Wind Loading Considerations in Transmission Line Design

Load effects due to extreme wind events are considered in the design of most structures. A component of this calculation in ASCE Standard 7 (i.e., ASCE 7-16) is the effect of wind directionality, which acts to reduce the nominal design wind load imposed on the structural system. A reduction such as this is traditionally not applied in transmission line design for many reasons, including a large geographic extent of the line, varying line orientations, and that the load factor used in design is typically 1.0. This creates a difference between the wind loading procedures used for transmission lines and those used for other structures, although the base criteria (i.e., mean recurrence interval or MRI) are often directly compared. In light of the ever-increasing reliance of society on a constant and reliable electricity source, there is currently debate as to the classification of transmission lines as more critical structures and therefore greater design loads than those used currently. This is relevant at the time of writing as a committee for a new ASCE Loading Standard is under formation and the implications of the above differences are under review. This paper is intended to begin a discussion on developing wind loading procedures for this new ASCE Loading Standard which achieve the intended performance and how the level of intended performance compares with structures designed using ASCE 7.