A risk-targeted seismic performance assessment of elephant-foot buckling in walls of unanchored steel storage tanks

Unanchored steel storage tanks are used in industrial plants to store oil and other petrochemical liquids. In a major earthquake, such tanks may sustain different types of damage, including elasto-plastic buckling in the shape of an elephant's foot, which is the object of the research. The methodology introduced in this paper consists of cloud-based 1D site response analysis (SRA) and pushover-based seismic performance assessment of the tank wall using a 3D non-linear model of the tank. The SRA, which considers the recorded ground motions on the rock outcrop and the sample of interval shear-wave velocity profiles, is carried out to estimate spectral accelerations at the tank impulsive period. By adopting the code-based model of hydrodynamic pressures, the seismic demand on the tank wall is then calculated by pushover analysis. The risk-targeted decision model is used for safety verification. The proposed methodology is demonstrated through an example of a large liquid storage tank for which it is shown that the fragility function for peak ground acceleration at the rock outcrop is on the left side of the target fragility function, indicating that the tank cannot be considered safe from elephant-foot buckling. The introduced assessment process is relatively simple if the cloud-based SRA is automated. However, further experimental and numerical investigations are required to confirm the validity range of the pushover analysis for the seismic performance assessment of tanks.