Ultimate shear strength of Perfobond Rib (abbreviated as PBL) in a push-out test was examined using the lower bound theorem of limit analysis under modeling of perfectly plastic material for 3D compressive concrete. Linearized Mohr-Coulomb criterion was applied to yield and fracture of concrete, and discontinuous stress fields were assumed to concrete part within a steel rib hole and on its vicinity. Numerical analyses showed the effect of the hole diameter and thickness on the ultimate concrete dower strength of PBL. Discussion was made on comparison between the numerical results and the existing test ones.