Minimization of the weight of ribbed cylindrical shells made of a viscoelastic composite

The minimization of the weight of ribbed viscoelastic composite cylindrical shells under a long-term external pressure is considered. The shells are strengthened with six inner stiffening rings with identical geometric parameters and a square cross section. It is assumed that the shell material obeys the linear law of hereditary creep and the displacements across the shell wall are distributed according to the Timoshenko hypothesis. The shell must withstand an external pressure of –0.5 MPa without the loss of stability for an unlimited time. The parameters of optimization are the intensity of reinforcement and thickness of its covering and the height and width of the stiffening rings. It is found that the weight of an optimum ribbed shell is 24% lower than that of an optimum cylindrical shell without ribs.