Optimum design of composite channel cross-section columns under compression

Thin-walled open cross-section bars are effective structural members (with respect to overall stability). But the weight efficiency of bars with flat walls is constrained by their low stiffness in local buckling. The use of composites and multi-layer materials is one of perspective ways to overcome this shortage. The minimum-weight problem for such laminated bars has not been studied until now. In the paper a solution to the structural optimization problem for three-layer channel cross-section columns under compression is presented. The optimization problem is formulated as a nonlinear programming problem. Basic constraints are conditions of overall and local stability. In addition, strength, wrinkling and geometrical constraints (on minimal thickness of skin layers and maximal total thickness) have been accounted for. For the given material properties the optimal dimensions of the cross-section and the optimal thickness ratio (for the steel and composite layers) are determined. The three-layer members are shown to be much more efficient in comparison with columns made of homogeneous materials. The sensitivity of optimal projects to
changes in the material properties (in particular, to changes of the modulus of elasticity in tension and in shear) is also studied.