Concrete Poles

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Guide for the

Design and

Use of

CONCRETE

POLES

Prepared by the

Concrete Pole Task Committee of the

Committee on Electrical Transmission Structures

of the Structural Division of the

American Society of Civil Engineers

April 1987

Published by the

American Society of Civil Engineers

345 East 47th Street

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PREFACE

A Task Committee of the Committee on Electrical Transmission Structures was formed in

1984 to prepare a concrete pole design and use guide. The Task Committee has produced this

Guide which brings together in one document, as much information as time and the collective

knowledge of the Task Committee permits. No claim is made that this document is complete as

it stands. Through future use, additional thoughts and ideas will be identified that should be

included. Hopefully this will be a living, working document that will be updated as additional

knowledge becomes available.

The potential exists for the proliferation of Design Guides and Standards written under the

auspices of various organizations. There are already documents relating to concrete poles that

have been published by IEEE, ASTM and PCI and all of them refer to ACI-318. Now comes

ASCE with its document. Such a proliferation soon becomes both confusing and counterproductive if there is no coordinating force.

This Task Committee was chosen carefully to include people that were not only knowledgeable in the field of concrete poles, but who were also active in IEEE, ASTM, PCI and

AC1. Indeed, not all of the Task Committee members are members of ASCE. It is the hope of

the Task Committee that this Guide will be jointly endorsed by all of these organizations as a

focal point for information on concrete poles. The intent is not to usurp the prerogatives and

responsibilities of the other organizations, but for this committee to serve as a coordinating

group to insure that other documents do not become overlapping and contradictory.

The Task Committee recognizes that there are areas in which information is lacking or

incomplete. There is certainly work that needs to be done under the auspices of ASTM. We hope

to be able to work with that committee to develop the necessary techniques and knowledge to be

able to write testing standards associated with the manufacture of concrete poles. The committee

also recognizes the need for research into some areas in which there is an abysmal lack of

knowledge. It is hoped that somewhere in the industry, this research can be funded and

undertaken with the results being available for the good of the industry. Users of this Design and Use Guide are encouraged to ask questions or send comments and

information that should affect the content of the Guide. Since neither the chairman nor the

committee as a whole intend to abandon the project, comments and questions may be addressed

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to the chairman for consideration in future meetings. Anyone with a strong interest in becoming

a committee member should contact the chairman.

Respectfully Submitted.

Concrete Pole Task Committee

Steven Bull Dennis Mize William Ford Tarun Naik Fouad Fouad Robert Roane Tim Hardy Thomas Rodgers, Jr.

Samuel Hogg Vincent Schuster Michael McCafferty Jerry Tang

William Mickley William Howard. Chairman

Committee on Electrical Transmission Structures William M. Howard Ronald E. Randle John D. Mozer Gene M. Wilhoite

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CONCRETE POLE DESIGN AND USE GUIDE William M. Howard

Committee Chairman INTRODUCTION

This guide presents the generally accepted procedures for the design, fabrication, inspection, testing and installation of concrete poles. It addresses poles which are either spun cast or statically cast and which are prestressed, partially prestressed or conventionally rein-forced. The primary emphasis is on spun, prestressed poles which are widely recognized as the ultimate in light weight and durability. Most prestressed poles are of the pretensioned variety and, therefore, post tensioned poles receive little attention in this guide. Also, although many uses for concrete poles are recognized, the guide is heavily weighted 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 updates of this guide.

Many portions, but certainly not all, of ACI-318 and ACI-318R are applicable to concrete poles and various references to ACI— 318 will be made. It is intended that the definitions and notations used in this guide are consistent with those used in ACI-318. (See Appendix B of this Guide for Notations used herein.)

This guide is performance oriented. It presents certaip theories and methods that are generally recognized as good practice, but allows for innovative and unique circumstances to be fully acceptable upon presentation 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 new methods, nothing should stand in the way of implementing such methods. This philosophy is consistent with Commentary on ACI 318-83 in which paragraph 18.4.3 states, "This section provides a mechanism whereby development of new products, materials, and techniques in prestressed concrete construction need not be inhibited by limits on stress which represented the most advanced requirements at the time the code provisions were adopted".

*

President, Power Line Systems, Inc., 6701 Seybold Road, Madison, WI 53719

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2 CONCRETE POLES DESIGN

1.0 INITIAL DESIGN CONSIDERATIONS

This section is written especially for the user. It specifically details the information which users should include in their specifi-cation to allow the structure designers to properly and efficiently accomplish their tasks.

1.1 General

The structure design requires consideration of many aspects including loading, fabrication techniques, method of shipment, con-struction and maintenance methods, terrain, types of foundations, corrosion, structural and electrical geometry and clearances, local restrictions and codes.

