Wind Loads Acting on Transmission Tower under Combined Yawed and Tilted Wind

Transmission towers situated on mountains are exposed not only to horizontal winds but also to vertical winds blowing along the slope. Moreover, sudden downward or upward winds can impact transmission towers during downbursts or tornadoes. The objective of the present study is to investigate the aerodynamic force coefficients of transmission towers subjected to combined yawed and tilted wind. Wind tunnel tests were conducted on a 1:25-scale model of a lattice transmission tower. Test results indicated a linear relationship between vertical aerodynamic force coefficients and tilt angle, with a significant increase at ±30° tilt angle, amounting to 39% of the maximum longitudinal aerodynamic force. Additionally, there was about 7% reduction in resultant horizontal force coefficients at ±30° tilt angle. Although horizontal wind aligns well with codal predictions, the limitations of the current standard in representing tilt wind effects is underscored. The study proposes a new equation, extending current international code requirements, providing a comprehensive assessment of horizontal and vertical aerodynamic forces under yawed and tilted wind conditions. This research stresses the importance of considering tilted wind in tower design, particularly in sloped terrains, and highlights limitations in current design standards.