Design wind loads for tubular-angle steel cross-arms of transmission towers under skewed wind loading

Abstract

Wind tunnel tests on two cross-arm models of a 500kV tubular-angle steel transmission tower at three mean wind speeds were carried out. The drag coefficients in wind directional axis for 19 incidence angles were obtained. The skewed wind load factors, the wind load distribution factors in transversal and longitudinal direction were calculated. Two fitting functions for the skewed wind load factors of tubular-angle steel cross-arms were determined by nonlinear fitting analysis. The wind incidence angle corresponding to the maximum skewed wind load is near 80° or 85°. With the assumption that the drag coefficients are valued based on the experimental results, the effective projected areas (EPA) of the cross-arms were calculated. The parameters for calculating the skewed wind loads developed from the wind tunnel tests were compared to the regulations in some applicable standards. Suggestions on the drag coefficients, the skewed wind load factors and the wind load distribution factors were proposed. Especially for Chinese standard, the drag coefficient of single member should be substituted by that of the single frame in calculating the global drag coefficients of cross-arms. The transversal wind load for 0° wind incidence angle and the longitudinal wind load for 30° wind incidence angle are conservative.