Georgia Power Co. was one of the first utilities in the United States to embrace steel-reinforced spun-concrete poles. The experience to date has been excellent, but no pole can withstand the damage for which it was not intended.

In mid-2003, the Transmission Line Support team was notified of a 90-ft concrete pole that had been struck by a vehicle on the Bull Creek — Oliver Dam 115-kV line. The pole was located on a busy street in Columbus, Georgia, and had distribution underbuild with a three-phase pothead attached. There was severe damage in the most critical area. At the point where the vehicle made contact with the concrete pole just above groundline, a 24-inch hole was exposing the supporting longitudinal cables. The remaining intact concrete had several vertical cracks up to 6 ft above the ground.

For this type of damage, no repair process was available that would restore the concrete pole without taking the lines out of service. After careful evaluation of the pole, it was determined the damage was too severe to attempt a field repair with the limited repair processes available. The decision was made to ask Osmose Utility Services (Griffin, Georgia, U.S.), a wood and steel inspection provider, to install pole splints to secure the pole until a Georgia Power Co. (Atlanta, Georgia) construction crew could arrange an outage to replace the pole.

Georgia Power has more than 13,000 concrete structures. It was obvious that with the increasing number of concrete poles being used on the transmission system, and the increased exposure to this type of problem, the utility needed some type of repair process. The goal wasto develop a concrete pole repair process that could be used not only by Georgia Power, but also by sister utilities Alabama Power Co., Gulf Power, Mississippi Power and Savannah Electric.

Search for a Solution

A literature search revealed that in California, bridge supports are often made earthquake-proof by reinforcing the concrete column with fiberglass. Southern Company had used a similar process to strengthen the groundline of wood poles in the past with success. After some discussion with Nelson Bingel, Werner Kralick and Robby Bryan of Osmose Inc., the company was confident it could develop a repair process that could be performed without removing the line from service.

Paul Springer of NEETRAC (National Electric Energy Testing, Research and Application Center), a research center of the Georgia Institute of Technology, was also brought into discussions. It was decided to reinstall the damaged concrete pole at the Jonesboro steel yard, repair it and test the repaired structure. Working with Rainbow Technologies (Pelmar, Alabama) and Hugh's Supply, a pole setting foam product was used as backfill. This decision would allow testing of the pole setting foam and the concrete pole repair technique at the same time. Osmose made the calculations to determine the number of layers of fiberglass needed to restore the damaged area for this particular size concrete pole.

The Repair Process

After the final determination to replace the damaged pole, it was hauled 90 miles to the Jonesboro steel structure yard where the fiber-wrap repair and test was conducted. The damaged pole was installed using Rainbow pole-setting foam backfill. The excess material from the damaged section was chipped out beyond the reinforcement cables area. Voids were then filled with 4000 lb/inch² (psi) Quick-Crete to a smooth circumference. The damaged area was then wrapped with Osmose Fiber-Wrap.

Testing the Pole

The research center, NEETRAC assisted in the test, performing a load analysis on the repaired pole on Jan. 27, 2004. This included attaching a sagging double-winch line with snatch block connected at one end to a winch on a tractor located 113 ft from the base of the pole. The other end of the winch line was attached to a nylon sling, wrapped around the concrete pole approximately 35 ft above grade on the repaired pole. The pulling angle was approximately 17 degrees from horizontal. During the actual pull-to-failure test, a tension meter logged 25 readings per second to record the stress sequence and the breaking point of the pole.

The pole and repair failed at 512,500 ft-lb due to the compression failure of the 4000 psi grout and the compression failure of the wrap. The earth and pole setting foam ruptured at 424,000 ft-lb, which is 2% above the nominal pole rating of 417,000 ft-lb. The load at the rupture exceeded the nominal pole groundline moment rating by 24%. Even after the pole had broken, there was still sufficient strength to prevent it from falling to the ground. NEETRAC's final report concluded, “The pole wrap restores the full strength of the concrete pole.”

Conclusions

From the successful repair, Georgia Power concluded that concrete poles typically could be repaired in the field without interrupting service to customers. The process will help better manage and maintain the transmission lines and structures without de-energizing the line. The repair process is estimated to be 30% of the replacement cost, thus saving more than 70% of what a replacement would be, plus manhours and line outage loses.

Acknowledgments

The author would like to acknowledge the following people for making this research project a success: Georgia Power's Buddy Phillips from Line Support, Steve Williams and Ulysses Ponder from Transmission Training, and Tim Harrison from Transmission Construction assisted with the pole repair project, as did La-Tunya Goodwin from Columbus TMC. Rob Bryan, Werner Kralick and Nelson Bingel gave technical support from Osmose Inc. (Griffin, Georgia). Pat Ridding from Hugh's Supply and Larry Steeley and Dale Gray from Rainbow Technologies (Pelham, Alabama) provided expertise and materials. Paul Springer and Dale Callaway represented NEETRAC.

Alan Holloman is senior transmission specialist for Georgia Power Co. He began his career by working on a transmission construction crew in 1978. In 1980, he transferred to the Metro Transmission Maintenance organization, where he worked as a bare-hand lineman, bare-hand crew leader, bare-hand crew foreman and transmission line supervisor. In 1994, he joined Transmission Line Support as a transmission specialist and was promoted to senior transmission line specialist in 1999. Holloman serves on the Southern Company Transmission Maintenance Committee. He is a member of The American Wood Preservers' Association, The Society of Protective Coatings, Electric Power Research Institute's Live Line Working Group. He is also a transmission section officer for the Southeaster Electric Exchange and a member of IEEE.