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Strengthening and rehabilitation of steel bridge girders using CFRP laminates

Dissertation
Author: Ahmed Sabri Abd-El-Meguid
Abstract:
While traditional retrofitting methods for steel bridge girders could be time consuming and uneconomical, an alternative repair method is suggested using Carbon Fiber Reinforced Polymers (CFRP) laminate strips, providing engineers with a competitive solution that will increase the life-cycle of repaired bridges. This study investigated its feasibility as an option to strengthen and rehabilitate steel bridges. The main advantages of using CFRP laminates are their light weight and durability, which results in ease of handling and maintenance. The dissertation conducted experimental and analytical work to evaluate the effectiveness of strengthening steel beams by the use of novel CFRP laminate strips configurations. The research involved the testing of five experimental composite beams, in addition to the development of approximately 100 finite element models. The results showed a significant gain in the beam's elastic and ultimate capacities. The conclusion is that there are specific sensitive parameters controlling the effectiveness of the CFRP laminate rehabilitation technique. An adequate AASHTO design of the rehabilitation method, which takes into consideration the effective parameters, would result in an effective bridge structure. Keywords : CFRP, Steel Beams, Bridge Girders, Rehabilitation, Strengthening, Finite Element Modeling, ABAQUS, SAP 2000, Design Guidelines

v TABLE OF CONTENTS Page ABSTRACT ....................................................................................................................... ii DEDICATION.................................................................................................................. iii ACKNOWLEDGMENTS ............................................................................................... iv LIST OF TABLES ........................................................................................................... ix LIST OF FIGURES ........................................................................................................ xii 1 INTRODUCTION ...............................................................................................1 1.1 Background ....................................................................................................1 1.2 Problem Statement .........................................................................................2 1.3 Research Objectives .......................................................................................2 1.4 Methodology and Approach ..........................................................................3 1.5 Scope of Study ...............................................................................................5 1.6 Organization of the Dissertation ....................................................................5 1.7 Study Contribution and Innovation ................................................................7 2 LITERATURE REVIEW ...................................................................................8 2.1 Introduction ....................................................................................................8 2.2 Common Rehabilitation Field Applications ..................................................8 2.3 Guidelines of Using FRP Reinforcement in the United States ....................10 2.4 Guidelines of Using FRP Reinforcement Worldwide .................................10 2.5 FRP Types and Applications .......................................................................11 2.5.1 AFRP ....................................................................................................15 2.5.2 GFRP ....................................................................................................16 2.5.3 CFRP ....................................................................................................17 2.6 CFRP Structural Characteristics ..................................................................19 2.7 CFRP in Steel Beam Applications ...............................................................20 2.8 CFRP Bond Behavior ..................................................................................20 2.9 Fatigue Behavior of Steel Beams Reinforced with CFRP ...........................21

vi 2.10 Summary ......................................................................................................22 3 THE EXPERIMENTAL PROGRAM .............................................................23 3.1 Specimen Details .........................................................................................23 3.2 Instrumentation ............................................................................................33 3.2.1 Strain Gages ..........................................................................................33 3.2.2 Load Cell and LVDT Sensor ................................................................34 3.2.3 Data Acquisition System ......................................................................35 3.3 Experimental Testing ...................................................................................36 3.4 Results ..........................................................................................................37 3.5 Material Properties of Steel and CFRP Plates .............................................46 3.5.1 Steel Tension Testing ...........................................................................46 3.5.2 CFRP Tension Testing..........................................................................48 3.6 Summary ......................................................................................................54 4 VERIFICATION OF FE MODEL ..................................................................56 4.1 Modeling Technique ....................................................................................56 4.2 Model Details ...............................................................................................57 4.3 Element Interaction Simulation and Special FE Models .............................62 4.3.1 Cohesive Elements and Adhesive Material Modeling .........................62 4.3.2 Mesh Tie Constraints ............................................................................65 4.4 Compatibility of Steel Top Plate to Concrete Slab ......................................66 4.4.1 Concrete ................................................................................................67 4.4.2 Compressive Behavior of the Concrete Model .....................................70 4.5 Failure Modes in FE Models........................................................................71 4.5.1 Steel Beam Failure................................................................................72 4.5.2 Concrete Failure ...................................................................................73 4.5.3 CFRP Rupture.......................................................................................76 4.5.4 CFRP Debonding – Epoxy Failure .......................................................81 4.6 Results ..........................................................................................................84 4.6.1 Concrete Slab versus Steel Top Plate ...................................................84 4.6.2 Verification of FE Model by the Tested Beams ...................................87 4.6.3 Strain-Depth Verification .....................................................................90 4.7 Summary ......................................................................................................92

