Recommended Practice for Fiber-Reinforced Polymer Products for Overhead Utility Line Structures

ASCE Manuals and Reports on Engineering Practice No. 104

RecommendedPractice for

Fiber-ReinforcedPolymer Products

for Overhead UtilityLine Structures

Prepared byThe Task Committee on Fiber-ReinforcedComposite Structures for Overhead Lines

of the Structural Engineering Institute of theAmerican Society of Civil Engineers

Abstract: This manual provides guidelines for the design, manufacture, testing, installation,and erection of fiber-reinforced polymer products for overhead utility line structures. Thismanual was developed by the Task Committee on Fiber-Reinforced Composite Structuresfor Overhead Lines of the Structural Engineering Institute of the American Society ofCivil Engineers.

Library of Congress Cataloging-in-Publication Data

American Society of Civil Engineers. Subcommittee on Fiber-Reinforced CompositeStructures for Overhead Lines.

Recommended practice for fiber-reinforced polymer products for overhead utility linestructures / prepared by the Subcommittee on Fiber-Reinforced Composite Structures forOverhead Lines of the Structural Division of the American Society of Civil Engineers.

p. cm—(ASCE manuals and reports on engineering practice ; no. 104)Includes bibliographical references and index.ISBN 0-7844-0648-01. Electric lines—Poles and towers—Design and construction. 2. Electric lines—Polesand towers—Materials. 3. Fiber reinforced plastics. I. Title. II. Serires.

TK3242 .A525 2002621.319'22—dc21

2002043614

Any statements expressed in these materials are those of the individual authors and donot necessarily represent the views of ASCE, which takes no responsibility for any statementmade herein. No reference made in this publication to any specific method, product, process,or service constitutes or implies an endorsement, recommendation, or warranty thereof byASCE. The materials are for general information only and do not represent a standard ofASCE, nor are they intended as a reference in purchase specifications, contracts, regulations,statutes, or any other legal document. ASCE makes no representation or warranty of anykind, whether express or implied, concerning the accuracy, completeness, suitability, orutility of any information, apparatus, product, or process discussed in this publication, andassumes no liability therefore. This information should not be used without first securingcompetent advice with respect to its suitability for any general or specific application.Anyone utilizing this information assumes all liability arising from such use, including butnot limited to infringement of any patent or patents.

ASCE and American Society of Civil Engineers—Registered in U.S. Patent and Trade-mark Office.

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Copyright 2003 by the American Society of Civil Engineers.All Rights Reserved.ISBN 0-7844-0648-0Manufactured in the United States of America.

PREFACE

Advancements and innovations in fiber-reinforced polymers (FRP)and process technologies have resulted in lightweight high-strength FRPmaterials that are more cost-competitive with traditional constructionmaterials such as wood, steel, and prestressed concrete. While there are avariety of possible structural applications for FRP materials, this documentfocuses primarily on conductor support applications and FRP poles.

Every effort has been made through various reviews to strive foraccuracy and clarity. The user is reminded to consider the structuresdescribed herein as an integral part of a larger system. The user is,therefore, cautioned that the application of these structures should comeonly after sound engineering judgment has been applied with regard toa particular desired result. Furthermore, as an overall treatise covering awide variety of applications, this document cannot conceivably satisfy allconditions. The user should bear in mind that often there will be specificlocal conditions and requirements that may dictate design and usageconditions that differ from those described herein.

The committee is grateful for the input of its advisory members and thecomments from those who participated in the development of this reportthrough correspondence and numerous working sessions.

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CONTENTS

1 STRUCTURES AND APPLICATIONS 1

1.1 Introduction 11.2 Structure Configurations 2

1.2.1 Cantilevered Structures 21.2.2 Guyed Structures 31.2.3 Framed Structures 41.2.4 Combined Structures 41.2.5 Latticed Tower Structures 5

1.3 Applications 71.3.1 Transmission and Distribution Structures 71.3.2 Substation Structures 71.3.3 Lighting Supports, Highway Signs, and Traffic

Signal Structures 81.3.4 Communications Structures 9

2 INITIAL CONSIDERATIONS 11

2.1 Introduction 112.2 Physical Considerations 112.3 Guying 112.4 Grounding 112.5 Deflection 122.6 Transportation and Erection 122.7 Climbing 132.8 Attached Items 132.9 Aesthetic Considerations 13

2.10 Load Testing 132.11 Durability 142.12 Foundations 14

ix

x CONTENTS

3 MATERIALS AND MANUFACTURING PROCESSES 15

3.1 Introduction 153.1.1 Definition of FRP 153.1.2 Benefits 163.1.3 Composition 16

3.2 Materials 173.2.1 Polymer Resin Matrix 183.2.2 Fiber Reinforcements 193.2.3 Protective Material Systems 19

3.3 Manufacturing Processes 193.3.1 Pultrusion 203.3.2 Filament Winding 213.3.3 Centrifugal Casting 223.3.4 Resin Infusion 23

4 DESIGN LOADS 25

4.1 Introduction 254.2 Load Considerations for Transmission and Distribution

Overhead Construction 254.3 Wood Pole Equivalent Design Loads 27

5 PERFORMANCE-BASED CRITERIA FOR FRP PRODUCTSAND MATERIALS 29

5.1 Introduction 295.2 Designing FRP Products 295.3 Poles 30

5.3.1 Mechanical Properties 305.3.2 Durability 32

5.4 Connections 335.4.1 Step Attachments 335.4.2 Guying Attachments 335.4.3 Ground Wire Attachments 345.4.4 Slip Joints 345.4.5 Flange and Other Mechanical Joints 345.4.6 Foundations 34

6 SUGGESTED GUIDELINES FOR PERFORMANCE-BASEDTESTS 37

6.1 Introduction 37

CONTENTS xi

6.2 Recommended Mechanical Tests 376.2.1 Static Bending (Horizontal Loading) Test 376.2.2 Bolt Torque Test 386.2.3 Bolt Pull-Through Test 386.2.4 Direct Load Shear Test 386.2.5 Field Drillability Test 386.2.6 Step Bolt Compatibility Test 39

6.3 Optional Mechanical Tests 396.3.1 Torsional Load Test 39

6.4 Surface Durability Tests 396.4.1 Ultraviolet (UV) Radiation Tests 396.4.2 Coating Tests 39

6.5 Electrical Tests 40

7 QUALITY ASSURANCE 41

7.1 Introduction 417.2 Design and Drawings 417.3 Manufacturing Process 427.4 Material Standards Conformance 427.5 Tolerances 427.6 Surface Coatings 427.7 Inspection During Manufacture 427.8 Shipping and Receiving 437.9 Rejection 43

7.10 Full-Scale Structure Testing 437.11 Installation and Maintenance 43

8 ASSEMBLY AND ERECTION 45

8.1 Introduction 458.2 Pole Structures 45

8.2.1 Handling 458.2.2 Hauling 468.2.3 Framing 478.2.4 Field Drilling 478.2.5 Erection 488.2.6 Climbing 48

8.3 Foundations 498.3.1 Direct Embedment 498.3.2 Anchor Base 50

8.4 Storage 50

xii CONTENTS

9 IN-SERVICE CONSIDERATIONS 51

9.1 Introduction 519.2 Factors Influencing Performance of FRP Materials 51

9.2.1 Environment 519.2.2 Mechanical Fatigue 539.2.3 Electrical Stress and Leakage Current 53

9.3 Field Inspection 549.3.1 Visual Inspection 549.3.2 Tap Test 549.3.3 Other Tests 54

APPENDIX I GLOSSARY 55

APPENDIX II BIBLIOGRAPHY 65

APPENDIX III SUGGESTED MANUFACTURINGTOLERANCES 69

APPENDIX IV LOADING REQUIREMENTS FOR FRPPOLES UTILIZED IN OTHER THAN UTILITY LINEAPPLICATIONS 71

APPENDIXV COMMENTARY 73

INDEX 75

Chapter 1

STRUCTURES AND APPLICATIONS

1.1 INTRODUCTION

Fiber-reinforced polymer (FRP) utility structures and the use of FRPmaterials are not new to the electric power industry. Many productsused by the industry that are made of, or incorporate, FRP materialsinclude ladders, grating, construction tools, lift truck booms, transformerpads, hot sticks, bus bar supports, insulators, pole line hardware, andcrossarms. Lighting poles made entirely of FRP material have been usedfor decades. By the late 1990s, installations of FRP lighting poles numberedin the millions. Also by that time, electric utilities had installed a growingnumber of FRP poles designed to support power and telecommunicationlines. The earliest FRP distribution poles were installed in the HawaiianIslands in the mid 1960s. These early Hawaiian poles have withstooda highly corrosive island environment and strong winds without anysignificant signs of deterioration.

FRP materials are used widely in many applications because they canbe engineered to offer important advantages over traditional materials.Such advantages include a high strength-to-weight ratio (light weight),low maintenance, dimensional stability, high dielectric strength, recycle-ability (nontoxicity), and resistance to rot, corrosion, chemicals, and pestdamage. FRP materials also offer product engineers extraordinary designlatitude. Engineers can choose from a wide range of material systemsand processing techniques. This degree of flexibility distinguishes FRPmaterials from "traditional77 materials. The benefits and limitations of afinished FRP product largely depend on the selected materials, the selectedprocess, and the relationship between the two. In fact, the relationshipbetween materials and process is a more significant consideration withFRP products than with products made of "traditional" materials likewood, steel, aluminum, and so forth. Unlike poles made from traditional

1

2 PRACTICE FOR FIBER-REINFORCED POLYMER PRODUCTS

materials, FRP poles are available in a wide range of geometric shapes,colors, and surface textures.

Advancements and innovations in FRP materials and process tech-nologies have resulted in lightweight high-strength FRP materials thatare more cost-competitive with traditional construction materials such aswood, steel, and prestressed concrete. While there are a variety of possiblestructural applications for FRP materials, this document focuses primarilyon conductor support applications and FRP poles.

1.2 STRUCTURE CONFIGURATIONS

FRP structures fall into one of five basic configurations:

Cantilevered structuresGuyed structuresFramed structuresCombined structuresLatticed tower structures

These configurations can be used in applications such as distribution lines,transmission lines, substations, highway signs, traffic signals, street light-ing, sports lighting, and telecommunication (both wire and wireless). Thissection includes descriptions of these configurations and their applicationfor use for overhead lines.

1.2.1 Cantilevered Structures

Most FRP pole structures are Cantilevered single poles directly embed-ded in the earth. Typical Cantilevered structures are shown in Figures 1-1and 1-2.

FIGURE 1-1. A, Installation of Direct-embedded FRP Pole. B, Self-Supporting69 kV Single-Pole Structure Supporting Transmission Line Facilities.

STRUCTURES AND APPLICATIONS

FIGURE 1-2. A, Lightweight Single-Pole Structure Hand-Carried to BackyardInstallation. B, Helicopter Installation of Single-Pole Structures in DifficultTerrain. C, Single-Pole Self-Supporting Structure, in Unguyed, Light Angle

Application.

Cantilevered structures, which are often called self-supporting or tan-gent structures, are designed to withstand various combinations of verticaland horizontal loads. Although shear and torsional loads cause stresseson the structure, the design of a cantilevered structure is predominantlycontrolled by the bending stresses associated with horizontal loads. Hori-zontal loads are usually the result of wind or combined wind-on-ice forceson the structure, equipment, and conductors.

Eccentric vertical loads can also cause bending stresses. Eccentric ver-tical loads can be caused by equipment and conductor loads and by thevertical load of the structure in a deflected state. A discussion of loadingsfor FRP structures is included in Chapter 4.

1.2.2 Guyed Structures

Another category of FRP structures is guyed structures. In order toreduce the bending stresses associated with cantilevered structures, guyscan be installed to transmit the horizontal loads imposed on the structureto the ground. Although guys significantly reduce the bending stressesin the pole, the vertical component of the guy force adds to the verticalload on the pole. These vertical loads should be considered in the design.Examples of guyed FRP transmission structures are shown in Figure 1-3.

It is important to recognize that guyed structures must be analyzed asa system. The guy wire size, orientation, pretension, and maximum guyload should be specified to the structure designer.

3

PRACTICE FOR FIBER-REINFORCED POLYMER PRODUCTS

FIGURE 1-3. A, Guyed Application for Single-Pole Structure SupportingDistribution Lines and Equipment. B, Single-Pole Structure Supporting

Multiple Attachments. C, Termination Structure Supporting Transformerunder Construction.

