rehabilitation and field evaluation of...

REHABILITATION AND FIELD

EVALUATION OF DISCARDED TIMBER

RAILROAD TIES USING THERMOSET GFRP

COMPOSITES

AMIR HOSSEIN HOUSHMANDYAR

Problem Report submitted to the

Benjamin M. Statler College of Engineering and Mineral Resources

at

West Virginia University

in partial fulfillment of the requirements

for the degree of

Master of Science

in

Civil and Environmental Engineering

P.V.Vijay, Ph.D, P.E.

Hota. V.S. Ganga Rao, Ph.D, P.E.

Udaya B. Halabe, Ph.D, P.E.

Morgantown, West Virginia

2013

KEYWORDS: GFRP, Epoxy Vinyl Ester, Railroad Ties, Composite Ties, Plastic Ties, Wood

Ties.

http://www.statler.wvu.edu/

ABSTRACT

Rehabilitation and Field Evaluation of Discarded Timber Railroad

Ties Using Thermoset GFRP Composites

AMIR HOSSEIN HOUSHMANDYAR

This study presents the effectiveness of glass fiber reinforced polymer (GFRP) composite

thermoset shells in strengthening discarded timber railroad ties. In this work, a total of 18

composite shell-timber ties were manufactured through GFRP wrapping of discarded wood ties

at the Constructed Facilities Center in West Virginia University (CFC-WVU) and tested under

three-point bending to evaluate their properties such as Young’s modulus, rupture modulus and

bending strength. Elastic moduli of all the 18 ties were measured before and after wrapping.

Following laboratory testing, composite ties were field installed and evaluated at Transportation

Technology Center, Inc. (TTCI) Pueblo, Colorado. The composite ties showed excellent strength

and stiffness properties under TTCI lab testing of few million cycles. Field implementation

indicated successful performance of thermoset composite ties up to 63 Million Gross Tonnes

(MGT). Zero MGT Single Tie Push Tests (STPT) indicated doubling of push test loads after few

cycles of loading and initial values met threshold push strength requirements. In addition,

electrical impedance values were also found to meet the required threshold values. Some of the

thermoset composite ties showed plate cutting characteristics, where it is noted that previously

cracked and discarded wood core could create those localized responses under tie-seat area. This

work concluded that polyurethane acts as an effective primer in facilitating full-composite

behavior between wood and GFRP. It is also noted that thermoset GFRP wrapping provided

better mechanical properties than thermoplastic GFRP both for lab and commercially

manufactured products (IntegriCo., Tietek, Dynamic and PRT companies).

i

I want to dedicate this thesis to each and every member of my family,

especially my beloved sister Sharareh.

ii

ACKNOWLEDGMENT

I am grateful to my mentor Dr. Hota GangaRao, who gave me an opportunity to fulfill my eternal wish of

being a Structural Engineer. Not only for his patience but also for the knowledge he taught me through

my studies. I am also thankful to Dr. P.V. Vijay for the guidance on my research work and motivation

from the time I knew him. I also, would like to thank Dr. Udaya B. Halabe for his training during

coursework and encouragement during discussions.

I would like to thank my parents Nader Houshmandyar and Maryam Taghaei for being there with

me no matter what. Otherwise finishing my studies without their support was impossible.

I highly appreciate the financial support by Federal Railway Administration through CFC-WVU. I

want to thank past and current graduate student friends who helped me with this study during tie-

manufacturing or testing: Venugopal Reddy Chada, Anudeep Paraitham, Reza Shisheie, Mehrzad Zahabi,

Praveen Kumar Reddy, Daniel Stanislawski, Denny Dispennette, Vardhan Kumar Perisetty. I also want to

thank staff at Constructed Facilities Center, West Virginia University (CFC-WVU): Jerry Nestor, Mark

Skidmore and Lynne Jacobs.

I would like to take a moment to thank my past teachers who inspired me through continuation of

my graduate study: Dr. Farhad K. Birjandi, Dr. S. Mehdi Zahrai, Dr. Nader Fanaie, Dr. Shahriar

Keshavarz, Dr. Ali Torabian, Dr. Mohammad Ali Abduli, Dr. Gholamreza Nabi Bidhendi and Dr. Sadegh

Zibakalam.

The last but not the least, I would like to thank Dr. Parviz Famouri and my brother Dr. Saeid

Houshmandyar for their constant encouragement, guidance, and help in pursuing my graduate studies at

West Virginia University.

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TABLE OF CONTENTS

Acknowledgment .......................................................................................................................................... ii

1. Introduction ........................................................................................................................................... 1

1.1. Background ................................................................................................................................... 1

1.2. Objectives ..................................................................................................................................... 1

1.3. Scope and Report Organization .................................................................................................... 2

2. LITERATURE REVIEW: WOOD-FRP .............................................................................................. 3

2.1. Bonding of FRP Materials to Wood Using Thin Epoxy Gluelines [Raftery et al. 2009] ............. 3

2.1.1. Introduction ........................................................................................................................... 3

2.1.2. Materials ............................................................................................................................... 4

2.1.3. Lab Experiments ................................................................................................................... 5

2.1.4. Results and Conclusions ..................................................................................................... 10

2.2. Strengthening of Gulfport 230 kV Wooden Transmission Structures with GFRP Wrap [Shahi et

al. 2010] .................................................................................................................................................. 11

2.2.1. Introduction ......................................................................................................................... 11

2.2.2. Materials ............................................................................................................................. 12

2.2.3. Sample preparation ............................................................................................................. 12

2.2.4. Experimental Results .......................................................................................................... 14

2.2.5. Conclusions ......................................................................................................................... 14

2.3. Structural Characterization of Hybrid FRP-Glulam Panels for Bridge Decks [Lopez-Anido and

et al. 2002] .............................................................................................................................................. 14

2.3.1. Introduction ......................................................................................................................... 15

2.3.2. Materials ............................................................................................................................. 16

2.3.3. Experimental Evaluation ..................................................................................................... 18

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2.3.4. Conclusions ......................................................................................................................... 19

2.4. Flexural Stiffness and Strength of GFRP-Reinforced Timber Beams [Alhayek et al.2012] ...... 19

2.4.1. Introduction ......................................................................................................................... 20

2.4.2. Materials ............................................................................................................................. 20

2.4.3. Specimen Preparation ......................................................................................................... 20

2.4.4. Experimental Results .......................................................................................................... 21

2.4.5. Conclusions ......................................................................................................................... 23

3. Manufacturing of COUPONS AND Full-scale Composite Railroad Ties .......................................... 24

3.1. Introduction ................................................................................................................................. 24

3.2. Materials ..................................................................................................................................... 24

3.2.1. Properties of Derakane 510A-40 (ASHLAND , 2011) ....................................................... 24

3.2.2. Properties of Glass Fibers ................................................................................................... 25

3.3. Manufacturing Process ................................................................................................................ 25

3.3.1. Wood Core Preparation ....................................................................................................... 26

3.3.2. Resin Preparation ................................................................................................................ 27

3.3.3. Fibers Orientation ............................................................................................................... 28

3.3.4. Fiber Volume Fraction ........................................................................................................ 30

3.3.5. Polyurethane (primer) ......................................................................................................... 31

3.3.6. Fabricating of Wood-GFRP Coupons ................................................................................. 31

3.3.7. Fabricating of Full-scale GFRP Composite Railroad Ties.................................................. 31

3.3.8. Curing and Monitoring of Composite Ties ......................................................................... 31

3.4. GFRP-Wood Composite Specimens ........................................................................................... 33

3.5. Companies Producing Composite Ties ....................................................................................... 33

4. Effect of POLYURETHANE ON ADHESSION BETWEEN WOOD AND GFRP ......................... 35

v

4.1. Introduction ................................................................................................................................. 35

4.2. Objective ..................................................................................................................................... 35

4.3. Scope ........................................................................................................................................... 35

4.4. Test Description .......................................................................................................................... 36

4.4.1. Coupons .............................................................................................................................. 36

4.4.2. Full-scale Composite Railroad Ties .................................................................................... 36

4.5. Instrumentation and Measurements ............................................................................................ 37

4.6. Test Procedure ............................................................................................................................ 37

4.6.1. Three Point Bending Test for MOR Evaluation-Coupon Tests .......................................... 37

4.6.2. Composite Railroad Ties Three Point Bending Test for MOE and MOR Evaluating ........ 43

4.7. Test Results ................................................................................................................................. 46

4.7.1. Coupons .............................................................................................................................. 46

4.7.2. Full-scale Composite Ties ................................................................................................... 52

4.8. Conclusions ................................................................................................................................. 58

5. Evaluating Flexural Rigidities OF DISCARDED Wood TieS WITH and without frp shell .............. 60

5.1. Introduction ................................................................................................................................. 60

5.2. Objective ..................................................................................................................................... 60

5.3. Scope ........................................................................................................................................... 60


5.5. Instrumentation ........................................................................................................................... 61

5.6. Test Procedure ............................................................................................................................ 61

5.7. Sectional Properties .................................................................................................................... 62

5.7.1. Calculations of Transformed Moment of Inertia (It) for GFRP Composite Ties ................ 63

5.8. Test Results ................................................................................................................................. 66

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5.8.1. Calculation of Flexural Rigidity through Bending Stress .................................................. 66

5.8.2. Evaluation of Flexural Rigidity of the Two Configurations ............................................... 69

5.9. Conclusions ................................................................................................................................. 69

6. STATIC RUPTURE TESTS ON WOOD AND GFRP TIES: A COMPARISON ............................ 71

6.1. Introduction ................................................................................................................................. 71

6.2. Objective ..................................................................................................................................... 71

6.3. Scope ........................................................................................................................................... 71


6.5. Instrumentation ........................................................................................................................... 72

6.6. Test Procedure ............................................................................................................................ 72

6.6.1. Three Point Bending Test (Modulus of Elasticity) ............................................................. 73

6.6.2. Three Point Bending Test (Rupture Stress) ........................................................................ 73

6.7. Sectional Properties .................................................................................................................... 73

6.7.1. Calculations of Transformed Moment of Inertia (It) for GFRP Composite Tie .................. 73

6.7.2. Calculation of Moment of Inertia for Discarded Wood Tie ................................................ 74

6.8. Test Results ................................................................................................................................. 74

6.8.1. Calculation of Flexural Rigidity and Bending Stress .......................................................... 74

6.8.2. .Tie # 4 ................................................................................................................................ 75

6.8.3. Tie # 16 ............................................................................................................................... 76

6.8.4. Wood Tie ............................................................................................................................ 77

6.8.5. Evaluation of Flexural Rigidity of GFRP Composite and Discarded Wood Ties............... 80

6.8.6. Evaluation of Static Bending Strength and MOR of GFRP Composite and Discarded

Wood Ties ........................................................................................................................................... 80

6.9. Conclusions ................................................................................................................................. 81

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7. Theoretical Calculations ..................................................................................................................... 83

7.1. Introduction ................................................................................................................................. 83

7.2. Calculation of Young’s Modulus (micromechanics) .................................................................. 83

7.2.1. Coupons with Configuration ‘A’ (15 layers) ...................................................................... 83

7.2.2. Coupons with Configuration ‘B’ (19 layers) ...................................................................... 86

7.2.3. Full-scale Tie with Configuration ‘A’ (15 layers) .............................................................. 87

7.2.4. Full-scale Tie with Configuration ‘C’ (22 layers) ............................................................... 88

7.2.5. Test Results ......................................................................................................................... 89

7.3. Calculations of Shear Deflection for Full-scale Composite Ties ................................................ 89

7.4. Test results .................................................................................................................................. 90

7.5. Conclusion .................................................................................................................................. 90

8. Field Implementation and Testing ...................................................................................................... 91

8.1. Introduction ................................................................................................................................. 91

8.2. Objective ..................................................................................................................................... 91

8.3. Scope ........................................................................................................................................... 91

8.4. Materials ..................................................................................................................................... 91

8.5. Tie Installation Locations............................................................................................................ 91

8.6. Tie Installed Procedure ............................................................................................................... 92

8.7. Field testing ................................................................................................................................. 94

8.8. Test Results ................................................................................................................................. 97

8.9. Conclusions ................................................................................................................................. 99

8.10. Field Installation and Testing (Thermoplastic Ties) ............................................................... 99

8.11. Field Visual Observations ..................................................................................................... 103

8.12. Conclusions ........................................................................................................................... 104

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9. CONCLUSIONS AND RECOMMANDATIONS ........................................................................... 105

9.1. Conclusions ............................................................................................................................... 105

9.1.1. Chapter 4 (Manufacturing: Effectiveness of Polyurethane) .............................................. 105

9.1.2. Chapter 5 and 6 (Flexural Rigidity and Rupture Modulus) .............................................. 105

9.1.3. Chapter 7 (Experimental vs. Theoretical Results) ............................................................ 107

9.1.4. Chapter 8 (Field installation and testing) .......................................................................... 108

9.2. Recommendations and Future Study ........................................................................................ 108

9.2.1. Manufacturing Process ...................................................................................................... 108

9.2.2. Composite Products ................................................................................................................ 109

9.2.3. Field Installation ..................................................................................................................... 109

10. References ..................................................................................................................................... 110

APPENDIX-A review of Composites and FRP-steel structures ............................................................... 112

A.1 Review OF COMPOSITES ............................................................................................................... 112

A.2 Literature review: Steel-FRP.............................................................................................................. 115

A.2.1. An Experimental, Analytical and Numerical Study of the Static Behavior of Steel Beams

Reinforced by Pultruded CFRP Strips [Colombi et al. 2005] ............................................................... 116

A.2.1.1. Introduction ............................................................................................................................. 116

A.2.1.2. Materials/ Specimen Preparation ............................................................................................ 117

A.2.1.3. Results ..................................................................................................................................... 120

A.2.1.4. Conclusions ............................................................................................................................. 120

A.2.2. Behavior of Steel Monopoles Strengthened with High-modulus CFRP Materials [Lanier et al.

2008] ..................................................................................................................................................... 121

A.2.2.1. Introduction ............................................................................................................................. 121

A.2.2.2. Materials.................................................................................................................................. 122

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A.2.2.3. Test Procedure ......................................................................................................................... 123

A.2.2.3.1. Fabrication of scaled monopoles .......................................................................................... 123

A.2.2.3.2. Surface preparation .............................................................................................................. 123

A.2.2.3.3. Strengthening configuration ................................................................................................. 123

A.2.2.3.4. Testing configuration and instrumentation .......................................................................... 124

A.2.2.4. Test Results and Discussion .................................................................................................... 125

A.2.2.5. Conclusions ............................................................................................................................. 126

A.2.3. Strengthening of an Artificially Degraded Steel Beam Utilizing a Carbon/glass Composite

System [Photiou et al. 2006] ................................................................................................................. 126

A.2.3.1. Introduction ............................................................................................................................. 126

A.2.3.2. Materials.................................................................................................................................. 128

A.2.3.3. Sample Preparation ................................................................................................................. 129

A.2.3.4. Test Procedure ......................................................................................................................... 130

A.2.3.5. Conclusions ............................................................................................................................. 130

A.2.4. Upgrading Steel–concrete Composite Girders and Repair of Damaged Steel Beams Using

Bonded CFRP Laminates [Fam et al. 2009] ......................................................................................... 131

A.2.4.1. Introduction ............................................................................................................................. 132

A.2.4.2. Materials.................................................................................................................................. 133

A.2.4.3. Fabrication of Test Specimens ................................................................................................ 134

A.2.4.4. Test Setup and Instrumentation ............................................................................................... 136

A.2.4.5. Test Results and Discussions .................................................................................................. 138

A.2.4.6. Conclusions ............................................................................................................................. 139

APPENDIX-B MODULUS OF RUPTURE ............................................................................................. 141

1. Calculation of Bending Stress ................................................................................................... 141

2. Coupon # 3 (without Polyurethane & 19 layers) ...................................................................... 142

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3. Coupon # 7 (with Polyurethane & 19 layers)............................................................................ 142


5. Coupon # 4 (without Polyurethane & 19 layers) ...................................................................... 144


APPENDIX-C TRANSFORMED MI ...................................................................................................... 145

1. Calculations of Transformed Moment of Inertia (It) for GFRP Composite Ties ...................... 145

APPENDIX-D FLEXURAL RIGIDITY .................................................................................................. 146

1. Calculation of Flexural Rigidity ............................................................................................... 146

2. Tie # 1 ....................................................................................................................................... 146

3. Tie # 2 ....................................................................................................................................... 147

4. Tie # 3 ....................................................................................................................................... 147

5. Tie # 5 ....................................................................................................................................... 148

6. Tie # 6 ....................................................................................................................................... 148

7. Tie # 7 ....................................................................................................................................... 149

8. Tie # 8 ....................................................................................................................................... 149

9. Tie # 9 ....................................................................................................................................... 150

10. Tie # 10 ................................................................................................................................. 150

11. Tie # 11 ................................................................................................................................. 151

12. Tie # 12 ................................................................................................................................. 151

13. Tie # 13 ................................................................................................................................. 152

14. Tie # 14 ................................................................................................................................. 152

15. Tie # 15 ................................................................................................................................. 153

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LIST OF TABLES

Table 2. 1.Properties of FRP materials from manufacturer’s data sheets ..................................................... 5

Table 2. 2.Experimental results for crossarms with FRP (Shahi et al. 2010) ............................................. 14

Table 2. 3.Mechanical properties of GFRP composite (Lopez-Anido et al. 2002) ..................................... 17

Table 2. 4.Panel Specimens Dimensions and Moment of Inertia (Lopez-Anido et al. 2002) ..................... 17

Table 2. 5.Bending modulus of Eastern Hemlock glulam panel (Lopez-Anido et al. 2002) ...................... 18

Table 2. 6.Experimental ultimate load for two-span continuous panels (Lopez-Anido et al. 2002) .......... 19

Table 2. 7.Experimental results for group T (Alhayek et al.2012) ............................................................. 22

Table 2. 8.Experimental results for group TC (Alhayek et al.2012) ........................................................... 22

Table 2. 9.Experimental results for group T (Alhayek et al.2012) ............................................................. 22

Table 2. 10.Experimental results for group TC (Alhayek et al.2012) ......................................................... 23

Table 3. 1.Mechanical properties of Derakane 510A-40 resin and glass fiber ........................................... 24

Table 3. 2.Fiber/Fabric Configurations ....................................................................................................... 29

Table 3. 3.Configuration definition............................................................................................................. 29

Table 3. 4.Fiber volume fraction (Vf) calculations ..................................................................................... 30

Table 3. 5.Typical physical properties of GFRP composite ....................................................................... 31

Table 3. 6.Mechanical properties of different companies’ products ........................................................... 34

Table 4. 1.Fiber/fabric Configuration of Specimens ................................................................................... 35

Table 4. 2.Wood coupon dimensions .......................................................................................................... 38

Table 4. 3.GFRP dimensions ...................................................................................................................... 38

Table 4. 4. Young’s modulus of GFRP coupons ........................................................................................ 39

Table 4. 5.Wood-GFRP composite specimens dimension .......................................................................... 39

Table 4. 6.Transformed moment of inertia for different fiber/fabric configurations .................................. 43

Table 4. 7.Wood ties dimensions ................................................................................................................ 44

Table 4. 8.Fiber/fabric configurations......................................................................................................... 44

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Table 4. 9.GFRP composite tie average dimension .................................................................................... 44

Table 4. 10.Transformed Moment of Inertia for different fiber/fabric configurations ............................... 46

Table 4. 11.Summary of test results of Wood-GFRP composite coupons .................................................. 49

Table 4. 12.Summary of test results of composite ties (with/without polyurethane) .................................. 56

Table 5. 1.Fiber/fabric configuration of specimens .................................................................................... 60

Table 5. 2.GFRP Composite Ties Dimensions ........................................................................................... 62

Table 5. 3.Transformed moment of inertia It for different fiber/fabric configurations .............................. 66

Table 5. 4.Flexural rigidity of GFRP composite ties .................................................................................. 68

Table 6. 1.Fiber/fabric configuration of specimens .................................................................................... 71

Table 6. 2.GFRP composite tie dimensions ................................................................................................ 73

Table 6. 3.Transformed moment of inertia for different fiber/fabric configurations .................................. 74

Table 6. 4.Summary of test results of GFRP composite and wood tie ....................................................... 78

Table 8. 1.STPT results ............................................................................................................................... 96

Table 8. 2.Crack length and position on FRP tie ...................................................................................... 103

Table 8. 3.Push tie test results ................................................................................................................... 103

Table 8. 4.Strain values on the tie at 16.6 MGT ....................................................................................... 103

Table A. 1.Specimens configuration ......................................................................................................... 117

Table A. 2.Property of the reinforcement material ................................................................................... 117

Table A. 3.Test results .............................................................................................................................. 120

Table A. 4.Dry fiber material properties for high-modulus carbon fibers ................................................ 122

Table A. 5.Material properties for pultruded HM-CFRP strips. ............................................................... 123

Table A. 6.Summary of elastic stiffness increase ..................................................................................... 125

Table A. 7.Mechanical properties of FRP materials and adhesive film .................................................... 128

Table A. 8.Summary of test results of girders. ......................................................................................... 138

Table A. 9.Summary of test results of beams. .......................................................................................... 138

Table B. 1.Test results summary for GFRP-Wood composite coupons ................................................... 141

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Table C. 1. Calculation of transformed moment of inertia (MI) ............................................................... 145

xiv

LIST OF FIGURES

Figure 2. 1.Typical GFRP–wood test bar and test specimens (Raftery et al. 2009) ..................................... 7

Figure 2. 2.Fulcrum–wood test specimen (Raftery et al. 2009) .................................................................... 8

Figure 2. 3.Solid control test specimen. ........................................................................................................ 8

Figure 2. 4.Gulfport structure and critical region of crossarm (Shahi et al. 2010) ..................................... 12

Figure 2. 5.Schematic test configuration and critical region of crossarm (Shahi et al. 2010) .................... 13

Figure 2. 6.Laboratory setup (Shahi et al. 2010) ........................................................................................ 13

Figure 2. 7.Cross section of hybrid FRP glulam panel prototype (Lopez-Anido et al. 2002) .................... 16

Figure 2. 8.Stress-strain models for materials: (a) FRP composite; (b) Eastern hemlock glulam (Lopez-

Anido et al. 2002) ....................................................................................................................................... 17

Figure 2. 9.Shear and bending moment diagrams for two-span continuous panel (Lopez-Anido et al.

