8 - Welded Stiffened Cylindrical and Conical Shells

Abstract

This chapter discusses welded stiffened cylindrical and conical shells. The economy of some structural types is demonstrated by the comparison of minimum costs of different structural versions. Such a comparison has been performed for various kinds of stiffened cylindrical shells, such as ring stiffeners, external pressure, ring stiffeners, bending, stringer stiffeners, axial compression and bending, stringer stiffeners, bending, ring and stringer stiffeners, axial compression, and external pressure. The optimum design problem is solved for a slightly conical shell loaded in external pressure with equidistant ring-stiffeners of a welded square box section. The optimum number of shell segments is found, which minimizes the cost function and fulfils the design constraints. The thickness of each shell segment is calculated from the shell buckling constraint. This constraint is similar to that for circular cylindrical shells, but an equivalent thickness and segment length is used according to the DNV design rules. The dimensions of ring-stiffeners for each shell segment are determined on the basis of the ring buckling constraint. This constraint is expressed by the required moment of inertia of the ring-stiffener cross-section. The cost function includes the cost of material, forming of plate elements into shell shape, assembly, welding, and painting. The fabrication cost function is formulated according to the fabrication sequence. The forming, welding, and painting costs play an important role in the total cost.