1.2.3 Framed Structures

Framed structures are assembled from numerous members and connec-tions. They consist of two or more single cantilevered poles attached to oneanother by other members such that the poles and connecting membersact as a system to resist applied loads. Framed structures are configuredin a manner that allows for horizontal loads to be transmitted to theground through the total stiffness of the structural support system. Thestiffness is achieved by using bracing members with pinned connections,moment-carrying connections, or a combination of the two. Examples ofFRP H-frame structures are shown in Figure 1-4.

Like guyed structures, framed structures should also be analyzed as asystem. The structure designer should determine the size, orientation, andconnection details of all members in the frame. The user is the structuredesigner if he specifies these details.

1.2.4 Combined Structures

Structures may be designed for some combination of cantilevered,guyed, and framed members. Two examples include an H-frame structurethat is cantilevered above the crossarm and an H-frame structure that isguyed at the bottom of the X-brace. For two-pole structures, the simpleinstallation of bracing may serve to reduce structure deflection, reduceearth pressure, permit the use of smaller poles, or result in longer spans.The application of knee or "vee" braces to the crossarm assembly permits

4

STRUCTURES AND APPLICATIONS 5

FIGURE 1-4. A, Erection ofH-frame Transmission Structure. B, H-frameTransmission Line Test Verification Structure.

the pole tops to act similar to guyed cantilevers by introducing a pointof inflection between the crossarm and the top of the X-bracing. Withoutthese braces, the structures have reduced stiffness because they are simplecantilevers above the top of the X-bracing. An H-frame structure, however,acts as a cantilevered structure when loaded in the longitudinal direction.It is important to recognize that poles tested as a simple cantilever mayperform differently as framed members.

1.2.5 Latticed Tower Structures

As opposed to single-pole and framed structures, latticed towers arecomprised of numerous main members and redundants using primarytriangles in their geometry (Figure 1-5). Design and analysis of latticedtowers is a complicated task, and end users are not typically responsible forstructure or structural member design; however, innovations in memberconnections, member fabrication and assembly and erection techniqueshave allowed FRP materials to enter the latticed tower market (Figure 1-6).


FIGURE 1-5. A, Demonstration Self-Supporting Latticed Towers Installed atCalifornia High Contamination Regions. B, Prototype 230 kV Line Segment

Constructed on Self-Supporting FRP Latticed Towers.

FIGURE 1-6. Installation of FRP Tower Leg onto a Steel StubAngle Foundation.

6


1.3 APPLICATIONS

1.3.1 Transmission and Distribution Structures

Single-pole cantilevered structures are typically used for tangent andsmall angle applications. Guyed pole structures are typically reserved forlarge angles, long spans, and dead-end applications. Horizontal loads dueto conductor tensions may be too large for angle and dead-end structuresto be cantilevered. In these cases, the most common method for supportingthe load is to guy the structure at some or all of the conductor positions(Figure 1-7).

A common configuration of a framed structure is the transmissionline H-frame. The H-frame structure is often used for long cross-countrytransmission lines. Because of the additional load that can be carried byframe structures, utilities are able to use longer span lengths and/or largerwire sizes than with single-pole structures. H-frame structures are usuallynot used in urban areas because they require a wider right-of-way.

Electrical utilities use combinations of cantilevered, guyed, and framedstructures for several applications. Two such applications are guyed H-frame structures and dead-end structures that are guyed in only onedirection. Guyed H-frames are often used where uplift is a problem.Dead-end structures guyed in only one plane are often used at locationswhere conductors on one side have slack tension and conductors on theother side have full tension.

1.3.2 Substation Structures

While currently limited in application, FRP materials are nonconductivemaking them well-suited for use in substation structures (Figure 1-8). Can-tilevered pole structures are the most commonly used configurations for

FIGURE 1-7. Typical FRP Applications.


FIGURE 1-8. Flexible Bus Tubular Support Structures in SubstationApplications.

substation structures. Bus-support structures for higher voltages typicallyuse one single-pole structure per phase. For lower voltages, structures canbe installed using either one per phase or a "tee" structure to carry all threephases. Single- or multipole structures can be used to support disconnectswitches, lightning arrestors, potential and current transformers, wavetraps, and other electrical equipment. Cantilevered and guyed structurescan also be used to support shield wires for lightning protection.

1.3.3 Lighting Supports, Highway Signs, and Traffic Signal Structures

While not a focus of this document, FRP poles of various shapes, tex-tures, and colors are commonly used with steel and aluminum luminairearms to provide support for streetlights (Figure 1-9). Similar poles usetenons or inserts to support lights for area and walkway lighting. Anothercommon application of poles is to support fixtures for sports lighting byuse of crossarms or steel cages.

Cantilevered or guyed FRP poles are used as supports for highway signsand traffic signals. The highway signs and traffic signals are attached tospan wires or arms that are supported by FRP poles.

8


FIGURE 1-9. A, Installation ofLuminaire on Self-Supporting Pole. B,Self-Supporting Pole Supporting Arm-Type Luminaire.

1.3.4 Communications Structures

FRP poles are used to support antennas for all classes of communicationservice including AM, CATV, FM, microwave, TV, and VHP.

Chapter 2

INITIAL CONSIDERATIONS

2.1 INTRODUCTION

The purpose of this section is to aid the line designers in developingtheir specifications for fiber-reinforced polymer (FRP) materials utilized inelectric overhead line structures. There are certain considerations that playan important role in the design of the structures. This chapter highlightsthese considerations.

2.2 PHYSICAL CONSIDERATIONS

To properly design a pole structure, the structure designer must beaware of the location of all attachments and all applicable loads. Only withthe knowledge of this information can the structure designer efficientlyanalyze and design the structure.

2.3 GUYING

The line designer should also define all guying configurations. Theinformation to be provided includes, but is not limited to, guy angles,number of guys, terrain variances, size and grade of wire, attachmentconsiderations, and all guy load limitations.

2.4 GROUNDING

The line designer should detail the method and details for structuregrounding. An FRP utility pole can be grounded either externally orinternally. An external ground wire should be anchored to the pole at

11


multiple locations using wire clips and self-tapping screws (or other typeof threaded fastener). This method provides for easy maintenance accessshould there be a problem with the ground wire. An internal ground wireis installed in the hollow interior of the pole at the factory. The top end ofthe wire would exit the pole at a predetermined location near the tip. Thebase of the wire would be embedded in the ground during installationof the pole. The internal grounding method creates more difficulty inassessing the wire for maintenance or additional taps.

2.5 DEFLECTION

Two attributes that primarily define the structural performance of apole are load capacity and flexibility. Flexibility is normally measuredas the amount of pole top deflection realized under load. Pole deflectionhelps to promote an even distribution of longitudinally unbalanced loadsacross adjacent structures. Too little deflection is undesirable becauselongitudinal loads will not be distributed effectively and the structuresnearest the source of unbalance will realize most of the effect. However,too much deflection is also undesirable because it frequently provestroublesome when stringing conductor. Too much deflection can also bedetrimental to maintaining electrical clearances.

Pole top deflection is a function of the materials used and the pole'sgeometry. FRP materials have a very high strength-to-stiffness ratio, andthus poles made from these materials can often be designed to be as flexibleas desired. Line designers should consider the effects of pole deflectionon load and clearance requirements as well as construction practices and,as necessary, provide restrictions on the amount of deflection that ispermissible. It should be noted, however, that imposing overly restrictivedeflection limits would often adversely affect the economics of FRP poleconstruction. If deflections must be significantly restricted, guying is anoption that may be considered. The line designer should consult with themanufacturer when deflection limits are required.

2.6 TRANSPORTATION AND ERECTION

Composite structures are lightweight, and thus structure weight isseldom a design factor. Almost all fiberglass poles can be handled andinstalled utilizing single pick points. However, the line designer shouldhave a general understanding of the weight of the structure and ensurethat proper equipment is available for installation. Length is a consider-ation in the transportation of utility structures. Generally, the longer thestructure, the more difficult it is to ship. Spliced poles are an option forthe transportation and erection of very tall utility structures.

INITIAL CONSIDERATIONS 13

2.7 CLIMBING

A number of climbing systems are used on FRP poles. Pole manufac-turers typically offer climbing hardware, and alternative hardware canbe obtained from the industry's standard hardware suppliers. Often thecomponents from both sources are combined. Regardless of the climbinghardware selected for use on an FRP pole, the line designer should informthe FRP pole manufacturer of the load-bearing requirements for climbingsystems. The load-bearing capability of any given climbing system designmay vary from one FRP product to another even though the same climbinghardware is used. This is true because the physical and mechanical prop-erties of the pole and pole wall may vary from one FRP product to another,and the overall system (combination of the hardware and the pole) maybehave differently as a result. If desired, the line designer may wish toprevent pest intrusion by closing open holes with temporary plugs. Stepintervals and spacing on FRP poles should conform to user requirements.

2.8 ATTACHED ITEMS

The line designer should identify all accessories that will be attachedto the structure and should specify their geometry, weight, and boltingpattern, including any applicable tolerances.

2.9 AESTHETIC CONSIDERATIONS

The color and surface finish of FRP poles vary among manufacturersand products. Some manufacturers offer a variety of color and finishoptions. Coatings are primarily the means for achieving the desired colorfor the structure. If desirable, pigment can be added to the polymerresin matrix during manufacturing to more closely match the color of theunderlying structural material with the color of the surface coating.

Colors like gray, green, and brown usually harmonize best with sur-rounding outdoor environments. All colors can fade with continuouslong-term exposure to sunlight. Pigments are no exception.

2.10 LOAD TESTING

The user should specify what types of testing the manufacturer isrequired to do. Such tests may include full-scale static ultimate load,full-scale static design load, full-scale deflection versus load, full-scaledynamic loading, sample ultraviolet (UV) exposure, abrasion resistance,


hoop strength, wall pull-through and/or step bolt load/deflection. Afull-scale destructive test (ultimate load) is sometimes performed to val-idate the ultimate strength and deflection of the structure. During theproduction run, scheduled nondestructive full-scale design load tests maybe performed to ensure consistent quality in all structures. Other tests,such as UV resistance and step bolt tests, have often been completed atan earlier date by either in-house technicians or third-party testers. Themanufacturer should be able to provide a copy of this documentation tothe user upon request.

2.11 DURABILITY

FRP poles are more resistant to many environmental factors than polesmade of other materials. The line designer should consider the localenvironmental factors and discuss with the FRP pole manufacturer howthese factors may or may not affect the life of the specified FRP structures.The most common environmental factors include wind, rain, and sunlight.Other conditions, such as soil type, area maintenance (weed trimming,etc.), human and animal interaction, chemicals, and vandalism, can affectthe durability of the structure. As described in Section 3.2.3, various stepsare typically taken with FRP material systems to maximize the abilityof FRP structures to withstand the affects of prolonged exposure to theenvironment.

2.12 FOUNDATIONS

Most FRP structures will be directly embedded in the ground. BecauseFRP material is inert, FRP poles do not adversely affect the environmentand do not require special protective coatings or treatments before beingembedded. FRP poles can be direct embedded using typical burial depthas would be used for most other types of poles unless special loadingor soil conditions dictate otherwise. Like all tubular poles, a bottom cap(or base plate) is required to prevent further settling after the FRP poleis installed. If an anchor-bolted foundation is required, the manufacturermust be consulted.

Chapter 3

MATERIALS AND MANUFACTURINGPROCESSES

3.1 INTRODUCTION

This chapter introduces the basic materials used in the manufacturingof composite structures. It will help the line designer in understandinghow the different elements of the fiber-matrix system interact. Given themany possibilities of materials and manufacturing methods, it is helpfulto be familiar with the building blocks of composites. Also included inthis chapter are discussions detailing several different methods of manu-facturing composite structures. Understanding the basic advantages anddisadvantages of each method can be helpful in evaluating fiber-reinforcedpolymer (FRP) manufacturers and products and in understanding whydifferent FRP products with the same basic geometry may differ withregard to mechanical properties and manufacturing cost.

3.1.1 Definition of FRP

An FRP composite is defined as a polymer matrix, either thermosetor thermoplastic, that is reinforced (combined) with a fiber or otherreinforcing material with a sufficient aspect ratio (length to thickness) toprovide a discernible reinforcing function in one or more directions. FRPcomposites are different from some other construction materials such assteel or wood. FRP composites are anisotropic (properties only apparentin the direction of the applied load), whereas steel is isotropic (uniformproperties in all directions, independent of applied load). Therefore, FRPcomposite properties are directional, meaning that the best mechanicalproperties are in the direction of the fiber placement. Composites aresimilar to reinforced concrete where the rebar is embedded in an isotropicmatrix called concrete.

