In this thesis improved expressions for elastic local plate buckling and overall panel buckling of uniaxially compressed T-stiffened panels are developed and validated with 55 ABAQUS eigenvalue buckling analyses of a wide range of typical panel geometries. These two expressions are equated to derive a new expression for the rigidity ratio (EIx/Db)CO that uniquely identifies ¡°crossover¡± panels ¨C those for which local and overall buckling stresses are the same. The new expression for (EIx/Db)CO is also validated using the 55 FE models. Earlier work by (Chen, 2003) had produced a new step-by-step beam-column method for predicting stiffener-induced compressive collapse of stiffened panels. An alternative approach is to use orthotropic plate theory. As part of the validation of the new beam-column method, ABAQUS elasto-plastic Riks ultimate strength analyses were made for 107 stiffened panels ¨C the 55 crossover panels and 52 others. The beam-column and orthotropic approaches were also used. A surprising result was that the orthotropic approach has a large error for crossover panels whereas the beam-column method does not. Some possible reasons for this are suggested. Collapse patterns for the crossover panels are studied and classified from von Mises stress distribution at collapse. The collapse mechanism and load-deflection diagrams suggest stable inelastic post collapse behavior for most panels and an abrupt drop in load carrying capacity in only nine of the 55.