In addition, a further set of design curves for stiffened panels were published by Smith et al. (1991). These investigated stiffened panels with tee-bar and flat-bar stiffeners under compressive load. The structures were defined with a range of different plate slenderness ratios (β) and column slenderness ratio (λ). The parameters investigated also included the plate imperfections which were divided in three cases as slight, average and severe imperfections with 3-percentile, 50-percentile and 97-percentile of initial plate displacement (W0) and compressive residual stress (σRC) respectively. The results of this study show that the imperfection becomes more influential for a slender structure that has λ over 0.8.