Contemporary Feminisms

One of the most critical handling phases for any pole is lifting it clear of all supports while it is in the horizontal position because the moment generated by its own weight may be significant. Since concrete poles tend to be heavier than other types, more attention must be paid to the manner in which they are lifted.

Some poles are designed to be lifted with a single point pick at the center of gravity and some require multiple point picks. It is the manufacturer's responsibility to provide the user with lifting instruc-tions for their particular poles and it is the user's responsibility to insure that those instructions are relayed to the construction forces.

5.3 Hauling

Common sense is important in determining good hauling practices. A particular set-up that may be highly acceptable for hauling over a smooth paved highway may be entirely inappropriate for hauling the same load over a plowed and frozen field. In general, no more than 1/3 of the length of the pole should be unsupported and, if the terrain conditions indicate that the pole will be handled roughly, the unsupported length should 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 pole along the ground. Concrete poles will withstand this abuse as well as wood poles. If hardware is already attached to the pole, it will be necessary to secure the pole in such a manner as to keep it from rolling around its longitudinal axis as it is dragged. As is expected with the dragging of any pole, common sense is required to avoid damage to the pole.

The construction forces are responsible for the proper handling of poles and if they do not have any handling instructions or if the in-structions are unclear, they are responsible for contacting the user for the necessary information.

5.4 Framing

Concrete poles are generally framed like wood poles, (i.e. with the use of through bolts) but they will be easier to frame than wood poles because the holes can be more accurately drilled. Bolts should be ened according to the assembly drawings but in the absence of any tight-ening instructions, reference to paragraph 2.11 of this guide and some common sense will work well. In most cases, the bolts will generally break 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 be sure they are still snug.

Again, normal construction techniques such as raising the pole with 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 the entire pole is lifted clear of the ground, the same procedures used in

CONCRETE POLES DESIGN 35 unloading 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 necesneces-sary to drill one or more holes in the field. This can be easily accomplished with a rotary hammer drill, a carbide tipped bit of the appropriate size and a cutting torch. First determine which of the following two types of poles 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 by the ground line design moment capacity and carry that quantity of ten-dons throughout the entire length of the pole even though less steel could be used in the upper parts of the pole. Since holes are normally drilled in the upper parts of a pole where there is a considerable excess of steel, it is permissible to cut limited numbers of strands in the drilling process. CAUTION - DO NOT DRILL HOLES NEAR THE GROUND LINE FOR POLES USED IN SINGLE POLE TANGENT APPLICATIONS. DO NOT ERILL NEAR THE LOWER END OF THE TOP SECTION OF A TWO PIECE POLE AND DO NOT DRILL NEAR A CROSSBRACE ATTACHMENT IN H-FRAME CONSTRUCTION. These are the areas for which the steel requirements were determined and cutting the steel 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 can occur without cutting prestressing steel.

Once it has been determined that it is permissible to drill the pole, mark the location and drill with a rotary hammer drill and a carbide tipped bit. If steel is struck, stop drilling and burn the steel with the cutting torch. Then continue drilling. For best accuracy, mark the pole on both sides and drill both sides toward the middle. Mold marks, which are usually visible on the pole, make handy reference points 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 tendons out through the side wall of the pole or they may install additional steel in critical areas by the use of post tensioned strand. In these methods, there is not the excess of steel near the pole tops and the steel should not be cut. This does not preclude drilling these poles. It means, however, that care should be used to insure that steel is not cut. 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 during the drilling process but cutting a strand means that the pole may be weakened below its design strength.

The actual drilling of these poles is accomplished in the same

36 CONCRETE POLES DESIGN

manner 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 a high probability of having to cut through the spiral steel.

5.5.3 Circumferential Steel

Cutting of circumferential steel is difficult to avoid, but is acceptable 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 pole in the field. This can be accomplished without damage to the pole by cutting with a small, hand held concrete saw and an abrasive cut off blade. The blade will cut both the concrete and the steel. For hollow spun poles, carefully mark a straight line around the circumference and saw 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, a single point pick with a choker is usually permissible. The choker should be placed well above the center of gravity unless the drawings indicate 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 of the weight stays on the ground until the pole is nearly in the vertical position. Once it reaches the vertical position, it will not be damaged by lifting its full weight with a single point pick.

Because the surface of a concrete pole is smooth and hard, safe operations require use of the same choker techniques as for steel poles.

IMPROPER USE OF CHOKERS CAN RESULT IN THE POLE SLIPPING AND CAUSING INJURY OR PROPERTY DAMAGE. Chokers must be tight around the pole. If the chokers are slippery, they may be padded with a sticky material. A positive stop against sliding can be provided by attaching the choker below a solid piece of hardware (Note that a ladder clip does NOT qualify as solid hardware).

Guyed poles, whether or not they are raked, should be initially set in what ever positions they will be under normal every-day loads. This means that regardless of what ever bending and flexing occurs during construction and long term use, once the conductor installation is com-plete and the guys are adjusted under normal everyday loads, the top of the 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. Just as most steel poles are climbed with the standard climbing ladders, all of the manufacturers provide attachments to concrete poles to accomodate the same ladders. Other climbing arrangements are also available and may have been selected by the user.

CONCRETE POLES DESIGN 37 5.9 Field Inspections

Questions about cracks in concrete poles are frequent. It should be realized that although some types of cracks may be detrimental, concrete poles are expected to crack under certain conditions.

