Directionality effect in the seismic fragility of long-span supporting frames in ultrahigh-voltage substation

Abstract

A 1000 kV outgoing line frame (OLF1000), which is an important and long-span supporting frame in ultrahigh-voltage substations (UHVSs), is prone to damage or collapse under strong earthquakes, resulting in serious power system outage. This study numerically investigates the seismic fragility of OLF1000, which has complex and multiple interactions with transmission towers and lines, subjected to earthquakes with multiple angles of seismic incidence (multi-ASI). A new multi-ASI seismic fragility analysis method (N-MASI-SFAM) considering the orientation layout of the structure and strike of the fault zone is proposed; it fully reflects record-to-record, structure-to-structure, and direction-to-direction uncertainties. The samples of structure-record-ASI pairs and structure-record pairs are generated using Latin hypercube sampling to develop probabilistic seismic capacity models and probabilistic seismic demand models for OLF1000. In addition, fragility planes of OLF1000 for different limit states are generated by performing the N-MASI-SFAM, which provide suggestions for the orientation layout of OLF1000-tower-line coupling system outside the UHVSs. Further, the results obtained by N-MASI-SFAM and seismic fragility analysis method based on the traditional excitation method (TEM-SFAM) are compared, and they demonstrate that the TEM-SFAM cannot identify the maximum seismic risk of the OLF1000; the guarantee rates of TEM-SFAM are 51% and 45% under far-field and near-fault pulse-like earthquakes, respectively, indicating that its reliability in the seismic fragility analysis of OLF1000 is very low. Finally, a seismic risk assessment method based on the epicenter position is proposed, and the seismic risk of built engineering structures is quantitatively evaluated.