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LICENTIATE THESIS 2002:xx

Preliminary Design and Analysis of a

Pedestrian FRP Bridge Deck

Patrice Godonou


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Fel! Anvnd fliken Start om du vill tillmpa Heading 1 fr texten som ska visas hr.

Division of Structural EngineeringDepartment of Civil and Mining Engineering

Lule University of TechnologySE 971 87 Lule

Sweden

Preface

The present report is the result of the research carried out between the autumn1999 and the spring 2002 at SICOMP AB, Pite and the Division of StructuralEngineering, Department of Civil and Mining Engineering at Lule Universityof Technology (LTU). In between, I spent nearly half a year as a guest researcherat the Structural Engineering Department of the University of California SanDiego (UCSD), in the USA, during the year 2000.

This project wouldnt have been possible without the financial support from the

Development Fund of the Swedish Construction Industry (SBUF), the Board ofDirectors of the Institute SICOMP AB, and last but not least the ResearchCouncil of Norrbotten (Norrbottens Forskningsrd, NFR). Specialacknowledgement goes to Anders Nilsson at the NFR and his assistance inmaking my visit as a guest researcher at the UCSD a reality.

I would like to start by thanking my supervisors Prof. Tech Dr Thomas Olofssonat the Division of Structural Engineering, Department of Civil and MiningEngineering at LTU and Tech Dr Anders Holmberg at SICOMP AB for theirinvaluable assistance during the writing of the thesis. I would also like to thankall the personal at SICOMP AB who helped me in one way or another during

my work. My thanks will also go the members of the Snake Hill Project, inparticular Olov Holmvall, Lule Kommun, Sture Berglund, Artist, Pite, TordGustafsson, APC Composit AB and Jan-Olof Lampinen, NCC Anlggning,Lule. Many of the achievements in the conceptual design are the direct result ofthe enriching discussions during the meetings of the project group. Many thanksalso to Joseph Forslund from the Department of Civil and Mining at LTU, who


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produced some excellent computer visualisations of the concepts presented bySture Berglund. Special thanks go to Lars Liljenfeldt, the project manager atSICOMP, whose enthusiasm has been the driving force of the whole project. Mythanks go also to Hans Ptursson for enriching discussions and sketch on thebridge concepts and for the moral support during the times when the report

writing felt like an endless task. My thanks will also go to Prof. Tech Dr VistaspKarbhari, Tech Dr Lei Zhao and Ph. D. Candidate Mikael Brostrm all at theStructural Engineering Department of the UCSD for making my visit someaningful.

Finally, I would like to tell my girlfriend Lolo, who supported and encouraged

me lovingly, that she means so much to me. Thanks for being there, Lolo. To mychildren Malik, Chtima and Bibi, who didnt get the attention they deserveduring that period, I would like to say: I love you!


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Abstract

The interest for Fiber Reinforced Polymers (FRP) as an alternative buildingmaterial is constantly increasing within the building construction sector

worldwide. In order to allow for a commercial breakthrough of FRP basedbuilding structures, it is necessary to combine the design philosophy from thebridge engineering industry to the design practices specific to the FRP industry.

A brief introduction of the constituents of FRP materials is given (section 2)together with a description of the manufacturing processes. Some applications of

FRP in civil infrastructures are presented. The bridge design methodology andterminology are described and the design philosophy of the Swedish BridgeDesign Code BRO94 is introduced (Section 3)

A comprehensive survey of existing FRP bridges around the world is carried outtogether with the presentation of some cases studies (Section 4). The mechanicsof structural components made of FRP and the sandwich beam model aredescribed (Section 5).

The core of the report is partly based on the conceptual design of the wholebridge system and the development of a concept for the deck cross-section(Section 6). The second core part of the report is the preliminary design and

analysis of the bridge deck, based on the methodology of BRO94 and the designpractices particular to FRP structures and sandwich beam construction (Section7). A design proposal for the remaining structural components such as thecolumns and the guardrails is also presented (Section 8).

Keywords: Fiber Reinforced Polymer, FRP bridge survey, FRP Bridge Design,Conceptual design, Sandwich construction, Stiffness driven design.


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Division of Structural EngineeringDepartment of Civil and Mining Engineering

Lule University of TechnologySE 971 87 Lule

Sweden

Sammanfattning

Intresset for fiberkompositer som ett alternativt byggmaterial har kat konstantunder de senaste ren inom byggbranschen vrlden ver. Fr att gra ettkommersiellt genomslag mjligt fr fiberkompositer r det ndvndigt att frenadimensioneringsmetodik som r typiskt fr brokonstruktion till demdimensioneringsprinciper som anvnds inom fiberkompositbranschen.

De bestndsdelar som ingr i fiberkompositer presenteras i sektion 2tillsammans med en beskrivning av tillverkningsmetoder. Vissa tillmpningar av

fiberkompositer inom infrastruktursektorn presenteras ocks.Dimensioneringsmetodiken och terminologin typisk fr brokonstruktionbeskrivs tillsammans med BRO94 i sektion 3.

En omfattande kartlggning av befintliga fiberkompositbroar vrlden runt grs isektion 4. Detta frstrks med fallstudie ver ngra enstaka fiberkompositbroar.Fiberkompositers mekanik och dimensionering av sandwichkonstruktionerbeskrivs under sektion5.

Krnan i denna rapport utgrs delvis av konceptutvecklingsarbetet for hela bronoch i synnerhet fr brodcket, som beskriven i sektion 6. Andra huvuddelen irapporten bestr av frdimensionering av brodcket, som grs med BRO94 i

tanke och redovisas i sektion 7. Ett frslag till dimensionering av de terstendebrande delarna ssom pelare och rcken ges i sektion 8.

Nyckelord: fiberkompositer, kartlggning av befintliga fiberkompositbroar,dimensionering av fiberkompositbroar, konceptutveckling,sandwichkonstruktioner, styvhetsstyrd dimensionering.


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IX

Table of contents

PREFACE ............................................................................................................... I

ABSTRACT ..........................................................................................................V

SAMMANFATTNING ...................................................................................... VII

TABLE OF CONTENTS .................................................................................... IX

NOTATIONS AND ABBREVIATIONS ......................................................... XIVRoman upper case letters ......................................................................... XIVRoman lower case letters ......................................................................... XIVGreek upper case letters ........................................................................... XIVGreek lower case letters ........................................................................... XIVSpecial sub- or superscripts ...................................................................... XIV

Abbreviations and acronyms ................................................................... XIV

1 INTRODUCTION ..................................................................................... 11.1 Background ........................................................................................ 11.2 Motivation and goals .......................................................................... 31.3 Thesis outline ..................................................................................... 5


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2 FIBER REINFORCED POLYMERS: MATERIALS,MANUFACTURING AND APPLICATIONS CIVILINFRASTRUCTURES ............................................................................... 62.1 FRP materials ..................................................................................... 6

2.1.1 The fibers .................................................................................. 72.1.2 The resins ............................................................................... 102.1.3 Miscellaneous ......................................................................... 14

2.2 Manufacturing processes .................................................................. 142.2.1 Hand Lay-up / Spray Lay-up ................................................... 152.2.2 Pultrusion ............................................................................... 162.2.3 Filament winding ................................................................... 172.2.4 Resin Transfer Molding (RTM) ............................................. 182.2.5 Vacuum Infusion (VI) ............................................................ 19

2.3 Applications of FRP in Civil Infrastructures ................................... 222.3.1 Primary FRP building components ........................................ 232.3.2 Secondary FRP building components .................................... 242.3.3 Strengthening and Repair ...................................................... 25

3 BRIDGE DESIGN: METHODOLOGY, TERMINOLOGY ANDTHE SWEDISH CODE ............................................................................ 263.1 Bridge design methodology .............................................................. 26

3.1.1 The bridge design process ...................................................... 263.1.2 Key factors .............................................................................. 27

3.2 Bridge classification and bridge components .................................. 283.2.1 Bridge classification ................................................................ 283.2.2 Structural load-carrying system ............................................... 283.2.3 Bridge components ................................................................ 29

