The wind resistance of transmission towers is not only affected by wind load, but also by service environment. This study uses the world's second Ultra High Voltage Direct Current transmission project - Xinjiang & PLUSMN;800 kV Tianzhong Line UHV DC transmission project - to develop a fragility analysis method for transmission towers in saline soil under wind loads to investigate the change of wind loads fragility of transmission towers in long-term service in the saline soil environment. It develops a tower-line-foundation (3 T-2L-F) system model considering soil-structure interaction. In addition, this research addresses the durability damage of the transmission tower using field investigation data and material degradation models and analyzes the influence of various durability damage components on the natural vibration mode of the basic of 3 T-2L-F model. Finally, it builds the structure-wind samples utilizing a Latin hypercube sampling method and explores the time histories analysis, the pushover analyses, and the time-varying fragility analyses considering the uncertainty of materials and wind loads. The findings indicate that the 3 T-2L-F model accurately simulates the actual situation of the transmission tower. The fragility of a transmission tower subjected to wind loads is proportional to the degree of material damage and the strength of wind loads.

Based on a prototype of the Beijing subway tunnel, this research conducts large-scale model experiments to systematically investigate the vibration response patterns of tunnels with different damage levels under the influence of measured train loads. Initially, the polynomial fitting modal identification method (Levy) and the model test preparation process are introduced. Then, using time-domain peak acceleration, frequency response function, frequency-domain modal frequency, and modal shape indicators, a detailed analysis of the tunnel's dynamic response is conducted. The results indicate that damage significantly amplifies vibration acceleration, with the amplification increasing with the severity of the damage. When the crack lengths are 2 cm, 4 cm, and 6 cm, the peak acceleration increases by 25.12%, 36.35%, and 50.29%, respectively, while adjacent segments show increases of 13%, 29%, and 45%. Damage decreases the tunnel structure's modal frequency, with the first two modal frequencies showing the most significant reductions of 9.87% and 7.34%, respectively. The adjacent segments show reductions of 7.7% and 4.2%. As the severity of the damage increases, the amplitude of the modal shape at the damaged location also increases, with the first modal shape rising by 43.37% for 4 cm damage compared to 2 cm damage and by 72.21% for 6 cm damage. The second modal shape increases by 9.04% and 26.51%, respectively. Additionally, the effectiveness of the polynomial fitting modal identification method (Levy) for tunnel structural damage detection was validated. Finally, based on the methods outlined above, the tunnel responses measured on-site in the Beijing metro were also analyzed. The findings of this study provide important theoretical support for the assessment and routine maintenance of metro tunnels.