The effect of stiffeners on the optimal ply orientation and buckling load of rectangular laminated plates

Optimal designs of symmetrically laminated rectangular plates with different stiffener arrangements are presented. The plates are subject to a combination of simply supported, clamped and free boundary conditions, and the design objective is the maximisation of the biaxial buckling load. This is achieved by determining the fibre orientations optimally with the effects of bending–twisting coupling taken into account. Square tubing is used as stiffeners, and the finite element method coupled with an optimisation routine is employed in analysing and optimising the laminated plate designs. The effect of the stiffener arrangement and boundary conditions on the optimal ply angles and the buckling load are numerically studied. It is demonstrated that in some cases, stiffeners can sometimes reduce, rather than increase the buckling strength of an optimally designed plate.