3.3 The Swedish bridge design code BRO 94........................................ 303.3.1 The concept of Limit State ..................................................... 303.3.2 Safety Factor and Partial Safety Factors ................................. 313.3.3 Design loads ........................................................................... 33

3.3.4 Load combinations ................................................................. 353.3.5 Design verification.................................................................. 37

4 SURVEY OF EXISTING FRP BRIDGES .................................................. 14.1 Common structural systems used for FRP bridges ............................ 14.2 FRP bridges round the world and case studies .................................. 2

4.2.1 List of FRP bridges ................................................................... 2


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4.2.2 Case studies ............................................................................ 204.3 Research organizations working on FRP in bridge structures ......... 30

5 MECHANICS OF FRP, SANDWICH CONSTRUCTION ANDFRP-CONCRETE COMPOSITES ........................................................... 345.1 FRP and the Classical Laminate Theory .......................................... 34

5.1.1 The Lamina ............................................................................ 345.1.2 The Laminate ......................................................................... 395.1.3 Strength and failure analysis ................................................... 45

5.2 Mechanics of Sandwich construction .............................................. 49

5.2.1 Faces and core material .......................................................... 515.2.2 Design of sandwich structural components ........................... 525.3 Composite action of concrete and FRP in structural

components ...................................................................................... 585.3.1 Composite action concrete-FRP ............................................. 585.3.2 concrete filled FRP shells ....................................................... 59

5.4 Joint design for FRP components .................................................... 665.4.1 Bolted Joints ........................................................................... 665.4.2 Adhesively Bonded Joints ....................................................... 715.4.3 Combining Bolted and Bonded Joints ................................... 715.4.4 Other joining methods ........................................................... 715.4.5 Joining FRP and concrete ....................................................... 71

6 DESIGN REQUIREMENTS AND OVERALL CONCEPTSELECTION ............................................................................................. 716.1 Design requirements ........................................................................ 71

6.1.1 Conditions imposed by clients requirements ........................ 716.1.2 Conditions imposed by the aesthetic requirements ............... 726.1.3 Other design requirements ..................................................... 72

6.2 Overall shape selection ..................................................................... 736.2.1 Structural beam system concepts ............................................ 77

6.2.2 Structural beam system concept for the horizontalcurvature ................................................................................. 79

6.2.3 Selecting boundary conditions and span lengths ................... 796.3 Selecting material system .................................................................. 81

6.3.1 General considerations prior to material selection ................ 816.3.2 Determination of the Partial Safety Factor m........................ 826.3.3 Selecting FRP system .............................................................. 83


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6.3.4 Selecting core material ........................................................... 866.4 Selecting concept for deck cross section .......................................... 876.4.1 Results from previous experiences ......................................... 876.4.2 Parameter study on depth of Classical Sandwich

construction ........................................................................... 896.4.3 Classical Sandwich with internal webs ................................... 906.4.4 Comparing different sandwich beam cross sections .............. 916.4.5 Carbon fiber as face web material ........................................ 926.4.6 Final selected cross section ..................................................... 956.4.7 Alternative cross-section varying with moment curve ............ 95

7 PRELIMINARY DESIGN OF THE BRIDGE DECK ............................. 967.1 Summary of design loads and requirements .................................... 97

7.1.1 Design Loads and other quantitative structuralrequirements .......................................................................... 97

7.1.2 Determining the worse loading case ...................................... 997.1.3 Summarizing load reactions ................................................. 100

7.2 Initial design input data ................................................................. 1027.2.1 FRP and core materials ........................................................ 1027.2.2 Cross-section geometry ......................................................... 103

7.3 Structural verification of selected deck .......................................... 1037.3.1 Compression and punching shear resistance of core

material under wheel load .................................................... 1037.3.2 Summary of reaction from Load Combinations .................. 1077.3.3 Stiffness control using Load Combination V:C .................. 1087.3.4 Ultimate strength investigation using Load Combination

IV:A ...................................................................................... 1097.3.5 Service strength investigation using Load Combination

V:A ....................................................................................... 1107.3.6 Investigating moisture, creep and relaxation using LC V:B. 1117.3.7 Investigating temperature effects .......................................... 111

7.3.8 Fatigue investigation using LC VI ........................................ 1147.3.9 Eigenfrequency and buckling investigation using LC VII ... 1147.3.10 .............................. Accidental loads verification using LCVIII 1157.3.11 ............................................................................. Miscellaneous 115

7.4 Final selected bridge deck section .................................................. 116


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XIII

8 DESIGN PROPOSAL FOR REMAINING STRUCTURALCOMPONENTS ..................................................................................... 1168.1 Design of columns ......................................................................... 116

8.1.1 Selecting column concepts ................................................... 1178.1.2 Load applied on the columns ............................................... 1188.1.3 Material Selection ................................................................. 1198.1.4 Selected cross section............................................................ 119

8.2 Design Proposal for the guardrails ................................................. 1198.3 Design Proposal for the wearing surface ........................................ 1198.4 Design Proposal for Abutments and foundations ......................... 1198.5 Design Proposal for the Connections ............................................ 119

9 CONCLUSIONS AND FUTURE WORK ............................................ 1199.1 Conclusions ................................................................................... 120

9.1.1 General conclusions ............................................................. 1209.1.2 Summary of Preliminary Design Proposal ............................ 120

9.2 Discussions ..................................................................................... 1209.2.1 Design issues and BRO94 .................................................... 1209.2.2 Bill of quantities and cost estimate ...................................... 1229.2.3 Bridge Section Assembly on Site .......................................... 1229.2.4 Miscealleneous issues (Manufacturing and quality control,

Predicted Service Life, etc...) ................................................. 1229.3 Future work .................................................................................... 122

10 APPENDICES ......................................................................................... 12210.1 Appendix 1 ..................................................................................... 12310.2 Appendix 2 ..................................................................................... 12310.3 Appendix 3 ..................................................................................... 12310.4 Appendix 4 ..................................................................................... 124

11 REFERENCES ........................................................................................ 124


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Notations and abbreviations

Roman upper case letters

Roman lower case letters

Greek upper case letters

Greek lower case letters

Special sub- or superscripts

Abbreviations and acronyms


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1 Introduction

1.1 Background

The use of Fiber Reinforced Polymers (FRP) for structural building componentsis a relatively new phenomenon in Sweden. By a structural component, we meana part of a structure that is designed to carry primary loads. For instance panelelements for housing facades are not considered as structural components. Inthe US, Canada, Japan and some west European countries, FRP materials havebeen used in building constructions for about three decades as described in

works by Karbhari (1998), Busel (1999) and Sims (1999). FRP use in civilstructures is particularly frequent in the fields of repair, retrofit andstrengthening of existing building constructions made of conventional materials.Conventional materials refer to concrete, Reinforced Concrete (RC), steel andstructural wood. Structures such as bridge decks, beams or columns, chimneys,parking decks and water tanks have been treated with excellent results asreported in the publication by Busel (1995) or by the Conference Proceedings ofthe 3rdACMBS (2000). Today, many commercial solutions are available forthese applications worldwide. Moreover, the design methods have beenintegrated into the national bridge design standards of many countries as is the

case in Sweden, and design handbooks are readily available. See for instance thesection Supplement 4 in the Swedish Design Code BRO94 (1999), in whichstrengthening using FRP is presented. The implementation of CFRPstrengthening of concrete structures in the Swedish BRO94 is essentially basedon work by Tljsten (1998)

Besides, research has been going on for the use of FRP in new structures such asbridges for nearly two decades. Up to date, more than 90 bridges have been built


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worldwide with integration of FRP components to some extent. The FRPcomponents vary from tendons, cables, internal grids and rebars, to girders,beams, columns, decks and whole bridges.

FRP materials are sometimes called FRC (Fiber Reinforced Composites) or PMC(Polymer Matrix composites). FRP has been traditionally used to designateproducts manufactured by Hand- or Spray-Lay-Up and PMC appears to be themost appropriate denomination for the whole category of materials. Howeversince FRP is the most common term within the civil engineering researchcommunity, we will keep that acronym throughout this report.