The user is to select the necessary structure design loading criteria. Structure loading may use /d^ta furnished in the ANSI C2 "National Electrical Safety Code" (NESC)'-' the ASCE "Guidelines for Transmission Line Structural Loading" , AASHTO "Standard Specifica-tions fofcStructural Supports for Highway Signs, Luminaires and Traffic Signals" , Electronic Industries Association (EIA) Standards or independent selections based on known local environmental conditions (such as high winds or heavy ice conditions).

When using the ASCE "Guidelines for Transmission Line Structural Loading" an exclusion limit is required for pole strengths. Each manu-facturer should conduct a full scale testing program to develop its own values for the exclusion limit. (The exclusion limit is simply the per-centage of poles that fail at less than nominal design strength.) In the absence 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 load trees, using an orthogonal coordinate system as shown in Figure 1-1 on the next page. Conductor and shield wire loads should be shown at the conductor and shield attachment points. The weight of the hardware and insulators should be included in these loads. Wind on structure should be expressed in psf (pounds per square foot). Loads should be ultimate including all safety and overload factors.

1.3 Determination of Performance Requirements

Poles are designed by the ultimate strength method, to resist the largest factored load. It is the user's responsibility to determine if the word "resist" means to resist the maximum loads without permanent, unacceptable deformation (damage) to the pole, or if it means to resist the loads without failure (collapse) of the pole, recognizing that it requires a stronger pole to resist damage than to resist collapse. In the case of a damaged pole, the steel will have been stretched beyond its elastic limit and/or some concrete will have spalled off the pole. The pole will be permanently deformed, will no longer perform as it was designed to, and will need to be replaced; but it is still maintaining

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the conductors in such a configuration that the line remains energized. A pole which has collapsed is one which has reached such a state that the 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 to consider deflections under "normal everyday" loads. A pole with large deflections under such conditions is undesirable. User should specify what loads are to be considered "normal everyday".

1.5 Longitudinal Loading

Because of the possibility of catastrophic cascading failure, the most important loading condition to be evaluated for any transmission line is that caused by the simultaneous loss of tension on all condu-tors. For pole type self-supporting structures, the deflection of the structure itself, will provide a significant tension reduction in the wires. The length of suspension insulator strings can also greatly influence the structure loading under unbalanced longitudinal loading conditions since the decrease in tension caused by the swing of long insulator strings can be significant. Both of these factors should be included in the unbalanced loading condition as long as proper consid-eration is given to any impact loading imposed on the structure. For longitudinal loading calculations, spans used should approximate actual line spans.

A longitudinal analysis is particularly essential when comparing alternate designs and materials because it is necessary to be sure that the alternates being considered are, indeed, equivalents. For example, a lattice 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 poles make them more resistant to cascading failures than are structures made of other materials.

Under individual broken conductor conditions, restraint will be offered to the structures by the intact wires. Calculations should properly reflect the structure deflection and insulator swing, and the resulting change in wire spans and tensions.

Proper evaluation of the effects of broken conductors requires the use of sophisticated computer programs. From such an analysis, an equiv-alent static load can be established for the design and testing of the structure. If testing of the structure does not confirm the expected deflections, additional evaluations should be made.

1.6 Geometry

The basic pole structure configuration, conductor and shielding geometry (i.e., horizontal, vertical, delta, single poles, H-frames, etc.), insulation assembly length, swing angles, electrical clearances

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CONCRETE POLES DESIGN 5

and shielding angle should be made clear to the structure designer. However, the structure designer should be allowed as much latitude as possible to determine the design details of the structure.

1.7 Foundations

Consider the type of foundation, foundation rotational allowance and 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 performance requirements for the combined pole and foundation installation. In determining this value, the user may consider aesthetics, phase-to-structure clearances, phase-to-ground clearances, phase-to-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 a refinement in analysis and design which allows the user to match types and probability of loads with foundation response. For instance, under rarely occurring conditions such as a 50-year extreme wind load, one might allow more foundation deflection and rotation than under more common loads with the expectation that the cost of occasionally straightening a structure will be less than the cost of stronger, more expensive foundations.

In the case where foundation rotation-deflection is specified, the manufacturer should include such effects in the calculations of final deflected 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 or other limitations imposed due to local codes or conditions.

1.9 Deflection 1.9.1 General

Structures must be analyzed for deflection to insure that they have adequate strength. The large deflections frequently observed in pole structures under horizontal loads cause additional stress due to the vertical loads being applied while the pole is in the final deflect-ed position. The stress analysis for this is coverdeflect-ed 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 pole deflections except, perhaps, on special long span or line angle condi-tions. The user must be aware of this possibility and must compensate for reduced clearances where they can occur. Clearances to the structure itself may be maintained by specifying certain combinations of conductor

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down drop and line angle at the structure and the required clearance. This clearance should be maintained to the deflected structure under the specified loading condition.

