Seismic analysis of base-isolated liquid storage tanks incorporating a new probabilistic long-period critical excitation method

This paper investigates the seismic behavior of base-isolated cylindrical liquid storage tanks under the effects of long-period ground motions by proposing a new critical excitation method (CEM). The proposed CEM establishes an upper bound on earthquake input energy per unit mass—derived from site‐specific records—to generate synthetic ground motions that realistically represent worst-case seismic scenarios. A novel, piecewise power spectral density (PSD) function is also introduced with explicitly calibrated parameters that accurately capture long‐period characteristics. This PSD formulation improves analysis accuracy by precisely controlling the excitation’s intensity and frequency content. Moreover, a three degrees of freedom (3DOF) model is developed to represent slender, medium, and broad liquid storage tanks equipped with two types of isolators—Lead Rubber Bearings (LRB) and Friction Pendulum Systems (FPS)—along with a fixed-support scenario included as a baseline for comparison. To assess the reliability of the findings, a benchmark is established by selecting sample real accelerograms that exhibit a significantly high level of total input energy. Subsequently, dynamic analyses are performed utilizing the accelerograms associated with the generated critical excitations. The proposed objective function—the sum of the mean-square relative displacements of the three lumped masses—provides a robust measure of global structural seismic demand. The findings indicate that the produced long-period excitations can offer a satisfactory approximation of the structural response compared to the actual benchmark accelerograms.