Abstract
This paper aims to investigate the seismic vulnerability of an existing unanchored steel storage tank ideally installed in a refinery in Sicily (Italy), along the lines of performance-based earthquake engineering. Tank performance is estimated by means of component-level fragility curves for specific limit states. The assessment is based on a framework that relies on a three-dimensional finite element (3D FE) model and a low-fidelity demand model based on Gaussian process regression, which allows for cheaper simulations. Moreover, to approximate the system response corresponding to the random variation of both peak ground acceleration and liquid filling level, a second-order design of experiments method is adopted. Hence, a parametric investigation is conducted on a specific existing unanchored steel storage tank. The relevant 3D FE model is validated with an experimental campaign carried out on a shaking table test. Special attention is paid to the base uplift due to significant inelastic deformations that occur at the baseplate close to the welded baseplate-to-wall connection, offering extensive information on both capacity and demand. As a result, the tank performance is estimated by means of component-level fragility curves for the aforementioned limit state which are derived through Monte Carlo simulations. The flexibility of the proposed framework allows fragility curves to be derived considering both deterministic and random filling levels. The comparison of the seismic vulnerability of the tank obtained with probabilistic and deterministic mechanical models demonstrates the conservatism of the latter. The same trend is also exhibited in terms of risk assessment.
Highlights
1.1 Background and motivationThe integrity of the oil and gas industry, and in particular of large-capacity atmospheric tanks for hazardous material storage, is important for maintaining the flow of energy products and for preventing significant potential catastrophic events
Two crucial steps of the performance-based earthquake engineering (PBEE) are represented by the damage analysis that incorporates any engineering demand parameter (EDP) distribution into fragility functions; and the loss analysis that is typically expressed in the form of mean annual frequency (MAF) of exceeding a threshold of interest for industrial owners and stakeholders
3D FE models outperform because: (1) they account for full interaction between limit states; (2) they distinctly indicate the interaction between tank and liquid as well as tank and foundation; (3) they minutely allow for the estimation of system fragility curves
Summary
The integrity of the oil and gas industry, and in particular of large-capacity atmospheric tanks for hazardous material storage, is important for maintaining the flow of energy products and for preventing significant potential catastrophic events. The basic idea of Kriging is to predict the value of a function at a given point by computing a weighted average of known values of the function in proximity of the point This approach treats the function of interest as a realization of a Gaussian random process whose parameters are estimated from available inputs and model responses (Rasmussen and Williams 2006; Lu et al 2018). In order to set seismic fragility functions, both HF and LF models of a steel storage tank with unanchored support conditions based on a Kriging model and a design of experiments (DOE) method are proposed Though both Eurocode 8, part 4 (2006) and API 650 (2007) restrict uplift of unanchored above-ground storage tanks, their seismic response is highly nonlinear, dependent on several parameters and much more complex than that predicted by design standards based on a mechanical spring-mass analogy.
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