1.9.3 Appearance

Deflections can play an important part in the appearance of a structure. At line angles or where all vertical conductors are on one side of a pole structure, the constant load in one direction will cause the structure to bow and, if the pole was originally set vertically, it may appear to be near failure. There are several methods that can be used to compensate for this. One method is to rake the pole when setting it. The deflection at the top of the pole is determined for the everyday loading and the pole is tilted this predetermined amount so that, under the everyday loading, the top of the pole is vertical. In this case, the pole 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 be required.

Precambered poles are another possibility. It should be recog-nized, however, that the predictability of results in precambering concrete poles is poor, at best, and few manufacturers are prepared to precamber at all.

Finally, guys may be used to limit deflections. 1.10 Transportation and Erection

The design should consider equipment or access limitations and loads caused by methods of loading, unloading, hauling, assembly, erec-tion and stringing (including longitudinal load due to line snagging in traveller).

It should be kept in mind that the largest stress level a concrete pole may see in its lifetime can occur by lifting it clear of the ground while it is in a horizontal position, as is common in loading and un-loading. Indeed, the induced stresses can be so great that it may sometimes be necessary to require the use of multiple point picks to avoid 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 under the 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 the weight of the pole is supported on the ground until the pole is in an upright position. Since poles and structures are normally erected by lifting at a point well above the center of gravity, the pole butts remain on the ground until the pole is erect and excessive bending loads during erection are thus avoided.

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erection drawings, any restrictions to be observed by the contractor in the handling, transportation and erection processes. However, both users and manufacturers should realize that restrictions add to the cost of installation and should be kept to a minimum. For example, it may be desirable 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 of unusual handling procedures during construction.

Poles most likely to be susceptible to damage during transportation and erection are poles designed for light loading conditions, guyed poles, unusually long poles, poles with substantial weights in attached accessories and poles that must be lifted at or near their center of gravity. Unless the poles have been designed to withstand a single point pick at the center of gravity after complete assembly (including a 1.5 overload factor), special handling instructions should be clearly indicated on the erection drawings.

In general, then, it is usually the lifting of the entire pole weight while the pole is in the horizontal position that is the control-ling handcontrol-ling condition. This load is caused by the weight of the pole itself (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 the pole and attached accessories. It is also necessary for the user to specify whether the pole is to withstand a single point pick or whether multiple point picks can be required by the manufacturer.

1.11 Attached Items

User is responsible for informing the manufacturer what accessories are 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 or anchor types, guy angles, quantity of guys, placement tolerances and terrain considerations. The structure designer should be allowed as much latitude as possible in determining the details of the guying scheme to be used.

1.13 Climbing and Maintenance

Identify climbing, working and hot line maintenance provisions required.

The primary means of climbing concrete poles is with the same removable ladder system used to climb steel poles. This system is available from all pole manufacturers. Many other options are available if the user prefers. The particular method to be used will need to be discussed with the individual manufacturers since not all producers are prepared to offer all options.

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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 pole heights and classes. As more users and designers begin to treat concrete poles conceptually like wood poles for design purposes, the costs of both design and manufacturing will decrease substantially.

2.0 - DESIGN 2.1 General

For each loading condition considered, it is necessary to analyze the 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 material is to take advantage of the best attributes of both concrete and steel. Concrete is relatively inexpensive, excellent in compressive strength and, when properly made, is relatively unaffected by the environment. The primary disadvantage is its low tensile strength. Steel, on the other 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 tension zones of the member and to use the concrete to protect the steel from the elements. In some ordinary reinforced applications, steel may, on occasion, be used to resist compression.

2.2 Design Theory 2.2.1 General

As outlined in paragraph 1.3, concrete poles are designed by the ultimate strength method wherein the applied service loads are multiplied by overload factors and the pole is designed to resist the

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CONCRETE POLES DESIGN 9 largest factored load.

A pole Section should also be designed -so that normal everyday (frequent condition) unfactored loads will not cause the concrete to. go into tension. (See paragraph 1;.4)

2.2.2 Bending

The most common loading conditions for poles result in the pole being called upon to resist bending moments. When the bending moments are large enough, the concrete on the outside curvature of the pole will go into tension and, perhaps, crack.

Tangent poles (the most common case) designed according to NESC light, medium or heavy loading are unlikely to ever crack under service loads. The 2.5 overload factor used in these cases to determine the required ultimate strength, means that the service load is 40% of the ultimate load. Concrete in a prestressed concrete pole normally does not go into tension until the load is around 40% to 50% of the ultimate load. Thus the service load is about equal to or less than the load which causes the concrete to go into tension.

