Stress Analysis and Strength Design for the Bottom Node of Cylindrical Metal Tanks

The bottom node of a cylindrical metal tank consists of bottom shell course, fillet weld and annular plate, and the strength design of the bottom node is of great importance to the whole tank. For the correction of the maximum circumferential stress (primary stress) in tank shell, firstly considered is the combined effect of three circumferential stresses: ①σ_a: resulting from M₀ for axial shell displacement, ②σ_b from M₁ and Q₁ for axial deformation of bottom shell course, and σ_c from the axial bending stress. For the correction of fillet weld, M₀ is used as the bending moment in the junction between bottom shell course andfillet weld, which is the critical point for secondary stress correction. For the strength correction for annu-al plate, calculations show that the maximum bending moment exists in the two sides near the central lineof shell plates, and the correction method is the same as for the secondary stress. In addition to the theo-ratical analysis and classification for primary and secondary stresses in bottom node, strength correction is also made for existing tanks and suggestions are given for tank modification.