Enhanced Seismic Fragility Analysis of Unanchored Steel Storage Tanks Accounting for Uncertain Modeling Parameters

Abstract

Catastrophic failure of the above ground steel storage tanks was observed during past earthquakes, which caused serious economic and environmental consequences. Many of the existing tanks were designed in the past with outdated analysis methods and with underestimated seismic loads. Therefore, the evaluation of the seismic vulnerability of these tanks, especially ones located in seismic prone areas, is extremely important. Seismic fragility functions are useful tools to quantify the seismic vulnerability of structures in the framework of probabilistic seismic risk assessment. These functions give the probability that a seismic demand on a given structural component meets or exceeds its capacity. The objective of this study is to examine the seismic vulnerability of an unanchored steel storage tank, considering the uncertainty of modeling parameters that are related to material and geometric properties of the tank. The significance of uncertain modeling parameters is first investigated with a screening study, which is based on nonlinear static pushover analyses of the tank using the abaqus software. In this respect, a fractional factorial design and an analysis of variance (ANOVA) have been adopted. The results indicate that the considered modeling parameters have significant effects on the uplift behavior of the tank. The fragility curves of two critical failure modes, i.e., the buckling of the shell plate and the plastic rotation of the shell-to-bottom plate joint, are then developed based on a simplified model of the tank, where the uplift behavior is correctly modeled from the static pushover analysis. The uncertainty associated with the significant parameters previously identified are considered in the fragility analysis using a sampling procedure to generate statistically significant samples of the model. The relative importance of different treatment levels of the uncertainty on the fragility curves of the tank is assessed and discussed in detail.

Seismic vulnerability of above-ground storage tanks with unanchored support conditions for Na-tech risks based on Gaussian process regression

“…Salzano et al (2003) or (2) analytical approaches covering single failure modes that use simplified or refined models for fluid-structure interaction modelling, e.g. Iervolino et al (2004), Buratti and Tavano (2014), , (2017), Cortes and Prinz (2017) and Phan et al (2019). Regarding analytical approaches, fragility functions are derived using the results of nonlinear dynamic analyses of structural models; therefore, the accuracy of fragility functions strongly depends on the reliability of relevant models.…”

“…Generally, uncertain modelling parameters of storage tanks include both geometry and material properties. In this respect, in order to find which modelling parameters entail a significant effect on the seismic response of unanchored tanks, Phan et al (2019) carried out a screening study; the authors found that the liquid filling level, among other geometry and material random variables such as shell plate thickness, baseplate thickness, steel yielding strength and liquid density, is the most significant one for the purpose of determining fragility functions. They have also found that fragility curves developed considering only the most significant modelling parameter are almost the same as those considering all random variables.…”

Seismic Fragility Analysis of Steel Liquid Storage Tanks Using Earthquake Ground Motions Recorded in Korea

“…This study aims to derive the seismic fragility of a steel tank containing liquids, which is an important facility of industrial complexes, considering the hydrodynamic forces caused by oscillating liquids. Steel tanks can be classified to two groups, anchored and unanchored tanks, and it has been reported that their dynamic behaviors are quite different [35,36]. This study examines the seismic fragility of an anchored steel liquid storage tank, which was relatively less well studied in previous studies but still an important facility of industrial complexes.…”

Seismic vulnerability analysis of storage tanks for oil and gas industry

“…The uplift mechanism of the tanks can be simulated by a rotation spring that represents the rocking resistance of the base, as shown in Fig.7. The behaviour of the resistance spring can be obtained using either the simplified approach presented by Malhotra and Veletsos (1994) [8] or the more refined approach presented by Phan et al (2018) [9].…”