vii 5 PARAMETRIC STUDY ...................................................................................93 5.1 Introduction ..................................................................................................93 5.2 Parametric Study Program ...........................................................................94 5.2.1 Flowchart Calculating Plastic Neutral Axis .........................................98 5.2.2 Flowchart Calculating Plastic Moment Capacity ...............................102 5.2.3 Effective Parameters ...........................................................................106 5.2.4 Beam Designation...............................................................................106 5.3 Results ........................................................................................................111 5.3.1 CFRP Configuration ...........................................................................112 5.3.2 CFRP Thickness .................................................................................119 5.3.3 CFRP Length ......................................................................................120 5.3.4 CFRP Width .......................................................................................122 5.3.5 CFRP Manufacturer ............................................................................123 5.3.6 CFRP Elastic Modulus .......................................................................125 5.3.7 Results Summary ................................................................................126 5.4 Conclusions ................................................................................................126 5.5 Recommendations ......................................................................................132 6 BRIDGE DESIGN: REHABILITATION GUIDELINES ..........................134 6.1 Background ................................................................................................134 6.2 Scope ..........................................................................................................134 6.3 Finite Element Bridge Modeling ...............................................................134 6.3.1 Bridge Description ..............................................................................134 6.3.2 Bridge Modeling .................................................................................135 6.3.3 Bridge Loading ...................................................................................138 6.3.4 Utilizing the FE Model to Evaluate Rehabilitation using CFRP ........139 6.4 Steel Bridge Girder – Solved Example ......................................................150 6.4.1 Develop General Section ....................................................................150 6.4.2 Develop Typical Section and Design Basis ........................................151 6.4.3 Design Conventionally Reinforced Concrete Deck............................153 6.4.4 Select Resistance Factors ....................................................................154 6.4.5 Select Load Modifiers ........................................................................154 6.4.6 Select Applicable Load Combinations ...............................................154 6.4.7 Calculate Live Load Force Effects [A3.6.1.1.1] .................................155 6.4.8 Calculate Force Effects from Other Loads .........................................161 6.4.9 Design Required Sections ...................................................................163 6.4.10 Dimension and Detail Requirements ..................................................175 6.5 Steel Bridge Girder Strengthened using CFRP – Solved Example ...........180 6.5.1 Design Required Sections ...................................................................181

viii 6.6 CFRP Contribution to Steel Bridge Girders ..............................................191 6.6.1 Section Inertia and Modulus ...............................................................191 6.6.2 Stresses ...............................................................................................193 6.6.3 Fatigue Stresses ..................................................................................194 6.6.4 Deflections ..........................................................................................194 6.7 Design Guidelines ......................................................................................195 6.8 Summary ....................................................................................................196 7 SUMMARY, CONCLUSIONS & FUTURE RESEARCH .........................198 7.1 Summary ....................................................................................................198 7.2 Conclusion .................................................................................................200 7.3 Future Research .........................................................................................201 LIST OF REFERENCES ..............................................................................................203 APPENDIX .....................................................................................................................209 A. Plastic Neutral Axis Calculations ....................................................................210 B. Plastic Moment Capacity Calculations ............................................................213

ix LIST OF TABLES Table Page 1. Test Matrix for the Large-Scale Steel-CFRP Composite Beam Tests ...................24 2. Experimental Beam Results ...................................................................................45 3. Carbon Fiber Material Properties...........................................................................49 4. CFRP Tension Test Results ...................................................................................50 5. Laminate Properties of CFRP From Several Manufacturers Comparison.............54 6. W200 x 19.3 – Input Data Sheet ............................................................................96 7. W200 x 19.3 – Output Data Sheet .........................................................................97 8. W200 x 19.3 Parametric Study Table – Four-Point Loading ..............................109 9. W200 x 19.3 Parametric Study Table – Uniform Loading ..................................110 10. W310 x 38.7 and W410 x 53 Parametric Study Table, Four-Point Loading .......111 11. W200 x 19.3 with CFRP 90% Length and 1.40 mm Thickness – Four-Point Loading ................................................................................................................113 12. W200 x 19.3 with CFRP 60% Length and 2.00 mm Thickness – Four-Point Loading ................................................................................................................114 13. W200 x 19.3 with CFRP 60% Length and 2.00 mm Thickness – Uniform Loading ................................................................................................................117 14. W200 x 19.3 with CFRP 75% Length and 2.00 mm Thickness – Uniform Loading ................................................................................................................118 15. W200 x 19.3 Results Table, Four-Point Loading – CFRP Length Variable .......121

