Stiffener Effect
Orthogrid, stringer-frame, ring-only — stiffening shifts both the global and local buckling modes. MDC verifies every mode, not just the first.
Why this matters
Adding stiffeners to a shell does not simply raise the allowable stress by a scalar factor. Stiffening introduces new failure modes — local skin buckling between stiffeners, web buckling of the stiffener itself, flange crippling, torsional buckling — any of which can govern below the global buckling load.
Traditional smeared-stiffness methods collapse the stiffened shell into an equivalent monocoque and miss the local modes entirely. The “optimum” from such an analysis is often infeasible because a local mode is violated.
How MDC handles it
MDC treats every stiffener configuration — orthogrid, stringer-frame, ring-only — with both smeared and discrete-mode checks. Web buckling, flange crippling, torsional buckling, and skin buckling are verified at every candidate point in the optimisation loop. No infeasible optima are returned.
The full mode ladder, with the governing one flagged, is exported with the report so the reviewer can see exactly which check is critical.
Compare stiffener configurations.
Open the Codex, switch between orthogrid / stringer-frame / ring-only, and watch the governing mode change.