Guide for theDesign andUse ofCONCRETEPOLES

Prepared by theConcrete Pole Task Committee of the

Committee on Electrical Transmission Structuresof the Structural Division of theAmerican Society of Civil Engineers

April 1987Published by the

American Society of Civil Engineers345 East 47th Street

New York, New York 10017-2398

PREFACE

A Task Committee of the Committee on Electrical Transmission Structures wasformed in1984 to prepare a concrete pole design and use guide. The Task Committee hasproduced thisGuide which brings together in one document, as much information as time and thecollectiveknowledge of the Task Committee permits. No claim is made that this document iscomplete asit stands. Through future use, additional thoughts and ideas will be identifiedthat should beincluded. Hopefully this will be a living, working document that will be updatedas additionalknowledge becomes available. The potential exists for the proliferation of Design Guides and Standardswritten under theauspices of various organizations. There are already documents relating toconcrete poles thathave been published by IEEE, ASTM and PCI and all of them refer to ACI-318. NowcomesASCE with its document. Such a proliferation soon becomes both confusing andcounterproductive if there is no coordinating force. This Task Committee was chosen carefully to include people that were not onlyknowledgeable in the field of concrete poles, but who were also active in IEEE,ASTM, PCI andAC1. Indeed, not all of the Task Committee members are members of ASCE. It isthe hope ofthe Task Committee that this Guide will be jointly endorsed by all of theseorganizations as afocal point for information on concrete poles. The intent is not to usurp theprerogatives andresponsibilities of the other organizations, but for this committee to serve asa coordinatinggroup to insure that other documents do not become overlapping andcontradictory. The Task Committee recognizes that there are areas in which information islacking orincomplete. There is certainly work that needs to be done under the auspices ofASTM. We hopeto be able to work with that committee to develop the necessary techniques andknowledge to beable to write testing standards associated with the manufacture of concretepoles. The committeealso recognizes the need for research into some areas in which there is anabysmal lack ofknowledge. It is hoped that somewhere in the industry, this research can befunded andundertaken with the results being available for the good of the industry. Users of this Design and Use Guide are encouraged to ask questions or sendcomments andinformation that should affect the content of the Guide. Since neither thechairman nor thecommittee as a whole intend to abandon the project, comments and questions maybe addressed

to the chairman for consideration in future meetings. Anyone with a stronginterest in becoming a committee member should contact the chairman. Respectfully Submitted.

Concrete Pole Task CommitteeSteven Bull Dennis MizeWilliam Ford Tarun NaikFouad Fouad Robert Roane

Tim Hardy Thomas Rodgers, Jr.Samuel Hogg Vincent Schuster

Michael McCafferty Jerry Tang

William MickleyWilliam Howard. Chairman

Committee on Electrical Transmission StructuresWilliam M. Howard Ronald E. RandleJohn D. Mozer Gene M. Wilhoite

Anthony M. DiGioia, Jr., Chairman

CONCRETE POLE DESIGN AND USE GUIDE

William M. Howard Committee Chairman

INTRODUCTION

This guide presents the generally accepted procedures for thedesign, fabrication, inspection, testing and installation of concretepoles. It addresses poles which are either spun cast or statically castand which are prestressed, partially prestressed or conventionally rein-forced. The primary emphasis is on spun, prestressed poles which arewidely recognized as the ultimate in light weight and durability. Mostprestressed poles are of the pretensioned variety and, therefore, posttensioned poles receive little attention in this guide. Also, althoughmany uses for concrete poles are recognized, the guide is heavilyweighted toward electric utility uses. Other new types of concrete poles, such as fiber reinforced poles,will be developed in the future and must be addressed by later updatesof this guide. Many portions, but certainly not all, of ACI-318 and ACI-318Rare applicable to concrete poles and various references to ACI— 318 willbe made. It is intended that the definitions and notations used in thisguide are consistent with those used in ACI-318. (See Appendix B of thisGuide for Notations used herein.) This guide is performance oriented. It presents certaip theoriesand methods that are generally recognized as good practice, but allowsfor innovative and unique circumstances to be fully acceptable uponpresentation of sufficient test data to demonstrate that proper perfor-mance can be achieved. The fundamental premise is that where strength,durability and aesthetics can be equalled or improved upon through newmethods, nothing should stand in the way of implementing such methods.This philosophy is consistent with Commentary on ACI 318-83 in whichparagraph 18.4.3 states, "This section provides a mechanism wherebydevelopment of new products, materials, and techniques in prestressedconcrete construction need not be inhibited by limits on stress whichrepresented the most advanced requirements at the time the codeprovisions were adopted".* President, Power Line Systems, Inc., 6701 Seybold Road, Madison, WI 53719

2 CONCRETE POLES DESIGN 1.0 INITIAL DESIGN CONSIDERATIONS This section is written especially for the user. It specificallydetails the information which users should include in their specifi-cation to allow the structure designers to properly and efficientlyaccomplish their tasks.1.1 General The structure design requires consideration of many aspectsincluding loading, fabrication techniques, method of shipment, con-struction and maintenance methods, terrain, types of foundations,corrosion, structural and electrical geometry and clearances, localrestrictions and codes. The user is to select the necessary structure design loadingcriteria. Structure loading may use /d^ta furnished in the ANSI C2"National Electrical Safety Code" (NESC)'-' the ASCE "Guidelines forTransmission Line Structural Loading" , AASHTO "Standard Specifica-tions fofcStructural Supports for Highway Signs, Luminaires and TrafficSignals" , Electronic Industries Association (EIA) Standards orindependent selections based on known local environmental conditions(such as high winds or heavy ice conditions). When using the ASCE "Guidelines for Transmission Line StructuralLoading" an exclusion limit is required for pole strengths. Each manu-facturer should conduct a full scale testing program to develop its ownvalues for the exclusion limit. (The exclusion limit is simply the per-centage of poles that fail at less than nominal design strength.) In theabsence of adequate test data, an exclusion limit of 35 shall be used.1.2 Load Expression It is recommended that loading conditions be expressed as loadtrees, using an orthogonal coordinate system as shown in Figure 1-1 onthe next page. Conductor and shield wire loads should be shown at theconductor and shield attachment points. The weight of the hardware andinsulators should be included in these loads. Wind on structure shouldbe expressed in psf (pounds per square foot). Loads should be ultimateincluding all safety and overload factors.1.3 Determination of Performance Requirements Poles are designed by the ultimate strength method, to resist thelargest factored load. It is the user's responsibility to determine ifthe word "resist" means to resist the maximum loads without permanent,unacceptable deformation (damage) to the pole, or if it means to resistthe loads without failure (collapse) of the pole, recognizing that itrequires a stronger pole to resist damage than to resist collapse. Inthe case of a damaged pole, the steel will have been stretched beyondits elastic limit and/or some concrete will have spalled off the pole.The pole will be permanently deformed, will no longer perform as it wasdesigned to, and will need to be replaced; but it is still maintaining

4 CONCRETE POLES DESIGNthe conductors in such a configuration that the line remains energized.A pole which has collapsed is one which has reached such a state thatthe line can no longer carry power.1.4 Determination of "Normal Everyday" (Frequent Condition) Loads For unguyed angle or deadend pole structures, it is desirable toconsider deflections under "normal everyday" loads. A pole with largedeflections under such conditions is undesirable. User should specifywhat loads are to be considered "normal everyday".1.5 Longitudinal Loading Because of the possibility of catastrophic cascading failure, themost important loading condition to be evaluated for any transmissionline is that caused by the simultaneous loss of tension on all condu-tors. For pole type self-supporting structures, the deflection of thestructure itself, will provide a significant tension reduction in thewires. The length of suspension insulator strings can also greatlyinfluence the structure loading under unbalanced longitudinal loadingconditions since the decrease in tension caused by the swing of longinsulator strings can be significant. Both of these factors should beincluded in the unbalanced loading condition as long as proper consid-eration is given to any impact loading imposed on the structure. Forlongitudinal loading calculations, spans used should approximate actualline spans. A longitudinal analysis is particularly essential when comparingalternate designs and materials because it is necessary to be sure thatthe alternates being considered are, indeed, equivalents. For example, alattice tower, being a much more rigid structure than a pole structure,

must be designed significantly stronger in order to provide the same de-gree of protection against cascading failures. The combination of flex-ibility, mass and mode of failure that are inherent in concrete polesmake them more resistant to cascading failures than are structures madeof other materials. Under individual broken conductor conditions, restraint will beoffered to the structures by the intact wires. Calculations shouldproperly reflect the structure deflection and insulator swing, and theresulting change in wire spans and tensions. Proper evaluation of the effects of broken conductors requires theuse of sophisticated computer programs. From such an analysis, an equiv-alent static load can be established for the design and testing of thestructure. If testing of the structure does not confirm the expecteddeflections, additional evaluations should be made.1.6 Geometry The basic pole structure configuration, conductor and shieldinggeometry (i.e., horizontal, vertical, delta, single poles, H-frames,etc.), insulation assembly length, swing angles, electrical clearances

CONCRETE POLES DESIGN 5and shielding angle should be made clear to the structure designer.However, the structure designer should be allowed as much latitude aspossible to determine the design details of the structure. 1.7 Foundations Consider the type of foundation, foundation rotational allowanceand soil parameters (e.g. evaluate bearing and uplift criteria and strength of both natural soil and backfill). When specifying the maximum value for foundation rotation and de-flection for all load cases, the user should establish the performancerequirements for the combined pole and foundation installation. Indetermining this value, the user may consider aesthetics, phase-to-structure clearances, phase-to-ground clearances, structure to ob-struction clearances or even the ability to replumb a structure. The specifying of a rotation and deflection for each load case is arefinement in analysis and design which allows the user to match typesand probability of loads with foundation response. For instance, underrarely occurring conditions such as a 50-year extreme wind load, onemight allow more foundation deflection and rotation than under morecommon loads with the expectation that the cost of occasionallystraightening a structure will be less than the cost of stronger, moreexpensive foundations. In the case where foundation rotation-deflection is specified, themanufacturer should include such effects in the calculations of finaldeflected pole stresses. The rotation and deflections, when specified,should be for the respective loads with overload factors.1.8 Design Restrictions Examples of design restrictions are length, weight, deflection orother limitations imposed due to local codes or conditions.1.9 Deflection 1.9.1 General Structures must be analyzed for deflection to insure that theyhave adequate strength. The large deflections frequently observed inpole structures under horizontal loads cause additional stress due tothe vertical loads being applied while the pole is in the final deflect-ed position. The stress analysis for this is covered in Section 2.0. 1.9.2 Clearances Clearances from conductors to supporting structures, ground,or edge of right-of-way are usually not affected significantly by poledeflections except, perhaps, on special long span or line angle condi-

tions. The user must be aware of this possibility and must compensatefor reduced clearances where they can occur. Clearances to the structureitself may be maintained by specifying certain combinations of conductor

