Development of Analytical Fragility Curves for Cylindrical Steel Oil Tanks

Abstract eng:
Aboveground cylindrical liquid storage tanks are important components of industrial plants especially oil refineries and petrochemical facilities. Performance of liquid storage tanks during the past earthquakes showed that these structures are seismically vulnerable. For this reason the evaluation of seismic vulnerability of existing liquid storage tanks is an important task in high seismic risk zones of the world. Seismic performance functions (such as fragility curves) are useful tools in order to quantify seismic vulnerability of structures. These functions formulate loss or probability of occurrence or exceeding of damage state in terms of seismic hazard level. There are at least four approaches for development of seismic fragility functions: judgmental, empirical, analytical and hybrid methods. The purpose of this study is development of seismic fragility curves for on-ground steel oil tanks based on analytical and empirical approach. For this purpose, existing liquid storage tank of one of the Iranian oil refineries selected and modeled by using FEM. Nonlinear time-history analysis carried out to estimate seismic performance of tanks of different height to diameter (H/D) ratios and different volume of contained liquid (%full). The seismic fragility curves of oil storage tanks developed by using the results of numerical analyses. The seismic fragility curves, developed herein presented in terms of H/D ratio and % Full and compared to available seismic fragility curves of cylindrical steel tanks. The results of this study showed that H/D ratio and % full are major sources of uncertainty in seismic fragility curves of cylindrical steel oil tanks. It has also shown that improper distribution of tanks in the earthquake affected area may cause noticeable dispersions in empirical fragility curves.

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