en Research Paper Research Paper One main factor in design of panels subjected to axial loading is their buckling behaviour. The design of stiffeners in a metal or composite plated structure is the key factor for safety and weight reduction. This work presents a parametric study on the optimal types and geometrical properties of stiffeners in plates under in-plane axial loads. The results show that flanged type (such as T or L) longitudinal stiffeners increase the normal critical stresses by at least 28% compared to non-flanged stiffener. It is also shown that the optimum geometric properties of stiffeners correspond to the point when the buckling shape of a plate changes from the overall to local mode. Also it is illustrated that for these optimal instances, there always is a linear relationship between the cross-sectional area ratio and the rigidity ratio of the stiffeners to the plates. Finally, Sample relationships for plates having different number of stiffeners are presented. Plate buckling; Axial loading; Stiffener; Optimization 246 256 http://ijce.iust.ac.ir/browse.php?a_code=A-10-3-272&slc_lang=en&sid=1 M.M. Alinia m.alinia@aut.ac.ir 180031947532846002052 180031947532846002052 Yes