Wind Tunnel Testing of Steel Tube-Angle Steel Composite Transmission Tower Members

Literature Overview

This research paper by Niu Huawei and colleagues from Hunan University and China Electric Power Research Institute, published in the Journal of Hunan University (Natural Science Edition) in 2021, presents wind tunnel test results for wind-sensitive transmission tower structures composed of steel tube and angle steel members. The work was supported by the National Natural Science Foundation of China and addresses a critical aspect of wind-resistant design for electrical transmission infrastructure. Transmission towers are tall, slender structures that are highly sensitive to wind loading, and accurate determination of wind load parameters such as shape coefficients and windward-windward shielding factors is essential for safe and economical design.

Test Configuration and Methodology

The authors designed scaled rigid segment models of transmission tower components for wind tunnel testing. For the tower body, a scale ratio of 1:8.5 was used, while for the cross-arm, a scale ratio of 1:2.5 was employed. These different scale ratios reflect the different geometric characteristics and wind loading behavior of the tower body and cross-arm. The models were tested in a wind tunnel at three different uniform inflow wind speeds and multiple wind direction angles, with synchronized pressure measurement to capture the spatial distribution of wind pressure on the structure.

Key Findings on Shape Coefficients and Shielding Factors

The experimental results reveal several important trends. First, the inflow wind speed has almost no effect on the shape coefficient of angle steel members in both the tower body and cross-arm, which simplifies the design process by reducing the number of parameters that need to be considered. Second, at a wind direction angle of 0°, the shape coefficient of angle steel members in the tower body shows a trend of decreasing from bottom to top along the tower segment, which is attributed to the shielding effect of the lower members on the upper members. Third, the shielding factor for angle steel members in the tower body is in good agreement with the values specified in Japanese design codes, while the Chinese code values are somewhat conservative.

The overall drag coefficients for the tower body and cross-arm segment models are also in good agreement with Japanese code values, with Chinese code values being 7.2% and 4.5% lower, respectively. This suggests that Chinese design codes may be slightly less conservative than Japanese codes for this type of structure, which has implications for design safety and economic optimization.

Comparison with Design Codes and Engineering Implications

The comparison between experimental results and code-specified values provides valuable guidance for engineers. The good agreement with Japanese codes suggests that these codes may be more appropriate for the design of steel tube-angle steel composite transmission towers, at least in terms of wind load parameters. However, the Chinese codes are not significantly unconservative, and the differences are within acceptable engineering tolerances. Engineers should be aware of these differences when designing transmission towers for different code jurisdictions and should consider the specific wind loading conditions and structural configuration when selecting appropriate design parameters.

The finding that wind speed has minimal effect on shape coefficients is particularly useful for design simplification, as it means that wind speed variations do not require separate consideration for shape coefficient determination. The Reynolds number insensitivity of the shielding factors further supports the use of scaled model testing for full-scale design, as the results can be applied across a range of Reynolds numbers without significant correction.

Study Insights and Concluding Remarks

This paper provides rigorous experimental data for the wind-resistant design of steel tube-angle steel composite transmission towers, which are increasingly used in modern electrical infrastructure due to their advantages in strength-to-weight ratio and fabrication efficiency. The wind tunnel testing methodology is sound, with appropriate scale ratios, multiple wind speeds and direction angles, and synchronized pressure measurement. The comparison with international design codes provides valuable context for engineers working in different regulatory environments. This research contributes to the ongoing effort to improve the accuracy and economy of wind load estimation for transmission tower structures, ultimately leading to safer and more cost-effective electrical infrastructure.