Random modeling of dynamic wind loads in tropical cyclones and its application to transmission tower fragility and reliability analyses

Transmission lines are highly sensitive to wind, making their safety under tropical cyclones (TCs) critical. While reliability theory provides a framework for assessing structural performance, uncertainties in dynamic wind loads, which are commonly represented by gust response factors (GRFs), remain insufficiently characterized, limiting accurate risk assessment. This paper develops probabilistic models of GRFs to capture the randomness of dynamic loads on transmission tower-line systems (TTLSs). Three representative TTLSs with voltages of 110 kV, 220 kV, and 500 kV are employed, and the static finite element analysis (FEA) using equivalent static wind loads (ESWLs) is compared with the nonlinear time-history analysis (NLTHA) to quantify tower-line coupling effects. Random GRF models accounting for TC wind turbulence are developed, and sensitivity analysis is performed to identify the key factors driving GRF variability. Nonlinear static pushover analysis (NSPA) and incremental dynamic analysis (IDA) reveal differences in failure modes and structural capacity under TC winds. Fragility and reliability assessments indicate that GRF randomness increases tower failure probability at moderate wind speeds but reduces fragility under extreme winds, whereas neglecting GRF variability leads to overestimated tower reliability, underscoring the importance of incorporating dynamic load uncertainty in design and risk management of transmission lines.