x LIST OF TABLES (CONTINUED) 16. W200 x 19.3 Results Table, Four-Point Loading – CFRP Width Variable .........122 17. W200 x 19.3 Beam Stiffness Comparison with CFRP from Different Manufacturers ......................................................................................................124 18. W200 x 19.3 Results Table, Four-Point Loading ................................................130 19. W200 x 19.3 Results Table, Uniform Loading ....................................................131 20. W310 x 38.7 Results Table, Four-Point Loading ................................................132 21. W410 x 53 Results Table, Four-Point Loading ...................................................132 22. Truck Loading Data .............................................................................................138 23. LRFD Load Modifiers .........................................................................................154 24. Multiple Presence Factors ....................................................................................155 25. Dynamic Load Allowance Factors.......................................................................155 26. Interior Girder Un-factored Moments and Shears ...............................................162 27. Exterior Girder Un-factored Moments and Shears ..............................................163 28. Steel Section Properties .......................................................................................165 29. Short-Term Composite Section Properties, n=8, b i = 2380 mm ..........................168 30. Long-Term Composite Section Properties, 3n=24 ..............................................170 31. Maximum Flexural Stress in the Web for Positive Flexure (Interior Girder) ...................................................................................................170 32. Compressive Stresses in Top of Steel Beam Due to Factored Loading (Interior Girder) ...................................................................................................171 33. Tensile Stresses in Bottom of Steel Beam Due to Factored Loading ..................171 34. Stresses in Top of Flange of Steel Beam Due to Service II Moments .................178

xi LIST OF TABLES (CONTINUED) 35. Stresses in Bottom Flange of Steel Beam Due to Service II Moments ...............178 36. Exterior Beam Deflection Due to Dead Loads ....................................................179 37. Interior Beam Deflection Due to Dead Loads .....................................................179 38. Section Properties (Steel + CFRP) .......................................................................181 39. Short-Term Composite Section Properties, n=8, b i = 2380 mm ..........................184 40. Long-Term Composite Section Properties, 3n=24 ..............................................185 41. Maximum Flexural Stress in the Web for Positive Flexure (Interior Girder) ...................................................................................................186 42. Compressive Stresses in Top of Steel Beam Due to Factored Loading (Interior Girder) ...................................................................................................186 43. Tensile Stresses in Bottom of Steel Beam Due to Factored Loading ..................187 44. Stresses in Top of Flange of Steel Beam Due to Service II Moments .................189 45. Stresses in Bottom Flange of Steel Beam Due to Service II Moments ...............189 46. Exterior Beam Deflection Due to Dead Loads ....................................................190 47. Interior Beam Deflection Due to Dead Loads .....................................................190

xii LIST OF FIGURES Figure Page 1. Comparison of Stress-Strain Behavior of Steel and FRPs (QuakeWrap, 2008)................................................................................................12 2. Beam Dimensions and Strain Gage Locations.......................................................24 3. Steel Beam and Steel Plate Centered Before Welding ..........................................26 4. Weld Size and Spacing Dictated ............................................................................26 5. Automatic Welding Machine Used ........................................................................27 6. Steel Beam and Steel Plate During the Welding Process ......................................27 7. Different CFRP Configurations .............................................................................28 8. (a) CFRP & Fiber Wraps, (b) Epoxy and Gun Applicator ....................................29 9. Roughening the Surface of CFRP ..........................................................................31 10. Adding Epoxy and Spreading it on the Prepared Surface......................................31 11. The Strengthened Beam After Adding the CFRP Layer .......................................32 12. Applying Pressure on the CFRP Layer Using Clamps ..........................................32 13. Experimental Setup of Steel Beam Strengthened by CFRP ..................................33 14. Installation of Strain Gages ....................................................................................34 15. Wiring Strain Gages to the Data Acquisition System ............................................35 16. A View of Beam 4 Showing the Deflection at the End of the Experiment ...........36 17. Load-Strain Curve for Beam 1 ...............................................................................38 18. Load-Strain Curve for Beam 2 ...............................................................................38

