Loadings for Electrical Transmission Structures

As the costs of high-voltage electrical transmission lines have increased, greater attention is being given to the weather element loads that influence the structure cost. Minimizing the cost of structures can only be accomplished by increased knowledge of loading conditions which influence the possible risks involved. To obtain experience data and utility practice relative to weather element loads an extensive questionnaire was sent to every major utility in the United States. This report has been compiled using the responses from 130 major utilities that own and operate approximately 290,000 miles of high-voltage transmission lines rated 69-kV and above. The report provides data on the practices followed in the design, fabrication, testing, and procurement of transmission structures. Questionnaire responses cover presently applicable legislative codes. Wind, ice, and longitudinal loadings are shown. Utilities evaluate factors such as wind gusts, density of ice formations, wind height factors, and span reduction factors. These factors are normally incorporated into the structure loadings by comparing the special load to a standard load case which controls the design.