Behavior of GFRP Bridge Decks for Highway Bridges

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Abstract

NELSON, JAMES LEE. Behavior of GFRP Bridge Decks for Highway Bridges. (Under the direction of Dr. Sami Rizkalla)

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Behavior of GFRP Bridge Decks for Highway Bridges

by

JAMES LEE NELSON III

A thesis submitted to the graduate faculty of North Carolina State University

in partial fulfillment of the

requirements for the degree of

Master of Science

CIVIL ENGINEERING

Raleigh, NC September 2005

Approved By:

Dr. Sami Rizkalla (Chair)

Dr. Emmett Sumner L-A ~

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© Copyright 2005 by

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Acknowledgements

I would like to acknowledge the generous financial and technical support that I received from Martin Marietta Composites. I would like to thank Grant Godwin and Greg Solomon for their continuing support. I would also like to thank Dan Richards and Larry Dickenson for their support.

Next, I would like to thank the members of my committee, Dr. Emmett Sumner and Dr. Eric Klang. Their support and encouragement throughout the process was invaluable.

I would like to express my sincere gratitude to my advisor and mentor, Dr. Sami Rizkalla, for his unwavering and continuing support.

Special thanks go to Mr. Jerry Atkinson and Mr. William Dunleavy who provided me with outstanding guidance and technical assistance as well as friendship while in the laboratory.

I would like to acknowledge the guidance and help that I received from Dr. Amir Fam and Dr. Tarek Mohamed.

I thank Mrs. Pat Rollins and Mrs. Amy Yonai for their help with many administrative tasks.

Thanks to all my fellow graduate students at the Constructed Facilities Laboratory for both their friendship and assistance.

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Biography

Lee Nelson began his study of engineering in 1996 at Virginia Military Institute (VMI) in Lexington, VA where he received a full merit based scholarship through the Institute Scholar program. As part of this scholarship program, Lee spent two semesters studying in the United Kingdom. The first semester was spent at the University of Aberdeen in Aberdeen Scotland while the second semester was spent at the Royal Military College of Science in Shrivenham England. While at VMI, Lee received many awards for academic achievement in the department of civil engineering. In 2000, Lee obtained his Bachelor’s of Science in Civil Engineering with a minor in Mathematics. After spending six months on a successful thru-hike of the Appalachian Trail, Lee continued his academic pursuits at North Carolina State University under the supervision of Dr. Sami Rizkalla. In 2004 Lee was hired by NC State University as Research Engineer and Laboratory Manager of the Constructed Facilities Laboratory where his focus is structural code compliance testing for industrial clients.

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Table of Contents

List of Tables ...viii

List of Figures...ix

List of Symbols ...xiii

1 INTRODUCTION...1

1.1 GENERAL...1

1.2 OBJECTIVES...1

1.3 SCOPE...2

2 LITERATURE REVIEW ...4

2.1 CORROSION PROBLEM...4

2.2 CORROSION IN REINFORCED CONCRETE BRIDGE DECKS...4

2.3 THE COST OF CORROSION...5

2.4 THE FRPSOLUTION...6

2.5 THE DURASPAN®COMPOSITE BRIDGE DECK...6

2.5.1 Constituent Materials ...7

2.5.2 Manufacturing...8

2.6 ADVANTAGES OF FRPBRIDGE DECKS...9

2.7 CHALLENGES TO THE USE OF FRPBRIDGE DECKS...10

2.8 HISTORY OF THE DURASPAN®BRIDGE DECK...11

2.8.1 Experimental Programs for the DuraSpan® Bridge Deck ...11

2.8.2 Analytical Modeling of the DuraSpan® Bridge Deck...13

2.8.3 DuraSpan® Coordinate System ...13

3 EXPERIMENTAL PROGRAM AND TEST RESULTS ...16

3.1 OVERVIEW...16

3.2 FLEXURAL TEST SPECIMENS...16

3.2.1 Specimen 766-4-7.2 ...18

3.2.2 Secimens 766-1-4a and 766-1-4b...22

3.2.3 Specimen 500-1-4a ...25

3.2.4 Specimen 500-1-4b ...28

3.2.5 Specimen 500-2-4...32

3.2.6 Specimen 766-2-4...35

3.2.7 Specimen 500-1-3...38

3.3 FLEXURAL TEST RESULTS...42

3.3.1 Influence of Girder Spacing on the DuraSpan® 500 ...42

3.3.2 Effect of Number of Bonded Modules on the DuraSpan® 500 ...43

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3.4 TRANSVERSE TEST...46

3.5 CONNECTION BEHAVIOR...50

3.6 COEFFICIENT OF THERMAL EXPANSION TESTING...53

4 MODELING OF THE BEHAVIOR ...58

4.1 OVERVIEW...58

4.2 BENEFITS OF MACRO BASED PROGRAMMING...59

4.3 MODELLING OF THE DURASPAN® BRIDGE DECK...59

4.3.1 Modeling of the steel loading plate ...65

4.3.2 Modeling of the neoprene supports and load pad ...65

4.3.3 Material Properties...67

4.4 OPTIMIZATION OF MATERIAL PROPERTIES...75

4.4.1 Optimization Results ...78

4.4.2 Interpretation of Results ...80

5 SUMMARY AND CONCLUSIONS...82

5.1 GENERAL SUMMARY...82

5.2 IMPORTANT CONCLUSIONS...82

5.3 RECCOMENDATIONS FOR FUTURE RESEARCH...83

References...85

Appendix A - Dimensions of the DuraSpan® Bridge Deck...87

Appendix B - The Pultrusion Process ...90

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List of Tables

Table 1 – Summary of Flexural Testing ...18

Table 2 – Maximum Loads Prior to First Loss of Load for Connection Tests...51

Table 3 – Results of CTE Testing ...57

Table 4 – Summary of Optimization Ranges...68

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List of Figures

Chapter 2

Figure 1 – DuraSpan® 766 Bridge Deck Profile ...7

Figure 2 – DuraSpan® 500 Bridge Deck Profile ...7

Figure 3 – Schematic of the Pultrusion Process ...9

Figure 4 – DuraSpan® Coordinate System ...15

Chapter 3

Figure 5 – Schematic of Typical Flexural Test Setup ...17

Figure 6 – Test Setup for Specimen 766-4-7.2 ...19

Figure 7 – Load Deflection Behavior of Specimen 766-4-7.2 from 0 to 70 kips of Applied Load ...20

Figure 8 – Load Deflection Behavior of Specimen 766-4-7.2 from 0 to 100 kips of Applied Load ...20

Figure 9 – Vertical Deflection Profile Across the Longitudinal Span of Specimen 766-4-7.2 ...21

Figure 10 – Vertical Deflection Profile Across the Lateral Span of Specimen 766-4-7.2 ...21

Figure 11 – Failure of Specimen 766-4-7.2 ...22

Figure 12 – Test Setup for Specimen 766-1-4a ...23

Figure 13 – Load Deflection Behavior of Specimens 766-1-4a and 766-1-4b ...23

Figure 14 – Rotation of Cross Section for Specimen 766-1-4b ...24

Figure 15 – Cracks Opening in Web-Flange Interface of Specimen 766-1-4b ...24

Figure 16 – Cracks Opening in Corners of Specimen 766-1-4b ...25

Figure 17 – Test Setup for Specimen 500-1-4a ...26

Figure 18 – Load Deflection Behavior for Specimen 500-1-4a ...26

Figure 19 – Vertical Deflection Profile Across the Lateral Span for Specimen 500-1-4a ...27

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Figure 21 – Delamination of Web Flange Interface for Specimen 500-1-4a ...28