15


Many terms have been used to define FRP composites. Modifiershave been used to identify a specific fiber such as glass fiber-reinforcedpolymer (GFRP), carbon fiber-reinforced polymer (CFRP), and aramidfiber-reinforced polymer (AFRP). Another familiar term used is fiber-reinforced plastics. In addition, other acronyms were developed overthe years and their use depended on geographic location or market use.For example, fiber-reinforced composites (FRC), glass reinforced plastics(GRP), and polymer matrix composites (PMC) can be found in manyreferences. Although different, each of the aforementioned terms meansthe same thing: FRP composites.

3.1.2 Benefits

FRP composites have many benefits to their selection and use. Theselection of the materials depends on the performance and intended useof the product. The composites designer can tailor the performance of theend product with proper selection of materials. It is important for the enduser to understand the application environment, load performance, anddurability requirements of the product and convey this information tothe composites industry professional. A summary of composite materialbenefits includes:

Light weightHigh strength-to-weight ratioDirectional strengthCorrosion resistanceWeather resistanceDimensional stability— low thermal conductivity— low coefficient of thermal expansionRadar transparencyNonmagneticHigh impact strengthHigh dielectric strength (insulator)Low maintenanceLong-term durabilityPart consolidationSmall to large part geometry possibleTailored surface finish

3.1.3 Composition

Composites are composed of resins, reinforcements, fillers, and addi-tives. Each of these constituent materials or ingredients plays an important

MATERIALS AND MANUFACTURING PROCESSES 17

role in the processing and final performance of the end product. The resinor polymer is the "glue" that holds the composite together and influencesthe physical properties of the end product. The reinforcement providesthe mechanical strength. The fillers and additives are used as process orperformance aids to impart special properties to the end product.

The mechanical properties and composition of FRP composites canbe tailored for their intended use. The type and quantity of materialsselected, in addition to the manufacturing process to fabricate the prod-uct, will affect the mechanical properties and performance. Importantconsiderations for the design of composite products include:

• Type of fiber reinforcement• Percentage of fiber or fiber volume• Orientation of fiber (0°, 90°, ±45°, or a combination of these)• Type of resin• Cost of product• Volume of production (to help determine the best manufactur-

ing method)• Manufacturing process• Service conditions

3.2 MATERIALS

Regardless of the manufacturing process used, the FRP material systemwill always include two main components—fiber reinforcements and apolymer resin matrix. The relationship between the fiber reinforcementsand polymer resin matrix in an FRP product is analogous to the rela-tionship between the reinforcing rods and cement mixture in a concreteproduct. The reinforcing fibers provide directional strength and load-carrying capacity. These fibers are immersed and supported by a polymerresin matrix that transfers load between the individual fiber strands. Inmost cases, the matrix also contributes to the stiffness of the product.

Once the materials are combined, they are set and cured to hardness.Curing is the process by which the properties of an FRP material areirreversibly changed by chemical reaction. The curing process usuallyinvolves a combination of curing agents, heat, and pressure. Before curingbegins, it is important that fiber reinforcements be sufficiently saturatedwith resin. Dry fiber and resin voids will result in lower strength proper-ties. It is also important to have an effective adhesion of the polymer resinmatrix to the reinforcements. Proper adhesion is achieved by selectingcompatible materials and processing techniques. It should also be notedthat adhesion has been greatly advanced by the development of couplingagents (e.g., silane) that are applied to the reinforcing fibers.


3.2.1 Polymer Resin Matrix

The basic components of the polymer resin matrix are the resin, addi-tives, and fillers discussed in the following sections.

3.2.1.1 Polymer Resin

Polymer resins are the result of sophisticated chemical engineering andprocessing. The type of resins most commonly used in FRP poles are calledthermoset resins. Such resins feature cross-linking polymer chains that arecured to hardness using heat, a catalyst, or a combination of both. Whenan FRP pole made with a thermoset resin is cured, it achieves its finaland irreversible chemical and physical form. Once this occurs, the partcannot be reshaped. Thermoplastic resins, conversely, can be reshaped ormodified with sufficient heat.

There are several different types of general-purpose and specialtythermoset polymer resins, including polyesters, epoxies, vinyl esters,polyurethanes, and phenolics. Each type of resin provides for differentmechanical, electrical, chemical, and other properties to the finished part.Each type of resin also has definite characteristics that must be consideredin the manufacturing process.

3.2.1.2 Fillers

Inorganic fillers are sometimes used to enhance certain characteristicsof the finished part; characteristics such as water resistance, weathering,surface smoothness, stiffness, temperature resistance, and dimensionalstability can be improved with the proper use of fillers. Widely used fillersinclude calcium carbonate, kaolin, alumina trihydrate, mica, feldspar,silica, talc, and various microsphere products, among others. Fillers aretypically the lowest cost of the major ingredients, yet they play an impor-tant role in improving the performance and reducing the cost of anFRP product.

3.2.1.3 Additives

A wide variety of additives can be used to modify material proper-ties and tailor the performance of an FRP. These materials are used insmall quantities, compared to resin and reinforcements, but they fulfillcritical functions. For example, additives control or influence air release,color, cure rate, electrical conductivity, fire resistance, shrinkage, staticreduction, surface smoothness, thermal conductivity, viscosity, and othercharacteristics associated with processing and the finished product. Addi-tives can act as catalysts, accelerators or inhibitors. For example, FRPproducts designed for outdoor installation usually contain UV inhibitorsthat resist the effects of long-term exposure to sunlight.


3.2.2 Fiber Reinforcements

In high-strength FRP poles, fiber reinforcement usually represents amajority of the overall material content. Controlling the orientation andplacement of fiber reinforcements is essential to achieving the strengthrequired in the finished product. Many materials are capable of acting asreinforcements, but by far the reinforcement used most is glass fiber, hencethe term "fiberglass." Other available reinforcements include carbon fiber,aramid, nylon, polyethylene, boron, polyester, and many other materials.

Fiberglass reinforcements are available in many different forms, forexample, multiend roving, chopped strands, milled fiber, continuousstrand mat, and chopped mat. Unidirectional reinforcements are usuallyfound in tapes, unidirectional fabrics, and bundles of fibers (or strands)called rovings. Multidirectional reinforcements are usually found in glassfiber fabrics that are woven, knitted, matted, or braided. Directionalityof the fiber reinforcements is important in determining the strengthproperties of the pole structure.

High-strength structural FRP products usually require a significantcontent of long continuous fibers, as opposed to short fibers. Within thecategory of fiberglass reinforcements, E-glass fibers are considered thepredominant reinforcement for polymer resin matrix composites. E-glassoffers advantageous mechanical properties, high dielectric strength, andlow susceptibility to moisture.

3.2.3 Protective Material Systems

Advances in material science have produced very effective life-ex-tending protective material systems. FRP poles should incorporate suchsystems to enhance the service life of the structure. The main elementsof the most effective systems include (1) UV inhibitors in the polymerresin matrix, (2) a resin-rich nonstructural surface veil, and (3) an exteriorUV-resistant coating. Manufacturers should provide the details about theprotective material system they recommend.

3.3 MANUFACTURING PROCESSES

The general process used to manufacture FRP products is one of placingand retaining fiber reinforcements in the direction and form needed toprovide the finished product its desired shape and properties. Certainshapes and fiber reinforcement orientations are more easily achieved byone process than another. In addition, the cost of the FRP product is highlydependent on the process used to manufacture it. When designing withFRP materials, the structure designer must consider the advantages anddisadvantages of the manufacturing process. As with any material, the


degree of automation is important in high-rate commercial manufacturingof FRP products.

There is a broad array of basic processes used to manufacture FRPproducts. These range from hand layup (with no automation) to highlyautomated, computer-controlled processes that mass-produce preciseshapes with consistent quality. Experienced manufacturers often incor-porate proprietary techniques that distinguish their use of the processfrom that of others. As a result, there are many variations of each process.However, the following general descriptions provide the reader with aworking knowledge of the basic underlying processes that are proven andcommonly used to make FRP products for overhead power lines.

3.3.1 Pultrusion

Pultrusion is a highly automated, low-labor, closed-mold process formanufacturing FRP shapes having a uniform cross section. The process iswell suited for high-volume commercial production of both custom andstandard shapes because it can be operated continuously. Standard shapesinclude tubes, rods, beams, channels, angles, and sheets. Custom shapescan range from simple to complex. The term "pultrusion" was coined todifferentiate the process from "extrusion/7 a term that refers to a processin which plastics or metals are pushed through a die opening.

As illustrated in Figure 3-1, the pultrusion process relies on reciprocat-ing or caterpillar-type mechanisms that clamp and pull fiber reinforce-ments continuously through a heated die at speeds typically ranging from1 to 4 ft per min (0.3 to 1.2 m per min). Pulling forces can be significant. Theprimary reinforcement is generally in the longitudinal direction, but mul-tidirectional reinforcements can be pultruded as well. Before entering thedie, the reinforcements are saturated with resin. Excess resin is squeezedout by bushings that guide and position the resin-impregnated fiber as itmoves toward the die entrance. As the compacted fiber and resin materialpasses through the heated die, it is shaped and cured to hardness. Thecured profile, now having a uniform cross section, is drawn forward and

FIGURE 3-1. Pultrusion: Schematic of Typical Process Setup.


into an in-line operation that cuts the profile at set intervals to producethe desired lengths. The cutting mechanism can be a simple cutoff saw or,alternatively, more sophisticated machinery that performs one or moreother operations, for example, cuts the part to length, drills holes, cutsopenings, contours edges, and so on. The pultrusion process often allowsmore than one stream of material to be processed side-by-side throughthe use of multiple dies or multiple die cavities.

Complex shapes can also be produced using the pultrusion process.To produce hollow or multiple-cell parts, the fiber and resin material istypically wrapped around mandrels that extend into and through thedie. In addition, various forms of reinforcements can be incorporatedinto the finished product. Continuous strand mats, surfacing veils, andother multidirectional fiber reinforcements can be folded, wrapped, andotherwise incorporated into the finished product. Furthermore, becausethe pultrusion process is continuous (like a production line), it can becoupled with other operations that add finishing details and surfacecoatings to the pultruded part.

3.3.2 Filament Winding

Filament winding is an automated low-labor process typically usedto manufacture cylindrical, conical, parabolic, box beam, and other FRPtube shapes. Such shapes are made by continuously wrapping resin-impregnated fiber reinforcements around a mandrel.

In basic terms, the process involves a winding machine that pullsdry fiber reinforcement from supply racks through a resin applicatorsystem and winds the wet fiber around the mandrel. As illustrated inFigure 3-2, the mandrel is rotated while a fiber application head laysdown adjacent reinforcement bands along the length of the mandrel ina precise geometric pattern. There are various types of fiber applicationheads, or delivery systems, including hoops through which the mandrelpasses. The winding pattern can be simple or intricate, depending on thedegree of sophistication of the equipment and motion control systems.

Filament winding requires either the mandrel or the fiber applicationhead to reciprocate so that the reinforcement eventually covers the entirelength of the mandrel. In simple terms, the general motion of the processcan be compared to that of a lathe. The speed of rotation and reciprocationis controlled and synchronized to produce the desired winding angle(s),which typically range from 7° to near 90°.

Unless microwave systems are used, the curing process is initiated fromthe inside or the outside of the part. Both methods have advantages andimplications for the finished part. Once the part is cured, the mandrel iseither removed and discarded or reused, or allowed to remain perma-nently inside the part. Either way, it is the mandrel that establishes thebasic geometry of the finished product.


FIGURE 3-2. Filament Winding: Two Schematic Views of theFundamental Process.

In the filament winding process, the placement of the primary fiber-glass reinforcement is tightly controlled and can be oriented in eithera circumferential or longitudinal direction or anywhere in between asneeded to develop the necessary strength properties in the circumfer-ential (hoop) direction. Controlling fiber tension and winding angle isan integral part of the filament winding process because these factorsgreatly determine the performance of the finished part. Since the rein-forcement is wound around the outside of a mandrel, the external surfaceof the finished FRP tube is usually somewhat rougher than the smoothinterior surface.

3.3.3 Centrifugal Casting

Centrifugal casting is a process used primarily to manufacture cylin-drical, conical, and parabolic FRP shapes that are tubular. The process isan adaptation of a long-established process for producing various typesof large tubing and pipe, notably spun-cast concrete. As illustrated inFigure 3-3, fiber reinforcements and activated resins are loaded into acylindrical mold that rotates at high speed about the longitudinal axis.Centrifugal force presses the fiber reinforcement to the interior surfaceof the mold while resin distributes through the reinforcement. Heat isusually applied to accelerate curing of the part. The cured part is thenreleased from the mold.


FIGURE 3-3. Centrifugal Casting: Schematic of the Fundamental Process.

