Stiffener & Frame Sizing
The next link in the chain after the plating. A stiffener collects a strip of pressure one spacing wide — line load w = p·s — and carries it to its end supports as a beam. Continuous over its frames the peak moment is wl²/12 at the support; cut at every frame it is wl²/8 at mid-span, 50% more for the same steel.
The plating is the stiffener's other flange. On a shallow bar it carries most of the section modulus, so it is included here — leaving it out is not conservative, it is wrong by a factor of two. The flange width is taken as one full spacing, which is generous on a short span: that is what the effective-breadth rules exist to trim.
Load and span
Section
Elastic beam bending with the attached plating as a flange, isotropic material, one uniform pressure. It does not check tripping, web buckling, the end connection, or fatigue at the weld — and a classification rule adds its own design pressure, effective breadth, allowable stress and minimum scantlings on top. A helper, not a substitute for engineering judgment.