Effect of wind direction on the response and capacity surface of a transmission tower

Electrical transmission structures play a vital role in power transmission networks throughout the world and are often subject to strong wind loads. The present study investigates the inelastic response of a self-supported lattice transmission tower under different wind events, including traditional atmospheric boundary layer wind (ABL) and downburst wind, and for wind loading at different directions relative to the tower. The nonlinear static pushover (NSP) analysis is used to obtain the capacity curve of the tower, defined by the force-deformation relationship, at each considered wind direction. The results show that the yield and maximum capacities vary with wind direction. The deformation trajectory is projected on the horizontal plan for each wind direction, illustrating the out-of-plane loading deformation. Since the trajectories are sufficiently smooth and do not overlap for closely spaced wind directions, it is suggested that the capacity curves obtained for different wind directions can be used to form the capacity surface of the tower. Moreover, the results indicate that the capacity for ABL and rectangular (uniform) winds could provide an approximate envelope for the capacity estimated for different sizes of downburst events. These findings could assist in the evaluation of the adequacy of existing towers under downburst events, as well as in the design of new towers.