3.3.4 Resin Infusion

Resin infusion is a method of fiberglass manufacturing that utilizeseither a vacuum or a pressure force to introduce liquid resin into adry fiberglass laminate. It allows for the placement of dry fiberglassin preshaped male or female molds. Once the resin is infused into thelaminate, the part is allowed to cure before its extraction from the mold.

There are two general categories of resin infusion manufacturing. Thefirst, resin transfer method (RTM), utilizes both male and female molds.The molds are usually metal forms. After dry fiberglass is placed intothe open bottom mold, a matching mold is closed and held tight withpressure. Resin is injected under high pressure into the dry glass laminatebetween the two molds. The resin is precatalyzed to initiate the curingprocess after the entire laminate has been saturated. Once the part hasreached an adequate hardness level, the molds are opened and the partis removed. This manufacturing process is controllable and repeatable.The laminate's physical properties remain consistent among parts. RTMallows the operator to tightly control the glass-to-resin ratio in order tooptimize the physical properties.

The second type of resin infusion manufacturing is vacuum-assistedresin infusion. Like RTM, the vacuum-assisted method utilizes a dryfiberglass layup. The vacuum-assisted method, however, uses only onemold, either male or female. The dry glass is placed into the moldin accordance with the design parameters. Although the molds can befabricated from metal, they are usually constructed using a fiberglassmatrix. Instead of using a second matching mold (like RTM) to compressthe dry glass, this system uses a vacuum bag. The bag, usually constructedof nylon or silicone, is sealed at the edges of the mold and pulled against themold face by a vacuum force. The same vacuum pressure that compressesthe dry fabric and forces the bag against the mold is also utilized to drawresin into the laminate. Resin infusion ports are strategically placed on


the opposite end of the mold from the vacuum ports. The dry fiberglassis wet out as resin is drawn into the laminate and searches for the sourceof the vacuum. Once the part has cured, the vacuum bag is removed andthe part is taken out of the mold. Like the RTM process, vacuum-assistedinfusion is also very controllable and repeatable.

Chapter 4

DESIGN LOADS

4.1 INTRODUCTION

This chapter discusses the types of loadings that should be consideredwhen designing overhead power lines utilizing fiber-reinforced polymer(FRP) poles. For infrastructure applications other than support structuresfor overhead power lines, see Appendix IV.

In addition to the discussion of loadings for these applications, a generaldiscussion of other loads is included. For consistency throughout thisdocument and consistency with other ASCE manuals and specifications,service loads multiplied by load factors are referred to as "factored loads."

4.2 LOAD CONSIDERATIONS FOR TRANSMISSION ANDDISTRIBUTION OVERHEAD CONSTRUCTION

Distribution lines are designed to withstand loadings that have beenspecified by the line designer for ensuring the safe, reliable, and economicoperation of the system.

The loading conditions typically considered to determine the requiredstrength of distribution structures are given by the National Electri-cal Safety Code (NESC) loads; state and local safety code loads; localmeteorological loads such as combinations of wind, ice, and tempera-ture conditions; longitudinal loads such as line terminations and brokenconductor loads; and construction and maintenance loads.

For certain load cases, structure deflection may govern the design. Loadfactors are applied to the various loading cases as required by code or asdetermined to be appropriate by the line designer. The "overload factors"of the NESC (NESC, 1997) are one example of code load factors, but noneat this time are specified for FRP structures. Other than load factors forcode loads, there is no required standard for the various load cases, and

25


thus the load factors should be determined using engineering judgmentof utility guidelines.

The NESC provides a set of minimum loads (heavy, medium, light,and extreme wind), with specified overload factors, for the various gradesof construction. Most utilities have adopted the NESC; however, somestates or local governments have written and/or adopted their own safetycode to satisfy regional safety requirements. California, for example, hasadopted General Order 95 in lieu of NESC. The Rural ElectrificationAdministration (REA) has adopted the NESC but has modified someoverload factors and strength requirements.

Meteorological loads are associated with local climatic conditions thatmay occur during the life of the line. These loads are generally set by theutility or selected by the designer. Typical loads consist of wind, ice, andtemperature, taken singly or in combination. Generally, a high (extreme)wind load and a combination of wind and ice load are both used for thedesign. "Guidelines for Electrical Transmission Line Structural Loading"(ASCE, 1991) may be referred to for the development of meteorologicalloads as well as other typical loads.

Longitudinal loads on a structure fall into three major categories:(1) permanent loads due to line termination or change in ruling span;(2) temporary loads due to unbalanced ice and wind conditions; and(3) loads due to a broken or slack wire.

Longitudinal loads resulting from a difference in wire tensions fromone side of the structure to the other are relatively easy to determine fordead-end structures. Suspension structures are more difficult to analyzebecause of the displacement of the suspension insulator, which acts tobalance wire tensions with the longitudinal load experienced by thestructure. A longitudinal load that approximates the loading conditionsof the suspension structure may be selected.

Unbalanced longitudinal loads may induce torsion in pole-type struc-tures, and this torsion should be considered in the strength evaluation ofthe structure design. Broken wire loads may also be considered.

Construction and maintenance loads should be considered to ensurethe safe assembly, erection, loading, and operation of the system. Loadscommonly considered as construction loads are wire-stringing loads,snub-off loads, and clipping-in loads.

Wire-stringing loads are unbalanced wire tensions when the runningboard or wire may become caught in the stringing block and get "hungup." Snub-off loads are the temporary dead-ending of the conductorsand shield wires on one longitudinal side of the structure to the groundduring stringing operations. Clipping-in loads are the loads for lifting theconductor from the block after the conductor has been brought to theinitial sag position.

DESIGN LOADS 27

Maintenance loads are worker and equipment loads associated withprocedures such as changing insulator strings and hardware. The con-struction and maintenance loads usually occur with a nominal wind at atemperature likely to occur during those operations.

Various combinations of loads are considered to predict structuredeflections. These deflections are used to determine clearances, right-of-way width, raking of the pole, and other special requirements.

It is recommended that the line designer present all loading conditionsin the form of load trees. Conductor and shield wire loads should beshown at the conductor and shield attachment points. The weight of allattachments, such as hardware, insulators, and wires, should be includedin these loads. Wind pressure on the structure itself should also bespecified. All loads should be shown as factored loads. Appendix IVprovides loading considerations for FRP poles utilized in other thanoverhead line structures.

4.3 WOOD POLE EQUIVALENT DESIGN LOADS

For the district loads associated with Rule 250B, the NESC has tradi-tionally recognized a difference between wood and engineered materials,such as concrete and steel, by specifying transverse wind load factors of 4and 2.5, respectively. Such factors may vary under federal, state or localregulatory codes such as General Order 95 in California. Currently, noload factors have been established for FRP. Therefore, it is recommendedthat FRP poles be classified by the manufacturer in accordance to theultimate load-carrying capacity of the structure.

Chapter 5

PERFORMANCE-BASED CRITERIA FOR FRPPRODUCTS AND MATERIALS

5.1 INTRODUCTION

In most ways, fiber-reinforced polymer (FRP) structures perform similarto wood and steel structures. There are, however, certain differences andthese differences are described in this chapter.

5.2 DESIGNING FRP PRODUCTS

Being a manufactured product, FRP structures and their propertiesand performance are typically predictable and consistent. However, thedegree of automation used to manufacture an FRP product can greatlyaffect performance consistency and predictability. For the most part, FRPstructures can be designed and analyzed using classical structural theory,as long as material directional properties are taken into account. One ofthe key positive attributes in designing with FRP material is the abilityof the designer to tailor the properties in the desired direction, similar tothe way prestressing strands are used in concrete poles to improve theirlongitudinal tensile strength. For example, an FRP pole can be designedto provide more strength and stiffness in the axial direction than in thetransverse direction, thus tailoring it to more optimally meet the actualstructural performance requirements.

Unlike solid cross-section poles, FRP poles are relatively thin-walledstructures, which is an important consideration in certain areas of design,such as local buckling, and in the accommodation of through-bolts, stepattachments, guy attachments, and so forth.

FRP structures have a high degree of load-deflection linearity anda very low permanent set. The deflections of FRP structures stay verynearly linear throughout their loading sequence even as loads approach

29


the ultimate strength of the structure. For FRP structures, at normalmaximum design loading there is virtually no appreciable creep over thelong term. In addition, as structures are unloaded they will return towithin 1 to 2% of their original position.

5.3 POLES

5.3.1 Mechanical Properties

All strength requirements described herein should be based on mechan-ical properties that have been established using a 5% lower exclusion limitvalue. Chapter 6 provides suggested guidelines for performance-basedtests to establish mechanical properties for FRP products.

5.3.1.1 Bending Strength

FRP poles must meet the same specified bending performance criteriaapplied to poles made of other materials. FRP poles must also meetall bending strength requirements dictated by the specific application,including any combined bending and loading conditions produced byguying the pole at one height to resist a load at another height. In this case,the localized loads on the pole cross-sections must be carefully analyzedto ensure that premature failure due to localized overloading is avoided.

5.3.1.2 Local Buckling Strength

Local buckling must be considered because most FRP pole designsutilize relatively thin-wall construction. Pole structures maybe polygonal,round, or oval, and they may or may not include internal stiffeners or foamto increase their local buckling capacity. Being thin-walled structures, thekinematics of bending demand that the pole cross section will begin toflatten or become oval as the pole bends. This causes a reduction in thecross-sectional moment of inertia of the pole all along the pole length,differing in those areas where taper is a factor and where there may belocalized ring reinforcement.

5.3.1.3 Axial Strength

The axial material strength of a pole must be sufficient to meet allaxial load (compression and tension) requirements in all sections of thepole. The material strength data for poles made by various manufacturerswill likely differ due to the differences in materials and manufacturingprocesses. As a general rule, however, axial material allowable stress ison the order of 20,000 to 40,000 psi (138 to 276 Mpa) for both compressionand tension.

PERFORMANCE-BASED CRITERIA FOR FRP PRODUCTS AND MATERIALS 31

The allowable stress data for a specific pole should be able to beprovided by the structure designer. Axial strength is rarely a controllingdesign factor for nonguyed structures. For guyed structures, however,axial strength and column buckling are often the controlling design factors.

The column buckling capacity of an FRP pole should meet or exceed themaximum axial load requirements. In determining the column bucklingstrength of an FRP structure, consideration should be given to burialdepth, elevation of guy wire attachment points, and structure taper rate.For constant cross-section poles the bending stiffness (El) calculation isstraightforward. However, for tapered FRP poles the bending stiffnessdecreases from the ground up due to both material and geometric nonlin-earities. It is recommended that these poles be analyzed using appropriatestructural analysis software.

5.3.1.4 Pull-Through Strength

Pull-through strength requirements must be assessed at points whereloads are being introduced to the pole, such as at through-bolt or single-wall attachment locations. Pull-through strength is dependent on thematerial, manufacturing process, and pole geometry used. Large washersor gain plates may be needed to evenly distribute the load and reducethe stress caused by these concentrated loads. The structure designeris responsible for ensuring that all pull-through strength requirementsare met.

5.3.1.5 Hoop Strength

Hoop strength in FRP poles is an important consideration for loadsresulting from pole transport and handling and through-bolt installation.The maximum through-bolt torque allowed is a function of the pole designand manufacturing process used. Within the same manufacturing process,thicker wall poles will typically have higher hoop strength than thinnerwall poles. Because this is process- and thickness-dependent, the structuredesigner should be responsible for supplying allowable maximum valuesfor bolt torque for each pole design.

Long-term history has shown that fully cured thermoset resin FRPpoles do not result in significant creep that would allow for hoop strengthload relaxation over time in the presence of load attachment such asthrough-bolts.

5.3.1.6 Torsional Strength

For closed-section geometries, such as are typically used for an FRPpole, torsional strength and stability is generally not a design issue. How-ever, different FRP materials and processes provide different torsional


capability. The structure designer should be responsible for ensuring thatall torsional strength requirements are met.

5.3.1.7 Fatigue Strength

FRP materials in general have superior fatigue strength. Structurescan be cyclically loaded to maximum design load without showing anyevidence of appreciable long-term creep or fatigue failure. The structuredesigner should determine when an FRP component should be fatigue-tested.

5.3.1.8 Deflection

Structural deflections can be an important factor in a pole's per-formance. The line designer should specify any maximum deflectionrequirements for the structure. However, these requirements should notbe more restrictive than necessary to ensure adequate performance. FRPstructures can be engineered to meet almost any deflection requirements,and the structure designer should be able to provide this information.