2002) ........................................................................................................................................................... 18

Figure 2. 10.Load-deflection curve of FRP-glulam panels with angle-ply reinforcement versus control

glulam panels (Lopez-Anido et al. 2002) .................................................................................................... 19

Figure 2. 11.Load-deflection response of FRP-glulam panels with unidirectional reinforcement versus

control glulam panels (Lopez-Anido et al. 2002) ....................................................................................... 19

Figure 2. 12.Beam cross section (Alhayek et al.2012) ............................................................................... 21

Figure 2. 13.Typical schematic drawing of beam instrumentation (Alhayek et al.2012) ........................... 21

Figure 3. 1.Checks (splits) on discarded wood tie ...................................................................................... 26

Figure 3. 2.Sharp edge of a wood tie .......................................................................................................... 27

Figure 3. 3.Different fiber/fabric configuration in composite ties .............................................................. 29

Figure 3. 4.Different fiber/fabric configurations with different thicknesses............................................... 30

Figure 3. 5.Cured full-scale composite tie mounted on manufacturing frame ............................................ 32

Figure 3. 6.Specimen cured without regular rotation showing resin accumulation at bottom .................... 32

Figure 4. 1.Three point bending test for coupons ....................................................................................... 36

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Figure 4. 2.Schematic of three point bending test configuration for composite ties ................................... 37

Figure 4. 3. Tension testing of GFRP coupons with different fiber/fabric configurations ......................... 38

Figure 4. 4.Configuration ‘A’ with 15 layers .............................................................................................. 40

Figure 4. 5.Transformed cross section for both fiber/fabric configurations (15 & 19 layers) .................... 40

Figure 4. 6.Configuration ‘B’ with 19 layers .............................................................................................. 42

Figure 4. 7.Configuration ‘A’ with 15 layers .............................................................................................. 45

Figure 4. 8.Full-scale composite tie profile ................................................................................................ 45

Figure 4. 9.Schematic of three point bending test for coupons ................................................................... 46

Figure 4. 10.Load vs. Deflection graph for Coupon # 6 ............................................................................. 47

Figure 4. 11.Load vs. Deflection graph for Coupon # 2 ............................................................................. 48

Figure 4. 12.Static bending strength of Wood-GFRP coupons ................................................................... 49

Figure 4. 13.MOR testing of Wood-GFRP coupons ................................................................................... 50

Figure 4. 14.Deflection at failure of GFRP composite coupons ................................................................. 50

Figure 4. 15.Deflection at reference load of GFRP composite coupons ..................................................... 51

Figure 4. 16.Coupons with and without Polyurethane application ............................................................. 52

Figure 4. 17.Schematic of coupon loading ................................................................................................. 53

Figure 4. 18.Stress vs. Strain graph for GFRP composite tie # 17 ............................................................. 54

Figure 4. 19.Load vs. Deflection graph for composite tie # 17 .................................................................. 54

Figure 4. 20.Stress vs. Strain graph for GFRP composite tie # 18 ............................................................. 55

Figure 4. 21.Load vs. Deflection graph for composite tie # 18 .................................................................. 56

Figure 4. 22.Flexural rigidities of GFRP composite ties with/without Polyurethane ................................. 57

Figure 4. 23.Static bending strength of GFRP composite with/without Polyurethane ............................... 57

Figure 5. 1.Schematic of three point bending test configuration for composite ties ................................... 61

Figure 5. 2.Three point bending test setup .................................................................................................. 62

Figure 5. 3.Configuration C ........................................................................................................................ 63

Figure 5. 4.Composite cross section ........................................................................................................... 64

xvi

Figure 5. 5.Configuration A ........................................................................................................................ 64

Figure 5. 6.Composite cross section ........................................................................................................... 65

Figure 5. 7.Schematic of deflected tie under three point bending test ........................................................ 66

Figure 5. 8.Stress vs. Strain graph for tie # 4 .............................................................................................. 67

Figure 5. 9.Stress vs. Strain graph for tie # 16 ............................................................................................ 67

Figure 5. 10.MOE testing for flexural rigidities of discarded wood ties vs. GFRP ties ............................. 68

Figure 6. 1.Schematic of three point bending test for composite ties ......................................................... 72

Figure 6. 2.Schematic of deflected tie under three point bending test ........................................................ 74

Figure 6. 3.Stress vs. Strain graph (tie # 4) ................................................................................................. 75

Figure 6. 4.Load vs. Deflection graph (tie # 4) ........................................................................................... 75

Figure 6. 5.Stress vs. Strain graph (tie # 16) ............................................................................................... 76

Figure 6. 6.Load vs. Deflection graph (tie # 16) ......................................................................................... 76

Figure 6. 7.Stress vs. Strain graph (wood tie) ............................................................................................. 77

Figure 6. 8.Load vs. Deflection graph (wood tie) ....................................................................................... 77

Figure 6. 9.Matrix in failure ........................................................................................................................ 78

Figure 6. 10.Debonding was failure cause .................................................................................................. 78

Figure 6. 11.MOR testing for flexural rigidities of GFRP composite and discarded wood ties ................. 79

Figure 6. 12.Static bending strength of GFRP composite and discarded wood ties ................................... 79

Figure 6. 13.MOR of GFRP composite and discarded wood ties ............................................................... 80

Figure 8. 1.Field installed ties ..................................................................................................................... 92

Figure 8. 2.Field installation ....................................................................................................................... 93

Figure 8. 3.Single tie push test (STPT) ....................................................................................................... 94

Figure 8. 4.FRP composite ties load vs. displacement at 0 MGT of load (STPT) ...................................... 95

Figure 8. 5FRP composite ties load vs. displacement at 11 MGT of load (STPT) ..................................... 96

Figure 8. 6.Tie and rail seat inspection at 27.75 MGT on 5/14/12 TTCI ................................................... 98

Figure 8. 7.Tie and spike inspection at 36.9 MGT on 5/21/12, TTCI......................................................... 98

xvii

Figure 8. 8.Tie removal after 63 MGT of loading ...................................................................................... 99

Figure 8. 9.Cracks on FRP thermoplastic ties ........................................................................................... 100

Figure 8. 10.Typical FRP composite ties displacement at 0 MGT of load ............................................... 101

Figure 8. 11.FRP composite ties displacement at 1.95 MGT of load ....................................................... 102

Figure 8. 12.FRP composite ties at 16.6 MGT of load ............................................................................. 102

Figure A. 1.Bottom side of typical retrofitted girder (Colombi et al. 2005) ............................................. 118

Figure A. 2.Strain gages locations for beams TR1 and TR2 (Colombi et al. 2005) ................................. 119

Figure A. 3.Strain gages locations for beams TR3 (Colombi et al. 2005) ................................................ 119

Figure A. 4.Lateral supports setup for specimens TR2 and TR3 (Colombi et al. 2005) .......................... 120

Figure A. 5.Typical mono pole supporting wireless services (Lanier et al. 2008) ................................... 121

Figure A. 6.Longitudinal strengthening configuration of Monopole HM-WL (Lanier et al. 2008) ......... 124

Figure A. 7.Testing configuration for monopoles (Lanier et al. 2008) ..................................................... 124

Figure A. 8.Comparison of load-deflection behavior of Monopole HM-ST before and after strengthening

(Lanier et al. 2008) .................................................................................................................................... 125

Figure A. 9.(a) Schematic diagram of a RHS steel beam upgraded with a hybrid composite system. (b)

tacking sequence of the hybrid composite system (Tc is 0.6 mm for UHM-CFRP and 1.2 mm for HM-

CFRP) (Photiou et al. 2006) ...................................................................................................................... 129

Figure A. 10.Tensile stress–strain response of steel and FRP materials (Photiou et al. 2006) ................. 130

Figure A. 11.Arrangement for beam tests (Photiou et al. 2006) ............................................................... 130

Figure A. 12.Cross-section configurations of test specimens: (a): strengthening intact composite girders

and (b): repair of notched beams (Fam et al. 2009) .................................................................................. 132

Figure A. 13.Fabrication of test specimens: (a) girders and (b) beams (Fam et al. 2009) ........................ 136

Figure A. 14.Test setup and instrumentation for: (a) girders and (b) beams (Fam et al. 2009) ................ 137

Figure A. 15.Summary of analytical model components: (a) Cross-section analysis and (b) Constitutive

models (Fam et al. 2009). ......................................................................................................................... 139

xviii

Figure B. 1.Load vs. Deflection graph for composite coupon # 7 ............................................................ 142



Figure D. 1.Stress vs. Strain graph for GFRP composite tie # 1 ............................................................... 146








Figure D. 9.Stress vs. Strain graph for GFRP composite tie # 10 ............................................................. 150

Figure D. 10.Stress vs. Strain graph for GFRP composite tie # 11 ........................................................... 151





1

1. INTRODUCTION

1.1. Background

Composites have been used as structural materials for a long time; especially in aviation industry since

1950s, because of their lighter self-weight, avoidance of radar and acoustic signatures. Composites have

played a significant role in marine applications (i.e. in Navy) as well as in automobile and defense

industries. Some important features of composites are: 1. high strength to weight ratio, 2. high stiffness to

weight ratio, 3. high tensile strength, 4. durability in marine/harsh environment (e.g. acid rain), 5. ability

in damping seismic and blast loading and 6. low maintenance cost and endurance in mechanical and

thermal fatigue under dynamic loads. Thanks to their tailorable and favorable mechanical properties, Civil

Engineers have been able to apply composites cost effectively in rehabilitation of existing infrastructures

and for the construction of new structures. Applications of FRP composites range from strengthening and

retrofitting of reinforced and unreinforced masonry walls, seismic retrofitting of bridges and buildings,

repair/strengthening of girders and slabs, and rehabilitation of structures.

This report mainly focuses on the following topics:

1. Introduction to composites (chapter 1).

2. Literature review on applications of FRP composites for wood (chapter 2) and steel structures

(Appendix ‘A’).

3. External application of thermoset GFRP composite shells for rehabilitating and retrofitting

discarded wood railroad ties (chapter 4-9).

1.2. Objectives

The objectives of this study are to:

1. Conduct literature review of the application of FRP composites to rehabilitate and retrofit wood

structures.

2. Conduct literature review of the application of FRP composites on steel and bridge members.

2

3. Manufacture full-scale thermoset GFRP composite railroad ties with discarded timber ties as core

through hand lay-up process and conduct field installation.

Estimate flexural rigidity of composite ties under three point bending test and evaluate the

increment from wood to composite member.

Evaluate modulus of rupture and static bending strength of composite ties under three point

bending test.

Monitor practical use of ties (field installation) and perform single lateral push test (STPT).

1.3. Scope and Report Organization

This study tries to elaborate the effectiveness of GFRP composite shells for rehabilitating discarded wood

ties and find the increase in flexural rigidity and static bending strength. The research is organized into

eight chapters. Chapter 1 presents objectives and scope of the study. Chapter 2 presents literature review

including application of FRP composites on wood structures and members. The literature reviews

primarily cover the 2002-2012 periods. Chapter 3 describes manufacturing of bending coupons and full

scale ties. Chapter 4 discusses the importance of polyurethane primer in bonding between wood and

GFRP shell. In chapter 5, flexural rigidity of composite ties under three point bending test configuration

have been compared. In chapter 6, static bending strength and flexural rigidity of both discarded wood

and composite ties were evaluated and compared. In chapter 7, theoretical calculations are compared to

test results. Chapter 8 discusses the field implementation and testing of 14 composite ties. Chapter 9

presents conclusions and recommendations for the future study. Appendix A presents literature review

dealing with FRP application on steel and bridge members. Test results are presented in Appendices B to

D.

3

2. LITERATURE REVIEW: WOOD-FRP

This chapter presents the literature review on FRPs application on wood structural members. Papers

reviewed here focus on application of FRPs to following structures:

I. Bonding between FRP and Wood Using epoxy Matrix [Raftery et al. 2009].

II. Strengthening of Gulfport 230 kV Wooden Transmission Structures with GFRP Wrap [Shahi et

al. 2010].

III. Structural Characterization of Hybrid FRP-Glulam Panels for Bridge Decks [Lopez-Anido et al.

2002].

IV. Flexural Stiffness and Strength of GFRP-Reinforced Timber Beams [Alhayek et al.2012].

2.1. Bonding of FRP Materials to Wood Using Thin Epoxy Gluelines

[Raftery et al. 2009]

Raftery et al. (2009) studied the bonding quality between FRPs and low-grade spruce wood using

commercial epoxies. They compared the bonding of non-moisture cycled FRP-wood specimens, non-

moisture cycled wood-wood and solid control specimens with moisture cycled FRP-wood specimens. The

wood was from the same board and they were directly compared by means of the block shear test

(Talakanti and Gangarao, 1997).

2.1.1. Introduction

Good bonding provides stress transferring among different materials in a composite section and prevents

local stress concentrations. Other problems are because of differences in Young’s moduli, creep

properties and reaction to moisture or environment. FRP materials are well-known to be durable, which

depends on polymer matrix type, laminate thickness, production quality, curing method, fiber volume

fraction and many other factors. Research shows that aging due to environment reduces the flexural and

tensile properties of pultruded GFRPs with vinyl ester matrix (Liao K et al. 1999). Moisture exposed

wood can distort and fracture because of rapid dimensional changes specifically perpendicular to

longitudinal wood fibers. Because wood and FRP are different in their reactions to changes in humidity

4

and ambient temperature, an important consideration in the adhesive bonding between two materials is

the shear stress. The shear stress is the result of differential shrinkage and swelling at the bond interface.

Epoxy adhesives are considered to be the most suitable material for bonding of FRP. Advantages include

good gap-filling characteristics with low clamping pressures. Some examples include employing of

epoxies in anchoring bonded-in rods and bars for upgrading or repairing of timber members (Wheeler AS

et al. 1998 and Broughton JG et al. 2001). Some limitations of epoxies include products cost and

additional expenses resulting from health and safety issues.

In a study (Olson WZ et al. 1962), the main cause of low bonding quality was lack of enough using

of resin known as starved joints (inadequate bonding). In this manner, theoretical calculations and

experimental findings are not found to be similar. In another research (American Institute of Timber

Construction. Use of epoxies in repair of structural glued laminated timber, 2005), inappropriate moisture

content, poor adhesive mix, inadequate curing period or improper curing temperature were listed as

possible cause of interfacial bond loss. Another study (Brandon R, 2005) emphasized after applying FRP

on wood, the composite bonds exceeded the strength of the wood itself. But after water soaking of

specimens, the bonding weakened rapidly.

Rowlands et al. (1986) found that epoxy adhesives formed an excellent bonding to glass, aramid

and carbon fiber reinforced products in dry conditions but that after being subjected to a severe moisture

cycling procedure, they were unable to maintain even 50% of their dry bond strength.

Despite the above findings, epoxy adhesives remain the choice of researchers in FRP–wood bonded

connections because of their good gap-filling properties, limited shrinkage during curing and their ability

to achieve full cure at ambient temperatures. Furthermore, they do not release volatile waste products

such as water upon chemical curing, which could result in poor bond quality or the development of

adverse dimensional transformations in wood.

2.1.2. Materials

1. FRP: Two pultruded fiber-reinforced composite materials were selected for the bonding test based on

their mechanical properties as given by the manufacturers and presented in Table 2.1.

5

Table 2. 1.Properties of FRP materials from manufacturer’s data sheets

FRP type Tensile modulus (ksi) Tensile strength (ksi)

Fulcrum 6527 142

GFRP 5802 N.A.

Both FRP materials comprised of glass fibers aligned uni-directionally in a matrix. E-glass was

selected as the most appropriate fiber type because of its relatively low cost in comparison to carbon

and other glass fiber types. The Fulcrum material was manufactured using an engineered

thermoplastic polyurethane matrix (recyclable) with a potential to achieve fiber volume fractions as

high as 70%. Vinyl ester was chosen over polyester and epoxy resins because of its capacity to

withstand moisture presence at the bonding surface of wood.

2. Type of wood was Irish-grown Sitka spruce. The timber was kiln dried to approximately 18%

moisture content. The mean tensile modulus and mean tensile strength were 1171 and 3.29 ksi,

respectively.

3. Three commercially available structural epoxy adhesives were used in the test were: Epoxy 1

(Timberset), Epoxy 2 (CB10T Slow Set) and Epoxy 3 (Sikadur 31 Normal). Young’s moduli of

Epoxy 1, Epoxy 2 and Epoxy 3 were 725, 159 and 1160 ksi, respectively.

The adhesion promoter used involved a one-part composition of silanes supplied in a dilute aqueous

solution to enhance adhesion by improving the chemical reaction of the adhesive and good surface

wetting of the two substrates.

2.1.3. Lab Experiments

The experiments to examine the bonding interface quality between the wood and two FRP materials with

respect to three epoxy resins with and without the adhesion promoter is discussed in following sections:

Proper pre-treatment of bonding surface is critical to the durability of the bonding, particularly when

using cold cure epoxy adhesives to bond FRPs.

The expected service environment of an FRP-reinforced glulam beam is 65 ± 5% relative humidity

and 68 ± 35 °F temperature. Therefore, the FRP materials were initially conditioned in this

6

environment for at least 40 days prior to use. The surfaces of the FRP materials were maintained free

from contamination by storing in a cling-film wrapping.

The surface of the GFRP material was gently abraded wet and dry emery paper so that the top layer

of the material (which was likely to contain release agents used in the manufacturing process and possibly

other contaminants) was removed. Subsequently, the abraded surface was wiped clean, which was wetted

fresh with methylated spirits for each wipe in order to minimize a residue of grease remaining on the

adherend surface prior to bonding. The production of the Fulcrum thermoplastic polyurethane did not

require the use of any demolding agents. In addition, Fulcrum is associated with an inherently coarse

surface and did not require further abrasion. Clear wood pieces were selected from the wood stock so that

irregularities such as knots, fissures and resin pockets, which would inhibit the formation of a quality

bonding, were omitted. Knife planing was the preferred choice of surface preparation. The adhesive was

applied within 2 hours of planing in order to limit oxidation of the wood surface.

2.1.3.1. Bond specimen fabrication

From the timber stock of approximately 200 boards, clear wood laminations, approximately 310 mm × 50

mm × 20 mm (12 in × 2 in × 0.8 in), were prepared. These types of test bars were prepared as:

1) Wood-wood

2) GFRP-Wood (Figure 2.1)

3) Fulcrum-Wood

7

Figure 2. 1.Typical GFRP–wood test bar and test specimens (Raftery et al. 2009)

After planing, a bond line thickness of 0.5 mm (0.2 in) was obtained at the shear bonding interface

and it was cured after 24 hour at the temperature of approximately 68 °F.

Fabrication of the FRP–wood test bars (GFRP and Fulcrum) followed the same procedure those of

the wood–wood bonded test bars except that an FRP plate was incorporated adjacent to the center line of

the test bar. The thicknesses of the FRP plates that were used were 4 mm (0.15 in) and 1.4 mm (0.06 in),

respectively.

The bond shear test specimens were cut to obtain a notch of 5 mm (0.2 in) on each loading face and

were associated with a bond interface area of approximately 40 mm × 50 mm (Figure 2.2).

8

Figure 2. 2.Fulcrum–wood test specimen (Raftery et al. 2009)

2.1.3.2. Solid wood specimen testing

Shear tests on solid wood specimens used the same double- notched geometry as that stated in the ISO

6238 standard. However, because of a restriction in size of the boards from which the solid specimens

were cut, they were constrained to 40 mm in width in comparison to 50 mm used in the bonded

specimens. Notches were located at either end such that shearing parallel to the grain could be facilitated.

All solid specimens were non-moisture cycled and were conditioned to an environment of 65 ± 5%

relative humidity and a temperature of 20 ± 2 °C. A typical solid specimen and its associated geometry

are shown in Figure 2.3.

Figure 2. 3.Solid control test specimen.

9

2.1.3.3. Moisture cycling

Specimens were initially transferred from the conditioning chamber to a pressure vessel in which they

were completely submerged in de-aired water, which was maintained at a temperature of 20 °C.

Following steps were used for moisture cycling of the specimens:

1) A vacuum pressure of 70 kPa (10 psi) was drawn for approximately 2hour so that air trapped

in the voids of the wood was extracted. A back pressure of 600 kPa was subsequently applied

in the vessel for a minimum of 30 min so that complete saturation of the specimens could be

obtained.

2) 2) Drying of the specimens was then performed in an environment of 25 ± 5% relative

humidity and to 35 ± 5 °C temperature.

3) This cycle of wetting and drying was repeated five times.

4) The specimens were then transferred to a conditioning chamber, which was maintained at 65

± 5% relative humidity and a temperature of 20 ± 2 °C, for a period of at least 15 days prior

to testing.

This methodical procedure allowed for the direct comparison of the mechanical performance of the

moisture cycled specimens with that of the non-moisture cycled specimens, and hence, by reconditioning

the specimens to their original in- service moisture content, evaluated only the effect of the hygrothermal

stresses imposed on the adhesive bonds during moisture cycling (Wang, 2006).

2.1.3.4. Specimen testing

A guillotine-type tool was used to carry out the shearing of the test specimens. A 100 N preload (22 lbs)

was applied to each specimen after placement in the shearing apparatus so that its correct position could

be maintained prior to load application. The target failure time for execution of each test was 60 ± 20 s.

The specimens were tested at a constant loading rate, in preference to a constant stroke rate (cross head

displacement). Grease was applied at the contact locations between the specimen and the shear tool to

minimize friction. After each specimen was tested, a visual assessment of the percentage adherend failure

was done, to the nearest 5%, using a superimposed grid. An FRP/adhesive combination was attributed a

10

‘‘Pass’’ if the mean adherend failure percentage obtained was greater than or equal to 80%. A high

adherend failure percentage indicates a strong bond has been formed and that the adherend in question

was the weakest link at the bond interface. The compressive shear strength of each specimen was

determined by dividing the ultimate load of the failed specimens by the measured dimensions of the

theoretical shear plane. This approach assumes an instantaneous failure and a uniform stress distribution

across the theoretical shear plane. While this is the accepted approach to determine the shear strength, the

actual shear stress distribution is characterized by peaks at the end of the bonded length. Findings from

three-dimensional nonlinear finite element analyses have demonstrated the existence of stress

concentrations adjacent to the loading edges beside the notches as well as the presence of tensile peel

stresses perpendicular to the shear plane in both single-notched and double-notched block shear

specimens. The stiffness imbalance that arises from the bonding of dissimilar materials was noted as

being an important consideration in the shear stress distribution in other studies. Furthermore, when two

materials of different stiffness are bonded together, numerical modeling has shown that the maximum

shear stresses occur at the free end of the adhesive region close to the adherend of the higher stiffness.

2.1.4. Results and Conclusions

Block shear strengths and adherend failure percentages of FRP–wood specimens (severe 5-cycle

vacuum pressure and soaking-drying cycles) were as high as those of non-moisture cycled FRP–wood

specimens, wood–wood bonded specimens and solid control specimens.

Use of silane-based adhesion promoter prior to adhesive application increased the delamination

resistance.

Thin epoxy bondlines can give strong and durable FRP-wood bonds (0.5 mm).

Based on the results of this study, effectiveness of primer coating before wrapping and thin

bondlines was considered.

11

2.2. Strengthening of Gulfport 230 kV Wooden Transmission Structures

with GFRP Wrap [Shahi et al. 2010]

Shahi et al. (2010) studied the feasibility of application of GFRP on strengthening of deteriorated wooden

electrical transmission structures. A total of 14 strengthened and 5 (control) timber crossarm specimens

were tested to failure with different degree of deterioration. A strengthening system consisting of GFRP

fabric wrap was applied adjacent to the critical section of the crossarms. The overall research findings

suggest that a GFRP-wrap strengthening system can increase the strength of deteriorated crossarm

elements and thus extends the service life of existing Gulfport structures.

2.2.1. Introduction

Electricity current is provided by transmission lines between high voltage generation (electric power

plant) and industrial or residential users. In urban areas, this is carried out by steel structures. But in

remote areas, electrical transmission is performed by wooden structures. Gulfport-type wood structures

are categorized as wooden truss structures. There are approximately 6000 of these structures transmitting

electricity in 1600 km in Ontario with the ages between 30 to 40 years and several of them are in need of

replacement. Due to remote location of transmission network their replacement is very expensive and

difficult. An alternative for this issue was the rehabilitation and strengthening of them with GFRP wraps.

Because of their light weight, high strength and ease of installation without any interruption while the

transmission structure had been functioning, GFRPs were used. From material stiffness considerations,

GFRP wrap is much more compatible with timber than CFRP wrap.

Previous research has identified the most critical element of the Gulfport structures to be the

crossarms, particularly between the main poles and brace supports (Figure 2.4).

12

Figure 2. 4.Gulfport structure and critical region of crossarm (Shahi et al. 2010)

2.2.2. Materials

1. Wood: Since the nominal strengths of jack pine, red pine, and western red cedar are similar, all of the

crossarms were conservatively assumed to be made of jack pine.

Note: The writer of this paper did not say anything about mechanical properties of wood (i.e. Young’s

modulus) as control specimens and number of wraps on strengthened specimens.

2. GFRP: E-glass fabric by Fyfe Co. with two different widths: 0.6 and 1.2 m.

3. Repairing material for wood cracks: Sika AnchorFix-3.

4. Resin: Epoxy 1: TYFO S, and Epoxy 2: TYFO WP by Fyfe Co.

2.2.3. Sample preparation

Surface sanding: due to heavy deterioration of the poles, the surfaces were cleaned.

Cracks: To repair cracks, a two-part black and white epoxy was mixed together and used to achieve a

constant gray viscous epoxy with a set time of 5 minutes.

GFRP: Each specimen was wrapped on both sides of the loading piece, as shown in Figs. 2.5 & 2.6.

13

Figure 2. 5.Schematic test configuration and critical region of crossarm (Shahi et al. 2010)

Figure 2. 6.Laboratory setup (Shahi et al. 2010)

A number of strain gauges were installed on the GFRP wrap to record the hoop strain around the diameter

of the pole and along its length. Deflections were observed by LVDTs.

14

2.2.4. Experimental Results

Experimental results under three point bending test are shown in Table 2.2:

Table 2. 2.Experimental results for crossarms with FRP (Shahi et al. 2010)

Sample Diameter

(in)

Effective E

(ksi)

Max load

(kips)

Max defl.

(in)

Max. bending

stress (ksi) Failure mode

1 10.51 384 21.80 2.75 5.23 Flexure-tension

2 11.14 535 23.83 1.69 4.78 Flexure-tension

3 10.78 534 20.68 1.69 4.58 Flexure-tension

4 10.15 806 27.87 1.93 7.44 Flexure-tension

5 11.02 489 20.91 1.69 4.32 Flexure-tension

6 10.59 796 26.75 1.57 6.23 Flexure-tension

7 10.59 718 25.18 1.65 5.89 Flexure-tension

8 9.44 1092 28.55 1.97 7.35 Flexure-tension

2.2.5. Conclusions

All control specimens failed in combined shear flexure or splitting with varying failure strengths

reflecting the varying degrees of deterioration.

All strengthened specimens failed in flexure.