Figure 22 – Shear in Web of Specimen 500-1-4a ...28

Figure 23 – Test Setup for Specimen 500-1-4b ...29

Figure 24 – Load Deflection Behavior of Specimen 500-1-4b ...30

Figure 25 – Vertical Deflection Profile Across the Lateral Span for Specimen 500-1-4b ...30

Figure 26 – Vertical Deflection Profile Across the Longitudinal Span for Specimen 500-1-4b ...31

Figure 27 – Shear in Web of Specimen 500-1-4b ...31

Figure 28 – Shear in Web of Specimen 500-1-4b ...32

Figure 29 – Test Setup for Specimen 500-2-4 ...33

Figure 30 - Load Deflection Behavior for Specimen 500-2-4 ...33

Figure 31 – Vertical Deflection Profile Across the Lateral Span for Specimen 500-2-4 ...34

Figure 32 – Vertical Deflection Profile Across the Longitudinal Span for Specimen 500-2-4 ...34

Figure 33 – Shear and Delamination of Specimen 500-2-4 ...35

Figure 34 – Test Setup for Specimen 766-2-4 ...36

Figure 35 – Load Deflection Behavior of Specimen 766-2-4 ...36

Figure 36 – Vertical Deflection Profile Across the Lateral Span for Specimen 766-2-4 ...37

Figure 37 – Vertical Deflection Profile Across the Longitudinal Span for Specimen 766-2-4 ...37

Figure 38 - Delamination of Specimen 766-2-4 ...38

Figure 39 – Shear Failure in the Web of Specimen 766-2-4 ...38

Figure 40 – Test Setup for Specimen 500-1-3 ...39

Figure 41 – Load Deflection Behavior of Specimen 500-1-3 ...40

Figure 42 – Vertical Deflection Profile Across the Lateral Span for Specimen 500-1-3 ...40

Figure 43 – Vertical Deflection Profile Across the Longitudinal Span for Specimen 500-1-3 ...41

Figure 44 – Failure of Specimen 500-1-3 ...41

Figure 45 – Comparison of Specimen 500-1-4a and Spceimen 500-1-3...43

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Figure 47 – Vertical Deflection Profile Across the Lateral Span for Specimen

500-2-4 ...45

Figure 48 – Comparison of Specimen 766-1-4a and Specimen 766-2-4 ...46

Figure 49 – Test Setup for Transverse Test of DuraSpan® 766 ...48

Figure 50 – Load Deflection Behavior of Transverse Specimen ...49

Figure 51 – Strain Measurements in Top Flange of Transverse Specimen ...49

Figure 52 – Strain Measurements in Bottom Flange of Transverse Specimen ...50

Figure 53 – Test Setup for Connection Tests...51

Figure 54 – Load Deflection Behavior of Pin Connections ...52

Figure 55 – Load Deflection Behavior of Bolt Connections...52

Figure 56 – DuraSpan® Bridge Decks in the Environmental Chamber for CTE Testing...56

Figure 57 – Instrumentation for CTE Testing. ...56

Figure 58 – Samples of Polymer Concrete Overlay, Titanium Silicate Glass, Steel and Carbon Fiber in the Environmental Chamber for CTE Testing. ...57

Chapter 4

Figure 59 – Geometric Simplifications Used for the DuraSpan® 500 Shell Model ...62

Figure 60 – Geometric Simplifications Used for the DuraSpan® 766 Shell Model ...63

Figure 61 – Delaminations Due to Rotation at the Web-Flange Interface...64

Figure 62 – Testing of Neoprene Pad ...66

Figure 63 – Stress Strain Curve for Uniaxial Compression Test of Neoprene ...66

Figure 64 - Probability Density Distribution Determined by Three Laboratories for Ex,flange for the DuraSpan® 500 ...68

Figure 65 - Probability Density Distribution Determined by Two Laboratories for Ey,flange for the DuraSpan® 500 ...69

Figure 66 - Probability Density Distribution Determined by One Laboratory for Gxy,flange for the DuraSpan® 500...69

Figure 67 - Probability Density Distributions Determined by One Laboratory for Ex,web for the DuraSpan® 500...70

Figure 68 - Probability Density Distributions Determined by One Laboratory for Ey,web for the DuraSpan® 500...70

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Figure 70 - Probability Density Distributions Determined by Four Laboratories for

Ex,flange for the DuraSpan® 766 ...71

Figure 71 - Probability Density Distributions Determined by Three Laboratories for Ey,flange for the DuraSpan® 766 ...72

Figure 72 - Probability Density Distributions Determined by Two Laboratories for Gxy,flange for the DuraSpan® 766...72

Figure 73 - Probability Density Distributions Determined by Two Laboratories for Ex,web for the DuraSpan® 766...73

Figure 74 - Probability Density Distributions Determined by Two Laboratories for Ey,web for the DuraSpan® 766...73

Figure 75 - Probability Density Distributions Determined by Two Laboratories for Gxy,web for the DuraSpan® 766...74

Figure 76 – Test Setup for Specimen 766-4-7.2...76

Figure 77 – Model of Specimen 766-4-7.2...76

Figure 78 – Deformed Shape for Model of Specimen 766-4-7.2...77

Figure 79 – Longitudinal Deflection Profile for Model of Specimen 766-4-7.2 ...78

Figure 80 – Lateral Deflection Profile for Model of Specimen 766-4-7.2 ...78

Figure 81 - Ex,flange and Gxy,web versus the objective function, ∆norm...79

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LIST OF SYMBOLS

norm – The deflection norm, a normalized comparison of measured versus predicted

deflections, used as a convergence criteria in optimization.

∆i – Measured vertical service load deflections across both the later and longitudinal spans,

used in the deflection norm convergence criteria for optimization.

δi – Predicted vertical service load deflections across both the lateral and longitudinal

spans, used in the deflection norm convergence criteria for optimization. η – Estimated Poisson’s Ratio for DuraSpan® bridge deck materials.

Ex, flange – Longitudinal modulus of elasticity in the flange material of the DuraSpan®

bridge deck profiles.

Ex, web – Longitudinal modulus of elasticity in the web material of the DuraSpan® bridge

deck profiles.

Ey, flange – Transverse modulus of elasticity in the flange material of the DuraSpan® bridge

deck profiles.

Ey, web – Transverse modulus of elasticity in the web material of the DuraSpan® bridge

deck profiles.

Ez – Thruogh thickness modulus of elasticity for the DuraSpan® bridge deck profiles

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1

Introduction

1.1

General

For over half a century composite materials have been used extensively in the aerospace and marine industries. Recently, as the result of significant reductions in material costs and increasingly cost effective manufacturing techniques, the use of composite materials is becoming common for a wide range of structural engineering applications. One of the most innovative applications is the use of fiber reinforced polymer (FRP) materials rather than traditional concrete and steel for the decking of highway bridges. Composite materials have many advantages in comparison to traditional materials such as being lightweight, non-corrosive, and easy to install. This study deals primarily with the DuraSpan® composite bridge deck system which is produced by Martin Marietta Composites of Raleigh, NC.

1.2

Objectives

The General objectives of this research program are to investigate and develop techniques for predicting the behavior of composite bridge deck systems. This research focused on the DuraSpan® deck system, however, many of the techniques used and the conclusions reached are applicable to similar composite bridge decks. The specific objectives of this research program can be summarized as follows:

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ii.) Investigate the load-deformation response and failure modes of GFRP bridge decks.

iii.) Develop an analytical model based on finite element analysis for bridge deck slabs and to verify the model with the measured behavior.

iv.) Investigate the influence of key parameters believed to affect the structural behavior and mode of failure of FRP bridge deck systems.

1.3

Scope

Chapter Two of this thesis provides an extensive discussion of various aspects of GFRP bridge decks. A review of the current research in the field of composite bridge decks is presented along with a discussion of the present and future field applications of the DuraSpan® bridge deck.