The increasing interest for FRP materials is mainly due to the many problems

experienced with civil structures made of conventional materials, such asconcrete decay, steel corrosion or wood corruption. These problems requireincreased maintenance operations with relatively high costs for society.Researchers specialized in civil infrastructures have been investigating the issuesin order to provide practical solutions. One of the research directions has beento improve design and analysis methods when using the conventional buildingmaterials. Another direction is to improve the mechanical properties and longterm behavior of the materials. A third alternative has been to introducematerials that are well proven from other industries into the building sector.This is the case with FRP materials that have been successfully used for decades

in many different industries such as the boat industry, the off shore industry, theaeronautic industry, etc

Although a wealth of knowledge on FRP material and their excellent behavior isavailable from other industries, it is not possible to transfer the technology anddesign methodology straightforward to the Building Construction industry thathas its own design traditions. Moreover, there is a lack of systematic knowledgeon the durability of FRP materials. The Building Industry has higher demandsfor low material cost and long service life for structures. Finally, FRP asanisotropic materials require other stress analysis tools than the ones used forconventional building materials that are considered isotropic (at least

macroscopically). All these considerations make it obvious that there is anenormous need for research and methodology development regarding theapplications of FRP for Building Construction.

In view of the many successful applications and promising demonstrationprojects using FRP materials recorded around the world, a number of Swedishorganizations decided in 1997 to form an Advisory Board and set up a Researchand Development program (R&D). The R&D program is aimed at promoting


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the use of FRP in the Swedish building industry as described by Liljenfeldt(1998). The Advisory Board consist of the research institute SICOMP specializedin manufacturing processes of FRP, the Swedish national roadway and railwayadministrations, the Civil Buildings Maintenance Department of severalSwedish city councils and some building contractors and consulting companies.The Advisory Board concluded that the application fields considered to have thelargest potential for Swedish building industry were:

Repair and strengthening of existing concrete and steel structures

Design of new pedestrian bridges and enlargement of existing traffic bridgesby hanging pedestrian decks on the sides.

Developing the concept of cast-in-place shells for concrete molding withoutsteel reinforcement.

1.2 Motivation and goals

The motivation for the Advisory Board to initiate the research on FRPapplications in building construction in Sweden were:

To help FRP product manufacturers and concrete component manufacturersfind new applications and new products in order to enhance theircompetitiveness and expand their business.

To introduce and evaluate the benefits of FRP for civil structures hencecontributing to a better use of public funds and providing more sound civilinfrastructures.

To establish SICOMP and the structural engineering department of the LuleUniversity of Technology as centers of knowledge for FRP applications inbuilding construction in Scandinavia.

To develop design methods for Swedish practitioners towards an efficient andcost effective use of FRP in building construction.

To address and ultimately provide some answers to key problems related tothe use of FRP in building construction.

For SICOMP in particular, to promote and expand the use of theenvironment friendly manufacturing process called Vacuum Infusion in theproduction of relatively large structures.

As a result two Ph.D. programs were initiated to study commercial applicationsof FRP in close collaboration with partners from the building industry. The first


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Ph.D. program located at the Structural Engineering Department of the LuleUniversity of Technology, Sweden concentrates on repair and strengthening ofexisting structures. See the report by Carolin (2001) for more details on therepair and strengthening research activities. The second Ph.D. program focusingon the design and analysis of new structures, in particular bridges, is supervisedby SICOMP AB, Pite, Sweden. The present report presents some of the resultsfrom the work on designing FRP bridges. It is expected that the two researchprograms will result in at least four commercial applications by the year 2003.Some of the projects realized so far such as strengthening of bridges, chimneysand silos are reported at the homepage http://nnc.ce.luth.se.

Within the scope of the Ph.D. program at SICOMP, it was decided in 1999 tostart a research project on the design and analysis of a FRP bridge together withthe Structural Engineering Department of the Lule University of Technology.One major goal for the research work at SICOMP in general is to contribute toan increase of the competitiveness of existing industries by technology transfer.Therefore, it was decided at an early stage to couple the research project to a realapplication involving industries operating in the region. It was found that thecouncil of the neighboring city of Lule in northern Sweden was planning for apedestrian bridge in a near future. A local FRP manufacturer APC, Lule,Sweden was also associated as well as a local department of a major Swedishcontractor NCC. The area where the bridge is to be built is called Snake Hillin Swedish. Therefore, the whole project was labeled The Snake Hill BridgeProject.

The bridge is to cross over a traffic road occasionally used for transportation ofvery high objects, which implies the need for a lift bridge or at least that thebridges mid-span is removable. This requirement makes FRP with theirrelatively lightweight an excellent alternative material. After studying the Lulecity councils usual requirements on cost, aesthetics, functionality, reliability andenvironmental concerns for a bridge of this type, some concepts were developedto provide a viable solution.

The purpose of this report is partly to introduce the use of FRP materials to theSwedish Building sector and partly to present the results of the preliminaryconceptual design and analysis of the Snake Hill Bridge. The report also includesa survey of existing FRP bridges around the world and basic principles on designusing FRP as well as related research issues. Finally, the report settles the framefor a continued research program including a refined design, analysis and

verification of the Snake Hill bridge, as well as defining Swedish standards forbridge components made of FRP.


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1.3 Thesis outlineThis report is intended for both bridge engineers and material engineers familiar

with FRP. Our hope is that practicing civil engineers will be able to use sections2 and 5 as a fast introduction to design and structural analysis using FRPmaterials. In the same way, sections 3, 4 and 6 will hopefully provide the FRPmaterial engineer with basic knowledge of the design philosophy specific tobridge engineering.

In section 2, FRP as a material class is introduced. Basic constituents like fibersand resins are described. The most common manufacturing processes arepresented with a special focus on Vacuum Infusion, which is the manufacturing

process of interest for our study. Examples of applications of FRP specific to thebuilding construction are given.

In section 3, bridge design methodology and terminology are introduced. TheSwedish Bridge Design Code BRO94 is described with special focus on theguidelines applicable to FRP pedestrian bridge.

A comprehensive (but certainly not complete) list of existing FRP bridges aroundthe world is given in section 4. Some available commercial solutions andresearch trends are presented.

In section 5, the mechanics of FRP material is presented. The mathematical

tools and methods necessary for structural design using FRP materials andsandwich constructions are introduced. Moreover, the design of joint for FRPstructural components are looked upon.

In section 6, design criteria and requirements from the client and the SwedishRoad Administration are described, as well as restrictions imposed by thematerial, available manufacturing processes and aesthetics. The Swedish nationalbridge design code BRO94 is introduced.

Section 7 presents the concept selection procedure for the overall geometry ofthe bridge. The preliminary design and analysis of the bridge deck, which is the

core of this thesis, is described here. An attempt is also made to introduce someproposal for the preliminary design of the remaining structural components.These components consist of the columns, the guardrails, the wearing surface,the abutments and the foundations.

Section 8 concludes by presenting some general reflections about the designproposed by our study. The directions of future work related to this particularFRP bridge and to the use of FRP in building construction are discussed.


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2 FIBER REINFORCED POLYMERS: MATERIALS,MANUFACTURING AND APPLICATIONS CIVIL

INFRASTRUCTURES

Once FRP has been selected in the bridge design, the engineer needs todetermine the most suitable material system. The environmental conditions atthe bridge site will determine the choice of resin and fiber. For instance, if thebridge is to be used indoors, in a place fairly frequented by people, one of the

basic requirement from most Building Authorities would be the Fire Resistanceof the final structure. Thus, an FRP system including resin and additives foroptimal fire resistance should be selected. If the bridge is located in an corrosiveenvironment, like a chemical plant, water and waste handling plant or an animalfarm, the FRP chosen would include CR-glass and/or vinyl ester. For a bridgeexposed to impact loads, the FRP material will most probably include Aramidfibers in order to enhance ductility. In this section, the physical, chemical andmechanical properties of the most commonly used fibers and resins forstructural building components are described.