The strength and stiffness of the strengthened specimens were greater than that of the control

specimens.

Based on the results of this study, complete strengthening (wrapping) of specimens instead of

partial wrapping for composite ties was considered.

2.3. Structural Characterization of Hybrid FRP-Glulam Panels for

Bridge Decks [Lopez-Anido and et al. 2002]

Lopez-Anido et al. (2002) studied structural characterization of FRP glulam (glued laminated) panels for

bridge deck construction. The structural system is based on the concept of sandwich construction with

strong and stiff FRP composite skins bonded to an inner glulam panel. The FRP reinforcement was

applied on the top and bottom faces of the glulam panel by wet layup and compacted using vacuum

bagging (Figure 2.7). An experimental protocol based on a two-span continuous bending test

configuration was used to characterize the stiffness, ductility, and strength response of FRP-glulam panels

under simulated loads. Half-scale FRP-glulam panel prototypes with two different fiber orientations,

15

unidirectional (0°) and angle-ply (±45°), were studied and the structural response correlated with control

glulam panels.

2.3.1. Introduction

Glued laminated (glulam) wood material has been used in bridges for approximately 30 years. Glulam

panels have been used in bridge decks, by being supported on steel or glued laminated stringers. Glulam

panels exhibited good performance for bridge deck replacement due to the following advantages:

1) Reduction in out-of-service time;

2) Ease of installation;

3) Reduction in dead loads;

4) Increase in resistance to road chemicals;

5) Wider tolerance to weather conditions during installation.

FRPs offer new opportunities to repair or strengthen existing wood structures in buildings and

bridges. However, the use of FRP composites for wood reinforcement is limited, due to the relatively

higher cost of the materials and the fabrication process. Various systems for FRP reinforcement of wood

structural members have been developed.

Examples are:

1) FRP wrapping of wood members with E-glass and carbon fabric reinforcement using the wet layup

method (Sonti and GangaRao1995; GangaRao 1997)

2) FRP tendons for prestressing of laminated wood decks (Dagher et al. 1997)

3) reinforced railroad ties (Sonti and GangaRao 1996)

4) FRP-glulam beams integral with a concrete slab (Brody et al. 2000).

It was found that FRP-glulam beams with sufficient tension reinforcement had significant strength

increases in addition to wood ductile compression failure, rather than the typical brittle tension failure of

wood.

16

2.3.2. Materials

1. Wood: Eastern hemlock (Tsuga Canadensis), a widely distributed wood species in New England, is

not a high-performance material for structural usage because of its low strength, and is prone to check

properties.

The dimensions of wood laminations were (2 in × 4 in) and dried to a desired moisture level of 16%

or less, prior to gluing. Phenol resorcinol formaldehyde (PRF) adhesive was used to laminate the

glulam panels. (Ew = 8.94 GPa (1297 ksi))

2. GFRP: E-glass stitched fabric (directional continuous fibers) with binderless chopped strand mat

(CSM) backing.

3. Resin: Thermoset polymer matrices DERAKANE 411, an epoxy-based vinyl ester.

Figure 2. 7.Cross section of hybrid FRP glulam panel prototype (Lopez-Anido et al. 2002)

17

Figure 2. 8.Stress-strain models for materials: (a) FRP composite; (b) Eastern hemlock glulam (Lopez-

Anido et al. 2002)

Three types of panel prototypes were characterized experimentally:

(1) glulam control panels (CO).

(2) FRP-glulam panels with angle-ply reinforcement (XM).

(3) FRP-glulam panels with unidirectional reinforcement (UM).

The cross section of the hybrid FRP-wood panel is shown in Figure 2.11. Mechanical Properties of

GFRP Composite are shown in Table 2.3. XM1808 has two layers with fiber/fabric configuration of

[±45º/CSM] and UM1810 has two layers with configuration of [0º/CSM].

Table 2. 3.Mechanical properties of GFRP composite (Lopez-Anido et al. 2002)

GFRP Thickness

(mm)

Fiber Volume

Fraction (Vf)

Young’s Modulus

(ksi)

XM1808 0.11 54% 1566

UM1810 0.14 45% 3365

Moment of Inertia of specimens is shown in Table 2.4.

Table 2. 4.Panel Specimens Dimensions and Moment of Inertia (Lopez-Anido et al. 2002)

Panel b (in) hw (in) hf (in) Moment of inertia (in4)

CO-1 5.86 3.46 0 20.32

CO-2 5.82 3.50 0 20.87

XM-1 5.82 3.22 0.05 16.45

XM-2 5.86 3.50 0.05 21.15

UM-1 5.74 3.18 0.07 14.96

UM-2 5.82 3.34 0.07 18.18

18

The stress-strain relationship modeled for the unidirectional FRP composite material [0°/CMS] is

Figure 2.8(a). A bilinear stress-strain model, Figure 2.8(b), calibrated for Eastern hemlock laminations

was adopted as an approximation to the actual wood constitutive relation for the glulam panel specimens.

2.3.3. Experimental Evaluation

Prototypes with a two-span continuous configuration were subjected to a pair of central loads (e.g., five-

point bending load). The two-span continuous experimental setup is assumed to simulate the actual

structural response of a deck panel supported by stringers (involving regions with positive and negative

bending moment), as shown in Figure 2.9.

Figure 2. 9.Shear and bending moment diagrams for two-span continuous panel (Lopez-Anido et al.

2002)

Bending Modulus of Eastern Hemlock Glulam Panel are shown in Table 2.5

Table 2. 5.Bending modulus of Eastern Hemlock glulam panel (Lopez-Anido et al. 2002)

Panel EI (kips.in2) E (ksi)

CO-1 27289 1343

CO-2 30199 1447

Average 28744 1395

19

Table 2. 6.Experimental ultimate load for two-span continuous panels (Lopez-Anido et al. 2002)

Panel Ultimate load (kips) Mode of Failure

CO-1 26.73 Tension

CO-2 24.43 Tension

XM-1 23.17 Tension

XM-2 22.50 Shear and tension

UM-1 37.54 FRP buckling, shear in wood

UM-2 38.00 FRP delamination, shear and tension in wood

Figure 2. 10.Load-deflection curve of FRP-glulam

panels with angle-ply reinforcement versus control

glulam panels (Lopez-Anido et al. 2002)

Figure 2. 11.Load-deflection response of FRP-

glulam panels with unidirectional reinforcement

versus control glulam panels (Lopez-Anido et al.

2002)

2.3.4. Conclusions

Angle-ply reinforced [±45°/CSM] panels exhibited no significant strength increase (Figs. 2.10 and

2.11).

FRP composite skins [0°/CSM] resulted in an ultimate load capacity increase of 47% and a load

increase of 24% corresponding to the deflection service limit with a maximum tensile strain of 30%

in tension (Figure 2.11).

2.4. Flexural Stiffness and Strength of GFRP-Reinforced Timber Beams

[Alhayek et al.2012]

Alhayek et al. (2012) studied the effect of GFRP lamina on 20 creosote treated Douglas Fir stringers with

dimension of 130 mm × 330 mm × 4500 mm (5.11 in × 13 in × 177 in) in three-point bending. 10 beams

grouped to “T”; tension zone reinforced and other beams grouped to “TC” tension and compression zone

20

reinforced. The research indicated that with this kind of reinforcing, on average, the strength and the

stiffness of the beams were increased by 36 and 3%, respectively for group T and by 31 and 3.5% for

group TC.

2.4.1. Introduction

A large number of timber bridges in North America, in coming future, needs to be rehabilitated or

replaced. Also, the low stiffness of these bridges is assumed to worsen the problem. In order to reduce

maintenance costs, Manitoba Infrastructure and Transportation supported the research to investigate

stiffening options for timber bridges. The estimated cost of infrastructure replacement in the Province of

Manitoba only is assumed to be more than $ 40 billion CAD. With respect to the cost of bridge

replacement, rehabilitation of timber bridges is assumed to be one solution.

2.4.2. Materials

Wood: 20 creosote treated beams with the dimension of 130 mm × 330 mm × 4500 mm (5.11 in × 13

in × 177 in)

GFRP: Rectangular lamina with the dimension of 5 mm × 50 mm (0.19 in × 1.96 in) manufactured by

Rotafix in the UK with the tensile modulus of 27 GPa (3916 ksi) and ultimate strength of 650 MPa

(94.27 ksi).

Adhesive: Epoxy Fibreglass Evercoat (FIB 622)

2.4.3. Specimen Preparation

For group T, two grooves were routed along the bottom (tension zone) of the beam. For group TC, in

addition to grooves in tension zone, another two grooves were bored in compression zone (on top) of the

beam. The roves were cleaned to be free of debris. Then epoxy was squeezed into holes and the GFRP

strips were inserted in epoxy to bond the lamina to the timber. Cross-sections of the two specimen groups

are shown in Figs. 2.12 and 2.13.

21

Figure 2. 12.Beam cross section (Alhayek et al.2012)

Figure 2. 13.Typical schematic drawing of beam instrumentation (Alhayek et al.2012)

2.4.4. Experimental Results

The report discussed the experimental results of ultimate strength and stiffness of the beams. Before

strengthening, stiffness of the beams was obtained. Span length was 4500 mm and three point bending

test was conducted.

22

Table 2. 7.Experimental results for group T (Alhayek et al.2012)

Beam

Stiffness of

unstrengthened

beam (lbs.in2 × 10

8)

Stiffness of

strengthened

beam (lbs.in2 × 10

8)

% Change

Failure

load

(kips)

T1 16.54 17.04 3.08 32.34

T2 20.97 21.43 2.15 33.15

T3 15.78 15.96 1.10 26.40

T4 14.56 15.23 4.54 22.84

T5 18.46 19.30 4.56 22.61

T6 15.57 15.96 2.30 22.59

T7 14.21 14.74 3.61 28.26

T8 14.14 14.95 5.33 22.70

T9 19.06 19.58 2.88 31.32

T10 15.82 15.85 0.20 25.78

Table 2. 8.Experimental results for group TC (Alhayek et al.2012)

Beam

Stiffness of

unstrengthened

beam (lbs.in2 × 10

8)

Stiffness of

strengthened

beam (lbs.in2 × 10

8)

% Change

Failure

load

(kips)

TC1 19.54 21.42 9.45 159.60

TC2 13.72 13.68 -0.36 62.56

TC3 18.00 18.32 1.66 158.38

TC4 15.18 16.61 9.41 78.70

TC5 15.50 15.57 0.41 145.4

TC6 18.63 18.70 0.19 148.30

TC7 14.66 16.02 9.11 83.58

TC8 13.72 14.17 3.33 107.96

TC9 15.08 15.08 0.01 117.40

TC10 18.28 18.63 1.96 122.30

Experimental MOR of beams is as follows:

Table 2. 9.Experimental results for group T (Alhayek et al.2012)

Beam MOR (ksi)

T1 8.54

T4 6.33

T5 6.54

T6 6.22

T7 7.78

T8 6.64

T10 7.16

23

Table 2. 10.Experimental results for group TC (Alhayek et al.2012)

Beam MOR (ksi)

T2 3.83

T6 9.07

T7 5.10

T8 7.74

2.4.4.1. Load-Deflection Behavior

The average failure load for group T and TC was found to be 119.2 kN (26.80 kips) and 118.4 kN (26.62

kips), respectively. The load-deflection behavior of the beams in the two groups clearly showed that the

beams in Group T and TC behaved in a linear-elastic fashion until failure.

2.4.5. Conclusions

The report indicated that application of GFRP lamina is a good approach to increase the flexural capacity

of the creosote treated timber bridge. Since the wood core was deteriorated, no significance increase in

beam stiffness was observed.

Applying GFRP in compression zone is not as efficient as its use in tension zone. Average

strength increase in group T and TC was found to be 36 and 31%, respectively.

The average increase in stiffness was found to be 3.5 and 3% in group T and TC, respectively.

For timbers with more deterioration, increase in strength was found to be up to 40% as compared

to 15% for timbers in good condition.

Based on strength increases in wood members with the use of FRP, we planned to improve the

strength and stiffness of discarded timber railroad ties with tensile GFRP combined with a carefully

selected primer material for bonding GFRP to wood.

24

3. MANUFACTURING OF COUPONS AND FULL-SCALE

COMPOSITE RAILROAD TIES

3.1. Introduction

GFRP composite coupons and composite ties with FRP shells were manufactured with Derakane 510A-

40 Epoxy Vinyl Ester Resin as the matrix and glass fiber/fabrics as the reinforcement.

Vinyl ester is compatible with glass fibers and was used for manufacturing process done in CFC-

WVU Laboratory. Initially, a layer of glass fabric was bonded to wood core using the resin and following

fabric layers were bonded to previous layers with the resin according to the required fiber/fabric

configuration.

3.2. Materials

Materials used for manufacturing of the composite ties consisted of, glass fibers, Derakane 510A-40

Epoxy Vinyl Ester Resin (by ASHLAND Company, Table 3.1) and discarded railroad oak wood ties.

Table 3. 1.Mechanical properties of Derakane 510A-40 resin and glass fiber

Mechanical properties Derakane 510A-40 Glass Fiber

Young’s Modulus (psi) 0.49 × 106 10.6 × 10

6

Tensile Strength (psi) 0.123 × 106 0.27 – 0.37 × 10

6

Poisson Ratio 0.38 0.22

Specific Gravity (lbs/in3) 0.044436 0.091763

3.2.1. Properties of Derakane 510A-40 (ASHLAND , 2011)

1. Derakane 510A-40 is a brominated Vinyl ester which is designed to offer fire retardance combined

with enhanced chemical resistance and toughness.

2. Derakane 510A-40 has higher fracture strain, mechanical properties, impact resistance, and fatigue

life than typical polyesters.

3. Since the fire retardance is achieved without additives, chemical resistance is maintained.

25

4. Derakane 510A-40 provides excellent resistance to caustic alkalis, hypochlorite bleaching

chemicals and hot water, as well as corrosion.

3.2.2. Properties of Glass Fibers

1. Glass fibers have higher ratio of surface area to weight.

2. The freshest and thinnest fibers are the strongest because the thinner fibers are more ductile. The

more the surface is scratched, the less the resulting tenacity.

3. Humidity is an important factor in the tensile strength of glass fibers. Moisture is easily absorbed and

can worsen microscopic cracks and surface defects, and lessen tenacity. Glass fibers have lower

moisture absorption.

4. Glass fibers have good resistance to fire and corrosion as well as feasibility for different environment.

5. Glass fibers are cheaper and significantly less brittle than carbon fibers but they are not as strong as or

as rigid as Carbon fibers.

6. Glass fibers have good resistance to electric conductivity and are used for electrical insulation.

3.3. Manufacturing Process

Following MSDS (Material Safety Data Sheet) procedures must be followed:

Inhaling resin vapors can cause dizziness. In order to resolve this issue, outdoor

manufacturing is highly recommended where there is plenty of fresh air flow and no rain. In

case of indoor processing, ventilation would be necessary. In both cases, using respirator is

highly recommended. Respirator/mask will prevent entry of minute fiber particles into lungs

while cutting the fibers.

Burning will be the consequence of contacting of resin and body skin. Having a long pair of

gloves on is recommended.

Since resin is in liquid form, safety glasses are needed to prevent accidental/possible entry of

cut-fiber particles into the eye.

26

3.3.1. Wood Core Preparation

3.3.1.1. Coupons

Wood cores for the coupon specimens were cut to dimensions of 0.725 in × 1.0 in × 6 in. Since these

cross sections were clean, just a few rounds of planing were carried out on the surfaces of the specimens.

3.3.1.2. Full-scale Railroad Ties1

Discarded railroad ties were used as wood core in the fabrication of the GFRP composite ties. Visible

damages such as holes, cracks, splits and even warping were found on those discarded oak ties (Figure

3.1) measuring approximately 7 in × 9.2 in × 102 in. Since the ties were stacked and exposed to

environment, considerable amount of dirt, mud and debris were present on the surface of the ties.

Figure 3. 1.Checks (splits) on discarded wood tie

In order to have a good bonding between wood and GFRP composite, having clean and debris-free

surface is recommended (Vick, 1999). To achieve surfaces with necessary specifications, wood core was

planed to the required surface by using Wood Planer. Overall, profile of wood cores had the average

dimensions of 6.7 in × 8.6 in × 102 in after planing. Because the ties were treated with creosote, planing

1 This core preparation is for the ties described in chapters 5 and 6. In chapter 4, only the importance and

effectiveness of Polyurethane influence between wood and GFRP was studied.

27

was done to reveal untreated surface of the wood. Creosote as a preservative drastically increases the

service life of wood ties; however, it adversely affects GFRP adhesion to wood.

The edges of wood cores were rounded to reduce stress concentration and improve bonding at sharp

corners (Figure 3.2).

Figure 3. 2.Sharp edge of a wood tie

Following above said preparation on each of the tie, wood core was mounted on the manufacturing frame.

3.3.2. Resin Preparation

Derakane 510A-40 resin was used with catalyst and accelerator combination of Methyl ethyl ketone

peroxide (MEKP) and Cobalt naphthenate. Catalyst is a substance that causes or accelerates a chemical

reaction without itself being affected. The proportions of MEKP and Cobalt naphthenate were about 0.8%

and 0.5% by weight.

28

First, MEKP was added to resin container. Then the contents were stirred completely so that the

transparent yellow color of resin changed to an opaque amber color. Then Cobalt naphthenate was added

and it was stirred until the color became more opaque.

Caution was taken to avoid adding (purring) MEKP on top of Cobalt naphthenate, which causes

smoke generation with heat release and possible mini explosion. In addition, it results in a poor resin mix

in terms of bonding.

3.3.3. Fibers Orientation

Eighteen ties were manufactured through hand lay-up process and fourteen were sent to TTCI facilities,

Pueblo, Colorado for field implementation and evaluation.

Three ties had 15 layers of unidirectional fibers oriented in 0°, 90° and ± 45° angles, here after

referred to as Configuration ‘A’ (Figure 3.3 (a)).

Fifteen ties had 22 layers of unidirectional fibers oriented in 0°, 90° and ± 45° angles, here after

referred to as Configuration ‘C’ (Figure 3.3 (c)).

Eight coupons were manufactured through two different configurations.

Four coupons were manufactured with respect to Configuration ‘A’ (Figure 3.3 (a)).

Other four coupon specimens had 19 layers of unidirectional fibers oriented in 0°, 90°

and ± 45° angles, here after referred to as Configuration ‘B’ (Figure 3.3 (b)). Table 4.2

shows for different fiber/fabric configurations details and number of layers.

Continuous Strand Mat (CSM) was observed to extremely kink and deform during tie wrap around (hand

lay-up) process and hence it was not used in the manufacturing.

29

Table 3. 2.Fiber/Fabric Configurations

Configuration No. of layers Fiber/fabric orientation

A 15 3[0°/90

°]/1[45

°/0

°/+45

°]/3[90

°/0

°]

B 19 4[0°/90

°]/1[45

°/0

°/+45

° ]/4[90

°/0

°]

C 22 4[0°/90

°]/2[45

°/0

°/+45

° ]/4[90

°/0

°]

a. Configuration A b. Configuration B c. Configuration C

Figure 3. 3.Different fiber/fabric configuration in composite ties

Table 3. 3.Configuration definition

Fiber angle Configuration A Configuration B Configuration C

0°/90

° (3 + 3) × 2 (4 + 4) × 2 (4 + 4) × 2

0°/± 45

° 3 × 1 3 × 1 3 × 2

Total 15 Layers 19 Layers 22 layers

30

3.3.4. Fiber Volume Fraction

Calculations for Configurations A, B and C with different thicknesses (Figure 3.4) are shown below.

Configuration A Configuration B Configuration C

Thickness (in): 0.1, 0.22 Thickness (in): 0.1 Thickness (in): 0.36

Figure 3. 4.Different fiber/fabric configurations with different thicknesses

Table 3. 4.Fiber volume fraction (Vf) calculations

Configuration A Configuration B Configuration C

No. of unidirectional

fabrics 15 15 19 22

Avg. thickness (in) 0.1 0.22 0.1 0.36

Total density of glass

fabrics (oz/sq.yd) 111 111 141 163

Vol. of composite part

(in3)

130 336 130 466

Fiber volume (in3) 75.60 75.60 95.76 110

Fiber volume fraction 58.34% 26.52% 73.89% 23.77%

Resin vol (in3) 54 261 34 355

Weight of resin (lbs) 2.4 11 1.5 15

31

Table 3. 5.Typical physical properties of GFRP composite

Configuration

Average

thickness

(in)

No. of

layers

Weight

of resin

(lbs)

Fiber

volume

fraction

Manufactured

in Chapter

A 0.1 15 2.4 58.34% Coupon 4

0.26 15 11 26.52 % Full Scale Tie 5 & 6

B 0.1 19 1.5 73.89 % Coupon 4

C 0.36 22 15 23.77 % Full Scale Tie 5 & 6

3.3.5. Polyurethane (primer)

The advantage of Polyurethane is discussed in Chapter 4. In order to have good adhesion between GFRP

and wood, Polyurethane was applied within 24 hours before wrapping. Polyurethane was applied on the

ties # 1 to 17 and coupons # 2, 6, 7 and 8. Composite tie # 18 and coupons # 1, 3, 4 and 5 were

manufactured without Polyurethane.

3.3.6. Fabricating of Wood-GFRP Coupons

Preparation of wood for wood-GFRP coupons is explained in section 3.4.1.1. However, coupon

specimens were easier to fabricate than tie specimens. Due to smaller dimension in coupons, higher fiber

volume fraction was achieved during wood-GFRP specimens.

3.3.7. Fabricating of Full-scale GFRP Composite Railroad Ties

The wood core was wrapped using continuous glass fabric and resin, with required fiber/fabric orientation

and configuration. Since manufacturing was done by hand lay-up method relatively, high void ratio is

computed when compared to other manufacturing processes. Successive layers of wraps were gently

rolled over previous layers to release and reduce any entrapped air as much as possible and achieve better

bonding.

3.3.8. Curing and Monitoring of Composite Ties

Curing of the composite shell is affected by temperature. Warmer ambient temperature, results in lower

cure time. Based on laboratory observations, 74 ° to 80 °F provided a good ambient temperature range for

curing.

32

Because of the viscosity of vinyl ester, resin flow was rapid in the beginning and was slow later due

to addition of layers and passage of time. Initially, dripping was noticed from the mounted specimen and

it was turned 180 degrees to prevent resin loss and void formation (Figure 3.3). Curing was monitored

until the dripping was stopped. Without rotation, resin would accumulate only on one side of the mounted

specimen (Figure 3.4). Generally 4 hours were needed for a specimen to be manufactured and cured.

Figure 3. 5.Cured full-scale composite tie mounted on manufacturing frame

Figure 3. 6.Specimen cured without regular rotation showing resin accumulation at bottom

33

3.4. GFRP-Wood Composite Specimens

The hand lay-up process was successfully used to manufacture discarded rectangular wood ties having

defects such as holes and warping. Results in this research indicate the effects of Polyurethane primer,

mechanical properties of wood (in full-scale composite railroad ties and coupons) and fiber/fabric

configuration of GFRP composite on the final Wood-GFRP product.

Polyurethane application on the surface of wood before wrapping of glass fabrics proved to be

critical in producing good bonding between wood and GFRP. Coupons with Polyurethane

provided better values of deflection, MOR and static bending strength than those without

Polyurethane. In terms of full-scale railroad ties with Polyurethane, similar results were observed.

Since GFRP is stiffer than wood core (in composite ties), addition of in GFRPs lead to better

mechanical properties of wood ties wrapped with GFRP. Accordingly, full-scale composite

railroad ties with more glass fiber layers (configuration ‘C’ with 22 layers vs. configuration ‘B’

with 19 layers) generally had higher flexural rigidity, higher MOE2, MOR

3 and static bending

strength than of those with fewer layers which are discussed in chapters 5, 6 and 7.

3.5. Companies Producing Composite Ties

As compared to wood ties, composite ties offer the advantage of being decay resistant and durable.

Composite ties last longer than wood ties. A number of companies producing composite ties using

recycled plastics, resins and rubber listed below. The result of this study was compared to composite ties

of commercially produced ties by IntegriCo, Tietek, Dynamic and PRT companies.

2 Modulus of Elasticity

3 Modulus of Rupture

34

Table 3. 6.Mechanical properties of different companies’ products

Material and strength

properties

IntegriCo

Composite Tie

Tietek

Composite Tie

Dynamic

Composite Tie

PRT’s

Composite

Tie

Materials Plastic waste Plastic &, rubber

waste, fiberglass

Recycled

polyethylene,

rubber, steel and

concrete.

