How do you analyze crippling stress in stiffener sections?

Crippling is local buckling failure in stiffener sections (angles, Z's, hat sections) under compression. Analysis using Gerard's method divides sections into flat plate elements classified as: one-edge-free (outstanding flanges), two-edges-supported (webs), and computes weighted average crippling stress. Factors include: plate b/t ratios, edge support conditions, corner radii effects, and material plasticity (Ramberg-Osgood). Modern methods use effective width concepts and FEM with geometric nonlinear analysis. Crippling allowable (Fcc) becomes column yield strength for stringer-skin interaction analysis. Design targets crippling stress above material yield for maximum efficiency.