Where very low overload factors are used (such as are common in the 1.0 to 1.1 range for high winds), the poles will crack under the unfactored loads. However, since loads of such a great magnitude are applied to the pole seldom, if ever, opening of cracks under such loads will not occur often enough to be detrimental to the long term durability of the poles. Indeed, for tangent structures which have been properly designed for ultimate strength under factored loads, it is difficult 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 proach is impractical, unnecessarily restrictive and, ultimately, it

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cannot be guaranteed that the pole did not crack anyway.

2.2.2.4 The stress/strain relationships must be determined for the specific materials used. A balanced design is one in which the yield strain of the steel and the limit strain of the concrete are reached simultaneously. A balanced design produces the most efficient section.

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 may be intentionally allowed to exceed its elastic limit. Except in a rare case of a highly under reinforced section, the failure will occur in the concrete, and the steel will not rupture. This is due to the steel going into a plastic state, thereby picking up an ever increasing load; while the neutral axis moves toward the compression side of the section, which must 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 concrete poles. However, when unusually large vertical loads are encountered (e.g. large guyed loads or guys with short guy leads) it is necessary to check for a buckling condition, particularly on taller poles.

2.2.4 Shear

Shear is seldom a consideration in concrete pole design. For normal direct burial conditions, soil strengths dictate that the pole must be buried deeply enough to preclude shear problems. Normal burial depths will equal or exceed 10% of the pole length plus 2 feet and poles with such burial depths need not even be checked for shear. The critical conditions that bear checking occur when very large moments are applied near either end of the pole. For example, poles set into solid rock or buried into a concrete foundation socket, may not be buried very deeply, in which case, it is necessary to check for shear to ensure that the pole does not split lengthwise along the neutral axis due to exceeding the 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 the stresses occurring in a prestressed concrete pole which is subjected to simultaneous bending, column loading, prestress loading and torsional loading is so complex as to defy reasonable mathematical modeling. Only after extensive research will it be possible to develop mathematical formulas and prove them out to the point where they can be used with confidence. In the meantime, little can be done to assure proper per-formance under torsional loads other than to test a pole for those conditions that suggest the liklihood of significant torsional loads being applied.

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CONCRETE POLES DESIGN 11 2.3 Concrete Properties

2.3.1 Stress/Strain Relationships

Curves showing the relationship between stress and strain for concrete 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-high strength 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 318 provide a satisfactory basis for design parameters for concrete in the ordinary strength ranges. For higher strength concretes, ACI provisions may 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 strength in substantial agreement with the results of comprehensive tests". Manu-facturers are, therefore, expected to conduct "comprehensive tests" to develop their own stress/strain curves for any concrete with strengths beyond the applicability of ACI provisions.

2.3.2 Concrete Compressive Strengths - f

The specified compressive strength of the concrete (f ) is determined by the manufacturer based on a number of considerations (see discussion under 3.0 Fabrication) but should not be less than 5000 psi and preferrably 7000 psi or more.

Although concrete compressive strengths are conventionally determined at 28 days, it is not required that strengths be measured at that time, and the manufacturer should be allowed to specify strengths at later times to utilize the continuing growth in concrete strength which occurs over time. The use of longer times should, however, be clearly indicated at the time of bidding and on the drawings so that a pole is not fully loaded before the time that the concrete reaches its specified compressive strength.

2.4 Reinforcing Steel

2.4.1 Stress/Strain Relationships

Stress/Strain curves for steel do not vary as much as they do for concrete. These curves are provided to the pole manufacturers by the steel 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 the moment of collapse, ACI 318-83 paragraph 10.2.4 states that for non-prestressed reinforcing steel, the stress in the reinforcement that is below yield stress level shall be taken as E times steel strain. For s

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strains greater than that corresponding to f , stress in reinforcement shall be considered independent of strain and equal to f . Since prestressing sttand behaves differently than reinforcing steely the PCI Design Handbook suggests the following formulas for the stress/strain relationships of the prestressing steel:

When using a combination of prestressed and non-prestressed steel in a member, the provisions of ACI 318 shall apply.

2.4.2 Longitudinal Reinforcement

The primary purpose of longitudinal reinforcement is to resist the tension forces in the pole caused by bending moments applied to the pole and, in the case of prestressing steel, to impart prestressing loads into the concrete. The steel must be properly held in place during the placement, consolidating and curing of the concrete, so that proper concrete cover and steel to steel clearance is achieved. The methods used should be left to the manufacturer who may be called upon by the user to demonstrate the adequacy of its methods.