Chapter Three describes the experimental program that was undertaken as part of this research. The details of the test set-ups and instrumentation are presented along with the experimental results and analysis. The chapter includes discussions on the flexural behavior of the deck under simulated wheel loads, the failure mode of the deck, the behavior of bolted and pinned connections, the behavior of the bond lines in the negative moment region located over a bent, and the thermal expansion behavior of the system.

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2

Literature Review

2.1

Corrosion Problem

With the Federal-Aid Highway Acts of 1944, 1952, and 1956 the United States set the foundation for a massive federal interstate highway system. Over the next couple of decades massive amounts of civil infrastructure was constructed throughout the US with similar construction booms throughout most first world countries. Today, problems associated with this aging infrastructure are posing a dilemma for infrastructure owners throughout the world. In the United States alone the American Society of Civil Engineers estimates that 27.5 percent of the nation’s bridges (162,000) are structurally deficient or functionally obsolete [2] and are in need of replacement or rehabilitation. One of the major factors affecting almost all of these obsolete and deficient bridges is corrosion, so whether the bridges are replaced or rehabilitated, bridge engineers throughout the world are actively seeking corrosion resistant alternatives.

2.2

Corrosion in Reinforced Concrete Bridge Decks

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deicing chemicals which are used regularly in regions with colder climates. These deicing chemicals slowly seep through the concrete until they reach the reinforcing steel. Once in contact with the steel, the chemicals react with the steel and greatly accelerate the corrosion process. The byproducts of the corrosion process take up more volume than the original steel, thus the concrete cracks to allow expansion. The newly formed cracks form a conduit which allows moisture, oxygen, and deicing chemicals to reach the steel at an accelerated rate. Eventually the concrete spalls or falls away, necessitating repair or replacement of the bridge deck.

2.3

The Cost of Corrosion

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these factors combined help illustrate the tremendous potential for a corrosion resistant alternative.

2.4

The FRP Solution

Many fiber reinforced polymer (FRP) products are available today as alternatives to traditional reinforced concrete and steel construction. FRP materials are the combination of continuous fibers and a matrix. The two materials are combined in such a way that the matrix works to distribute stress to the fibers as well as to protect the fibers. The combination of the two materials produces a composite material whose properties are greater that the sum of its constituents. For structural engineering applications the common fibers are carbon, glass, or aramid while the common matrix materials include epoxy, vinylester, and polyester resins. These materials can be bonded as sheets or strips to concrete for strengthening or repair, made into reinforcing bars or prestressing tendons for new construction, or molded into structural components such as beams and bridge decks.

2.5

The DuraSpan® Composite Bridge Deck

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deck is 7.66 in. deep, weighs 19 psf, and has a maximum allowable girder spacing of 10 ft. Each module of DuraSpan® 766 provides approximately 12 inches of surface width. The DuraSpan® 500 bridge deck is 5.00 in deep, weighs 13 psf, and has a maximum allowable girder spacing of 5 ft. Each module of DuraSpan® 500 provides approximately 24 inches of surface width. Appendix A includes detailed dimensioned drawings of both the DuraSpan® 766 and DuraSpan® 500 configurations. These pultruded shapes are bonded together using a urethane adhesive. Systems are available for mating the deck to the supporting girders, for attaching railing systems, and for the application of a wearing course for traction purposes.

Figure 1 – DuraSpan® 766 Bridge Deck Profile

Figure 2 – DuraSpan® 500 Bridge Deck Profile

2.5.1

Constituent Materials

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fabrics (not woven fabrics) and unidirectional tows. For the stitched engineered fabrics, individual fibers are gathered into a roving, or bundle. These rovings are then placed side by side to form a layer with all of the fibers oriented in the same direction. Several of these layers of fibers are placed one on top of the other with each layer having a different orientation (typically -45/+45/90). These layers of fabrics are then stitched together on regular intervals to form stitched engineered fabrics. These fibers are suspended in an isophthalic polyester resin. Isophtalic polyester resin is known for being tough and resilient and also for being resistant to the effects of moisture and harsh chemical environments.

2.5.2

Manufacturing

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Stitched

Engineered

Fabrics

resin tank

shaping

and

heating die

puller

Stitched

Engineered

Fabrics

resin tank

shaping

and

heating die

puller

Figure 3 – Schematic of the Pultrusion Process

2.6

Advantages of FRP Bridge Decks

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2.7

Challenges to the use of FRP Bridge Decks

The primary disadvantages of FRP bridge decks are higher material cost and the reluctance of the bridge engineering community to choose new technology over proven techniques. While reinforced concrete has many problems, its cost per square foot is significantly less than that of all available FRP alternatives. Even though FRP decks have the potential to save money in the long term through an extended service life and reduced life cycle costs, these benefits remain unproven making bridge owners and engineers reluctant or unwilling to accept higher initial costs.

The very proprietary nature of composite products is also a disadvantage. Many designers are reluctant, or even unable to due to open competition laws, to specify a proprietary product for a public bridge. The proprietary nature also hinders the development of standard design procedures and guidelines. Often the manufacturer must provide engineering services for the use of the bridge deck as well as accept liability for the design.

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2.8

History of the DuraSpan® Bridge Deck

Development of the DuraSpan® bridge deck began in 1992 at Lockheed Martin Corporation’s Missiles & Space Division’s Palo Alto Research & Development Laboratory. During times of low funding for defense research, companies like Lockheed Martin would often seek to diversify by applying space age technology to everyday problems. In 1994 Martin Marietta Materials split from Lockheed Martin and is currently the nation’s second largest producer of construction aggregates. Martin Marietta Materials purchased the DuraSpan® technology from Lockheed Martin Corp. in 1995 and formed Martin Marietta Composites. Today Martin Marietta Composites is extremely active in the field of FRP materials. In addition to the bridge deck, they also produce composite truck trailers, rail car components, and other products.

2.8.1

Experimental Programs for the DuraSpan® Bridge Deck

Since its initial design in 1992, a tremendous amount of testing has been performed on the DuraSpan® bridge deck. The general goal of this testing has been to develop design guidelines to help bridge engineers safely design and specify the DuraSpan® bridge deck. This testing included, among other things, flexural tests to look at strength and stiffness, fatigue tests, material property tests, coefficient of thermal expansion testing, testing for deck to girder connections, testing of railing systems, and testing for composite action between the girder and deck. Some of the more notable experimental programs are listed below.

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included the results of a flexural test, a fatigue test (performed at the University of Deleware), shell and solid finite element models, and coupon flexural tests of web and flange materials.

ii.) Christina Helene Ficarra performed testing and analysis on the bonded joints of the DuraSpan® bridge deck at NC State University [6].

iii.) A large scale flexural test took place at Lehigh University.

iv.) An extensive testing program was undertaken at the Swiss Federal Institute of Technology, Lausanne by Dr. Thomas Keller, Herbert Gurtler, and Martin Schollmayer [10, 11, 12, and 13]. This testing included large scale testing to evaluate the composite action between the bridge deck and the bridge girders as well as some tests to evaluate the plate bending behavior of DuraSpan® panels with the goal of defining an effective width of load distribution. Solid element finite element models were generated and compared to the results.

v.) The Transportation Research and Development Bureau of the New York State Department of Transportation conducted a field load test of a 60 year old truss bridge retrofitted with the DuraSpan® bridge deck [1].

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Other useful research conducted in the field of GFRP bridge decks, but not necessarily the DuraSpan® bridge deck, has been performed at Virginia Polytechnic Institute and State University (Virginia Tech).

i.) The dissertation of Aixi Zhou includes numerous large scale flexural tests, finite element modeling, and numerical analysis [15]. Zhou concentrates on the idea of developing generalized design guidelines and performance based criteria.

