This work presents a new approach for deterministic and robust thickness sizing optimization of a stiffened panel subject to geometric imperfections. Fully nonlinear pre- and postbuckling analyses determine time-dependent reaction forces using the backward Euler integration method. The global buckling resistance is optimized by maximizing the sum of reaction forces in the pre- and postbuckling regions without the necessity to directly evaluate the buckling point. The robust design optimizations consider geometric imperfections as parametrized random fields using an approach based on Fourier series. The first-order second-moment method (FOSM) determines the mean and the variance of the objective function in each optimization iteration. Monte Carlo simulations validate the FOSM approach for the present optimization formulation. The robust optimized designs show significantly increased buckling loads and robustness compared to the initial design and deterministically optimized designs even for the deterministic use case.