Plastics and

molded metal

parts

Length (in) 102 102 102 102

Width (in) 9 9 9 9

Depth (in) 7 7 7 7

Moment of inertia

(in4)

257.25 257.25 257.25 257.25

Flexural Rigidity

(psi) 319 303 321 368

MOE

(× 106 psi)

1.24 > 1.18 1.25 1.431

Static bending strength

(kips-in) 198 147 191 247

MOR

(psi) 2700 2000 2600 3356

35

4. EFFECT OF POLYURETHANE ON ADHESSION

BETWEEN WOOD AND GFRP

4.1. Introduction

In this chapter, rupture tests on both coupons and GFRP composite ties were performed. Before

manufacturing of full-scale composite railroad ties, interaction between GFRP composite and wood with

and without the application of polyurethane primer was studied on GFRP-wood coupons. The wood in the

coupon specimens had two different moisture contents of 40% and 12%. For the evaluation of composite

adhesion to wood, polyurethane was applied on clean and debris-free wood bottom surface. Two types of

fabric configurations were used to prepare those coupon specimens. After curing, they were tested for

rupture test. Similarly, two full-scale composite ties, with the same fabric configuration with and without

polyurethane were manufactured and tested.

4.2. Objective

The objective was to test and evaluate the maximum bending load (rupture test) for each sample (coupons

and full scale composite ties) under three-point bending with and without using of polyurethane primer.

4.3. Scope

The three-point static bending rupture tests were carried out on eight coupon specimens and two

composite railroad ties. The aim of these tests was to evaluate and determine the ultimate load and

maximum bending stress for specimens. The span lengths for coupon samples and full-scale ties were 4 in

and 90 in, respectively. The strains at bottom (tension zone) and deflections at mid-spans were measured

and recorded for each specimen. Two types of fabric configurations used in this evaluation and classified

in chapter 4 are listed in Table 4.1.

Table 4. 1.Fiber/fabric Configuration of Specimens

Configuration No. of layers Fiber/fabric orientation

A 15 3[0°/90

°]/1[45

°/0

°/+45

°]/3[90

°/0

°]

B 19 4[0°/90

°]/1[45

°/0

°/+45

°]/4[90

°/0

°]

36

4.4. Test Description

4.4.1. Coupons

Tests were conducted using CFC-WVU lab facilities. Instron 8501 machine wedge shaped simple

supports were used with a span of 4 in and mid-point loading for testing the coupon specimens (Figure

4.1).

Figure 4. 1.Three point bending test for coupons

4.4.2. Full-scale Composite Railroad Ties

The simply supported boundary condition for 90 in span tie specimens was provided by steel round stock

fixed on the concrete supports. The center to center 90 in supports lead to 6 in overhang for ties (90 + 6 +

6 = 102 in). Load was applied at the middle of specimens by hand pump operated hydraulic jack clamped

to a steel frame (Figure 4.2).

37

Figure 4. 2.Schematic of three point bending test configuration for composite ties

4.5. Instrumentation and Measurements

Test measurements and data collection consisted of: Loads, Strains and Deflections. Uniaxial strain gages

were installed at the bottom center of specimens (tension zone). For calculation, maximum tensile strain

and maximum deflection at mid-span were considered. Strain smart equipment and software of Instron

8501 Universal Testing Machine was used to collect and measure the data (loads and strain) for coupon

specimens. And for composite ties, Strain Smart software program was used to collect Stress vs. Strain

and Load vs. Deflection data using Data Acquisition system. Data for flexural rigidity evaluation of ties

was collected under static 2 kip load.

4.6. Test Procedure

4.6.1. Three Point Bending Test for MOR Evaluation-Coupon Tests

The test specimen was placed on the wedge shaped support of the Instron machine with the overhang of 1

in at each support and the span of 4 in. Before any load application, bottom strain and load values were

calibrated (zeroed). Loading was centered on top of the specimens and applied through auto-controlled

hydraulic system of the Instron machine until rupturing of the specimens.

4.6.1.1. Wood cross section properties

Dimensions of the wood coupons are shown in Table 4.2. The transformed moment of inertia calculations

for both fiber fabric configurations are as follows:

38

Table 4. 2.Wood coupon dimensions

Wood Dimensions Specimen

Length (in) 6.0

Width (in) 1.0

Thickness (in) 0.725

4.6.1.2. GFRP composite

GFRP composite shells (Table 4.3) having two different fiber orientations were manufactured on prepared

surface of wood coupon specimen. Polyurethane was applied on four wood coupon specimen and other

four specimens were manufactured without Polyurethane application.

Table 4. 3.GFRP dimensions

Configuration No. of

layers Fabric Orientation

Avg. thickness

(in)

Width

(in)

A 15 3[0°/90

°]/1[45

°/0

°/+45

°]/3[90

°/0

°] 0.10 1.0

B 19 4[0°/90

°]/1[45

°/0

°/+45

°]/4[90

°/0

°] 0.10 1.0

Tensile modulus of GFRPs with different fiber/fabric configuration was measured using Instron

1000HDX machine after installing of strain gage and extensometer (Figure 4.3). The GFRP coupons were

tested under the rate of 0.1 in/min. Table 4.4 shows the Young’s modulus of GFRP coupons with

different fiber/fabric configurations.

1. Coupons with installed strain gages

2. Ultimate tension failure of a coupon

Figure 4. 3. Tension testing of GFRP coupons with different fiber/fabric configurations

39

Table 4. 4. Young’s modulus of GFRP coupons

Specimen

ID Configuration

Load at

peak

load

(kips)

Strain

gage

modulus

(Msi)

Gage

Modulus

average

(Msi)

Extensometer

modulus

(Msi)

Modulus

average

(Msi)

1 C 6951 N/A

2.08

2.19

2.23

2 C 8204 1.69 1.91

3 C 8294 N/A 2.43

4 C 6663 2.24 2.24

5 C 7690 2.32 2.40

6 A 7662 1.99

1.82

2.02

2.10

7 A 7919 1.76 2.07

8 A 8449 2.12 2.29

9 A 8274 1.72 2.05

10 A 7645 1.53 2.09

Note: The coupons tested were cut from full-scale composite ties with fabric configuration ‘C’ and ‘A’.

Based on thicknesses of FRPs in wood-GFRP coupons (0.1 in), Young’s moduli for different fiber/fabric

configurations were calculated and compared through inplane stiffness and inverse inplane stiffness

matrices (Barbero, 1998). The calculations can be found in chapter 7, sections 7.1 and 7.2.

4.6.1.3. Sectional properties

Dimensions of Wood-GFRP composite coupon sections after binding fiber/fabric configuration

(configuration ‘A’ or ‘B’) are shown in Table 4.5.

Table 4. 5.Wood-GFRP composite specimens dimension

Configuration Total thickness

(in)

Width

(in)

Length

(in)

A 0.825 1.0 6

B 0.825 1.0 6

40

4.6.1.3.1. Calculations of transformed moment of inertia (It)

1. Configuration ‘A’

Figure 4. 4.Configuration ‘A’ with 15 layers

Elastic Modulus of the Composite (EComp) from chapter 7, section 7.1:

EComp = 3.71 × 106 psi

EW = 1.29 × 106 psi

Modular Ratio: η =

(4.1)

= 2.88

Figure 4. 5.Transformed cross section for both fiber/fabric configurations (15 & 19 layers)

41

Centroid distance of the Composite cross section from bottom of the specimen

C = ∑

∑ (4.2)

= 0.35 in

Distance between Neutral Axis depth and composite centroid

d = 0.29 in

Area of composite on the bottom of the cross section

Af = (1 × 0.1) = 0.1 in2

Distance between Neutral Axis depth and wood centroid

D = 0.11 in

Transformed Moment of Inertia

It = Iwood + Icomp

Iwood =

+

(4.3)

=

= 0.039 in

4

Icomp =

(4.4)

= = 0.023 in4

It = 0.067 in4

42

2. Configuration ‘B’

Figure 4. 6.Configuration ‘B’ with 19 layers

Elastic Modulus of the Composite (EComp) from chapter 7, section 7.2:

EComp = 4.78 × 106 psi

EW = 1.29 × 106 psi

Modular Ratio: η =

(4.5)

= 3.71

Centroid distance of the Composite cross section from bottom of the specimen

C = ∑

∑ (4.6)

= 0.32 in

Distance between Neutral Axis depth and composite centroid

d = 0.27 in

Area of composite on the bottom of the cross section

Af = (1 × 0.1) = 0.1 in2

43

Distance between Neutral Axis depth and wood centroid

D = 0.13 in


It = Iwood + Icomp

Iwood =

+ (4.7)

=

= 0.044 in

4

Icomp = (4.8)

= = 0.026in4

It = 0.073 in4

Table 4. 6.Transformed moment of inertia for different fiber/fabric configurations

Fiber/fabric

configuration

Fiber volume

fraction (Vf) ECom (psi) EW (psi)

Modular

ratio (η) It (in

4)

A 58.34% 3.71 × 106 1.29 × 10

6 2.88 0.067

B 73.89% 4.78 × 106 1.29 × 10

6 3.71 0.073

4.6.2. Composite Railroad Ties Three Point Bending Test for MOE and

MOR Evaluating

For the purpose of MOE, specimens were simply supported with a span length of 90 in. Uniaxial strain

gages were installed and LVDT was mounted at the bottom of composite ties and load cell was positioned

and centered at the top of the specimen. The strain gages, load cell and LVDT were zeroed using Strain

Smart software and Data Acquisition System. Two kip loading was applied to the specimens in two

loading and unloading test cycles.

For the purpose of MOR, all the procedures discussed above were followed for conducting.

Loading was applied until of failure specimens. The load, deflection and strain data were monitored and

collected.

44

4.6.2.1. Wood cross section properties

In in this section, the effect of Polyurethane on adhesion between wood and composite was evaluated.

Neither wood planing, nor edge rounding was performed on the ties. However, however planing and

edge rounding operations were performed on all ties described in chapters 5 and 6.

Table 4. 7.Wood ties dimensions

Sample

dimensions

Tie # 17 with

polyurethane

Tie # 18 without

polyurethane

Length (in) 102 102

Width (in) 7.6 7.55

Height (in) 6.9 6.8

4.6.2.2. GFRP full-scale composite ties

Discarded railroad ties with clean appearance were wrapped with GFRP Composites with configuration

‘A’. Before wrapping the composites, Polyurethane was applied on just one wood tie and other composite

tie was manufactured without applying Polyurethane.

Table 4. 8.Fiber/fabric configurations

Configuration No. of

layers Fiber/fabric orientation

Avg.

thickness (in)

A 15 3[0°/90

°]/1[45

°/0

°/+45

° ]/3[90

°/0

°] 0.26

4.6.2.3. Sectional properties

The dimensions of the two GFRP Composite ties are as follows. Transformed moment of inertia for tie #

17 is calculated as follows. Calculation of transformed moment of inertia of tie # 18 can be found in

Appendix ‘B’.

Table 4. 9.GFRP composite tie average dimension

Sample dimensions Tie # 17 Tie # 18

Length (in) 102 102

Width (in) 8.25 8.20

Height (in) 7.55 7.45

45

4.6.2.3.1. Calculations of transformed moment of inertia (It)

Configuration ‘A’

Figure 4. 7.Configuration ‘A’ with 15 layers

Elastic Modulus of the Composite (EComp) from Table 5.4:

EComp = 2.10 × 106 psi

Tie # 17

EW = 1.18 × 106 psi

Modular Ratio: η =

(4.9)

= 1.79

Figure 4. 8.Full-scale composite tie profile

46

Depth of Neutral Axis from the center of the top flange of the Composite

d = 3.61 in

Area of the cross section of the top and the bottom flange (composite parts)

Af = 2(8.26 × 0.33) = 5.45 in2

Transformed moment of inertia

It =

(4.10)

=

= 336 in

4

Table 4. 10.Transformed Moment of Inertia for different fiber/fabric configurations

Tie

ID

Fiber

configuration

Fiber

volume

fraction (Vf)

EComp

(psi) EW (psi)

Modular

ratio (η) It

(in4)

Dimension:

Length × Width

× Height

17 A 26.52% 2.10 × 106 1.18 × 10

6 1.79 336 102 × 8.25 × 7.55

18 A 26.52% 2.10 × 106 1.01 × 10

6 2.06 340 102 × 8.20 × 7.45

4.7. Test Results

4.7.1. Coupons

The ultimate load and maximum deflection in failure of the coupons was measured under three point

bending test conditions. Calculation of static bending strength and MOR of specimens for fiber/fabric

configuration ‘A’ (Table 4.3) for specimens # 8 and 1 (with and without Polyurethane, respectively) is

shown below. Calculations for the rest of the coupons can be found in Appendix ‘B’.

4.7.1.1. Calculation of bending stress

Figure 4. 9.Schematic of three point bending test for coupons

47

Bending Stress: σ =

(4.11)

Where:

Bending Moment: M =

(4.12)

Point load: P

Span length: L= 4 in.

Neutral Axis distance to farthest tensile fiber: C = ∑

∑ (4.13)

Transformed Moment of Inertia: It

4.7.1.2. Coupon # 6 (with polyurethane & 15 layers)

Figure 4. 10.Load vs. Deflection graph for Coupon # 6

C = 0.34 in

It = 0.067 in4

The maximum load to failure: P = 915 lbs

Static Bending Strength: M =

= 915 lbs–in

MOR: σ =

= 4760 psi

0

200

400

600

800

1000

1200

0 0.2 0.4 0.6 0.8

Load (lbs)

Deflection (in)

Load vs. Deflection

48

4.7.1.3. Coupon # 2 (without polyurethane & 15 layers)

Figure 4. 11.Load vs. Deflection graph for Coupon # 2

C = 0.34 in

It = 0.067 in4



= 688 lbs–in

MOR: σ =

= 3577 psi

0

100

200

300

400

500

600

700

800

0 0.1 0.2 0.3 0.4 0.5 0.6

Load (lbs)

Deflection (in)

Load vs. Deflection

49

Table 4. 11.Summary of test results of Wood-GFRP composite coupons

Coupon

ID

Fiber/

fabric

config.

PU* Moisture

content

Transformed

moment of

inertia (in4)

Static

bending

strength

(lbs-in)

MOR

(psi)

Deflection

at failure

(in)

Deflection

at

reference

load (in)

1 A No 40% 0.067 254 1321 0.24 0.134

2 A No 12% 0.067 687 3577 0.38 0.038

3 B No 40% 0.073 819 3627 0.54 0.054

4 B No 12% 0.073 711 3150 0.31 0.060

5 A Yes 40% 0.067 885 4607 0.56 0.061

6 A Yes 12% 0.067 915 4760 0.63 0.084

7 B Yes 40% 0.073 935 4141 0.51 0.055

8 B Yes 12% 0.073 986 4369 0.52 0.054

Note: Fiber/fabric configuration ‘A’ has 15 and fiber configuration ‘B’ has 19 layers (Table 3.2); PU-

Polyurethane.

Figure 4. 12.Static bending strength of Wood-GFRP coupons

0

200

400

600

800

1000

1200

Moment (ibs - in)

Static Bending Strength

50

Figure 4. 13.MOR testing of Wood-GFRP coupons

Figure 4. 14.Deflection at failure of GFRP composite coupons

0500

100015002000250030003500400045005000

MOR (psi)

Modulus of Rupture

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Deflection (in)

Deflection at Failure

51

Figure 4. 15.Deflection at reference load of GFRP composite coupons

4.7.1.4. Evaluation of the effect of polyurethane primer

Static bending strength and MOR of specimens with polyurethane was higher than those in specimens not

coated with polyurethane (930 kips-in vs. 617 kips-in) (Figure 4.12). At failure and similar loads,

specimens with Polyurethane provided higher deflection than those without Polyurethane, indicating the

effectiveness of polyurethane in bonding FRP to timber (Figs. 4.14 & 4.15).

During testing, specimens with Polyurethane showed bond integrity between wood and GFRP

while the ones without Polyurethane showed de-bonding between wood and GFRP during failure (Figure

4.16).

Polyurethane coating helped bonding between wood and GFRP so that the compositeness between

wood and GFRP was facilitated. At the interface of wood and GFRP, Polyurethane acted like shear studs

between concrete and steel in a composite deck.

0

0.020.04

0.060.08

0.1

0.12

0.14

0.16

Deflection (in)

Deflection at Reference Load (150 lbs)

52

1. Polyurethane was applied (GFRP plate still

attached)

2. Polyurethane was not applied (GFRP plate

detached)

Figure 4. 16.Coupons with and without Polyurethane application

4.7.1.5. Evaluation of the effect of fiber volume fraction

Static bending strength and MOR of the coupons with more layers were higher than those of coupons

with fewer layers (Figure 4.12). Average deflection at failure load and reference load of specimens with

fewer layers were more than that of specimens with more layers (Figs. 4.14 & 4.15).

It was found that using more number of layers resulted in slightly higher voids and more resin drifting

away from the wood-GFRP interface due to gravity

4.7.1.6. Evaluation of the effect of moisture content on specimens

Static bending strength and MOR of the specimens with lower moisture (12%) content were higher than

those with higher moisture content (40%) with similar fiber/fabric configuration. Deflection at failure of

the specimens with lower moisture content with similar fiber/fabric configuration was higher than

specimens with higher moisture content.

4.7.2. Full-scale Composite Ties

From the data collected under three point bending tests, flexural rigidity, stiffness and static bending

strength of both ties with and without polyurethane application were evaluated.

53

4.7.2.1. Calculation of flexural rigidity and bending stress

Figure 4. 17.Schematic of coupon loading

Bending stress: σ =

(4.14)

Where:

Bending Moment: M =

(4.15)

Point load: P



∑ (4.16)


54

4.7.2.2. Tie # 17 (with Polyurethane & 15 layers)

1. trial # 1

2. trial # 2

Figure 4. 18.Stress vs. Strain graph for GFRP composite tie # 17

C = 3.78 in

It = 336 in4

EI = 1.31 × 106 × 336 = 4.41 × 10

8 lbs-in

2

Figure 4. 19.Load vs. Deflection graph for composite tie # 17

y = 1.3132x - 7.0969

0

100

200

300

400

500

600

0 100 200 300 400 500

Stress vs. Strain

y = 1.3164x + 9.1877

0

100

200

300

400

500

600

0 200 400 600

Stress (psi)

Strain (µԑ)

Stress vs. Strain

0

5000

10000

15000

20000

25000

0 0.5 1 1.5 2 2.5 3 3.5

Load vs. Deflection

55

Maximum load to failure: P = 23.60 kips


= 531 kips–in

MOR: σ =

= 5982 psi

4.7.2.3. Tie # 18 (without Polyurethane & 15 layers)

1. trial # 1

2. trial # 2

Figure 4. 20.Stress vs. Strain graph for GFRP composite tie # 18

C = 3.73 in

It = 340 in4

EI = 0.45 × 106 × 340 = 1.56 × 10

8 lbs-in

2

Note: The difference between stiffness (of the slopes: (0.45 × 106 psi vs. 0.32 × 10

6 psi) of the stress

vs. strain curves) showed that Polyurethane is essential to provide the compositeness. Without it, the

stiffness value dropped by about 29% (Figures. 4.19 & 4.20).

y = 0.4591x + 8.5568

0

100

200

300

400

500

600

0 500 1000 1500

Stress (psi)

Strain (µԑ)

Stress vs. Strain

y = 0.3227x + 9.6911

0

50

100

150

200

250

300

350

0 500 1000 1500

Stress vs. Strain

56

Figure 4. 21.Load vs. Deflection graph for composite tie # 18



= 246 kips–in

MOR: σ =

= 2706 psi

Table 4. 12.Summary of test results of composite ties (with/without polyurethane)

Mechanical & Strength Properties Tie # 17

(PU)

Tie # 18

(No-PU)

Length (in) 102 102

Width (in) 7.6 7.55

Height (in) 6.9 6.8

Moment of inertia (in4) 336 340

MOE ( × 106 psi) 1.31 0.459

Flexural rigidity ( × 106 lbs-in

2) 441 156

Failure load (kips) 23.60 10.96

MOR (psi) 5982 2706

Static bending strength (kips-in) 531 246

Deflection at failure (in) 1.386 3.716

0

2000

4000

6000

8000

10000

12000

0 1 2 3 4

Load (lbs)

Deflection (in)

Load vs. Deflection

57

Figure 4. 22.Flexural rigidities of GFRP composite ties with/without Polyurethane

Figure 4. 23.Static bending strength of GFRP composite with/without Polyurethane

4.7.2.4. Evaluation of flexural rigidity of GFRP composite ties

The test data indicated that the GFRP tie with polyurethane (tie # 17) had higher flexural rigidity than the

other tie without polyurethane by a factor of 2.8 (441× 106 lbs-in

2 vs. 156 × 10

6 lbs-in

2).

0

50

100

150

200

250

300

350

400

450

500

Tie # 17 (PU) Tie # 18 (No-PU)

(1.0x106 lbs-in2)

Flexural Rigidity (EI)

0

100

200

300

400

500

600

Tie # 17 (PU) Tie # 18 (No-PU)

Moment (kips-in)


58

4.7.2.5. Evaluation of static bending strength and MOR of GFRP composite ties

The MOR of composite tie with polyurethane was higher than that of the composite tie without

polyurethane by a factor 2.2 (5982 psi vs. 2706 psi). Static bending strength of tie # 17 was higher than

that of the tie # 18 by a factor of 2.1 (531 kips-in vs. 246 kips-in).

The reason for better functioning of tie # 17 was that its cross section had a better bonding than

composite when comparing to tie # 18 due to the application of polyurethane primer.

4.8. Conclusions

1. The average static bending strength of coupons with Polyurethane was higher than that of

coupons without Polyurethane by a factor of 1.5 (930 lbs-in vs. 617 lbs-in).

2. The average static bending strength of coupons with Polyurethane having 12% moisture content

was higher than that of coupons having 40% moisture content by about 4.4% (950 lbs-in vs. 910

lbs-in).

3. The average static bending strength of coupons with 19 layers was slightly higher than that of

coupons with 15 layers by about 6.7% (960 lbs-in vs. 900 lbs-in) (with Polyurethane).

4. The average MOR of coupons with Polyurethane was higher than that of coupons without

Polyurethane by a factor of 1.5 (4469 psi vs. 2919 psi).

5. The average MOR of coupons with 12% moisture content was slightly higher than that of

coupons 40% moisture content by about 4.3% (4564 psi vs. 4374 psi) (with Polyurethane).

6. The average MOR of coupons with 15 layers was higher than that of coupons with 19 layers by

about 10% (4683 psi vs. 4255 psi) (with Polyurethane).

7. The average deflection at failure of coupons with Polyurethane was higher than that of coupons

without Polyurethane by a factor of 1.51 (0.555 in vs. 0.368 in).

8. The average deflection at failure of coupons with 15 layers was higher than that of coupons with

19 layers, due to higher void content, by about 1.15 (0.595 in vs. 0.515 in).

59

9. After one and a half year, coupons with polyurethane after testing showed both wood and GFRP

bond layers being bonded whereas the ones without Polyurethane showed de-bonding between

wood and GFRP (Figure 4.16).

10. The flexural rigidity of the tie with polyurethane primer coating was higher than that of the tie

without Polyurethane by a factor of 2.8 (441× 106 lbs-in

2 vs. 156 × 10

6 lbs-in

2).

11. The MOR of composite tie with polyurethane primer coating was higher than that of the

composite tie without polyurethane by a factor of 2.2 (5982 psi vs. 2706 psi).

12. The static bending strength of tie with polyurethane coating was higher than that of the tie

without Polyurethane by a factor of 2.1 (531 kips-in vs. 246 kips-in).

13. Bond failure at initial stage of loading was observed for tie without polyurethane (tie # 18).

Results of the evaluation described in this chapter indicated that Polyurethane is very effective in

facilitating full composite behavior between wood and GFRP.

60

5. EVALUATING FLEXURAL RIGIDITIES OF DISCARDED

WOOD TIES WITH AND WITHOUT FRP SHELL

5.1. Introduction

Railroad ties with discarded wood core and FRP composite shell were tested in CFC-WVU laboratory to

determine the gains in strength properties through FRP shell. In this regard, tie stiffness is dependent on

both fiber configuration and (wood) core size. Initially, Young’s modulus of each discarded wood tie was

evaluated under three point bending test with respect to two different fiber configurations. For each

composite tie, three point bending test was conducted two times to determine their flexural rigidity. The

load was kept to a minimum 2 kips to prevent any load related damage.

5.2. Objective

The objective was to test and evaluate flexural rigidity of full-scale composite ties under three point

bending loads.

5.3. Scope

Three point bending tests were performed on sixteen full scale GFRP Composite ties to determine their

flexural rigidity. Three point static bending tests were conducted by applying 2kips load at mid-span with

a clear span of 90 in. Strains at top and bottom of the ties and deflections at mid span were measured for

each specimen.

