% Pu 40% Pu 60% Pu 80% Pu 100% Pu

PAGE 163

142 ( a ) Fig 4. 54. a. Failure mode of G HM 25 : (a) flex ural cracks at mid span ; (b) CFRP debonding; (c) overview final failure; (d) close view final failure. ( b ) ( c ) ( d )

PAGE 164

143 Fig.4. 54. b . Global failure of beam GHM 25. Fig 4.54.c . Failure mode of beam GHM 25.

PAGE 165

144 Fig. 4.55 . Test result for GHC 100: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different locations. 0 20 40 60 80 100 0 5 10 15 20 Load (kN) Displacemant (mm) 0 20 40 60 80 100 -0.006 -0.004 -0.002 0 0.002 Load (kN) Strain Tension Compressi on 0 10 20 30 40 50 60 70 80 90 100 110 -0.001 0.004 0.009 0.014 Load (kN) Strain G3 G2 G1 (a) (b) (c)

PAGE 166

145 Fig. 4. 56 . Effect of cyclic load on beam GHC 100: (a) stiffness; (b) damage index 0 5 10 15 20 0 5 10 15 20 Stiffness (kN/mm) Number of cycles (a) 0 0.2 0.4 0.6 0.8 1 0 5 10 15 20 Damge Index Number of cycles (b)

PAGE 167

146 ( a ) Fig 4. 57 .a . Failure mode of G HC 100 : (a) flex ural cracks at mid span ; (b) CFRP debonding; (c) overview final failure; (d) close view final failure. ( b ) ( c ) ( d )

PAGE 168

147 Fig.4. 57. b . Global failure of beam GHC 100. Fig 4.57.c . Failure mode of beam GHC 100.

PAGE 169

148 Fig. 4.58 . Test result for GHC 75: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different locations. 0 20 40 60 80 100 0 5 10 15 20 Load (kN) Displacemant (mm) 0 20 40 60 80 100 -0.002 0 0.002 0.004 0.006 Load (kN) Strain Tension Compression 0 10 20 30 40 50 60 70 80 90 100 110 -0.001 0.004 0.009 0.014 Load (kN) Strain G3 G2 G1 (a) (b) (c)

PAGE 170

149 Fig. 4.59 . Effect of cyclic load on beam GHC 75: (a) stiffness; (b) damage index . 0 5 10 15 20 0 5 10 15 20 Stiffness (kN/mm) Number of cycles (a) 0 0.2 0.4 0.6 0.8 1 0 5 10 15 20 Damge Index Number of cycles (b)

PAGE 171

150 ( a ) Fig 4.60. a. Failure mode of GHC 75 : (a) flexural cracks at mid span; (b) CFRP debonding; (c) overview final failure; (d) close view final failure. ( b ) ( c ) ( d )

PAGE 172

151 Fig.4. 60. b . Global failure of beam GHC 75. Fig 4.60. c . Failure mode of beam GHC 75.

PAGE 173

152 Fig. 4.61 . Test result for GHC 50: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different location. 0 20 40 60 80 100 0 5 10 15 20 Load (kN) Displacemant (mm) 0 20 40 60 80 100 -0.002 0 0.002 0.004 0.006 Load (kN) Strain Tension Compression 0 10 20 30 40 50 60 70 80 90 100 110 -0.001 0.004 0.009 0.014 Load (kN) Strain G3 G2 G1 (a) (b) (c)

PAGE 174

153 Fig. 4.62 . Effect of cyclic load on beam GHC 50: (a) stiffness; (b) damage index 0 5 10 15 0 5 10 15 20 Stiffness (kN/mm) Number of cycles (a) 0 0.2 0.4 0.6 0.8 1 0 5 10 15 20 Damage Index Number of cycles (b)

PAGE 175

154 ( a ) Fig 4. 63 .a . Failure mode of GHC 50 : (a) flexural cracks at mid span; (b) CFRP debonding; (c) overview final failure; (d) close view final failure. ( b ) ( c ) ( d )