xiii LIST OF FIGURES (CONTINUED) 19. Load-Strain Curve for Beam 3 ...............................................................................39 20. Load-Strain Curve for Beam 4 ...............................................................................39 21. Load-Strain Curve for Beam 5 ...............................................................................40 22. Strain-Depth Curve for Beam 1 .............................................................................41 23. Strain-Depth Curve for Beam 2 .............................................................................42 24. Strain-Depth Curve for Beam 3 .............................................................................42 25. Strain-Depth Curve for Beam 4 .............................................................................43 26. Strain-Depth Curve for Beam 5 .............................................................................43 27. Experimental Load-Deflection Curves for the Five Beams ...................................45 28. Steel Specimen Mounted for a Tension Test – Strain Gage Installed ...................47 29. Steel Specimen After the Tension Test ..................................................................47 30. Stress-Strain Curve for Steel from Tension Test Results ......................................48 31. Tension Test Setup: Testing Machine and Data Acquisition System ....................49 32. First Signs of CFRP Rupture: Outer Fibers Ruptured ...........................................51 33. Successive CFRP Fiber Rupture Towards the Specimen Center...........................51 34. Stress-Strain Curve for CFRP Tension Test 1 – 100 mm x 1.40 mm ....................52 35. Stress-Strain Curve for CFRP Tension Test 2 – 100 mm x 1.40 mm ....................52 36. Stress-Strain Curve for CFRP Tension Test 3 – 50 mm x 1.40 mm ......................53 37. Stress-Strain Curve for CFRP Tension Test 4 – 100 mm x 1.40 mm ....................53 38. An Isotropic View of the Three-Dimensional FE Model ......................................59 39. Isometric View of the Beam Model – Loads Shown .............................................60 40. Concentrated Load Definition ................................................................................60

xiv LIST OF FIGURES (CONTINUED) 41. Boundary Conditions – Hinged Support ................................................................61 42. Boundary Conditions – Roller Support..................................................................61 43. Debonding Along a Skin-Stringer Interface: Typical Situation for Traction- Separation-Based Modeling (Abaqus Analysis User Manual, 2007) ....................64 44. Cohesive Element Definition Form .......................................................................65 45. Surface Constraints Definition ...............................................................................66 46. Tension Stiffening Model (Abaqus Analysis User Manual, 2007) ........................69 47. Fracture Energy Cracking Model (Abaqus Analysis User Manual, 2007) ............70 48. Uniaxial Behavior of Plain Concrete (Abaqus Analysis User Manual, 2007) ......71 49. Steel Elastic Material Properties ............................................................................72 50. Steel Plastic Material Properties ............................................................................73 51. Concrete Elastic Material Properties .....................................................................74 52. Concrete Smeared Cracking Material Properties ...................................................75 53. Concrete Tension Stiffening ..................................................................................75 54. Concrete Failure Ratios..........................................................................................76 55. CFRP Damage Strength .........................................................................................78 56. CFRP Damage Evolution .......................................................................................78 57. CFRP Damage Stabilization ..................................................................................79 58. CFRP Elastic Material Properties ..........................................................................80 59. CFRP Section Definition .......................................................................................81 60. Epoxy Damage Properties......................................................................................82 61. Epoxy Damage Evolution ......................................................................................83

xv LIST OF FIGURES (CONTINUED) 62. Epoxy Elastic Material Properties .........................................................................83 63. Load-Deflection – Steel Plate vs. Concrete Slab – Beam 1 ...................................85 64. Load-Deflection – Steel Plate vs. Concrete Slab – Beam 2 ...................................85 65. Load-Deflection – Steel Plate vs. Concrete Slab – Beam 3 ...................................86 66. Load-Deflection – Steel Plate vs. Concrete Slab – Beam 4 ...................................86 67. Load-Deflection – Steel Plate vs. Concrete Slab – Beam 5 ...................................87 68. Load Deflection Curve for Beams 1 & 2 –Experimental vs. Abaqus ....................88 69. Load Deflection Curve for Beams 1 & 3 –Experimental vs. Abaqus ....................88 70. Load Deflection Curve for Beams 1 & 4 –Experimental vs. Abaqus ....................89 71. Load Deflection Curve for Beams 1 & 5 –Experimental vs. Abaqus ....................89 72. Beam Depth-Strain – Experimental vs. Abaqus – Beam 1 ....................................91 73. Beam Depth-Strain – Experimental vs. Abaqus – Beam 2 ....................................91 74. Beam Depth-Strain – Experimental vs. Abaqus – Beam 3 ....................................92 75. Beam W200 x 19.3 with CFRP 90% Length and 1.40 mm Thickness. ...............113 76. Beam W200 x 19.3 with CFRP 60% Length and 2.00 mm Thickness. ...............115 77. Beam P60080B4T Failure Outside the CFRP Reinforced Zone. ........................116 78. Beam W200 x 19.3 with CFRP 60% Length and 2.00 mm Thickness. ...............117 79. Beam W200 x 19.3 with CFRP 75% Length and 2.00 mm Thickness. ...............118 80. Beam W310 x 38.7 with CFRP 75% Length and Variable Thickness. ...............120 81. Beam W200 x 19.3 with CFRP 2.00 mm Thickness and Variable Length .........121 82. Beam W200 x 19.3 with CFRP 75% Length with Variable CFRP Laminate Width ...................................................................................................123