2.1 FRP materialsComposite materials are obtained by combining two or more materials withdifferent mechanical and/or physical properties to obtain a new material betterfitted for a specific purpose. Some reinforcing solid phase is embedded in aliquid matrix phase, and the whole system is solidified by cooling, applyingpressure and/or through chemical reactions to obtain the final compositematerial. The reinforcing part could be a particle, a platelet or a fiber while the


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matrix may be metallic, ceramic or polymeric. The present report will essentiallydeal with FRP made of some kind of solid fiber reinforcement embedded in apolymeric matrix to provide a discernible reinforcing function in one or moredirections. The reinforcement carries applied static loads while the matrixtransfers stresses between fibers and protects them from environmental effects.Section 5.1 introduces the mechanics of FRP. In the following, FRP materials,the manufacturing processes and some structural civil applications will bepresented. For a more exhaustive study, the reader may consult for instance Hull(1988), the Handbook of Polymer Composites (1998) and strm (2000).

2.1.1 The fibers

The fibers provide the FRP material with its strength and high stiffness. Thefibers are filaments with a very small diameter in the order of 10 m. They mayexhibit different mechanical properties in the longitudinal and cross sectional(transverse) directions. For instance, for carbon and aramid fibers the elasticmodulus (or the fiber strength) in the longitudinal direction denoted ELis muchhigher than the elastic modulus in the transverse direction denoted ET. SeeFigure 1 for a description of the coordinate system for a single fiber.ction.

Table 1 presents typical mechanical properties of some common fibers. Strengthand stiffness are given for the longitudinal direction.

Table 1: Average mechanical & physical properties of some fibersFiber type Elastic tensile

modulus, EL(GPa)

Tensile

strength L(GPa)

Failure strain L(%)

Density(kg/m3)

Max.Temp.

Tmax(oC)

E glass 69 - 72 2.4 3.8 4.5 4.9 2550-2600 250-350

S-2 glass 86-90 4.6-4.8 5.4-5.8 2460-2490 250-300

Carbon (HS/S) 160-250 1.4-4.93 0.8-1.9 1700-1900 500-600

Carbon (IM) 276-317 2.3-7.1 0.8-2.2 1700-1830 500-600

Aramid (Kevlar 29) 83 2.5 - 1440 180

Aramid (Kevlar 49) 131 3.6-4.1 2.8 1440 250

The data in Table 1 are from strm (1999) and Halloway (2000)


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Figure 1: Coordinates system for a single fiber. 1 indicates the longitudinaldirection while 2 and 3 stand for the transverse direction.

For industrial use, fibers are normally delivered in form of stitched or wovenfabrics or randomly oriented mats. The fibers, short or continuous in each layerof the fabric will have a certain alignment or orientation, as shown in Figure 2.In our study, we will deal with structural components made of continuousaligned fibers.

Glass fibers

Glass fibers are made of silica (SiO2) mixed with (mainly) other oxides. Themixture is melted and extruded into fibers with a diameter of 10 to 20 m. Themost common glass fiber is the E-glass where E stands for electrical. This typeof glass fiber, which is a general-purpose grade, offers excellent electricalinsulation properties. For applications with higher demands on stiffness andstrength, the S-glass is used with S denoting strength. There are other types ofglass fiber like the ECR- and the C-glass that offer improved corrosion andchemical resistance respectively. A- glass exhibits superior alkaline resistance.Higher requirements on mechanical or physical properties do however increasethe price. Some of the advantages of glass fiber lie in the high strength, very good

tolerance to high temperature and corrosive environments and the relatively lowprice. The main disadvantages are the relatively low stiffness (especially whencompared to conventional building materials) and sensitivity to stress corrosionin humid environments. Glass fibers are usually used in combination withpolyester or vinyl ester matrices in order to obtain lightweight and low cost FRPstructural components. Common industrial applications are some automobile,truck and bus components, leisure boats, aircraft interiors, electrical equipmentand sporting goods.


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Figure 2: Glass fiber woven bi-directional fabric (left) and chopped strandmat (right)

Carbon fibers

Carbon fibers are usually made of three different kinds of raw materials, namelyrayon, polyacrylonitrile (PAN) or petroleum pitch. In the cases of rayon andPAN, the original textile fibers are usually subjected to different thermal,mechanical and/or chemical treatment. They are finally sized to a diameter 7m. Petroleum pitch is first melted into fibers and then subjected to similarphysical and chemical treatments. The different types of carbon fibers used bythe industry are the HS (High Strength), IM (Intermediate Modulus), HM (High

Modulus) and UHM (Ultra High Modulus). Carbon fibers have higher stiffnessand strength than glass fibers. They exhibit excellent environmental propertiesbut have a higher price than glass fibers. They are also brittle and conductive.Carbon fibers are used for applications where excellent mechanical propertiesand low weight are the main requirements. Examples are high performanceracing vehicles, yatches, space crafts, aircraft and sporting goods.


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Figure 3: Carbon fiber rovingAramid fibers

This type of fiber is an organic fiber, as opposed to carbon and glass fibers thatare inorganic. The most common aramid is known under the trade name Kevlarcommercialized by Du Pont. Aramid is a short for aromatic polyamide. Kevlar ismade from a polymer powder dissolved in sulfuric acid and extruded to a fiber

with a diameter of 12-m. Aramid fibers have excellent toughness and damagetolerance properties. They are very difficult to cut, can absorb moisture and arevery expensive. Common applications are impact-prone areas of aircraft, ballisticarmor and some sporting goods.

Other types of fiber

The three types of fibers mentioned above are the most interesting for thestructural components in building construction treated in this report. However,there are many other fibers and reinforcement materials such as Polyethylenefibers, boron and ceramic fibers, metal wires and natural fibers such as jute, flax,copra and wood.

2.1.2 The resins

The term resin or matrix is used to designate the polymer precursor materialand/or mixture with various additives or chemically reactive components. Itschemical composition and physical properties fundamentally affect theprocessing and final properties of the FRP material. Processability, lamina and


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polyesters; low styrene emission resins or closed form processes such asVacuum Infusion. Orthophtalic polyester is the most common type of polyester.It is cheap but exhibits relatively low mechanical properties and poorenvironmental resistance. Isophtalic polyester exhibits much better mechanicaland environmental properties but also more expensive. Applications ofpolyesters are found in automobile and bus components, leisure boats, high-speed passenger ships, building panels, beams, pipes, electrical equipment, etc

Epoxies:

They extend over a family of polymers based on molecules that contain epoxidegroups. An epoxide group is an oxirane structure, a three-member ring with one

oxygen and two carbon atoms. Epoxies are polymerizable thermosetting resinscontaining one or more epoxide groups curable by reaction with amines, acids,amides, alcohols, phenols, acid anhydrides, or mercaptans. They are available ina variety of viscosities. The advantages of epoxies are high strength and highmodulus, low levels of volatiles, excellent adhesion, low shrinkage, goodchemical resistance, and ease of processing. Their major disadvantages arebrittleness and the reduction of properties in the presence of moisture. Theprocessing or curing of epoxies is slower than polyester resins. The cost of theepoxy resin is also significantly higher than that of polyesters. Epoxies are widelyused in resins for prepregs and structural adhesives. They are also extensively

used for strengthening and repair of concrete and steel structures.Vinyl esters:

The vinyl ester resins were developed to take advantage of both the workabilityof the epoxy resins and the fast curing of the polyesters. The vinyl ester hashigher physical properties than polyesters but costs less than epoxies. The acrylicesters are dissolved in a styrene monomer to produce vinyl ester resins that arecured with organic peroxides. A composite product containing a vinyl ester resincan provide high toughness and offer excellent corrosion resistance. One can saythat Vinyl esters lie between polyesters and epoxies as far as properties and costare concerned.

Other thermosets

Apart from the thermosets described above, there are some other types that areused in specific applications. Phenolics for instance are rated for good resistanceto high temperature, good thermal stability, and low smoke generation.Polyurethanes (PUR) are mainly used with little or no reinforcement and arecommon in the automobile industry. Polyamides (PI) with their excellent high


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Thermoplastic

type

Elastic tensile

modulus EL(GPa)

Tensile strength

L

(GPa)

Strain tofailure

L

(%)

Density

(kg/m3)

GlassTransitionTemperature

Tg.