6 CONCRETE POLES DESIGNdown drop and line angle at the structure and the required clearance.This clearance should be maintained to the deflected structure under thespecified loading condition. 1.9.3 Appearance Deflections can play an important part in the appearance of astructure. At line angles or where all vertical conductors are on oneside of a pole structure, the constant load in one direction will causethe structure to bow and, if the pole was originally set vertically, itmay appear to be near failure. There are several methods that can beused to compensate for this. One method is to rake the pole when settingit. The deflection at the top of the pole is determined for the everydayloading and the pole is tilted this predetermined amount so that, underthe everyday loading, the top of the pole is vertical. In this case, thepole will be curved, but because the top portion is vertical, the curva-ture is unlikely to be noticeable. Designing the structure to limit deflection is a possibility,but this can be expensive because of the extra heavy pole that will berequired. Precambered poles are another possibility. It should be recog-nized, however, that the predictability of results in precamberingconcrete poles is poor, at best, and few manufacturers are prepared toprecamber at all. Finally, guys may be used to limit deflections.1.10 Transportation and Erection The design should consider equipment or access limitations andloads caused by methods of loading, unloading, hauling, assembly, erec-tion and stringing (including longitudinal load due to line snagging intraveller). It should be kept in mind that the largest stress level a concretepole may see in its lifetime can occur by lifting it clear of the groundwhile it is in a horizontal position, as is common in loading and un-loading. Indeed, the induced stresses can be so great that it maysometimes be necessary to require the use of multiple point picks toavoid damaging the poles. Experience suggests that transportation and erection loads gener-ally should not be controlling among the various construction loads.Transportation loads can be controlled by using adequate support underthe poles (i.e. do not allow long overhangs or unsupported lengths).Erection with single point picks is not a problem as long as much of theweight of the pole is supported on the ground until the pole is in anupright position. Since poles and structures are normally erected bylifting at a point well above the center of gravity, the pole buttsremain on the ground until the pole is erect and excessive bending loadsduring erection are thus avoided. It is the manufacturer's responsibility to clearly indicate on the

CONCRETE POLES DESIGN 7erection drawings, any restrictions to be observed by the contractor inthe handling, transportation and erection processes. However, both usersand manufacturers should realize that restrictions add to the cost ofinstallation and should be kept to a minimum. For example, it may bedesirable to additionally-reinforce those guyed poles which would other-wise require little prestressing steel to handle the service loads, so

that the pole can be handled in a normal manner during construction,because the cost of the extra steel will likely be less than the cost ofunusual handling procedures during construction. Poles most likely to be susceptible to damage during transportationand erection are poles designed for light loading conditions, guyedpoles, unusually long poles, poles with substantial weights in attachedaccessories and poles that must be lifted at or near their center ofgravity. Unless the poles have been designed to withstand a single pointpick at the center of gravity after complete assembly (including a 1.5overload factor), special handling instructions should be clearlyindicated on the erection drawings. In general, then, it is usually the lifting of the entire poleweight while the pole is in the horizontal position that is the control-ling handling condition. This load is caused by the weight of the poleitself (plus the weight of any items that may be attached to the pole).To allow for shock loads that may occur while the pole is being lifted,an overload factor of 1.5 should be appled to the dead weight of thepole and attached accessories. It is also necessary for the user tospecify whether the pole is to withstand a single point pick or whethermultiple point picks can be required by the manufacturer.1.11 Attached Items User is responsible for informing the manufacturer what accessoriesare to be mounted on the poles as well as the weight of those accessor-ies so that the poles may be properly designed.1.12 Guying It is important to define as many knowns as possible, such as re-strictions, right-of-way limitations, use of particular guy wire oranchor types, guy angles, quantity of guys, placement tolerances andterrain considerations. The structure designer should be allowed as muchlatitude as possible in determining the details of the guying scheme tobe used.1.13 Climbing and Maintenance Identify climbing, working and hot line maintenance provisionsrequired. The primary means of climbing concrete poles is with the sameremovable ladder system used to climb steel poles. This system isavailable from all pole manufacturers. Many other options are availableif the user prefers. The particular method to be used will need to bediscussed with the individual manufacturers since not all producers areprepared to offer all options.

8 CONCRETE POLES DESIGN 1.14 Grounding Pole grounding can best be accomplished by utilizing one or more of the prestressing strands as the electrical path to ground. In addition, a separate ground wire may be attached to the exterior surface of the pole or it may be placed in the cavity in the center of the pole. In either case, it should be bonded to the prestressing steel to avoid lightning damage to the pole. User should specify the desired method of

grounding. 1.15 Other Considerations Any other special conditions that may affect the design should be considered (e.g. reverse wind on bisector guyed light angle structure may control design or environmental conditions may suggest special concrete mixes). Finally, it should be remembered that, like wood poles, concrete poles lend themselves to use under standardized design conditions using a strength/length classification system. In fact, concrete poles can be designed so as to meet the same loading conditions as the wood poleheights and classes. As more users and designers begin to treat concretepoles conceptually like wood poles for design purposes, the costs ofboth design and manufacturing will decrease substantially. 2.0 - DESIGN2.1 General For each loading condition considered, it is necessary to analyzethe effects of the loads on the structure to determine the tensions,compressions, moments, shears and torsions that the structure must re-sist at its different locations and the resultant deflections. The reason for using reinforced concrete as a construction materialis to take advantage of the best attributes of both concrete and steel.Concrete is relatively inexpensive, excellent in compressive strengthand, when properly made, is relatively unaffected by the environment.The primary disadvantage is its low tensile strength. Steel, on theother hand, is excellent in tension but it is more expensive than con-crete and is also readily attacked by the environment. Thus the objec-tives are to use as little steel as possible, to place it in the tensionzones of the member and to use the concrete to protect the steel fromthe elements. In some ordinary reinforced applications, steel may, onoccasion, be used to resist compression.2.2 Design Theory 2.2.1 General As outlined in paragraph 1.3, concrete poles are designed bythe ultimate strength method wherein the applied service loads aremultiplied by overload factors and the pole is designed to resist the

CONCRETE POLES DESIGN 9largest factored load. A pole Section should also be designed -so that normal everyday(frequent condition) unfactored loads will not cause the concrete to. gointo tension. (See paragraph 1;.4) 2.2.2 Bending The most common loading conditions for poles result in thepole being called upon to resist bending moments. When the bendingmoments are large enough, the concrete on the outside curvature of thepole will go into tension and, perhaps, crack. Tangent poles (the most common case) designed according toNESC light, medium or heavy loading are unlikely to ever crack underservice loads. The 2.5 overload factor used in these cases to determinethe required ultimate strength, means that the service load is 40% ofthe ultimate load. Concrete in a prestressed concrete pole normally doesnot go into tension until the load is around 40% to 50% of the ultimateload. Thus the service load is about equal to or less than the loadwhich causes the concrete to go into tension. Where very low overload factors are used (such as are commonin the 1.0 to 1.1 range for high winds), the poles will crack under theunfactored loads. However, since loads of such a great magnitude areapplied to the pole seldom, if ever, opening of cracks under such loadswill not occur often enough to be detrimental to the long termdurability of the poles. Indeed, for tangent structures which have beenproperly designed for ultimate strength under factored loads, it isdifficult to imagine any set of circumstances where a pole would be in a cracked condition even 0.017. of its life. Unguyed angle or dead-end poles do, however, require careful attention to insure that they are not in a cracked state under "normal everyday" (frequent condition) loads. The detailed methodology for determining the bending strength of a reinforced concrete section is well documented in various text books on Reinforced Concrete. However the fundamental assumptions bear repeating here: 2.2.2.1 The section must satisfy the basic test of static equilibrium (i.e. the tension loads and the compression loads must be equal; and the summation of the internal moments about the neutral axis must be equal to the external moment applied to the section). 2.2.2.2 Strains for both concrete and steel shall be assumed to be directly proportional to the distance from the neutral axis. 2.2.2.3 Tensile strength of concrete shall be neglected in flexural calculations except for the express purpose of determifling when the first cracks are expected to appear, (i.e. determining the cracking moment). This is done to account for the fact that once the pole has cracked (and poles are expected to crack), the concrete no longer has any tensile strength. Some have suggested that poles might be designed, handled and used in such a manner that they never crack. Such an ap- proach is impractical, unnecessarily restrictive and, ultimately, it

10 CONCRETE POLES DESIGNcannot be guaranteed that the pole did not crack anyway. 2.2.2.4 The stress/strain relationships must be determinedfor the specific materials used. A balanced design is one in which theyield strain of the steel and the limit strain of the concrete arereached simultaneously. A balanced design produces the most efficientsection. 2.2.2.5 When designing to allow damage but resist collapse,the concept of balanced design is not valid since some of the steel maybe intentionally allowed to exceed its elastic limit. Except in a rarecase of a highly under reinforced section, the failure will occur in theconcrete, and the steel will not rupture. This is due to the steel goinginto a plastic state, thereby picking up an ever increasing load; whilethe neutral axis moves toward the compression side of the section, whichmust balance the increasing steel load on a decreasing concrete area,until the concrete strain reaches the point where the concrete ruptures. 2.2.3 Column Loading Buckling is seldom a limiting factor in the design of concretepoles. However, when unusually large vertical loads are encountered(e.g. large guyed loads or guys with short guy leads) it is necessary tocheck for a buckling condition, particularly on taller poles. 2.2.4 Shear Shear is seldom a consideration in concrete pole design. Fornormal direct burial conditions, soil strengths dictate that the polemust be buried deeply enough to preclude shear problems. Normal burialdepths will equal or exceed 10% of the pole length plus 2 feet and poleswith such burial depths need not even be checked for shear. The criticalconditions that bear checking occur when very large moments are appliednear either end of the pole. For example, poles set into solid rock orburied into a concrete foundation socket, may not be buried very deeply,in which case, it is necessary to check for shear to ensure that thepole does not split lengthwise along the neutral axis due to exceedingthe concrete shear stress limits. 2.2.5 Torsion Good theory for the design of concrete poles to resist tor-sional loads does not exist. Furthermore, the combined effect of thestresses occurring in a prestressed concrete pole which is subjected tosimultaneous bending, column loading, prestress loading and torsionalloading is so complex as to defy reasonable mathematical modeling. Onlyafter extensive research will it be possible to develop mathematicalformulas and prove them out to the point where they can be used withconfidence. In the meantime, little can be done to assure proper per-formance under torsional loads other than to test a pole for thoseconditions that suggest the liklihood of significant torsional loadsbeing applied.

