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The analysis and optimum design of stiffened, shear webs in aircraft structures is addressed. The post-buckling behaviour of the webs is assessed using the interactive algorithm developed by Grisham. This method requires only linear finite element analyses, while convergence is typically achieved in as few as five iterations. The Grisham algorithm is extensively compared with empirical analysis methods previously used for aircraft structures and also with a refined, non-linear quasi-static finite element analysis. The Grisham algorithm provides for both compressive buckling in two directions as well as shear buckling, and overcomes some of the conservatism inherent in conventional methods of analysis. In addition, the method is notably less expensive than a complete non-linear finite element analysis, even though global collapse cannot be predicted. While verification of the analysis methodology is the main focus of the stud, an initial investigation into optimization is also made. In optimizing stiffened thin walled structures, the Grisham algorithm is combined with a genetic algorithm. Allowable stress constraints are accommodated using a simple penalty formulation. / Dissertation (MEng (Mechanical and Aeronautical Engineering))--University of Pretoria, 2006. / Mechanical and Aeronautical Engineering / unrestricted