(oC)

Thermalexpansion

10 6oC-1

1320

2.1.3 Miscellaneous

Additives

Additives are often used to improve a particular physical property of a FRP. Thedesired effect could be to improve fire or UV resistance or to get better

processability. Sometimes, chemicals called accelerators or retardators are usedto control the speed of curing during the manufacturing process. These additivesor accelerators are usually mixed to the resin prior to the curing. Finally, sp-called gel-coats are commonly used to enhance the surface protection or theaesthetic appearance of the finished product.

Hybrid FRP

In some applications, it might be desirable to combine the properties of differentfibers in one structural component. For instance, carbon fibers might becombined with aramid fibers to design a product in which both high stiffness

and strength as well as excellent impact resistance are required. In this situation,a multidirectional fabric including both types of fibers will be used. The finalproduct is called a hybrid composite.

2.2 Manufacturing processes

When choosing the most cost efficient manufacturing technology for a structuralpart made of FRP, the following aspects should be taking into consideration:

The production volume (quantity of components needed)

The size and geometry of the component

The required performance (i.e. stiffness and strength per unit weight) The required quality on surface finish and tolerances

Selecting the manufacturing process is often based on end-use purpose,structural requirements, economical and increasingly environmentalconsiderations. In the following sections, some of the most commonmanufacturing processes are presented. Fel! Hittar inte referensklla.to Fel!


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Hittar inte referensklla.give a schematic description of the presentedmanufacturing techniques

2.2.1 Hand Lay-up / Spray Lay-up

In the hand lay up method, the fibers are laid in a male or female mould and theresin is poured on and spread by means of a roller to facilitate a thoroughimpregnation. After completed impregnation, the curing process starts. Thismethod is one of the most common because no big investments in tools andmachines are required. Still the quality of the final product is good enough formany applications. Fel! Hittar inte referensklla.shows a schematic descriptionof the hand lay-up method. Spray lay up is a variant technique where chopped

fibers and resin are applied by means of a spray gun. These techniques are usedfor manufacturing small boats, storage tanks and bathroom interiors. See alsoFel! Hittar inte referensklla..

Figure 4: Schematic of Hand Lay Up. After http://www.spsystems.com


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Pulling device

Final product

Resin applicatorContinuousstrand roving

Heated mandrel

Figure 6: Schematic of the pultrusion process

2.2.3 Filament winding

Products manufactured using filament winding are usually hollow, generallycircular or oval sectioned components, such as pipes and tanks. Fiber tows arepassed through a resin bath before being wound onto a mandrel in a variety oforientations, controlled by the fiber feeding mechanism, and rate of rotation ofthe mandrel. This is a fast and economical process with little material waste andresults in products with excellent mechanical properties. Some of thedisadvantages are that only convex shaped components can be manufacturedand axial (longitudinal) fiber orientation is difficult to achieve. See Fel! Hittarinte referensklla.for a schematic description of the filament winding process.


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Moving carrier

Rotating

mandrel

To creel

Nip Rollers

Resin bath

Fibers

Angle of fiber warp controlled by ratioof carriage speed to rotational speed

Figure 7: Filament winding process2.2.4 Resin Transfer Molding (RTM)

Fabrics are laid up as a dry stack of materials. These fabrics are sometimes pre-pressed to the mould shape, and held together by a binder. These pre-formsare then more easily laid into the mould tool. A second top-mould is thenclamped over the first and resin is injected into the cavity. Once all the fabric is

wet out, the resin inlets are closed, and the laminate is allowed to cure. See Fel!Hittar inte referensklla.for a schematic of RTM.


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Dry Reinforcement

Resin injectedunder pressure

Optionalvacuumassistance

Press or clamps to holdhalves of tool together

Mould tool

Figure 8: The RTM process

2.2.5 Vacuum Infusion (VI)

Vacuum can also be applied to a mould cavity of the type used for the RTMprocess, in order to assist resin in being drawn into the fabrics. This is known as

Vacuum Assisted Resin Injection (VARI). Vacuum Infusion (VI) is a variant ofthe Vacuum Assisted Resin Injection. In vacuum infusion, the pressure gradientis created by vacuum at the outlet. The following description of VacuumInfusion is essentially based on literature provided by Holmberg (2001).


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Proper selection of resin that can resist very large exothermal in thick parts.The main advantages of Vacuum Infusion compared to other FRPmanufacturing processes:

Vacuum Infusion is a closed process, with low styrene emission, which makesit very environmentally friendly. The styrene emission is well below theminimum values set by Swedish Health Authorities.

No strong and stiff thus expensive tooling is required. Vacuum infusion isvery suitable to the production of large products that are made in smallquantities. Both parts with low and high fiber content can be achieved. A

good quality surface on one side of the part is very well feasible. Vacuum Infusion offers one of the best alternative for large components with

flexible geometry and requirements on cost effectiveness. Architects anddesigners can conceive shapes that will be hard or expensive to achieve withconcrete or steel.

It is possible to produce FRP components with various fiber volume contentswithin the range 15 to 65 %.

If required, small tolerances can be achieved using stiff tooling. Specialtooling can be used to ensure small tolerances in specific areas of the

component. Improved consistency of the product properties (properties are less dependent

on the craftsmanship of the employee). This can enable use of lower designsafety factors, resulting in a more efficient design.

Although Vacuum Infusion has proven to be an excellent manufacturing processfor FRP structural components, it also presents some few disadvantages:

Some scrap components might be manufactured prior to obtaining a partwith good quality. This may increase the total cost of the final product. The

overall quantity waste material is bigger than that due to pultrusion forinstance.

In sandwich structures, honeycomb cannot be used straightforward. A sealingfoil in order to avoid infiltration of the resin into the honeycomb.

Net shape manufacture is rare with vacuum infusion. Usually edges need tobe trimmed. In addition, the foil side of the part can have sharp ridges of


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resin due to folds in the foil. In some cases, these ridges need to be removedby sanding.

Furthermore, the following drawbacks can occur during Vacuum Infusion.These can be avoided if the work is performed by a skilled and experiencedteam:

There are no control tools that can be used to assist the workshop employees.For example mistakes in laying down the dry reinforcement can not beidentified before the injection starts. Therefore, good skill is necessary for asuccessful placement of the reinforcement.

Sensitivity to leakage, which makes the process critical for mistakes. Anysource of leakage must be taken care of before resin injection starts.

A good surface finish can be difficult to achieve especially when thin andthick laminates are combined. Skilful workmanship can minimise theoccurrence of wrinkles before resin injection. Unevenness in the final surfaceshape can be trimmed off.

The manufacturing process affects the mechanical, physical and durabilityproperties of the final structural component. For instance, when using filament

winding, it is usually not possible to align the fibers in the 0o-orientation. Whenusing Vacuum Infusion, it is difficult to obtain a fiber volume fraction over

60%. Pultrusion does not permit a varying cross section in the longitudinaldirection. Finally, the Spray Lay Up can result in a poor laminate quality andlow fiber content. It may also give a poor thickness tolerance. It is thusimportant for the structural designer to have some knowledge of the process that

will be used to manufacture the component.

Vacuum Infusion is the manufacturing process that SICOMP is specialized at. Itis also the process of interest for the bridge deck described in this report.

2.3 Applications of FRP in Civil Infrastructures

Military and aerospace applications were the early driving forces for thedevelopment and use of FRP. During the last three decades or so, FRP have alsobeen used for manufacturing leisure boats, some parts in cars and heavy vehicles,sporting goods and infrastructure facilities. When mentioning infrastructurefacilities, we refer to two categories. In the first category, we consider private andpublic houses and facilities, industrial sites, bridges, waterfronts, dams, etc. Inthe second category, we consider pipes, tanks, electrical masts, lightning polesand so on. FRP are extensively used for producing components mentioned


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under the second category. In the following, we will concentrate on productsclassified under the first category.

The range of applications of FRP in civil infrastructures and buildingconstruction is very wide. FRP applications in building construction can beclassified in primary structures, secondary structures and Retrofit, Repair andRehabilitation. Some examples are found in housing, masts, pipelines and

walkways. In bridge applications, FRP are mostly encountered as internalreinforcements instead of conventional steel in some special cases. See the reportComposites for Infrastructure (1998). Carbon FRP are used as tendons andcables in suspension bridges. Glass FRP enclosures serve for protection against

moisture to bridge decks.One of the most spread applications of FRP in bridge construction today arehowever found in external repair, strengthening and retrofitting of existingbridges made of conventional building materials such as concrete and steel. Theinterested reader will find a wealth of information on this topic by consultingTljsten (19xx) or Karbhari (1998).