CONCRETE POLES DESIGN 112.3 Concrete Properties 2.3.1 Stress/Strain Relationships Curves showing the relationship between stress and strain forconcrete vary widely depending primarily upon the strength of the con-crete. For normal strength concrete, the curves are distinctly non-linear and allowable strain is usually limited to 0.003 inches/inch.However as the strength of the concrete is increased to the ultra-highstrength level, the curves become very linear all of the way to rupture,which may occur at strains considerably less than 0.003 inches/inch. For those manufacturers who prefer not to perform the neces-sary testing to develop their own curves, the provisions of ACI 318provide a satisfactory basis for design parameters for concrete in theordinary strength ranges. For higher strength concretes, ACI provisionsmay or may not provide acceptable results. According to ACI 318-83 par-agraph 10.2.6, "Relationship between concrete compressive stress distri-bution and concrete strain may be assumed to be rectangular, trapezoid-al, parabolic, or any other shape that results in prediction of strengthin substantial agreement with the results of comprehensive tests". Manu-facturers are, therefore, expected to conduct "comprehensive tests" todevelop their own stress/strain curves for any concrete with strengthsbeyond the applicability of ACI provisions. 2.3.2 Concrete Compressive Strengths - f The specified compressive strength of the concrete (f ) isdetermined by the manufacturer based on a number of considerations (seediscussion under 3.0 Fabrication) but should not be less than 5000 psiand preferrably 7000 psi or more. Although concrete compressive strengths are conventionallydetermined at 28 days, it is not required that strengths be measured atthat time, and the manufacturer should be allowed to specify strengthsat later times to utilize the continuing growth in concrete strengthwhich occurs over time. The use of longer times should, however, beclearly indicated at the time of bidding and on the drawings so that apole is not fully loaded before the time that the concrete reaches itsspecified compressive strength.2.4 Reinforcing Steel 2.4.1 Stress/Strain Relationships Stress/Strain curves for steel do not vary as much as they dofor concrete. These curves are provided to the pole manufacturers by thesteel suppliers and from the curves can be determined Modulus of Elast-icity (E ), Yield Stress (f ), and Ultimate Stress (f ). For purposes of determining the strength of the section at themoment of collapse, ACI 318-83 paragraph 10.2.4 states that for non-prestressed reinforcing steel, the stress in the reinforcement that isbelow yield stress level shall be taken as E times steel strain. For s

12 CONCRETE POLES DESIGNstrains greater than that corresponding to f , stress in reinforcementshall be considered independent of strain and equal to f . Sinceprestressing sttand behaves differently than reinforcing steely the PCIDesign Handbook suggests the following formulas for the stress/strainrelationships of the prestressing steel:

When using a combination of prestressed and non-prestressedsteel in a member, the provisions of ACI 318 shall apply. 2.4.2 Longitudinal Reinforcement The primary purpose of longitudinal reinforcement is to resistthe tension forces in the pole caused by bending moments applied to thepole and, in the case of prestressing steel, to impart prestressingloads into the concrete. The steel must be properly held in place duringthe placement, consolidating and curing of the concrete, so that properconcrete cover and steel to steel clearance is achieved. The methodsused should be left to the manufacturer who may be called upon by theuser to demonstrate the adequacy of its methods. Longitudinal reinforcement is normally placed uniformlythroughout a symmetrical cross section. It is possible to obtain somedegree of increased strength about one bending axis, even though thecross section has a symmetrical shape, by placing the steel as far aspossible from the axis about which the bending occurs. Such a techniqueis rare, however, because the additional strength which can be generatedabout a particular axis is not large, and handling problems may be en-countered due to the resultant weakness about the weaker axis. 2.4.3 Circumferential Reinforcement In order to control longitudinal cracking from several poten-tial sources and to improve the shear and torsional strength of thepole, circumferential reinforcing is required throughout the full lengthof the pole. Theories to allow for good design practice are not welldeveloped, particularly for prestressed pole sections. However, drawingupon common practice that generally provides satisfactory results, theratio of the volume of circumferential steel to the volume of the con-crete shall not be less than 0.1%. The spacing between the circumferen-tial reinforcements shall not be greater than 4 inches or the radius ofthe pole. Because of prestressing loads near the ends of poles andpossible shear or torsion loads, additional circumferential steel may berequired. A spacing greater than 4 inches may be allowed if the manufac-

CONCRETE POLES DESIGN 13turer presents evidence of satisfactory performance and user agrees.2.5 Concrete Cover Over Steel In addition to structural requirements, the purpose of concretecover over steel is to protect the steel from corrosion. The thicknessof cover required, may vary according to the degree of corrosiveness ofthe environment in which the pole will be used as well as the quality ofthe concrete and its ability to protect against the hostile environment.More cover provides greater protection only to the point where the steelcannot be attacked. Excess cover adds nothing to the durability of thepole but does add unnecessary weight and cost. For static cast, ordinary reinforced concrete the provisions of ACI318 apply for determining cover requirements. In the case of static cast, prestressed concrete poles, ACI.g318-83and the PCI "Guide Specification for Prestressed Concrete Poles" bothcall for 1 inch of cover. This appears to be consistent with othergenerally accepted practices and provides satisfactory results in mostcases. A review of specifications for spun concrete poles from widelydiffering parts of the world where they have many years of experienceshows that required cover varies between 13mm (approximately 1/2 inch)to 19mm (approximately 3/4 inch). As an average for the standard prac-tices both domestic and abroad, it is recommended that design cover be3/4 inch over the primary steel with 5/8 inch being allowed over thespiral reinforcement. Lesser covers should be allowed if the manufac-turer can demonstrate through tests that its concrete is of extremelylow porosity so as to protect the steel and develop structural strengthwith less cover and that the steel can be placed with sufficient accur-acy to provide adequate cover under reasonable fabrication deviations.2.6 Concrete/Steel Bond Due to the fact that large moments are seldom applied near the endsof poles, the analysis of the development of the bond between concreteand steel is largely ignored. In circumstances where there are largemoments near the ends of poles (e.g. a davit arm at the top of a pole, ajoint connecting parts of a multi-piece pole or a pole set shallow intoa rock hole) it is necessary to examine the bond development. It is alsoimportant to consider bond development in the event that some of thesteel is cut by drilling holes in a part of the pole in which the steelis highly stressed. ACI 318 covers bond development. In addition to normal bond devel-opment, end anchorages of various descriptions can be used. It is possible that, because of high prestress forces, longitudinalcracks may develop at the ends of the pole. If this occurs, it may benecessary to increase the concrete cover or the amount of spiral rein-forcement or both.

14 CONCRETE POLES DESIGN2.7 Prestress Loads 2.7.1 Steel ACI 318 provides guidance as to allowable tensile stress inthe prestressing tendons both at the time of application of the jackingforce and immediately after prestress transfer. At jacking it allows0.94 f but not greater than 0.85 f or maximum value recommended bythe manufacturer. Immediately after pres'tress transfer the maximum al-lowable stresses are 0.82 f but not greater than 0.74 f . 2.7.2 Concrete ACI 318-83 paragraph 18.4.1(a) states that stresses in theconcrete immediately after prestress transfer (before time-dependentprestress losses) shall not exceed 0.60 f . where f. is the compres-sive strength of concrete at time of initial prestress. However para-graph 18.4.3 states that the permissible stresses in the concrete may beexceeded if shown by test or analysis that performance will not beimpaired. 2.7.3 Loss of Prestress In the Commentary on ACI 318-83 paragraph 18.6.1 severalreferences are cited which indicate how "reasonably accurate estimatesof prestress losses can be easily calculated". It also points out thatthe accuracy of the calculations have little effect on the ultimatestrength of the member. It does, however, have some effect on the crack-ing load and the deflections of the member. Loss of prestress requires calculations that consider anchorageseating, elastic shortening of the concrete, creep of the concrete,shrinkage of the concrete and relaxation of the tendons.2.8 Direct Burial Considerations Because no special treatment is required for the portion of thepole that is buried, the poles can be buried any convenient depth. Therule—of-thumb, which many engineers use as a left-over from their woodpole experience, is to bury the pole 10% of its length plus 2 feet. Forlower strength concrete poles this may provide satisfactory results.

However, since concrete poles are, in general, much stronger than woodpoles, it follows that stronger (and presumably deeper) foundationswould be in order. It is also necessary to determine whether it is morecost effective to use a conservative foundation design or to plan tostraighten an occasional leaning pole. There is a tendency (which shouldbe avoided) to penalize the cost of a concrete pole line in comparisonto a wood pole line by using more stringent foundation criteria forconcrete poles while using the old rule-of-thumb criteria for the woodpoles. As far as the integrity of the pole is concerned, any type ofbackfill is satisfactory. Many people use either native soil or crushedrock backfill. Some use concrete backfill but it is doubtful that theresults are any different than with a well compacted granular backfill

