the shell resists external loads mainly by the medium surface stresses uniformly distributed along the thickness, rather than by the bending stresses varying along the thickness. this internal force characteristic of the shell makes it able to fully utilize the material strength than the flat plate, and thus has a large load carrying capacity. In water conservancy projects, shell is widely used, such as hyperbolic flat-shell gates, arch dams, etc.. In addition shell theory belongs to the category of applied elastodynamics, need to quote new assumptions in addition to the basic assumptions of elastodynamics, it includes thin shell theory and medium-thick shell theory.