The pultrusion industry offers off-shells FRP profiles similar to conventionalsteel profiles. These pultruded profiles are used in many Short- and Medium sizebridges. In the USA, pultrusion companies such as Strongwell and Owens-Cornings provide pultruded profiles and bridge deck panels that are being usedin some bridge replacement projects. In Europe, The Fiberline company hasbeen promoting the design of FRP bridges as described in Section 4.2. Severalmanufacturers involved in FRP bridge projects are also presented in Table 4.

2.3.1 Primary FRP building components

FRP bridges: Entire bridges or primary components such as decks, girders,columns or towers have been made of FRP. This class of primary FRP buildingcomponents is described in more details in Section 4.

The Naval Training Base in Fort Storey, VA, USA, a 19 meter-tall stair-tower wasentirely made of FRP pultruded profiles. It is designed to resist hurricane loads.

Glass fiber and fire retardant polyester were used.

Glass fiber and fire retardant polyester were also used to manufacture theworlds largest FRP stack liners.

Many pier decks have been made of FRP in the USA. One of them was placed atthe Navys Advanced Waterfront Technology Test Site in Port Hueneme, CA in1994. The 48-meter long deck is made of FRP beams with dimensions 6 m x 5.6

x 1.6 m. Glass fiber and isophtalic polyester was used. The same year, a 483 m


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long pier deck made of FRP was installed at Huntington Beach. Glass fiber andisopolyester was used for the girders. The gratings constituting the walkingsurface were covered with a special silica-epoxy bonded layer. At theinauguration, close to millions people walked on the structure. It is designedfor the Federal Highway specification HS20 and can support a three-axle truck

with a load of 15 tons.

The Arch Antennae is an 25 m high, 49 m clear span, fiberglass tripod used bythe US Naval Station at Point Loma, CA, USA. FRP was selected for its uniquecombination of strength and RF transparency. Additional advantages were thecorrosion resistance and low maintenance need.

In 1999, The Eyecatcher building was installed as the tallest ever residential oroffice building made of FRP. The building was 14.5 m long with 5 stores. Theground area was 10 x 12 m. The structural system was a framwork and the load-bearing capacity was 3 kN/m2. Glass fiber and isophtalic polyester were use tomanufacture the pultruded profiles.

2.3.2 Secondary FRP building components

Translucent FRP siding panels have been used in the facades of many buildings,thus increasing the aesthetic appearance of the building. They are also used inroof monitor panels. To prevent corrosion and minimize future maintenance

problems, FRP wall panels are often used to cover entire facades. FRP dropceilings are also used for the same purpose in some interiors subjected tocorrosive environment.

Water storage tanks made of FRP are used instead of steel to store highlyaggressive soft water. FRP tanks have also been used for fuel storage for theirexcellent durability properties. A fuel tank made of glass fiber and isophtalicpolyester was buried together with conventional steel tanks in Schaumburg, IL,USA in 1964. It was excavated 26 years later in 1990, when it was time toreplace the steel tanks. It was found out that the FRP tank was structurallysound and was buried again for further use.

The Eurotunnel connecting Great Britain to France is considered to be thelargest single application site for FRP pultruded profiles existing today. Morethan 3600 tons of FRP profiles were used to support 1300 km of electricalfacilities and to provide walkways for the maintenance personal. FRP wereselected instead of steel for higher resistance to saline corrosion, safety in fireconditions, easy installation, minimum maintenance and overall cost. Glass fiberand modified acrylic resin were used.


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Another use of huge volumes of pultruded FRP profiles is found along the 280km long walkways at the Elevated Train Tracks of the New York City Transitfacilities. FRP were preferred to wood and steel because they, among otherthings, offered better working safety for the railway maintenance workmanship.Glass fiber and polyester are used and the surface was coated with epoxy.

The examples of primary and secondary structural FRP components abound.The interested reader may consult the reports FRP Composites in Construction

Applications (1995) and Composites for Infrastructure.

2.3.3 Strengthening and Repair

As mentioned in section 1.1, the retrofit, strengthening and repair of civilstructures made of conventional building materials is an established engineeringpractice in the US and Japan. See Karbhari (1998). In Europe, the Swiss researchinstitute EMPA is a pioneer with comprehensive research that led to establishedcommercial applications. The interested reader may find more about EMPA athttp://www.empa.ch. In England, the group Mouchel provides commercialsolutions for structural repair and strengthening. The interested reader may findmore about Mouchel at http://www.mouchel.com.

In Sweden the building contractor Stabilator carries on strengthening work onan industrial basis. The methodology is incorporated in the Swedish bridge

design code BRO94 thanks to work conducted by Tljsten (1998). In Sweden,comprehensive research work has been made by Tljsten (1997) in developingtechnical tools for the strengthening of RC structures in bending. Carolin(2001) has investigated some case applications of strengthening RC in Sweden.


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3 BRIDGE DESIGN: METHODOLOGY,

TERMINOLOGY AND THE SWEDISH CODE

3.1 Bridge design methodology

Bridges are essential for the good functioning of transportation in all moderneconomy. They are also subjected to very high traffic safety measures and usuallyrequire enormous investments from taxpayers for building and maintenancre.Therefore, the design and building of bridges is regulated by codes in mostcountries. The Swedish national design code is known as BRO94 and is basicallyset up in the same manner as its American equivalent, AASHTO.

3.1.1 The bridge design process

In general, the bridge design process will involve over the following 3 main steps: Establishing design requirements from the client. Usually the client will

provide exact data about the geographical position of the location, theclimatic conditions (temperature and RH), water flow if the bridge is to crossover a river, extent and nature of traffic to go on the future bridge and if thatis the case, on the underlying road. Then a bidding process takes placethrough which different design firms will compete on offering the best

solution, with regards to function, aesthetics and economy. In order to deliver a proposal, the engineering team evaluates a concept for

the geometry and materials to be used. Next, a suitable structural load-carrying model is discussed. Some initial input data are required at this level.Often, these data are obtained from a similar bridge submitted to equivalentloading conditions and the optimal result is computed through iterations.


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Producing the final documents, after a refined analysis, that will be used bythe contractor to actually build the bridge. Prior to construction work,verification and quality control are carried on.

The main task of the bridge structural engineer is usually to produce theappropriate design for the primary structural components of the superstructure(deck guardrails and wearing surface). The design of the primary structuralcomponents of the substructure (columns, abutments and foundations) may alsoinvolve the structural engineer. Through these steps, the designer will specify allthe static and dynamic loads that the bridge will be subjected to. Next, drawingsare produced to illustrate the overall shape of the bridge and the differentcomponents. Different concepts regarding material, geometry and aesthetics arecompared and a preliminary cost analysis is performed. The selected concept willthen undergo a refined analysis to accurately determine the state of stress in thestructural bridge system. Most ground fortification and ground leveling work isusually done by engineers specialized in geotechnics. During the bridgeproduction phase, structural engineers might be consulted for verification, andsometimes modification of the initial design.

3.1.2 Key factors

The most decisive factors that affect the selection of the bridge design are thefollowing: FunctionalityThe primary function of the bridge is to allow for the transportation of peopleand goods in a safe and reliable manner. CostThe function of the bridge should be achieved at the minimum possible cost fortaxpayers. A Life Cycle Cost (LCC) of different bridge alternatives should clearlyshow which solution is economically optimal. The LCC includes the originalinvestment related to the bridge building, all expected maintenance coststhroughout the bridges service life and other costs such as traffic disturbanceduring construction and maintenance work.

AestheticsA bridge can alter a landscape by its mere presence. Once built, an expensiveand ugly bridge can hardly be replaced before the end of its service life, which isoften above a century. The visual experience of the bridge by users and peopletravelling close to it is important and therefore, its aesthetics play an importantrole during the design procedure. Environmental related issues


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Finally, it has become increasingly important to investigate the environmentalimpact of bridges. Life Cycle Analysis (LCA) are made in order to evaluate theimpact of different bridge concepts and material alternatives on theenvironment.