xvi LIST OF FIGURES (CONTINUED) 83. Beam W200 x 19.3 with CFRP 75% Length from Different Manufacturers ......125 84. Beam W200 x 19.3 with Different CFRP Young’s Modulus ..............................126 85. Steel Girder Dimensions and Area Properties .....................................................136 86. Bridge Cross Section and Lane Positions ............................................................136 87. Composite Section Dimensions and Area Properties ..........................................137 88. Strain Reduction After Rehabilitation with CFRP – Truck 1 ..............................139 89. Strain Reduction After Rehabilitation with CFRP – Truck 2 ..............................140 90. Strain Reduction After Rehabilitation with CFRP – Truck 3 ..............................140 91. Strain Reduction After Rehabilitation with CFRP – Truck 4 ..............................141 92. Strain Reduction After Rehabilitation with CFRP – Truck 5 ..............................141 93. Strain Reduction After Rehabilitation with CFRP – Truck 6 ..............................142 94. Strain Reduction After Rehabilitation with CFRP – Truck 7 ..............................142 95. Strain Reduction After Rehabilitation with CFRP – Truck 8 ..............................143 96. Strain Reduction After Rehabilitation with CFRP – Truck 9 ..............................143 97. Strain Reduction After Rehabilitation with CFRP – Truck 10 ............................144 98. Moment Increase After Rehabilitation with CFRP – Truck 1 .............................145 99. Moment Increase After Rehabilitation with CFRP – Truck 2 .............................145 100. Moment Increase After Rehabilitation with CFRP – Truck 3 .............................146 101. Moment Increase After Rehabilitation with CFRP – Truck 4 .............................146 102. Moment Increase After Rehabilitation with CFRP – Truck 5 .............................147 103. Moment Increase After Rehabilitation with CFRP – Truck 6 .............................147 104. Moment Increase After Rehabilitation with CFRP – Truck 7 .............................148

xvii LIST OF FIGURES (CONTINUED) 105. Moment Increase After Rehabilitation with CFRP – Truck 8 .............................148 106. Moment Increase After Rehabilitation with CFRP – Truck 9 .............................149 107. Moment Increase After Rehabilitation with CFRP – Truck 10 ...........................149 108. Bridge Example – Bridge Cross Section .............................................................151 109. Bridge Example – (a) General elevation and (b) plan view .................................152 110. Lever Rule for Determination of Distribution Factor for Moment in Exterior Beam, One Lane Loaded .......................................................................157 111. Truck, Tandem, and Lane Load Placement for Maximum Moment at Location 105 ........................................................................................................158 112. Truck, Tandem, and Lane Load Placement for Maximum Shear at Location 100 ........................................................................................................160 113. Steel Section at Midspan ......................................................................................166 114. Composite Section at Midspan ............................................................................167 115. Fatigue Truck Placement for Maximum Moment ...............................................169 116. Truck Placement for Maximum Deflection .........................................................176 117. General Placement of Point Load P .....................................................................176 118. Point Load P at Center of Span............................................................................177 119. Steel Section with CFRP at Midspan ...................................................................182 120. Composite Steel Section with CFRP at Midspan ................................................184

1 1 INTRODUCTION 1.1 Background Throughout the U.S., there are thousands of steel bridges that are at various levels of advanced deterioration due to many years of service and exposure to the environment (Liu, Silva, & Nanni, 2001). Rehabilitation can involve various strategies and application methods. These strategies include adding steel plates to the girders in order to increase the girder capacity, adding new girders between the old ones (McRae & Ramey, 2003), or replacing the whole bridge superstructure. Moreover, load ratings decrease as bridges deteriorate, which affects truck routing and loading limits and in turn affects freight costs dramatically. CFRP materials have been predominantly used by the aerospace industry, where cost is generally a secondary consideration to weight (Jones R. , 1998). Carbon fibers were first used in civil applications at Swiss Fedral Testing Laboratories (Burgoyne, 1999). The bridge collapse in Minnesota in 2007 was a wakeup call for bridge engineers and departments of transportation. Current bridge inspection is mainly visual and lacks in-depth inspection, such as strain and stress evaluation of different structural elements. Besides the rehabilitation method using carbon fiber reinforced polymers (CFRP) laminates discussed in the dissertation, modeling techniques using FE to verify the usefulness of the method are also presented.