CONCRETE POLES DESIGN 15since either backfill is likely to be considerably stiffer than thesurrounding natural soil. Concrete backfill has the advantage that itneed not be compacted, but that advantage is likely to be more thanoffset by the disadvantage of having to temporarily support the struc-ture while the concrete sets. When designing the pole, there are two items to be considered inrelation to the foundation. The most common is to realize that themaximum moment in the pole occurs below ground and not at the groundline. Since most poles are tapered and their strength continues toincrease below ground line, it appears quite safe and common to ignorethe additional below ground moment and design the pole based on themoment at the ground line. The other consideration comes up only rarely. If a pole is set inan unusually shallow manner (e.g. in a rock excavation or in a barrelledhole) the shear forces developed along the longitudinal neutral axisneed to be considered to avoid having the pole split longitudinally atthe butt. In the case of spun poles which have thin walls and a large void,consideration should be given to the magnitude of the down load and theability of the soil to keep the pole from being forced further into theground. In general, unguyed single poles do not need to have the bottomsof the poles plugged. Guyed poles either need the bottoms plugged or mayneed large bearing plates placed under the butt to resist the down load.For unguyed H-frames, uplift shoes that are commonly used may provideenough down load capability as well, to avoid the need for plugging thepole bottom. When uplift shoes are not used, plugging or bearing platesmay be necessary in poor soil conditions.2.9 Guyed Structures To properly analyze a guyed structure, certain assumptions must bemade regarding guy tensions and pole deflections. In the absence ofclear directives to the contrary, it should be assumed that the axis ofthe pole will be straight under normal, everyday loads. This means thatonce the conductors are sagged, the guys will be adjusted so that thepole top is returned to the position in which it was originally set(regardless of whether or not the pole was raked when it was set). Fordesign purposes it will be assumed that there is no moment in the poleunder a no wind condition at the specified temperature (60 degreesFarenheit if no other temperature is specified).2.10 Grounding It is apparent that concrete poles are sufficiently good conductorsthat current will travel through the pole on its way to the ground.Therefore the question is not whether to use the pole as a ground, buthow to best protect the pole, the operating system and people. The reasonable choices are to use the steel in the pole as theexclusive path to ground or to place a separate ground wire down eitherthe interior of a hollow pole or the exterior of any pole to carry someof the current to ground. If a separate wire is used, it should be

16 CONCRETE POLES DESIGN bonded by any of several available alternatives to the steel within the pole. Bonding of hardware to concrete poles may or may not be necessary. The two primary reasons for bonding hardware on wood structures is to prevent pole fires and to control radio noise. Obviously pole fires are not a concern with concrete poles and, since the hardware does not loosen on concrete poles as it does on wood poles, radio noise is not a problem. Some are concerned about damage to the pole if lightning should travel through unbonded hardware and seek a path to ground through the pole. Although there are recorded instances of small areas of concrete being knocked loose due to lightning travelling this route, the damage has always been minor, repairable and extremely rare. Most users appar- ently find that the cost of bonding far outweighs any possible savings in cost of repairing damage. 2.11 Bolted Connections Most hardware is bolted to concrete poles with galvanized through bolts.Good practice dictates that the bolts not overload the concrete and that they be properly tightened. Also, low strength machine bolts should be used. Bolts such as ANSI C135.1 or AS1M A307 are the types commonly used in power line construction. Designing for use of lower strength bolts helps to insure that the bolt loads do not exceed the concrete bearing strength, and, since the low strength bolts are com- monly available, lost bolts will be replaced with bolts of the correct strength. Recognizing that, in certain cases, higher strength bolts may be required to carry the loads, the designer should check bolt to concrete bearing loads. Sleeving of holes may be necessary as a means of reducing concrete bearing stress. To spread the concentrated loads under the head of the bolt and under the nut, a square curved washer or other similar plate should be placed between the head or nut and the pole. For A 307 bolts over 1 inch in diameter or A 325 bolts over 3/4 inch in diameter, use either two 1/4 inch thick washers or a single 3/8 inch washer. Use of cast washers is not recommended. The turn-of-the-nut method for tightening bolts is superior to torquing bolts and nuts, particularly when they are galvanized. In most cases the bolt will be properly tightened if the nut is first tightened snugly (snugly is defined as the degree of tightness caused by the first impacting of an impact wrench) and then the nut receives an addi- tional turn depending on bolt length as follows: Short bolts (length less than 4 times the diameter) - 1/3 turn; Medium length bolts (length between 4 and 8 diameters) - 1/2 turn; and long bolts (length greater than 8 diameters) - 3/4 turn. Except near the ends of a spun pole that does not have the end plugged, the strength of the pole is sufficient to withstand any reasonable degree of bolt tightness. If a hollow spun pole shows signs of cracking longitudinally when the bolts are tightened, a decision can be made to tighten the bolts less or to use a steel sleeve in the hole or to plug the end of the pole if that is where the cracks are occurring.

CONCRETE POLES DESIGN 17 It is recognized that low strength bolts are not usually preten-sioned. However, this recommended tightening procedure will both keepthe bolts tight and protect the pole from damage by over tightening. For shear connections in which the bolt will bear against the sideof the through hole, the maximum bolt bearing load will be determined bymultiplying the diameter of the bolt times the wall thickness times f .In the absence of confirming tests, it is assumed that the bolt toconcrete interface carries all of the load and none of it is carriedthrough friction. For solid poles (or hollow poles with very thickwalls), a maximum effective wall thickness for calculating the bearingload is 3 inches.2.12 Climbing Attachments The primary means of climbing concrete poles is with the sameremovable ladder system used to climb steel poles. This system isavailable from all producers. Many other options are available if theuser prefers. Per paragraph 1.13, the particular method to be usedshould be discussed with the individual producers if it is other thannormal ladders since not all producers are prepared to offer alloptions. It is recommended that every individual part of the climbing systemwhere a lineman could conceivably place his foot should be able to with-stand a static load of 750 pounds without permanent deformation. Inaddition, any part of the climbing system which is considered to be asafety attachment point should be able to withstand without breaking, aload of 500 pounds dropped 18 inches.2.13 Inserts Inserts should be made of materials which will not deteriorate inthe environment in which they are placed. Care should be taken to insurethat the materials in the concrete, the insert and the bolt do not reactunfavorably with each other. The anchorage of the inserts in the concrete should be such thatthey do not pull loose under the design load or any unusual loads thatcould conceivably be applied. Preferrably they are designed and anchoredin such a fashion that the bolts will break before the inserts pullloose. It is necessary to insure that bolts do not bottom out in the insert. This may require coordination between user and/or one or more suppliers. 2.14 Pole Splices There are occasions in which it is desirable to connect two or more pole parts together into a single pole. This is accomplished with some form of a splice. Many different versions are available but they all have one thing in common that needs to be addressed in the design. Since large moments are generated at the mating ends of the pole sections, it

18 CONCRETE POLES DESIGNis necessary to insure that the reinforcing steel and the connection ap-paratus are properly anchored as a part of the pole (see discussion insection 2.6 Concrete/Steel Bond). Since the connections are made of steel, reference to ASCE Steel Pole Design Guide for design and fab-rication practices is recommended.2.15 Pole Identification Data All poles (including each piece of two piece poles) will have cer-tain data indicated on a data plate or cast into the pole itself. At aminimum, data to be shown will include: Manufacturer's name. Weight of pole (or weight of pole section). Ultimate design moment (at ground line except for the top sec- tion of a two piece pole where ultimate design moment will be that at the connection). Length of pole (or length of pole section). Date of manufacture. Identification number (to allow manufacturer to match a specific pole with the manufacturing data records).2.16 Attachments and Accessories An almost unlimited variety of attachments and accessories areappropriate for use with concrete poles. The design of steel attach-ments, accessories and guys should follow applicable provisions of theASCE Steel Pole Design Guide. Pieces made of wood, fiberglass, aluminumor other materials should be designed to meet established standards forthose materials as appropriate to the intended end use.3.0 FABRICATION3.1 General Since one of the primary reasons for using concrete poles is toachieve a long, maintenance free life as a support structure, it followsthat the concrete and other materials should reflect the use of thefinest available materials and workmanship. The design and manufacturingtechniques should make use of the latest and best thinking in terms ofproducing durable and high strength concrete. Not only does the emphasison high strength produce lighter poles, the various techniques and pro-cedures that produce high strength concrete also make for more durableconcrete. The particular mix to be used is at the discretion of the manufac-turer and should be considered as proprietary information. The manu-facturer is responsible to the purchaser to demonstrate that finished

CONCRETE POLES DESIGN 19concrete is being provided that meets the strength, durability and aes-thetic requirements of the specifications. Only materials that are certified for specified properties shall beused. Certification of all materials shall be checked and in-house labo-ratory tests shall be performed on concrete ingredients before materialis used. Traceability of material tests and certifications shall bemaintained a minimum of 15 years after fabrication has been completed.3.2 Concrete 3.2.1 Cement Portland cement shall conform to the requirements of ASTM C150or shall be portland blast-furnace slag cement or portland-pozzolan ce-ment conforming to the requirements of ASTM C595. The provisions of ACI 318 address situations where sulfateresistant concrete is desirable. The use of Type II or Type V cementsare sometimes specified. It is important to recognize that sulfateresistance is obtained in ways other than use of the two special typesof cement. A low C.,A content in the cement is required. Type II isspecified at less than 87. while Type V is specified at less than 57..Cement with up to 10% of C^A can be used where the w/c ratio is 0.40 orless. Many Type I cements meet these requirements. Also, the use of fly-ash can make Type I cements more sulfate resistant than the specialtypes. The user should specify the type of environment in which thepole is to be used and allow the manufacturer to determine the bestmixes to be used. 3.2.2 Aggregates The aggregates shall conform to ASTM C33 or C330 except thatthe requirements for grading shall not apply. The manufacturer willestablish the gradation requirements for aggregates used in its ownconcrete, based on testing and experience. However, the maximum sizeaggregate shall be 3/4 of the clear spacing between reinforcing steeland the surface of the pole or between individual bars or wires. Certain aggregates have undesirable reactions with alkalicompounds. Tests and requirements to insure that aggregates are notalkali reactive are covered by ASTM C227, C289 and C295. 3.2.3 Water Mixing water shall be free of oils, organic matter and othersubstances in amounts that may be harmful to concrete or reinforcement.It shall not contain chloride ions in excess of 500 PPM or sulfate ionsin excess of 1000 PPM. In general, water from normal drinking supplywill meet the requirements necessary to produce quality concrete.