3.2 Bridge classification and bridge components

3.2.1 Bridge classification

A bridge is in a general manner defined as a man made load-bearing structurethat enables people and goods to travel across a physical hinder. There aredifferent ways of classifying bridges. The most common classification methods

are described below. Depending on the type of traffic, a bridge can be classified as road traffic,

railway or tramway bridge or bike and pedestrian bridge. Special casesbelonging to this classification are aqueduct and self-assembly military bridge.

When referring to the main structural materials, bridges are called stone orbrick bridges, wood bridges, steel bridges, aluminum bridges, FRP bridges orcomposite action bridges where 2 or more materials constitute the structuralcomponents of the bridge deck. Composite action bridge materials are oftena combination of steel and concrete.

If the structural load bearing system is considered, bridges are classified as

girder bridges, frame bridges, arch bridges, suspension bridges or cable stayedbridges. There exist many variations derived from these main groups. The legal ownership is sometimes used to classify bridges. In Sweden, there

exist state owned bridges, municipal bridges and private bridges. Bridges are also sometimes classified depending on whether they are

stationary, movable or floating. Movable bridges are a type of bridge weresome span section of the bridge can be moved in order to allow fortransportation of very high objects beneath. Depending on the span movingsystem, these bridges are called swing bridges, bascule bridges, span drivebridges or vertical lift bridges.

3.2.2 Structural load-carrying system

There are three main principles for defining the structural bearing system of abridge. Other alternatives are derived from these main principles. Theseprinciples utilize different ways of transferring loads to the ground. Thefollowing description is based on work by Sundquist (1995). The structural beam system is the simplest and often the most practical

method. The beams or plates top face is mainly under compression while


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the bottom face is under tension. The beam structural system is usually usedfor total bridge lengths up to 200 m. Above this length, the dead load of thesuperstructure makes the system less efficient. However, by using acontinuous beam system, up to 300 m long bridges can be built using thissystem. In combination with the use of structural console framework, bridgesover 500 m long have been built.

When the bridge length is over 200 m and the ground conditions aresuitable, the arch structure is very convenient and an aestheticallyappealing bridge type. The loads are essentially transferred to the ground bycompression action. The longest bridges of this type are roughly over 500 m.

For even longer bridges, with lengths over 800 m, the structural suspensionsystem is the most efficient. In this method, the load transfer to the groundoccurs mainly through tension action. The longest bridges of this type arearound 2000 m long.

A variant of the structural beam system that is commonly used for relativelylong bridges is the cable stayed bridge. Bridges nearly 900 m long havebeen built using this method.

There is no general rule for selecting structural system based on length solely. Acombination of length, material, ground conditions as well as economical andaesthetic considerations will usually affect the structural system selection.

3.2.3 Bridge components

Bridges are normally subdivided into superstructure and substructure. Theseparts are made of the bridge components as described in Figure 10.

Figure 10: Details of super- and substructureSuperstructure


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The superstructure constitutes the part of the bridge that is in direct contactwith the traffic surface. It consists of the wearing surface, the deck, the girdersand the guardrails. Another definition is that all components that are above thebottom face of the deck (or the beams under the deck) are part of thesuperstructure. Bearings, joints between deck segments, girders and plates are allpart of the superstructure. In the case of an arch bridge, the arches are part ofthe superstructure. Even other utilities such as drainage equipment areconsidered as part of the superstructure.

SubstructureAll components needed to transfer stresses to the ground are part of the

substructure. This includes the abutments and the columns. Footings andground reinforcement plates are also part of the substructure. Othercomponents that are part of the substructure are the earth or water retaining

walls.

3.3 The Swedish bridge design code BRO 94

The Swedish BRO94 regulates bridge design in a similar way as AASHTO, itsAmerican equivalent. BRO94 is based on the national building constructioncode Boverket issued by the Swedish National Housing Board (1996). One ofthe main purposes of the code is to provide the bridge engineer with an

adequate tool for minimizing risks and cost. The code is developed from thetheory of reliability and some other concepts described below. This resulted inthe so-called Load and Resistance Factor Design (LRFD) methodology used inmost national bridge design codes. During the design procedure, some initialmaterial and geometry are assumed for a structural sub-component, acomponent or a whole system. Then the state of stresses is analyzed and thematerial and geometry are varied until the Ultimate Limit State (ULS) isfulfilled. Finally, the design is verified using the Service Limit State (SLS) and the

Accidental Loads Limit State (ALLS). The design procedure is described inFigure 11. The concepts presented in sections 3.3.1 and 3.3.2 are derived fromthe national building construction code Boverket issued by the SwedishNational Housing Board (1996).

3.3.1 The concept of Limit State

The Ultimate Limit State, also called Strength Criteria, considers the limit atwhich a structure becomes unusable under normal loading conditions. TheService Limit State or Service Criteria, is the limit under which the structuredoes function in a satisfactory manner. This limit could be indicated by the


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presence of excessive deflection, vibrations and oscillations, visible cracking ofthe material or other aesthetic defects. Finally, the Accidental Load Limit State(ALLS) or Performance Criteria takes into account unusual loads that couldcause a fatal damage. Accidental load can be Vehicular Collision Load (VCL)ona column or loads from acts of vandalism.

Figure 11: Schematic of bridge design steps3.3.2 Safety Factor and Partial Safety Factors

The notion of safety is central to the bridge design philosophy and will thereforebe presented briefly in the following. The notions introduced are mainly basedon work by Sundquist (1994) and Xanthakos (1994).

Safey Factor

The expression Safety Factor is used to define the level of guaranteed safety fora bridge under a specific set of loads. The Safety Factor concept is based on theassumption that the quantities S,or loads acting on a bridge, and R, theresistance of materials, components or structural systems in the bridge, are


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deterministic. In reality, both are stochastic. If we consider a given distributionof load effects, the corresponding probability of failure can be minimized byincreasing the resistance. An expression of the safety margin is given as Y = R S.Failure occurs for a negative value of Y, which is associated to a probability of

failure Pf. The stochastic value Yhas a mean value Y-

and a standard deviation

Y. The parameter Y-

/Yis called the safety index. Since strengths and loads varyindependently, a safety factor or fis associated to load effects and a safetyfactor or mto material resistance.

Partial Safety factor

Since total safety implies unreasonably high costs, the concept of Partial Safety isadopted instead. The Partial Safety method is based on available statistical dataon both Skand Rk.Skand Rkare called characteristic values. To account for theuncertainty related to their stochastic nature, their values are taken from normaldistribution curves. Hence, Skis taken as the 5 % highest values on thedistribution of statistically known applied loads while Rkrepresents the 5 %lowest fractal on the distribution of the resistance values as described in Figure12.

Figure 12: Strength and resistance distributionsPartial Safety Factors are used to account for uncertainties. Some of theuncertainties considered are:

The uncertainty on the highest magnitude of the loads expected over thebridges service life.


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Inaccuracies in calculations and assumed mathematical model Defects and variations in material properties

Mistakes during the construction work

How serious is the impact of a of total structural collapse with respect toeconomical and human casualties

For every occurring load that is considered, the following equation must besatisfied:

or where andk kk S d d d d k S R R

R RS R S R S S

(1)

The subscript dstands for the design value. All are derived from sub-coefficients as described below:

1 2 3 for the material or component resistance valueR R R R n

where R1accounts for uncertainties other than those related to thestochastic nature of Rk. e.g. the geometric differences between the designand the real structure, R2stands for uncertainties on calculations andtheoretical model, R3relates to uncertainties related to variations in workexecution and nthat considers the consequence and nature of a potentialfailure.

1 2 for the values of the loadingS S S

where S1accounts for uncertainties on the load that are time dependentand S2accounts for uncertainties on the loading model and relatedcalculations.

Characteristic values of material, components and structural system resistanceare given in national material design handbooks such as the Swedish ConcreteHandbook BBK94 (1994), Steel Handbook BKR94 (1994) or the Structural

Wood Handbook (Trbyggnadshandboken 1994). Characteristic values ofapplied loads on bridge structures are given in BRO94.

