Unified force-based design approach for the seismic analysis and design of liquid storage tanks

Historical observations reveal that Liquid Storage Tanks (LST) have suffered significant earthquake-induced damages. The structural response of LST are sensitive to earthquakes due to dynamic fluid-tank interaction. Since designing with consideration of fluid-tank interaction in the time domain is complex, simplified calculation approaches have been developed to calculate base shear and overturning moments, but not pressure distributions. These approaches distinguish between flexible and rigid tanks, which is difficult to decide prior analysis. This paper presents a unified calculation concept that determines support reactions and pressure distributions independently of the tank’s stiffness by applying static equivalent loads. The research focuses on the distinction between rigid and flexible design approaches, review existing codes, their limitations, and challenges associated with relative acceleration response spectra. It scrutinizes varying definitions of impulsive components and superposition principles. A unified force-based design approach is suggested that integrates rigid and flexible design principles into a unified method. The approach uses standardized pressure curves of individual hydrodynamic pressure components, linked with absolute and relative spectral accelerations and appropriate superposition methods. The unified formulation is validated through a previously conducted experimental and numerical research on above-ground steel tank. The validation and application of the unified approach forms the basis for the new generation of Eurocode FprEN 1998-4 (2025), which is demonstrated for different tank geometries. The practical application is demonstrated on a squat and a slender tank using linear finite element model, and the results are compared with various approaches in the international standards and literature.