20 CONCRETE POLES DESIGN 3.2.4 Admixtures Chemical admixtures shall conform to ASTM C494. Air-entrainingagents shall conform to ASTM C260 and fly-ash or other pozzolanic admix-tures shall be in accordance with ASTM C618. Admixtures shall not con-tain chloride ions in quantities that will cause the total water solublechloride ion content of the concrete to exceed 0.06% of the weight ofthe cement. Other additives have been and will continue to be developedwhich are desirable to use for various reasons such as combatting chlor-ide attack or to color the concrete or to increase the strength anddurability of the pole. Use of such additives should be permitted aslong as the manufacturer submits satisfactory evidence to indicate thatproper testing has been done to insure adequate performance in the envi-ronment in which the pole is to be used.3.3 Reinforcing Steel 3.3.1 Prestress Steel Uncoated 7 wire, stress relieved (including low relaxation) strand will be in accordance with ASTM A416. Uncoated, stress relieved wire will conform with ASTM A421. For uncoated high strength steel bar the provisions of ASTM A722 will apply. Both galvanized and epoxy coated strands are manufactured but experience is limited and it is likely that for properly manufactured concrete poles, little, if any, benefit would accrue from the use of coated strand in pole applications. 3.3.2 Reinforcing Bars Deformed billet steel will be according to ASTM A615. Deformed axle steel will comply with ASTM A617 Deformed low alloy steel will meet the provisions of ASTM A706. 3.3.3 Spiral Wire Cold drawn steel for the spiral wire will meet the provisions of ASTM A82. Deformed steel wire shall meet the provisions of ASTM A496

CONCRETE POLES DESIGN213.3.4 WeldingWelding of prestress strand is not permitted except at exposedends and only after the pretension has been released.Mild steel reinforcing may be welded only near the ends of thepole.Circumferential steel may be welded as long as sufficientstrength remains after welding to meet design requirements.Where welds are to carry structural loads, they must meet theprovisions of AWS Dl.l and develop suitable strength.3.4 Accessories Many accessories are available to be cast into or attached toconcrete poles. Materials should meet the provisions of the followingspecifications: Structural steel - ASTM A36, A572, A588, A633GrE. Bolts and nuts - ANSI C135.1 or ASTM A307, A325 Welding - AWS Dl.l and D1.4 Malleable iron - ASTM A47 Zinc Alloy AC41A - ASTM B240 Plastic - ASTM D2133 Stainless steel - ASTM A666 PVC conduit - ASTM D2729 Alluminum alloy 355 - ASTM B26 Almag - ASTM B108 Hot dipped galvanizing - ASTM A123, A153 and A385. It shall meet the provisions of A143 for the prevention of em- brittlement. No double dips will be allowed. Zinc-rich coating - MIL-P-2135, self curing, one component, sacrificial.3.5 Bolt Holes And Block-Outs At the manufacturer's option, bolt holes and or block-outs may beeither cast, drilled or otherwise cut into the pole. Cutting of thesteel in the pole is acceptable as long as the manufacturer warrantsthat the remaining strength in the pole meets or exceeds the designrequirements. When steel is cut, it is not necessary to provide any

22 CONCRETE POLES DESIGNparticular protection from corrosion (except in the severe case wherethe pole will be placed in or immediately adjacent to salt water) sincethe probability of a detrimental level of corrosion occuring inside theholes is very small.3.6 Finishing The manufacturer's basic responsibility is to provide poles thatmeet or exceed the design strength requirements, that have a pleasingand workmanlike appearance and that have smooth, dense and hard surfacesthat will not deteriorate in the elements. Patching will be acceptableprovided that the structural adequacy and the appearance of the productare not impaired. Many other custom services are available at a price. Items in thiscategory include but are not limited to such things as plugging eitheror both ends of a hollow pole, providing a rain cap for the pole, cre-ating a special textured finish for the pole, installing hardware itemson the poles in the factory, painting the pole, etc.3.7 Fabrication Tolerances Following is a list of tolerances that manufacturers usually meetin the normal course of business. Stricter tolerances can usually be metif that should be necessary, but tighter tolerances have a cost. Length - Plus 12 inches and minus 6 inches. Cross Section - Plus or minus 5% with a minimum 1/4 inch. Wall Thickness - Plus 20% and minus 10% with a minimum of 1/4 inch. Note that the wall thickness requirements are nor- mally determined for some critical section such as the groundline. Other areas of the pole may not require as much thickness. Therefore, greater minus tolerances are acceptable in some areas of the pole where calculations and/or tests indicate that the pole will perform satis- factorily. Weight - Plus 20% and minus 10% except that, with the approval of the purchaser, poles heavier than 20% over the esti- mated weight may be used. (Caution: Be certain that poles are marked with actual or greater than actual weights to avoid accidents during construction.)

Sweep - 1/4 inch per 10 feet of length. Bolt Holes - Plus or minus 1/8 inch for holes within a bolting group and plus or minus 1 inch for the centerline of the group from the end of the pole. Bolt hole diameters will be 1/8 inch greater than the bolt diameter. Blockouts - Plus or minus 1 inch. End Squareness - Plus or minus 1/2 inch per foot of diameter.

CONCRETE POLES DESIGN 23 Reinforcement Placement - Plus or minus 1/4 inch for indi- vidual pieces and plus or minus 1/8 inch for the centroid of a group. Spacing of individual circumferential rein- forcements may vary plus or minus 25% as long as the total required quantity per foot is maintained.3.8 Quality Control 3.8.1 General The best assurance of a quality product is a consistent,thorough testing program. It begins with testing the raw materials,continues through the manufacturing process and finally includes testson the finished product. Mill certifications, test data and manufactur-

ing data should be filed and saved for a period of 15 years or longer. 3.8.2 Raw Materials 3.8.2.1 Cement With each new load of cement, the mill certificationsshould be checked to insure that the cement is not only within the ASTMstandards, but that the new load is similar to previous loads. Varia-tions in the cement, even within the ASTM tolerances, can produce dif-fering end results in the finished concrete. 3.8.2.2 Aggregate Daily, the aggregate should be checked for moisturecontent (ASTM C566) and a seive analysis should be run (ASTM C136).Weekly, Specific Gravity (ASTM C127) and Absorption (ASTM C128) testsshould be performed. 3.8.2.3 Reinforcement Mill certifications for the reinforcing steel should bechecked even though it is seldom that any problems are found. 3.8.3 Concrete 3.8.3.1 Wet Samples Two primary tests are run on wet concrete. One of theseis Air Content (ASTM C231). For static cast poles this test should berun on a daily basis. Since for spun poles most of the air is spun outanyway, the test is of lesser importance and can probably be run on aweekly basis as a means of keeping track of the uniformity of theconcrete The other test for wet concrete is Unit Weight (ASTMC138). This test should be run daily.

24 CONCRETE POLES DESIGN 3.8.3.2 Cured Samples ASTM C39, C172 and C192 as well as ACI 318 outline most of the requirements for taking, curing and testing concrete samples. (Note: Pad capping of samples will be acceptable if the manufacturer presents satisfactory data correlating the results with standard ASTM results.) These methods are very adequate for statically cast concrete,but need some modifications for spun concrete. In order to be most representative of the concrete in a spun pole, the test samples must be spun and cured similarly to the pole itself (i.e. spun with the same G forces, for the same time and cured for the same times at the same temperatures). The manufacturer should beprepared to demonstrate through full scale testing, that the strength ofthe spun concrete samples are representative of the strength of the con-crete in the pole. If the manufacturer wishes to take advantage of thehigher strength of spun concrete in the pole, but still wishes to use static cast samples as the primary manufacturing control, he may chooseto statistically correlate the static samples to pole strengths throughfull scale testing. Thereafter, the static samples may be the primarycontrol, even though the sample test results are less than both the de-sign strength and the actual concrete strength in the pole. The val-idation process must be repeated at least every six months and upon therequest of the user. The manufacturer may use the results of static castsamples directly, without any correlation, but design strength may notexceed the test results achieved according to the ASTM specifications. In summary, it is recommended that the foregoing ASTM andACI specifications be followed with the exception that the samplesshould be spun. Tests should be run either daily or for each 25 cubicyards of concrete, whichever occurs more often. Each test should consistof 4 cylinders. One is tested at the time of application of the pre-stress, one at 7 days and one at the age at which f is determined. Theremaining sample is a spare in the event there is a^roblem with one ofthe tests, or it can be saved for long term strength and durability in-vestigations . 3.8.3.3 Meeting the Requirements of f There is variability in the strength of both the concreteand the concrete samples from batch to batch. In order to insure thatthe concrete in the pole is almost always at least as strong as thedesign strength (f ) it is necessary to manufacture concrete at anaverage strength Chat is greater than the desired design strength. Ingeneral, those manufacturers whose concrete has less variability canmanufacture to a lower average strength than can those with greatervariability. Determining the specific answers is a statistical problemwhich is covered well in ACI 318. It should also be noted that in theCommentary for ACI 318, it states that if the standard deviation isdetermined using cement from only one source, the data is valid only forcement from that source.

CONCRETE POLES DESIGN 25 It should be pointed out that although concrete strengthsare usually determined and specified at 28 days, there is no hard andfast rule that this particular age must be adhered to. Any otherreasonable time such as 56 days or 90 days may be specified by themanufacturer but, per ACI 318, the test age shall be indicated in thedesign drawings or specifications. 3.8.3.4 Use of Core Tests

In the case of spun poles which have thin walls and largeamounts of steel, it is not usually possible to take a core sample thatmeets the ASTM requirements for overall size and dimensional ratios.Therefore the use of core samples to determine concrete strength in spunpoles is inappropriate. 3.8.3.5 Requirements for Tensioning Steel Most prestressing steel is tensioned with hydraulic ramsand the tension in the steel can be directly related to the hydraulicpressure in the ram. Under the provisions of ACI 318 and PCI MNL 116the rams must be calibrated with a direct measurement of the tendonelongation and any differences in excess of 57. must be ascertained andcorrected.3.9 Inspection The purpose of the manufacturer's pole inspections is to insurethat the pole that is delivered to the construction forces has beenproperly fabricated and shipped. The inspection is largely visual,although a Schmidt Rebound Hammer can be utilized to give a rough ideaas to the uniformity of the strength of the concrete within a pole oramong a group of poles. It should not be expected to provide informationas to the absolute strength of the concrete. A complete visual inspection would include: Check the appearance of the surfaces of the pole for soundness of the concrete and possible spalling of the concrete as well as the color. Minor honey-combing, surface spalling and mold seam-line bleeding is normally acceptable if the structural strength is not impaired. Check the straightness of the pole. Be sure that the holes are properly located. Insure that all items that are supposed to be attached to the pole are indeed there and in good condition. Note the existence of cracks, if any, and determine the significance of such cracks. The most common question to arise during inspections is thesignificance of different types of cracks. It should be pointed out that