The load-deflection relationship of FRP structures is essentially linear,and elastic analysis and design methods are appropriate for most appli-cations. The most popular current method for a more exact analysis anddeflection estimate is the use of finite element analysis (FEA). When FEAmodeling is used, it should include consideration of the thin-walled natureof the FRP pole design and the model should account for the reductionin cross-sectional structural moment of inertia along the pole length asbending occurs.

5.3.2 Durability

FRP poles should be designed to withstand (1) normal transportingand handling as per guidelines applied to steel poles per Institute forElectronics and Electrical Engineers' "IEEE Guide to the Assembly andErection of Metal Transmission Structures") (IEEE, 1996), (2) the effectsof environmental factors pursuant to Section 2.11, (3) climbing for main-tenance and construction purposes, and (4) minor acts of vandalism.Depending on its installed location, it may also be important for a pole towithstand potential damage by landscape maintenance equipment (e.g.,weed-cutters and lawn care equipment).

FRP poles are inherently resistant to long-term degradation effects ofsoil conditions; fungi, insects, and bird attack; and corrosive environments.FRP materials withstand bullet impacts better than other thin-walledmaterials because damage to FRP material stays localized and does notnormally propagate over time. FRP materials are also nonbrittle.


5.4 CONNECTIONS

The thin-walled nature of FRP poles is an important consideration in thearea of connections and attachments. It is recommended that attachmentsusing through-bolts be backed up by rectangular flat or curved washers, orgain plates, to keep the bolt from pulling through the FRP pole wall. SinceFRP pole structures vary by design and process in the area of connections,the manufacturer should be contacted for attachment area data for thepole being considered for the application. The structure designer shouldensure the adequacy of the pole to withstand the loads specified by theline designer, including the concentrated loads at all connection points.

5.4.1 Step Attachments

Step attachments in FRP poles can be installed at the factory or in thefield. They can be permanent or removable. Step attachments come inseveral configurations and are available from pole manufacturers or fromstep attachment manufacturers. Many attachments now come in singlewall variety, although through-bolts can be used. The commonly acceptedpractice within the industry is to require the step to take a downwardvertical load of 750 Ibs. (3.34 kN) applied at the tip of the step. Pole wallthickness and resistance of the FRP wall material to downward and punch-through loads are the key contributing factors to step attachment strength.The FRP pole should be designed to accommodate step attachments usinga spacing as specified by the line designer.

5.4.2 Guying Attachments

Guying attachments can be accommodated on FRP poles. Guyingattachments can be installed as an integral member of other attach-ments, as additional through-bolt load points, or sometimes as singlewall attachments. Severe guy loads on thinner wall poles may causeovaling of the pole structure at the point of attachment. If this potentialexists, the manufacturer should be consulted to determine a mitigat-ing design. For example, an additional through-bolt can be installed 90°to the guy through-bolt immediately above or below the guy through-bolt, or a through-bolt sleeve and washer combination can be used forthe connection.

Since FRP poles are typically thin-walled structures, particular designattention must be given to the downward component of the guy loadattachment. The pole must have enough bolt hole-bearing strength to sup-port the vertical component of load from the bolt. The structure designershould ensure the adequacy of the pole to withstand all components ofguy forces.


5.4.3 Ground Wire Attachments

FRP poles should accommodate ground wires and ground wire attach-ments much the same as for poles made of other materials. It is commonpractice to run the grounding wire on the outside of the pole so thatthe grounding wire can be easily inspected and replaced when needed.One method of attaching ground wire to the pole uses wire clips and|-in. (6.35-mm) self-tapping screws. Manufacturers may have alternativemethods. However, wire staples are not recommended.

5.4.4 Slip Joints

Pole slip joints are possible where multiple section poles are needed.FRP pole slip joints may need to be mechanically fastened together ifthere is potential for a tension (uplift) load to be introduced into the pole.They can be bonded before slipping together, bolted after, or both. FRPpole slip joints are typically designed with a nominal specified overlaplength slipping the butt of the top section over the top of the lower section.(Note: The bending strength of pole in the slip joint area is typically muchstronger than the lower section or top section of the pole by itself. The jointarea itself with overlap is much thicker than the remainder of the polesections. Also, since the joint slip area is thicker, ovaling is much less, andovaling is a key factor in pole bending failure.) The structure designer isresponsible for determining the minimum overlap length and specifyingthe requirements for mechanical fastening, and the manufacturer shouldprovide assembly instructions.

5.4.5 Flange and Other Mechanical Joints

Flange and other mechanical joints may be used to join multiple sectionpoles. The structure designer is responsible for ensuring the adequacy ofthe flange or mechanical joint to transfer the required load.

5.4.6 Foundations

Foundation design for an FRP pole structure should consider both theloads that will be transmitted to the foundation and the surroundingsoil conditions.

Direct embedment is the most common type of foundation used forFRP pole structures. It consists of placing the pole directly into the groundeither by excavating a hole or by using a jetting device. Backfill materials,tools, and techniques for FRP structures are typically the same as thoseused for poles made of other materials. Care should be taken to avoidimpacting the pole wall with tools during backfill and tamping operations.


Although not very common for FRP utility poles, but very commonfor FRP light poles, FRP utility poles can be installed using anchor baseplates. The foundation must be engineered and installed based on accepteddesign and construction practice. The manufacturer can be contacted forinformation relating to a base plate pole design.

Chapter 6

SUGGESTED GUIDELINESFOR PERFORMANCE-BASED TESTS

6.1 INTRODUCTION

Although several standard tests are cited in this chapter, these testsare not designed specifically for fiber-reinforced polymer (FRP) overheadline structures. There are, in fact, no standards for FRP structures usedfor line construction. There are two standards, ANSI C136.20 and ASTMD4923-92, for FRP lighting poles; however, these standards are for lightingpoles and are not applicable to FRP poles that are used for overhead lineconstruction.

6.2 RECOMMENDED MECHANICAL TESTS

The following tests are listed as recommended tests for all FRP poles.

6.2.1 Static Bending (Horizontal Loading) Test

A static bending test or horizontal loading test should be performedfollowing the procedures specified in "Standard Test Methods of StaticTests of Wood Poles'7 (ASTM, D1036-98). This test presumes a standardburial depth of 10% of the pole length, plus 2 ft (0.6096 m). It also providesthat the load be applied 2 ft (0.6096 m) from the pole tip and that deflectionbe measured at the pole tip. Practical considerations allow that a pole betested in the horizontal position. These tests should be conducted with thepole clamped or strapped in the test fixture to simulate direct embedment.Ultimate capacity should be no less than the manufacturer's minimumload rating. During the test, the pole should be oriented such that themajority of holes and openings in the pole are on the extreme compression

37


and tension faces. This orientation will result in the maximum reductionin section modulus due to these holes.

6.2.2 Bolt Torque Test

The purpose of the bolt torque test is to determine the optimum bolttorque for a through-bolt. This test is to be performed using a minimum3ft (0.9144m) section of pole with a 5/8 in. (1.5875cm) diameter boltinstalled in the center of the section. A through-bolt should be installedusing a minimum sized square curved washer (flat washer for flat surfaces)of 2 1/8 in. x 2 1/8 in. x 1/8 in. (53.975 mm x 53.975 mm x 3.175 mm) onboth sides of the bolt. It is recommended that an FRP structure shouldwithstand at least 55 ft-lbs (75 N-M) of torque load on a through-bolt.At such torque, there should be no significant deformation or ovaling ofthe structure.

6.2.3 Bolt Pull-Through Test

The bolt pull-through test is to evaluate the pull-through strength of a5/8 in. (16 cm) galvanized steel bolt with a standard 2 1/8 in. x 21/8 in. x1/8 in. (53.975 mm x 53.975 mm x 3.175 mm) square curved (flat for flatsurfaces) washer. This test is to be performed using a minimum 3 ft(0.9144 m) section of pole with the bolt installed centered in the section ofpole. A tensile load should be progressively applied to the bolt until thepole wall fails. The minimum tensile load that the pole should take withoutdamage is 5000 Ibs. (22.24 N) or as specified by the structure designer.

6.2.4 Direct Load Shear Test

The direct load shear test is designed to evaluate the ability of the polewall to support a heavy load when applied to only one side of the pole.Examples of loads that will apply direct shear loading to only one sideof a pole are guy attachments where short leads and heavy guying loadsexist, very large single transformers installed on one side of the structure,etc. This test is to be performed using a minimum 3 ft (0.9144 m) section ofpole with the load applied at the center of one of the sides. The minimumload that the pole should take without damage is as specified by theline designer.

6.2.5 Field Drillability Test

The field drillability test is intended to evaluate the ability of the poleto be field drilled without significant damage to the pole surface (bothinside and out) or the pole wall. The test is to be conducted on a minimum

SUGGESTED GUIDELINES FOR PERFORMANCE-BASED TESTS 39

3 ft (0.9144 m) section of pole. The test can be conducted as either a singlewall test or a double wall test (i.e., pole is drilled all the way through fromone side).

6.2.6 Step Bolt Compatibility Test

All FRP structures, when furnished with step bolts or other climbingprovisions, should hold a minimum downward vertical load of 750 Ibs.(3.34 kN) without permanent damage to the pole. When step bolts aretested, the test should be conducted on a minimum of a 3 ft (0.9144 m)section of the pole.

6.3 Optional Mechanical Tests

Optional mechanical tests are not required tests but rather are tests thatare situational in nature. These tests are not needed on all applications.When the situation dictates, they may be specified.

6.3.1 Torsional Load Test

When in service, poles may be subjected to torsional loading due tounequal longitudinal loading. A torsional load may be applied to a poleby using a cantilever arm with a longitudinal load at its tip. The momenttested should be a simulation of possible field conditions such as those ofa broken conductor.

6.4 SURFACE DURABILITY TESTS

Surface durability tests evaluate the ability of FRP structures to with-stand the effects of normal weathering and handling.

6.4.1 Ultraviolet Radiation Tests

The standard test for determining a coating's resistance to UV degra-dation is specified by ASTM G53-96. The test typically uses a fluorescentUV-condensation type apparatus. One such apparatus is the UV accel-erated weathering tester. The test specimen should undergo a minimumof 1500 hours of accelerated UV exposure without showing any signs ofcracking, blooming, or embrittlement.

6.4.2 Coating Tests

FRP structures typically use a surface coating to enhance the struc-ture's resistance to the effects of normal weather and handling. A number


of readily available and reputable coatings are available for this pur-pose. High-quality coatings will have performance specifications based onAmerican Architectural Manufacturers Association (AAMA) tests referredto by AAMA Publication No. 615-96 "Voluntary Specification for HighPerformance Organic Coatings on Plastic Substrates." Such tests include:

Dry Film Hardness AAMA 615-96 7.3Film Adhesion, Dry AAMA 615-96 7.4.1.1Film Adhesion, Wet AAMA 615-96 7.4.1.2Film Adhesion, Performance AAMA 615-96 7.4.2Abrasion Resistance AAMA 615-96 7.6Chemical Resistance AAMA 615-96 7.7

Weathering AAMA 615-96 7.8Humidity Resistance AAMA 615-96 7.9Cold Crack Cycle AAMA 615-96 7.10Oven Aging AAMA 615-96 7.11Solvent Wipe Test AAMA 615-96 7.12Color Retention AAMA 615-96 7.8.1.2

On FRP structures, minor dings, scrapes, and scratches caused during han-dling are not considered to have a long-term effect on structural integrity.

6.5 ELECTRICAL TESTS

FRP structures are typically made with materials that inherentlyprovide excellent electrical insulation, and therefore are not generallysusceptible to electrically induced erosion. If required, the same electricaltests used to determine the electrical performance of wood structures canbe used to test FRP structures. However, FRP pole and tower structuresshould not be used as insulators without further testing beyond what isoutlined herein.

Chapter 7

QUALITY ASSURANCE

7.1 INTRODUCTION

The user is responsible for ensuring the quality of products purchased.Therefore, the user of fiber-reinforced polymer (FRP) products determinesthe level of quality that will be accepted. Specifications covering requiredperformance and quality characteristics of the product to be purchasedshould be developed and provided to bidders with the request for bids.

Manufacturing processes, methods, and materials differ from vendor tovendor. Therefore, before fabrication, the user should determine whetherthe manufacturer has quality control programs and standards in place(e.g., ISO 9001) that will ensure consistency in the level of quality required.Accordingly, the user should obtain and review the manufacturer's qualityassurance program documentation. The user may also consider a siteinspection of the manufacturer's facilities as part of a complete vendorapproval program.

The following information will assist users in preparing specificationsthat include a quality control program.