PAGE 176

155 Fig.4. 63. b . Global failure of beam GHC 50. Fig 4.63. c . Failure mode of beam GHC 50.

PAGE 177

156 Fig. 4.64 . Test result for GHC 25: (a) load displacement; (b) PI gage strain in tension and compression; (c) CFRP strain at different locations. 0 20 40 60 80 100 0 5 10 15 20 Load (kN) Displacemant (mm) 0 20 40 60 80 100 -0.003 -0.001 0.001 0.003 Load (kN) Strain Tension Compressi on 0 10 20 30 40 50 60 70 80 90 100 110 -0.001 0.004 0.009 0.014 Load (kN) Strain G3 G2 G1 (a) (b) (c)

PAGE 178

157 Fig. 4.6 5. Effect of cyclic load on beam GHC 25: (a) stiffness; (b) damage index 0 5 10 15 0 5 10 15 20 Stiffness (kN/mm) Number of cycles (a) 0 0.2 0.4 0.6 0.8 1 0 5 10 15 20 Damge Index Number of cycles (b)

PAGE 179

158 ( a ) Fig 4. 66 .a. Failure mode of GHC 25 : (a) flexural cracks at mid span; (b) CFRP debonding; (c) overview final failure; (d) close view final failure. ( b ) ( c ) ( d )

PAGE 180

159 Fig.4. 57. b . Global failure of beam GHC 25. Fig 4.66. c . Failure mode of beam GHC 25.

PAGE 181

160 50.5 (kN) (0.5*Pu) 56.1 (kN) (0.55*Pu) 61.2 (kN) (0.6*Pu) 66.3 (kN) (0.65*Pu) 71.4 (kN) (0.7*Pu) 81.6 (kN) (0.8*Pu) 91.8 (kN) (0.9*Pu) 101.51 (kN) (1*Pu) Fig. 4. 6 7 . Crack pattern of GEM 25 tested under monotonic load obtained by DIC.

PAGE 182

161 Fig.4.68 . Crack propagation with load of specimen GEM 25. 0 20 40 60 80 100 120 0 30 60 90 120 150 180 210 240 270 300 Load (kN) Crack length (mm)

PAGE 183

162 52.5 (kN) (0.5*Pu) 57.75 (kN) (0.55*Pu) 63 (kN) (0.6*Pu) 68.25 (kN) (0.65*Pu) 73.5 (kN) (0.7*Pu) 84 (kN) (0.8*Pu) 94.5 (kN) (0.9*Pu) 105 (kN) (1*Pu) Fig. 4.69 . Crack pattern of GEM 50 tested under monotonic load obtained by DIC.

PAGE 184

163 Fig.4.70 . Crack propagation with load of specimen GEM 50. 0 20 40 60 80 100 120 0 30 60 90 120 150 180 210 240 270 300 Load (kN) Crack length (mm)

PAGE 185

164 53.5 (kN) (0.5*Pu) 58.85 (kN) (0.55*Pu) 64.2 (kN) (0.6*Pu) 69.55 (kN) (0.65*Pu) 75 (kN) (0.7*Pu) 86 (kN) (0.8*Pu) 96.3 (kN) (0.9*Pu) 107.5 (kN) (1*Pu) Fig. 4.71 . Crack pattern of GEM 75 tested under monotonic load obtained by DIC.

PAGE 186

165 Fig.4.72 . Crack propagation with load of specimen GEM 75 . 0 20 40 60 80 100 120 0 30 60 90 120 150 180 210 240 270 300 Load (kN) Crack length (mm)

PAGE 187

166 55 (kN) (0.5*Pu) 61.6 (kN) (0.55*Pu) 67.2 (kN) (0.6*Pu) 72.8 (kN) (0.65*Pu) 78.4 (kN) (0.7*Pu) 89.6 (kN) (0.8*Pu) 100.8 (kN) (0.9*Pu) 111 (kN) (1*Pu) Fig. 4.73 . Crack pattern of GEM 100 tested under monotonic load obtained by DIC.

