Beyond orthogonal wind loading: Direction-sensitive flexuraltorsional response of transmission towerline systems

Transmission towers are conventionally designed for orthogonal wind directions, although skew winds may induce flexural–torsional coupling that is poorly represented in current design practice. This study investigates wind-induced responses of a transmission tower–line system over wind attack angles of 0°–90°. A 5° angular increment is applied within critical ranges, and the torsional contribution to member stress is quantified through stress decomposition. Skew winds generate a pronounced M-shaped, double-peaked distribution of dynamic unbalanced tension at conductor attachment points. Wind directions of 45° and 75° emerge as critical cases for torsional vibration. At 45°, the peak dynamic tension difference reaches 10.83 kN and the relative torsional angle reaches 9.81 × 10 -3 rad, approximately 75 times the value under orthogonal wind. Structural responses also vary sharply over 30°–45° and 75°–90°, demonstrating strong sensitivity to small directional changes. Under the most adverse 45° case, torsion induced by the unbalanced tension contributes 15.6% of the total member stress. These findings highlighted the skew wind–dynamic tension imbalance–torsional response mechanism and demonstrate that neglecting skew-wind-induced torsion may lead to unconservative transmission-tower design.