Table 5. 1.Fiber/fabric configuration of specimens

GFRP

composite

ties ID

Fiber/fabric

configuration4

Fiber/fabric orientation No. of

layers

1-15 C 4[0°/90

°]/2[45

°/0

°/+45

°]/4[90

°/0

°] 22

16 A 3[0°/90

°]/1[45

°/0

°/+45

°]/3[90

°/0

°] 15

4 Fiber/fabric configurations are provided in chapter 3, table 3.2, and section 3.4.3.

61



fixed on the concrete supports. The center to center 90 in supports lead to 6 in overhang for ties (90 + 6 +

6 = 102 in). Load was applied at the middle of specimens by hand pump operated hydraulic jack clamped

to a steel frame (Figure 5.1).

Figure 5. 1.Schematic of three point bending test configuration for composite ties

5.5. Instrumentation

Test measurements and data collection consisted of: Loads, Strains and Deflections. Uniaxial strain gages

were installed at the bottom center of specimens (tension zone). For calculation, maximum tensile strain

and maximum deflection at mid-span were considered. Strain smart equipment and software of Instron

8501 Universal Testing Machine were used to collect and measure the data (loads and strain) for coupon

specimens. And for composite ties, Strain Smart software program was used to collect Stress vs. Strain

and Load vs. Deflection data using Data Acquisition system. Data for flexural rigidity of ties was

collected under static 2 kip load.

5.6. Test Procedure

Test procedure was similar for all specimens. Strain gage, load and LVDT values were zeroed by using

the Strain Smart Software and Data Acquisition System. Specimens were tested with a span length of 90

in. with the overhang being addition 6 in on each side. Center of the hydraulic was aligned with the center

of the specimen. Load cell was placed on the top at the center of the specimen and LVDT was arranged at

the bottom of the mid span. Then, the 2 kip load was gradually applied to the specimen using hydraulic

62

jack (Figure 5.2). The Stress vs. Strain and Load vs. Deflection data were collected. Above procedure was

repeated two times for each specimen to ensure proper functioning of strain gages, LVDT and wire

connectivity given. Stress vs. Strain and Load vs. Deflection plots were compared to obtain MOE from

both approaches.

Figure 5. 2.Three point bending test setup

5.7. Sectional Properties

The dimensions of the GFRP Composite ties are shown in Table 5.2. Transformed moments of inertia for

tie # 4 and # 16, with configuration ‘C’ and configuration ‘A’, respectively (Table 5.1); were calculated as

follows and summarized in Table 5.3. Calculations of transformed moment of inertia of other ties can be

found in Appendix ‘C’.

Table 5. 2.GFRP Composite Ties Dimensions

Specimen

dimensions Tie # 4 Tie # 16

Length (in) 102 102

Width (in) 9.9 9.20

Height (in) 7.7 7.31

63

5.7.1. Calculations of Transformed Moment of Inertia (It) for GFRP Composite Ties

Calculation of transformed moment of inertia for ties 4 and 16 are as follows. Calculation for other ties

can be found in Appendix ‘C’.

1. Configuration ‘C’

Figure 5. 3.Configuration C


EComp = 2.23 × 106 psi

Tie # 4

EW = 1.28 × 106 psi

Modular Ratio: η =

(5.1)

= 1.75

64

Figure 5. 4.Composite cross section


d = 3.9 in


Af = 2(9.75 × 0.39) = 7.59 in2


It =

(5.2)

=

= 401 in

4

2. Configuration ‘A’

Figure 5. 5.Configuration A

65


EComp = 2.10 × 106 psi

Tie # 16

EW = 1.14 × 106 psi

Modular Ratio: η =

(5.3)

= 1.84

Figure 5. 6.Composite cross section


d = 3.66 in


Af = 2(9.19 × 0.28) = 5.13 in2


It =

(5.4)

=

= 338 in

4

66

Table 5. 3.Transformed moment of inertia It for different fiber/fabric configurations

Tie

ID

Fiber/fabric

configuration

Fiber

volume

fraction

EComp EW

(× 106 psi)

Modular

ratio It

Dimension: Length

× Width × Height

Vf psi psi η in4 in × in × in

1

C 23.77% 2.23 × 106

1.25

1.79 408 102 × 9.75 × 7.60

2 0.871 2.57 490 102 × 9.90 × 7.70

3 1.27 1.76 396 102 × 10.0 × 7.40

4 1.28 1.75 401 102 × 9.75 × 7.80

5 1.21 1.85 412 102 × 9.75 × 7.80

6 1.17 1.91 429 102 × 10.0 × 7.70

7 0.880 2.54 495 102 × 9.85 × 7.70

8 1.01 2.21 458 102 × 9.90 × 7.80

9 1.24 1.80 415 102 × 9.70 × 7.70

10 1.27 1.76 376 102 × 9.70 × 7.50

11 1.24 1.80 363 102 × 9.70 × 7.40

12 1.17 1.91 365 102 × 8.40 × 7.60

13 1.10 2.03 432 102 × 9.45 × 7.65

14 0.900 2.48 411 102 × 8.50 × 7.60

15 1.29 1.73 339 102 × 8.80 × 7.60

16 A 26.52% 2.10 × 106 1.14 1.84 338 102× 9.20 × 7.30

5.8. Test Results

Stress vs. Strain and Load vs. Deflection plots obtained under three-point bending tests were used to

evaluate and measure the flexural rigidity of ties. Ties # 4 and 16 were considered as representatives of

fiber/fabric configuration ‘C’ and ‘A’, respectively (Table 3.1). Calculation of flexural rigidity for other

ties can be found in Appendix ‘D’.

5.8.1. Calculation of Flexural Rigidity through Bending Stress

Figure 5. 7.Schematic of deflected tie under three point bending test

67


(5.5)

Where:

Bending Moment: M =

(5.6)

Point load: P



∑ (5.7)

Transformed moment of inertia: It

Figure 5. 8.Stress vs. Strain graph for tie # 4

Figure 5. 9.Stress vs. Strain graph for tie # 16

C = 3.90 in.

It = 401 in4

EI = 2.64 × 106 × 401 = 10.61 × 10

8 lbs-in

2

C = 3.65 in.

It = 338 in4

EI = 1.54 × 106 × 338 = 5.21 × 10

8 lbs-in

2

y = 2.6465x - 6.5246

0

100

200

300

400

0 50 100 150

Stress (psi)

Strain (µԑ)

Stress vs. Strain

y = 1.5433x + 0.8995

0

100

200

300

400

500

600

0 100 200 300 400

Stress (psi)

Strain (µԑ)

Stress vs. Strain

68

Table 5. 4.Flexural rigidity of GFRP composite ties

Tie

ID

Fabric/fiber

configuration

MOE

(× 106 psi)

Transformed

moment of inertia

(in4)

Flexural rigidity (EI)

(× 106 lbs-in

2)

1

C

1.76 408 720

2 1.38 490 677

3 2.06 396 817

4 2.65 401 1061

5 2.72 412 1121

6 2.66 429 1139

7 1.11 495 548

8 1.33 458 610

9 1.87 415 777

10 1.79 376 671

11 1.68 363 609

12 1.18 365 431

13 2.20 432 950

14 1.42 411 583

15 2.16 339 730

16 A 1.54 338 521

Note: See Appendix ‘D’ for MOE test details for the rest of the ties. Flexural rigidity of the

discarded wood ties and other composite ties are provided in Figure 5.10.

Figure 5. 10.MOE testing for flexural rigidities of discarded wood ties vs. GFRP ties

0

200

400

600

800

1000

1200

EI (× 106 lbs-in2)

Wood

GFRP

69

5.8.2. Evaluation of Flexural Rigidity of the Two Configurations

Ties with fiber/fabric configuration ‘C’ (more layers) mostly have higher flexural rigidity than ties with

fewer layers (configuration ‘A’). In this regard, increasing the number of layers lead to stronger and

stiffer cross sections. As expected, ties with more layers carried higher bending moments or bending

stresses. Tie # 6 had the highest flexural rigidity because this tie and few other ties (#4, 5) had minimum

distress in terms of cracking, splitting and knots. Test results show significant increase in mechanical

properties of discarded wood ties with the help of composite wraps.

5.9. Conclusions

1. Using additional layers of (0°/90

°/+45

°) GFRP fabrics (configuration ‘C’ vs. ‘A’) lead to higher

stiffness.

2. The average flexural rigidity of composite ties with more layers (configuration ‘C’) was higher

than composite ties with fewer layers (configuration ‘A’) by a factor of 1.4 (763 × 106 lbs-in

2 vs.

521 × 106 lbs-in

2).

3. The average flexural rigidity of GFRP composite ties was higher than discarded wood railroad

ties by a factor of 3 (748 × 106 lbs-in

2 vs. 249 × 10

6 lbs-in

2).

4. The result for average flexural rigidity of this study (thermoset) was compared to previous study

(Chada and Vijay, 2012). It was shown that the average flexural rigidity of thermoset ties was

higher than that of thermoplastics by a factor of 2.1 (748 × 106 lbs-in

2 vs. 341 × 10

6 lbs-in

2).

Thermoset materials enhanced MOE from a range of 44% to 75% while thermoplastic materials

enhanced MOE from a range of 15% to 20%. This was due to stronger matrix material in

thermoset (vinyl ester) than ABS resin in thermoplastics.

5. The average flexural rigidity of composite ties of this study was greater than new oak ties from

Railway Tie Association (Tie guide, 2005) by a factor of 2.7 (748 × 106 lbs-in

2 vs. 272 × 10

6 lbs-

in2).

70

6. The average flexural rigidity of composite ties in this study was higher than Dynamic’s and

PRT’s values, respectively, by factors of 2.3 and 2.0 (748 × 106 lbs-in

2 vs. 321 × 10

6 lbs-in

2 and

368 × 106 lbs-in

2) (Table 2.6).

7. The average flexural rigidity of composite ties was higher than IntegriCo and Tietek’s values,

respectively, by factors of 2.3 and 2.4 (748 × 106 lbs-in

2 vs. 319 × 10

6 lbs-in

2 and 303 × 10

6 lbs-

in2) (Table 2.6).

It is also noted that thermoset GFRP wrapping provided better mechanical properties than

thermoplastic GFRP both for lab manufactured and commercially manufactured ties. Use of machine

wrapping would lead to better fiber wetting, higher Vf, tight fiber wrapping, and enhanced mechanical

properties.

71

6. STATIC RUPTURE TESTS ON WOOD AND GFRP TIES: A

COMPARISON

6.1. Introduction

For static rupture test, three point bending test were conducted with a span length of 60 in. to determine

the tensile fracture strength and modulus of rupture of both discarded wood tie and GFRP. Tensile

fracture strength is important because ties usually fail in tension zone under of heavy axle loads. GFRP

composite ties with two different fiber/fabric configurations were tested in CFC-WVU laboratory to

determine their strength properties. From the test data, rupture modulus and other mechanical features of

GFRP Composite ties and wood ties, were compared.

6.2. Objective

The objective was to test wood and GFRP ties and evaluate their rupture modulus and static bending

strength under three point bending tests to determine the gains in strength and stiffness of the ties due to

GFRP wrapping.

6.3. Scope

The tests were conducted on two full-scale GFRP composite ties and three control specimens discarded

wood ties in CFC-WVU structures labs. Span length of the specimens for three point bending tests was 60

in. Based on the test results, GFRP composite ties with two different fiber/fabric configurations were

compared to (new and discarded) red oak wood ties and composite ties of IntegriCo, Tietek, Dynamic and

PRT companies. In this regard, strains (at top and bottom) and deflections at mid-span of the ties were

measured. Wood tie moisture content was 20 percent for this test.

Table 6. 1.Fiber/fabric configuration of specimens

Tie

ID

Fiber/fabric

configuration Fiber/fabric orientation

No. of

layers

4 C 4[0°/90

°]/2[45

°/0

°/+45

°]/4[90

°/0

°] 22

16 A 3[0°/90

°]/1[45

°/0

°/+45

°]/3[90

°/0

°] 15

72



fixed on the concrete supports. The center to center 60 in supports lead to 21 in overhang for ties (60 + 21

+ 21 = 102 in). Load was applied at the middle of specimens by hand pump operated hydraulic jack

clamped to a steel frame (Figure 6.1).

Figure 6. 1.Schematic of three point bending test for composite ties

6.5. Instrumentation

During the test, Stress vs. bottom Strains and Load vs. Deflections were plotted at the mid-span. The

strain gages were installed at top (compression zone) and bottom (tension zone) of beams at the middle.

For calculation, the maximum strain at the tension zone was considered. LVDT was placed at the mid-

span to measure the maximum deflection and load cell was placed at the middle on the specimens. Strain

Smart software program was used to collect Load vs. Strain and Load vs. Deflection data using Data

Acquisition system.

6.6. Test Procedure

After the strain gages were bonded to the beams, the specimen was placed on the support with an

overhang of 21 in, whilst the center to center distance of the supports was 60 in. Load cell, LVDT and

strain gages were connected to Data Acquisition System. After ensuring proper connections of gages,

LVDT and load cell with Data Acquisition System, they were zeroed. This procedure was the same for all

specimens.

73

6.6.1. Three Point Bending Test (Modulus of Elasticity)

Whilst the load cell was centered on top of the specimens, 2 kips of load was applied through the

hydraulic jack. The data collected included strains, loads and deflection through Strain Smart Software

and the test was repeated twice.

6.6.2. Three Point Bending Test (Rupture Stress)

By the above three point bending test, Young’s moduli of specimens were evaluated. For evaluating

rupture stress under three point bending, test procedure was similar to the MOE test except that the

loading would be continued even after 2 kips till the tie would be ruptured. Tie rupturing is indicated

when the load value data drops down during testing. Strains, loading and deflection data was collected

through Strain Smart Software.

6.7. Sectional Properties

With the application of fibers and resin (manufacturing), cross section of discarded wood ties increases.

Mechanical properties of GFRP composite ties with different fiber/fabric configurations were individually

calculated and final dimensions of composite ties are shown in Table 6.2.

Table 6. 2.GFRP composite tie dimensions

Specimen dimensions Tie # 4 Tie # 16

Length (in) 102 102

Width (in) 9.75 9.20

Depth (in) 7.8 7.31

6.7.1. Calculations of Transformed Moment of Inertia (It) for GFRP Composite Tie

The calculations are identical to what was done for ties # 4 and 16 in Chapter 5, Sector 5.7.1. Table 6.3

shows the results for the calculations.

74

Table 6. 3.Transformed moment of inertia for different fiber/fabric configurations

Tie

ID

Fiber/fabric

configuration

Fiber

volume

fraction (Vf)

EComp

(psi) EW

(psi)

Modular

ratio (η) It

(in4)

Dimension:

Length × With ×

Height

in × in × in

4 C 23.77% 2.23 × 106 1.28 × 10

6 1.75 401 102 × 9.75 × 7.80

16 A 26.52% 2.10 × 106 1.14 × 10

6 1.84 338 102 × 8.63 × 6.75

6.7.2. Calculation of Moment of Inertia for Discarded Wood Tie

I =

(6.1)

=

= 221 in

4

6.8. Test Results

The flexural rigidities of GFRP composite ties were calculated from Stress vs. Strain and Load vs.

Deflection graphs through three point bending tests. Stiffness of both composite and used wood tie was

calculated and measured using Strain and Deflection plots during static bending tests. Also, static bending

strength for both composite and used wood ties was calculated. Flexural rigidity of fiber/fabric

configuration ‘C’ and ‘A’ and a discarded wood tie was indicated as follows.

6.8.1. Calculation of Flexural Rigidity and Bending Stress

Figure 6. 2.Schematic of deflected tie under three point bending test

75


(6.2)

Where:

Bending Moment: M =

(6.3)

Point load: P


∑ (6.4)


6.8.2. .Tie # 4

Figure 6. 3.Stress vs. Strain graph (tie # 4)

Figure 6. 4.Load vs. Deflection graph (tie # 4)

C = 3.90 in

It = 401 in4



EI = 2.61 × 106 × 401 = 10.48 × 10

8 lbs-in

2


= 936 kips–in

MOR: σ =

= 9103 psi

y = 2.614x - 0.7878

0

100

200

300

400

0 50 100 150

Stress (psi)

Strain (µԑ)

Stress vs. Strain

0

20000

40000

60000

80000

0 1 2 3

Load (lbs)

Deflection (in)

Load vs. Deflection

76

6.8.3. Tie # 16

Figure 6. 5.Stress vs. Strain graph (tie # 16)

Figure 6. 6.Load vs. Deflection graph (tie # 16)

C = 3.65 in

It = 338 in4



EI = 1.57 × 106 × 338 = 5.31 × 108 lbs-in2


= 640 kips–in

MOR: σ =

= 7009 psi

y = 1.5721x - 3.8847

0

100

200

300

400

0 100 200 300

Stress (psi)

Strain (µԑ)

Stress vs. Strain

0

10000

20000

30000

40000

50000

0 1 2 3

Load (lbs)

Deflection (in)

Load vs. Deflection

77

6.8.4. Wood Tie

Figure 6. 7.Stress vs. Strain graph (wood tie)

Figure 6. 8.Load vs. Deflection graph (wood tie)

C = 3.3 in.

I = 220 in4


Span length: L = 40 in

EI = 1.27 × 106 × 220 = 2.80 × 10

8 lbs-in

2


= 218 kips–in

MOR: σ =

= 3307 psi

y = 1.2754x + 7.122

0

200

400

600

800

0 100 200 300 400

Stress (psi)

Strain (µԑ)

Stress vs. Strain

0

5000

10000

15000

20000

25000

0 1 2 3

Load (lbs)

Deflection (in)

Load vs. Deflection

78

Table 6. 4.Summary of test results of GFRP composite and wood tie

Mechanical &

Strength Properties Tie # 4 Tie # 16 Wood Tie

Length (in) 102 102 102

Width (in) 9.75 9.19 8.6

Depth (in) 7.81 7.31 6.7

Moment of inertia

(in4)

401 338 221

MOE

( × 106 psi)

2.61 1.57 1.26

Flexural rigidity

( × 106 lbs-in

2)

1048 531 280

Failure load (kips) 62.43 42.69 21.82

MOR

(psi) 9103 7009 3307

Static bending strength

(kips-in) 936 640 218

Deflection at failure

(in) 1.13 1.217 1.084

Figure 6. 9.Matrix in failure

Figure 6. 10.Debonding was failure cause

79

Figure 6. 11.MOR testing for flexural rigidities of GFRP composite and discarded wood ties

Figure 6. 12.Static bending strength of GFRP composite and discarded wood ties

0

200

400

600

800

1000

1200

GFRP Tie # 4 GFRP Tie # 16 Wood

(x 106 lbs-in2)

Flexural Rigidity (EI)

0

100

200

300

400

500

600

700

800

900

1000


Moment (kips-in)


80

Figure 6. 13.MOR of GFRP composite and discarded wood ties

6.8.5. Evaluation of Flexural Rigidity of GFRP Composite and Discarded

Wood Ties

The three point bending test results showed that GFRP composite ties had higher flexural rigidities than a

wood tie. Flexural rigidities of tie # 4 with more layers (22 layers) and tie # 16 with 15 layers were higher

than discarded wood tie (no wrap) by factors of 3.7 and 1.8, respectively (1048 × 106 lbs-in

2 & 531 × 10

6

lbs-in2 vs. 280 × 10

6 lbs-in

2).

6.8.6. Evaluation of Static Bending Strength and MOR of GFRP

Composite and Discarded Wood Ties

Static bending strength of the tie # 4 with more layers (22) and the tie # 16 with fewer layers (15) by

factors of 4.2 and 2.9, respectively (936 kips-in & 640 kips-in vs. 218 kips-in).

The MOR of the tie # 4 with 22 layers and tie # 16 was higher than the discarded wood tie by

factors of 2.7 and 2.1, respectively (9103 psi & 7009 psi vs. 3307 psi).

GFRP ties failed under the point load and eventually bond failure between GFRP composite and

Polyurethane coated on wood surface was noted.

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000


Moment (kips-in)

Modulus of Rupture

81

6.9. Conclusions

1. Flexural rigidity of composite ties was higher than the discarded wood ties and ranged between

factors of 1.9 to 3.7, respectively (531 × 106 lbs-in

2 for tie # 16 and 1048 × 10

6 lbs-in

2 for tie # 4

vs. 278 × 106 lbs-in

2 in wood tie)

2. Static bending strength of composite ties was higher than the discarded ties and ranged between

factors of 2.9 to 4.2, respectively (640 kips-in for tie # 16 & 936 kips-in for tie # 4 vs. 218 kips-

in for wood tie).

3. The MOR of the composite ties was higher than the wood ties with the factors ranged between

2.1 to 2.7, respectively (7009 psi for tie # 16 & 9103 psi for tie # 4 vs. 3307 psi for discarded

wood tie).

4. The average MOR of composite ties in this study was higher than Dynamic’s and PRT’s values,

respectively, by factors of 3.0 and 2.4 (8056 psi vs. 2600 psi and 3356 psi).

5. The average MOR of composite ties was higher than IntegriCo and Tietek’s values, respectively,

by factors of 2.9 and 4.0 (8056 psi vs. 2700 psi and 2000 psi).

6. Flexural rigidity, static bending strength and MOR of tie # 4 was higher than tie # 16, by a factor

of 1.97, 1.46 and 1.30, respectively.

The numbers of layers (22 layers vs. 15 layers) of tie # 4 was higher than that in tie # 16. Also,

mechanical properties (i.e. modulus of elasticity) of wood core in both cases were quite different (1.28

Msi vs. 1.14 Msi, respectively). Because, both the wood ties # 4 and 16 were periodically in service,

however, the average MOE of new red oak wood tie is 1.29 Msi).

7. Final failure of the GFRP composite ties was preceded by rupturing strands of the wood core.

8. Mode of failure started by compression failure in FRP, followed by wood rupturing and

eventually, GFRP debonding from wood core not matrix failure (Figures. 6.9 & 6.10).

9. Polyurethane application resulted in vastly improved composite behavior of the GFRP products

and no bond failure was observed in composite ties before failure.

82

10. Results of this study shows that discarded wood ties have lower MOE and MOR than new Oak

ties (1.14 × 106

vs. 1.29 × 106

psi for MOE and 3307 vs. 8680 psi for MOR). Using GFRP shell

increased the strength (MOR) by a factor of 3.

83

7. THEORETICAL CALCULATIONS

7.1. Introduction

This chapter deals with the comparison of experimental and theoretical values of stiffness and deflection

(shear and deflection) for FRP composite coupons and tie specimens.

7.2. Calculation of Young’s Modulus (micromechanics)

Young’s modulus is calculated through stiffness matrix. For calculating in-plane stiffness values,

lamination theory will be used. Lamination theory takes into account stiffness of each layer (lamina).

Further, these in-plane stiffness values can be used to compute mid-plane strains and curvatures for the

laminate under a given set of forces and moments, which will lead to in-plane strains and stresses for each

lamina (Mallick, 1993). In this study, we will focus on the evaluation of stiffness values for the laminate

and calculation of modular ratio, transformed moment of inertia, and related mechanical properties of the

ties with GFRP shell.

7.2.1. Coupons with Configuration ‘A’ (15 layers)

Table 7.1 shows mechanical properties of fabrics and resin from Tables 3.1 & 3.4

Table 7.1: Mechanical properties of glass fiber/fabrics and Derakane 510A-40 resin

(Msi) (Msi) (Msi) (Msi)

10.6 0.49 0.22 0.38 4.34 0.178 58.34% 41.66%

Rule of mixture: (7.1)

Inverse rule of mixture:

(7.2)

Major Poisson’s ratio: (7.3)

Minor Poisson’s ratio:

(7.4)

84

(7.5)

Calculation of reduced stiffness matrix for angle : [ ]

Where:

(7.6)

(7.7)

(7.8)

(7.9)

(7.10)

And: [ ]

Where:

(7.11)

(7.12)

(7.13)

(7.14)

(7.15)

(7.16)

And:

(7.17)

85

(7.18)

(7.19)

(7.20)

(7.21)

Inplane stiffness stiffness matrix: [ ]

∑ [ ]

(7.22)

(7.23)

Inverse inplane stiffness matrix: [ ]

Calculation of reduced stiffness matrix for = 0, 90 and ±45 fiber/fabrics are as follows:

[ ]

[ ]

[ ]

[ ]

86

[ ]

Young’s modulus from [ ] matrix:

(7.24)


(7.25)

7.2.2. Coupons with Configuration ‘B’ (19 layers)




10.6 0.49 0.22 0.38 4.34 0.178 73.89% 26.11%

Reduced stiffness matrix for 0, 90 and ±45 fiber/fabrics:

[ ]

[ ]

[ ]

87

[ ]

[ ]



7.2.3. Full-scale Tie with Configuration ‘A’ (15 layers)




10.6 0.49 0.22 0.38 4.34 0.178 26.52% 73.48%


[ ]

[ ]

[ ]

88

[ ]

[ ]



7.2.4. Full-scale Tie with Configuration ‘C’ (22 layers)




10.6 0.49 0.22 0.38 4.34 0.178 23.77% 76.23%


[ ]

[ ]

[ ]

89

[ ]

[ ]



7.2.5. Test Results

Table 7.5 shows summary of experimental and theoretical results for full-scale composite ties.

