[PSUBS-MAILIST] help interpreting ABS rules

[Sean T. Stevenson via Personal_Submersibles]

I found a bit of time this weekend to work on the hull optimization
software, and was just revisiting the "Overall Buckling Strength"
calculation in Section 6/19.13 of the 2014 ABS Rules for Building and
Classing Underwater Vehicles, Systems and Hyperbaric Facilities, when I
noticed the following:

The limit pressure corresponding to the overall buckling mode between
heavy support members is obtained from the following equation:

Pn = (E*t/R)*A_1 + E*I*A_2/L*R^3

The section goes on to define some of those terms, but what caught my
attention was the "I" in the second term of this equation.  The
nomenclature "I" does not distinguish between "I" for a heavy stiffener
or a regular stiffener in the rules - it is contextual.  Given the
purpose of the section, I had assumed that it meant "I" for a heavy
stiffener, but the term in question also contains the term "L", or
distance between stiffeners, which is distinct from "L_c", or distance
between heavy stiffeners, leading to some ambiguity.  If the second term
is a correction for stiffness of the section in between heavy
stiffeners, the "I" could very well be the "I" for a regular stiffener
in between, but it isn't clear to me.

Thoughts?

Sean