Seismic fragility assessment of a transmission tower considering mainshock-aftershock sequences

Transmission towers are critical components in electricity transmission systems, and their damage or even collapse under earthquakes has drawn people's attention to the fragility assessment of transmission towers. Existing seismic analyses of transmission towers only focus on resisting a single mainshock and overestimate the seismic capacity of transmission towers under mainshock-aftershock (MS-AS) sequences. Considering this, this paper introduces a fragility assessment method to discuss the effect of MS-AS sequences on the seismic damage of a transmission tower. Dynamic analyses are performed to obtain the seismic damage of a transmission tower under 20 groups of as-recorded MS-AS sequences. Based on the predefined limit states (LSs) and the tower's damage characteristics, five different damage states (DSs) are determined to classify the cumulative damage of the transmission tower. Fragility curves are obtained to quantify the probability of exceeding the different DSs of the transmission tower under MS-AS sequences. The analysis results indicate that aftershocks can aggravate the cumulative damage to the tower and reduce its seismic capacity. As the intensity of aftershocks increases, the probability of exceeding the different LSs increases significantly. This study performs a reliable evaluation of the seismic performance of transmission towers under MS-AS sequences.