26 CONCRETE POLES DESIGNnot all cracks are detrimental to the product and, indeed, poles areexpected to crack under certain conditions. Hairline cracks, although they may be quite visible during timeswhen the pole has been wet and is surface dry, will probably not cause aproblem with long term durability. It is not likely that oxygen ormoisture will enter hairline cracks to cause degradation of either theconcrete or the steel. If a crack is opened wide enough to accept an ordinary sheet ofpaper (approximately 8 mils), it should be sealed to keep moisture out.Wide cracks are unacceptable except within one or two feet of the bottomof the pole which will be buried. Cracks within one or two feet of the ends of poles may occur duringthe detensioning process. Unless they are open cracks, they will notcause structural problems. Those cracks that are buried will never be aproblem. If there is concern about sufficient moisture penetratingcracks near the top of the pole to cause freeze/thaw damage, thosecracks can be waterproofed. Structurally, they are not a problem unlessa very large moment is to be applied to the end of the pole. Longitudinal cracks (other than hairline cracks) are generallyundesirable. Circumferential cracks that do not close generally indicatethat the steel has been stretched beyond its elastic limit. If that isdetermined to be the case, the pole will no longer perform the job forwhich it was intended and should not be used. 4.0 LOAD TESTING4.1 General The ultimate check on the adequacy of the entire design andmanufacturing process is the full scale test. Poles may be tested ineither a horizontal or an upright position. If only the pole is beingtested, a horizontal test is entirely satisfactory and easier than anupright test. In instances where the pole is being tested as a part ofan entire structure, it is likely that the entire assembled structurewill need to be tested in the vertical position. A pole structure test should be considered a guide to good struc-tural design practice. The contract documents shall designate theorganization that is responsible for the structural design specifica-tions set forth in the contract. Overall responsibility for the struc-ture testing should lie with one person representing this organization.This person should be totally familiar with the structure's design andapprove the proposed procedure for structure testing. Also, this personshould be present at all times during the testing sequence and approveeach decision made during the process. The single person having theseresponsibilities shall be called the Responsible Test Engineer. In a traditional proof test, the test set up is made to conform tothe design conditions (i.e. only static loads are applied), the struc-ture has level, well-designed foundations and the restraints at the load

CONCRETE POLES DESIGN 27points are the same as in the design model. This kind of test willverify the adequecy of the main components of the structure and theirconnections to withstand the static design loads specified for thatstructure as an individual entity under controlled conditions. Prooftests provide insight into actual stress distribution of unique config-urations, fit-up verification, performance of the structure in a de-flected position and other benefits. The test cannot confirm how thestructure will react in the transmission line where the loads may bemore dynamic, the foundations may be less than ideal and there is somerestraint from intact wires at the load points. Paragraphs 4.2 through 4.14 present guidelines based on performinga proof test using a test frame that has facilities to install a singlestructure in an upright position, to load and monitor pulling lines inthe vertical, transverse and longitudinal directions and to measuredeflections. Guidelines for a horizontal test are presented in Paragraph 4.15.4.2 Foundations It is unlikely that soil conditions at the test site will matchthose at the installation site. Fortunately, if a few precautions aretaken, it will make very little difference to the test results. 4.2.1 Single Pole Structures The primary consideration in designing and installing a singlepole foundation is to be able to control the ground line rotation so asnot to exceed the allowable design rotation. For test purposes, theactual amount of rotation makes very little difference within a widerange except under very heavy vertical loads where secondary moments canbe significant. 4.2.2 H-Frame Structures Normally for an H-Frame, the critical point in the structureis at the top of the cross brace. The magnitude of the ground line ro-tation has very little effect on the structure at the top of the crossbrace. It is important, however, that the uplift and down-thrust beadequately contained so that the structure does not suffer prematurefailure due to unanticipated loads as a result of twisting thestructure.4.3 Material The test structure should be made of materials that are repre-sentative of the materials that will be used in the production struc-tures. Mill test reports and other test results should be available foreach important member in the test structure. All test structure materialshould conform to the minimum requirements of the material specified indesign.

28 CONCRETE POLES DESIGN4.4 Fabrication Fabrication of the prototype structure for testing shall be donein the same manner and to the same tolerances and quality control aswill be done for the production structures.4.5 Stress Determination Stress determination methods, primarily strain gauging, may be usedto monitor the loads in individual components during testing.4.6 Assembly and Erection The test structure should be assembled in accordance with the manu-facturer's recommendations. It may be desirable to specify detailedmethods or sequences for the test structure to prove the acceptabilityof proposed field erection methods. Pick-up points designed into thestructure should be used during erection as part of the test procedure.The completed structure should be set within the tolerances permitted inthe construction specification. After the structure has been assembled, erected and rigged fortesting the user or his designated representative should review thetesting arrangement for compliance with the contract documents. Safety guys or other safety features may be loosely attached to thetest structure and used to minimize consequential damage to the struc-ture or to the testing equipment in the event of a premature failure,especially if an overload test to failure is specified.4.7 Test Loads The loads to be applied to the test structure shall be the loadsspecified for design and should include all appropriate overload fac-tors. Wind-on-structure loads are normally applied in a test as concen-trated loads at selected points on the structure in a pattern to make apractical simulation of the in-service uniform loading. The magnitudesand points of application of all design loads should be developed by thestructure designer and approved by the user before the test.4.8 Load Application Load lines shall be attached to the load points on the test struc-ture in a manner that simulates the in-service load application as muchas possible. The attachment hardware for the test shall have the samedegrees of movement as the in-service hardware. V-type insulator strings shall be loaded at the point where theinsulator strings intersect. If the insulators for the structures inservice are to be a style that will not support compression, it isrecommended that wire rope be use for simulated insulators in the test.If compressed or cantilever insulators are planned for the structures,members that will simulate those conditions should be used. As the test structure deflects under load, load lines may change

CONCRETE POLES DESIGN 29their direction of pull. Adjustments must be made in the applied loadsso that the vertical, transverse and longitudinal vectors at the loadpoint in the deflected shape are the loads specified in the structureloading schedule. Test rigging should be designed with an adequate safety factor forthe specified test loads.4.9 Loading Procedure The number and sequence of load cases tested shall be specified bythe structure designer and approved by the user. It is recommended totest first those load cases having the least influence on the results ofsuccessive tests. Secondly, the sequence should simplify the operationsnecessary to carry out the test program. Loads are normally incremented to 50, 75, 90 and 100 percent of themaximum specified load and to the load at which the concrete firstcracks (usually in the range of 50 to 60 percent). If the test facilitydoes not have the capability for continous recording of loads, an ad-ditional increment to 95 percent may be added. After each increment isapplied there shall be a hold to allow time for reading deflections andto permit the engineers observing the test to check for signs of struc-tural distress. The maximum load for each load case shall be held forfive minutes. Loads should be removed between load cases except that in some non-critical situations, with the permission of the Responsible TestEngineer, the load may be adjusted as required for the next load case.Unloading shall be controlled to avoid overstressing any members.4.10 Load Measurement All applied loads shall be measured as close to the point ofapplication to the test structure as possible. Loads shall be measuredthrough a suitable arrangement of strain devices or by predetermineddead weights. The effects of pulley friction should be minimized. Loadmeasurement by measuring the load in a single part of a multi-part blockand tackle arrangement should be avoided. Strain devices shall be usedin accordance with manufacturer's recommendations and calibrated priorto, and after the conclusion of the testing sequence.4.11 Deflections Structure deflections under load shall be measured and recorded.Points to be monitored shall be selected to verify the deflectionspredicted by the design analysis. Deflection readings shall be made forthe before-load and load-off conditions as well as at all intermediateholds during loading. All deflections shall be referenced to common basereadings, such as the initial plumb positions, taken before any testloads are applied. Upon release of test loads after a critical load case test, astructure will normally not return fully to its undeflected startingposition. The testing specifications should state how much deviation is

30 CONCRETE POLES DESIGNacceptable.4.12 Failures Following the provisions of Paragraph 1.3, the decision will havealready been made as to whether failure occurs when there is a per-manently deformed structure or when the structure collapses. If a premature structural failure occurs, the cause of the failuremechanism shall be determined and corrected. Failed and damaged membersshall be replaced. The load case that caused the failure shall be re-peated. Load cases previously completed need not be repeated. After the structure has successfully withstood all load cases, andassuming that the structure was not tested to destruction, the structureshall be dismantled and all members inspected.4.13 Disposition of Test Structure The test specification should state what use, if any, may be madeof the test structure after the test is completed. Undamaged componentsare usually accepted for use in the line. If an overload test to failurehas been performed, caution should be exercised in accepting the partsthat appear to be undamaged since they may have been overloaded.4.14 Report The testing agency shall furnish a test report in the number ofcopies required by the job specifications. The report should include: a. The designation and description of the structure tested. b. The name of the utility that will use the structure. c. The name of the organization that specifed the loading and test arrangement of the structure. d. The name of the Responsible Test Engineer. e. The name of the fabricator. f. A brief description and the location of the test facility. g. The names and affiliations of the test witnesses. h. The dates of testing each load case. i. Design and detail drawings of the structure including any changes made during the testing program. j. A rigging diagram with detail of the point of attachment to the structure. k. Calibration records of the load measuring devices.

CONCRETE POLES DESIGN 31 1. A loading diagram for each load case tested. m. A tabulation of deflections for each load case tested. n. In the case of a failure: Photographs of the failure. Loads at the time of failure. A brief description of the failure. The remedial actions taken. The physical dimensions of the failed members. Test coupon reports of failed members, if required. o. Photographs of the overall testing arrangement and rigging. p. Air temperature, wind speed and direction, any precipitation and other pertinent meteorological data. q. Mill test reports. r. Additional information specified by the Purchaser.4.15 Horizontal Testing 4.15.1 General Horizontal testing is primarily used to test free standingsingle pole structures. A majority of the previous paragraphs of thissection apply also to horizontal testing. A full scale nondestructivehorizontal test should verify the structural integrity of the pole towithstand the maximum design stresses. All critical points along thepole shaft should be tested to maximum design load. 4.15.2 Test Arrangement The structure is normally placed in a horizontal position asshown in Figure 4.1 or 4.2. One or more locations along the shaft willbe selected as the load pulling points. The purpose of the load pull(s)will be to duplicate maximum design stress at all critical points in thepole shaft based on the cross sectional geometry of the shaft and yieldstrength of the materials. (Critical points are those points on theshaft with the highest stress.) The design moment for the shaft will beless than the test moment. Additional bending moment is needed toaccount for axial, shear and torsional stresses that cannot be applieddue to the test configuration. 4.15.3 Equipment Used in the Test The load(s) are pulled at predetermined point(s) along theshaft by crane(s) or other suitable pulling structures. Loads shall bedetermined with calibrated load cell(s) located in the pulling line. Atransit should be set up away from the test structure and used to makethe deflection measurements.