2.8.2

Analytical Modeling of the DuraSpan® Bridge Deck

Lightweight composite bridge decks are known to have significantly less stiffness than reinforced concrete decks of equivalent capacity. As a result, the designs of composite bridge decks are driven by deflection based serviceability limit states. This necessitates the use of numerical design aids capable of predicting composite deck deflections at service load levels. Since its inception in 1992, many researchers have modeled the flexural behavior of the DuraSpan® bridge deck, often trying to correlate with the results of large scale testing, with varying levels of success. Most researchers experienced difficulty with the complex geometry, material properties, and boundary conditions associated with the DuraSpan® bridge deck and with GFRP bridge decks in general. These difficulties were greatly compounded by extreme variations in measured material properties (based on results from numerous academic and private testing laboratories).

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generation, the application of loads, and the application of boundary conditions for both the DuraSpan® 500 and DuraSpan® 766 bridge decks. These models are based on shell elements and they make it relatively simple for an engineer to generate and solve finite element models. However, many problems associated with boundary conditions and material properties still exist.

2.8.3

DuraSpan® Coordinate System

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3

Experimental Program and Test Results

3.1

Overview

The experimental program included testing of both the DuraSpan® 766 and DuraSpan® 500 bridge decks to study the effects of girder spacing, load distribution among multiple modules, transverse bending (to study the deck behavior within the negative moment region where a continuous deck spans over a bent), bolt and pin connections (to facilitate the connecting the railing systems), and coefficient of thermal expansion (to assess the effect of the different thermal expansion of the deck relative to the overlay wearing course).

3.2

Flexural Test Specimens

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schematic of a typical test setup is shown in Figure 5. A summary of the tests performed is provided in Table 1.

Figure 5 – Schematic of Typical Flexural Test Setup

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Table 1 – Summary of Flexural Testing

Specimen

ID Profile

Number of Bonded Modules

Span Specimen Configuration

766-4-7.2 DuraSpan® 766 4 7 ft. – 2 in.

766-1-4-a DuraSpan® 766 1 4 ft. – 0 in.

766-1-4-b DuraSpan® 766 1 4 ft. – 0 in.

500-1-4-a DuraSpan® 500 1 4 ft. – 0 in.

500-1-4-b DuraSpan® 500 1 4 ft. – 0 in.

500-2-4 DuraSpan® 500 2 4 ft. – 0 in.

766-2-4 DuraSpan® 766 2 4 ft. – 0 in.

500-1-3 DuraSpan® 500 1 3 ft. – 0 in.

3.2.1

Specimen 766-4-7.2

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longitudinal spans. The test setup is shown in Figure 6. The load deflection behavior of this specimen is shown in Figures 7 and 8. The vertical deflection profiles for both the longitudinal and lateral spans are shown in Figures 9 and 10 respectively. Failure of this specimen was due to bond failure between adjacent modules as shown in Figure 11. This debonding failure was attributed to poor preparation of the bond surfaces prior to the bonding of the modules. This type of failure was not experienced in any of the other specimens. Loading was stopped after the debonding failure at a load level of 100 kips to avoid further damage to the specimen. The specimen was then loaded to approximately 30 kips in order to evaluate residual strength and stiffness after debonding failure. After the completion of the test, the specimen was cut up to inspect the nature of the debonding failure.

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0 10000 20000 30000 40000 50000 60000 70000 80000

0 0.2 0.4 0.6 0.8 1 1.2

Deflection (in)

Loa

d

(

lbs)

HS25 + 30 % Impact = 26 kips

Deflection = 0.34 in. (L/265)

Figure 7 – Load Deflection Behavior of Specimen 766-4-7.2 from 0 to 70 kips of Applied Load 0 20000 40000 60000 80000 100000 120000

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

Deflection (in)

Load

(l

bs)

Initiation of joint failure under the load

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0 0.2 0.4 0.6 0.8 1 1.2

0 20 40 60 80

Distance from left support (in)

Deflecti

on

(i

n

)

Figure 9 – Vertical Deflection Profile Across the Longitudinal Span of Specimen 766-4-7.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2

0 12 24 36 48

Distance from edge (in)

Defl ec ti on s (i n )

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Figure 11 – Failure of Specimen 766-4-7.2

3.2.2

Specimens 766-1-4a and 766-1-4b

Two tests were performed on single DuraSpan® 766 modules. These modules were tested

using a 4 ft. clear span and were supported by 4 in. wide by 1/2 in. thick neoprene pads at

each end. The load was applied at midspan using a 6 in. by 10 in. steel loading plate on top

of a neoprene pad. For this test, the specimen was not wide enough to accommodate a

standard 10 in. by 20 in. AASHTO HS25 steel load plate. Potentiometers were used to

measure vertical deflections of the deck at two points across the lateral span and at three

points across the longitudinal span. Vertical deflections at the supports were monitored and

were used to determine the net vertical deflections across the lateral and longitudinal spans.

The test setup for one of the specimens is shown in Figure 12. The load-deflection

behavior of both specimens is shown in Figure 13. The behavior of these specimens was

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experienced at the flange web interfaces as shown in Figures 14, 15, and 16. The failures

were the result of instability as the section began to twist at high load levels.

Figure 12 – Test Setup for Specimen 766-1-4a

0 5000 10000 15000 20000 25000 30000 35000 40000 45000

0.0 0.1 0.1 0.2 0.2 0.3 0.3 0.4

Deflection (in)

L

oad

(l

b

s)

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Figure 14 – Rotation of Cross Section for Specimen 766-1-4b

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Figure 16 – Cracks Opening in Corners of Specimen 766-1-4b

3.2.3

Specimen 500-1-4a

A test was performed on a single DuraSpan® 500 module with the diagonal webs opening

down. This module was tested using a 4 ft. clear span and was supported by 4 in. wide by

1/2 in. thick neoprene pads at each end. The load was applied at midspan using a 10 in. by

20 in. steel plate resting on the top of an 11 in. by 21 in. by 1/2 in. neoprene pad. The load

pad was designed to simulate the effect of a AASHTO HS25 tire load on the bridge deck.

Potetentiometers were used to measure vertical deflections of the deck at three points along

the lateral direction and at three points along the longitudinal direction. Vertical

deflections at the supports were monitored and were used to determine the net vertical

deflections along both the lateral and longitudinal spans. The test setup is shown in Figure

17. The load deflection behavior of this specimen is shown in Figure 18. The deflection

profiles in both the longitudinal and transverse directions are shown in Figures 19 and 20

respectively. The failure of this specimen was due to debonding at the web-flange interface

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Figure 17 – Test Setup for Specimen 500-1-4a

0 10 20 30 40 50 60 70 80

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Deflection (in)

Lo

ad (

k

ips)

HS 25 + 30% impact = 26 kips

Deflection = 0.268" (L/179)

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0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0 6 12 18 24

Distance from edge of specimen (in)

D ef le ct ion ( in) Each line

represents 10 kips of load up to the final line which represents failure.

Figure 19 – Vertical Deflection Profile Across the Lateral Span for Specimen 500-1-4a 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0 12 24 36 48

Distance from Support (in)

Defl ecti on (i n ) Each line

represents 10 kips of load up to the final line which represents failure.

(42)

Figure 21 – Delamination of Web Flange Interface for Specimen 500-1-4a

Figure 22 – Shear in Web of Specimen 500-1-4a

3.2.4

Specimen 500-1-4b

A test was performed on a single DuraSpan® 500 module with the diagonal webs opening

up. This module was tested using a 4 ft. clear span and was supported by 4 in. wide by 1/2

in. thick neoprene pads at each end. The load was applied at midspan using a 10 in. by 20

(43)

was designed to simulate the effect of a AASHTO HS25 tire load on the bridge deck.

