Stiffened plates constitute nearly 60-70% of the total structural weight of Air Pollution Control (APC) equipment, which about 200-300 Tons. By allowing for plastic deformation for a very small region near the edges of the plates together with the consideration for large deflection, the required plate thickness can be minimized or the spacing between stiffeners can be increased, which will result in considerable reduction in the unit weight of the stiffened plate. The applicability of such a phenomenon for the design of stiffened plate used in APC equipment is verified in this study. A set of geometrical and material non-linear large deflection analysis is performed for a typical stiffened plate configuration found in APC equipment to study the impact of boundary conditions, effect of stiffener profile and loading directions on the simplified expressions proposed for the manual calculation of such plates. © 2016 Taylor & Francis Group, London.