Seismic Vulnerability Assessment and Fragility Functions Derivation for Steel Storage Legged Tanks

The major earthquakes that occurred worldwide in the last decades highlighted the seismic vulnerability of industrial structures and their components. Beyond the need to avoid human losses, the damages experienced by industrial facilities, both in terms of structural, non-structural and plant elements, significantly affected the economy of such areas. On the one hand, often the damages of non-structural components and their contents immediately lead to significant monetary loss. On the other hand, the leakage of toxic contents or the disruption of mechanical equipment can conduct to down-time of industrial plants. Following the 2012 Emilia earthquake in Italy, one of the most damaged components in industrial facilities, among others, was the steel storage legged tank. This research aims to investigate the seismic vulnerability of such elements by defining suitable fragility functions, also useful for future loss estimation studies. Several engineering demand parameters (EDPs) were selected in order to line up the damages observed in the aftermath of earthquakes. To draw general conclusions, several legged tanks were selected and analyzed. A suitable record selection has been performed, for which the average spectral acceleration (AvgSa) was selected as intensity measure (IM). Once adequate performance objectives were defined, the legged tank archetypes were analyzed by means of multiple-stripe analyses (MSA) to calculate the fragility functions and to highlight the most critical elements and tank configurations.