Potetentiometers were used to measure vertical deflections of the deck at three points along

the lateral direction and at three points along the longitudinal direction. Vertical

deflections at the supports were monitored and were used to determine the net vertical

deflections along both the lateral and longitudinal spans. The test setup is shown in Figure

23. The load deflection behavior of this specimen is shown in Figure 24. The deflection

profiles in both the lateral and longitudinal directions are shown in Figures 25 and 26

respectively. The failure of this specimen was due to debonding at the web-flange interface

and shear in the web as shown in Figures 27 and 28 respectively.

(44)

0 10 20 30 40 50 60 70 80

0.0 0.2 0.4 0.6 0.8 1.0 1.2

Deflection (in)

Lo

ad (

k

ips)

HS 25 + 30% impact = 26 kips

Deflection = 0.277" (L/173)

Figure 24 – Load Deflection Behavior of Specimen 500-1-4b

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0 6 12 18 24

Distance from Edge of Specimen (in)

D ef le ct ion ( in) Each line represents 10 kips of load up to the final line which represents failure

(45)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0 12 24 36 48

Distance from support (in)

D

ef

le

ct

ion (

in)

Each line

represents 10 kips of load up to the final line which represents failure.

Figure 26 – Vertical Deflection Profile Across the Longitudinal Span for Specimen 500-1-4b

(46)

Figure 28 – Shear in Web of Specimen 500-1-4b

3.2.5

Specimen 500-2-4

A test was performed on two bonded DuraSpan® 500 modules. This test was performed

using a 4 ft. clear span and was supported by 4 in. wide by 1/2 in. thick neoprene pads at

each end. The load was applied at midspan using a 10 in. by 20 in. steel load plate on top

of a 11 in. by 21 in. by 0.5 in. neoprene pad. The load pad was designed to simulate the

effect of a AASHTO HS25 tire load on the bridge deck. Potetentiometers were used to

measure vertical deflections of the bridge deck at five points along the lateral direction and

at three points along the longitudinal direction. Vertical deflections at the supports were

monitored and were used to determine the net vertical deflections along both the lateral and

longitudinal spans. The test setup is shown in Figure 29. The load deflection behavior of

this specimen can be seen in Figure 30. The deflection profiles in both the longitudinal and

transverse directions can be seen in Figures 31 and 32 respectively. The failure of this

specimen was due to debonding at the web-flange interface and shear in the web as shown

(47)

Figure 29 – Test Setup for Specimen 500-2-4

0 10 20 30 40 50 60 70 80

0.0 0.2 0.4 0.6 0.8 1.0

Deflection (in)

Lo

ad (

k

ips)

HS 25 + 30% impact = 26 kips

Deflection = 0.242" (L/198)

(48)

Distance from edge of specimen (in) -1.2 -1 -0.8 -0.6 -0.4 -0.2 0

0 12 24 36 48

de fl ec tion ( in) Each line

represents 10 kips of load up to the final line which represents failure.

Figure 31 – Vertical Deflection Profile Across the Lateral Span for Specimen 500-2-4

Distance from support (in)

-0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0

0 12 24 36 48

D ef le ct ion ( in) Each line

represents 10 kips of load up to the final line which represents failure.

(49)

Figure 33 – Shear and Delamination of Specimen 500-2-4

3.2.6

Specimen 766-2-4

Two bonded DuraSpan® 766 modules were tested in flexure. These modules were tested

using a 4 ft. clear span and were supported by 4 in. wide by 1/2 in. thick neoprene pads at

each end. The load was applied at midspan using a 10 in. by 20 in. steel loading plate

resting on the top of a similarly dimensioned neoprene pad to simulate the effect of an

AASHTO HS25 truck tire. Potetentiometers were used to measure deflections of the deck

at three points along the transverse direction and at three points along the longitudinal

direction. Vertical deflections at the supports were monitored and were used to determine

the net vertical deflections along both the lateral and longitudinal spans. The test setup is

shown in Figure 34. The load deflection behavior of this specimen can be seen in Figure

35. The deflection profiles in both the longitudinal and lateral directions can be seen in

Figures 36 and 37 respectively. The failure of this specimen was due to delamination at the

(50)

Figure 34 – Test Setup for Specimen 766-2-4

0 10 20 30 40 50 60 70 80

0.0 0.2 0.4 0.6 0.8 1.0

Deflection (in)

Lo

ad (

k

ips)

Deflection = 0.24 in. (L/217)

HS25 + 30 % Impact = 26 kips

(51)

-0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0

0 12 24

Distance from Edge of Specimen (in)

Defl

ect

ion (i

n)

Each line

represents 10 kips of load up to the final line which represents failure.

Figure 36 – Vertical Deflection Profile Across the Lateral Span for Specimen 766-2-4

-0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0

0 26 52

Distance from Support (in)

D

eflection (in) Each line

represents 10 kips of load up to the final line which represents failure.

(52)

Figure 38 - Delamination of Specimen 766-2-4

Figure 39 – Shear Failure in the Web of Specimen 766-2-4

3.2.7

Specimen 500-1-3

A test was performed on a single DuraSpan® 500 module. This specimen was tested using

a 3 ft. clear span and was supported by 4 in. wide by 1/2 in. thick neoprene pads at each

end. The load was applied at midspan using a 10 in. by 20 in. steel load plate resting on the

(53)

effect of a AASHTO HS25 tire load on the bridge deck. Potetentiometers were used to

measure deflections of the deck at three points along the lateral direction and at three points

along the longitudinal direction. Vertical deflections at the supports were monitored and

were used to determine the net vertical deflections along both the lateral and longitudinal

spans. The test setup is shown in Figure 40. The load deflection behavior of this specimen

can be seen in Figure 41. The deflection profiles in both the longitudinal and transverse

directions can be seen in Figures 42 and 43 respectively. The failure of this specimen was

due to debonding at the web-flange interface and shear in the web as shown in Figure 44.

(54)

0 10 20 30 40 50 60 70 80

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Deflection (in)

Lo

ad (

k

ips)

Deflection = 0.175 in. (L/205)

HS25 + 30 % Impact = 26 kips

Figure 41 – Load Deflection Behavior of Specimen 500-1-3

-0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0

0 12 24

Distance from edge of specimen (in)

D ef le ct ion ( in) Each line

represents 10 kips of load up to the final line which represents failure.

(55)

-0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0

0 10 20 30 40

Distance from support (in)

Defl

ec

ti

on

(in

)

Figure 43 – Vertical Deflection Profile Across the Longitudinal Span for Specimen 500-1-3

(56)

3.3

Flexural Test Results

3.3.1

Influence of Girder Spacing on the DuraSpan® 500

Two specimens were evaluated to determine the effect of girder spacing on the DuraSpan®

500. The specimen with a single DuraSpan® 500 module on a 3 ft. span and the specimen

with a single DuraSpan® 500 module on a 4 ft. span were used for this comparison.

Several loading and unloading cycles were performed on each specimen to evaluate the

change in deck stiffness as a result of cyclic loading. Figure 45 shows the load-deflection

behavior at mid-span for the test specimens. Both specimens experienced linear elastic

behavior during the loading and unloading cycles. A consistent response with almost no

loss in stiffness was observed for both specimens. The maximum deflections for the 3 ft.

specimen and the 4 ft. specimen under an equivalent service load of HS25 were L/180 and

L/140, respectively where L is the clear span of the test specimen. Test results showed that

increasing the span from 3 ft. to 4 ft. did not increase the deflection proportional to the

elastic beam analysis. This behavior is attributed to the effect of the shear deformation and

the influence of plate bending behavior versus beam behavior. Failure of both specimens

was due to excessive shear deformations in the web accompanied with delamination of the

web from the face sheets. As a result of this shear dominated failure, the failure loads for

both specimens were comparable and were independent on the span. The total safety factor

(57)

0 10000 20000 30000 40000 50000 60000 70000 80000

0.0 0.2 0.4 0.6 0.8 1.0

Deflection (in)

Lo

ad

(l

bs

)

3 ft 4 ft

Figure 45 – Comparison of Specimen 500-1-4a and Spceimen 500-1-3

3.3.2

Effect of Number of Bonded Modules on the DuraSpan® 500

For the DuraSpan® 500, the test of a single module in the strong direction and the test of

two bonded modules were used to evaluate the effect of the number of bonded modules.

