Comprehensive seismic performance analyses of pile-supported transmission tower-line systems considering ground motion spatial variation and incident direction

Pile-supported transmission tower-line systems (PTTSs) play a vital and indispensable role in reliable and efficient transmission of electricity. Their safety and normal operation under earthquake events are of great importance. Previous studies on seismic performance of PTTSs have typically been conducted under the assumptions of fixed foundations, uniform excitations, and deterministic seismic incident direction along the transmission lines, which do not necessarily reflect the real scenarios in earthquakes. To address this problem, a comprehensive seismic performance analysis approach is proposed for PTTSs spanning uneven sites, in which the influences of soil–structure interaction (SSI), depth-varying spatial ground motions (DSGMs), and seismic incident directions are thoroughly considered. In particular, the finite element model of a realistic PTTS is first established, and its accuracy is verified by static loading tests performed for the full-scale transmission tower. Then, the simulation approach for DSGMs considering the effects of wave passage, bidirectional coherence, and local site is introduced, and the DSGMs at heterogeneous site of the PTTS under various incident directions are stochastically synthesized. Finally, the seismic responses and fragilities of the PTTS are computed by utilizing the DSGMs from various incident directions as inputs. The results demonstrated that SSI, seismic excitation type, and incident direction can significantly affect the seismic performance of the PTTS, especially for the tower located at a soft site. Under various seismic incident directions, the difference between the largest and smallest fragility median peak ground acceleration (PGA) of the PTTS can reach more than 40%, and the conventional 0°, 90°, or 180° excitation may not be the most adverse incident direction. This study can provide an in-depth understanding of the seismic performance of PTTSs constructed along the sites with complex and varying geological conditions, which benefits the rational and reliable designs of large-scale transmission networks to ensure their safety and functionality under earthquake hazards.