7.2 DESIGN AND DRAWINGS

To the extent that the product is customized or specially fabricatedfor the user, the quality assurance specification should include theprocedure for reviewing and approving design concepts, detailed cal-culations, stress analyses, and the manufacturer's drawings. It shouldalso indicate the level of involvement the user desires to have in suchmatters. Stress analyses of the main structure and all its componentparts, including all attachments and connections, should be consid-ered. The manufacturer's drawings and other documents should bechecked to ensure that they contain proper and sufficient information

41


for handling and erection in accordance with the requirements of theuser's specifications.

7.3 MANUFACTURING PROCESS

There are a number of processes used to manufacture FRP productsas defined in Chapter 3. It may be advantageous for the user to seek abasic understanding of the process used by the manufacturer in order toreasonably assess the reliability of process and product quality.

7.4 MATERIAL STANDARDS CONFORMANCE

The manufacturer should maintain a record of all test data and suppliercertifications evidencing conformance to applicable American Society forTesting and Materials (ASTM) specifications. All tests should be conductedin accordance with applicable ASTM procedures and other generallyaccepted testing methods, regardless of whether they are performed bythe manufacturer or by an independent tester or laboratory.

7.5 TOLERANCES

Acceptable fabrication tolerances should be specified and agreedupon by the user and the manufacturer. See Appendix III for recom-mended tolerances.

7.6 SURFACE COATINGS

Where surface coatings are used, the systems, procedures, and methodsof application and quality control should be acceptable to both the user andthe manufacturer. The system should also be suitable for both protectingthe FRP product and for its intended exposure. Coatings should satisfythe durability and aesthetic requirements of the user.

7.7 INSPECTION DURING MANUFACTURE

If the user requires on-site inspection during manufacture, the methodof communication, period of notice, and requirements of both the user andthe manufacturer should be specified clearly. Protection of proprietaryinformation will be a concern of the manufacturer and considerationshould be given.

QUALITY ASSURANCE 43

7.8 SHIPPING AND RECEIVING

The user should review the manufacturer's methods and procedures forpackaging and transportation of FRP products. Any special requirementsfor delivery mode, destination, or notification should be included in therequest for bids.

When receiving FRP products, all items should be inspected for damagebefore acceptance. If damage is found, the user should immediately notifythe delivering carrier or the manufacturer, whichever is specified by thesales agreement. If shipments are F.O.B. destination and the carrier isresponsible for damage repair, the user should notify the manufacturer ofany damage and then cooperate in filing damage claims with the carrier.The specification should also indicate what types and level of damage canbe repaired and still be accepted by the user.

When receiving FRP products, the user is also responsible for ensuringthat all materials, hardware, and fittings are accounted for. When a dis-crepancy occurs, both the carrier and the manufacturer should be notified.

7.9 REJECTION

It is critically important that rejection criteria be established and agreedto by both the user and the manufacturer before fabrication. A clear andconcise definition of what will constitute grounds for rejection of FRPproducts should be included in the request for bids.

7.10 FULL-SCALE STRUCTURE TESTING

Where structure testing is required, the specification should indicatewhat tests are to be conducted, methods of load application, and whichload conditions require testing. If testing is required, the manufacturershould provide a test procedure for user's approval before testing. Allpost-test inspections, nondestructive testing, and evaluation proceduresshould be acceptable to the user. The cost of such test shall be borne bythe user, the manufacturer, or both as agreed upon.

7.11 INSTALLATION AND MAINTENANCE

The user should review and determine the acceptability of installationand maintenance guidelines that are published by the manufacturer.

Chapter 8

ASSEMBLY AND ERECTION

8.1 INTRODUCTION

This chapter is intended to provide recommendations on transporting,handling, assembling, and erecting fiber-reinforced polymer (FRP) poles.An important consideration is that FRP poles are much lighter in weightthan poles made of other materials. This weight differential means the linedesigner may be able to use lighter-duty equipment and anticipate minoradjustments in stacking cribs and lift balance points. In general, however,FRP poles should be transported, handled, assembled, and erected similarto steel poles according to the recommendations of IEEE 951-1996, "IEEEGuide to the Assembly and Erection of Metal Transmission Structures/7

8.2 POLE STRUCTURES

8.2.1 Handling

FRP poles can be handled like any other type of pole. Poles can beloaded, moved, and unloaded using nylon slings on a forklift positionedwith the tines perpendicular to the longitudinal axis of the pole and withthe load in balance (Figure 8-1). Forklift tines should never be placed intothe butt or tip of poles for lifting purposes. Care should also be takenin handling to prevent puncturing or cracking a pole with the forklifttines and to prevent damaging the ultraviolet (UV) surface. Nylon slingsshould always be used in lieu of chains, cables, or other metal hardwarewhen lifting FRP poles. FRP poles may also be handled with a crane usinga two-point pickup system and nylon slings attached to the pole(s). Poledollies may be used to transport poles as needed.

45


FIGURE 8-1. Use Nylon Slings to Unload FRP Pole.

8.2.2 Hauling

FRP poles can be transported in the same manner as poles madeof other materials. Over long distances, flatbed and less-than truckload(LTL) haulers can be used (Figure 8-2). There is a need to limit roadhazard damage to a very minimum. If extra protection is needed, the

FIGURE 8-2. Site Delivery of FRP Pole.

ASSEMBLY AND ERECTION 47

FIGURE 8-3. Framing ofFRP Pole with Standard Hardware.

user may request that the manufacturer use a protective covering on eachpole. Poles that are bundled should be properly cribbed to avoid shiftingor damage during transportation. For short distances, pole dollies andother pole handling vehicles can be used. If pole dollies are used, nylonstraps should be used in lieu of metal chains to secure the pole. BecauseFRP poles are lightweight, some distribution-size poles can be manuallycarried short distances between the hauler and the installation site.

8.2.3 Framing

Most standard, noncleated attachment hardware can be used on FRPpoles with conventional fasteners and practices (Figure 8-3). However,washers that conform to the pole surface should be used beneath the bolthead and nut. Procedures for installing attachments requiring through-boltassemblies should be provided by the manufacturer.

8.2.4 Field Drilling

FRP poles are usually predrilled by the manufacturer, but they canalso be easily drilled in the field using standard equipment and drill bits(Figures 8-4 and 8-5). If a substantial number of holes are to be drilled,consideration should be given to using carbide-tipped drill bits. Any dustparticles generated by a drilling or cutting process are nontoxic; however,it is recommended that construction personnel adhere to the same safetypractices used when drilling and cutting other materials.


FIGURE 8-4. Field Drilling with Conventional Hand-Held Drill

FIGURE 8-5. Field Drilling and Fabrication.

8.2.5 Erection

FRP poles are generally easier to erect than poles that are heavier.Conventional equipment and practices, as well as light-duty helicopters,can be used as appropriate for the terrain and site conditions (Figure 8-6).They can be erected using a single pickup point as recommended by themanufacturer depending on the intended application. Nylon slings arecommonly used to secure the pole to the lifting cable to avoid scratchingand gouging the pole finish. Care should also be taken to ensure thatthe top and bottom caps and all joints and connections are secure beforeerecting the structure.

8.2.6 Climbing

Climbing provisions are available but may vary depending on manufac-turer (Figure 8-7). They are usually vertically spaced every 15 to 18 in. (381to 457.2 mm) and are oriented at 180° (each side of a pole) to each other. For

ASSEMBLY AND ERECTION 49

FIGURE 8-6. Erection of Single-Pole FRP Pole with Conventional Equipment.

large pole diameters, the step orientation may be less than 180°. Consultthe manufacturer for information and recommendations on climbing.

8.3 FOUNDATIONS

8.3.1 Direct Embedment

FRP poles can be direct embedded using the same burial depth aswould be used for most other types of poles unless special loading or soilconditions dictate otherwise. Once the pole is placed in the augered hole,the hole can be backfilled with any material normally used, such as nativesoil, crushed aggregate, concrete, or structural foam. Direct embeddedpoles should be factory-equipped with a bottom cap to prevent the polefrom sinking into the soil. Nonstandard setting depths and foundationdesigns should be discussed with the manufacturer. As with any tubular


FIGURE 8-7. Climbing ofFRP Pole with Step-Bolt Assembly.

structure, precautions should be taken to avoid point contact with largerocks and other hard objects inside the hole.

8.3.2 Anchor Base

If necessary, FRP poles can be mounted to a concrete foundation usinga pole anchor base that is bolted to the anchor bolts in a foundation. FRPpoles can be provided with a variety of anchor base sizes to accommodatedifferent foundation designs. Anchor bolt circles should be specified bythe structure designer and approved by the line designer.

8.4 STORAGE

FRP poles can be stored outdoors or indoors. FRP poles are usuallydelivered with timber or other cribbing that facilitates stacking. To avoidunnecessary damage to the pole coating, use a similar cribbing plan tostore poles so that they are separated from one another. The timber orcribbing should also keep the pole high enough above the ground toallow lifting straps to be easily slipped under and around the pole. Whenstacking poles, note that oak or oiled wood can cause staining. If stackingpoles in more than two layers, consideration should be given to thepotential of the cribbing and stacking weight to ovalize the bottom poles.FRP poles that are stored horizontally for long periods and allowed to sagwill return to their original shape when erected.

Chapter 9

IN-SERVICE CONSIDERATIONS

9.1 INTRODUCTION

Generally, little or no preventative maintenance is required on fiber-reinforced polymer (FRP) poles. This chapter discusses factors that couldaffect the performance of FRP poles after installation, suggests fieldinspection methods, and provides basic maintenance and field repairtechniques that can be used to extend the life of FRP poles.

9.2 FACTORS INFLUENCING PERFORMANCE OF FRPMATERIALS

9.2.1 Environment

9.2.1.1 Introduction

In most environments, FRP structures are able to withstand the effects ofweather, soil contact, and chemical exposure as well as or better than mostother materials. The following information will assist users in preparingspecifications.

9.2.1.2 UV Radiation

To maximize the service life of FRP products, manufacturers should usematerials that incorporate ultraviolet (UV) light inhibitors to retard thesurface degradation that can occur when there is long-term exposure todirect sunlight. UV inhibitors are widely used and typically incorporatedinto the resin matrix and into any resin-rich surface veil and coating thatis applied to the product. Surfacing veils have an open fiber arrangementdesigned to accept a high ratio of resin to fiber, thereby producing a thickresin-rich surface.

51


The degree of UV degradation that can occur in a product dependson local sunlight conditions (e.g., angle and intensity) and the numberof years the product is exposed to those conditions. Excessive long-termresin degradation due to UV exposure can lead to "fiber blooming/'Blooming is the surface condition that exists when glass fiber filamentsnear the surface are prominently exposed because the resin has degradedand eroded away. A bloomed surface may appear white or bleachedin color and may have a texture similar to that of "peach fuzz." Onceblooming occurs, the bloomed surface fibers tend to shield the underlyingmaterial from further UV attack. Blooming is not a structural issue. It isgenerally considered an aesthetic or handling issue. However, bloomingmay also permit material near the surface to be exposed to moisture andother potentially harmful elements. Bloomed fibers can irritate the skin ifthe bloomed product is handled without gloves or other protection. Thepotential for blooming can be eliminated or minimized by incorporatinginto the product a surfacing veil that covers and contains glass fibernear the surface. Manufacturers should be able to provide long-term UVperformance test data for their material systems.

9.2.1.3 Temperature

FRP products are capable of withstanding the most extreme climatictemperatures without loss of structural integrity. Due to its low thermalcoefficient of linear expansion, FRP products are relatively unaffected bywide variations in ambient and surface temperature. FRP poles typicallyuse thermoset resin materials that do not change shape or chemistry underextreme temperatures.

9.2.1.4 Moisture

FRP is a moisture-resistant material. FRP poles can be subjected to mostenvironmental conditions ranging from very wet (e.g., marshes, rivers,etc.) to very dry (e.g., desert soils) without degradation.

9.2.1.5 Ice and Snow Accumulation

FRP is unaffected by ice or snow. Accumulation of ice and snow needonly be considered in the structural design performance of an FRP polewith regard to loading.

9.2.1.6 Fire

FRP products have low thermal conductivity and tend to act asthermal insulators slowing the progress of heat through the material.Consequently, the material does not easily support combustion. Tran-sient flames will usually produce limited charring of the surface coating

IN-SERVICE CONSIDERATIONS 53

and the surface laminate. Sustained long-term exposure to flames mayproduce more extensive charring. Polyester resins begin to char at about700°F(371.H0C) with direct nontransient exposure. If required, FRPproducts can be manufactured with a fire-retardant additive that allowsthe product to meet UL94 and/or ASTM D635 standards.

