Wall-Bottom Joint Rotation of Cylindrical Concrete Water Tank

Abstract

Cylindrical concrete water tanks resting on the ground are widely used in water and wastewater treatment plants. The hoop force in the cylindrical wall is a critical design force. Rotation of the wall-bottom joint directly influences the design forces, i.e., hoop force and bending moment of the tank wall. The prevalent method of design suggests the assumption of hinge and fixed conditions at the wall bottom for the maximum value of hoop force and bending moment, respectively. However, many recent studies have shown that there is a possibility of the wall-bottom joint rotation being more than the hinged wall-bottom joint rotation. This happens in case of tanks resting on deformable strata. This paper presents a simplified analytical expression for rotation at a hinged wall-bottom joint and further develops analytical expressions for design forces for a known wall-bottom joint rotation for any tank with finite dimensions. The analytical expressions developed are ratified by finite-element analysis (FEA) as well as with standard design tables. By knowing the exact value of rotation at the wall-bottom joint and corresponding design forces, practicing engineers can assess the possible adverse effect of the deformable strata.