Optimum design of a welded stringer-stiffened steel cylindrical shell subject to axial compression and bending

A column fixed at the bottom and free on the top is made of stringer-stiffened cylindrical shell and loaded by axial compression as well as by a horizontal force acting on the top. Halved rolled I-section stringers are welded outside of the shell by longitudinal fillet welds. The aim is to study the economy of stiffened shells. Therefore both the stiffened and the unstiffened version are optimised and their costs are compared to each other. The stiffening is economic when the shell thickness can be decreased in such a measure that the cost saving caused by this decreasing is higher than the additional cost of stiffening material and welding. The cost function to be minimized includes the costs of material, forming of shell elements into the cylindrical shape, assembly, welding and painting. The constraints relate to the shell buckling, stringer panel buckling and limitation of the horizontal displacement of the column top. The cost comparison shows that the cost of stiffened version is lower than that of the unstiffened one only in those cases, when the constraint on horizontal displacement is active.