Table 7.5: Summary of results (experimental and theoretical)

Experimental results Theoretical result Difference

Configuration A (15 layers) 2.1 Msi 1.90 Msi 10%

Configuration C (22 layers) 2.2 Msi 2.06 Msi 6.8%

7.3. Calculations of Shear Deflection for Full-scale Composite Ties

Shear deflections for ties # 4, 16, 17 and 18 (ties with and without polyurethane) are calculated and

compared to deflections of the ties. Shear deflections due to changing moments often need to be

determined for wood, since its modulus of elasticity in bending and in shear differ approximately by a

factor of 16. The factor is only 2.5 for steel, and 2.3 to 2.7 for concrete. Calculation of modulus of shear

(G) for isotropic materials is given in following formula:

(7.24)

Where, E is elastic modulus and is Poisson’s ratio of the red oak wood. However, this

formula leads to a high G for wood. G of wood is known to vary based on its species. For example,

( ) ratio for Douglas fir varies from 1/15 to 1/16 (Newlin & Trayer, 1956). Similarly, ratio of

( ) for Northern White Spruce is (Green et al., 1999) and for Red Oak is about (Newlin

90

& Trayer, 1956, Green et al., 1999). Effect of shear deflection on the total deflection of our discarded red

oak wood ties (no wrap) with ( ) = is shown in table 7.6.

Shear deflection for singly supported beams is calculated through the following formula:

(7.25)

Where P is the point load, l is the span length, G is the shear modulus, k = 1.2 rectangular section,

and A is the area of the cross section.

7.4. Test results

Experimental total deflections ( ) and theoretical shear deflections ( under applied point load for

simply supported wood ties are tabulated in Table 7.6. Ratio of shear to total deflection ( ⁄ ) in Table

7.6 shows that shear deflection is less than 8.8% of the total deflection and can be ignored.

Table 7.6: Shear deflection component for wood ties (prior to wrapping)

Tie

ID

E

( psi)

G= (1/12)E

( psi)

P

(kips)

l

(in)

A

(in2)

(in)

(in)

4 1.28 0.107 62.43 60 59.52 0.177 2.02 8.8%

16 1.14 0.0.95 42.69 60 58.22 0.138 2.17 6.4%

17 1.02 0.085 10.96 90 51.34 0.045 3.94 1.1%

18 1.18 0.098 23.60 90 52.44 0.082 3.62 2.3%

7.5. Conclusion

1. Comparison of Young’s moduli of configuration ‘A’ showed that experimental elastic modulus is

higher than the theoretical one by about 10% (2.10 Msi vs. 1.90 Msi).

2. Comparison of Young’s moduli of configuration ‘C’ showed that experimental elastic modulus is

higher than the theoretical one by about 6.8% (2.20 Msi vs. 2.06 Msi).

3. Comparison of shear deflection of the composite ties under different span length indicated that

the effect of shear deflection can be neglected in the composite ties. Shear deflections ranged

between 1.1-8.8% of the total deflection and are expected to be less with the addition of wrap.

91

8. FIELD IMPLEMENTATION AND TESTING

8.1. Introduction

Following TTCI track installation and evaluation of thermoplastic RR ties in Moorefield, WV, CFC-

WVU designed thermoset GFRP shells for strengthening and reusing discarded wood RR ties. In order to

study the fatigue performance of composite ties in the field under heavy axle loads, 16 ties were

manufactured and 14 of them were sent for field installation and testing at TTCI, Pueblo, Colorado.

Single Tie Lateral Push tests (STPT) were conducted for 0 MGT5 and 11 MGT loads and maximum load

and displacement of the ties were evaluated.

8.2. Objective

To study the performance of installed composite ties under heavy axle loads and to conduct the Single

Tie Push test (STPT).

8.3. Scope

Among the sixteen ties manufactured, two were lab tested and the rest were field implemented. Fourteen

ties were sent to TTCI, Pueblo, CO. for field implementation and testing. Lab evaluations included

bending tests for evaluating MOE, MOR and EI. Single tie lateral push tests were conducted in the field

for 0 MGT and 11 MGT loads and maximum load and displacement of the ties were evaluated.

8.4. Materials

Composite RR ties sent for field evaluation had glass fiber/fabric configuration ‘C’ (Table 4.1) and epoxy

vinyl ester resin was used to wet the fibers.

8.5. Tie Installation Locations

Thirteen of the ties were field installed in the field on TTCI test track system (Figure 8.1).

5 Million Gross Tones

92

Figure 8. 1.Field installed ties

8.6. Tie Installed Procedure

After removing wood ties, ballast was prepared by using a machine to insert the composite ties. Then

positioning and installation of the ties were carried out for Single tie push test (STPT) (Figs. 8.2 and 8.3)

93

1. Ballast preparation for tie insertion

2. Tie installation in progress

3. Tie positioning during installation

4. Completed ties installation

Figure 8. 2.Field installation

94

1. Zero MGT test setup

2. Zero MGT test

3. Tie after 11 MGT load

4. Tie seat view after 11 MGT load

Figure 8. 3.Single tie push test (STPT)

8.7. Field testing

Following laboratory evaluations, 14 GFRP composite ties were installed on TTCI track (Figure 8.2),

Pueblo, CO. All ties had 22 uni-directional layers with similar fiber/fabric configurations ‘C’ (Figure 4.1).

These ties were subjected up to 63 MGT of load by a 39 ton axle load train in track field. The single tie

push test (STPT) (Figure 8.3) results of six ties were measured after 0 MGT and 11 MGT of load and are

presented in (Table 8.1) and (Figs. 3.8 and 3.9). At 0 MGT, push load ranged from 1100 to 1400 lbs.,

which exceeds the required limit load of 1000 lbs. At 11 MGT, push load ranged between 1900 to 2500

lbs. With increased loading from 0 to 11 MGT, STPT values were observed to be doubled (Table 8.1).

95

The electrical conductivity (impedance) tests conducted on thermoset composite ties at TTCI indicated

their suitability for railroad track installation.

1.Tie # 38

2.Tie # 40

3.Tie # 42

4.Tie # 44

5.Tie # 46

6.Tie # 48

Figure 8. 4.FRP composite ties load vs. displacement at 0 MGT of load (STPT)

96

1.Tie # 38

2.Tie # 40

3.Tie # 42

4.Tie # 44

5.Tie # 46

6.Tie # 48

Figure 8. 5FRP composite ties load vs. displacement at 11 MGT of load (STPT)

Table 8. 1.STPT results

0 MGT 11 MGT

Tie No. Max load (lbs) Displacement (in) Max load (lbs) Displacement (in)

38 1100 0.25 2000 0.225

40 1100 0.45 1900 0.225

42 1100 0.25 2500 0.1

44 1200 0.6 2100 0.075

46 1000 0.1 1900 0.15

48 1400 0.4 2500 0.225

Avg. 1150 0.342 2150 0.167

97

8.8. Test Results

Ties were periodically observed during loading and following observations were made:

Close to 27.75 MGT of loading (field temperature of 79 ºF), some spike/plate cutting and end-

splitting of the tie were observed in few ties (Figure 8.6). It should be noted that discarded wood

tie with moderate to significant damage were used in this study for strengthening with thermoset

FRP shell.

At around 36.9 MGT of loading (field temperature of 82 ºF), uplifting of some outer spikes were

noted at temperatures of 100ºF (Figure 8.7).

At the end of 63 MGT loading (field temperature of 100 ºF), the ties were removed and visually

observed. The FRP surface of the ties (Figure 8.8) showed ballast aggregate imprints, which

explains the improved push test values with increasing axle loads. FRP wraps successfully carried

the applied loads up to 63 MGT.

98

Figure 8. 6.Tie and rail seat inspection at 27.75 MGT on 5/14/12 TTCI

1. Spike lift up on outer edge

2. Close up of lifted spike

Figure 8. 7.Tie and spike inspection at 36.9 MGT on 5/21/12, TTCI

99

Figure 8. 8.Tie removal after 63 MGT of loading

8.9. Conclusions

1. The single tie push test (STPT) results of 6 ties showed a load ranging from 1100 to 1400 lbs at

zero MGT, which exceeds the required minimum load of 1000 lbs. However, at 11 MGT, push

load was found to double and ranged between 1900 to 2500 lbs, which is attributed to surface

indentations created by aggregates (Table 8.1).

2. Electrical conductivity (impedance) tests conducted on thermoset composite ties at TTCI

indicated their suitability for railroad track installation.

3. TTCI installed thermoset FRP ties successfully withstood 63 MGT of track loads. Further testing

was halted due to additional funding requirements.

4. Thermoset composite shell ties with discarded wood core were found to have successfully

overcome some of the limitations exhibited by thermoplastics GFRP ties.

Thermoset composite shell ties can be further strengthened to meet any higher axle speeds and load

requirements, if necessary.

8.10. Field Installation and Testing (Thermoplastic Ties)

In order to estimate the fatigue life, thirteen GFRP-composite ties were field installed at TTCI, Pueblo,

Co. All the ties had similar fiber fabric configurations with unidirectional, 0, 90 and ±45 fibers. These ties

were subjected to 0, 2 and 16.6 MGT of load by a 39 ton axle load train in the field. The crack length,

100

strains and push tie test results were measured after 2 MGT and 16.6 MGT of load. The crack lengths on

5 ties are presented in Table 8.2. Cracks were noticed mostly at 1½” below the top and some were 2”

below the top (Figure 8.9). Length of cracks varied mostly from 4 to 10” and some were up to 14” long.

Some cracks were also noticed going all the way across the tie in the top middle of the tie. Tie Push test

results are presented in Table 8.3. Maximum push load was observed to be 2080 lbs (Table 8.3). These

ties had indentations only on the top and bottom surface. Providing additional indentations on the side

surfaces are expected to increase the push test values and offer better stability in the track. Maximum

strains were observed to be 1000 and 2300 µԑ at 2 and 16.6MGT of load, respectively. The maximum

value of 2300 µԑ was about 6 to 7 times lower than the failure strain of FRP composite (Table 8.4). The

electrical conductivity (impedance) tests conducted on thermoplastic composite ties at TTCI indicated


Figure 8. 9.Cracks on FRP thermoplastic ties

1 TTCI lab testing

2 Cracks under the rail seat areas

101

1. Tie # 167

2. Tie # 173

3. Tie # 175

4. Tie # 177

Figure 8. 10.Typical FRP composite ties displacement at 0 MGT of load

102

Figure 8.11.1: Tie # 167

Figure 8.12.2: Tie # 173

Figure 8.12.1: Tie # 167

Figure 8.12.2: Tie # 173

Figure 8.12.3: Tie # 175

Figure 8.12.4: Tie # 177

Figure 8. 11.FRP composite ties displacement at 1.95 MGT of load

Figure 8. 12.FRP composite ties at 16.6 MGT of load

103

Table 8. 2.Crack length and position on FRP tie

Tie

location

side

+/-

Crack

length

at 0

MGT

Crack

length

at 2

MGT

Crack

length

at 16.6

MGT

Crack

below

top of tie

at 0

MGT

Crack

below

top of tie

at 2

MGT

Crack

below

top of tie

at 16.6

MGT

Crack location

167 pos 0 12" 14" 0 0 0 at the very top

167 neg 0 0 5" 0 0 0 Top of tie

171 neg 4" 10" 11" 0 0 0 at the very top

171 neg 0 0 5" 0 0 0 at the very top

171 pos 0 0 1 1/2" 0 0 0 very top to hold

down spike

173 neg 8" 14" 14" 2" 2" 2"

173 N/A 0 5" 8" 0 0 1 1/2" Center top of tie

175 neg 0 9" 9" 0 0 0 at the very top

175 neg 0 0 6 1/2" 0 0 1"

176 pos 4" 8" 8" 1 1/2" 1 1/2" 1 1/2"

Table 8. 3.Push tie test results

MGT of

load

Number of

ties tested

Average pushing

load (lbs)

0 N/A 650

2 2 900

16.6 5 2080

Table 8. 4.Strain values on the tie at 16.6 MGT

Tie

location

Maximum strain

at 0 MGT (µϵ)

Maximum strain

at 2 MGT (µϵ)

Maximum strain

at 16.6 MGT (µϵ)

167 500 800 1900

169 600 N/A 2100

171 700 N/A N/A

173 900 1000 2300

175 900 N/A 2200

177 700 N/A 2200

8.11. Field Visual Observations

Field visual observations indicated cracks during higher MGT under the rail seat area and cracking in

some of the ties at the center. Based on the thermoplastic resin viscosity that results in fiber wetting

issues, next batch of strengthening was carried out using thermoset resins as explained under Section 3 of

104

this report. In addition to lower viscosity (consistency of maple syrup), thermoset resins offer additional

benefits such as higher strength, stiffness, and fabric saturation.

8.12. Conclusions

1. Recycled composite ties carried 16 percent higher bending moment than the theoretical value at

the center (73162lbs-in vs. 61266lbs-in) and 5 percent lower bending moment than the theoretical

value at the rail seat area. These variations are attributed to individual properties that are specific

to each of the wood tie and surrounding thermoplastic shell properties (e.g., variation in

thickness, resin flow, and fiber kinking during manufacturing process).

2. After one million cycles, the top and bottom maximum strains at the center of the tie were 560µε

and 1402µε, respectively. At the rail seat, the maximum top and bottom strains were -1441µε and

1269µε, respectively.

3. The increase in the top and bottom maximum strains after two million cycles was 34% and 17%,

which shows stress increase in composite laminates under fatigue loads.

4. The electrical conductivity (impedance) tests conducted on thermoplastic composite ties at TTCI

indicated their suitability for railroad track installation.

Thermoplastic RR ties showed good fatigue performance up to 2.5 million cycles at TTCI lab

testing. However, under TTCI track testing, signs of cracking under the tie seat area and edges were noted

in thermoplastic composite ties, which were not exhibited under laboratory conditions. Hence,

thermoplastic shells were replaced with thermoset composite shells.

105

9. CONCLUSIONS AND RECOMMANDATIONS

9.1. Conclusions

This chapter includes conclusions of laboratory testing for three point bending test and field installation of

thermoset GFRP composite products.

9.1.1. Chapter 4 (Manufacturing: Effectiveness of Polyurethane)

Eight GFRP-wood coupons were manufactured with respect to fiber/fabric configurations of ‘A’ and ‘B’

(15 and 19 layers, respectively). Eighteen full-scale ties with configurations of ‘A’ and ‘C’ (15 and 22

layers, respectively) were manufactured.

Among the above, four coupons and one tie were manufactured without application of polyurethane and

were tested in CFC-WVU laboratory.

1. Coupons and ties with polyurethane coating showed composite behavior during flexural rigidity

and rupture modulus testing.

2. Coupons with polyurethane had higher static bending strength and rupture modulus by factors of

1.5 and 1.53 (930 lbs-in vs. 617 lbs-in & 4469 psi vs. 2919 psi), respectively.

3. The flexural rigidity and MOR of the tie with polyurethane primer coating was higher than that of

the tie without polyurethane by factors of 2.1 and 2.2 (441× 106 lbs-in

2 vs. 156 × 10

6 lbs-in

2 &

5982 psi vs. 2706 psi), respectively.

9.1.2. Chapter 5 and 6 (Flexural Rigidity and Rupture Modulus)

Among the total number of 18 ties with fiber/fabric configurations ‘A’ and ‘C’, 15 ties with configuration

‘C’ an one with configuration ‘A’ were tested for measuring the flexural rigidity through three point

bending test and other 2 ties with different configurations ‘A’ and ‘C’ were tested under three point

bending test for evaluating the static bending strength and rupture modulus. The results were compared

with discarded and new timber ties.

106

1. The average flexural rigidity of GFRP composite ties was higher than discarded wood railroad

ties by a factor of 3 (748 × 106 lbs-in

2 vs. 249 × 10

6 lbs-in

2).

2. The average flexural rigidity of composite ties of this study was greater than oak ties from

Railway Tie Association (Tie guide, 2005) by a factor of 2.7 (748 × 106 lbs-in

2 vs. 272 × 10

6 lbs-

in2).

3. Higher stiffness was achieved by adding additional layers of (0°/90

°/+45

°) GFRP fabrics

(configuration ‘C’ vs. ‘A’)

4. The average flexural rigidity of composite ties with more layers (configuration ‘C’) was higher

than composite ties with less layers (configuration ‘A’) by about 46% (763 × 106 lbs-in

2 vs. 521 ×

106 lbs-in

2).

5. Comparing the result of this study (thermoset) to thermoplastics one, indicated that the average

flexural rigidity of thermoset ties was higher than that of thermoplastics by a factor of 2.2 (748 ×

106 lbs-in

2 vs. 341 × 10

6 lbs-in

2). Thermoset materials enhanced MOE from a range of 44% to

75% while thermoplastic materials enhanced MOE from a range of 15% to 20%. This was due to

stronger matrix material in thermoset (vinyl ester) than ABS resin in thermoplastics.

6. The average flexural rigidity of composite ties in this study was higher than Dynamic’s and

PRT’s values, respectively, by factors of 2.2 and 2.0 (748 × 106 lbs-in

2 vs. 321 × 10

6 lbs-in

2 and

368 × 106 lbs-in

2).

7. The average flexural rigidity of composite ties was higher than IntegriCo and Tietek’s values,

respectively, by factors of 2.3 and 2.4 (748 × 106 lbs-in

2 vs. 319 × 10

6 lbs-in

2 and 303 × 10

6 lbs-

in2).

8. The average MOR of composite ties in this study was higher than Dynamic’s and PRT’s values,

respectively, by factors of 3.1 and 2.14 (8056 psi vs. 2600 psi and 3356 psi).

9. The average MOR of composite ties was higher than IntegriCo and Tietek’s values, respectively,

by factors of 3 and 4 (8056 psi vs. 2700 psi and 2000 psi).

107

10. Static bending strength of composite ties was higher than the discarded ties and ranged between

the factors of 2.9 to 4.3, respectively (640 kips-in for tie # 16 & 936 kips-in for tie # 4 vs. 218

kips-in for wood tie).

11. MOR of the composite ties was higher than the wood ties ranged by a factor of 2.11 to 2.75,

respectively (7009 psi for tie # 16 & 9103 psi for tie # 4 vs. 3307 psi for discarded wood tie).

12. Flexural rigidity, static bending strength and MOR of tie with 22 layers was higher than tie with

15 layers, by factors of 1.97, 1.46 and 1.30, respectively.

13. Final failure of the GFRP composite ties was preceded by rupturing strands of the wood core.

14. Mode of failure was GFRP de-bonding from wood core.

15. Polyurethane application resulted in vastly improved composite behavior of the whole cross

section and no bond failure was observed in composite ties.

16. The load carrying capacity of wood-GFRP products can be increased with higher fabric modulus,

less moisture content on the wood core surface and machine wrapping (i.e., pultrusion) which

leads to higher fiber volume fraction.

9.1.3. Chapter 7 (Experimental vs. Theoretical Results)

1. Comparison of Young’s moduli of configuration ‘A’ showed that experimental elastic modulus is

higher than the theoretical one by about 10% (2.10 Msi vs. 1.90 Msi).

2. Comparison of Young’s moduli of configuration ‘C’ showed that experimental elastic modulus is

higher than the theoretical one by about 6.8% (2.20 Msi vs. 2.06 Msi).

3. Comparison of shear deflection of the composite ties under different span length indicated that

the effect of shear deflection can be neglected in the composite ties. Shear deflections ranged

between 1.1-8.8% of the total deflection and are expected to be less with the addition of wrap.

108

9.1.4. Chapter 8 (Field installation and testing)

Fourteen ties were sent for field installation and testing to TTCI, Pueblo, Colorado. Single Tie Lateral

Push tests (STPT) were conducted for 0 MGT and 11 MGT loads and maximum load and displacement of

the ties were evaluated.

1. The single tie push test (STPT) results of 6 ties showed a load ranging from 1100 to 1400 lbs at

zero MGT. Since the required minimum load is 1000 lbs, composite ties performance meet that

requirement. However, at 11 MGT, push load was found to double and ranged between 1900 to 2500

lbs.

2. Electrical conductivity (impedance) tests conducted on thermoset composite ties at TTCI indicated


3. TTCI installed thermoset FRP ties successfully withstood 63 MGT of track loads.

4. Thermoset composite shell ties with discarded wood core were found to have successfully

overcome some of the limitations exhibited by thermoplastics GFRP ties.

Further testing was halted due to additional funding requirements.

9.2. Recommendations and Future Study

9.2.1. Manufacturing Process

1. To avoid inhaling resin vapors use of protective respiratory mask is recommended with flow of

fresh air circulation. Respirator/mask will prevent entry of minute fiber particles into lungs while

cutting the fibers.

2. Skin contacting with resin could lead to irritation and possible burning during cure reaction.

Having a long pair of protective hand gloves is recommended.

3. Since resin is in liquid form, safety glasses are needed to prevent accidental/possible entry of wet

resin and cut-fiber particles into the eye.

4. For manual process, continuous monitoring would lead to proper GFRP curing and avoid resin

accumulation only on bottom side of the specimen.

109

9.2.2. Composite Products

1. It is important to achieve optimum level of fiber volume fraction by properly controlling the

thickness of GFRP on the tie similar to a coupon specimen to achieve higher Young’s modulus of

GFRP shell similar to those of coupons. It is also important to wrap the fiber/fabrics with some

pre-tension over the previous layers as per design fiber/fabric orientation and stacking sequence.

2. It is recommended to utilize balanced symmetric laminate configuration to minimize shear

stresses.

3. Automated manufacturing such as pultrusion and filament winding methods can be employed

over a wood core with standardized dimensions to enhance fiber wetting, production rate, and

product QA/QC leading to better mechanical properties of the GFRP product.

4. It is also suggested to repair any major surface defects in the discarded wood core to assure

proper GFRP wrapping over wood core.

9.2.3. Field Installation

1. In addition to sharp curves, ties should be installed on downhill slopes to monitor their

functioning under combination of longitudinal, centrifugal, and surface-normal forces.

2. To increase friction between tie surface and ballast, surface patterns could be included during

manufacturing to enhance tie integration with the ballast and increase single tie lateral push test

(STPT) values.

110

10. REFERENCES

1. Alhayek, H. and Svecova, D. (2012). ”Flexural Stiffness and Strength of GFRP-Reinforced

Timber Beams.” J. Compos. Constr., 16(3), 245–252, 2012

2. Barbero, E. J., “Introduction to Composite Materials Design”, 1999.

3. Basalo. F.J.D.C., Nanni. A., “Sustainable Composite Systems for Infrastructure Rehabilitation”,

Ph.D.’s Dissertation, University of Miami, 2010.

4. Chada. V.R., Vijay. P.V., “Manufacturing, Evaluation and Field Implementation of Recycled

GFRP-Composite Railroad Ties”, Master’s Thesis, West Virginia University, 2011.”

5. Charles, B. Vick., “Adhesive Bonding of Wood Materials “Chapter 9, 1999.

6. Green D.W., Winandy J.E., Kretschmann D.E., “Wood Handbook”, Chapter 4, Mechanical

Properties of Wood, 1999

7. Hota. V. S. GangaRao, P. V. Vijay., “Reinforced Concrete Design with FRP Composites” 2006.

8. Howard. I., Gangarao, H. V.S., “Development of Lightweight FRP Bridge Deck Designs and

Evaluations”, Master’s Thesis, West Virginia University, 2002.

9. Kalligudd. S.D., Vijay. P.V., “Characterization and Durability Evaluation of Recycled FRP

Composites and Sandwich Specimens”, Master’s Thesis, Civil Engineering, West Virginia

University, 2010.

10. Laosiriphong, K., Gangarao, H., “Theoretical and Experimental Analysis of FRP Bridge Decks

under Thermal Loads”,Ph.D. Dissertation, West Virginia University, 2004.

11. Lopez-Anido, R., Xu H., “Structural Characterization of Hybrid Fiber-Reinforced Polymer-

Glulam Panels for Bridge Decks,” J. Compos. Constr., 6(3), 194–203, 2002

12. Mallick, P.K., “Fiber-Reinforced Composites”, 1993.

13. Newlin J.A., Trayler G.W., “Deflection of Beams with Special Reference to Shear

Deformations”, USDA-FPL, No. 1309, March 1956.

