Fragility analysis and wind directionality-based failure probability evaluation of transmission tower under strong winds

Strong wind is one kind of the most destructive natural disasters devastating transmission towers. The damage and even collapse of transmission towers caused by strong winds occur frequently. Wind-induced fragility assessment of the transmission tower is of great significance for the safety and economy of transmission tower. It provides not only a basis for the disaster mitigation and risk assessment of the government, but the reference for the design, maintenance and retrofit of the transmission tower as well. In this paper, wind-induced fragility analysis and failure probability evaluation of the transmission tower with considering wind directionality are addressed. Firstly, the wind-induced fragility analysis method including two variants are presented. Then an engineering case is used to illustrate the fragility analysis of the transmission tower: the random finite element model of the transmission tower and the fluctuating wind speed and related wind load are simulated; the static non-linear buckling analysis under different wind attack angles is conducted to determine the threshold displacements in damage and collapse state of the tower; the incremental dynamic analysis is carried out to obtain the maximum displacement at the tower top and the fragility curve of the transmission tower is determined accordingly. Furthermore, the failure probability of the tower is determined considering wind directionality. Finally, the procedure to determine the optimal layout of the transmission tower is proposed, which is based on the overall damage and collapse probability of transmission tower under any layout in one year. The results show that the most unfavorable wind attack angle is 45°, then 0°, 60° and 90°, and the most favorable layout is 90° in damage and collapse state for the illustrated tower.