Dynamic gust response factors for transmission line structures

Transmission line structures are flexible, line-like, wind-sensitive structures used for distribution of electricity. Dynamic wind loads on these structures result from two components: wind loads on the tower and wind loads on the conductors. Various approaches are available for the calculation of the gust response factor. The Gust response factor (GRF) is the static equivalent of the dynamic loads acting on the transmission lines. The ASCE 7-95 Commentary Method (1995) has a procedure to evaluate the GRF based on the new 3-second gust wind speeds adopted in the code. This procedure is for general categories of structures. Davenport's model (1979) is tailored exclusively for transmission lines and is flexible with any averaging time. Simiu's model, which again is not developed for transmission line structures, uses graphs for the major part of the GRF calculations. In this study, Davenport's model is used as a reference model for the calculation of GRF and foundations of approaches put forward by ASCE 7-95 and Simiu are studied. All these methods are considered in evaluating the loads on representative transmission line systems using Static-Cast and Spun-Cast concrete poles. Sensitivity studies are carried out for understanding the effects of different parameters in the Davenport and ASCE 7-95 methods and modifications are suggested in the ASCE 7-95 method.