This paper presents a numerical approach to evaluate the optimum rib configuration in a catalytic converter shell in order to ensure the safest stress state in a cellular ceramic monolith under assembly conditions. Specifically, the paper seeks to determine the rib width and orientation.Numerical studies are conducted on an axisymmetric, orthotropic, finite element model of a ceramic monolith to simulate the stresses under converter assembly conditions. Different rib widths and orientations are modeled. The ceramic monolith is modeled as a homogeneous continuum. The macroscopic stress state is transformed into stresses in the cell walls. The microscopic stresses are then compared to the base material strengths in order to determine monolith integrity.