Lifetime multi-hazard fragility analysis of transmission towers under earthquake and wind considering wind-induced fatigue effect

• Fatigue damage of transmission tower is calculated exploiting measured wind data. • Lifetime multi-hazard fragility analysis for transmission towers is performed. • A fast lifetime safety assessment method for transmission towers is proposed. Wind-induced fatigue damage is a predominant factor eventuating in structural performance degradation of transmission towers exposed to long-term environmental wind. Moreover, transmission towers may suffer from multiple extreme natural hazards (such as earthquake and strong wind) during their service lives. However, these phenomena have not been well accounted for in current design specifications and previous studies for transmission towers. To this end, this paper proposes a comprehensive probabilistic analysis framework for achieving the lifetime multi-hazard fragility evaluation by considering the wind-induced fatigue, which is applied in a 1000 kV steel tubular transmission tower. Firstly, based on the field wind data measured at the meteorological station of Qingdao city, China, from Jan. 1, 1971 to Dec. 31, 2020, a fatigue analysis is performed on an actual transmission tower constructed in this region to compute the annual mean fatigue damage. Secondly, a series of time-dependent uncertain numerical models of the tower are established by integrating the accumulated fatigue damage and material deterioration model, and nonlinear time history analyses are imposed on these models to examine the effect of fatigue damage on lifetime responses under combined earthquake and wind loads. Analogously, the time-dependent probabilistic multi-hazard demand models are derived via the dynamic analyses and statistical regression, and these demand models are employed to further develop the lifetime multi-hazard fragility surfaces of the tower. Finally, a fast lifetime safety assessment method, i.e. the critical safety surface, is proposed to efficiently judge the collapse state of the transmission tower at various wind speeds, PGAs and service times. Numerical results indicate that the structural capacity of the transmission tower will experience significant deterioration due to wind-induced fatigue damage; the multi-hazard induced structural responses and fragilities will considerably increase with the service life although the tower is initially well-designed. The proposed analysis framework will be beneficial for the design and maintenance of transmission towers subjected to both earthquake and wind hazards for designers and decision-makers.