Discontinuity phenomena around the supports of stepwise-thickened spherical steel tanks. Part 1: Theoretical considerations and parametric results

Abstract

The present study examines the ‘edge-effect’ phenomena that occur at the upper and lower thickness-discontinuity locations of spherical steel tanks in which shell thickness is stepwise-increased in a band centred about the support circle of latitude. Such phenomena are considered in relation to the ‘edge effect’ occurring at the support itself as a result of the reactions and constraints there. The uniform local thickening of the shell in the vicinity of the supports is usually adopted to counter the excessive bending-disturbance stresses that would otherwise occur in this region were a constant shell thickness (chosen on the basis of peak membrane stresses) adopted throughout, especially where the vertical supports happen to be positioned well below the equatorial plane. Presently, the necessary expressions for a full static analysis of the structural problem are derived, and some parametric data given. In a follow-up paper (Zingoni and Pavlović, Int. J. Pres. Ves. & Piping, 53 (1993) 437-56, numerical examples are considered, and design implications pointed out.