Equivalent plate thickness

Equivalent plate thickness is the smeared thickness assigned to a stiffened panel so a plain plate element reproduces its membrane stiffness in a coarse finite element model. The stiffener cross-sectional area is spread over the plate field: t_eq = t_plate + A_stiffener / spacing, so the orthotropic panel is modeled isotropically for global stress. It is a modeling shortcut for full-ship and three-hold models where individual stiffeners are not meshed; the global stress is then read back, and local stiffener and plate checks run separately on the real geometry. The method captures axial and in-plane shear stiffness but not the panel’s true bending or buckling behavior, which needs the discrete stiffeners or an orthotropic formulation.