Longitudinal reinforcement is normally placed uniformly throughout a symmetrical cross section. It is possible to obtain some degree of increased strength about one bending axis, even though the cross section has a symmetrical shape, by placing the steel as far as possible from the axis about which the bending occurs. Such a technique is rare, however, because the additional strength which can be generated about 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 the pole, circumferential reinforcing is required throughout the full length of the pole. Theories to allow for good design practice are not well developed, particularly for prestressed pole sections. However, drawing upon common practice that generally provides satisfactory results, the ratio 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 of the pole. Because of prestressing loads near the ends of poles and possible shear or torsion loads, additional circumferential steel may be required. A spacing greater than 4 inches may be allowed if the

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turer presents evidence of satisfactory performance and user agrees. 2.5 Concrete Cover Over Steel

In addition to structural requirements, the purpose of concrete cover over steel is to protect the steel from corrosion. The thickness of cover required, may vary according to the degree of corrosiveness of the environment in which the pole will be used as well as the quality of the concrete and its ability to protect against the hostile environment. More cover provides greater protection only to the point where the steel cannot be attacked. Excess cover adds nothing to the durability of the pole but does add unnecessary weight and cost.

For static cast, ordinary reinforced concrete the provisions of ACI 318 apply for determining cover requirements.

In the case of static cast, prestressed concrete poles, ACI.g318-83 and the PCI "Guide Specification for Prestressed Concrete Poles" both call for 1 inch of cover. This appears to be consistent with other generally accepted practices and provides satisfactory results in most cases.

A review of specifications for spun concrete poles from widely differing parts of the world where they have many years of experience shows 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 be 3/4 inch over the primary steel with 5/8 inch being allowed over the spiral reinforcement. Lesser covers should be allowed if the manufac-turer can demonstrate through tests that its concrete is of extremely low porosity so as to protect the steel and develop structural strength with 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 ends of poles, the analysis of the development of the bond between concrete and steel is largely ignored. In circumstances where there are large moments near the ends of poles (e.g. a davit arm at the top of a pole, a joint connecting parts of a multi-piece pole or a pole set shallow into a rock hole) it is necessary to examine the bond development. It is also important to consider bond development in the event that some of the steel is cut by drilling holes in a part of the pole in which the steel is 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, longitudinal cracks may develop at the ends of the pole. If this occurs, it may be necessary to increase the concrete cover or the amount of spiral rein-forcement or both.

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14 CONCRETE POLES DESIGN 2.7 Prestress Loads

2.7.1 Steel

ACI 318 provides guidance as to allowable tensile stress in the prestressing tendons both at the time of application of the jacking force and immediately after prestress transfer. At jacking it allows 0.94 f but not greater than 0.85 f or maximum value recommended by the 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 the concrete immediately after prestress transfer (before time-dependent prestress 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 be exceeded if shown by test or analysis that performance will not be impaired.

2.7.3 Loss of Prestress

In the Commentary on ACI 318-83 paragraph 18.6.1 several references are cited which indicate how "reasonably accurate estimates of prestress losses can be easily calculated". It also points out that the accuracy of the calculations have little effect on the ultimate strength 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 anchorage seating, 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 the pole that is buried, the poles can be buried any convenient depth. The rule—of-thumb, which many engineers use as a left-over from their wood pole experience, is to bury the pole 10% of its length plus 2 feet. For lower strength concrete poles this may provide satisfactory results. However, since concrete poles are, in general, much stronger than wood poles, it follows that stronger (and presumably deeper) foundations would be in order. It is also necessary to determine whether it is more cost effective to use a conservative foundation design or to plan to straighten an occasional leaning pole. There is a tendency (which should be avoided) to penalize the cost of a concrete pole line in comparison to a wood pole line by using more stringent foundation criteria for concrete poles while using the old rule-of-thumb criteria for the wood poles.

As far as the integrity of the pole is concerned, any type of backfill is satisfactory. Many people use either native soil or crushed rock backfill. Some use concrete backfill but it is doubtful that the results are any different than with a well compacted granular backfill

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since either backfill is likely to be considerably stiffer than the surrounding natural soil. Concrete backfill has the advantage that it need not be compacted, but that advantage is likely to be more than offset 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 in relation to the foundation. The most common is to realize that the maximum moment in the pole occurs below ground and not at the ground line. Since most poles are tapered and their strength continues to increase below ground line, it appears quite safe and common to ignore the additional below ground moment and design the pole based on the moment at the ground line.

The other consideration comes up only rarely. If a pole is set in an unusually shallow manner (e.g. in a rock excavation or in a barrelled hole) the shear forces developed along the longitudinal neutral axis need to be considered to avoid having the pole split longitudinally at the 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 the ability of the soil to keep the pole from being forced further into the ground. In general, unguyed single poles do not need to have the bottoms of the poles plugged. Guyed poles either need the bottoms plugged or may need large bearing plates placed under the butt to resist the down load. For unguyed H-frames, uplift shoes that are commonly used may provide enough down load capability as well, to avoid the need for plugging the pole bottom. When uplift shoes are not used, plugging or bearing plates may be necessary in poor soil conditions.

