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.

本文旨在研究基于性能的地震工程，理想地安装在意大利西西里岛的一家炼油厂中的现有未锚固钢制储罐的地震脆弱性。通过针对特定极限状态的组件级脆性曲线估算储罐性能。该评估基于一个框架，该框架依赖于三维有限元（3D FE）模型和基于高斯过程回归的低保真需求模型，从而可以进行更便宜的仿真。此外，为了近似对应于峰值地面加速度和液位的随机变化的系统响应，采用了实验方法的二阶设计。因此，对特定的现有未锚固钢制储罐进行了参数研究。通过在振动台测试上进行的实验活动来验证相关的3D FE模型。由于在靠近焊接的底板到墙的连接处发生严重的非弹性变形，因此特别注意底板的隆起，从而提供了有关容量和需求的大量信息。结果，通过蒙特卡罗模拟得出的上述极限状态的组件级脆性曲线估算了储罐性能。所提出框架的灵活性允许在考虑确定性填充水平和随机填充水平的情况下得出脆性曲线。通过概率和确定性力学模型获得的储罐地震易损性的比较证明了后者的保守性。