9.2.1.7 Chemical Exposure

FRP products are naturally resistant to most chemicals found in subter-ranean and outdoor environments. In addition, urethane coatings canoffer further protection against any harmful chemicals that may bepresent in the environment. Due to their natural resistance to chemi-cals, FRP materials are the materials of choice commonly used in manyunderground structures.

9.2.1.8 Biodegmdation

FRP pole and coating materials are not biodegradable. They are notsusceptible to termite, woodpecker, or other biological attack. The materialis inert and can be disposed of in normal nonhazardous landfills.

9.2.2 Mechanical Fatigue

FRP poles are very fatigue-resistant. In fact, FRP is the material ofchoice in many high-fatigue applications (e.g., automobile leaf springs).Unlike in some other materials, holes and notches in FRP materials do notgenerate fatigue cracks when subjected to cyclic loading of the structure.

9.2.3 Electrical Stress and Leakage Current

High electrical field stresses on an FRP structure can result from inad-equate structure and hardware designs where positioning of energizedand corona-free conductors and insulators are too close to the pole. Thismay generate a high electrical field gradient at various locations internaland/or external to the FRP structure and cause corona discharge-relatedburning/tracking damage.

More severe damage caused by leakage current could occur if:

• The insulator is conducting electricity because it is internally shortedor punctured,

• The surface of the insulator is conductive from moisture and/orcontamination to the point that it is externally shorted, or

• The energized conductor has made contact with the pole.

Surface leakage currents can result from high electric field stresses butare more likely to occur when energized directly as described previously.


Leakage current on a structure is also a safety hazard for field personnel.It can also cause structural damage to the FRP structure from burn-ing/tracking caused by "dry band arcing/' Structural damage can alsooccur where a system power arc flashover to the structure has occurred.

9.3 FIELD INSPECTION

9.3.1 Visual Inspection

Visual inspection is a reliable method for surface damage assessmentof an FRP structure. It can roughly map out an area of surface damage,but will not necessarily reveal information about any underlying damage.Visual inspection of FRP structures by maintenance personnel shouldinclude inspection for the following:

• tracking on FRP surface• lightning damage• vandalism damage• mechanical impact damage• delamination

Items such as blooming or discoloration may be visually evident, but arenot considered to have significant impact on the structural integrity ofthe structure.

9.3.2 Tap Test

The tap test can be used as a routine test to further check for anysuspected localized damage. The test requires an inspector to use a smallhammer to tap all around the area of suspected damage. This is a fast,inexpensive, and easy way to roughly evaluate the condition of the FRPmaterial and locate delaminations, large voids, and cracks.

9.3.3 Other Tests

Other more sophisticated tests are being used in other industries fortesting FRP products but today are not deemed cost-effective or practicalfor use on FRP structures in the field. Such tests include pulse echo, dyepenetration, and thermography.

Appendix I

GLOSSARY

This glossary is provided as an aid to the reader to understand theterms as used in this design guide or which are commonly used bymanufacturers or structure designers. Many of these terms may havemore than one meaning. The definitions provided here have been wordedso as to be relevant to the practices used in the fiber-reinforced polymer(FRP) industry for overhead utility line structures.Accelerator—Chemical additive that hastens cure or chemical reaction.Additive—Ingredients mixed into resin to improve properties. Examples

include plasticizers, initiators, light stabilizers, and flame retardants.Adhesive—Substance applied to mating surfaces to bond them together

by surface attachment. An adhesive can be in liquid, film, or paste form.Aeolian Vibration—Wind-induced cyclic motion (excluding galloping).Anisotropic—Fiber directionality where different properties are exhibited

when tested along axes in different directions.Antimony Trioxide—Fire-retardant additive for use with resins.Aramid—High-strength, high-stiffness aromatic polyimide fibers.Aspect Ratio—The ratio of length to diameter of a fiber.Axial Capacity—Capacity of a member to withstand loads parallel to the

member's longitudinal axis.Band-Type Hardware—A wraparound style of line hardware used for

making connections to a pole.Basic Insulation Level (BIL)—A referenced electrical impulse insulation

strength expressed in terms of the withstand voltage crest value of astandard full impulse voltage wave.

Bent Member—Permanent member deformation often caused by a break-age of some of the fiberglass strands. Due to overloading.

Bidirectional Laminate—A laminate with fibers oriented in more thanone direction in the same plane.

Biodegradation—Decomposition by biological agents, particularly bacte-ria and insects.

55


Bleedout—Excess liquid resin appearing at the surface, primarily occur-ring during filament winding.

Blistering—Bubbles at surface of paint coating. Potential causes maybe moisture entrapment, the use of an improper solvent, or a largetemperature differential between the paint and the surface.

Blooming—Exposure of glass fibers in fiberglass products due to theerosion of the resin. Potential causes may be extreme weathering ofa member.

Bolt-on Hardware—A style of line hardware that connects to FRP mem-bers utilizing bolts.

Bond Strength—A ratio of load to bond area. The stress required toseparate one layer of material from another

Breakout—Separation or breakage of fibers when the edges of a compositepart are drilled or cut.

Buckling—The sudden large deformation of a structural component dueto an increase in compressive load.

Burning/Tracking—Irreversible degradation of the FRP and/or its coat-ing by formation of electrically conductive paths on the surface ofthe material.

Camber (or Pre-Camber)—Pole curvature used to balance expected poledeflection such that the pole will appear straight under a specifiednormal load condition.

Carbon Fiber—Reinforcing fiber known for its light weight, high strength,and high stiffness. Fibers are produced by high-temperature treatmentof an organic precursor.

Catalyst—A substance that promotes or controls curing of a compoundwithout being consumed in the reaction.

Centrifugal Casting—A processing technique for fabricating cylindricalstructures, in which the composite material is positioned inside a hollowmandrel designed to be rotated as resin is cured.

Chipping—Small areas of paint loss with surrounding paint intact. Gen-erally the result of mechanical damage (e.g., hurled stones or gravel,impact from heavy equipment, damage from firearms).

Coating System—The protective finish applied to the surface of a materialto enhance durability. Includes paints and other surface finishes.

Coefficient of Thermal Expansion—A materials fractional change inlength corresponding to a given unit change of temperature.

Composite—A material that combines fiber and a binding matrix tomaximize specific performance properties. Neither element mergescompletely with the other. Advanced composites use only continuous,oriented fibers in polymer matrices.

Compressive Strength—Resistance to a crushing or buckling force. Themaximum compressive load a specimen can support divided by itsoriginal cross-sectional area.

Appendix I: GLOSSARY 57

Conductivity (conductance unit/volume)—Reciprocal of volume resistiv-ity. The electrical or thermal conductance of a cubic unit of any material.

Contaminant—Impurity of foreign substance that affects one or moreproperties of composite material such as adhesion.

Continuous Roving—Parallel filaments coated with sizing, gatheredtogether into single or multiple strands, and wound into a cylindri-cal package. It may be used to provide continuous reinforcement inwoven roving, filament winding, pultrusion, prepregs, or high-strengthmolding compounds, or it may be used chopped.

Corrosion Resistance—The ability of a material to withstand contactwith ambient natural factors or those of a particular artificially createdatmosphere, without degradation or change in properties. For metals,corrosion can cause pitting or rusting; for composites, corrosion cancause crazing.

Crack—A visual separation that can either occur internally or penetratefrom the surface.

Crazing—Very shallow surface cracks that do not extend beyond theresin coating. Sometimes found in members with a "resin-rich" surface(heavy resin coating).

Creep—Dimensional change of a material caused by long-term loadduration.

Cross-Laminated—Material laminated so that some of the materials areoriented at various angles to the other layers with respect to the laminategrain. The cross-ply laminate usually has plies oriented only at 0°/90°(see Fiber Architecture).

Cure—To irreversibly change the molecular structure and physical prop-erties of a thermosetting resin by chemical reaction via heat and/orcatalysts, with or without pressure.

Curing Agent (hardener)—A catalytic or reactive agent that brings aboutpolymerization when added to a resin.

Damping—Diminishing the intensity of vibrations.Dead-End—A type of utility structure that resists unbalanced conduc-

tor tension.Degradation, Electrical—Deterioration of a composite product caused by

phenomena associated with high electric field stresses (i.e., corona dis-charge, dry band arcing, etc.) or passage of current along the insulatingsurface, (see Hydrophobicity, Burning/Tracking, etc.).

Degradation, Mechanical—Deterioration of a composite product causedby mechanical action.

Degradation, Thermal—Unfavorable alteration of the properties of aproduct due to exposure to extreme temperatures.

Degradation, Ultraviolet—Degradation of resin characterized by resinloss between fibers. Enabled by a breakdown of UV inhibitors used toprotect resin from ultraviolet rays (sunlight).


Delamination—In-plane separation of a laminate ply or plies due toadhesive failure. For pultruded composites, the separation of two ormore layers or plies of reinforcing material.

Delamination (resin-infusion process only)—Separation between pliesof fiberglass used in member manufacture. Can be caused either bymember overloading or improper manufacturing. Maybe detected onlyby mechanical means (ultrasound techniques).

Dielectric—An insulating material which impedes the conduction ofelectrical current to a negligible level or the ability of the material toresist the flow of electrical current.

Dielectric Strength—The property of an insulating material that enablesit to withstand electric stress. The average potential per unit thicknessat which failure of the dielectric material occurs.

Dry Band Arcing—A localized electrical phenomenon where arcingoccurs in a dry zone or area located between two or more wet-ted conductive surfaces. Hydrophilic surfaces, where water filmingis prevalent, are more prone to dry band arcing.

Dry Fiber—A condition to which fibers are not fully encapsulated byresin during manufacture.

Dry Spots—Fiberglass that is not fully surrounded by resin. Generallycaused by improper manufacturing technique.

Dynamometer—An instrument used to measure force. Dynamometerscommonly have dial-type scales that allow loads to be read in poundsor kips.

E-Glass—Stands for "electrical glass" and refers to glass fibers most oftenused in conventional polymer matrix composites.

Electrical Puncture—Damage through a solid dielectric causing perma-nent loss of dielectric strength resulting from an electrical disruptivedischarge (i.e., lightning, switching surge, etc.).

Elongation—The fractional increase in length of a material stressed intension. When expressed as a percentage of the original length, it iscalled percent elongation.

Epoxy Resin—A polymer resin characterized by episode molecule groups.Erosion—Irreversible and nonconducting degradation of the insulation

(i.e., fiberglass) surface that occurs by loss of surface material.Exclusion Limit—A limiting threshold value at which a specified percent-

age of members must exceed. Typically, a 5% lower exclusion limit isutilized referencing material properties such as strength and stiffness.

Extenders—Low-cost materials used to dilute or extend high-end resinswithout extensive lessening of properties.

Factored Load—A structural design load that has been multiplied by anoverload factor (OF).

Fading/Chalking—A dulling of the paint finish. Generally caused bydrying in improper atmospheric condition (too cold or too humid),


improper solvent, extreme conditions, or application over an alkaliresidue.

Fatigue—The tendency of a material to break under conditions of repeatedcyclic stressing below its ultimate tensile stress.

Faying Surfaces—The surfaces of two joined members in contact witheach other.

Fiber—A general term used to refer to filamentary materials. Often,"fiber" is used synonymously with "filament."

Fiber Architecture—The design of a fibrous part in which the fibersare arranged in a particular orientation to achieve the desired result.This may include braided, stitched, or woven fabrics, mats, rovings, orcarbon tows.

Fiber Orientation—Direction of fiber alignment in a nonwoven or matlaminate wherein most of the fibers are placed in the same direction toafford higher strength in that direction.

Fiber-Reinforced Polymer (FRP) Structures—Fiber-reinforced thermosetor thermoplastic resin structures and structural components. Also refersto aramid FRP, carbon FRP, glass FRP, fiber-reinforced composite (FRC),glass-reinforced plastics (GRP), and polymer matrix composites (PMC).

Filament Winding—An automated process for fabricating composites inwhich continuous roving or tows, either preimpregnated with resin ordrawn through a resin bath, are wound around a rotating mandrel.

Fire Resistance—The property of a material or product to withstand fireand/or give protection from it. As applied to structural elements, itis characterized by the ability to confine a fire and/or to continue toperform a given structural function during a fire.

Flexural Strength—The ultimate strength of a material loaded in bending.Fracture—Cracks, crazing, or delamination, or a combination thereof,

resulting from physical damage.G.O. 95 (Refers to California General Order 95)—Details material resis-

tance and load factors for the construction and maintenance of overheadlines in that state.

Gel Coat—Pigmented or clear coating resins applied to a mold or part toproduce a smooth, more impervious finish on the part.

Guy Hardware—Cables, anchors, and hardware used in the cable supportsystem of a "guyed pole."