2 1.2 Problem Statement Corroded steel bridge girders cause the severe reduction of cross section, hence the inertia of the cross section needed to sustain truck loads. Moreover, the increased demand on goods and gas prices lead some truck companies to drastically increase truck loads beyond the legal weight limits designated for bridges. This causes a significant increase in both live load stresses in the short term and the fatigue stress range over the long term. Drops in section inertia also cause increases in live load deflections. According to the American Association of State Highway and Transportation Officials (AASHTO), limits are set for live load stresses, fatigue stresses, and deflections. Exceeding these limits leads to the non-adequacy of bridges in the short or long term. Traditional repair solutions include adding steel plates or adding external prestressed tendons at the steel girders. The proposed rehabilitation and strengthening methodology for steel girder bridges is to install CFRP plates to the bottom flange of the girders. The hypothesis of this research is that CFRP laminates are significantly effective strengthening and rehabilitating technique for steel girder bridges. CFRP laminates added to the tension flange of steel girders will enhance their flexural capacity. 1.3 Research Objectives The objective of this research is to quantify the load improvement using novel CFRP configurations and develop design guidelines for using CFRP laminates to strengthen steel bridge girders.

3 1.4 Methodology and Approach In order to achieve the outlined objectives, a detailed plan was developed. Five steel beam specimens having CFRP laminate configuration variations were tested. Bending testing was conducted on the simply supported beams via four-point loading. Nonlinear finite element analysis software, ABAQUS (Abaqus Analysis User Manual, 2007), was used to verify the experimental results. The dissertation describes the tasks performed and the design process of steel beam strengthened using CFRP. Discussion of the FE models built to simulate the experimental beams is also presented. Evaluation of the rehabilitation technique is performed utilizing FE models. The list of tasks accomplished is as follows: • Experimental plan for the steel beams: this task was mainly focused on the preliminary design of steel beams to choose a suitable beam for laboratory experimentation given certain restrictions of the laboratory testing frame and equipment, such as length, depth, weight, and load capacity. • Excel design spreadsheet utilizing Visual Basic programming: an Excel spreadsheet that incorporated Visual Basic programming was developed to predict the failure load of various experimental beams. The experimental beam was chosen using this spreadsheet. • Steel beam purchase / fabrication: steel beams were fabricated and purchased from Garrison Steel Company. The bottom flange of the steel beams was sand blasted for proper attachment of the CFRP plate. Steel specimens for the tension tests were also provided.

4 • Experimental setup and testing: tension testing was performed on steel and CFRP specimens. Test setup for the beams involved the attachment of the CFRP laminates to the steel flange. The beam was equipped with strain gages at various locations, and a load cell and LVDT were placed at the midspan of the beam. All instruments were then connected to the data acquisition system, and testing followed. Analysis of experimental results: this task included graphing load deflection, load strain, and strain variation along the depth of the beam for all tested beams. Comparison of the results was performed. • Parametric study using finite element (FE) analysis: a parametric study was conducted to test several parameters, such as CFRP laminate length, thickness, configuration, and material properties, and the steel beam section. ABAQUS was the software package used for the FE modeling, which involved special bonding elements, contact surfaces, constraints, and material properties. • Analysis of parametric study results: load-deflection graphs were plotted to compare the effect of various parameters. A tabular form was then utilized to calculate elastic and plastic percentage gains. • Performing structural evaluation of bridges strengthened using CFRP: FE models were developed using SAP2000 software. • Developing design guidelines for rehabilitating bridges using CFRP laminates.

5 1.5 Scope of Study The scope of this research is limited to the strengthening of steel beams in flexure only. No shear strengthening is included. Steel beams for the experimental work were chosen to have enough shear-carrying capacity throughout the loading process. The main focus was to increase the load carrying capacity of the beams using CFRP plates’ configurations. Only laboratory strengthening was performed. 1.6 Organization of the Dissertation This dissertation consists of seven chapters. Chapter 1, Introduction, discusses the research problem background. It also presents the objective of the research work performed and the methodology utilized to approach the objectives. Chapter 1 concludes with the dissertation organization, a brief summary of the rest of the chapters. Chapter 2, Literature Review, reviews the previous research conducted on rehabilitating bridges. A historical background is presented on the evolution of rehabilitation methods and when FRP, specifically CFRP, came into use in bridge rehabilitations. Chapter 3, The Experimental Program; is concerned with the experimental work performed during the course of this study, starting with the tension tests performed on steel and CFRP specimens to obtain stiffness and strength properties. The bulk of the experimental work was performed on five steel W200 x 19.3 (W8 x 13) beams topped by a steel plate that replaced the reinforced concrete deck. The chapter describes the steps executed in order to perform the tests. A summary of the results concludes this chapter.

