Evaluation of wind loads on square transmission towers with angle members under skewed winds

In the current wind loading codes for transmission towers, the wind loads under skewed winds are characterized by the global drag coefficient, skewed wind load factor, and wind load distribution factor. The recommended global drag coefficients in the codes borrowed from the lattice frames and trusses show discrepancy with the wind tunnel test. The skewed wind load factor reflecting the amplification of wind loads at skewed directions is demonstrated to vary with the tower geometry, which is not factored in the codes. In addition, the wind load distribution factor in the codes is determined by assuming that the wind load direction is the same as the wind direction, whose rationality needs to be examined. In this paper, a series of wind tunnel tests on the body, cross-arm and head sections of the widely used square angle-steel transmission towers are performed under multi-directional winds. Based on wind tunnel tests, the three coefficients and factors in the codes are extensively examined, and new formulas for them are calibrated. The results of this study could provide more accurate estimate of wind loads on the transmission towers.