An experimental study of the effect of plate slenderness ratio and column slenderness ratio on the collapse load of simply supported stiffened plates with initial imperfections, loaded in compression, is presented. A generalized computer program for the semiempirical solutions based on the strut approach and the orthotropic plate approach is developed. A finite element analysis program based on the orthotropic plate approach is developed and a new collapse criterion is introduced. The analytical calculations are compared with the experimental results and uncertainty parameters are calculated. The effect of initial geometric imperfections, plate slenderness ratios, and column slenderness ratios on the collapse load of stiffened plates is studied. A set of conclusions is drawn based on the experimental and analytical studies carried out.