6 Chapter 4, Verification of FE Model, mainly describes the FE model built to simulate the steel beams tested experimentally in Chapter 3. Results from the verification models and the experimental results are compared in this chapter. Chapter 5, Parametric Study, utilizes the FE model built in Chapter 4 to perform an extensive parametric study to evaluate the sensitivity of each parameter of the CFRP rehabilitation process. Around a hundred models have been developed and executed using the ABAQUS FE program. Parameters investigated were CFRP laminate length, thickness, and configuration, and loading, and the steel beam section. Results are presented in the form of load deflection graphs and tables showing the strength gain in both the elastic and plastic load range. An Excel spreadsheet utilizing Visual Basic programming was developed for the design of steel beams strengthened with CFRP laminates. The Visual Basic modules were embedded in the spreadsheet and used as built-in functions to calculate the elastic and plastic neutral axis location, the plastic moment capacity, and the beam’s deflection. In chapter 6, Bridge Design: Rehabilitation Guidelines, two main topics are discussed: first, simulation work of a typical composite steel concrete bridge; second to evaluate the strengthening of steel girder bridges using CFRP plates through solved AASHTO bridge examples. This includes the gain in strength, section modulus, and stiffness of the bridge girders. The reduction of the deflections and the fatigue stress ranges are also discussed. Design guidelines for rehabilitating steel bridges using CFRP are introduced at the end of the chapter.

7 Chapter 7, Conclusions, presents conclusions regarding the effectiveness of CFRP laminates in the rehabilitation of steel bridge girders. Recommendations for future work are also presented. 1.7 Study Contribution and Innovation This research conducts both experimental and analytical testing on various novel CFRP laminate configurations used in the rehabilitation and strengthening of steel bridge girders. The tested CFRP configurations presented here were not presented previously in any of the research.

8 2 LITERATURE REVIEW 2.1 Introduction Many state and local agencies are faced with deteriorating bridge infrastructure composed of relatively short to medium-span bridges. In many cases, these older structures are hot-rolled or welded longitudinal steel stringers acting compositely with a reinforced concrete deck (Wipf T. J., Phares, Klaiber, & Lee, 2003). Bridge deterioration rates, durability and longevity performance have been discussed thoroughly during the last few decades. A factor that receives too little consideration in bridge work is durability (Ramey & Wright, 1997). This leads to the huge number of structurally deficient and functionally obsolete bridges all over the United States. 2.2 Common Rehabilitation Field Applications Conventional rehabilitation, such as welding steel plates to structural members has been the traditional method for a long time but induces high thermal stresses in the steel members. The induced stress reduces the member fatigue resistance. A rehabilitation design using conventional methods is discussed by Farhey (Farhey, et al., 2000), as applied to an existing historic bridge crossing Sandusky River in Fremont, Ohio. Although the conventional restoration methods are still applicable and preferred in some structural elements, such as the gusset plates, the CFRP method is on the rise as a rehabilitation technique to be used with bridge elements, such as main girders.

9 When total replacement is not an option and traditional retrofit methods are uneconomical and time consuming, an alternative retrofit method using CFRP composite material provide engineers with an effective solution that can increase the life cycle of these bridges. Research recently conducted on the use of CFRP for strengthening and repair of steel beams has been investigated (Mertz & Gillespie, 1996), (Tavakkolizadeh & Saadatmanesh, 2003) and (Al-Saidy, Klaiber, & Wipf, 2004). A number of different approaches have been studied to assess the effectiveness of various CFRP materials for the strengthening and repair of steel bridges, including the repair of overloaded girders (Sen, Libby, & Mullins, 2001). A proposed solution to strengthen the damaged reinforced concrete headstock of the Tenthill Creeks Bridge, Queensland, Australia, using FRP composites was presented by Nezamian (Nezamian & Setunge, 2007). A decision was made to consider strengthening the headstock using bonded carbon FRP laminates to increase the load- carrying capacity of the headstock in shear and bending. A reliability analysis of reinforced concrete bridge girders strengthened by CFRP laminates was developed by Okeil (Okeil, El-Tawil, & Shahawy, 2002). A resistance model is used to calculate the probability of failure and the reliability index of CFRP- strengthened cross sections. The reliability method is employed to calibrate the flexural resistance factor for a broad range of design variables. The study shows that the addition of CFRP improves reliability somewhat because the strength of CFRP laminates has a lower coefficient of variation than steel or concrete. The rehabilitation of an existing concrete bridge in Alabama through external bonding of FRP plates to the bridge girders was performed by Stallings (Stallings,

