Transmission Line Construction in Crossing Mountain Ranges

In crossing mountain ranges with a recent transmission line in the Pacific Northwest severe climatic conditions were encountered. Snow lies from ten to thirty feet deep, wind attains high velocities and the temperature ranges between wide limits. A strongly built steel tower line successfully met these conditions. At one point however, a somewhat unusual formation of frozen fog was found to successively build up and drop off of wires and towers producing stresses greater than it would have been reasonable to design a line to withstand, and as a result failures occurred. Conditions in the extreme loading area are outlined and the assumption made that the most severe stresses were largely of an intermittent nature. The subsequent modifications in the construction are discussed, which were designed to more efficiently stress the materials under intermittent strains, providing an increased flexibility by the substitution of suspension for strain forms of wire support. Where line construction fails from excessive dead loading a stronger design throughout is no doubt the proper remedy. If however this loading is only excessive in one span at a time it may be relieved by longitudinal flexibility. While not submitting the principle of the elimination of strain forms as universally applicable in transmission line construction, it is hoped that this paper will elicit a discussion from authorities on the subject that will define its range of application.