Seismic fragility analysis of transmission towers considering effects of soil-structure interaction and depth-varying ground motion inputs

Transmission towers are critical components of electrical transmission systems, whose damage and failure during earthquakes may cause extensive economic losses and significantly hinder the post-seismic rehabilitation. Seismic fragility analyses of pile-supported transmission towers are usually performed without regard for the influences of soil-structure interaction (SSI) and the site amplification of ground motions from the pile end to ground surface, which may lead to inaccurate structural performance evaluation results. In this context, the present study numerically investigates the seismic fragility of a typical pile-supported transmission tower considering SSI and depth-varying ground motion (DVGM) inputs. Specifically, a three-dimensional finite element model of the transmission tower is created in ABAQUS software, and SSI is simulated by adopting soil springs at the end of pile nodes. The three-dimensional DVGMs are stochastically synthesized to be used as seismic inputs. Moreover, the pushover analysis is employed to identify the threshold values of different limit states of the transmission tower. Then, probabilistic seismic demand models (PSDMs) are developed by nonlinear time history analyses and linear regression fitting, which are used to generate fragility curves. Furthermore, parameter studies are carried out to discuss the effects of SSI, DVGMs and structural parameter uncertainties on the seismic fragilities. Numerical results show that the seismic fragilities of the transmission tower can be affected substantially by the above mentioned three influencing factors. This research is expected to serve as an exploration to reliably and effectively evaluate the seismic fragility of a transmission tower with SSI.