PAGE 188

167 F ig.4.74 . Crack propagation with load of specimen GEM 100. 0 20 40 60 80 100 120 0 30 60 90 120 150 180 210 240 270 300 Load (kN) Crack length (mm)

PAGE 189

168 Fig. 4.75 . Crack pattern of GEM 100 0.75*0.75 tested under monotonic load obtained by DIC. 57 (kN) (0.5*Pu) 62.7 (kN) (0.55*Pu) 68.4 (kN) (0.6*Pu) 74.1 (kN) (0.65*Pu) 79.8 (kN) (0.7*Pu) 91.2 (kN) (0.8*Pu) 102.6 (kN) (0.9*Pu) 114 (kN) (1*Pu)

PAGE 190

169 Fig.4.76 . Crack propagation with load of specimen GEM 100 0.75*0.75. 0 20 40 60 80 100 120 0 30 60 90 120 150 180 210 240 270 300 Load (kN) Crack length (mm)

PAGE 191

17 0 50.1 (kN) (0.5*Pu) 55.1 (kN) (0.55*Pu) 60.1 (kN) (0.6*Pu) 65.1 (kN) (0.65*Pu) 70.1 (kN) (0.7*Pu) 80.1 (kN) (0.8*Pu) 90.1 (kN) (0.9*Pu) 100.1 (kN) (1*Pu) Fig. 4.77 . Crack pattern of G H M 25 tested under monotonic load with SMP hybrid obtained by DIC.

PAGE 192

171 Fig.4. 7 8 . Crack prop agation with load of specimen GH M 25. 0 20 40 60 80 100 120 0 30 60 90 120 150 180 210 240 270 300 Load (kN) Crack length (mm)

PAGE 193

172 53.1 (kN) (0.5*Pu) 58.4 (kN) (0.55*Pu) 63 .7 (kN) (0.6*Pu) 70 (kN) (0.65*Pu) 74.3 (kN) (0.7*Pu) 8 4.9 (kN) (0.8*Pu) 95.5 (kN) (0.9*Pu) 1 06.1 (kN) (1*Pu) Fig . 4.79 . Crack pattern of GH M 50 tested under monotonic with SMP hybrid load obtained by DIC.

PAGE 194

173 Fig.4.80 . Crack prop agation with load of specimen GH M 50. 0 20 40 60 80 100 120 0 30 60 90 120 150 180 210 240 270 300 Load (kN) Crack length (mm)

PAGE 195

174 53.8 (kN) (0.5*Pu) 59.2 (kN) (0.55*Pu) 64.6 (kN) (0.6*Pu) 70 (kN) (0.65*Pu) 75 .4 (kN) (0.7*Pu) 86 .1 (kN) (0.8*Pu) 96.9 (kN) (0.9*Pu) 107.7 (kN) (1*Pu) Fig. 4.81 . Crack pattern of GH M 75 tested under monotonic with SMP hybrid load obtained by DIC.

PAGE 196

175 Fig.4.82 . Crack prop agation with load of specimen GH M 75 . 0 20 40 60 80 100 120 0 30 60 90 120 150 180 210 240 270 300 Load (kN) Crack length (mm)

PAGE 197

176 55.9 (kN) (0.5*Pu) 61.5 (kN) (0.55*Pu) 67.1 (kN) (0.6*Pu) 72.7 (kN) (0.65*Pu) 78.3 (kN) (0.7*Pu) 89.5 (kN) (0.8*Pu) 100.6 (kN) (0.9*Pu) 111.8 (kN) (1*Pu) Fig. 4.83 . Crack pattern of GHM 100 tested under monotonic with SMP hybrid load obtained by DIC.