The length of the span for both of the specimens was constant and was equal to 4 ft. Figure

46 shows a comparison of the load-deflection behavior for the DuraSpan® 500 specimens.

The deflected profile along the transverse direction of specimen 500-2-4 is shown again in

Figure 47. The figure clearly demonstrates that only a portion of the width was effective

in carrying the applied concentrated load. Deflection of the outer 10 in. from each side of

the deck panel was constant, therefore, the effective width, which is influenced by the

wheel load, can be estimated to be about 24 in. which is approximately equal to the width

of a single module of DuraSpan® 500. Consequently, the behavior and the stiffness of a

(58)

Failure of both DuraSpan® 500 specimens was controlled by delamination of the web from

the face sheets and web capacity.

0 10000 20000 30000 40000 50000 60000 70000 80000

0.0 0.2 0.4 0.6 0.8 1.0

Deflection (in)

Load (lbs)

single 2 Bonded

(59)

Distance from edge of specimen (in)

-1.2 -1 -0.8 -0.6 -0.4 -0.2 0

0 12 24 36 48

de

fl

ec

tion (

in)

Each line

represents 10 kips of load up to the final line which represents failure.

Figure 47 – Vertical Deflection Profile Across the Lateral Span for Specimen 500-2-4

3.3.3

Effect of Number of Bonded Modules on the DuraSpan® 766

For the DuraSpan® 766, specimens 766-1-4a and 766-2-4 were used to evaluate the effect

of the number of bonded modules. The load-deflection behavior of the DuraSpan® 766

specimens is shown in Figure 48. Deflection of the specimen with two modules was

significantly affected by increasing of the width but was not quite proportional to doubling

the width. The deflection at service load of 26 kips for the specimen with two bonded

modules was 60 percent in comparison to the specimen with a single module, where the

applied load curved the entire width. Measurements of deflections along the transverse

direction of the specimens suggested that the width of both specimens were effective for

the DuraSpan® 766 bridge deck. The short coming of reducing the deflection to 50

(60)

specimens relative to each other. The specimen with a single module induced additional

torsional stresses and accelerated delamination of the web from the face sheets resulting in

failure at significantly lower loads in comparison to the specimen with two bonded

modules. Test results indicate the need for using a sufficient width of bridge deck to ensure

a uniform distribution of the load, stability for the deck, and an efficient load transfer

mechanism among the deck components. Failure of both of the DuraSpan®766 deck

specimens was due to delamination of the web from the face sheets at load levels of 36 kips

and 143 kips, respectively.

0 20000 40000 60000 80000 100000 120000 140000 160000

0 0.2 0.4 0.6 0.8 1

Deflection (in)

Load (lbs)

766-1-4a

766-2-4

Figure 48 – Comparison of Specimen 766-1-4a and Specimen 766-2-4

3.4

Transverse Test

The transverse test involved five 3’ long DuraSpan® 766 modules bonded together and

tested over a 4’ span in the transverse direction. The deck was instrumented with a total of

(61)

subsequently unloaded with a 10” x 20” load pad to levels of 5 kips, 10 kips, and then to a

mid-span deflection of approximately 1.8 inches where the test was halted prior to a

complete failure. A maximum load of 13.4 kips was reached. The test setup is shown in

figure 49. Figure 50 shows the load deflection diagram for the specimen. Figure 51 shows

a load versus strain plot for the four strain gages on the top flange of the bridge deck.

Gauges G1 and G6 had positive strain readings throughout the entire loading regime while

gauges 2 and 5 had negative strain readings throughout the entire loading regime. This

indicates a positive bending moment at location 5-6 and a negative bending moment at

location 1-2. It is believed that this reversal in bending moments in the top flange is due to

local plate bending behavior. Figure 52 shows a load versus strain plot for the four strain

gauges on the bottom flange of the bridge deck. Gauges 4 and 8 had mostly positive strain

readings throughout the loading regime while gauges 3 and 7 had negative strain readings

throughout the loading regime. This indicates a positive bending moment at both location

3-4 and location 7-8. The strain gauge readings indicated that the transverse load transfer

mechanism of the DuraSpan® bridge deck involves no composite action between the top

and bottom flanges. In other words, the minimal rotational stiffness of the web-flange

interface is not capable of transferring horizontal shear forces between the top and bottom

flanges in the transverse direction which would have caused significant amounts of direct

tension or direct compression rather that bending moments which were observed in the

flanges. The transverse load transfer mechanism is more accurately characterized by the

bending of two structurally independent plates where the webs transfer only axial forces

and not moments from one plate to the other. Furthermore, the top flange of the bridge

(62)

transverse span. On the other hand, the bottom flange of the bridge deck observes more of

a global bending without reversals in bending moment across the transverse span. This

lack of an efficient transverse load transfer mechanism is what leads to a small effective

area when the bridge deck is loaded in the longitudinal direction.

(63)

0 2000 4000 6000 8000 10000 12000 14000

0.0 0.5 1.0 1.5 2.0

Deflection (in) Lo ad (l bs )

Figure 50 – Load Deflection Behavior of Transverse Specimen

0 2000 4000 6000 8000 10000 12000 14000

-4000 -3000 -2000 -1000 0 1000 2000 3000 4000

Strain (mE) Lo ad ( lbs ) G1 G2 G5 G6 G1 G2 G4 G3 G5 G6 G8 G7

(64)

0 2000 4000 6000 8000 10000 12000 14000 16000

-1500 -1000 -500 0 500 1000 1500

Strain (mE) Loa d (lbs) G3 G4 G7 G8 G1 G2 G4 G3 G5 G6 G8 G7

Figure 52 – Strain Measurements in Bottom Flange of Transverse Specimen

3.5

Connection Behavior

Tests were performed to examine the behavior of different mechanical connection systems

typically used for bridge deck railing systems. Three different sizes of connections were

tested. Each connection size was tested with a pin and a bolt. It is well known that

vinylester resin has a tendency to creep under sustained load. Therefore, while it was

possible to bolt the railing system to the deck, the effect of tightening the bolt would not

last and the bolt could eventually come loose. The pin connection tests were designed to

avoid confinement of the material which represents the worst case scenario. The bolts were

installed in such a way as to provide passive confinement for the material. Figure 53

(65)

displacement plots for the pins and bolts respectively. Table 2 summarizes the results of

the connection tests.

Table 2 – Maximum Loads prior to first loss of load for Connection Tests

Connector Size Pin Bolt

3/8” 12.2 kips @ 0.072 in

1/2” 15.7 kips @ 0.070 in 19.2 kips @ 0.067 in 5/8” 20.8 kips @ 0.047 in 19.4 kips @ 0.074 in

(66)

0 5000 10000 15000 20000 25000

0.000 0.020 0.040 0.060 0.080 0.100

Deflection (in) L oad ( lb s) 3/8" 1/2" 5/8"

Figure 54 – Load Deflection Behavior of Pin Connections

0 5000 10000 15000 20000 25000 30000 35000

0.000 0.050 0.100 0.150 0.200

Deflection (in) L oad ( lb s) 1/2" 5/8"

(67)

3.6

Coefficient of Thermal Expansion Testing

Testing was performed on both the DuraSpan® 500 and DuraSpan® 766 bridge decks to

determine the coefficient of thermal expansion in both the lateral and longitudinal

directions. The purpose of this testing was to evaluate the effect that thermal cycling on the

bond between the bridge deck and a wearing surface. The testing was also designed to

isolate the effect of the bonded joint on the thermal expansion of the bridge deck system. A

sample of both DuraSpan® bridge deck profiles consisting of two modules, approximately

40 in. long, bonded together was placed in the environmental chamber. Three independent

methods were used to measure the thermal strains in the deck specimens.

i.) Strain gauges were used to measure the thermal expansion of the deck

specimens by measuring local material strains in two orthogonal directions.

