Optimization of a cylindrical shell housing a belt-conveyor bridge

A belt-conveyor bridge is built inside a ring-stiffened cylindrical shell, the belt-conveyor supports being independent of the stiffeners. Reliability-based and deterministic optimization results are compared. The design variables are the shell thickness as well as the thickness and the number of flat rings. Optimum solutions are evaluated for different bridge lengths in view of finding the most effective cost/span ratios. The design constraints relate to the local shell buckling strength, to the panel ring buckling and to the deflection of the bridge. The cost function includes the material and fabrication costs. A level II reliability method (FORM) is used to find the probability of failure. The overall structural reliability is obtained by using Ditlevsen method of conditional bounding. The costs of the plate designed to ensure a stipulated probability of failure will be compared with the solutions obtained for a code based method, which employs partial safety factors. A branch and bound strategy coupled with a entropy-based algorithm is used to provide discrete solutions.