Seismic behavior and collapse fragility of long-span truss structures in ultra-high voltage substations under multi-directional earthquakes

To improve the seismic design method of ultra-high voltage (UHV) transmission lines and mitigate earthquake disasters, this study numerically investigates seismic behaviors and collapse fragility of a long-span truss structure (LSTS, a supporting-equipment structure in UHV substations) subjected to multi-directional earthquakes. A finite element model of LSTS-tower-line coupling system is established and excited by 40 near-fault pulse-like (NFP) and 40 far-filed (FF) earthquakes with multiple incident directions. The seismic response, bearing capacity, failure mode, and collapse fragility of LSTS at different angles of seismic incidence (ASIs) are examined. The results indicate that the effect of ASI on seismic responses is significant, and it is diverse for different response quantities, under different earthquakes, and when the LSTS is in different damage states. The earthquake-dependent most unfavorable ASI (MUF-ASI) is uniformly distributed in the horizontal plane. The change of ASI may transform the LSTS failure from a favorable ductile mode to an unfavorable brittle mode, resulting in a great reduction of bearing capacity. The collapse risk of LSTS is obviously affected by the ASI, and this effect under FF earthquakes is greater than that under NFP earthquakes. The traditional excitation method cannot identify the maximum response and collapse risk of LSTS.