The strain gage readings were compensated for temperature effects by bonding

an identical strain gauge on a piece of titanium silicate glass, a reference

material which is known to have a coefficient of thermal expansion close to

zero. Strain gages were also placed on samples of polymer concrete (overlay

material for the bridge deck) and a piece of steel which was used as a reference

material.

ii.) High resolution DC LVDT’s were used to measure the global expansion of the

deck specimens in two orthogonal directions. The purpose of this

measurement was to capture the effect of the bonded joint on the thermal

behavior of the bridge deck system and to duplicate the measurements obtained

(68)

carbon fiber reinforcing bars were place on top of the deck specimens. One

end of the leadline bars was attached to the edge of the bridge deck while the

other end of the leadline bars was attached to a DC LVDT with the spring

loaded plunger resting on the edge of the bridge deck. Carbon fiber is

commonly known to have a very small negative coefficient of thermal

expansion (i.e. the material expands with a decreasing temperature). This

expansion was taken into account by placing a strain gauge on a sample of the

carbon fiber reinforcing bar. The readings from the LVDT’s were also

thermally compensated by placing “dummy” LVDT’s in the chamber.

iii.) Two PI gages were attached to the each deck specimen across the bonded joint.

The purpose of these gauges was to isolate the effect of the joint on the global

expansion of the bridge deck system. These gauges were compensated by

attaching a gauge to a piece of leadline carbon fiber reinforcing bar. The effect

of the expansion of the leadline was included in the compensation.

Several thermocouples as well as a calibrated digital thermometer were placed in the

chamber in order to measure the temperature. Figure 56 shows the bridge deck

specimens in the chamber. Figure 57 shows a close-up of one of the specimens with all

of the instrumentation labeled. Figure 58 shows the samples of polymer concrete

overlay, the steel sample, the titanium silicate glass, and the carbon fiber sample. The

chamber was run from the starting point of 70 degrees Farenhight to -50 degrees

Farenheight and then to 150 degrees Farenheight. Strains and displacements were

(69)

coefficients of thermal expansion for all materials. The results of the coefficient of

thermal expansion testing are summarized in Table 3. The results show that there was a

reasonable correlation between the various methods of measurement. There was a

consistently higher thermal expansion in the lateral direction when compared to the

longitudinal direction but the measurements from the PI gauges indicate that this is

likely the result of the fiber lay-up and not the result of the bonded joint. It is also

shown that the coefficient of thermal expansion of the polymer concrete is

approximately three times the coefficient of thermal expansion of the bridge deck in the

longitudinal direction and over twice the coefficient of thermal expansion of the bridge

deck in the lateral direction. This large difference in thermal expansion behavior could

have an adverse effect on the bond between the bridge deck and wearing surface, but

this behavior would also be dependent on the relative moduli of elasticity as well as the

ultimate shear strength, fatigue characteristics, and creep characteristics of the bonding

(70)

Figure 56 – DuraSpan® Bridge Decks in the Environmental Chamber for CTE Testing

Figure 57 – Instrumentation for CTE Testing

PI Gages

Strain Gages LVDT’s

Lateral

(71)

Figure 58 – Samples of Polymer Concrete Overlay, Titanium Silicate Glass, Steel and Carbon Fiber in the Environmental Chamber for CTE Testing.

Table 3 – Results of CTE Testing

Strain Gage LVDT PI Gage

766 7.3 8.0 7.4

500 9.0 7.2 7.7

766 4.4 4.6

500 5.1 5.2

5.8 -0.6 17.8 15.5

(in/in/degree F) x 10^-6

Polymer Concrete 1 Polymer Concrete 2 Carbon

Steel Lateral

Longitudinal Titanium Silicate Glass

(72)

4

Modeling of the Behavior

4.1

Overview

FRP bridge decks are generally known to be less stiff that traditional reinforced concrete

bridge decks of equivalent strength. The lower stiffness of GFRP bridge decks means that

deflection based serviceability criteria often control the design process. It is therefore

essential that design engineers be able to accurately predict deflections at service load

levels. The overall complex behavior of the DuraSpan® bridge deck, which includes the

effects of complex geometry, difficult to evaluate material properties, and undefined

boundary conditions, necessitated the use of finite element modeling to predict deflections

at service load levels. A shell based finite element model was developed using the ANSYS

general purpose finite element program. The model was then adapted for use as an

ANSYS Parametric Design Language (APDL) macro which automated the model

generation and solution processes. Optimization techniques were then used to calibrate the

model with large scale flexural test data. The effects of different material properties and

boundary conditions on the overall behavior of the bridge deck were evaluated. The

developed model is capable of predicting deflections at service load levels but not the

failure mode or ultimate strength since both depend mainly on the shear strength within the

laminates and local stability effects which are not taken into account in the modeling

(73)

4.2

Benefits of Macro Based Programming

Finite element models are a powerful tool often used by researchers to predict the behavior

of complex structures such as composite bridge decks. Unfortunately, finite element

models are time consuming to create and are generally not considered to be a practical tool

for design engineers, particularly for something as structurally simple as a bridge deck. In

order for finite element modeling to be considered as an effective design tool, the process

of creating the model geometry, assigning material properties and boundary conditions, and

solving the model must be simplified or automated. The best way to accomplish this is

through the use of a macro. The macro takes a limited number of high level inputs (bridge

length, bridge width, number of bays, location and size of loads, etc.) and uses that

information to generate and solve a model and thus provide the design engineer with

required service load deflection estimates.

4.3

Modelling of the DuraSpan® bridge deck

There are a number of difficulties that have been encountered in all attempts to model the

DuraSpan® bridge deck. Most of the difficulties are associated with either the material

properties used in the model or with the complex geometry and boundary conditions.

These issues can be summarized as follows:

Material Properties:

i.) Orthotropic material properties

ii.) Different compression and tension moduli

(74)

iv.) Difficulty in cutting and testing coupons (particularly in the lateral direction)

Geometry and boundary conditions:

i.) Many changes in flange thickness

ii.) Difficulty in modeling the effect of flange/web rotational rigidity

iii.) Difficulty in modeling the effect of the adhesive joint

iv.) Difficulty in modeling support and loading boundary conditions

Two approaches for dealing with these issues were considered. The first involved

developing a complex model capable of dealing with all of the above issues. It was

decided, however, that the introduction of more variables would have required more testing

and that the increased model complexity would have kept it from being a useful design

tool. It was decided that a more useful approach involved calibrating the simplified model

using deflection data from laboratory based flexural tests. The parametrically defined shell

element model from In2Solutions [8 and 9] was used as the basis for this calibration but

was significantly modified to correctly model the boundary conditions of the laboratory

testing.