32 CONCRETE POLES DESIGN 4.15.4 Test Procedure for Pole Test - Vertical Pull (Fig. 4-1) 4.15.4.1 Dead Load Pickup Before the test begins, the actual weight of thestructure should be known. When in a horizontal position, the deadweight of the structure will cause a bending moment in the pole shaft. The procedure should consist of picking the structure upat the pull point(s) to determine loads while the other end just restson the compression pad. The calculated reaction(s) at the pull point(s)should correspond fairly closely to the actual load cell reading inorder for the remainder of the test to be considered accurate. 4.15.4.2 Design Load Test With the structure in a horizontal position and the deadload pickup completed, loading should continue to engage the hold downstrap. Incremental loads should then be pulled, as indicated in the testrequirements, with deflection readings being taken at predeterminedpoints along the structure and the uplift and compression points. Eachincremental load will be held for the required time before proceeding tothe next load increment. After testing the structure, it should beunloaded to "Dead Load Pickup" so that final deflection readings can betaken. A final inspection will be made on the shaft for any damage. 4.15.5 Test Procedure for Pole Test - Horizontal Pull (Fig. 4-2) The pole is placed between the reaction blocks and locked inplace. One or more wheeled support devices shall be used to support theweight of the free end of the pole. An initial load of at least 10% ofthe maximum test load should be applied to "set" the pole into theblocking. When the "setting" load is removed, the zero position is thenestablished from which to measure subsequent deflections. It is very important for obtaining accurate results, that thewheeled support device operate with a minimum of friction. Ideally theset-up includes steel wheels with bearings or steel rollers, either ofwhich roll on steel plate. All of the rolling surfaces must be kept freeof debris. 5.0 Assembly and Erection5.1 General As a point of reference, spun, prestressed concrete poles arehandled during construction very similarly to wood poles. As with polesof other types, they can be damaged or broken if they are abused, butthey will withstand much more abuse than steel poles and roughly theequivalent abuse of wood poles. One advantage of concrete poles is thatif they are damaged during construction, it is usually obvious, whereasthere is the possibility of cracking a wood pole and never knowing that

it is cracked. Be sure to check construction drawings for any specialhandling instructions.

34 CONCRETE POLES DESIGN5.2 Handling One of the most critical handling phases for any pole is lifting itclear of all supports while it is in the horizontal position because themoment generated by its own weight may be significant. Since concretepoles tend to be heavier than other types, more attention must be paidto the manner in which they are lifted. Some poles are designed to be lifted with a single point pick atthe center of gravity and some require multiple point picks. It is themanufacturer's responsibility to provide the user with lifting instruc-tions for their particular poles and it is the user's responsibility toinsure that those instructions are relayed to the construction forces.5.3 Hauling Common sense is important in determining good hauling practices. Aparticular set-up that may be highly acceptable for hauling over asmooth paved highway may be entirely inappropriate for hauling the sameload over a plowed and frozen field. In general, no more than 1/3 of thelength of the pole should be unsupported and, if the terrain conditionsindicate that the pole will be handled roughly, the unsupported lengthshould be less than that. In those instances where hauling equipment cannot be driven ad-jacent to the setting location, it may be necessary to drag the polealong the ground. Concrete poles will withstand this abuse as well aswood poles. If hardware is already attached to the pole, it will benecessary to secure the pole in such a manner as to keep it from rollingaround its longitudinal axis as it is dragged. As is expected with thedragging of any pole, common sense is required to avoid damage to thepole. The construction forces are responsible for the proper handling ofpoles and if they do not have any handling instructions or if the in-structions are unclear, they are responsible for contacting the user forthe necessary information.5.4 Framing Concrete poles are generally framed like wood poles, (i.e. with theuse of through bolts) but they will be easier to frame than wood polesbecause the holes can be more accurately drilled. Bolts should be tight-ened according to the assembly drawings but in the absence of any tight-ening instructions, reference to paragraph 2.11 of this guide and somecommon sense will work well. In most cases, the bolts will generallybreak before any damage is done to the poles. Near the ends of the pole,however, it is possible to tighten the bolts to the point where longitu-dinal cracks develop. If this occurs, loosen the bolts slightly but besure they are still snug. Again, normal construction techniques such as raising the polewith a single choker at the erection pick point will present no pro-blems. The primary caution is that if the pole has to be moved and theentire pole is lifted clear of the ground, the same procedures used in

CONCRETE POLES DESIGN 35unloading must be followed again.5.5 Field Drilling Most concrete poles will be sent from the factory with the neces-sary holes already in place. Occasionally, however, it will be necessaryto drill one or more holes in the field. This can be easily accomplishedwith a rotary hammer drill, a carbide tipped bit of the appropriate sizeand a cutting torch. First determine which of the following two types ofpoles is to be drilled and then follow the appropriate set of instruc-tions . 5.5.1 Full Length Reinforcing Steel Some manufacturers determine the amount of steel required bythe ground line design moment capacity and carry that quantity of ten-dons throughout the entire length of the pole even though less steelcould be used in the upper parts of the pole. Since holes are normallydrilled in the upper parts of a pole where there is a considerableexcess of steel, it is permissible to cut limited numbers of strands inthe drilling process. CAUTION - DO NOT DRILL HOLES NEAR THE GROUND LINEFOR POLES USED IN SINGLE POLE TANGENT APPLICATIONS. DO NOT ERILL NEARTHE LOWER END OF THE TOP SECTION OF A TWO PIECE POLE AND DO NOT DRILLNEAR A CROSSBRACE ATTACHMENT IN H-FRAME CONSTRUCTION. These are theareas for which the steel requirements were determined and cutting thesteel in these areas may weaken the pole below its design requirement. If there is any question as to the advisability of cutting tendons,contact the pole manufacturer for guidance. By referring to the manufac-turer's drawings, it may be possible to find areas where drilling canoccur without cutting prestressing steel. Once it has been determined that it is permissible to drillthe pole, mark the location and drill with a rotary hammer drill and acarbide tipped bit. If steel is struck, stop drilling and burn the steelwith the cutting torch. Then continue drilling. For best accuracy, markthe pole on both sides and drill both sides toward the middle. Moldmarks, which are usually visible on the pole, make handy referencepoints from which to locate the hole on the opposite face of the pole. 5.5.2 Drop Out Reinforcing Steel As the need for steel decreases toward the top of the pole,some manufacturers stop a portion of the steel by dropping the tendonsout through the side wall of the pole or they may install additionalsteel in critical areas by the use of post tensioned strand. In thesemethods, there is not the excess of steel near the pole tops and thesteel should not be cut. This does not preclude drilling these poles. Itmeans, however, that care should be used to insure that steel is notcut. Since there is less steel in pole tops of this type, there is more space between the tendons and it is easier to miss the tendons duringthe drilling process but cutting a strand means that the pole may beweakened below its design strength. The actual drilling of these poles is accomplished in the same

36 CONCRETE POLES DESIGNmanner as for the previous poles. A cutting torch will still be neces-sary because even though the tendons are to be avoided, there is still ahigh probability of having to cut through the spiral steel. 5.5.3 Circumferential Steel Cutting of circumferential steel is difficult to avoid, but isacceptable at any time unless the pole is to be subjected to severe tor-sional loads.5.6 Field Cutting There will be occasions in which it is desirable to shorten a polein the field. This can be accomplished without damage to the pole bycutting with a small, hand held concrete saw and an abrasive cut offblade. The blade will cut both the concrete and the steel. For hollowspun poles, carefully mark a straight line around the circumference andsaw along the mark.5.7 Erection Concrete poles are erected in the same manner as other poles.Assuming that the poles were properly placed before they were framed, asingle point pick with a choker is usually permissible. The chokershould be placed well above the center of gravity unless the drawingsindicate that the pole can be single point picked at the center of gra-vity. This means that as the pole is raised from the horizontal, much ofthe weight stays on the ground until the pole is nearly in the verticalposition. Once it reaches the vertical position, it will not be damagedby lifting its full weight with a single point pick. Because the surface of a concrete pole is smooth and hard, safeoperations require use of the same choker techniques as for steel poles.IMPROPER USE OF CHOKERS CAN RESULT IN THE POLE SLIPPING AND CAUSINGINJURY OR PROPERTY DAMAGE. Chokers must be tight around the pole. If thechokers are slippery, they may be padded with a sticky material. Apositive stop against sliding can be provided by attaching the chokerbelow a solid piece of hardware (Note that a ladder clip does NOTqualify as solid hardware). Guyed poles, whether or not they are raked, should be initially setin what ever positions they will be under normal every-day loads. Thismeans that regardless of what ever bending and flexing occurs duringconstruction and long term use, once the conductor installation is com-plete and the guys are adjusted under normal everyday loads, the top ofthe pole should be in the same location as it was originally set.5.8 Climbing Concrete poles are climbed in the same manner as steel poles. Justas most steel poles are climbed with the standard climbing ladders, allof the manufacturers provide attachments to concrete poles to accomodatethe same ladders. Other climbing arrangements are also available and may

have been selected by the user.