2.9 Guyed Structures

To properly analyze a guyed structure, certain assumptions must be made regarding guy tensions and pole deflections. In the absence of clear directives to the contrary, it should be assumed that the axis of the pole will be straight under normal, everyday loads. This means that once the conductors are sagged, the guys will be adjusted so that the pole 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). For design purposes it will be assumed that there is no moment in the pole under a no wind condition at the specified temperature (60 degrees Farenheit if no other temperature is specified).

2.10 Grounding

It is apparent that concrete poles are sufficiently good conductors that 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, but how to best protect the pole, the operating system and people.

The reasonable choices are to use the steel in the pole as the exclusive path to ground or to place a separate ground wire down either the interior of a hollow pole or the exterior of any pole to carry some of the current to ground. If a separate wire is used, it should be

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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 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 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 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.

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It is recognized that low strength bolts are not usually preten-sioned. However, this recommended tightening procedure will both keep the bolts tight and protect the pole from damage by over tightening. For shear connections in which the bolt will bear against the side of the through hole, the maximum bolt bearing load will be determined by multiplying the diameter of the bolt times the wall thickness times f . In the absence of confirming tests, it is assumed that the bolt to concrete interface carries all of the load and none of it is carried through friction. For solid poles (or hollow poles with very thick walls), a maximum effective wall thickness for calculating the bearing load is 3 inches.

2.12 Climbing Attachments

The primary means of climbing concrete poles is with the same removable ladder system used to climb steel poles. This system is available from all producers. Many other options are available if the user prefers. Per paragraph 1.13, the particular method to be used should be discussed with the individual producers if it is other than normal ladders since not all producers are prepared to offer all options.

It is recommended that every individual part of the climbing system where a lineman could conceivably place his foot should be able to with-stand a static load of 750 pounds without permanent deformation. In addition, any part of the climbing system which is considered to be a safety attachment point should be able to withstand without breaking, a load of 500 pounds dropped 18 inches.

2.13 Inserts

Inserts should be made of materials which will not deteriorate in the environment in which they are placed. Care should be taken to insure that the materials in the concrete, the insert and the bolt do not react unfavorably with each other.

The anchorage of the inserts in the concrete should be such that they do not pull loose under the design load or any unusual loads that could conceivably be applied. Preferrably they are designed and anchored in such a fashion that the bolts will break before the inserts pull loose.

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

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is necessary to insure that the reinforcing steel and the connection ap-paratus are properly anchored as a part of the pole (see discussion in section 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 a minimum, 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 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 are appropriate for use with concrete poles. The design of steel attach-ments, accessories and guys should follow applicable provisions of the ASCE Steel Pole Design Guide. Pieces made of wood, fiberglass, aluminum or other materials should be designed to meet established standards for those materials as appropriate to the intended end use.

3.0 FABRICATION 3.1 General

Since one of the primary reasons for using concrete poles is to achieve a long, maintenance free life as a support structure, it follows that the concrete and other materials should reflect the use of the finest available materials and workmanship. The design and manufacturing techniques should make use of the latest and best thinking in terms of producing durable and high strength concrete. Not only does the emphasis on high strength produce lighter poles, the various techniques and pro-cedures that produce high strength concrete also make for more durable concrete.

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

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concrete is being provided that meets the strength, durability and aes-thetic requirements of the specifications.

Only materials that are certified for specified properties shall be used. Certification of all materials shall be checked and in-house labo-ratory tests shall be performed on concrete ingredients before material is used. Traceability of material tests and certifications shall be maintained 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 C150 or shall be portland blast-furnace slag cement or portland-pozzolan ce-ment conforming to the requirece-ments of ASTM C595.

The provisions of ACI 318 address situations where sulfate resistant concrete is desirable. The use of Type II or Type V cements are sometimes specified. It is important to recognize that sulfate resistance is obtained in ways other than use of the two special types of cement. A low C.,A content in the cement is required. Type II is specified 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 or less. Many Type I cements meet these requirements. Also, the use of fly-ash can make Type I cements more sulfate resistant than the special types.

The user should specify the type of environment in which the pole is to be used and allow the manufacturer to determine the best mixes to be used.

3.2.2 Aggregates

The aggregates shall conform to ASTM C33 or C330 except that the requirements for grading shall not apply. The manufacturer will establish the gradation requirements for aggregates used in its own concrete, based on testing and experience. However, the maximum size aggregate shall be 3/4 of the clear spacing between reinforcing steel and the surface of the pole or between individual bars or wires.