111

14. Raftery G.M., Harte A.M, Rodd, P.D., “Bonding of FRP Materials to Wood using Thin Epoxy

Gluelines”, International Journal of Adhesion and Adhesives, 2, 580-588, 2009

15. Sadat A.R., Gangarao, H., “Rehabilitation of Timber Railroad Bridges Using Glass Fiber

Reinforced Polymer Composites” Master’s Problem Report, West Virginia University, 2007.

16. Shahi, A, J.S. West, M. D. Pandey, Strengthening of Wooden Cross arms in 230 kV Transmission

Structures using Glass Fibre Reinforced Polymer (GFRP) Wrap, J. Compos. Constr., 15(3), 364–

373, 2011

17. Talakanti, D., Gangarao, H., “Testing and evaluation of wood-GFRC adhesive interface integrity

under accelerated aging and mechanical fatigue”, Master’s Thesis, West Virginia University,

1997

18. TTCI, “Update of Heavy Axle Load Revenue Service Testing at Mega Sites in Revenue Service”

RR08-32, FRA, U.S Department of Transportation, 2008.

19. Wang. Y., “A Coupled Hygrothermal Cohesive Layer Model for Simulating Debond Growth in

Bimaterial Interface”, Ph.D.’s Dissertation, Mechanical and Aerospace Engineering, Oklahoma

State University, 2006.

112

APPENDIX-A REVIEW OF COMPOSITES AND FRP-

STEEL STRUCTURES

A.1 REVIEW OF COMPOSITES

Composite materials development had come to being when animal hair or straw was used with mud or

clay to manufacture basic construction component (i.e. brick), or even in pottery as a reinforcing agent

since biblical times. Before World War II, lime plaster was traditionally reinforced with straw or animal

hair (e.g. bovine hair). The mentioned usage of composite was based on common sense and experiences,

with respect to knowing the properties of constituents individually and combination of them in order to

have improvements in mechanical properties (De Caso Y Basalo, 2010).

Civil (structural) engineers have been using different types of composites for a long time such as

natural composites (e.g. wood, human muscle and bone), laminated natural composites as in plywood and

reinforced concrete. The polymer composites can be called “Engineered” composites, because the

components with different mechanical and physical properties are stacked and combined together to form

a new material. This new material has significantly better mechanical properties when compared to its

constituents. Laminates are the most common forms in which fiber reinforced composites are

manufactured by stacking a number of thin layers of fibers and matrix. They can be consolidated into a

sheet with desired thickness.

Fiber Reinforced Polymer Composites (FRPs) are made up of reinforcing agent, such as fibers and

matrix such as polymer resins. Fibers with high strength and modulus are saturated with polymeric resins.

Hardened resin is called as matrix. Both fibers and matrix retain their physical and chemical properties,

while producing a combination of properties which cannot be achieved by either fiber or matrix alone

(Mallick, 2008). Fibers carry applied loads and matrices act as a binder and adhesive material so that the

whole component acts together. Nevertheless, matrix carries small portion of load, mostly transverse load

113

and provides rigid body to distribute loads uniformly. Fiber orientation of each layer is designed to

produce better mechanical property for composite laminate.

Typical fibers in structural components are Glass (E, S, C, D grades), Carbon, Organic (Aramid

such as Kevlar brand name and so on), Boron, alumina, silicon carbide (SiC) (Barbero, 1998). Glass

fibers are hard, stiff, corrosion resistant, flexible, and more importantly inexpensive which leads to their

usage in low cost industrial application. Carbon fibers are widely used in aerospace industry because they

are light weight and so strong with excellent chemical resistance.

Matrix Materials (resins) can be polymer, metals, or ceramics. Polymer matrices are popular

because of their ease of use in fabrication. Resin matrices used in FRPs are thermoset or thermoplastic

polymers.

Thermoset Matrix

Thermoset composites are mostly used in civil applications. Thermoset matrix is formed by irreversible

chemical transformation of a resin to an amorphous cross linked polymer matrix. They cannot be

reshaped upon reheating after addition of a catalyst. It does not melt into a liquid in high temperature but

has a glass transition temperature (Tg) at which the loss of mechanical properties will occur.

Polymer is called resin system when not cured and when cured, it is called matrix. The viscosity of

thermoset resins is low. This low resin flow and ease of use facilitates high rates of product

manufacturing. In case of using proper catalyst, the curing time and convenient choice of ambient

temperature can be determined. Examples of common thermoset resins are Polyesters, Vinyl ester, Epoxy

and Phenolics.

Epoxies are often expensive but have better moisture resistance and less shrinkage on curing than

polyesters and polyimides (Herakovich, 1998).

Generally, Vinyl esters have high strength and polyesters have moderate ones. Epoxy resins are

considered high performance resins because of their versatility, high mechanical properties and high

corrosion resistance and inexpensive.

114

Vinyl esters

Dimethacrylate oligomers diluted with styrene reactive diluents (so-called Vinyl ester resins) are

becoming increasingly important for composites in applications such as transportation vehicles, printed

wiring boards and civil infrastructure. Vinyl ester resins have higher mechanical properties when

compared to polyesters. These resins have high resistance to acids, alkalis and solvents. So it’s a good

choice when confronting harsh environments and getting spilled over by solvents (e.g. gas containers).

Other advantages of Vinyl esters are low viscosity, room temperature cure, high modulus, low weight and

low cost.

Thermoplastic Matrix

This kind of matrix does not undergo any chemical transformation during processing. It just goes from

solid to semi fluid state under heating and then gets back to solid state after cooling. Thermoplastics are

easily recyclable. Examples of thermoplastic matrices usage are Poly Ether Ether Ketone (PEEK) in high

performance applications, Polyphenylene Sulfinde (PPS) in chemically resistant, Polysulfone (PSUL)

products in creep situation with hot and moist.

FRPs are light weight (i.e. high strength to weight ratio), corrosion and chemical resistant,

anisotropic, high tensile strength, fatigue resistant, non-magnetic and linearly elastic until failure (i.e. no

yielding). Some of FRPs disadvantages over conventional construction materials (i.e., wood, steel and

reinforced concrete) are initial material cost, less education and experience of civil engineers, contractors

and construction crews with composites, sudden brittle failure, low modulus of elasticity (stiffness), uni-

directional properties, requirement of more sophisticated design (e.g. Finite Element Analysis)

flammability, creep and moisture absorption.

Types of fiber reinforced composites include continuous, woven, chopped, and hybrid composites.

Hybrid composites consist of mixed fiber types or fiber geometries. Continuous composites consist of

continuous fibers oriented in individual layers or lamina and bonded together to form a laminate.

Generally, FRPs processing involves:

Placement of fibers with the design point of view

115

Impregnation of fibers with resin

Consolidation of the laminates to remove voids and excessive resi

Removal from mold

Finishing procedure

Fabrication for FRPs typically includes:

Open molds such as hand lay-up and prepreg lay-up

Autoclave processing

Compression molding

Filament winding

Bag molding

Pultrusion and Resin transfer molding (RTM) such as reinforced reaction injection molding

(vacuum assisted resin injection molding (VARIM), structural reaction injection molding

(SRIM), flexible reaction injection molding (FRTM) and perform molding (Barbero, 1998).

A.2 LITERATURE REVIEW: STEEL-FRP

Literature review on FRPS application for steel structures and bridge members are elaborated in

Appendix ‘A’. Papers reviewed in the appendix elaborate on the recent application of FRPs to following

steel structures:

I. An experimental, analytical and numerical study of the static behavior of steel beams reinforced

by pultruded CFRP strips [Colombi et al. 2005]

II. Behavior of steel monopoles strengthened with high-modulus CFRP materials [Lanier et al. 2008]

III. Strengthening of an artificially degraded steel beam utilizing a carbon/glass composite system

[Photiou et al. 2006]

IV. Upgrading steel–concrete composite girders and repair of damaged steel beams using bonded

CFRP laminates [Fam et al. 2009]

116

A.2.1. An Experimental, Analytical and Numerical Study of the Static

Behavior of Steel Beams Reinforced by Pultruded CFRP Strips [Colombi

et al. 2005]

Colombi et al. (2005) studied static behavior of steel beams reinforcement by pultruded CFRP strips.

Traditional H shaped steel beams with different CFRP reinforcement geometries bonded to the tension

flanges using different epoxy adhesives were tested under three points bending configuration.

Beams were in good conditions before testing and were not naturally or artificially corroded or

notched. The main objective of the experimental program was the evaluation of the force transfer

mechanism, the increment of the beam load carrying capacity and the bending stiffness.

A.2.1.1. Introduction

Steel structures and especially steel bridges are found to be deteriorated due to corrosions, lack of

appropriate maintenance or fatigue damage. Furthermore, because of higher frequency in traffic and axle

loads, the bridges should be upgraded to meet new standards. Thus, rehabilitation and retrofitting of

bridges require great attention to save new bridge construction costs, time and minimize service

interruption.

The main disadvantage of traditional retrofitting (i.e. welding, bolting or adhesive bonding of steel

plates) are lack of durability and need for heavy equipment to place the plates in their position. Not to

mention that those system are fatigue sensitive as well as result in more dead weight.

FRPs are well known for high tensile strength and stiffness ratio to weight including excellent fatigue

resistance. CFRPs, have lower self-weight than GFRP (density of 1.95 vs. 2.54) and were used by the

authors for retrofitting of the bridges.

Disadvantages of CFRPs include requirement of regular bonding surface, potential brittle failure

modes, lack of data on durability of the adhesive layer as well as the cost of CFRP material. Since CFRPs

are electrically conductive, galvanic corrosion of the metal substrate could occur in an electrolyte solution

(i.e. sea water or water plus de-icing salts).

117

A.2.1.2. Materials/ Specimen Preparation

Unidirectional pultruded CFRP strips (Sika Carbodur M614) with a width of 60 mm and a thickness of

1.4 mm were used. The mechanical properties of the composite strips are reported in Table A.1 with a

Young’s modulus of 197 GPa (28570 ksi).

The two components epoxy resin Sikadur 30 was used for bonding the strips to the bottom flanges

of the specimens TR1 and TR3. The mixing ratio of the epoxy was three part of component A (resin) to

one part of component B (hardener) by weight. The epoxy had a pot life of 70 min and was cured at room

temperature. A less viscous epoxy Sikadur 330 was used to bond the CFRP strips to the tension flange of

specimen TR2. The same resin was also used to wrap the bottom strips of specimen TR3 using the textile

SikaWrap Hex 230C. The mixing ratio in this case was four part of component A (resin) to one part of

component B (hardener) by weight. The epoxy had a pot life of 30 min and was cured at room

temperature. The mechanical properties of the epoxy adhesives are reported in Table A.2.

Table A. 1.Specimens configuration

Specimen # Reinforcement type and dimensions

(mm)

# of

wrapped

layers

Adhesive type and

thickness (mm)

TR0 HEA 140 2.5 m. long - - -

TR1 HEA 140 2.5 m. long Sika Carbodur M614 2000×60×1.4 1 Sikadur 30 1.1

TR2 HEA 140 2.5 m. long Sika Carbodur M614 2000×60×1.4 1 Sikadur 330 0.8

TR3 HEA 140 2.5 m. long Sika Carbodur M614 2000×60×1.4

& 1800 ×60×1.4 2 Sikadur 30 1.1

Table A. 2.Property of the reinforcement material

Material property Sika Carbodur

M614 Sikadur 30 Sikadur 330

Young’s modulus [MPa] >200,000 4500 3800

Tensile strength [MPa] >2800 24.8 (curing time 7

days) 30

Shear strength [MPa] - 24.8 (curing time 7

days) -

Elongation at failure [-] 0.0135 0.01 -

118

Standard hot rolled profiles HEA 140 were used for the experiments. Uniaxial tension tests were

performed on coupons cut from flanges and web with average yield stress and tensile strengths being 331

MPa (48 ksi) and 469 MPa (68 ksi), respectively with a Poisson’s ratio of 0.3.

The steel beams were 2.5 m (8.2 ft) long and the CFRP sheets were cut to proper length. The specimens

TR1 and TR2 were reinforced at the bottom flange with one layer of CFRP made with a pair of parallel

strips of length 2.00 m (6.56 ft) (Figure A.1).

For the specimen TR3, reinforced with two layers, two pairs of CFRP strips of length 2.00 m (6.56

ft) and 1.80 m (5.90 ft), respectively, were used and bonded side by side to the steel girder. In this case,

the bottom strips were wrapped by CFRP sheets to the flange and the web of the beam in order to prevent

stress concentration (Figure A.1). For applying FRPs, the steel surface was treated by an abrasive disk

and then degreased by a xylene based solvent in order to remove grease, rust and oil and to achieve a

rough and clean, chemically active surfaces. Sandblasting was used to treat the CFRP surfaces of the

strips. The adhesive was applied to the steel adherent surfaces with a spatula and the surfaces were then

squeezed together with a small pressure to force out the air bubbles and excess epoxy. After two weeks,

the bondline was cured fairly uniformly with a measured average thickness equal to 1.1 mm (0.04 in) for

specimens TR1 and TR3 and 0.8 mm (0.03 in) for specimen TR2. The specimens were instrumented with

strain gauges shown in Figures. A.2 and A.3, respectively.

Figure A. 1.Bottom side of typical retrofitted girder (Colombi et al. 2005)

119

Figure A. 2.Strain gages locations for beams TR1 and TR2 (Colombi et al. 2005)

Figure A. 3.Strain gages locations for beams TR3 (Colombi et al. 2005)

A linear voltage displacement transducer (LVDT) was installed at the mid-span section of the beam

to verify the deflection. Then, three points bending test were performed (Figure A.4).

120

Figure A. 4.Lateral supports setup for specimens TR2 and TR3 (Colombi et al. 2005)

A.2.1.3. Results

Test results are shown in Table A.3.

Table A. 3.Test results

Test unit

Yield load

(calculated)

(kips)

Elastic

stiffness

(kips/ft)

Maximum

elongation in

the CFRP

strip

Ultimate load

(calculated)

(kips)

TR0 18.50 32.61 - 23.08

TR1 20.64 31.29 0.0039 26.41

TR2 20.64 33.17 0.0068 30.32

TR3 23.00 37.12 - 32.39

A.2.1.4. Conclusions

For all specimens, CFRP reinforcement bonding technique produced an improvement of the load-

carrying capacity within a range of 25 to 47%.

The effect of CFRP strips on the plastic stiffness (beyond steel yield) was significant, while 12%

increment in the elastic stiffness (before steel yield) was observed when the reinforcement

consisted of two layers of CFRP.

As a result of the retrofitting, yield load of the beams was increased up to 47%.

The use of two different epoxy adhesives did not cause significant change both of the load-

deflection curves and of the stresses in the strips (within about 6%).

121

A.2.2. Behavior of Steel Monopoles Strengthened with High-modulus

CFRP Materials [Lanier et al. 2008]

Lanier et al. (2008) studied strengthening technique for steel monopole towers using high modulus CFRP

(HM-CFRP). The design aspects were based on flexural elastic analysis and material properties of the

CFRP and steel monopole shaft. This paper recommends specific connection details to ensure the

development of the forces from the CFRP to the steel tower base plate.


During the past two decades, the telecommunications industry has experienced significant growth in the

wireless sector. Monopole towers are typically used to support the necessary cellular equipment, coaxial

cables and antennas. Community resistance to building new towers is common, so reuse and

strengthening of existing towers is vital and often the only option to support the additional services. As

the need to install additional cellular equipment grows, many of the existing monopoles are structurally

inadequate to support the cellular equipment expansion due to increased lateral wind loads. Thus, there is

a need to develop a cost effective, durable strengthening system that significantly increases the strength

and stiffness of monopoles (Figure A.5).

Figure A. 5.Typical mono pole supporting wireless services (Lanier et al. 2008)

122

Research conducted at North Carolina State University indicates that HM-CFRP materials can

provide an excellent solution to enhance the flexural strength and stiffness of monopoles. The inherent

strength and stiffness qualities of CFRP offer significant load carrying improvement while eliminating

welding or bolting of steel members to the existing structure. HM-CFRP has excellent fatigue as well as

corrosion resistance properties.

A.2.2.2. Materials

Carbon fiber (high-modulus) material was used (Table A.4). The fibers are typically fabricated into solid,

rigid, pultruded laminate strips that are bonded to steel structures as an external reinforcement using an

epoxy adhesive. Another application method is by wet-lay-up, whereby the dry fibers are fabricated in

flexible sheet form and are impregnated with resin and are bonded to the monopole to form a solid, rigid

material. Two types of high-modulus pitch-based carbon fibers were used in the test procedure. Pitch-

based carbon fiber utilizes petroleum pitch fiber as its precursor, unlike the more common

polyacrolonitrile (PAN) based carbon fiber. Material properties for the two types of carbon fiber are listed

in Table A.5.

Table A. 4.Dry fiber material properties for high-modulus carbon fibers

Material Property High-modulus carbon fiber (HM-WL)

Tensile strength (ksi) 377

Tensile modulus (Msi) 92.82

Ultimate elongation (milli strain) 4.0

Effective sheet thickness (in) 0.007

The first monopole was strengthened using HM-CFRP installed in sheet form and impregnated with

resin to increase the flexural capacity of the monopole. The remaining two monopoles were strengthened

using CFRP strips, pultruded from either the high or intermediate-modulus carbon fiber. The properties

for the two types of strips are listed in Table A.5. Steel coupons were taken from the unloaded portion of

the monopole near the tip and tested in accordance with ASTM A 370-02, using plate-type standard

specimens. The average yield strength for the steel and elastic modulus were 455MPa (66 ksi) (based on

the 0.2% offset method) and 194 GPa (28.14 Msi), respectively.

123

Table A. 5.Material properties for pultruded HM-CFRP strips.

Material property Intermediate-modulus CFRP strip High-modulus CFRP strip

Fiber volume fraction (%) 55.4 55.2

Tensile strength (ksi) 177.5 172

Tensile modulus (Msi) 33.21 49.02

Ultimate elongation (milli strain) 5.08 3.32

Compressive strength (ksi) 68.31 51.2

Compressive modulus (Msi) 25.67 45.98

Strip thickness (in) 0.12 0.06

A.2.2.3. Test Procedure

The test procedure consisted of three tests, referred to as Test HM-WL, HM-ST, IM-ST on three separate

steel monopoles. The first part of the designation indicates the modulus of the fibers used, either high

modulus (HM) or intermediate modulus (IM), and the second part of the designation indicates the

application method, either by wet lay-up of dry-fiber sheets (WL) or adhesive bonding of CFRP strips

(ST).

A.2.2.3.1. Fabrication of scaled monopoles

Tested monopoles were fabricated using A572 Grade 65, 5 mm (0.2 in) thick, steel plate and cold-formed

into two, equally sized, six- sided, cross-sections measuring 6096 mm in length. The bend radius between

the flat sections measured 40 mm (1.57 in).

A.2.2.3.2. Surface preparation

Surface preparation of the steel was conducted to ensure complete chemical bonding between the steel

and the adhesive using sandblasting until the white surface is achieved.

A.2.2.3.3. Strengthening configuration

Monopole HM-WL was strengthened by wet lay-up of 330 mm wide unidirectional, CFRP sheets in both

the longitudinal and transverse directions using a saturating epoxy resin. Strengthening was performed to

match the demand placed on the monopole due to the cantilever loading condition. From the preliminary

analysis, it was found that most of the strengthening was required at the base of the monopole and no

strengthening was required from mid-span to the tip (Figure A.6).

124

Figure A. 6.Longitudinal strengthening configuration of Monopole HM-WL (Lanier et al. 2008)

A.2.2.3.4. Testing configuration and instrumentation

The loading applied for the experimental program was designed to simulate flexural wind design loads in

field structures. It was impractical to apply a distributed wind loading, so each monopole was tested as a

cantilever with a single applied load approximately 5750 mm (226 in) from the pole base to generate

equivalent moments and shear forces (Figure A.7).

Figure A. 7.Testing configuration for monopoles (Lanier et al. 2008)

125

A.2.2.4. Test Results and Discussion

Results from the three tests indicate that significant additional flexural yield and ultimate strength and

stiffness can be developed with the use of CFRP strengthening. Table A.6 lists the stiffness of the

unstrengthened and strengthened monopoles at the tip and mid-span for each of the three tests.

Table A. 6.Summary of elastic stiffness increase

Monopole test Loading cycle Stiffness at 0.5L

(kips/in)

Stiffness at L

(kips/in)

Monopole HM-WL Unstrengthened

Strengthened

6.74

8.45

2.17

2.51

Monopole HM-ST Stiffness alone

Strengthened

7.59

10.90

2.28

3.25

Monopole IM-ST Stiffness alone

Strengthened

7.36

12.05

2.22

3.25

Figure A.8 illustrates the measured deflection results from the first and second load cycles of the

Monopole HM-ST test.

Figure A. 8.Comparison of load-deflection behavior of Monopole HM-ST before and after strengthening

(Lanier et al. 2008)

Note: 1 kip = 4.45 kN, 1 inch = 25.4 mm

126


Initial testing has shown that HM-CFRP materials may be used to provide flexural stiffness and

strength increases within the elastic range of the monopole.

To prevent debonding of the high-modulus CFRP material, it is important to consider the actual

state of stress near the end of the CFRP strip including shear and peeling stress components.

Proper installation of the high- modulus CFRP material is critical to ensure that the strengthened

member behaves as intended by the designer.

HM-CFRP materials are an effective alternative to conventional strengthening techniques for

steel monopole towers.

A.2.3. Strengthening of an Artificially Degraded Steel Beam Utilizing a

Carbon/glass Composite System [Photiou et al. 2006]

Photiou et al. (2006) studied rehabilitating of damaged steel structures to ensure the flexural load carrying

capacity of a steel girder by adhesively bonding CFRP composites to its tension flange. The study

discusses the experimental results to investigate the effectiveness of an ultra-high modulus (UHM), and a

high modulus (HM), CFRP prepreg in strengthening an artificially degraded steel beam of rectangular

cross-section under four-point loading. Fabrication of the prepreg material was undertaken in situ and all

the prepregs were bonded to the steel core with use of an adhesive film.


The main factor of steel structures deterioration is corrosion. In the UK, steel and composite bridges on

the national trunk road network managed by the Highways Agency. Although majority of these structures

are found to be relatively new, a large number of old (over 100 years) wrought iron and early steel

structures are found on the railway and canal network. In the USA, according to the National Bridge

Inventory compiled by the Federal Highway Administration, some 43% are made from steel. In addition

to corrosion, other problems such as fatigue, the need to increase the service load and a lack of proper

maintenance are considerable. In many cases, the deteriorated condition will be associated with certain

parts of the bridge and it would be more economical to consider repair and retrofit before a decision is

127

made to replace an entire bridge. Repairing, upgrading and rehabilitation are more economical than the

replacement of the whole structure. Furthermore, in the case of bridges the upgrading and rehabilitation

takes less time and reduces service interruption. A method of providing adequate strengthening capacity

to steel structures is welding or adhesively bonding and end bolting steel cover plates. Because these

structures were old, serious difficulties with application of these techniques were revealed, such as

requirement of heavy lifting equipment to place the plates in position and complicated bonding/welding

procedures. Welding can also impose residual stresses into the material and bring about possible fatigue

problems.

The superior mechanical, fatigue and in-service features of CFRP composites, make them excellent

choice not only for rehabilitating but also for retrofitting and strengthening bridges members. When

upgrading a structural steel member with a composite, the type of fiber used in the composite must be

chosen carefully. The HM CFRP composites will have a stiffness of the same order as that of the steel;

this implies that, in plate bonding applications, substantial load transfer can only take place after the steel

has yielded. With the UHM CFRP composites, where the stiffness of the composite material is

significantly higher than that of the steel, substantial load transfer will take place even before the steel has

yielded, but it should be noted that the ultimate strain value of this material is quite low (e.g., 0.4%). The

successful strengthening of a steel structure with FRP materials completely depends on the effectiveness

of the adhesive used (Photiou et al., 2003).

Another consideration, when adhering carbon fiber to steel, is that of galvanic interaction between

the two materials. Contact between CFRP and metals as an electrolyte in the case of seawater, or Chloride

(e.g. Cl¯) contaminated concrete is extremely undesirable (particularly if the metal is highly active and

low in the galvanic series). Both steel and CFRP composites may be adversely affected when in contact

and immersed in sea water. Blisters can form on the surface of the composite. Placement of GFRP layers,

between CFRP and steel, will solve this problem by preventing direct contact between the two materials.

Another advantage of incorporating the GFRP composite between the adhesive and the first layer of

CFRP, is obtaining higher failure strength of the joint. This is due to a more gradual change in shear

128

stress, when load is being transferred to the CFRP composite from the steel to adhesive and GFRP layers.