CONCRETE POLES DESIGN 375.9 Field Inspections Questions about cracks in concrete poles are frequent. It should berealized that although some types of cracks may be detrimental, concretepoles are expected to crack under certain conditions. Circumferential cracks that do not close when the pole is eitherproperly supported on the ground or is erected, indicate a pole in whichthe steel has been stretched beyond its elastic limit and it should berejected. Circumferential cracks may open during construction or duringsevere service conditions but they usually all close once the severeloads are removed, and the pole has not been harmed as long as they doclose. Due to the process of releasing the tension on the steel inprestressed poles, circumferential cracks may develop within a fewinches of either end of the pole. Those at the bottom end may be ig-nored. Those near the top should be weatherproofed with epoxy or othercoatings, if they are not tightly closed. Longitudinal cracks are less common. At either end, they may havebeen caused by the application of prestress loads. If longer longitu-dinal cracks occur near the bottom of the pole, they have likely beencaused by stacking the poles. Longer longitudinal cracks near the topmay be caused by over tightening of the through bolts. As long as thecracks are only hairline cracks, as opposed to open cracks, they are notdetrimental to the long life of the pole. Any open cracks should be investigated for the cause and a deter-mination should be made as to the structural adequacy of the pole. If itis decided that the pole is to remain in service, the cracks should befilled and sealed from the weather to prevent further degradation of thepole. 6.0 Quality Assurance6.1 General Quality assurance is the responsibility of the user. At the time ofbidding, user should specify the degree of perfection he desires in de-sign, fabrication, structure testing and field construction. The extentof the quality assurance program may vary based on initial investiga-tions, the user's experience, the manufacturer's experience and pastperformance, and the degree of reliability required for the specificjob. The following guidelines may serve in preparing specificationswhich include a quality assurance program.6.2 Design and Drawings The quality assurance specification should indicate the degree ofinvolvment by user, and the procedure for review of the design concept,detailed calculations, stress analyses and the manufacturer's drawings.Stress analyses of the main structure and all of its component parts,

38 CONCRETE POLES DESIGNincluding all attachments and connections, should be considered. Thefabricator's drawings need checking to ensure they contain proper andsufficient information for fabrication and erection in accordance withthe requirements of the user's specification. (Refer to Section 2.0Design.)6.3 Fabrication 6.3.1 Materials The specification should include the requirement for reviewand agreement on the manufacturer's material specifications, his sourcesof supply, material identification, storage, traceability procedures andacceptance of certified mill test reports. (Refer to Sections 3.2 Con-crete and 3.3 Reinforcing Steel.) 6.3.2 Material Preparation The user may specify that either he or his agent inspect themanufacturer's equipment and process facility to ascertain that theprocedures are satisfactory, the tolerances are within specified limitsand the existing quality control program is satisfactory. (Refer toSection 3.8 Testing.) 6.3.3 Nondestructive Testing The specification should indicate the requirements for ac-ceptance of the type and procedure of all nondestructive testing andinspection programs employed during each step in the fabricationprocess. The user may specify that the manufacturer furnish copies oftesting and inspection reports. The user may also perform independentrandom sample testing to verify results of manufacturer's testing.(Refer to Section 3.9 Inspection.) 6.3.4 Tolerances It is necessary that acceptable fabrication tolerances bespecified and agreed upon by the purchaser and manufacturer. Goodfabrication quality is an important factor in minimizing field con-struction and performance problems. (Refer to Section 3.7 FabricationTolerances.) 6.3.5 Surface Coatings Where painting or other coloring is required, the system,procedures and methods of application should be acceptable to both theuser and the manufacturer. Also the system should be suitable for boththe product and its intended exposure. If galvanizing of accessories is required, the procedure andfacilities should be agreed upon by the user and the manufacturer. Aftergalvanizing, nondestructive testing may be specified to ensure thatthere have been no adverse changes to the finished product.

CONCRETE POLES DESIGN 39 When metallizing is required, the procedures and facilitiesshould be in accordance with coating supplier's recommendations andacceptable to both user and manufacturer. 6.3.6 Shipping Prior to the start of fabrication, the user should review thefabricator's methods and procedures for packaging and shipping. When receiving materials, all product should be inspected forshipping damage prior to accepting delivery. If damage is apparent, theuser should immediately notify the delivering carrier. If the shipmentsare FOB destination, making the manufacturer responsible for correctingdamages, the user should notify the manufacturer of any damage and co-operate with him in filing damage claims with the carrier. User is also responsible for checking to see that all mater-ials listed on the accompanying packing lists are accounted for. Where adiscrepancy exists, both the carrier and the manufacturer should benotified. 6.3.7 Quality Control A review should be made and agreement reached on all qualitycontrol programs, organizational setups and procedures. It is necessarythat rejection criteria be established and agreed upon prior to the start of any fabrication. (Refer to Section 3.8 Quality Control.) 6.4 Structure Testing Structure tests may be specified. The specification should indicatethe position of the structure in the test, the test procedures, methodsof load application, the load for each loading condition, and who is tobe the Responsible Test Engineer. Agreement is necessary on all testing equipment and metering devices used for calibration. All post-testing inspection, nondestructive testing and evaluation procedures should be acceptable to the user. The report of the structure testing should determine the acceptability of the structure as speci- fied. 6.5 Field Construction The user should review proposed construction quality control pro- grams and procedures to determine that all phases of field construction will comply with the requirements as specified in the user's specifi- cations and the manufacturer's designs and drawings; and to assure that adequate records are being maintained during construction such that there will be sufficient data provided to accept the completed work.

Appendix A BIBLIOGRAPHY1) ACI Committee 318, "Building Code Requirements for Reinforced Concrete (ACI 318-83)", American Concrete Institute, Detroit, 1983, 111 pp.2) ACI Committee 318R, "Commentary on Building Code Requirements for Reinforced Concrete (ACI 318R-83)", American Concrete Institute, Detroit, 1983, 155 pp. 3) National Electrical Safety Code, 1987 Edition, American National Standards Institute ANSI C2, Institute of Electrical and Electronic Engineers, Inc., New York, NY. 4) Guidelines for Transmission Line Structural Loading, Committee on Electrical Transmission Structures, American Society of Civil Engineers, New York, 1984, 166 pp. 5) Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals, AASHTO Subcommittee on Bridges and Structures, 1986. 6) EIA-RS-222-C, Electronic Industries Association Standard, March 1960. 7) PCI Design Handbook, Precast and Prestressed Concrete, Third Edition. Prestressed Concrete Institute, Chicago, 1985. 8) PCI Committee on Prestressed Concrete Poles, "Guide Specification for Prestressed Concrete Poles", PCI Journal, V. 27. No. 3, May- June 1982, pp. 18-29. 9) PCI Committee on Prestressed Concrete Poles, "Guide for Design of Prestressed Concrete Poles", PCI Journal, V. 28, No. 3, May-June 1983. pp. 22-87.10) Task Committee on Steel Transmission Poles, "Design of Steel Transmission Pole Structures", Committee on Analysis and Design of Structures, ASCE Structural Division, 1978.11) Manual for Quality Control for Plants and Production of Precast and Prestressed Concrete Products, MNL-116-85, Prestressed Concrete Institute, Chicago, 1985.12) "State of the Art - Prestressed Concrete Poles", PCI Journal, Vol. 29, No. 5, Sept-Oct 1984.

41

Appendix C DEFINITIONSCASTING METHODS Precast Member - A member which is cast in some location other thanthe location in which it is to be used. All poles are likely to be pre-cast. Spun Cast Member - A member cast in a mold that spins during theconsolidation phase. The resulting centrifugal force causes the pole tobe hollow and the concrete to be highly consolidated. Since this forceis very large, dry (low water/cement ratio) concrete can be consolidatedin this manner, usually with some of the water spinning out to reducethe water/cement ratio even further. Because spun concrete has a lowerthan normal water/cement ratio and a higher than normal density it ismuch stronger and more durable than static cast concrete. The end resultis that the member can be lighter because less concrete is required whenit is stronger. The concrete is much more impermeable and, therefore,more durable. Static Cast Member - A member which is cast in a mold that does notmove during the casting and consolidating of the concrete (except forthe possibility of vibrating the mold as an aid in consolidating theconcrete).LOADINGS Maximum (Ultimate) Design Load - The load that the pole is designedto resist. This load is the maximum service load multiplied by someoverload factor. The user must select not only the load and the loadfactor, but also must determine whether the pole is to resist the maxi-mum design load without permanent unacceptable deformation (damage) orwithout failure (collapse). A stronger pole is required to resistwithout permanent deformation than without collapse. Maximum Service Load - The maximum load that the pole is everexpectedto encounter (exclusive of overload factors). This load may beused for checking deflections and clearances. Normal Everyday (Frequent Condition) Load - A load that a pole maybe expected to encounter on a frequent basis. User should specify thenormal everyday load.MOMENTS ultimate Moment - Depending on the user's choice as to whether thepole must resist permanent deformation or collapse, this is the momentat which the chosen one of these events occurs. The moment capacity ateach section must be equal to or greater than the ultimate moment pro-duced in the section by the maximum design loads. 45

46 CONCRETE POLES DESIGN Damage Moment - The maximum allowable moment at a section withoutcreating permanent, unacceptable deformation in the section. Note thatunder one of the possible assumptions in the previous definition, damagemoment and ultimate moment may be the same. Cracking Moment - The moment at a section when the concrete firstcracks. Although this moment is of little significance from a design anduse standpoint, it is useful in helping to determine the overall accu-racy of the design and manufacturing processes. During testing of acompleted pole, the concrete should not crack earlier than the antici-pated cracking moment. No Concrete Tension Moment - The maximum moment a section canwithstand without allowing the concrete to go into tension. The magni-tude of the pretensioning forces is the primary controlling factoraffecting this moment. The No Concrete Tension moment capacity of anysection must be equal to or greater than the moment caused at thatsection by the normal everyday loads.REINFORCEMENT Ordinary Reinforced Concrete - Concrete in which the reinforcingsteel(normallymildsteelrebar) is simply placed in its designedlocation. It is not used to impart a compressive force across the con-crete section. Partially Prestressed Concrete - Concrete in which some of thereinforcing steel is conventionally placed and some of it is stretchedin such a manner as to impart a compressive stress in the concrete. Thisresults in a member in which the concrete has some compressive forceunder a no-load condition, but not as much as a fully prestressed mem-ber, with the end result that cracks will appear at a larger moment thanin an ordinary reinforced member but at a smaller moment than in a fullyprestressed member. Prestressed Concrete - Concrete in which all of the primary rein-forcing steel is used to impart a compressive stress to the concretebefore the member is subjected to the loads it was designed to handle.Thus, under bending loads, a much larger load must be applied to themember before the internal compressive stress in the concrete is over-come and the concrete finally goes into tension and cracks. Since largerloads are required to open cracks, the cracks are open less often (if atall) during the life of the member and the member does not deterioratedue to the elements. Further, when the loads are removed from the mem-ber, the cracks close tightly due to the tension in the steel. Prestres-sing steel is special, very high strength steel (either strand or wire)which is stretched before it is bonded to the concrete. After it isbonded to the concrete, it is the spring action of the steel thatsqueezes the concrete and causes its initial compressive stress (pre-stress).

DEFINITION 47

TENSIONING Post Tensioned Member - A prestress member in which the concrete ispoured and cured without tensioning the steel. Usually ducts are castinto the concrete to keep the steel from bonding to the concrete or toprovide a space for placement of the steel after the concrete is cured.In this method, the steel is initially stretched against the cured con-crete itself rather than against the molds or bulkheads. The advantageof post tensioning is that bulkheads or heavy stressing molds are notrequired. The disadvantage is that it requires more work in manufac-turing. Pretensioned Member - A member in which the prestressing steel isstretched against bulkheads or the mold while the concrete is cured andforms its bond with the steel. When the steel is cut loose from the endsupports, the bond between the concrete and steel allows the steel toimpart the prestressing load to the concrete.