Certain aggregates have undesirable reactions with alkali compounds. Tests and requirements to insure that aggregates are not alkali reactive are covered by ASTM C227, C289 and C295.

3.2.3 Water

Mixing water shall be free of oils, organic matter and other substances in amounts that may be harmful to concrete or reinforcement. It shall not contain chloride ions in excess of 500 PPM or sulfate ions in excess of 1000 PPM. In general, water from normal drinking supply will meet the requirements necessary to produce quality concrete.

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20 CONCRETE POLES DESIGN 3.2.4 Admixtures

Chemical admixtures shall conform to ASTM C494. Air-entraining agents shall conform to ASTM C260 and fly-ash or other pozzolanic admix-tures shall be in accordance with ASTM C618. Admixadmix-tures shall not con-tain chloride ions in quantities that will cause the total water soluble chloride ion content of the concrete to exceed 0.06% of the weight of the cement.

Other additives have been and will continue to be developed which are desirable to use for various reasons such as combatting chlor-ide attack or to color the concrete or to increase the strength and durability of the pole. Use of such additives should be permitted as long as the manufacturer submits satisfactory evidence to indicate that proper 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.

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CONCRETE POLES DESIGN21 3.3.4 Welding

Welding of prestress strand is not permitted except at exposed ends and only after the pretension has been released.

Mild steel reinforcing may be welded only near the ends of the pole.

Circumferential steel may be welded as long as sufficient strength remains after welding to meet design requirements. Where welds are to carry structural loads, they must meet the provisions of AWS Dl.l and develop suitable strength.

3.4 Accessories

Many accessories are available to be cast into or attached to concrete poles. Materials should meet the provisions of the following specifications:

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 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 be either cast, drilled or otherwise cut into the pole. Cutting of the steel in the pole is acceptable as long as the manufacturer warrants that the remaining strength in the pole meets or exceeds the design requirements. When steel is cut, it is not necessary to provide any

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particular protection from corrosion (except in the severe case where the pole will be placed in or immediately adjacent to salt water) since the probability of a detrimental level of corrosion occuring inside the holes is very small.

3.6 Finishing

The manufacturer's basic responsibility is to provide poles that meet or exceed the design strength requirements, that have a pleasing and workmanlike appearance and that have smooth, dense and hard surfaces that will not deteriorate in the elements. Patching will be acceptable provided that the structural adequacy and the appearance of the product are not impaired.

Many other custom services are available at a price. Items in this category include but are not limited to such things as plugging either or both ends of a hollow pole, providing a rain cap for the pole, cre-ating a special textured finish for the pole, installing hardware items on the poles in the factory, painting the pole, etc.

3.7 Fabrication Tolerances

Following is a list of tolerances that manufacturers usually meet in the normal course of business. Stricter tolerances can usually be met if 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 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 factorily.

Weight - Plus 20% and minus 10% except that, with the approval of the purchaser, poles heavier than 20% over the 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.

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Reinforcement Placement - Plus or minus 1/4 inch for vidual pieces and plus or minus 1/8 inch for the centroid of a group. Spacing of individual circumferential 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 tests on 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 certifications should be checked to insure that the cement is not only within the ASTM standards, 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 moisture content (ASTM C566) and a seive analysis should be run (ASTM C136). Weekly, Specific Gravity (ASTM C127) and Absorption (ASTM C128) tests should be performed.

3.8.2.3 Reinforcement

Mill certifications for the reinforcing steel should be checked 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 these is Air Content (ASTM C231). For static cast poles this test should be run on a daily basis. Since for spun poles most of the air is spun out anyway, the test is of lesser importance and can probably be run on a weekly basis as a means of keeping track of the uniformity of the concrete

The other test for wet concrete is Unit Weight (ASTM C138). This test should be run daily.

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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 be prepared to demonstrate through full scale testing, that the strength of the spun concrete samples are representative of the strength of the con-crete in the pole.

If the manufacturer wishes to take advantage of the higher strength of spun concrete in the pole, but still wishes to use static cast samples as the primary manufacturing control, he may choose to statistically correlate the static samples to pole strengths through full scale testing. Thereafter, the static samples may be the primary control, 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 the request of the user.

The manufacturer may use the results of static cast samples directly, without any correlation, but design strength may not exceed the test results achieved according to the ASTM specifications. In summary, it is recommended that the foregoing ASTM and ACI specifications be followed with the exception that the samples should be spun. Tests should be run either daily or for each 25 cubic yards of concrete, whichever occurs more often. Each test should consist of 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. The remaining sample is a spare in the event there is a^roblem with one of the 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 concrete and the concrete samples from batch to batch. In order to insure that the concrete in the pole is almost always at least as strong as the design strength (f ) it is necessary to manufacture concrete at an average strength Chat is greater than the desired design strength. In general, those manufacturers whose concrete has less variability can manufacture to a lower average strength than can those with greater variability. Determining the specific answers is a statistical problem which is covered well in ACI 318. It should also be noted that in the Commentary for ACI 318, it states that if the standard deviation is determined using cement from only one source, the data is valid only for cement from that source.