3.3.3 Design loads

There are different methods of classifying the loads that are applied to a bridge.In one type of classification, we distinguish between gravity related and non-gravity related loads. In a second classification method, we distinguish betweennatural loads, human activity induced loads and loads caused by the action-


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reaction within the structure. Finally, we can classify loads into permanent loads(dead load of structure), transient loads (traffic, wind, snow) and accidentalloads. The last-mentioned classification method will be used to describe thedesign loads. All the information described throughout the sections Designloads and 3.3.4 are collected from BRO 94, section 2.

Permanent loads

DLor Dead Load. This is the load imposed by the weight of the structuralcomponents of the superstructure, including guard-rails and other accessories.For these loads, BRO94 gives standard figures for conventional buildingmaterials. For instance, for reinforced concrete, DL= 24 kN/m3, for steel DL

= 77 kN/m3and for pinewood and spruce wood DL= 6 kN/m3.

WSLor Wearing Surface Load. For this load, BRO94 gives figures rangingfrom 0.2 kN/m2to 3.5 kN/m2depending on a specific table of weightcategory.

EPLor Earth Pressure Load. Normally, EPLis applied to foundations andabutments. The load is obtained by multiplying the density of the earthmaterial by a factor specifying whether the case is earth pressure at rest,active earth pressure or passive earth pressure. These data are specified inTable 21-1. In table 21-2, account is taken for the presence of slope.

SSLor Support Settlement Load. In BRO94, it is required to verify the bridgestructure for the worst case of horizontal or vertical support settlements orcombination of support settlements. SSL= 10 mm in horizontal or verticaldirection and per support.

CL= Creep Load and RL= Relaxation Load are other types of permanentloads typical to bridges. These time dependent loads are also material specificand can be found in material design handbooks.

Transient loads

Traffic Loads are given for different traffic conditions. The most relevant in ourstudy are:

PLor Pedestrian Load

SCVLor Snow Clearance Vehicle Load

FLor Fatigue Load

VBLor Vehicle Breaking Load


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VSLor Vehicle Side Load SL= Snow load. Depends on the region where the bridge will be located and

the shape of the area upon which the snow rests.

UTVLor Uniform Temperature Variation Load

GTVLor Gradient Temperature Variation Load

WLor Wind Load

LGor Loads on Guard-rails

Accidental loads

VCL= Vehicular Collision Load with regard to the columns. This applies tocases where the columns are located less than 10 m away from the outerlimits of an underlying traffic road. F= 1000 kN and 500 kN should beapplied on the column 1 m above the traffic surface, in traffic direction andtransverse to traffic direction respectively

UTLor Unexpected Traffic Load accounts for unauthorized vehicular trafficthat might take place

3.3.4 Load combinations

In real life, the loads mentioned above seldom occur alone. What is oftenobserved is a combination of various loads. Therefore, a system of LoadCombinations has been developed to account for the worst possible cases of loadcombinations. Loads are reduced by means of a so-called Reduction Factor . accounts for the probability that a certain load occurs in a given set of loads.Equation (2) describes the general form of a load combination.

1 21 2: ..... nnLC I S S S (2)

In the design table 22-1, from BRO 94, values of are given instead of only .is the Partial Safety Factor as explained in section 3.3.2. The most relevant load

combinations for a pedestrian bridge are listed below.Load Combination IV:A

This is the main load combination for the Ultimate Limit State. It describes themaximum possible load the bridge will ever have to support. Statistically, thisload combination might occur a couple of times under the bridges service life.

All permanent loads are summed after multiplying them with the adequate .A maximum of four transient loads that give the worst possible load


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combination are then added to the case. The highest transient load is multipliedby the highest value of .

: 1.05 1.2 1 1

1.5 0.7 0.7 0.7

LC IV A DL WSL SSL CL

PL SL WL GTVL

(3)

The terms in the first parenthesis include permanent loads and those in thesecond parenthesis, transient loads. The load causing the highest stresses of thePedestrian Load PLand the Snow Clearance Vehicle Load SCVLis used in thesecond parenthesis of the equation above. Here we assume that PLis the higherload.

Load Combination V:A

This is the main loading case in the Service Limit State. It expresses themaximum load the bridge will have to carry in normal working conditions. It isgiven by:

: 1.05 1.2 1 1

1 0.7 0.7 0.7

LC V A DL WSL SSL CL

PL WL SL GTVL

(4)

Load Combination V:B

This combination is used to investigate the effect of long-term loading such asrelaxation. Creep and crack formation are also controlled using this LC.

: 1 1 1 1 0.3LC V B DL WSL SSL CL PL (5)

Load Combination V:C

This load combination is used to verify maximum deflection and movements ofbridge decks free ends.

: max( , )LC V C PL SVCL (6)

To account for the deflection due to self-weight (DL+ WSL), the deck is built

with a corresponding initial rise.Load Combination VI:

This is used to investigate fatigue. According to section 42.43 of BRO94, it isnot necessary to investigate the fatigue impact of traffic on a pedestrian bridge.However, for the completeness of our study and since FRP materials are notdiscussed in BRO94, a simple fatigue analysis will be conducted for the SnakeHill Bridge. The model used to analyze the fatigue behavior for conventional


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building materials will not be used. For FRP materials, maximum strain leveloffers a better model for fatigue analysis as recommended by the Military DesignHandbook (1998).

Load Combination VII

This case is used to analyze the structures egeinfrequency. DLand WSLare usedto compute the natural frequencies.

Load Combination VIII

This load combination is used to analyze the structure for accidental loads. Twocases of accidental loads are of interest in the case of our pedestrian bridge:

A Vehicular Collision Load VCLon the bridge columns is considered. It isapplied horizontally as a concentrated load of 1000 kN and 500 kN parallelrespectively transverse to the traffic direction on the underlying road.

A concentrated load of 155 kN on two wheels with an area 0.6 m x 0.2 meach, across the deck.

3.3.5 Design verification

During the design of a bridge using conventional construction materials such asconcrete and steel, the primary structural design will be based on LC IV:A. In

other words, the structure is designed for strength. Once the strength criterion issatisfied, all remaining load combinations are used to verify the design.However, previous design experiences with FRP, as described by Lei Zhao(1999) and Demitz (1999), show that the design is stiffness driven. This meansthat load combination LC V:Cwill be used first and all other LCwill serve fordesign verification purposes. LC V:C is used to verify the following:

Maximum deflection should be L/400, where Lis the span length. Loadcombination LCV is used.

Minimum eigenfrequency 3.5 Hz. Load combination LCV is used.

Life expectancy should be 40, 80 or 120 years. 40 years is the normalrequirement for wooden bridges. Load combination VI that is associated tofatigue would normally be used to assess of the bridges service life.


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4 SURVEY OF EXISTING FRP BRIDGES

As described in section 2.3.3, retrofitting, strengthening and repair of existingconcrete, steel or wood structures, FRP materials are now used on a commercialbasis. The use of FRP as internal reinforcement, tendons and cables is alsoexpanding as described in Composites for Infrastructure (1998). In this section,

we will present some applications of FRP materials as primary structuralmembers for new bridges. FRP materials have been used to build demonstrationbridges for the last two to three decades with appreciable success. In the listedbridges, components such as beams, columns, decks, panels or whole bridge

systems are made of FRP. When available, the following information will begiven: Physical dimensions of the bridge and or FRP components,manufacturing method, structural system and bridge bearing class.

To the authors knowledge, there is no available database on all FRP bridges thathave been constructed worldwide to date. Hence, no claim is made as of thecompleteness of the list presented in this report. Some universities, researchinstitutes and other organizations working with FRP in bridges as well ascompanies providing commercial solutions are also presented in this section.

4.1 Common structural systems used for FRP bridges

The most common structural system among existing FRP bridges is the simplysupported beam System. In most cases, a FRP deck rests on girders made ofconventional building materials. In some few cases, even the girders are made ofFRP materials. This is due to the fact that most FRP bridges to date are Short-and Medium size bridges. The simply supported beam system is suitable forshort spans.

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