"The analysis and design of shell structures is of interest in... the design of large-span roofs, liquid storage facilities, silos... pressure vessels, including nuclear reactor containment vessels and pipes... structural design of aircrafts, rockets and aerospace vehicles. All... require the analysis and design of shells... [T]he derivation of equations for plates or shells is only an extension of... bars or beams, based on equilibrium, , and . ...Using the understanding of shell behavior... including the approximate methods and... tables for quick solutions... a reader may be able to judge the computer results, before designing a shell structure. ...Theory of circular rings, concepts of stress resultants and middle surface are... introduced... Circular also forms an intermediate step for a gradual introduction or transition to shell analysis from the analysis of bars and beams."