10 Tedesco, El-Mihilmy, & McCauley, 2000). Field load tests were conducted before and after application of the FRP plates to evaluate the advance in structural response. 2.3 Guidelines of Using FRP Reinforcement in the United States Design guidelines and testing protocols for FRP reinforcement are nationally defined for concrete structures. The American Concrete Institute (ACI) presents a number of technical reports for the design, construction, and repair of concrete structures using FRP reinforcement. Recommendations for the design and construction of FRP reinforcement based knowledge gained from worldwide research can be found in ACI 440.1R-03 (ACI Committee, 2003). Flexure and shear design procedures, and FRP reinforcement detailing are presented in this report. The report also includes material characteristics of commercially available FRP. Although FRP design, construction, and rehabilitation guidelines are available for concrete structures, similar guidelines are not available for steel structures. 2.4 Guidelines of Using FRP Reinforcement Worldwide Limited literature was found for design guidelines of FRP worldwide. Deeks and Hao, (2004) mention some design guidelines and safety factors. Based on BS 8110 (1997), the guidelines identify critical areas to be assessed along the length of the beam. These are the areas of maximum moment and the ends of the FRP. It is recommended that internal steel reinforcement yield before failure from either concrete crushing or FRP rupture. BS 8110 (1997) also recommends that the characteristic material properties be divided by appropriate partial safety factors. The partial safety factors for concrete in flexure, γ c , and steel reinforcement, γ s , are 1.50 and 1.15, respectively. The partial safety

11 factor for strength of FRP is equal to the type of fiber, γ mf , multiplied by the stage in the manufacturing route in which the FRP samples were taken for testing, γ mm , (e.g. in-situ or factory). CFRP, GFRP, and AFRP (C: carbon, G: glass, and A: aramid) have γ mf values of 1.40, 3.50, and 1.50, respectively, while γ mm varies from 1.10 to 2.0. The recommended partial safety factors for modulus of elasticity, γ mE , are 1.10, 1.80, and 1.80, for CFRP, GFRP, and AFRP, respectively. To avoid any possibility of brittle failure, the ultimate moment capacity may be increased by 1.15. 2.5 FRP Types and Applications Fiber reinforced plastic (FRP), also known as fiber reinforced polymer, is a composite material consisting of a polymer matrix reinforced with fibers. Fibers are usually aramid, fiberglass, or carbon, while the polymer is usually a vinylester, polyester thermosetting plastic, or epoxy. Figure 1 shows a stress-strain comparison between steel and various FRPs. It shows that CFRP have similar stiffness to steel, while AFRP and GFRP have lower stiffness compared to steel. Both CFRP and AFRP have high strength compared to GFRP. Comparing the FRP modes of failure against steel, it is clear that all FRP have a brittle failure mode, while steel has its well-known ductile behavior.

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Abstract: While traditional retrofitting methods for steel bridge girders could be time consuming and uneconomical, an alternative repair method is suggested using Carbon Fiber Reinforced Polymers (CFRP) laminate strips, providing engineers with a competitive solution that will increase the life-cycle of repaired bridges. This study investigated its feasibility as an option to strengthen and rehabilitate steel bridges. The main advantages of using CFRP laminates are their light weight and durability, which results in ease of handling and maintenance. The dissertation conducted experimental and analytical work to evaluate the effectiveness of strengthening steel beams by the use of novel CFRP laminate strips configurations. The research involved the testing of five experimental composite beams, in addition to the development of approximately 100 finite element models. The results showed a significant gain in the beam's elastic and ultimate capacities. The conclusion is that there are specific sensitive parameters controlling the effectiveness of the CFRP laminate rehabilitation technique. An adequate AASHTO design of the rehabilitation method, which takes into consideration the effective parameters, would result in an effective bridge structure. Keywords : CFRP, Steel Beams, Bridge Girders, Rehabilitation, Strengthening, Finite Element Modeling, ABAQUS, SAP 2000, Design Guidelines