FEM Study of Double-slab Tank Foundations with and Without Bottom Slab Slits Considering Seismic Effect and Soil Structure Interaction

More than four decades ago, a double-slab reinforced concrete foundation concept for large-diameter steel storage tanks incorporating orthogonal slits in the bottom slab was proposed but not adopted because of concerns regarding structural continuity and seismic performance. With advances in finite element modelling and soil–structure interaction analysis, the structural behaviour of such an articulated foundation system can now be re-examined. This study compares two foundation configurations: (A) a conventional monolithic double-slab foundation and (B) a slitted configuration in which full-depth orthogonal slits are introduced in the bottom slab and connected through shear dowels. Three-dimensional finite element models are developed using solid elements to represent the concrete components and Winkler-type elastic springs to simulate soil support. The analysed system represents a 58 m diameter storage tank foundation subjected to a uniform pressure load of 150 kPa together with a horizontal seismic acceleration of 0.25 g. The complete structural system is modelled as one combined unit and analysed. The results indicate that the slitted configuration reduces peak soil contact pressure from approximately 210 kPa to 185 kPa, resulting in a more uniform pressure distribution under static loading. However, the associated reduction in global stiffness increases vertical deflection from 18.2 mm to 19.1 mm under static load and from 23.75 mm to 25mm under seismic loading. Stress concentrations are also observed near slit–dowel interfaces under seismic excitation. The findings demonstrate that controlled articulation of foundation slabs can modify load-transfer mechanisms and soil pressure behaviour, although its application requires careful detailing and consideration of seismic effects. The study provides analytical insight into articulated tank foundation systems and establishes a rational framework for evaluating such configurations within performance-based foundation design.