PAGE 198

177 F ig.4.84 . Crack prop agation with load of specimen GH M 100. 0 20 40 60 80 100 120 0 30 60 90 120 150 180 210 240 270 300 Load (kN) Crack length (mm)

PAGE 199

178 Fig. 4.85 . Fraction of cracked concrete. 0.4 0.5 0.6 0.7 0.8 0.9 1 0 2 4 6 8 10 12 14 Pi/Pu (%) Cracked area (%) GEM-25 GEM-50 GEM-75 GEM-100 GEM-100-0.75*0.75 GHM-25 GHM-50 GHM-75 GHM-100 CTB

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179 5. CONCLUSION The focus of staying tensile strength of strengthened steel specimens with temperature variation is to analyze the strengthened specimen's behavior and the failure mode. Also, the temperature effects on CFRP debonding and epoxy behavior. It can conclude the following: The tensile strength significantly improves steel specimens strengthened with CFRP which increase the steel stiffness and Young's modulus. The increase of temperature have a notable influence steel specimens' behav ior which affected on the steel tensile strength and stiffness; however, a small rise in the temperature does not have a significant influence on the load carrying capacity of steel specimens and CFRP adhesive with the steel interface. All steel specimens have a similar behavior regarding load deflection and stress strain response where it was linear up to the peak, but the temperature increase influenced the response slop which means the stiffness decreased. The failure modes were almost same of all streng thened specimens which were CFRP debonding either global or local. The specimens that subjected to 25 and 75 C the failure mode was brittle debonding, while the specimens that subjected to 125 and 175 C the failure mode was ductile debonding. The temper ature has a significant impact on the bond between steel specimens and CFRP as a result of temperature effects on the resin which was obvious through applying the load in this research. The future researchers should focus on using different type CFRP and resin, and its behavior under temperature variation. Also, different application of CFRP and layers should be used, and comparing it with one layer of CFRP that used in this research. Also, in this research RC beams were investigated to study the behav ior of the beams under different types of load, and the effects of strengthening RC beams using CFRP and C Grid composite. Externally strengthening RC beams with CFRP composite is an efficient method as a result of increased load carrying capacity of RC be ans.

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180 CFRP composite is a good alternative than traditional strengthening methods such as steel plate and mortar because of high tensile, lightweight and corrosion resistance of the CFRP sheet composite. The installation cost of CFRP and C Grid is an affordable and comfortable, and in term of the long term period the CFRP and C Grid do not need to regular maintenance as in case of steel plate and mortar. CFRP and C Grid U wrap were used of strengthening RC beams and preventing CFRP sheets debonding in the tension side of the RC beams. Strengthening RC beams using C Grid U wrap showed a significant performance and improved load carrying capacity compared with CTB beam load carrying capacity. C Grid U wrap and CFRP U wrap have almost the same load carr ying capacity which means using C Grid are more preferable in term of C Grid are more economical in material and cost. The main disadvantage of using C Grid is the rupture of C Grid U wrap as a result of CFRP sheet debonding and stress concentrations at t he beams corners. SMP hybrid was used in RC beams corners to release the stress concentration and to allow the beam to deflect more without C Grid U wrap rupture. The horizontal strain of RC beams using PI gages were different of RC beam, and the most comm on note is the tensile horizontal strain is higher than the compression horizontal strain of most RC beams. The failure mode of most the beams started firstly as flexural cracks, then shear flexural cracks propagate at the edges of the beams. The typical f inal failure was the concrete crash at applied point loads, and debonding of CFRP sheets at beams edges of CTB and UMG beams. However, CFRP debonding were prevented by using CFRP U wrap or C Grid U wrap with SMP hybrid. The DIC picture is an efficient way to study and monitor RC beams failure behavior. The stiffness of RC beams decreases with the increase of cycle's numbers. Also, by applying FEMA 2007 protocol which is two cycles at the same displacement, it is notable that the load of the second cycle is less than the first on even that both cycles have the same displacement as a result of stiffness decrease

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181 The stiffness losing and the failure index increase with cycles increase while that stiffness losing and the failure index can be controlled with the increase of C Grid strengthening area. In the future studies the micro crack prorogation should be investigated to check the effects of using C Grid on crack behavior of RC beams, and the effects of strengthening area on controlling the micro crack growth.

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