Circumferential cracks that do not close when the pole is either properly supported on the ground or is erected, indicate a pole in which the steel has been stretched beyond its elastic limit and it should be rejected. Circumferential cracks may open during construction or during severe service conditions but they usually all close once the severe loads are removed, and the pole has not been harmed as long as they do close. Due to the process of releasing the tension on the steel in prestressed poles, circumferential cracks may develop within a few inches 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 other coatings, if they are not tightly closed.

Longitudinal cracks are less common. At either end, they may have been caused by the application of prestress loads. If longer longitu-dinal cracks occur near the bottom of the pole, they have likely been caused by stacking the poles. Longer longitudinal cracks near the top may be caused by over tightening of the through bolts. As long as the cracks are only hairline cracks, as opposed to open cracks, they are not detrimental 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 it is decided that the pole is to remain in service, the cracks should be filled and sealed from the weather to prevent further degradation of the pole.

6.0 Quality Assurance 6.1 General

Quality assurance is the responsibility of the user. At the time of bidding, user should specify the degree of perfection he desires in de-sign, fabrication, structure testing and field construction. The extent of the quality assurance program may vary based on initial investiga-tions, the user's experience, the manufacturer's experience and past performance, and the degree of reliability required for the specific job.

The following guidelines may serve in preparing specifications which include a quality assurance program.

6.2 Design and Drawings

The quality assurance specification should indicate the degree of involvment 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 DESIGN

including all attachments and connections, should be considered. The fabricator's drawings need checking to ensure they contain proper and sufficient information for fabrication and erection in accordance with the requirements of the user's specification. (Refer to Section 2.0 Design.)

6.3 Fabrication 6.3.1 Materials

The specification should include the requirement for review and agreement on the manufacturer's material specifications, his sources of supply, material identification, storage, traceability procedures and acceptance 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 the manufacturer's equipment and process facility to ascertain that the procedures are satisfactory, the tolerances are within specified limits and the existing quality control program is satisfactory. (Refer to Section 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 and inspection programs employed during each step in the fabrication process.

The user may specify that the manufacturer furnish copies of testing and inspection reports. The user may also perform independent random 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 be specified and agreed upon by the purchaser and manufacturer. Good fabrication quality is an important factor in minimizing field con-struction and performance problems. (Refer to Section 3.7 Fabrication Tolerances.)

6.3.5 Surface Coatings

Where painting or other coloring is required, the system, procedures and methods of application should be acceptable to both the user and the manufacturer. Also the system should be suitable for both the product and its intended exposure.

If galvanizing of accessories is required, the procedure and facilities should be agreed upon by the user and the manufacturer. After galvanizing, nondestructive testing may be specified to ensure that there have been no adverse changes to the finished product.

CONCRETE POLES DESIGN 39

When metallizing is required, the procedures and facilities should be in accordance with coating supplier's recommendations and acceptable to both user and manufacturer.

6.3.6 Shipping

Prior to the start of fabrication, the user should review the fabricator's methods and procedures for packaging and shipping.

When receiving materials, all product should be inspected for shipping damage prior to accepting delivery. If damage is apparent, the user should immediately notify the delivering carrier. If the shipments are FOB destination, making the manufacturer responsible for correcting damages, 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 a discrepancy exists, both the carrier and the manufacturer should be notified.

6.3.7 Quality Control

A review should be made and agreement reached on all quality control programs, organizational setups and procedures. It is necessary that 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 indicate the position of the structure in the test, the test procedures, methods of load application, the load for each loading condition, and who is to be 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 fied.

6.5 Field Construction

The user should review proposed construction quality control grams and procedures to determine that all phases of field construction will comply with the requirements as specified in the user's 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

BIBLIOGRAPHY

1) 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, 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

DEFINITIONS CASTING METHODS

Precast Member - A member which is cast in some location other than the 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 the consolidation phase. The resulting centrifugal force causes the pole to be hollow and the concrete to be highly consolidated. Since this force is very large, dry (low water/cement ratio) concrete can be consolidated in this manner, usually with some of the water spinning out to reduce the water/cement ratio even further. Because spun concrete has a lower than normal water/cement ratio and a higher than normal density it is much stronger and more durable than static cast concrete. The end result is that the member can be lighter because less concrete is required when it 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 not move during the casting and consolidating of the concrete (except for the possibility of vibrating the mold as an aid in consolidating the concrete).

LOADINGS

Maximum (Ultimate) Design Load - The load that the pole is designed to resist. This load is the maximum service load multiplied by some overload factor. The user must select not only the load and the load factor, but also must determine whether the pole is to resist the maxi-mum design load without permanent unacceptable deformation (damage) or without failure (collapse). A stronger pole is required to resist without permanent deformation than without collapse.

Maximum Service Load - The maximum load that the pole is ever expectedto encounter (exclusive of overload factors). This load may be used for checking deflections and clearances.

Normal Everyday (Frequent Condition) Load - A load that a pole may be expected to encounter on a frequent basis. User should specify the normal everyday load.

MOMENTS

ultimate Moment - Depending on the user's choice as to whether the pole must resist permanent deformation or collapse, this is the moment at which the chosen one of these events occurs. The moment capacity at

ultimate Moment - Depending on the user's choice as to whether the pole must resist permanent deformation or collapse, this is the moment at which the chosen one of these events occurs. The moment capacity at