Abstract: An improved upstanding cylindrical tank is provided, in one aspect of the invention, with a ring-like stiffening member at its open upper end to resist flexure and deformation of the side wall structure under wind loading. The stiffening member has a cylindrical inner flange portion formed integrally with the tank wall, an annular web portion extending radially outward from an upper part of the upper flange portion, and a cylindrical outer flange portion depending from an outer part of the web portion and arranged concentrically with the inner flange portion. The stiffening member has a minimum vertical moment of inertia and is configured to have its vertical neutral axis located approximately midway between the furthermost fibers of the inner and outer flange portions.