# Fragility Assessment and Reinforcement Strategies for Transmission Towers Under Extreme Wind Loads
## 1 Introduction  
Transmission lines serve as critical components of power infrastructure, playing a central role in maintaining the stability and reliability of modern electrical grids. In response to the rapid growth of China's energy sector, transmission towers are being constructed with greater heights and longer spans to accommodate rising electricity demand. However, these structural features, i.e., increased height, extended span length, and high flexibility, make transmission towers particularly vulnerable to wind-induced forces, which havebecome a dominant factor in their structural design and performance considerations [1]. In recent years, the growing frequency and severity of extreme wind events have significantly elevated the risk of transmission tower failures. Such failures have resulted in widespread power outages, service disruptions, and substantial economic losses across affected regions [2; 3]. This trend underscores the urgent need to reassess wind-resistance design standards and develop more robust structural strategies to enhance the resilience of transmission infrastructure in wind-prone environments. Extensive research has been conducted on the wind resistance of transmission towers, focusing on key issues such as wind-induced vibrations, failure modes, and collapse mechanisms. To illustrate, [PERSON] et al. [4] performed wind tunnel tests on both individual towers and tower-line systems, revealing that the wind vibration coefficients specified in existing design standards are significantly underestimated. [PERSON] et al. [5] utilized numerical simulations to analyze the structural vulnerability of transmission towers under varying wind directions, identifying critical conditions leading to collapse and quantifying associated failure probabilities. [PERSON] et al. [6] introduced a simplified uncertainty analysis method for evaluating the combined effects of wind and rain loads on transmission towers, offering a more efficient approach for load estimation. Similarly, [PERSON] et al. [7] conducted full-scale experimental and numerical investigations to replicate collapse scenarios, thereby identifying common failure modes in lattice tower structures. [PERSON] et al. [8] identified collapse-prone regions within lattice frameworks and emphasized the need for targeted reinforcement. In another study, [PERSON] et al. [9] examined the aeroelastic behavior of tower-line systems through wind tunnel experiments, highlighting the strong dynamic coupling between towers and conductors. [PERSON] et al. [10] explored progressive collapse mechanisms under strong wind conditions, demonstrating that failure patterns are highly dependent on the initial location, extent, and distribution of structural damage, as well as the deformation trajectory during collapse. [PERSON] et al. [11] proposed a resilience assessment framework for transmission towers exposed to hurricane conditions, establishing vulnerability curves that support probabilistic structural evaluations and risk-informed decision-making. Transmission tower failures under extreme wind conditions are typically triggered by localized component failures that exceed critical load-bearing thresholds and subsequently propagate through the main structural framework, leading to progressive collapse [12]. To account for end moments generated by eccentric connections, many structural design codes incorporate simplified formulations that adjust the slenderness ratio, thereby reflecting the influence of end eccentricity on member stability [13; 14; 15; 16]. However, these advancements in code provisions have rendered many legacy transmission towers noncompliant with current performance and safety standards. In response to this discrepancy, extensive research has been directed toward understanding the stress distribution and failure mechanisms in transmission tower components through both mechanical testing and numerical simulation [17; 18].