Equations for the gust response factors (GRF) for transmission line loading were presented by Dr. Alan Davenport in 1979 and have since been used by numerous parties in the design of transmission lines for wind loading, including ASCE Manual of Practice No. 74: Guidelines for Electrical Transmission Line Structural Loading (ASCE-74). This technique provided an efficient method of estimating peak responses based on the consideration of the underlying statistics of the approaching wind, the dynamic characteristics of the transmission tower and wires, and a sustained wind speed. Although various measures of sustained wind speeds were used at the time (e.g., fastest-mile, hourly mean, 10-minute mean), the basic idea remained the same: to estimate a peak response based on a mean wind speed. When ASCE Standard 7 (Minimum design loads for buildings and other structures) adopted a 3-second gust wind speed as the averaging time for design wind speeds (as of ASCE 7-95), the existing GRF equations were no longer compatible. Thus, an update to the original Davenport GRF equations is required for compatibility. This process has been carried out, and has been proposed for the upcoming 4th Edition of ASCE-74. This paper describes the reasoning and theory leading to an update of Davenport's GRF approach for transmission line loading, which is compatible within the existing framework of ASCE-74 and consistent with the wind nomenclature in ASCE 7. A worked example is included at the end of the paper.
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