Photiou et al. have demonstrated the effectiveness of stress transfer by the addition of a GFRP layer

between two high stiffness components bonded together with a low stiffness polymer. Four beams have

been retrofitted, two by means of a U-shaped prepreg unit and the other two by a prepreg flat plate unit.

One of each of the geometric types was manufactured from an UHM, and from an HM CFRP. In all

cases, the laminates were bonded to the tensile flange by a compatible adhesive film. Both the U-shaped

and the flat plate units had identical laminate lay-ups; these consisted of unidirectional CFRP composites

and ±45° GFRP composites placed along the length of the beam. However, in the U-shaped composite,

the GFRP component was also taken up the vertical sides of the beams to the height of the modified

neutral axis. This vertical component was a continuation of the ±45° GFRP composite bonded onto the

tension flanges and no CFRP laminates were placed in the webs of the beam. Since the tensile strength of

the matrix dominated GFRP component is approximately one- fifth of that of the unidirectional CFRP

component and the strain to failure is more than four times greater than that of the CFRP, the GFRP

component does not exert a great influence on the overall strength of FRP laminate.

A.2.3.2. Materials

Rectangular steel cross section used in this study with Young’s modulus of 205 GPa (29.73 Msi) is shown

in Figure A.9.

FRP material properties are shown in Table A.7. Figure A.10 shows the tensile stress-strain

response of FRP and steel materials.

Table A. 7.Mechanical properties of FRP materials and adhesive film

Material Tensile strength

(ksi)

Elastic modulus

(Msi)

Ultimate strain

(%) Poisson ratio

UHM-CFRP

(unidirectional) 162.4 39.16 0.4 0.32

HM-CFRP

(unidirectional) 306 19.58 1.6 0.28

GFRP (±45° to line

of action load) 31.18 2.32 1.7 0.15

Film adhesive 4.64 0.54 0.9 0.37

129

Figure A. 9.(a) Schematic diagram of a RHS steel beam upgraded with a hybrid composite system. (b)

tacking sequence of the hybrid composite system (Tc is 0.6 mm for UHM-CFRP and 1.2 mm for HM-

CFRP) (Photiou et al. 2006)

A.2.3.3. Sample Preparation

The material used was made from a hybrid of unidirectional CFRP (either high or ultra-high modulus)

and ±45° GFRP composite. Both the ultra-high and the high-modulus CFRP comprised of two double ply

laminates with ply thicknesses being 0.3 and 0.6 mm, respectively, and carbon fibers aligned with the

longitudinal direction of the beam. Three single plies of GFRP were used with glass fibers positioned at

±45° to the longitudinal direction of the steel beam.

The various layers were stacked as follows: a single GFRP ply followed by one double-ply CFRP

laminate, followed by a single GFRP ply, followed by the other double-ply CFRP and finally another

130

single GFRP ply. The first GFRP ply was adjacent to the adhesive film and hence separated the steel from

the CFRP. Figure A.9(a) and (b) show the stacking sequence of the FRP components on to the steel beam,

as well indicate the strain gauge positions on the central section.

Figure A. 10.Tensile stress–strain response of steel and FRP materials (Photiou et al. 2006)

A.2.3.4. Test Procedure

Figure A.11 illustrates the instrumentation of the beam.

Figure A. 11.Arrangement for beam tests (Photiou et al. 2006)


HM-CFRP had lower MOE than steel but higher strain than steel and UHM-CFRP had higher

MOE than steel but lower strain than steel.

131

The composite containing the UHM CFRP failed when the ultimate strain of the carbon fiber was

reached in the pure moment region (fiber breakage), whereas HM-CFRP exhibited ductile

response with no fiber or adhesive failure up to a maximum deflection of span/40. The ultimate

load in theses beam was 10% higher than that achieved in the beams with UHM-CFRP. It can be

concluded that, the ultimate strains in the HM-CFRP are not exceeded and the bonding

mechanisms are sufficient and the steel beam can be deformed well into its plastic region.

The failure load exceeded the plastic collapse load of the undamaged beam, which elaborates the

effectiveness FRP application.

By extending the hybrid composite system, with GFRP prepregs only, up the vertical sides of the

beam, to the neutral axis height, it was shown that even failure due to fiber breakage was

localized and the steel beam continued to exhibit a degree of composite action with the FRP

composite material. Thus, the advantage of the U-shaped system over the flat plates is that it

seems to have the ability to contain the failure and to provide a degree of stiffening even after

substantial damage has taken place.

A.2.4. Upgrading Steel–concrete Composite Girders and Repair of

Damaged Steel Beams Using Bonded CFRP Laminates [Fam et al. 2009]

Fam et al. (2010) studied strengthening of intact steel-concrete composite (bridge) girders and damaged

notched steel beams by applying of CFRP layers on tension zone. Three large-scale steel-concrete

composite girders from actual bridge girders were scaled down (4:1) for testing in 4 point bending test

(Figure A.12(a)). Fifteen small-scale wide flange sections with different imposed degradation in tension

zone (notching) were tested in 4 point bending test (Figure A.12 (b)). Application of CFRP layers lead to

increments in flexural strength and stiffness of the girders as well as of those in wide flange beams.

132

Figure A. 12.Cross-section configurations of test specimens: (a): strengthening intact composite girders

and (b): repair of notched beams (Fam et al. 2009)


CFRP laminates were considered for bridge strengthening due to their excellent fatigue properties and

noncorrosive features. Standard modulus (SM), high modulus (HM), and ultra-high modulus (UHM)

CFRP refer to materials with Young’s moduli, less than 200 GPa (29 Msi), of 200–400 GPa (29-58 Msi),

and higher than 400 GPa (58 Msi), respectively.

Literature review by Fam et al. (2009) indicates that applying of SM-CFRP and HM-CFRP layers

on steel-concrete composite girders, lead to increases in ultimate load ranged from 44% to 76%,

depending on CFRP layers and thickness, though stiffness increment was insignificant. Compression

failure in concrete controlled the cross section failure. Schnerch and Dawood (2005) used externally

bonded HM-CFRP and UHM-CFRP laminates to strengthen steel–concrete composite beams (UHM-

CFRP’s MOE is significantly higher than steel). The HM-CFRP laminates increased both the elastic

stiffness and flexural strength of the beams by 10% and 16%, respectively, whereas the UHM-CFRP

system, with 70% larger cross- sectional area, increased both the elastic stiffness and flexural strength of

the beams by 36% and 45%, respectively. The beams failure was rupture of the CFRP laminates.

Research on the repair of steel beams using CFRP has focused on the repair of environmentally

damaged (corroded) beams taken from older bridges. Tavakkolizadeh and Saadatmanesh (2003), and

Shaat and Fam (2004) simulated fatigue damage in steel beams and steel–concrete composite beams by

133

cutting a notch in the tension flange of the steel. These studies have shown that the repair of damaged

steel beams using CFRP is promising.

In this study by Fam (2009), CFRP plates were bonded only to part of the span, unlike previous

studies where the plates covered the full length of the flange. The study also investigated the repair of

steel beams with simulated fatigue damage, using CFRP plates and sheets with Young’s moduli higher

than those used in most of the previous studies. The modulus of CFRP materials used in repair and

strengthening ranged from 152 to 396 GPa (22 to 57 Msi).

A.2.4.2. Materials

1. Steel-concrete composite girders

W 250 × 25 hot-rolled steel sections with yield strength of 345 MPa (50 ksi).

For the concrete slab, the average measured compressive strength of concrete cylinders was

39.8 MPa (5.77 ksi).

Two types of CFRP pultruded plates, 1.4 mm thick, were used in strengthening the girders,

namely, C1 (SikaCarboDurM914) and C2 (SikaCarboDurH514). For C1, the average

measured strength and MOE were 1914 MPa (277 ksi) and 152GPa (22 Msi), respectively,

and for C2 were 1475 MPa (214 ksi) and 313 GPa (45 Msi), respectively. Sikadur-30, a

viscous epoxy resin, was used to bond the CFRP plates to the steel.

2. Beams

W 100 × 19 hot-rolled steel sections with yield strength of 398 MPa (57 ksi).

Two different types of CFRP were used, namely, C3, which is a 0.19 mm thick carbon-fiber

sheet (Dialead F637400) and C4, which is a 2 mm thick pultruded CFRP plate (Dialead

HM1020). The C3 sheets were bonded using Tyfos epoxy resin. The thickness of a cured

single layer was 0.54 mm. SpaBond 345 viscous epoxy resin was used to bond the C4 plates.

For C3, the average measured strength and modulus of elasticity were 521MPa (75.56 ksi)

134

and 201GPa (29 Msi), respectively, and for C4 were 1431 MPa (207 ksi) and 396GPa (57.43

Msi), respectively.

A.2.4.3. Fabrication of Test Specimens

1. Girders

Pairs of steel studs were welded to the compression flanges of the 6100 mm long steel beams, as shown in

Figure A.13(a). The underside of the tension flanges was sand blasted (Figure A.13(a)). The CFRP plate

was placed on the steel surface and pressed with a rubber roller, using enough pressure to squeeze the

adhesive out from both sides (Figure A.13(a)). A 50 mm wide GFRP sheet was used at all termination

points of the CFRP plates as a transverse wrap around the tension flange and also extended 50 mm within

the web.

The concrete slabs were cast in an inverted position on a smooth flat floor for convenience (Figure

A.13(a)). A double layer of 150 mm × 150 mm × 5 mm (5.9 in × 5.9 in × 0.2 in) welded wire steel mesh

was provided at mid-thickness of the slab. The steel girders were supported on the edges of the formwork

in an inverted position with the shear studs projecting downwards into the forms. High-slump concrete

was poured into the formwork, vibrated, and the surface was finished. After seven days, the specimens

were released from the form and allowed to air cure.

2. Beams

Notches were created at mid-span of the W-sections using a band-saw (1.3 mm thick) or a grinder (3.3

mm thick). Beams B8–B15 were sandblasted and cleaned prior to CFRP installation. The wet lay-up

system was used to install three layers of CFRP type C3 sheets. The sheets were saturated with resin prior

to installation on the steel surface. Each layer was then rolled onto the steel flange to remove any air

pockets and align the sheets properly. The sheets were installed to provide a tapered termination, by

having the termination points of the three layers spaced at 25 mm. The sheets were left to cure for a

minimum of 7 days prior to testing. For CFRP type C4, the plates were beveled at an angle of 10° at the

ends, such that the thickness of adhesive was increased at the end, in order to minimize peeling stresses.

This practice was attempted as a different method from the GFRP end wraps used in girders. Figure

135

A.13(b) shows the application of the epoxy resin to the notched steel flanges. E-Glass beads of 0.8 mm

diameter were scattered on the surface to ensure a uniform adhesive thickness. The CFRP plates were

then placed on the surface, rolled to remove air pockets, and clamped. Extra adhesive was provided at

termination points.

136

Figure A. 13.Fabrication of test specimens: (a) girders and (b) beams (Fam et al. 2009)

A.2.4.4. Test Setup and Instrumentation

1. Girders

Girders were tested on a simply supported configuration (with the use of steel rollers) with a span of 5940

mm (19.5 ft). Tests were performed in four-point bending with a distance of 1000 mm (3.28 ft) between

the loads, (Figure A.14(a)). The two loads were applied across the full width of the flange. Specimens

were braced at support locations, using two vertical HSS posts mounted under the concrete slab, on each

side of the web. The girders were monotonically loaded at a rate of 1.75 mm/min, using a 1000 kN Riehle

machine. Two linear potentiometers (LPs) were used to measure deflections at both sides of the girders, at

mid-span. Longitudinal strains along the steel girder and CFRP plates were measured using several 5 mm

long electric resistance strain gauges (Figure A.14(a)). Two 100 mm displacement-type strain gauges

were also attached to both the top and bottom sides of the concrete slab.

2. Beams

Figure A.14(b) shows a schematic of the test setup (four-point bending configuration) with a span of 900

mm (2.95 ft) and a constant moment region of 200 mm (7.87 in). Two LPs (Linear potentiometers) were

installed at mid-span to measure deflection. All specimens were tested monotonically using a 1000 kN

capacity Riehle machine at a constant stroke rate of 0.75 mm/min.

137

Girders

Figure A. 14.Test setup and instrumentation for: (a) girders and (b) beams (Fam et al. 2009)

138

A.2.4.5. Test Results and Discussions

A summary of test results for girders and beams are in Table A.8 and A.9.

Table A. 8.Summary of test results of girders.

Spec.

ID

Transformed

moment of

inertia×106

(in4)

Percentage

gain

Stiffness

(kips/in)

Percentage

gain

Yield

load

(kips)

Percentage

gain

Ultimate

load

(kips)

Percentage

gain

G1 20.54 - 20.95 - 19.11 - 32.37 -

G2 23.04 12 24.50 17 21.81 14 48.56 50

G3 23.74 16 24.90 19 23.15 21 48.78 51

Table A. 9.Summary of test results of beams.

Beam

Change in elastic stiffness compared to Change in ultimate stiffness compared to

Control

unnotched

Notched

unrepaired

Control

unnotched

Notched

unrepaired

B3 0 - 0 -

B4 -15 - -9 -

B5 -40 - -58 -

B6 -49 - -66 -

B7 -21 - -60 -

B8 21 7 0 0

B9 -7 0 0 10

B10 18 107 -57 4

B11 31 125 -23 85

B12 24 122 -57 4

B13 5 107 -21 132

B14 3 86 -23 93

B15 21 54 -58 77

For analytical model, a strain compatibility model has been developed to predict the behavior of

CFRP-strengthened composite girders. Based on the test results of beams with dimensions realistically

proportional to an actual bridge, it was shown that CFRP plates bonded to the steel surface had excellent

bond and no debonding was observed prior to concrete crushing. Therefore, within the scope of this

study, the model does not account for CFRP debonding. The model was verified using test results of

beams and used in a parametric study. Figure A.15(a) illustrates the strain and stress distributions over a

composite section. An incremental strain approach is adopted, where the concepts of equilibrium and

139

strain compatibility are satisfied at each loading step. The following constitutive models were assumed, as

shown in Figure A.15(b):

i. Elastic–perfectly plastic stress–strain curve for steel

ii. A second degree parabola concrete in compression

iii. CFRP materials behave linearly up to rupture. The model neglects residual stresses in the

steel beam.

Figure A. 15.Summary of analytical model components: (a) Cross-section analysis and (b) Constitutive

models (Fam et al. 2009).


CFRP plates bonded over two thirds of the span have increased flexural strength and stiffness of

intact steel–concrete compo site girders significantly by 51% and 19%, respectively.

The outer CFRP short layer debonded prematurely, followed by concrete crushing. No debonding

occurred between the inner CFRP layer and steel.

140

Increasing MOE of CFRP leads to a reduction in flexural strength gain and ductility of steel–

concrete girders, as a result of the reduced tensile strength and strain of CFRP. However, it results

in increasing flexural stiffness of the girders.

Similar gains in elastic stiffness and yielding moment of steel–concrete girders are achieved by

either increasing MOE or cross-sectional area of CFRP. The effect of MOE of CFRP on flexural

stiffness is even more pronounced after yielding of steel.

Removing 100% of the flange in W-sections reduces stiffness and ultimate capacity significantly

(by about 60%). In this case, repair using CFRP is promising. Strength recoveries up to 79% of

the intact beam strength were achieved.

Removing 50% of the tension flanges of W-sections reduces stiffness and ultimate capacity very

little (by only up to 9%), with reducing the thickness being relatively more severe than reducing

the width of the flange. In this case gains due to CFRP repair systems were negligible.

High modulus CFRP plates used to repair W-sections with 100% loss of flange may fail by de-

bonding or rupture, depending on CFRP type and cross-sectional area.

141

APPENDIX-B MODULUS OF RUPTURE

1. Calculation of Bending Stress

Bending Stress: σ =

(B.1)

Where:


(B.2)

Point load: P



∑ (B.3)


Table B. 1.Test results summary for GFRP-Wood composite coupons

Coupon

ID

Fiber/

fabric

config.

PU* Moisture

content

Transformed

moment of

inertia (in4)

Static

bending

strength

(lbs-in)

MOR

(psi)

Deflection

at failure

(in)

Deflection

at

reference

load (in)

1 A No 40% 0.067 254 1321 0.24 0.134

2 A No 12% 0.067 687 3577 0.38 0.038

3 B No 40% 0.073 819 3627 0.54 0.054

4 B No 12% 0.073 711 3150 0.31 0.060

5 A Yes 40% 0.067 885 4607 0.56 0.061

6 A Yes 12% 0.067 915 4760 0.63 0.084

7 B Yes 40% 0.073 935 4141 0.51 0.055

8 B Yes 12% 0.073 986 4369 0.52 0.054

PU- Polyurethane

142

2. Coupon # 3 (without Polyurethane & 19 layers)

C = 0.32 in

It = 0.073 in4



= 819 lbs–in

MOR: σ =

= 3627 psi

3. Coupon # 7 (with Polyurethane & 19 layers)

Figure B. 1.Load vs. Deflection graph for composite coupon # 7

C = 0.32 in

It = 0.073 in4



= 935 lbs–in

MOR: σ =

= 4141 psi

0

100

200

300

400

500

600

700

800

900

1000

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Laod (lbs)

Deflection (in)

Load vs. Deflection

143



C = 0.34 in

It = 0.067 in4



= 886 lbs–in

MOR: σ =

= 4607 psi

0

100

200

300

400

500

600

700

800

900

1000

0 0.1 0.2 0.3 0.4 0.5 0.6

Load (lbs)

Deflection (in)

Load vs. Deflection

144

5. Coupon # 4 (without Polyurethane & 19 layers)


C = 0.32 in

It = 0.073 in4



= 711 lbs–in

MOR: σ =

= 3150 psi


C = 0.34 in

It = 0.067 in4



= 915 lbs–in

MOR: σ =

= 1321 psi

0

100

200

300

400

500

600

700

800

0 0.1 0.2 0.3 0.4 0.5 0.6

Laod (in)

Deflection (in)

Load vs. Deflection

145

APPENDIX-C TRANSFORMED MI

1. Calculations of Transformed Moment of Inertia (It) for GFRP

Composite Ties

Elastic Modulus of Derakane 510A-40 (Em) from Table 4.1

Em = 0.49 × 106 psi

Elastic Modulus of Glass Fibers (Ef) from Table 4.4

Ef = 10.6 × 106 psi

Elastic Modulus of the Composite (EComp) from Appendix ‘G’

EComp = 2.23 × 106 psi

Table C. 1. Calculation of transformed moment of inertia (MI)

Tie Iw Ew EIw EGFRP Modular d Af It

ID (in4) (psi) (psi) (psi) ratio (in) (in2) (in4)

1 232 1.25×106 2.90×10

8 2.23×10

6 1.79 3.61 7.59 408

2 226 8.71×105 1.96×10

8 2.23×10

6 2.57 3.66 7.70 490

3 228 1.27×106 2.90×10

8 2.23×10

6 1.76 3.51 7.78 396

4 219 1.28×106 2.81×10

8 2.23×10

6 1.75 3.71 7.59 401

5 219 1.21×106 2.65×10

8 2.23×10

6 1.85 3.71 7.59 412

6 231 1.17×106 2.70×10

8 2.23×10

6 1.91 3.66 7.78 429

7 235 8.80×105 2.06×10

8 2.23×10

6 2.54 3.66 7.66 495

8 224 1.01×106 2.26×10

8 2.23×10

6 2.21 3.71 7.70 458

9 233 1.24×106 2.89×10

8 2.23×10

6 1.80 3.66 7.55 415

10 208 1.27×106 2.65×10

8 2.23×10

6 1.76 3.56 7.55 376

11 196 1.24×106 2.43×10

8 2.23×10

6 1.80 3.51 7.55 363

12 203 1.17×106 2.38×10

8 2.23×10

6 1.91 3.61 6.54 365

13 235 1.10×106 2.59×10

8 2.23×10

6 2.03 3.63 7.35 432

14 198 9.00×105 1.78×10

8 2.23×10

6 2.48 3.61 6.61 411

15 184 1.29×106 2.38×10

8 2.23×10

6 1.73 3.61 6.85 339

16 221 1.14×106 2.53×10

8 2.10×10

6 1.84 3.52 5.13 338

146

APPENDIX-D FLEXURAL RIGIDITY

1. Calculation of Flexural Rigidity


(D.1)

Where:

Bending Moment: M =

(D.2)

Point load: P



∑ (D.3)


2. Tie # 1

Figure D. 1.Stress vs. Strain graph for GFRP composite tie # 1

C = 3.8 in. & It = 408 in4

EI = 1.76 × 106 × 408 = 7.19 × 10

8 lbs-in

2

y = 1.7645x - 0.3805

0

100

200

300

400

500

0 50 100 150 200 250 300

Stress (psi)

Strain (µԑ)

Stress vs. Strain

147

3. Tie # 2


C = 3.85 in & It = 490 in4

EI = 1.38 × 106 × 490 = 6.77 × 10

8 lbs-in

2

4. Tie # 3


C = 3.7 in. & It = 396 in4

EI = 2.063 × 106 × 396 = 8.17 × 10

8 lbs-in

2

y = 1.3845x + 0.014

0

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400

-50 0 50 100 150 200 250 300

Stress (psi)

Strain (µԑ)

Stress vs. Strain

y = 2.0633x + 0.3551

0

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450

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Stress (psi)

Strain (µԑ)

Stress vs. Strain

148

5. Tie # 5


C = 3.9 in. & It = 412 in4

EI = 2.72 × 106 × 412 = 11.21 × 10

8 lbs-in

2

6. Tie # 6


C = 3.85 in. & It = 429 in4

Flexural Rigidity: EI = 2.66 × 106 × 429 = 11.39 × 10

8 lbs-in

2

y = 2.7217x + 4.0227

0

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500

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Stress (psi)

Strain (µԑ)

Stress vs. Strain

y = 2.6554x + 16.037

0

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450

0 50 100 150 200

Stress (psi)

Strain (µԑ)

Stress vs. Strain

149

7. Tie # 7


C = 3.85 in. & It = 429 in4

EI = 1.11 × 106 × 548 = 5.48 × 10

8 lbs-in

2

8. Tie # 8


C = 3.9 in. & It = 458 in4

EI = 1.33 × 106 × 458 = 6.10 × 10

8 lbs-in

2

y = 1.1101x + 19.654

0

50

100

150

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400

0 50 100 150 200 250 300 350

Stress (psi)

Strain (µԑ)

Stress vs. Strain

y = 1.3314x - 1.8289

0

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450

0 50 100 150 200 250 300 350

Stress (psi)

Strain (µԑ)

Stress vs. Strain

150

9. Tie # 9


C = 3.85 in. & It = 415 in4

EI = 1.80 × 106 × 415 = 7.73 × 10

8 lbs-in

2

10. Tie # 10


C = 3.75 in. & It = 376 in4

EI = 1.77 × 106 × 376 = 6.71 × 10

8 lbs-in

2

y = 1.8033x + 3.0526

0

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100

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450

0 50 100 150 200 250

Stress (psi)

Strain (µԑ)

Stress vs. Strain

y = 1.7744x + 4.1572

0

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300

400

500

0 50 100 150 200 250 300

Stress (psi)

Strain (µԑ)

Stress vs. Strain

151

11. Tie # 11


C = 3.7 in. & It = 363 in4

EI = 1.66 × 106 × 363 = 6.09 × 10

8 lbs-in

2

12. Tie # 12


C = 3.8 in. & It = 365 in4

EI = 1.18 × 106 × 365 = 4.31 × 10

8 lbs-in

2

y = 1.6652x + 1.1443

0

100

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500

0 50 100 150 200 250 300

Stress (psi)

Strain (µԑ)

Stress vs. Strain

y = 1.1812x + 3.9794

0

100

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300

400

500

0 100 200 300 400 500

Stress (psi)

Strain ((µԑ)

Stress vs. Strain

152

13. Tie # 13


C = 3.83 in. & It = 432 in4

EI = 2.19 × 106 × 432 = 9.50 × 10

8 lbs-in

2

14. Tie # 14


C = 3.80 in. & It = 411 in4

EI = 1.41 × 106 × 411 = 5.83 × 10

8 lbs-in

2

y = 2.1982x - 15.487

0

50

100

150

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450

0 50 100 150 200

Stress (psi)

Strain (µԑ)

Stress vs. Deflection

y = 1.4172x - 1.1383

0

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450

0 50 100 150 200 250 300 350

Stress (psi)

Strain (µԑ)

Stress vs. Strain

153

15. Tie # 15


C = 3.80 in. & It = 339 in4

EI = 2.14 × 106 × 370 = 7.30 × 10

8 lbs-in

2

y = 2.1443x - 0.8852

0

100

200

300

400

500

600

0 50 100 150 200 250

Stress (psi)

Strain (µԑ)

Stress vs. Strain

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