The subject of this paper is the buckling behavior of thin bar stiffeners attached to plates which are subjected to normal pressure loadings. The stiffeners are mathematically modeled by a nonlinear beam theory recently derived. An analytical solution is obtained to the beam buckling equations. The curvature of the centerline along the beam's base at the buckling load is expressed in terms of the beam's thickness, height, and rotational stiffness. Analytical results are compared with an experiment recently performed. Keywords: Tripping, Buckling, Plates, Beams, Stiffeners, Structures, Solid mechanics, Submarines, Ships, Aircraft, Grillages, Bars, Frames, Pressure, Elasticity, Stability, Panel, Compression.