Guyed Pole—A utility structure that relies on support cables to carry atleast a portion of the tension load to the ground.

Hardness—Resistance to indentation. For FRP, it is measured by a testthat determines the load required to indent a spherical tool a fixeddistance into the surface.

Hoop Cracks—Circumferential cracks are the result of member overload-ing caused by either high in-service loads or mechanical damage.


Hoop Stress—Circumferential stress in a cylindrically shaped part as aresult of internal or external pressure.

Hydrolysis—Phenomenon due to water penetration in liquid form or aswater vapor which can take place in insulation or dielectric materials.

Hydrophobicity—Property of an insulating surface that causes mois-ture to bead on a surface when wetted. Hydrophobicity can have adirect result on the surface currents while energized under wet orwet/polluted conditions. A hydrophilic surface corresponds to a totallywater filmed or sheeted surface.

Impact, Dynamic—The force transmitted by a collision or sudden loading.Impact Strength—A material's ability to withstand shock loading as

measured by test.Impregnate—To saturate the voids and interstices of a reinforcement with

a resin.Inhibitor—Chemical additive that slows or delays cure cycle.Inspection Report—A document that accompanies a product through

its process of manufacture on which is recorded pertinent informationregarding its identity. Sometimes called a traveler.

Interlaminar Shear—Shearing force that produces displacement betweentwo laminae along the plane of their interface.

Kip—A unit of force equal to 1000 Ibs.Laminar Wind—Streamlined airflow in which the air molecules move in

straight, nonturbulent lines.Lateral Torsional Buckling—A combined twisting-bending mode of

buckling. Thin-walled members with open sections are normally weakagainst lateral torsional buckling.

Lay-up—Placement of layers of reinforcement in a mold.Line Designer—The engineer(s) with overall line design and specification

writing responsibilities. Either is employed by or is a hired consultantof a utility or company that uses the structures.

Load Cell—A device used to measure test loads. The most common typesare either hydraulic or electronic.

Load Sharing—The distribution of load between structures or struc-tural members.

Local Buckle—Member failure characterized by a distinct deformationand break in the pole wall. Caused by overloading the memberin bending.

Local Buckling—An introduction of a series of waves or wrinkles in oneor more elements of a column section or the compressive side of a beamsection due to the inability of the section to resist the compressive loadin its current geometric shape.

Longitudinal Cracks—Surface cracks that may extend through the polewall. Usually caused by member overloading due to high in-serviceloads or mechanical damage (e.g., impact from heavy equipment).


Mandrel—Elongated mold around which resin-impregnated fiber, tape,or filaments are wound to form structural shapes or tubes.

Manufacturer—The company responsible for the manufacture of theFRP products.

Mat—A fibrous reinforcing material composed of chopped filaments (forchopped-strand mat) or swirled filaments for continuous-strand matwith a binder applied to maintain form; available in blankets of variouswidths, weights, thicknesses, and lengths.

Modulus of Elasticity (MOE)—A material property equal to the ratio ofstress to strain, within the elastic range of a material.

Modulus of Rupture (MOR)—A material property equal to the maximumstress of the extreme fiber in bending, calculated from the maximumbending moment on the basis of an assumed linear stress distribution.

Mold—The cavity into or onto which resin/fiber is placed, and fromwhich a finished part takes form.

NOT—Nondestructive testing. A means of inspecting a product thatdoes not affect its structural integrity or significantly alter its physi-cal condition.

NESC—The National Electric Safety Code. Although it is not intended asa design manual, most states have adopted this ANSI standard as thebasis for minimum strength and loading requirements for the designand maintenance of overhead lines.

Open Section—A nontubular cross-sectional shape (e.g., angle, wideflange, channel).

Overload Factor (OF)—A factor by which working loads are multipliedto account for uncertainties in loading.

Peeling/Flaking—Poor paint adhesion. Several causes including poorsurface preparation, surface contaminants, excessive coating thick-ness and/or application outside of recommended temperature range(i.e., too hot or too cold).

Photodegradation (ultraviolet degradation)—The chemical degradationof a material by ultraviolet light.

Ply—One of the layers that makes up a laminate. Also, the number ofsingle yarns twisted together to form a plied yarn.

Polymer—Large molecule formed by combining many smaller moleculesor monomers in a regular pattern.

Pultrusion—An automated, continuous process for manufacturing com-posite rods, tubes, and structural shapes having a constant cross section.Roving and/or tows are saturated with resin and continuously pulledthrough a heated die, where the part is formed and cured. The curedpart is then cut to length.

Rake—The amount of horizontal pole top displacement created byinstalling a pole tilted out of plumb. It is typically used to negatethe pole top deflection anticipated for everyday loading conditions.


Reactivity—Tendency to participate readily in chemical reactions.Resilience—The property of a material that enables it to resume its

original shape or position after being bent, stretched, or compressed.Resin Infusion Process—A method of fiberglass manufacturing that

utilizes either a vacuum or a pressure force in order to introduce liquidresin into a dry fiberglass laminate.

Resistivity (surface)—The electrical resistance per until length of a sub-stance with uniform cross section.

Responsible Test Engineer—The person assigned overall responsibil-ity for structure test and subsequent analysis of physical or mate-rial properties.

Right-of-Way (ROW)—The strip of land on which an overhead lineis built.

Roving—A collection of bundles of continuous filaments either as untwist-ed strands or as twisted yarn.

Runs—Paint streaks that are generally caused by excess paint or improperapplication.

Secondary Moment—A measure of the increase in bending resultingfrom a structure's displacement under load.

Shear—An action or stress resulting from applied forces that causes ortends to cause two contiguous parts of a body to slide relative toeach other.

Slip Joint—A connection for joining two pieces of a manufactured poletogether by slipping one piece over the next in a telescoping mannerand pulling the sections together until a prescribed overlap is achieved.

Spider Cracks—Surface cracks that extend into the fiberglass layers andwhich run randomly from a central point. Often caused by mechanicaldamage (surface impact).

Spotting—Spots on coating surface caused by contact with water, e.g.,rain or heavy dew during drying process.

Stiffness—A measure of a material's ability to resist bending. The rela-tionship of load to deformation for a particular material or product.

Stress Crack—External or internal cracks in a composite caused by tensileloading. Cracking may be internal, external, or both.

Structure Designer—The engineer(s) with specific responsibility for struc-tural design of the product. Is usually employed by or is a hiredconsultant of the company that manufactures the product.

Surface Voids—Pockets of air on the surface of the resin. Generallyresulting from improper manufacturing.

Sweep—The measure of deviation of a member's surface from a straightline between two surface points in the same plane.

Tangent—A type of utility structure that does not support line-tensionloads and is used in a straight portion of the line. Tangent structures typ-ically make up the majority of structures in supporting overhead lines.


Taper—A ratio describing the change in dimension of a member over aunit of length. For FRP poles this is commonly measured in inches ofdiameter per foot of pole length.

Tensile Strength—Maximum stress sustained by a composite specimenbefore it fails in a tension test.

Test Rigging—Collectively, all the ropes, chains, cables, and tackle usedto apply load to a structure being subjected to testing.

Thermal Conductivity—Ability to transfer heat.Thermoplastic—A composite matrix capable of being repeatedly soft-

ened by an increase of temperature and hardened by a decrease intemperature. Not applicable to FRP overhead utility line structures.

Toughness—A material property equal to the mechanical energy per unitvolume required to produce fracture.

Twist—A condition of longitudinal rotation found in pultruded parts.Ultimate Load—A design load that includes the appropriate overload

factor and any additional factor of safety specified by the line designer.User—The party responsible for the acquisition of FRP pole structures

that meet the specifications developed by the line designer.UV Inhibitors—The components used in the manufacture of FRP poles

that impede degradation of a product caused by ultraviolet rays. Canbe a part of the resin formulation and/or a separate coating.

Veil Cloth—Thin woven fiberglass material used on the surface of anFRP product to enhance UV protection and resistance to weathering.

Water Absorption—Ratio of weight of water absorbed by a material tothe weight of dry material.

Wind Angle—The measure in degrees between the direction parallel tothe filaments and an established reference line.

Woven Roving—Heavy, coarse fabric produced by weaving continuousroving bundles.

This page has been reformatted by Knovel to provide easier navigation

INDEX

Index Terms Links

A

additives 18

aesthetics 13

attachments 33

ground wire 34

guying 33

step 33

B

bending stiffness 31

testing 37

blooming 52

braces 4

buckling: capacity 31

strength 30

bus-support structures 8

C

cantilevered structures 2

applications 7

substation structures 7

verticalloads 3

casting, centrifugal 22

climbing 13 48

code loads 25

combined structures 4

Index Terms Links


communication structures 9

loads 71

composite structures: see

entries under FRP

connections 33

curing 17

centrifugal casting process 22

filament winding process 21

pultrusion process 20

resin infusion process 24

D

dead-end structures 7

deflection 12 25 29 32

design loads 25

design review 41

distribution lines 25

drilling, field 47

E

E-glass fibers 19

electrical stress 53

environmental factors 14 32 51

erection 12 48

F

fatigue, mechanical 53

fiber-reinforced polymer: see entries

under FRP

fiber reinforcements 17 19

fiberglass 19

Index Terms Links


filament winding 21

fillers 18

flexibility 12

foundations 34 49

framed structures 4

FRP materials 1

applications 7

attributes 1

benefits 16

components 16

definition 15

designing 29

fiber reinforcements 17 19

manufacturing 15

manufacturing processes 19

polymer resin matrix 18

quality assurance 41

structure design 11


utility use 73

FRP structures 2

bus-support 8

cantilevered 2 7

combined 4

communications 9 71

dead-end 7

framed 4

guyed 3 7 11 31

33

H-frame 4 7

Index Terms Links


FRP structures (Cont.)

large angle 7

latticed 5

long span 7

small angle 7

tangent 7

traffic signal 8

FRP tube shapes: buckling strength 30

centrifugal casting process 22

filament winding process 21

pultrusion process 21

G

grounding 11

ground wire attachments 34

guyed structures 3 7

attachments 33

axial strength 31

design specifications 11

H

H-frame structures 4

guyed 7

transmission line 7

highway signs 8

loads 71

horizontal loads: cantilevered

structures 3

framed structures 4

testing 37

Index Terms Links


I

inspection 42 54

installa ion 43

J

joints: flange 34

slip 34

K

knee braces 4

L

large angle structures 7

latticed tower structures 5

lighting supports 8

loads 71

line design 11

loads 25

linearity, load-deflection 29

loads 25 71

capacity 12

clipping-in 26

code 25

construction 26

design 25

handling 72

horizontal 3 4 37

longitudinal 26

maintenance 26

meteorological 26

Index Terms Links


loads (Cont.)

shock 72

testing 13

vertical 3

wire-stringing 26

long span structures 7

M

manufacturing processes 19 42

manufacturing tolerances 69

N

National Electrical Safety Code 25

P

poles 1 29

aesthetics 13

characteristics 30

climbing 13 48

durability 14 32

electrical tests 39

erection 12 48

fatigue 53

field drilling 47

foundations 14 49

handling 45

inspection 54

maintenance 51

manufacturing tolerances 69

mechanical tests 37

spliced 12

Index Terms Links


poles (Cont.)

storage 50

structures 2

surface durability tests 39

transportation 12 45

poles, wood 27

polymer resin matrix 17 18

pultrusion 20

Q

quality assurance 41

design review 41

inspection 42

installation 43

manufacturing processes 42

structure testing 43

surface coatings 42

tolerances 42

transportation 43

R

resin infusion 23

resin infusion, vacuum-assisted 23

resin transfer method 23

Rural Electrification Administration 26

S

seismic forces 72

self-supporting structures:see

cantilevered structures

small angle structures 7

Index Terms Links


storage, poles 50

strength: axial 30

bending 30

buckling 30

fatigue 32

FRP poles 30

hoop 31

pull-through 31

torsional 31

structure design, factors 3

structures 7

bus-support 8

cantilevered 7

combined 4

communication 9 71

dead-end 7

design specifications 11

framed 4

guyed 3 7 11 31

33

H-frame 4 7

large angle 7

latticed tower 5

long span 7

small angle 7

substations 7

testing 43

traffic signal 8 71


surface coatings 39 42

Index Terms Links


T

tangent structures: see cantilevered

structures

tests: electrical 39

horizontal loading 37

static bending 37

structure 43

surface durability 39

torsional load 39

thermoset resins 18

tolerances 42

traffic signal structures 8

loads 71

transportation, poles 12 32 42 43

45

U

UV exposure 39 51

V

vertical loads 3

Recommended Practice for Fiber-Reinforced Polymer Products for Overhead Utility Line Structures

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