Fragility and Resilience Indicators for Portfolio of Oil Storage Tanks Subjected to Hurricanes

Abstract

This paper develops fragility functions and estimates of resilience indicators for aboveground storage tanks (ASTs) subjected to hurricanes, which can be efficiently applied to all the tanks in a regional portfolio of ASTs to assess their hurricane performance. Fragility and resilience assessment of a portfolio of ASTs is essential for planning mitigation strategies at the regional level and at the level of individual structures. Recently, studies have started assessing the fragility of ASTs under hurricane loads; most of the existing studies are focused on a specific AST type and a specific hurricane-related hazard. However, in order to facilitate performance assessment of an entire portfolio of ASTs, fragility functions for different types of tanks and hazards are necessary, which are lacking in the literature. Furthermore, estimates for resilience indicators such as repair costs and downtime are also not available in the literature. Therefore, to address these gaps, this study first develops fragility functions for different types of ASTs subjected to hurricane winds and storm surge. Next, estimates of repair costs and downtime are defined for different failure modes of ASTs by adapting costs and downtime for similar failure modes from different hazards. The fragility functions, repair costs, and downtime estimates developed herein are used to assess the performance of ASTs in the Houston Ship Chanel (HSC), which houses more than 4,5 ASTs, for two synthetic hurricane scenarios corresponding to 1 and 25-year return period events. For both scenarios, 1, Monte Carlo simulations are performed for each tank to determine the failure probability, repair costs, and downtime for all ASTs while propagating uncertainties in the fill level and density of contents stored in all ASTs. Furthermore, the influence of anchoring all tanks as a storm surge risk mitigation strategy on the performance of ASTs is also evaluated. The results provide several insights into the performance of tanks in the Houston Ship Channel during the two hurricanes: the tanks are not vulnerable to hurricane winds; however, failures are observed due to storm surge, which highlights the need for storm surge mitigation measures for the Houston Ship Channel region. Furthermore, tanks with the highest failure probability do not necessarily lead to high spill volumes or repair costs. Moreover, even minimum anchoring is observed to be effective in significantly reducing the spill volume and repair costs.