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It should be pointed out that although concrete strengths are usually determined and specified at 28 days, there is no hard and fast rule that this particular age must be adhered to. Any other reasonable time such as 56 days or 90 days may be specified by the manufacturer but, per ACI 318, the test age shall be indicated in the design drawings or specifications.

3.8.3.4 Use of Core Tests

In the case of spun poles which have thin walls and large amounts of steel, it is not usually possible to take a core sample that meets the ASTM requirements for overall size and dimensional ratios. Therefore the use of core samples to determine concrete strength in spun poles is inappropriate.

3.8.3.5 Requirements for Tensioning Steel

Most prestressing steel is tensioned with hydraulic rams and the tension in the steel can be directly related to the hydraulic pressure in the ram. Under the provisions of ACI 318 and PCI MNL 116 the rams must be calibrated with a direct measurement of the tendon elongation and any differences in excess of 57. must be ascertained and corrected.

3.9 Inspection

The purpose of the manufacturer's pole inspections is to insure that the pole that is delivered to the construction forces has been properly fabricated and shipped. The inspection is largely visual, although a Schmidt Rebound Hammer can be utilized to give a rough idea as to the uniformity of the strength of the concrete within a pole or among a group of poles. It should not be expected to provide information as 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 the significance of different types of cracks. It should be pointed out that

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not all cracks are detrimental to the product and, indeed, poles are expected to crack under certain conditions.

Hairline cracks, although they may be quite visible during times when the pole has been wet and is surface dry, will probably not cause a problem with long term durability. It is not likely that oxygen or moisture will enter hairline cracks to cause degradation of either the concrete or the steel.

If a crack is opened wide enough to accept an ordinary sheet of paper (approximately 8 mils), it should be sealed to keep moisture out. Wide cracks are unacceptable except within one or two feet of the bottom of the pole which will be buried.

Cracks within one or two feet of the ends of poles may occur during the detensioning process. Unless they are open cracks, they will not cause structural problems. Those cracks that are buried will never be a problem. If there is concern about sufficient moisture penetrating cracks near the top of the pole to cause freeze/thaw damage, those cracks can be waterproofed. Structurally, they are not a problem unless a very large moment is to be applied to the end of the pole.

Longitudinal cracks (other than hairline cracks) are generally undesirable. Circumferential cracks that do not close generally indicate that the steel has been stretched beyond its elastic limit. If that is determined to be the case, the pole will no longer perform the job for which it was intended and should not be used.

4.0 LOAD TESTING 4.1 General

The ultimate check on the adequacy of the entire design and manufacturing process is the full scale test. Poles may be tested in either a horizontal or an upright position. If only the pole is being tested, a horizontal test is entirely satisfactory and easier than an upright test. In instances where the pole is being tested as a part of an entire structure, it is likely that the entire assembled structure will 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 the organization 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 and approve the proposed procedure for structure testing. Also, this person should be present at all times during the testing sequence and approve each decision made during the process. The single person having these responsibilities shall be called the Responsible Test Engineer.

In a traditional proof test, the test set up is made to conform to the design conditions (i.e. only static loads are applied), the struc-ture has level, well-designed foundations and the restraints at the load

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points are the same as in the design model. This kind of test will verify the adequecy of the main components of the structure and their connections to withstand the static design loads specified for that structure as an individual entity under controlled conditions. Proof tests 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 the structure will react in the transmission line where the loads may be more dynamic, the foundations may be less than ideal and there is some restraint from intact wires at the load points.

Paragraphs 4.2 through 4.14 present guidelines based on performing a proof test using a test frame that has facilities to install a single structure in an upright position, to load and monitor pulling lines in the vertical, transverse and longitudinal directions and to measure deflections.

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 match those at the installation site. Fortunately, if a few precautions are taken, it will make very little difference to the test results.

4.2.1 Single Pole Structures

The primary consideration in designing and installing a single pole foundation is to be able to control the ground line rotation so as not to exceed the allowable design rotation. For test purposes, the actual amount of rotation makes very little difference within a wide range except under very heavy vertical loads where secondary moments can be significant.

4.2.2 H-Frame Structures

Normally for an H-Frame, the critical point in the structure is 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 cross brace. It is important, however, that the uplift and down-thrust be adequately contained so that the structure does not suffer premature failure due to unanticipated loads as a result of twisting the structure.

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 for each important member in the test structure. All test structure material should conform to the minimum requirements of the material specified in design.