Extended limit-collapsed surfaces using fragility analysis of high voltage transmission towers located in coastal areas under wind load

When evaluating the fragility of structures in response to wind loads, vulnerability analyses are often conducted under intact conditions. Therefore, the actual strength of aged transmission towers may be compromised, resulting in severe damage. Especially for steel structures used over a long period in coastal areas, there is a potential for performance degradation due to corrosion. One of the high-voltage transmission towers, the 765 kV transmission tower, is taller than other towers, making it more vulnerable to strong winds in the event of corrosion. In this study, the structural performance degradation of 765 kV transmission towers in coastal regions based on their service life was investigated. Capacity distributions were provided considering the uncertainties in various parameters, such as the wind attack angle and material properties. A fragility assessment process that accounts for uncertainties in the wind conditions and aerodynamic parameters is proposed. Using the research results, we created limit-collapsed surfaces to evaluate the structural safety of transmission towers based on their service life, wind speed, and wind attack angle. The results showed a quantitative decrease in structural safety due to corrosion depending on the service life, with the most unfavorable wind attack angle being 0°. The proposed limit-collapsed surface can help efficiently evaluate structural conditions considering wind speed, wind attack angle, and service life. Hence, this study can serve as a basis for the structural evaluation of modern transmission towers to avoid power disruptions in major cities.