How do you analyze buckling of stiffened panels in aircraft structures?

Stiffened panel buckling analysis considers multiple modes: Local skin buckling between stringers (often acceptable below limit load), Stringer crippling (local buckling of stringer flanges), Panel column buckling (stringer-skin combination as column), and Overall panel instability. Analysis uses classical buckling equations modified by plasticity corrections (Johnson-Euler), boundary condition factors, and curvature effects. FEM eigenvalue analysis captures complex geometry. Design typically allows post-buckled skin carrying reduced loads while stringers remain unbuckled to limit load. The effective width concept accounts for stress redistribution after local buckling.