ANALYSIS OF CIRCULAR TANK FOUNDATION ON MULTILAYERED SOIL USING VARIATIONAL APPROACH

Large circular storage tanks transmit the load from the stored liquid and self-weight to the ground beneath a tank foundation. Excessive differential settlement in the foundation may cause distress within the shell, bottom plate, connection of shell to bottom plate, and roof. Therefore, differential settlement between the center and edge of the circular storage tank is an important design consideration. However, there are no readily-available analysis tools to compute tank differential settlements of the bottom plate resting on a multilayered soil. This dissertation presents a continuum-based, semi-analytical, elastic analysis model for a uniformly-loaded circular tank foundation resting on a multilayered soil deposit. The analysis method can be applied to both concrete and steel tanks. The soil in each layer is assumed to behave as a linear-elastic material. The foundation is modeled as a circular plate which is assumed to be isotropic, homogeneous, and linear elastic based on Kirchhoff’s small-deflection theory of bending. The governing differential equations are derived based on variational principles and solved numerically. The input parameters needed for the analysis are the plate geometry, the thickness of soil layers, and the elastic properties of the soils and plate. The analysis method captures the three-dimensional nature of soil-structure interactions and produces settlement profiles of the tank foundation and the soil below it with much less computational effort than finite element analysis (FEA). Model validation was achieved by comparing results from the present analyses with those from the literature and from FEA. A parametric study highlights important insights into the effects of plate diameter, plate thickness, and stiffness ratio of plate to soil on differential settlement of the tank foundation. Based on the results from the parametric study, design charts are presented to estimate the differential settlement of a tank foundation for given plate and soil properties. The proposed semi-analytical method successfully captured the effects of soil layering such as thickness and stiffness ratio of multiple soil layers on behavior of the circular plate. Analyses for wide ranges of plate-to-soil stiffness ratios provide further insights on plate-soil interactions.