The FRP bridge deck was modeled using shell63 elements. The shell63 element has both

bending and membrane capabilities. Both in-plane and normal loads are permitted. The

element has six degrees of freedom at each node: translations in the nodal x,y, and z

directions and rotations about the x, y, and z-axes. Stress stiffening and large deflection

(75)

Each element was given orthotropic material properties. Different sets of properties were

used for the web material and the flange material. These material properties included an

Ey, Ex, and Gxy. Ez as well as η were determined to have a minimal effect on the overall

deck behavior and were thus assumed to be the same for all parts of the deck. Figures 59

and 60 show the geometry simplifications that were used to adapt the complex DuraSpan®

geometry into a simplified shell model for the DuraSpan® 500 and DuraSpan® 766

products respectively. The deck was meshed with element whose maximum dimensions

(76)
(77)

Figure 60 – Geometric Simplifications used for the DuraSpan® 766 Shell Model

Variation in flange thickness was not considered and the minimum thickness was adapted

for the flange shell elements. An attempt was made to account for the change in thickness

in the flanges by locating a line of nodes at the location of the thickness change and having

(78)

change in thickness did not improve the ability of the model to predict deflections and that

doing so unnecessarily complicates the model generation code in the macro.

The connection between the web and flange is assumed to be completely rigid. Several of

the tests performed (the single DuraSpan® 766 module test and the transverse DuraSpan®

766 test) showed the rotational rigidity of these joints to be a weak when subjected to

rotation. Figure 61 shows a delamination which occurs when these joints undergo a

significant rotation. In an attempt to account for this weakness the rotations between the

flanges and the webs were released. It was discovered that even when released, very little

relative rotation tends to occur between the flange and the web at service load levels. The

rigidity of the joint is likely somewhere between being completely fixed and completely

free but it was decided that releasing the joint did not significantly improve the ability of

the model to predict deflections and that the assumption of a rigid flange-web connection is

acceptable for service load level deflection estimates.

(79)

4.3.1

Modeling of the steel loading plate

The steel loading plate was modeled using solid45 elements. The solid45 element is

defined by eight nodes having three degrees of freedom at each node” translations in the

nodal x,y, and z directions. The steel plate was modeled as being 10”x20”x1” and was

meshed with elements constrained to be less than two inches for any dimension. The steel

was modeled as an isotropic material with an elastic modulus of 29,000 ksi, a Poisson’s

ration of 0.29, and a shear modulus of 11,800 ksi. A pressure load was applied to a portion

of the top surface of the steel plate to simulate the actual laboratory loading conditions.

4.3.2

Modeling of the neoprene supports and load pad

The neoprene supports and load pad were modeled using hyper58 elements. The hyper58

element is used for 3-D modeling of solid hyperelastic structures. Figure 62 shows the

uniaxial compression test of a square of neoprene that was used to calibrate the hyper58

elements. Figure 63 shows the hyperelastic material behavior of the neoprene in the form

of a stress-strain plot. The sample of neoprene was loaded to approximately 60% strain. A

5 constant mooney-rivlin material model was calibrated based on the stress strain data from

the laboratory test and was used to simulate the behavior of the neoprene using the hyper58

(80)

Figure 62 – Testing of Neoprene Pad

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Strain (E)

St

re

ss(

ps

i)

Figure

Figure 38 - Delamination of Specimen 766-2-4

Figure 38 -

Delamination of Specimen 766-2-4 p.52
Figure 42 – Vertical Deflection Profile Across the Lateral Span for Specimen 500-1-3

Figure 42

– Vertical Deflection Profile Across the Lateral Span for Specimen 500-1-3 p.54
Figure 41 – Load Deflection Behavior of Specimen 500-1-3

Figure 41

– Load Deflection Behavior of Specimen 500-1-3 p.54
Figure 43 – Vertical Deflection Profile Across the Longitudinal Span for  Specimen 500-1-3

Figure 43

– Vertical Deflection Profile Across the Longitudinal Span for Specimen 500-1-3 p.55
Figure 44 – Failure of Specimen 500-1-3

Figure 44

– Failure of Specimen 500-1-3 p.55
Figure 45 – Comparison of Specimen 500-1-4a and Spceimen 500-1-3

Figure 45

– Comparison of Specimen 500-1-4a and Spceimen 500-1-3 p.57
Figure 46 – Comparison of Specimen 500-1-4a and Specimen 500-2-4

Figure 46

– Comparison of Specimen 500-1-4a and Specimen 500-2-4 p.58
Figure 47 – Vertical Deflection Profile Across the Lateral Span for Specimen 500-2-4

Figure 47

– Vertical Deflection Profile Across the Lateral Span for Specimen 500-2-4 p.59
Figure 48 – Comparison of Specimen 766-1-4a and Specimen 766-2-4

Figure 48

– Comparison of Specimen 766-1-4a and Specimen 766-2-4 p.60
Figure 49 – Test Setup for Transverse Test of DuraSpan® 766

Figure 49

– Test Setup for Transverse Test of DuraSpan® 766 p.62
Figure 51 – Strain Measurements in Top Flange of Transverse Specimen

Figure 51

– Strain Measurements in Top Flange of Transverse Specimen p.63
Figure 50 – Load Deflection Behavior of Transverse Specimen

Figure 50

– Load Deflection Behavior of Transverse Specimen p.63
Figure 52 – Strain Measurements in Bottom Flange of Transverse Specimen

Figure 52

– Strain Measurements in Bottom Flange of Transverse Specimen p.64
Table 2 – Maximum Loads prior to first loss of load for Connection Tests

Table 2

– Maximum Loads prior to first loss of load for Connection Tests p.65
Figure 54 – Load Deflection Behavior of Pin Connections

Figure 54

– Load Deflection Behavior of Pin Connections p.66
Figure 55 – Load Deflection Behavior of Bolt Connections

Figure 55

– Load Deflection Behavior of Bolt Connections p.66
Figure 57 – Instrumentation for CTE Testing

Figure 57

– Instrumentation for CTE Testing p.70
Figure 56 – DuraSpan® Bridge Decks in the  Environmental Chamber for CTE Testing

Figure 56

– DuraSpan® Bridge Decks in the Environmental Chamber for CTE Testing p.70
Table 3 – Results of CTE Testing

Table 3

– Results of CTE Testing p.71
Table 4 – Summary of Optimization Ranges

Table 4

– Summary of Optimization Ranges p.82
Figure 65 - Probability Density Distribution Determined by

Figure 65 -

Probability Density Distribution Determined by p.83
Figure 66 - Probability Density Distribution Determined by  One Laboratory for Gxy,flange for the DuraSpan® 500

Figure 66 -

Probability Density Distribution Determined by One Laboratory for Gxy,flange for the DuraSpan® 500 p.83
Figure 68 - Probability Density Distributions Determined by  One Laboratory for Ey,web for the DuraSpan® 500

Figure 68 -

Probability Density Distributions Determined by One Laboratory for Ey,web for the DuraSpan® 500 p.84
Figure 67 - Probability Density Distributions Determined by

Figure 67 -

Probability Density Distributions Determined by p.84
Figure 70 - Probability Density Distributions Determined by  Four Laboratories for Ex,flange for the DuraSpan® 766

Figure 70 -

Probability Density Distributions Determined by Four Laboratories for Ex,flange for the DuraSpan® 766 p.85
Figure 69 - Probability Density Distributions Determined by

Figure 69 -

Probability Density Distributions Determined by p.85
Figure 72 - Probability Density Distributions Determined by  Two Laboratories for Gxy,flange for the DuraSpan® 766

Figure 72 -

Probability Density Distributions Determined by Two Laboratories for Gxy,flange for the DuraSpan® 766 p.86
Figure 71 - Probability Density Distributions Determined by  Three Laboratories for Ey,flange for the DuraSpan® 766

Figure 71 -

Probability Density Distributions Determined by Three Laboratories for Ey,flange for the DuraSpan® 766 p.86
Figure 73 - Probability Density Distributions Determined by

Figure 73 -

Probability Density Distributions Determined by p.87
Figure 74 - Probability Density Distributions Determined by  Two Laboratories for Ey,web for the DuraSpan® 766

Figure 74 -

Probability Density Distributions Determined by Two Laboratories for Ey,web for the DuraSpan® 766 p.87

References